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CCBB
28th October 2008, 12:04 PM
(Michael's Note - Buyers of the Goat Island Skiff plan are entitled to a free drawing for the Birdsmouth mast. Also see page three of this discussion for the start of questions.)

I will likely be building a couple GIS masts using the Birdsmouth technique. There is a simple formula and article I used when I learned the technique that I'd share:

http://www.frankhagan.com/weekender/bm.htm

I used this formula with great success on my current dinghy. One of the problems I forsee now that I did not then is that the formula does not take account of the fact that wall thickness does not need to stay constant as the outer diameter of the mast tapers down. On my dinghy the taper was constant, but on the Goat it is not a constant taper. Before, I tapered each stave according to the formula so that the taper was built into the mast when the staves were glued up. To get the changing taper is not difficult, just a little more time consuming. However, since the stave thickness stays the same to the top, the actual wall thickness of the mast is more than necessary, especially right at the top where we don't want the extra weight. So I am not sure how to deal with that except to taper the staves less such that the mast is bigger at the top and then to shave down the outside diameter to what is specified. This would effectively reduce wall thickness.

At the max diameter of the mast, the staves would need to be 34.8 mm wide (~1 3/8") and .685 thick (~11/16"). At the top the staves only need to be 20 mm wide (heavy 3/4") and thus the staves only need to be 10mm thick (heavy 3/8"). So the staves at the top can be nearly half the thickness they do at the max diameter of the mast!

How to fix this is the question. At this point I figure, make the mast taper to a bigger OD at the top and shave down to the spec'd OD after the glue up. Would I make the mast taper down about 5/16" bigger than spec'd then shave to the spec'd? The advantage of B'mouth starts to get lost.

What would be great is to work it out so that the staves can be tapered on the table saw (i.e., this would make the OD become a straight taper, which it is not on the plans) and to make the taper bigger by an unknown amount and shave down a minimal amount to reduce wall thickness. Just talking about this makes me want to do the rectangular mast, but I have not taken a huge liking to the look and I like the design challenge I present here.

Phew.

Thoughts, comments, bad jokes?

Cheers,
Clint

jmk89
28th October 2008, 12:31 PM
Clint

How about calculating the birdsmouth pieces on the inside of the mast - then you can taper the pieces while having constant wall thickness? That is, design it so that the inside taper is correct (assuming tapering staves) but make it with constant thickness staves (tapered in width).

Then when the mast is made up, you can plane each stave so that the outside dimensions are correct, ie so that the top is at the correct thickness (thinness?), and it tapers correctly from foot to cap.

To make it properly, so the peak of the v in the joint runts down the middle of the tapered piece, the birdmouth part itself will need to get smaller (shallower) and move towards the inside. I think you may need to use a gentle taper jig on a router table to do this properly (it won't be much of a taper but it will be appreciable). However, the advantage of that is that it will make the planing easier - you just need to plane off the bits that stand pround of the birdmouth joints.

PAR
28th October 2008, 12:49 PM
There are two ways to build a birdsmouth mast, an asymmetrical and a symmetrical stave layout. I strongly recommend the asymmetric arrangement. It's stronger, is cleaner on the inside and is easier to smooth on the outside. Frank's staves were arranged in a symmetric layout.

Michael could easily work out the dimensions of a birdsmouth stick for the GIS. If you posted the general dimensions, I could do it (no charge), including the weights for different species and stave thicknesses and tapers.

The taper can be preformed easily with a taper jig on a table saw. I usually just plane the staves as a clamped together unit (all at once) on a bench, but to each their own. I build several birdsmouth masts per year, including the odd flag pole or two. I use stave taper when weight and mast bend is a design consideration. Ditto mast taper.

keyhavenpotter
28th October 2008, 09:28 PM
Does this Duckworks article help at all

http://www.duckworksmagazine.com/08/howto/birdsmouth/index.htm

Brian

CCBB
28th October 2008, 10:01 PM
Thanks guys. I'll need to have a lot more coffee to figure this all out.

Cheers,
Clint

Boatmik
29th October 2008, 08:13 AM
Howdy Clint,

I do specialise in weak jokes!

With the GIS, specifically, you can change the mast to birdsmouth without increasing the diameter at all to compensate for the slightly less stiff hollow section.

This is not a joke.

To get the taper (don't you DARE put an untapered mast or any untapered spars on one of my boats!!!!) just copy the taper rate for the overall mast as designed. So ... whatever height the mast is 25% thinner than at the partner, then the stave will have to be 25% tapered at that point too.

The don't DARE ... was a little bit of a weak joke. I think NORM who did the Canadian BETH recently used alloy masts with timber inserts at the top.

Actually the taper of the mast is not Quite that simple for two reasons.

There was no joke in that sentence at all that I could detect

1/ The actual taper rate is between the flat face of the stave and the apex of the birdsmouth notch. But .. I don't think that it is that important to be 100% accurate ... maybe I would worry a bit with a bermudan bendy mast rig or a gaff or lug yard ... but for a lug mast it is not very important.

2/ There will need to be a compromise at the top ... the way I do my mast tapers for spars carrying a gaff or yard is to assume the mast is going to the top of the sailplan and do a traditional taper at the normal heights. I then dock off the part of the mast I don't need and put in some extra taper to get the weight out of the tip by bringing it down quickly to the diameter of the top of the mast in the traditional taper. The birdsmouth will be more restricted in this as I think the stave thickness will prevent the taper from coming down quite as far as a specify in the GIS mast.

3/ As far as tapering the wall thickness ... it is too much labour, I think, unless an owner really likes the idea and is prepared to spring for the extra work. My mate Dusty gets a nice taper in the wall thickness by making the staves, tapering them normally and cutting the birdsmouth. Then he tapers the wall thickness by setting a power plane to about a millimetre and taking some equally off the two faces (that define the wall thickness) of the tops of the birdsmouth staves. So maybe he does one run starting from a couple of feet from the top of the stave. Then another run from 3.5ft from the end of the stave etc.

I have used the glue up the whole thing then take something off the outside at the top type method. We used that for the hardwood birdsmouth mast on the Fenwick Williams Catboat.

Did you see how subtle my weak jokes can be ... I gave you three points ... not two (guffaw).

Maybe a good way with the GIS is to glue up use the same wall thickness to the top but make the top a bit larger diameter as you will be forced to do by the birdsmouth method. Then plane the top bit down to something like the original tip diameter making sure it doesn't reduce the wall thickness too much.

Best wishes
MIK
(who hopes you got a giggle)

CCBB
29th October 2008, 08:41 AM
I was thinking I MIGHT even do a reverse taper, Michael...make the top of the mast about an inch larger and make a little flat spot on top and put my son's little toy goat at the top. The goat might make a good wind vane.

That would be way too labor intensive. And ugly. Like a reverse sheer.

Okay, I was thinking along the last line you said, gluing up the mast with the constant wall thickness and taper the outside down to get that last bit of taper. Perhaps a few swipes of the plane to knock down the stave thickness wouldn't hurt either. Good, sounds like the right plan.

