Thread: Building Shesha, a Hunter Valley GIS, Australia

Howdy,

I can't give a standard stiffness, I am afraid. I promise you that what you have built will work though and work better than most spar designs for dinghies.

I think that the Dutch group of GIS sailors will be most likely to work out an optimum stiffness by sailing the boats together and making changes like this in a systematic way.

Best wishes
Michael

I am quite impressed by your nice low mast weight!
Joost and I did not get it below 9 kg .
I am pretty sure it will be strong enough, mine still feels so strong as if it is an overkill.
About the yard, see also my thread about measuring.
It seems that having a 5cm curve with 10-15kg in the middle is a normal range. Mine is much more heavy ( 3.2 kg finished weight ) and stiffer ( needs 20kg to get 5cm flex ) and probably needs some planing after I have tested my sail. Joost is making a stiffer mast and boom to try out.
It is all very much depending on your sail too, it's a matter of choice. You can have a stiffer yard with less curved leach, or a more flexible yard with more curved leach. Both have different caracteristics. The flexible set-up is more versatile, but could lack some power in certain conditions. The stiffer set-up has more overall power, but could be hard to handle in certain conditions.
I would go for a more or less "standard GIS " leach curve and play with different yards.
Making another yard is a nice fun-job, ordering a new sail is pretty expensive .
I have made my yard of a laminate, that's mostly stiffer than a single piece of wood. Besides that it is mostly cheaper to get thinner planks.

Good points.

That is the exact problem. Without comparing two boats which are differently set up it is impossible ot know what will work best.

A flatter sail with a stiffer yard or a fuller sail with a more flexible yard?

Lamination doesn't make anything stiffer. Changing the density of the timber or making the spart thicker will both have an effect, with small changes in diameter having a very big effect. I can help calculate that if anyone needs it down the line.

Comparisons are easy ... it is the starting points that are hard to come up with!

Best wishes
Michael

Originally Posted by Watermaat

It seems that having a 5cm curve with 10-15kg in the middle is a normal range. Mine is much more heavy ( 3.2 kg finished weight ) and stiffer ( needs 20kg to get 5cm flex ) and probably needs some planing after I have tested my sail. Joost is making a stiffer mast and boom to try out.

My suspicions are confirmed that my yard and boom may be too flexible. Although I only used a spring balance and not a digital one, it only took 7.2kg to put 5cm of flex at the centre. That's about 50% of the stiffness of Joost's spars and 30% of Ralph's. Note also that I have not even made them round, and merely rounded over the edges with a 9mm round-over router bit. They may make good heavy weather spars but I think I'll shop around for some more timber.

Obtaining good timber in Maitland is much more difficult than it used to be. Ever since Bunnings arrived in town, two good timber merchants have disappeared. I went shopping for some 2x4 pine for my sawhorses and it took me all morning to find some fairly ordinary quality stuff. Certainly, Bunnings no longer sell any untreated 2x4.

I may have to get on the phone tomorrow to try and source some fine grained Oregon or Hoop. Perhaps the other alternative I suppose is to wrap them in glass?

Originally Posted by Boatmik

Good points.

That is the exact problem. Without comparing two boats which are differently set up it is impossible ot know what will work best.

A flatter sail with a stiffer yard or a fuller sail with a more flexible yard?

Lamination doesn't make anything stiffer. Changing the density of the timber or making the spart thicker will both have an effect, with small changes in diameter having a very big effect. I can help calculate that if anyone needs it down the line.

Comparisons are easy ... it is the starting points that are hard to come up with!

Best wishes
Michael

Hi MIK
You are right about laminating in general. My statement is based on the fact that for me it is easier to find more straight fine grain in thinner planks, comparing to thicker pieces. In that case laminating makes a denser piece of wood.

For me it's interesting to sort out how this "density" and "diameter" factor relates comparing with overall weight of a non-hollow spar? I have seen very light spruce yards with large diameters on those 12ft dinghies. I wonder how that compares with a thinner oregon yard if you look at weight and stiffnes. ( and eliminate windage , than it realy becomes complicated )
Do you have any idea where to go.....light wood/large diameter or heavier wood/small diamater ?

