Discovery 20 Trimaran (Chris White design)

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Discovery 20 Trimaran (Chris White design)

Postby Fellow Traveler » Wed Jun 08, 2011 9:46 pm

I received the plans today for the Discovery 20 Trimaran. It is a bit more of a complicated build than the two jpg drawings Chris send made it seem, but still, I think, manageable.

Basically, the construction method is similar to Kurt Hughes cylinder mold method. A mold is built out of plywood, with two sides 4 feet apart and curved "frames" every 24 inches. The boat is then cold-molded over this (or vacuum-bagged, if you are equipped for it) using 3mm (1/8") veneer or ply. The same mold is used to create each side of the hull as well as the sides for the amas. Once the half hulls are created and covered with a layer of 10oz cloth and epoxy, they are removed from the mold, stitch and glued together along the bottom, and finished out.

I will post more if and when I decide to pursue this project....step one is finding a place to build it!

Doug
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Postby Fellow Traveler » Sun Jun 19, 2011 11:21 am

My attachment limits were increased, so here are the JPG's Chris sent me on construction on the Discovery 20. What these images fail to show is the molding process for the hulls themselves. I have loaned out my camera, but when it gets back from Alaska, I will take some pics that show the mold that the hull is formed around, as I am sure the description I gave only confuses people. I will also show the basics of how the Akas are constructed.

Doug
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Postby Fellow Traveler » Sat Jul 02, 2011 7:32 am

My camera returned from Alaska, so here are some not very good pics of a couple more pages of the construction plans. They show the Discovery 20 profile and sailplan (just for inspiration!) and also the diagrams for building the construction jig or mold, around which the two layers of ply or plywood are formed. I erased most of the measurements so that Mr. White would not object to sharing his plans: they show the method, but not the specific dimensions.

Fair winds!

Doug
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Postby Lorenzo » Sun Jul 03, 2011 6:11 am

Hi Doug,

Looking at your Tri's general dimensions, I see that we have the same Aka spacing at 8' on centers. It provides a good length for the seats of 7' at the least, the same dimension as bed. Good for camping, right?

What's the beam of both Vaka and Ama?


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Postby Fellow Traveler » Sun Jul 03, 2011 11:17 am

Hey Lorenzo,

Chris says the cockpit is 7x7, and that is part of the sales pitch for the design: so comfortable he took his grandmother out sailing in it!

I do not know the exact maximum width, as the plans only show width accurately drawn at the akas. However, based on this, I figure the vaka is about 30" max beam, and the amas about 12". At the waterline, I get about 18" for the vaka.
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Postby Fellow Traveler » Thu Oct 20, 2011 11:52 pm

After much delay, construction has begun on the Discovery 20' Tri I've been contemplating. Work so far has just been on the construction form (mold, or jig). I will attach some pics.

The photos show first, the sides of the form, which I think are a constant curve. As you can see, though, the ribs that go between the two sides have a variable curve. They are all build identically. The form is used to mold 1/2 of a hull (both Vaka and ama come from the same mold). Since the mold is symmetrical end to end, when you cut out the hull shape from the laminated section, one side of the hull uses on end of the form for the bow, the other uses the opposite end, so you end up with a mirrored pair.

The form is 24 feet long (finished hull is 20 feet). The next stage is to put 3/4" x 1 1/2" strips of wood, on 6" centers, running the length of the form on the ribs. This is what the plywood (or veneers) will actually bend around and be attached too.

I contacted Chris White, the designer, with a few questions, but got 0 response. It seems he is too busy with his high-dollar catamaran deals to worry about this little daysail tri. Too bad, it's an excellent design, and might get more self-builders interested if he offered the support Mike Waters does with his W-17 and W-22 designs.

I will continue to document the build, and feel free to contact me here or directly if anyone has specific questions about the process.