Until later...

Clint

PAR
30th October 2008, 07:10 AM
Michael, your buddy Dusty does his tapers similar to mine. I just plane the taper on the notched side, before I notch them. I do them all at once, starting with a power plane to rough them in, then finishing with a hand plane. I can do several feet of taper in a few minutes this way. On large masts (over 30'), I use a tapered ramp, which is little more then a couple of boards, shimmed up to the taper I need and the plane in feed shoe rides on these. These long tapers require more control and the ramps insure I don't get hollows or humps.

There is a point of diminishing returns in regard to how aggressive you can get with the tapers, but generally you can have conventional looking shapes, using this method. I've found on larger sticks, this isn't as true as smaller masts, mostly because you have more material to work with, I suspect.

Heed Michael's advise about sectional and stave dimensions. Scaling a stick to specific loads can be a profound weak leak in a rig. There's not much more exciting then having a catastrophic mast failure while showing off you sailing skills to friends. Having exploded more then just a few poles over the years (there was a season or two that I just seemed to excel at it, for some reason), it's not some thing you really want to experience. Besides the long row back to shore, you have the tattered remains of the tangled gear dangling in and out of the boat. If you're fortunate enough to have not bonked someone on the head with the "event", you still have the painful embarrassment of loading your broken masterpiece, at the normally vacant launching ramp, which of course this time, will have a dozen or so people milling around, most giggling, as you forlornly drag your busted up contraption home.

As a rule, you can safely add 25% to the diameter of a solid or square sectioned mast, to make a hollow birdsmouth. It'll be heavier then necessary, but it will probably not fall down on you. You can also control sectional modulus with species selection to some degree, as well as stave thickness and notch cutout method. An asymmetric notch is slightly stronger then a symmetric arrangement. This can produce a lighter stick for a given bend rate.

In the end, it's best to let the designer engineer diameters and stave dimensions, as the calculations can be rather daunting for a novice. This isn't to say you couldn't do one, you can, but it'll likely be heavier then necessary and this is a performance killer in small craft.

Boatmik
30th October 2008, 09:07 AM
The 25% rule is good conservative advice that won't cause any problems.

Sure both Paul and I will sit down and work it out ... just to save that extra pound or so.

The calc is not really hard.

Michael

PAR
30th October 2008, 11:19 AM
Michael is right, the calculations aren't especially hard, unless you get into some close tolerance stuff (racers, highly strung setups, high tech materials, low safety thresholds, etc.). Most folks, I found, have difficulty getting their head around some of the formulas, the math and concepts, a few of which seem abstract (which kind of explains people like Ross, Michael and me don't it).

I'm a weight freak, okay, possibly just a freak, at least she says so. A recent example was deck beams and stringers that I cut lightening holes in, because of materials substitutions. I used a lumber that was almost 40% heavier then what I'd original planed, but it was also much more rot resistant and considerably stronger. My lightening holes reduced the weight to that of the original species, but I gained an additional 15% in strength (so, of course I made them smaller still). A lighter, stronger structure resulted. Anal, you bet . . . though I will carry more weight on the bottom then an equal model built to specs. I made several other "enhancements" to the design, which ultimately could yield a few degrees less heel then the same boat, sailing along side. I'll kick their butt, just because I was a wee tad anal about weight in the design and building process.

I built a popular (in the USA any way) cat ketch recently. The design was from a buddy and a good one. The client expected to met others of the same design at gatherings and didn't want to be at the back of the fleet. Though it was a spartan design, typical of his work, I paired it down a little more. His 17' dry hull weight was about 550 pounds. I got it done at 475 pounds, for a 14% reduction in weight. The first meeting of the same model boats, included the designer in the prototype and a pickup race to a small island for lunch. My client didn't win in the light airs of the day, but was just off the transom of the designer's boat (the winner). Afterwards the designer openly admitted that he'd been beaten, but noted that Ray (my client) wasn't as attentive with sail shape as he should have been, so he took advantage. Sailed better he'd have lost easily. Such is the difference 14% can make and likely why I chase down weight when possible.

Okay, rant over . . .

CCBB
30th October 2008, 03:16 PM
Let me ask this one: what does a hollow square mast, which Michael has drawn for the Goat, have over solid and B'mouth? I still think the B'mouth is nicer looking, but maybe I should see some more detailed photos...maybe I can be convinced. The simplicity of it is nearly enough...is it better or not than going B'mouth for the Goat? (I also 'feel' like it is less aerodynamic, but only at high speeds?)

Cheers,
Clint

PAR
30th October 2008, 05:40 PM
A hollow square section mast is stronger then a hollow round section of the same diameter. Also, amazingly enough the square section has better aerodynamics then a round section, unless the round section has a sock type luff, which then makes is better. A square section is easier to make, but doesn't look as nice as a round stick.

Birdsmouth masts are hollow. Solid masts can be built up from pieces or simply a whittled down tree of suitable diameter. Both of the hollow mast styles will be much lighter (if designed properly).

On the wind is the only time the mast section really effects the aerodynamics of the sail, unless you're up on plane and dragging the apparent wind forward, while off the wind.

In the case of the GIS, mast section isn't nearly as important as it is when the luff is attached.

Personally I'd want a pretty mast for a GIS, which is in direct contrast to Michael's function over form ideas. I relate it to a prospective wife, who could function very well, cooking cleaning, pleasing, though being butt ugly, I'd have difficulty. This forces me to insist on the whole ball of wax and one who cooks, cleans, pleases and is easy to look at too. Interestingly enough, the designs I admire the most, not only perform very well, but also happen to look great doing it. I consider this the hallmark of a great designer, making very functional shapes look good while they're chewing up the competition.

To me it's not enough to function well. An example of point - if you take a regular household door, preferably smooth faced, make a small bracket and hang a 5 HP outboard on it, the thing will get up and scoot. Maybe some of you have seen the photo of the 'fella that has done this to a kitchen table and is blasting along on a lake. Well it functions well, but lacks in the style department, unless you count weird as a good thing. I would have had to use a nice piece of Chippendale or a hollowed out Steinway baby grand, just to satisfy the "form" aspect.

Boatmik
30th October 2008, 07:22 PM
Howdy,

The original mast for the Goat was the traditional solid round one. It is a nice intro to some traditional skills and the use of the spar guage.

However the solid round mast is quite heavy and a fair bit of work.

So along came the square hollow mast which saves about 45% of the weight and often something off the material bill too and saves labour. I believe the construction is completely non scary.

The reason I did not straightaway go for a birdsmouth mast is I considered it too specialised - requiring specific machinery to do the job and had a good chance of causing significant problems in tool use and procedure for most of my target builders.

Assumption was that if someone really wanted one they would either work it out with my help (as above) or if not equipped to do the calcs, give me a push (as also seems to be happening now) and I would draw one up to become a third mast option for the boat.