Sunday, November 29, 2009
Saturday's temperature reached 40degC, so decided not to coat the mast in epoxy in that heat. Instead, we visited to hardware store to buy some 2x4 pine so make some sawhorses, and I spent the afternoon knocking them up ....and of course, hydrating.
Like Bob who is also building a GIS in Sacramento CA, I too decided to build Chris Baylor's solid looking horses. These are without doubt the most solid sawhorses you'll ever come across. Check out his free sawhorse plans here: Wooden Sawhorses - Woodworking Plans to Build Wooden Sawhorses

Here's how they turned out. After taking this pic, I slapped on a coat of linseed oil.
Attachment 123238

Today's temperature was a decidedly cooler 33degC, still hot, but I decided to get the mast epoxy coated anyway. I'm using the West System 105 epoxy with the 206 slow hardener. This provides plenty of working time, even in this heat. The big problem was that a VERY strong, warm and gusty wind whipped up and soon the dust from South Australia was blowing in
Oh well, too late, I'd already started the first of 3 "wet-on-wet" coats of epoxy. Wet-on-wet is a technique that saves a lot of labour. Once the epoxy goes stiff and tacky, you roll on the next coat, and then you repeat it. This is a really good method and one that MIK advocates. 3 Hours later, the dust, insects and leaves sticking to the mast had to be seen to be believed! Never mind, the Bosch random orbit sander, took care of that

About 3 hours after rolling on the last coat, the epoxy was quite hard. This is the stage when sanding epoxy is much easier rather than waiting for a full cure, and it doesn't cause a fine dust that floats in the air. I like to use No Fill sand paper, because it doesn't clog. In fact, the epoxy in this state actually cleans the paper and it stays sharp.

Just some quick pointers on sandpaper:

*The most expensive sandpaper is the cheapest in the long run. Believe me, don't baulk at the price of the expensive stuff, it really is good and will save you money because it lasts 4-5 times longer and you'll need to buy far less of it.
I've found the "No Fill" stuff, made in Australia to be the best available by far.
*It has a teflon-like coating that helps prevent clogging.
*The good brands produce a much better swirl free finish too. This is for three main reasons:
1.The grit particles are more uniform in size, are harder material and are sharper.
2.The grit particles have a stronger bond to the paper substrate and don't dislodge. If you are getting a lot of swirls appearing on your timber (frustrating!), this is because the grit particles are dislodging and being rolled around between the paper and your timber, producing those hard-to-remove swirls.
3.The grit particles are actually wider at the bottom (the side bonded to the paper), and have a sharper point that does the cutting.

OK, that's a very brief tip about sandpaper.

My mast is now nice and smooth and awaits a few coats of UV resistant marine spar varnish.
This pic shows the mast suspended by two screws through a couple of timber scraps clamped in the jaws of these terribly cheap (and very crap) work benches. (These things are rubbish, and only good for this sort of use. A sticker on them says they will support 300kg, but I think that's very optimistic)
Attachment 123239

Howdy, heavier wood, smaller diameter is a bad choice for a couple of reasons.

First of all, diameter is much more effective in giving you stiffness for a minimal weight increase, so the timber chosen is normally the lightest that can be expected not to die under the load - that explains both oregon and spruce as spar timbers. It is about as light as you can go and keep reliability.

For example a wood twice the density of oregon/fir would only allow the diameter to be reduced by 16%. It means that it will be heavier overall.

You can't really go to much lighter timbers ... there are not many to choose from and Western Red Cedar has wandering grain, so it is possible that an end can just fall off your spar and paulownia would probably dent from the lashings.

The second one relates to that. You might be able to save some diameter with a hardwood stick but it also makes the spar more vulnerable to defects. If a stick is smaller diameter it increases the chance that a small defect can make it considerably weaker.

Best wishes
Michael

Originally Posted by woodeneye

I've found the "No Fill" stuff, made in Australia to be the best available by far.

Is that the white paper? I've used that on paint and was impressed, didn't think of using it on epoxy. Good tip that, I'll try it.

Yeah, coating in 40C is fun. I was using the fast hardener and was sanding it after and hour and a half. Your three hours sounds about right for the slow then. At least I didn't have to sand critters out of the pox.

