Thread: Birdsmouth for GIS Main Mast

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

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

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 . . .

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

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

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)



This is probably a more sustainable level!

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

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.







MIK

Originally Posted by Boatmik

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)



This is probably a more sustainable level!

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
would you recommend a certain kind of fitting them straps?

Greetings - Jörn

Howdy,

See this and the following few images
http://www.flickr.com/photos/boatmik...7594524425079/

Here is a sample image from that series


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

Michael

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

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

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

Mik that all sounds quite brilliant to me!