Also, interestingly, birdsmouth has become the "flavour of the month" and I think many who would not have considered it a few years ago, would consider it a strong possibility now. Perhaps ... this is exactly what we were all hoping about wooden boatbuilding skills not disappearing .. here we have quite a sophisticated, non traditional method becoming reasonably commonplace. Quite exciting I think!!!

So ... 15 years ago we had the solid mast, about 3 years ago we had the hollow square one, next the birdsmouth.

On the technical side, PAR and I are close than brothers, we seem to make similar design decisions again and again - something to do with quite broad boating backgrounds with a lot of racing in them. Probably the slight differences in our approaches also reflects something of our backgrounds. Paul is highly skilled but understand how to make things easy for amateurs and, well, I am really an amateur builder who has done some professional building as well.

From that I learned that I am intrinsically fairly lazy in boatbuilding terms (I did have some inkling before then) ... so this does tend to reflect the types of boats I design.

Like you will never find me designing a Cape Cod Catboat ... and am fairly unlikely to design a multihull ... my resistance is purely one of surface area!!! I have seen enough surface area in my life to not want to see any more of it needing fairing!!!

Anyway ... this is a great thread and some new things are coming out of it. Much better than threads that go round and round endlessly as they do in some other places ... so once again I'd like to thank everyone for their contributions! (to boating and world peace) ... geez .. just thought ... what has happened to Bjarne ... haven't heard from him for a while!

Anyway .. best wishes
Michael

CCBB
31st October 2008, 08:53 AM
Bjarne is busy building, hopefully!

Michael, well I am still open to the hollow square mast, but would sure like a plan showing details for a B'mouth mast. I am so tired right now that I am lacking the mental energy to think about it, but hopefully that will pass when my current project finishes. I would be VERY interested is obtaining plans for a B'mouth mast plan.

Cheers,
Clint

Boatmik
31st October 2008, 09:20 AM
Howdy Clint,

If you want 'em ... I will do 'em.

ie work out a birdsmouth mast for the GIS.

But next week.

This week is RAID RAID RAID RAID

MIK

PAR
31st October 2008, 12:09 PM
I've been using the birdsmouth method since before they called it the birdsmouth method. I've built a few dozen sticks with this method over the last 15 years. We used to call it "the notched stave" method, but I guess it didn't have quite "ring" birdsmouth has. Which makes me wonder what the used to call the Nova Scotia "Hookers" before they were hookers.

Michael, I'm putting the finishing touches on a Friendship Sloop. It's not light (357 D/L), nor fast (forever captured by it bow and stern waves). It has mast hoops (ouch), a big old bonking boom that's 90% of it's hoist, but it does have a nicely tapered birdsmouth pole sticking up through the foredeck and a wainscoting lined cockpit. Almost 27' on deck, 38' spared length. It's a pig and if you're going to sail a pig it should be a pretty one. Actually in a good blow, it should do fairly well. On a more interesting note, it has a metal armature, internal within it's keel. This saved 40% of the weight of a traditional deadwood assembly.

CCBB
2nd November 2008, 07:07 AM
Michael, I looked at Dana's mast partner/step and he built his to fit the square-hollow mast you drew. Will the B'mouth mast be bigger than the square? If so I'll be interested in seeing how much bigger as we'll have to modify to fit the round mast.

I agree with PAR, this new mast will be much prettier as well as superior to the square and solid versions. I look forward to building the first one as soon as it is drawn up.

Michael, I will be using Northern White Spruce preferably (a.k.a., Maine Spruce) as this is what I have on hand ready to go. Makes wonderful sticks.

Cheers,
Clint

Boatmik
2nd November 2008, 08:57 AM
Howdy Clint,

I think that you are agreeing with PAR that the birdsmouth is NICER! He gave the technical reasons that the square mast is technically better on the previous pages.

I have just checked quickly ... if you use the step and partner for the original round mast it will all work out OK.

The birdsmouth version with a 20% wall (wall thickness divided by diameter) will work out about 15% more flexible.

You cannot see the stick move much at all with two adult men leaning out hard ... it is stressed for three men leaning out hard ... so not surprising.

So the outer diameters of the mast will be the same as the original round mast, at least in all areas except the tip.

MIK

PAR
2nd November 2008, 02:41 PM
I use white spruce frequently and love the stuff. It's light, straight grained and can be had in reasonable, clear lengths. It's comparable to Sitka in compression and slightly lighter (though not enough to get excited about).

Michael, I would have thought you'd use a slightly thicker section for the birdsmouth version of this stick to address stiffness? Maybe foam filled . . .

Boatmik
2nd November 2008, 04:16 PM
Howdy PAR,

I don't think it is worth worrying about. The mast "as is" is beyond robust. So we will take it as a weight saving and assume that no more than two big blokes and an average women are going to be leaning their hearts out at any one time.

Under two people hiking hard the mast barely seems to move.

So I am happy to take it as a weight saving. Assuming this fits in with Clint's likely pattern of use. Frankly ... I think it will be adequate for the three big men scenario.

Cheers
MIK

CCBB
2nd November 2008, 11:08 PM
Mik, My likely pattern of use will certainly include hiking out hard on blowy fall days...probably 2-3 adults in the boat with two hiking if it is that windy. I am 225lbs and 6'6" so if I hike most of the others in the boat can relax! Here is a shot: even in a dory overcanvassed I was on he rail and Dan was on the thwart, on the high side. However, I reef when it is time rather than punishing the crew and boat. That is when the little mizzen will be so handy. A typical fall day of hiking out hard will be 15-20kts of breeze gusting to mid 20s. MOST of the time I'll be sailing in 5-15 kts of steady seabreeze type of conditions with 1-2 people in the boat, sometimes 3 people, the third likely my 4-year old.

Cheers,
Clint

Boatmik
3rd November 2008, 08:20 AM
That's not hiking ...

THIS is hiking and the mast will handle three people doing this (someone is going to try some time .... aren't they ... but not necessarily on your boat)

http://www.laserchampionships.org/worlds03/photos/d1_2/images/Gustavo_Lima.jpg

This is probably a more sustainable level!

http://ns14.org/images/large/dsc_0035.jpg

CCBB
3rd November 2008, 09:20 AM
That is how I was hiking much the time in the dory sail...my point was more that my big (&%$ is enough to flatten a boat without much work! I race flying 15s, the only fleet in Maine and the US I believe, and I've usually got my butt over the water. This summer a hiking strap snapped while I was hiked out for all I was worth. That was the quickest dunking I've ever experienced!

I look forward to getting the Goat into some good wind and hiking like that! The beefy mast will be reassuring.

Clint

Boatmik
3rd November 2008, 09:41 AM
Flying 15s in the USA ... now I know ANYTHING is possible.

Cool boat aren't they!

Found a pic of a WOODEN one that was for sale ... I think the links will break when they take the ad down or because they are not direct links at all.