True story. Back in the seventies, during a bad drought in the riverland, an ad appeared in the newspaper: "Lost. One paddock. Last seen blowing towards Loxton."

Richard

Bruce,

Good looking mast! Heat or no heat, you do fine work.

Thanks for the tips re sandpaper. I'll look for No-Fill paper (is that a brand name? Hope to find it on the shelf here.)

Those sawhorses are pretty solid. I'm glad I built a set.

Bob

Often it is an "alumina" paper and is white. Some of the yellow ones on a roll are the same.

3M used to make a wonderful paper about 20 years ago. They used to get paper made in every country, so the one made in OZ was the bees knees. They then changed over to manufacturing in one place and transporting it - so it started to be imported to here. Thinner backing and it didn't go for half or a quarter of the time.

I was working on marinas and all the guys and gals doing professional varnish and paint work noticed at the same time.

The 3M paper now is still pretty good in comparison with the others, but the point is ... YES ... the best quality sandpaper is often the best and the effect is immediately noticeable.

The only thing I would add is if you are machine sanding then using dust extraction makes the sandpaper go a LOT longer, so if you do lots of sanding work (or just for the health reasons) I would strongly recommend setting up some type of basic dust extraction for as many of your power tools as possible.

Best wishes
Michael

Originally Posted by BobWes

Bruce,

Good looking mast! Heat or no heat, you do fine work.

Thanks for the tips re sandpaper. I'll look for No-Fill paper (is that a brand name? Hope to find it on the shelf here.)

Those sawhorses are pretty solid. I'm glad I built a set.

Bob

Hi Bob
Actually, the spelling is "No Fil" and it's made by Norton abrasives. Also called No Fil Adalox. If you can, make sure it's the commercial grade. You generally don't fine find it in the handyman paint areas, so look where the trade tools are or in a trade shop. If you buy the trade packs, it's cheaper than the inferior handyman versions too.

I haven't seen the 3M stuff that MIK mentions, but I imagine it would have to be good stuff too.

My eyes are red and sore this morning from all that South Aussie red dust yesterday. I suppose we should be grateful for the free load of topdressing soil

Bruce,

Thanks for the added information.

Earlier today I was running errands and stopped at an Orchard Supply & Hardware (OSH, a long-time regional farm-supply-home-improvement chain now under the Sears umbrella). Looked for No-Fill (went shopping before your spelling update) white disks of paper for the ROS. Saw nothing whitish or labeled No-Fill (or variation of that). I did buy some Norton 220 grit (bought 60 and 150 last week).

When I saw your update and learned No-Fil is a Norton product, I checked my purchase. Nothing on the packaging suggests "No-Fil" but when I opened the wrapper here is what I found:



Which is what you described! Checking last week's purchase, the 60 and 150 are also No-Fil. Interesting that the packaging does not describe the product as No-Fil.

This stuff was $4 for a pack of 4 disks. Don't know if that is expensive or not, but that seemed to be the going price for ROS sanding disks. They did have larger packages and I'll probably need those when I sand the hull.

Sometimes, when I don't know what I am doing, things work out anyway...

Originally Posted by BobWes

Sometimes, when I don't know what I am doing, things work out anyway...

Haha, that's quite funny Bob. Glad you could find it!!!

My ROS has a square plate so I just by the stuff on the roll. It works out somewhat cheaper than the round ones. Now, if only I could find my hole punching template......

Originally Posted by Watermaat

Hi MIK
You are right about laminating in general. My statement is based on the fact that for me it is easier to find more straight fine grain in thinner planks, comparing to thicker pieces. In that case laminating makes a denser piece of wood.

For me it's interesting to sort out how this "density" and "diameter" factor relates comparing with overall weight of a non-hollow spar? I have seen very light spruce yards with large diameters on those 12ft dinghies. I wonder how that compares with a thinner oregon yard if you look at weight and stiffnes. ( and eliminate windage , than it realy becomes complicated )
Do you have any idea where to go.....light wood/large diameter or heavier wood/small diamater ?

Beides being able to mix timbers, the main advantage in a lamination is to achieve greater stability in your timber. Provided of course that you orient the grain so that the timbers oppose one another.