Cheers,

Doug
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The form, with ribs attached, but still lacking the stringers.
Gluing blocks at the joints in the sides of the construction form.
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Postby MOX » Thu Oct 27, 2011 3:36 am

Hi, Doug! I plan to start building D20 in the spring and so I am very interested in your message. I wish you success and waiting for new photos. Sorry for my English, I was not the most diligent pupil. :D

Andy
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Postby Fellow Traveler » Tue Nov 15, 2011 8:24 pm

Progress continues on the project. Photos below. The plans call for 10oz. fiberglass, one layer, on the outside. I have only sourced 6oz, so I've added two layers to the outside, and decided to add one layer to the inside since the local plywood is softwood. The inside layer made the hulls much stiffer (but, of course, heavier).
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Second layer of ply down on the jig. This is for one of the amas (katig) so it does not completely cover the mold.
The jig, or mold, with part of the first layer of 3mm ply stapled in place.
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Postby Fellow Traveler » Tue Nov 15, 2011 8:30 pm

Putting the hull pieces together.
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"Stitching" the pieces together with wire ties.
The two halves, checking for how they will fit.
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Postby Fellow Traveler » Tue Nov 15, 2011 8:35 pm

The bow has a laminated, curved piece of wood that the two sides attach too and that takes the chain plate for the forestay.
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The bow, waiting for the stem piece to be finished. It is cut in a long V, 24" long, 3 1/2" wide at the top, down to 0 at the bottom.
Laminating the curved stem piece.
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Postby Fellow Traveler » Tue Nov 15, 2011 8:38 pm

And, finally starting to look like a boat!
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Vaka, bottom stitched, ready to be puttied and glassed inside Thur.
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Postby pinoypiper » Tue Nov 15, 2011 9:11 pm

looking good! :) keep the photos coming...
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Postby Lorenzo » Tue Nov 15, 2011 9:17 pm

WOW! I envy those curves. Any idea how many hours you spent on that ama skin?


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Postby Fellow Traveler » Tue Nov 15, 2011 11:21 pm

Lorenzo

First one, of course, took a bit longer as we figured out the technique, but now, with two helpers, we can put 1/2 a hull together in about 4 days. The amas are a bit smaller, so that might save us a 1/2 a day if all goes well, but the epoxy takes the same amount of time to dry! Of course, we now have other projects we can be working on while watching epoxy dry, like putting the 2 pieces already built together.

We put both layers on dry, then pull up the second layer and epoxy it down, one piece at a time. I've been rolling a thinned layer of epoxy onto the ply before using the regular, in hopes of it soaking into the plies to help hold they ply together (I noted the posts about Tuffply delaminating a while back!). I'm using monel staples for the first layer since they stay in place. The second layer uses cheap staples, and lots of pan-head screws to hold the plies down and together. These all come out once the epoxy has set up. I also put a row of screws in the first layer right at the bottom edge (the more curved part of the mold), then start the next layer just above those screws. Otherwise, the bottom layer tends to spring loose if bumped or something.

Each piece needs to be scribed and cut. I made a simple tool to do the scribing: a piece of 3/4 x 1 x 8" wood. A small piece (3/4 x 1) of the 3mm ply is attached to this to follow the edge of the ply, and a hole just beyond the piece of ply holds a pencil for drawing the line. two pieces of wood 1" long hold the new piece of plywood the proper distance away so that the scribed line means only a small trim on the piece. I will take a few pics of the "device" and us using it.

Three people is really the minimum for building the hulls as it takes two people to force the plywood into shape while the third person either scribes it, or staples/screws it down. Four is good the day we glue the second layer on: same requirements, but then a third person just mixes epoxy. Of course, one or two people could do it with clamps...but the time factor would go WAY up.

Epoxy: I am using Pioneer Clear thinned to coat the plywood in the inside faces, and then not thinned for the glue-up. The gluing ability of this epoxy is stronger than the plywood....so no need for greater strength. The thick consistency is good for filling the space between the layers which is inevitable. I am using Cord Laminating epoxy to apply the cloth.... Here the extra strength and thinner consistency are of benefit. Of course, I am using WAY more epoxy than a chined, single-skinned boat would use...and epoxy is by far the most expensive part of building the hulls (sails and rigging will, of course, rival it).

I have never cold-molded a boat before, but have built several hard-dodgers for cruising boats using a similar technique. The difference is the dodgers had a simple curve, although rather extreme, so the thin plywood was needed to achieve the shape. The trimaran is not as severe a bend as the dodgers, but it is a compound curve, so you are "torturing" the plywood a little, and also cutting it in strips narrow enough that the "steps" created by the fore/aft bend becomes negligible.

If all goes well Thur. putting the vaka pieces together, I will start pulling my order together for sails (Hyde) and rigging and other parts (balikbayan box, with most stuff from Rigging Only, in Mass., US). I hope to be sailing in Feb.

Cheers,

Doug
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Postby maligno101 » Wed Nov 16, 2011 6:06 am

All that trouble is rewarding you with a beautifully shaped hull! Love those curves!
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