But we can enjoy them for a few hours maybe.

http://www.uncommonboats.com/website/image.asp?id=735

http://www.uncommonboats.com/website/image.asp?id=738

http://www.uncommonboats.com/website/image.asp?id=741

MIK

joern
6th November 2008, 07:55 AM
That's not hiking ...

THIS is hiking and the mast will handle three people doing this (someone is going to try some time .... aren't they ... but not necessarily on your boat)

http://www.laserchampionships.org/worlds03/photos/d1_2/images/Gustavo_Lima.jpg

This is probably a more sustainable level!

http://ns14.org/images/large/dsc_0035.jpg


Howdy Mik,
How do you manage three blokes hiking with the Goat?
No hiking straps specified - do you hook your ankles just under the middle seat?
Would like to give it a try (with hiking straps) if and when the boat is ready:roll:
would you recommend a certain kind of fitting them straps?

Greetings - Jörn

Boatmik
6th November 2008, 01:55 PM
Howdy,

See this and the following few images
http://www.flickr.com/photos/boatmik/383639974/in/set-72157594524425079/

Here is a sample image from that series
http://farm1.static.flickr.com/98/383640054_3c7b0a47ae.jpg

Use bolts 4mm (3/16") through the centrecase bulkhead to hold the blocks of ply down.

Michael

Boatmik
12th November 2008, 10:35 PM
Howdy Clint,

Have just sent you the dimensioned birdsmouth drawing for the GOAT.

Anyone else with a set of GIS plans can have this extra sheet no charge.

I need to think a little more about an infill at the top, the partner and the base But this is enough to go on for the moment.

The diameter will be close to the original round mast so the mast partner and step in the plans will work.

Michael

CCBB
13th November 2008, 04:28 AM
Mik, Awesome. For infills, how about gluing plugs into the mast as it is glued up...one at the top and bottom and perhaps a plug where the mast goes through the partner to add strength...this is where stress risers pop up. Plugs could be turned up on a lathe and made to fit the inside diameter at each section. Plently of glue during glue-up will help ensure no voids are produced by accident. The top infill, Mik, would have to go down pretty far to reinforce where the halyard block is, right? That measurement would be handy as well as where the partner is located...I always hear about masts breaking just above the partner.

Cheers,
Clint

Boatmik
13th November 2008, 08:39 AM
Howdy Clint,

I will add the blocks to the drawing I am sending out later but the block at the bottom probably only needs to be about 40mm thick.

At the top it would be good to be about 80mm deep or to take the fastenings for the halyard attachment point.

At the partner it really is to take crushing loads, So I would probably recommend two 20mm thick blocks - put them in about 60 mm apart.

You could turn them on a lathe, but I would just mark the octagons on some 20mm thick stock and jigsaw away. The thick one at the top can be made out of 4 pieces.

ASSEMBLY

I would glue up the mast without the spacers but put the brown packaging tape along two opposite joins so the mast can be opened up after gluing.

Generally people use hose clamps, brown packaging tape, but elastic bands, big cable ties or similar to hold them together as the glue sets up I would certainly have some brown plastic packaging tape handy whatever clamping method you use - when it is wrapped around and stretched at the same time its holding power is quite strong.

Like with all complex gluing jobs it is best to check your clamping method will work BEFORE you put glue on the structure.

Then the spacers can be fitted and glued. The mast dry assembled to make sure it still goes together. Then opened.

Then the interior can be epoxied with three coats wet on wet. When the third coat goes on, glue mix can be put on the remaining two joins and the mast assembled permanently.

When glued it can be rounded following the instructions for planing and sanding the round mast in the GIS plan - all the detail is there already!

Best Wishes
Michael Storer

CCBB
13th November 2008, 12:59 PM
Mik that all sounds quite brilliant to me!

nsimms
12th June 2009, 01:24 PM
I'll be building my GIS this fall, but am planning to get a jump on the build by constructing the spars and possibly the boards this summer, on the cooler days.

I've bought the lumber for the birdsmouth mast build, and am looking over the plans preparatory to cutting and tapering the staves.

Michael's birdsmouth addendum specifies the various stave widths as you progress up the mast. My question is, do you just draw straight lines between each of these measurement points, and cut the taper, or should you draw a nice curve through the points (ie, with a batten), and cut to that?

Most of the taper is pretty gentle, so I suspect for that part it wouldn't really matter, but the taper increases significantly at the top of the mast...

Thanks,

Neil
Carrboro, NC, USA

Boatmik
12th June 2009, 02:03 PM
Hi Neil,

It will be good to get another birdsmouth mast under way. Clint made one for Dana's boat.

The staves are marked with a curve through all the points using a batten. You are correct.

Michael

nsimms
13th June 2009, 04:16 AM
Thanks, Michael!

alzuger
12th October 2009, 04:58 AM
Hi all,
So I just bought my 1/4" Okumee ply for my GIS build, and at the same time I bought my mast and spar timber. I really didn't want to have to do a bunch of scarfing, so i picked up two 16' long 7" wide by 4/4" sitka spruce boards for the mast. Not cheap, but considering how light and flexible they are, i think it was worth it. My dilema, is that to make the box mast i'm going to have to turn 50% of these planks into sawdust. I dont have any problem with the square mast, it is nice enough on my pdracer, ant that one is made up of an ancient doug fir scaffolding plank with a million nail holes. At the same time i'd kind of like to give the Birdsmouth mast a try, after all, i have all winter, and i'd love to take a little extra time and learn a new process. I dont want to bug MIK while he's on Vacation, the colorado river pics are really something else! But i would like to know if I can accomplish the birdsmouth mast with the material I already have. If it looks like i can do it with existing materials I might just bug him for the supplement when he gets back down under. In the meantime I think i'll start gluing up my foils and drawing lines on plywood. This is going to be one cool boat!
Thanks in advance,
Al

Watermaat
12th October 2009, 07:47 AM
Hi Al,

I just finished my square boxmast for GIS, made of 18mm light fir with slighty rounder corners than specified in the plans. Finished weight incl epoxy and some glass at 9.0 kg. I just put a second coat of varnish today. 118813
Just to get you an idea of a light-wood boxmast. I have used 18mm european fir and planed that down to 15mm towards the top. Outside shape is (about) according to plan. I made a square foot where it is stepped, because I like that. It is a very strong and stiff mast now, I probably could have planed it down even more, but I want to be on the safe side. With spruce you must be able to cut weight even more.

PAR
12th October 2009, 12:59 PM
The same mast, with good white or sitka spruce it would be in the 6.5 kg range completed, 6.7 - 6.8 with some of the other spruces.

