Thread: Goat Island Skiff

Stitch and glue only really works when the timber can't split. This might mean the mast is made of plywood.

Plywood is not an efficient material for spars because you lose half the strength and something like that in stiffness too.

Did you see this page a bit further down ... on Birdsmouth masts. Anyone can give me a yell for the drawings by email if you have a Goat Plan already.
https://www.woodworkforums.com/f169/birdsmouth-gis-main-mast-81462

I can put you onto someone who can cut the staves and do the birdsmouths for you if you want.

MIK

Hi MIK

In the the article I read, the mast was made of tapered timber staves (No not ply. I agree ply won't work) similar to the birdsmouth method, except that the staves had simple 90deg edges and were stitched in the same manner as a boat is. The mast was made in two halves, over a series of about six shaped moulds. The moulds were either round or oval shaped depending on the desired shape of the mast. Then the two halves were brought together and glued. After that they were epoxy filleted in the same way as you would a plywood boat, and a layer of fibreglass finished off the process.

I think I have enough info in my head to draw a plan of the process, but the article has vanished. I did find the remnants of the page in Google's archives, but the pics and drawing are missing, which is somewhat frustrating.

Dear Bruce,

For my 4.5 M long lugsail mast for my Apple 16, I made a wooden core of 4 quarter-round pine decorative ceiling moldings from the lumberyard stitched and glued together. This produced an 8-sided tube with a slight oval hollow core and wall thichness of about 4-5mm. I coated the inside with a couple of layers of epoxy. I rounded it with a plane. The stiffened it with 3 layers of heavy carbon cloth sleeves and a thin protective sleeve of light glass. weight 9.0 kg and VERY stiff. Diam about 70 mm. Choose the molding that suits your use if you don't want to use carbon.

Peter Lord

I forgot to say that I tapered the top of the mast above the yard by just planing a bit off the edges of the 4 moldings. As the mast is attached to the sail only at the yard and via the downhaul just above the partners, and on "the disadvantageous" tack the sail presses evenly on the entire mast, I didn't think it should be tapered below the yard. Mik's requirement (and mine, for appearance's sake), was fulfilled by the taper above the yard, about 50 cm to the halyard block.
Peter

Hi Bruce,

It does sound like a messy and complicated job. Moulds don't sound easy if the mast is tapered.

Either a birdsmouth or the square hollow masts will get down to the target weights without the complication and look .... well ... wooden

Depends what you want of course. It is your boat after all!

I did have one person on the PDR forum say last week that he spent more effort not building the square hollow mast (he went through a number of iterations, solid, coopered, aluminium with a tapered top and another which I can't remember) than actually building it.

MIK

Originally Posted by Glug

Dear Bruce,

For my 4.5 M long lugsail mast for my Apple 16, I made a wooden core of 4 quarter-round pine decorative ceiling moldings from the lumberyard stitched and glued together. This produced an 8-sided tube with a slight oval hollow core and wall thichness of about 4-5mm. I coated the inside with a couple of layers of epoxy. I rounded it with a plane. The stiffened it with 3 layers of heavy carbon cloth sleeves and a thin protective sleeve of light glass. weight 9.0 kg and VERY stiff. Diam about 70 mm. Choose the molding that suits your use if you don't want to use carbon.

Peter Lord

Just checked here https://www.woodworkforums.com/showth...=74360&page=41
MAM used an aluminium flagpole available cheaply locally that weighed 20lbs.

Same weight. A tiny bit longer, stressed for two people hiking hard. The Goat Mast doesn't move much either.

I don't have a weight on the birdsmouth mast yet, but I would expect somewhere in that ballpark too.

That's always the problem with designing things. If they are too strong or stiff, you never find out. I do suspect the Goat mast is too stiff and thus too heavy - looking forward to sailing trials of Dana's birdsmouth mast. If successful it means all the Goat masts can be scaled down a bit.

A pure carbon mast could be designed to have a very significant weight advantage. But whether the effort in doing it makes enough of the difference to the function of the Apple or the Goat.

It is fun to play around with different methods, so if it is fun to build one ... why not?

MIK

I didn't find the article I was looking for, but I found this image with some options. The centre one using 1/4 round beading can produce a nice oval shape, but be more expensive than the square one naturally. Still relatively cheap to make yourself though.

My dad (an electrical engineer) made my wooden Sprog mast in the 70's when everybody had aluminium. It was very unique because it was a hollow triangular section that was heavily tapered and had the bolt rope track routed out. It was made quite light with jelutong and meranti and bend was controlled with forward facing jumpers at 90deg to each other. The mast could bend like a Finn mast for windward legs and be made as stiff one dared for downwind, even forward bend! I believe that jumpers are now banned in Sprogs so sadly wooden masts are now no longer competitive.

As you say MIK, wooden masts are a lot more fun. Also, they give you more options than any other material, and if you want more bend you can shave some wood off (a good way to find where the optimum is MIK; you keep doing this until it breaks!) In the same way you can add stiffness to certain spots by glueing more wood on.

Here is the pic I found:

For those interested in a locally made balanced lug sail for the GIS, Duckflat Wooden Boats (Australia) has quoted me $855.00 for a 5oz cream coloured dacron sail with 2 reef points. Slightly more expensive than plain white in a lighter weight, but I believe the cloth is very nice.

http://www.duckflatwoodenboats.com/index.php

You can see why I chose the second! No complex shaping at all.

.. and also non obviously the square or rectangular mast can be designed way stiffer than a round one for the same weight of materials. Or lighter for the same stiffness.

But nice to see so many options! Well done.

MIK

If you are in Sydney, there is a beautiful GIS on display this weekend at the TWWW show. Just go and drool. This is a boat that looks so much better in the flesh than in pictures!

Originally Posted by jmk89

If you are in Sydney, there is a beautiful GIS on display this weekend at the TWWW show. Just go and drool. This is a boat that looks so much better in the flesh than in pictures!

Awwwww......

Whose boat is it?

Might be the guy who is the agent for Lie Nielson tools if it is there. Or an unidentified one.

What colour is it? Cool that it is there.

MIK

MIK

Didn't get a photo. FIL will be there tomorrow and I will ask him to take a picture.
Red exterior, varnish interior
Said that it was made at Duck Flat, and was a first boat, so may have been at Spring or Autumn School

I wonder if it's this one?