PAR
12th October 2009, 01:30 PM
Just to show the difference between an asymmetric and an symmetric stave arrangement. Note you can do oval too. The asymmetric type is the the one I prefer. It's easier to round and make octagonal columns too. This is handy for mast lowers and bow sprits.

alzuger
12th October 2009, 04:41 PM
Watermaat,
you are really tearing through your build, and i am very impressed with the quality of the work you are doing. It is quite inspiring! I can't wait to get properly started myself. The last two days here were nice blustery days albiet a little cool, and i could neither sail my PDR or work on my GIS cause I had a rush job i had to complete.
So i dont want to hem and haw about it too much, because as far as i see it the birdsmouth and the square mast are essentially the same from a performance standpoint, the difference is more an aesthetic choice, round or square. Personally I normally lean toward the simple, more rugged choice, and if you had a look at my PDRacer up close, most of you would be appauled by the slopped on glue and really, really, really cheap materials. But if i am going to build a Goat I want something I can at least be proud of. (not a museum piece though as launching it from where i am means lowering it 8 feet down a rotten wooden bulkhead onto the barnacles) Also, I am a pretty accomplished woodworker (at least in my own head) and would like to try hollow round mast if it will hold up as well long term as the square one (asymmetric method PAR, i've been over your earlier posts on the subject, and really appreciate the depth of information) Most important in the end though is rugged and light, I am still not a very good sailor, and this boat will be launched and pulled out every time it is sailed, and there aren't many ramps where i live.
Thanks for the feedback,
Al

Boatmik
17th October 2009, 10:12 AM
Hi Al,

That's one of the things I like about this boat gig ... every boat has a different approach - even from the same person!

Infinitely variable!
MIK

CCBB
17th October 2009, 02:56 PM
Hi Al,

That's one of the things I like about this boat gig ... every boat has a different approach - even from the same person!

Infinitely variable!
MIK

So true! I made a B'mouth yard for my 11' sailing dinghy using the symmetrical approach PAR mentions and using two staves a little wider to get an oval shape. It was more for the exercise of it than gaining a real performance edge.

I made a square-hollow mast for Dana, actually. Currently, I have staves cut for a GIS mast. I have been playing with techniques and trying to nail down a process for doing them on a more production basis as part of my business. I have been mostly tuning the process for the table saw and have yet to use a router table with a B'mouth bit. My router table is sub-PAR (no pun intended). Do you use a table saw, PAR, or a router?

Keys to doing quality staves on a TS:
-a sharp blade! I still have not concluded whether a regular 24T or a 40T does better
-a 0-clearance table insert that is stiff nice and flush with table (make your own)
-featherboards to hold staves down and in tight to fence (you can make your own too)
-make extra staves to use as test pieces for setting blade angle, height and fence position. Set fence position first, cut a scrap piece of wood until you get a 45 degree cut, perfect. The raise blade height until it meets the exact middle of the stave.
-mill and rip staves dead square and use one square edge to test fit when cutting test staves. Again, cut a scrap of wood to make sure your saw is ripping a square edge
-don't be too tempted to cut the birdsmouth/dado such that the cut produces a feather edge on stave...leave a millimeter or of wood
-cut all staves in one operation and don't change any settings midstream, thus the importance of the test pieces.

Have fun!

alzuger
17th October 2009, 06:08 PM
Can you do a batch of staves however works best for you, tablesaw, router, etc. and then trim the taper to size with a flush trim router bit and a hard plastic template that you screw down to the part? you could probably even use aluminum strip for the template if you had a number of parts to make. more difficult to fabricate the first time around, but very durable and available in long lengths.
just a thought,
al

CCBB
18th October 2009, 03:06 PM
The simplest way to cut tapers on a non=production basis is to clamp 4 together and plane to the taper per the plans. Then do the other four.

Al's idea is a good one but wouldn't really work. You could do it if the 'part' was bigger.

Clint

PAR
18th October 2009, 03:16 PM
I use a set of highly trained beavers. They were orphaned when a boat prop took out their mother, so I brought them in. They eat a lot, so I decided they could earn their keep and in a fit of brilliance one evening, I knocked the bigger of the two out with a few raps of a wooden soup spoon. While he slept, I used a rotary file and ground a perfect 45 degree straight cut into his front teeth. While I was "in the mood" I took advantage of his sibling and ground a cove a bead set into his front teeth, which makes strip plank edging a lot easier now. They truly love their work, literally eating it up and though it has taken some effort teaching them to chew in a straight line, a few simple jigs has them well employed.

CCBB
18th October 2009, 03:23 PM
Now that joke is truly sub-PAR!

PAR
18th October 2009, 04:31 PM
I should add that oval masts need to be stayed and shouldn't be used as a free standing stick.

I've found most doing birdsmouth spars, make more work for themselves then they need. Custom ground router bits, tapering jigs, etc. most of this isn't necessary.

I taper all the staves at once on small spars, what ever I feel comfortable with really. I set up an inclined ramp on each side of the staves, usually a couple of 2x4's wedged to position. Then the staves are solidly wedged in position, between the two ramps. One of the ramps always has the in feed shoe of the power plane or hand plane riding on it. This keeps the taper angle correct and the plane square with the work. A few passes with a power plane, followed with several swipes by hand, I don't spend a lot of time on them. Good setup always make your job easy and short.

Cutting the notch is easiest on the table saw and I use a datto on larger stock, but make two passes on skinny stuff, unless of course you've got some trained beavers. You don't even want to know how I get steam bent wood . . .

woodeneye
18th October 2009, 08:35 PM
I use a set of highly trained beavers. They were orphaned when a boat prop took out their mother, so I brought them in. They eat a lot, so I decided they could earn their keep and in a fit of brilliance one evening, I knocked the bigger of the two out with a few raps of a wooden soup spoon. While he slept, I used a rotary file and ground a perfect 45 degree straight cut into his front teeth. While I was "in the mood" I took advantage of his sibling and ground a cove a bead set into his front teeth, which makes strip plank edging a lot easier now. They truly love their work, literally eating it up and though it has taken some effort teaching them to chew in a straight line, a few simple jigs has them well employed.

That Aussie has been there too long and the BS is rubbing off:;

m2c1Iw
18th October 2009, 11:30 PM
I use a set of highly trained beavers. They were orphaned when a boat prop took out their mother, so I brought them in. They eat a lot, so I decided they could earn their keep and in a fit of brilliance one evening, I knocked the bigger of the two out with a few raps of a wooden soup spoon. While he slept, I used a rotary file and ground a perfect 45 degree straight cut into his front teeth. While I was "in the mood" I took advantage of his sibling and ground a cove a bead set into his front teeth, which makes strip plank edging a lot easier now. They truly love their work, literally eating it up and though it has taken some effort teaching them to chew in a straight line, a few simple jigs has them well employed.

:oo: must be the greater nothern Florida beaver as compared to the buck toothed long haired beaver commonly found in Canada.

Much easier to train. :D

Watermaat
19th October 2009, 07:01 AM
I use a set of highly trained beavers. They were orphaned when a boat prop took out their mother, so I brought them in. They eat a lot, so I decided they could earn their keep and in a fit of brilliance one evening, I knocked the bigger of the two out with a few raps of a wooden soup spoon. While he slept, I used a rotary file and ground a perfect 45 degree straight cut into his front teeth. While I was "in the mood" I took advantage of his sibling and ground a cove a bead set into his front teeth, which makes strip plank edging a lot easier now. They truly love their work, literally eating it up and though it has taken some effort teaching them to chew in a straight line, a few simple jigs has them well employed.

I guess these will be renamed "beavermouth" spars :U

Daddles
19th October 2009, 08:08 AM
I want to ask a serious question ... but I'm not game enough too :(

Okay, I've put the siamese on Beaver Alert and given the dog a shotgun to go with his normal defensive armoury (which doesn't really extend past rolling over and looking cute :rolleyes:)







I should add that oval masts need to be stayed and shouldn't be used as a free standing stick.

Why is that that PAR? If you've taken a round spar and just made it wider in one direction, wouldn't it be strong enough? Or are you referring to spars that have been narrowed?

Richard

PAR
19th October 2009, 12:05 PM
Mostly Richard, the beaver's take exception to the wider staves in oval section spars.

Seriously, (this is difficult at times) the oval section will not offer a uniform radius of gyration (or modulus) that a round section stick does, in a free standing application. This is also true of a square section mast, though to a lesser degree, but the corners are still farther away from the center then the sides. When you have this variance in stiffness in a free standing column, you have differing bending moments at different angles of attack. This means the mast bend will go from stiffer to less stiff, then back to stiffer as the boat and wind direction change. This cycling through less stiff and stiffer sections of the mast, means the stick will break much sooner then one of uniform section.

In a stayed rig this is also true, but the stays hold the stick in column for the most part and it's not an issue. In fact, using non-round sections can let the designer use thinner, lighter wall thicknesses, because of localized stiffness in the direction the most movement is expected. This is why you see oval sections on larger stayed masts and tear drop in the smaller ones.

arbordg
19th October 2009, 03:05 PM
Paul,

I guess I'd never thought of it, but it makes sense from an engineering point of view. I wonder, though, if there's a point where a stick is short enough, carrying a small enough sail, that it makes no significant difference - functionally?

PAR
19th October 2009, 04:04 PM
It's not the height of the stick that's most important, but the section diameter for the sail area it must endure. In other words, a slightly smaller diameter section, can have a huge impact on the ability of a mast to stand, but a slightly shorter (or longer) stick isn't affected as adversely. In regard to the GIS, I'd say the stick is overly strong. This is usually the case with small craft, except for full up racers, who might shave a stick until it breaks, just to have an advantage in light airs on the race course.

arbordg
19th October 2009, 04:27 PM
Paul,

I'd say the GIS mast is strong. Ours is the original solid, round version. Our PDR mast , otoh, is the hollow, square version for the 85 sq. ft. balanced lug rig.

I've thought of replacing the GIS mast with a round birdsmouth type (same diameter). I love the lightness of the PDR stick, but it's experiencing some abnormal wear at the squarish corner where the yard rides on it. Might could do a round birdsmouth for that one too... but that's further down the wish list.

PAR
20th October 2009, 08:57 PM
Steal your wife's plastic cutting board (HDPE) and rip a 1" strip off the edge and put it back before she catches you. Screw this strip to the corner of the mast where it's getting eaten up by the yard. Round over the crisp edges and you'll not have this problem again. Don't tell your wife where you got the idea, I got my own troubles.

85 square feet on a low aspect rig like that, you can use a 2.5" round birdsmouth mast, tapering to 1.75" at the top, with a .75" thick stave at the bottom tapering to .5" at the top.

Boatmik
24th October 2009, 12:37 AM
Hey PAR,

A biiiig thankyou for filling the technical breach while I am travelling - it has been a huge help!

MIK

PAR
24th October 2009, 09:12 AM
What technical help. I've been making things up as I go along . . .

m2c1Iw
24th October 2009, 11:41 PM
What technical help. I've been making things up as I go along . . .


:D now that is worth a chuckle.

Boatmik
27th October 2009, 05:18 AM
Worked for me!

CCBB
5th January 2010, 05:04 AM
Thought I'd bump this because I'm playing Birdsmouthology in my shop this month and ....

Does anyone know the weight of your rig w/o sail? The hollow box + spars would be most accurate.

Thanks,
Clint

Joost
5th January 2010, 06:21 AM
Clint,

9250 grams for my completed mast with all fittings and the halyard rigged.

This is the box mast as drawn by MIK for the GIS according to the exact specs provided in the plans:
- mast staves - 12 mm spar quality oregon pine
- core filler for the bottom part - softwood
- 2 layers of light (160 grams) glass on the bottom 3 ft of the mast, mast fully coated in 3 layers of epoxy
- mastfittings: 1 saddle in the top of the mast attached with 2 bolts and 1 small block, 1 small saddle with screws, 1 cleat with screws
- halyard of 12 meters 6 mm dyneema
- 6 layers of varnish

My (standard) completed GIS boom weighs 2400 grams (oregon pine, 3 layers of epoxy, 6 layers of varnish, leather at mast area). I guess the yard will be about the same.

Hope this helps.

Best regards, Joost

woodeneye
5th January 2010, 07:35 AM
Thought I'd bump this because I'm playing Birdsmouthology in my shop this month and ....

Does anyone know the weight of your rig w/o sail? The hollow box + spars would be most accurate.

Thanks,
Clint

Box mast made to plan with 11mm Hoop pine staves and Paulownia infills. Fully sealed with epoxy and varnished 7.3kg

Yard: Monterey Pine 2.2kg

Boom: Hollow Box - Hoop 2.2kg (estimated as incomplete)

Boatmik
5th January 2010, 10:05 AM
I think Bruce is the current titleholder!

MIK

Joost
5th January 2010, 06:36 PM
Hello MIK,

I think so as well.

The yard and boom are probably the same (my 2400 grams is with a large piece of leather in place on the yard and boom to protect the mast). Clean weight epoxy coated and varnished cannot be more than 2200 grams.

All the mast fittings and halyard and such might weigh 750 grams which would mean a clean weight of 8500 grams for my mast.

So Bruce's mast is clearly a lot lighter with 7300 grams. The weight difference is probably mostly in the bottom part of the mast since I have 2 layers of glass on it for the first meter. This probably also accounts for most of the difference in weight (I believe Bruce has not glassed the bottom part).

Joost

PAR
5th January 2010, 07:08 PM
What are the general dimensions of the GIS main mast (height, diameter, tapers, sail area, etc.) and I'll work out a cruising and racing birdsmouth scantlings. I prefer feet and inches, but I'll supply both. If my quick math is right, you have a 16 - 18 pound mast? Seems heavy, but I'm not working with all the details.

Joost
8th January 2010, 05:36 AM
Hello Par,

Bruce's mast weighs 16 pounds, my mast 18,75 pounds. Both coated in epoxy and varnished, otherwise clean of fittings.

Difference in weight is probably caused by difference in wall thickness of the staves, different types of wood and 2 layers of glass on the bottom part of my mast.

Both masts are hollow boxes tapering from 82 mm at the bottom to 47 mm at the top. Mast height is 4.7 meters, sail area 9.7 m2.

Best regards,

Joost

PAR
8th January 2010, 07:53 AM
A birdsmouth mast 3.25" (82 mm) at the heel and tapering to 2.25 (57 mm) at the head would weigh about 14 pounds (6.3 kilo) is Douglas fir and would easily handle the 104 sq. ft. of sail. If sitka spruce was used it would be about 11 pounds (4.9 kilo) and if white spruce about 10 pounds (4.5 kilo). All assuming a 20% wall thickness.

This is on a 15' 5" (4.7 m) mast carrying 104 square feet (9.7 m2) of sail area on a free standing stick. This offers a reasonable set of dimensions, though at 15% wall thickness you can lose a few pounds off the mast (Douglas fir drops to 11 pounds, sitka to 9), but it will be delicate. I made several guesses about the GIS, but they shouldn't be very far off.

The heaviest mast mentioned here (14 pound Douglas fir) is 26% lighter then the 18.75 pound mast mentioned above. The lightest mast here (10 pound white spruce) is nearly 40% lighter then the 16 pound mast listed above. A few pounds (kilos) do make a difference.

Boatmik
8th January 2010, 08:36 AM
Thanks for that Paul,

Particularly the weights of the different species.

The problem with boats that can be built world wide is that the wood itself is so variable as well.

I would not be too worried about using the white spruce for building either because the mast is quite conservative ... too strong. It assumes three people hiking hard which could happen some time.

I don't recommend the 15% wall thickness for the same reasons you add the caveat. This is a general use boat, not a raceboat which have rescue not far away and is almost expected to break things occasionally!

The thinner wall might be fine but it adds some little risk.

MIK

Joost
8th January 2010, 09:35 AM
Thanks for that Paul,

Particularly the weights of the different species.

The problem with boats that can be built world wide is that the wood itself is so variable as well.
MIK

That is quite the difficult thing here in the Netherlands: it is hard to get any decent timber nowadays, especially for spars. And if available, it does have its price.

I have an outstanding order for some Douglas fir since the beginning of October. The specialist just has not been able to put his hands on some decent quality wood yet.

Ordinary European pine is the only readily available (and cheap) stuff over here, but will always have some knots and pinholes in it. Ralph has made quite a nice mast out of it though, so it might be worth some more experimenting.

PAR
8th January 2010, 10:48 PM
I have a client in Finland building one of my schooner designs (a glued lap build) who's having the same difficulty with lumber. The nice thing about birdsmouth masts is you can piece together the staves from fairly crappy lumber, scarf around the knots and the stick is no worse off.

CCBB
22nd January 2010, 01:40 PM
What would be the thoughts with going with a hybrid aluminum-birdsmouth spar? The Core Sound's that B & B designed have mostly aluminum sticks. It would cost them more to go with wood if they were to have someone build it for them. What about an aluminum base and wood top since they are often two-piece anyway? What would be the advantage over all aluminum or all wood?

PAR
23rd January 2010, 02:23 AM
The Core Sound series has three different mast building options on the plans, an all wood version and two hybrid aluminum/birdsmouth versions. The all wood version is likely the least costly, but requires the most labor (a non-issue on home built), but is the most flexible and not something that Graham really likes. The two hybrids are compromises over more costly versions (aluminum/carbon fiber).

Maintenance and ease of construction would be two primary reasons for these hybrid sticks. I'm not so much of a traditionalist to not want aluminum masts, gaffs, booms, etc. It's an easy material to work, has consistent physical properties and much of the hardware on the market is geared for this material.

CCBB
25th January 2010, 02:45 PM
On these hybrids, are the bottoms or tops aluminum? What does an all aluminum set of spars go for on a Core Sound? I'd be curious to know.

PAR
25th January 2010, 10:13 PM
Costs are a funny thing, especially with aluminum. The last time I purchased T-6 was this summer and I drove about 5 mile to my buddy the welder, who'd ordered two 2.75", 6061 with a .125" wall 24' long tubes. I cut what I needed and paid about $3.50 a foot. I don't know anyone that can get 6061 that cheap. I'm lucky, living in an area where doing marine stuff is common, so this alloy isn't unusual, plus having old Bob right down the road, so shipping is as difficult as whatever I can toss on the trailer. I know folks that are paying 3 times this for the same tubing, in different parts of the country.

The aluminum tubing is the lower section(s) on the Core Sound series. Again one of the methods shows a two piece aluminum and wooden top. While the other shows an aluminum lower and a wooden upper section.

CCBB
29th January 2010, 01:19 PM
I am doing some demos on making birdsmouth things...feel free to check out my page I created for this

Birdsmouth Masts & Spars - Maine Boatbuilder + Repairer Wood + Plywood Boats Oarmakers Birdsmouth Mast + Sparmakers Foils Boat Plans + Kits (http://tinyurl.com/birdsmouth)

http://www.clintchaseboatbuilder.com/resources/sparhalvesandplugs.jpg

I always take comments, questions or bad jokes.

Cheers,
Clint

SimonLew
29th January 2010, 01:37 PM
Those bird's mouths are looking really sharp!

woodeneye
2nd February 2010, 09:39 PM
I enjoyed your tutorial immensely Clint, and your pics are excellent.

If one had wider stock of the correct thickness, would it make any difference to rip the staves first with a router, and then cut the dados like you do, or rip the dado, then cut the stave off the stock?

By the way, I saw the write-up on your "Drake" in Small Boats which arrived yesterday. I cannot for the life of me figure out how that silly wheelbarrow boat made it into the mag and Michael missed out with his offerings. Looking at the materials used, it would NEED to have wheels just to move it... I doubt two people could carry the thing.

CCBB
2nd February 2010, 10:40 PM
I tried getting the Goat in the magazine, but they felt I had too much commercial interest in the boat. They want third party writers. I couldn't write anything about Drake, an editor or a random guy walking down the street could. Tom did a great job on the article.

I'm off to teach Boat School guys about Birdsmouthing! Thanks for your feedback, Bruce. With the asymmetric birdsmouths I think it is best to taper the stave first then route the groove. You could plane a wide board down the the stave thickness, but there is more wood and time wastage there. You could resaw a board, like a 4/4 or 5/4 or 6/4 board, plane it to the stave thickness and rip off your staves, sure. But it seems easier to get a thick board, rip the staves off such that the rips are set for stave thickness plus some, then plane down the staves to exact specified thickness.

Hope that makes sense, it's early.

Joost
2nd February 2010, 11:11 PM
Wouldn't one of the editors of Woodenboat be able to sail, for example, Dana's GIS?

I truly enjoyed reading the article on Drake in the 2010 Small Boats issue. Job well done I think and the purpose, history and limitations of the boat were explained very well..

Joost

CCBB
4th February 2010, 02:22 AM
Joost, It sounds like the editor at WB is going to try to contact you and Dana...that is great. I was kinda persistent that he look at the Goat, and it seems like that is working.

yes, Tom did a great job on the Drake article. When I rowed with him across the cove at WB, about halfway across to the island, he said "wow, we're already halfway there, she can really move".

I think a similarly sized Goat would make a great addition...meaning I could use an extra foot or two on the Goat.

CCBB
14th April 2010, 08:12 AM
Can someone confirm the diameter of the hollow birdsmouth mast.

THANKS!

SimonLew
14th April 2010, 02:15 PM
I'm out of town so can't check my mast to give you an exact number. I think mine's just a bit over 3" probably not more than 3 1/8"

Boatmik
20th April 2010, 01:35 PM
Just shot off Clint a set of the drawings. Anyone who has purchased a goat plan can get a set of the birdsmouth mast drawings for free.

Just email or PM me with your email address.

MIK

nickpullen
21st April 2010, 03:56 PM
How about a birdsmouth for the PDR for those of us who like to complicate and tinker?

Boatmik
21st April 2010, 05:45 PM
It can be fun to do, but it doesn't really make sense as the two will end up being pretty much the same weight. Also complicates the step and partner - maybe it could be left octagonal in the bottom part.

If you are serious I wlll owrk out the maximum mast diameter and the birdsmouth stave dimensions, but after that you have to work out the rest yourself.

MIK

nsimms
26th June 2012, 05:39 AM
Reviving an old thread here, but I might actually get around to building a GIS this summer after being distracted by a couple of other builds the last few years. I have a question for Mik and/or those who have built the bm mast for the GIS.

Probably a stupid question, but in looking at Mik's bm mast design for the GIS (12/11/2008 revision), it appears half the taper is applied to each side of the staves, rather than all of it to one side only (which would seem to be easier to measure up and plane). Is this correct/necessary?

Never having built a bm spar before, I'm trying to imagine the effect a one sided taper would have - would it produce a spiral effect looking down the spar (which might look kind of cool, actually)? Would it have any effect on mast strength/function?

Thanks!

Neil

PAR
26th June 2012, 08:32 AM
You can taper both sides or one side on a birdsmouth stick. Neither will produce a twist, though most find it easier to taper just one side of the staves. The only way you can introduce twist is during assembly and you'd have to work at it, as the staves tend to self align straight.

SimonLew
26th June 2012, 08:54 AM
I tapered just one side of the staves and it worked like a charm. Scroll about half way down on this (http://planingaround.blogspot.com/search?updated-min=2009-01-01T00:00:00-05:00&updated-max=2010-01-01T00:00:00-05:00&max-results=22) page of my blog to see how I did it.

nsimms
26th June 2012, 10:54 AM
Thanks very much guys, will just taper one side then...

Neil

Boatmik
26th June 2012, 11:27 AM
Howdy, The others are right. It is best to just take it off one side and that means there is a datum for the material removal. The mast does take up a subtle spiral done this way ... or at least when I do it!!! But you would have to be looking really closely for a chance of spotting it. And it won't make any difference anyhow :)

Michael

BrianMCarney
27th January 2015, 02:26 AM
Simon, I note from your blog that you used Home Depot 1x2s for your staves. Did you allow any pieces with knots? How hard did you find it to find reasonably clear lumber in those dimensions?

SimonLew
27th January 2015, 01:04 PM
Simon, I note from your blog that you used Home Depot 1x2s for your staves. Did you allow any pieces with knots? How hard did you find it to find reasonably clear lumber in those dimensions?

Home Depot carries clear Douglas Fir in various sizes so knots are not a problem. I picked through the pile to find the lightest and straightest grain ones. Several boat builders have told me that a somewhat lighter mast could be built using the lightest 2x4s but you have to pick through a ton to find good knot free ones.

Simon

BrianMCarney
1st February 2015, 05:05 AM
Simon,
The stuff my Home Depot has is thishttp://tapatalk.imageshack.com/v2/15/01/31/c4bafe5701d5625b920b9a40339f0b49.jpg
Much of it is fairly clear. Could certainly find enough clear ones for a mast.
http://tapatalk.imageshack.com/v2/15/01/31/6254c4747f3b983f961417d084da33f3.jpg
But it's listed as premium pine. The Doug fir in small dimensions is pretty horrible.

SimonLew
1st February 2015, 01:00 PM
The pine will be plenty strong enough and you'll likely end up with a lighter mast. I used doug fir because the stuff at our HD was very nice. I it's availability varies from store to store. The HD website does not list the sizes of doug fir lumber that are in stock at three of our local stores.

BrianMCarney
2nd February 2015, 02:01 PM
thanks Simon.As I mentioned in my build thread, I decided the 1x2s at another local HD were Doug fir and loaded up on them. Now waiting for my scarfs to cure before I cut the birdsmouths.

BrianMCarney
3rd February 2015, 05:26 AM
The simplest way to cut tapers on a non=production basis is to clamp 4 together and plane to the taper per the plans. Then do the other four.

Clint


I should add that oval masts need to be stayed and shouldn't be used as a free standing stick.

I've found most doing birdsmouth spars, make more work for themselves then they need. Custom ground router bits, tapering jigs, etc. most of this isn't necessary.

I taper all the staves at once on small spars, what ever I feel comfortable with really. I set up an inclined ramp on each side of the staves, usually a couple of 2x4's wedged to position. Then the staves are solidly wedged in position, between the two ramps. One of the ramps always has the in feed shoe of the power plane or hand plane riding on it. This keeps the taper angle correct and the plane square with the work. A few passes with a power plane, followed with several swipes by hand, I don't spend a lot of time on them. Good setup always make your job easy and short.
.

You guys always make this stuff sound so easy--"just taper per the plans"!--when we're talking about ~6mm of taper over a 15' spar. This seems non-trivial to an amateur like me. I realize that the 0.2mm sections just kind of have to be eyed in along the greater run of the taper, but even setting up an accurate jig over that length is merely pushing the problem back a step. I still have to figure out how to taper my _jig_ a tiny, but accurate and fair, amount over about 15'. And I can't see getting that right really, much less transferring it consistently to 8 staves. Maybe I should have stuck with the box mast... :?.

Maybe I should try tapering before thicknessing. Then I could get two bites of the apple. But I can't thickness on the planer after tapering, so I'd have to rip to width on the table saw, which seems fraught with potential for error too.

So perhaps I should go back to trying to glass my foils. Seems less stressful in comparison.

:;

scooterpontus
4th February 2015, 09:03 PM
PAR's method sounds really good. With a 2x4 on each side there is no risk of taking off too much and if you use a hand plane everything will happen slow enough for you to feel in control (or set the power plane if you use one to take of just a little bit at a time). Good luck!

Pontus

BrianMCarney
4th February 2015, 09:51 PM
Thanks Scooter. But getting the 2x4 shaped and positioned right seems like the challenge... Maybe I'm overthinking it. Wouldn't be the first time....