Looking forward to building one day,  a small cruising proa, 24-30ft.  From my sailing experience and what I have picked from postings, I feel reasonable confident about the shape. 

What I am not so sure of is the scantlings for plywood construction.  Is there anywhere to get general advice:  Thickness of board, size of spacing of stringers and frames.  Size and construction of the beams.

One route is to buy a set of catamaran plans and build mirror images of the bow for the main hull.  I have currently downloaded the Woods Janus study plan.

What is the easiest way to construct?  I think the Wharram Tiki methods may be the winner, (but have yet to buy their study plan).  My thought is to join all the sheets for each side before assembly,  ready fitted with stringers.  Fairing up stringers to fit stringers, sounds tedious and would not be required.

For a quick and cheap first boat, no epoxy.  Polyurethane glue stringers,  resin /tape chines, perhaps sheath bottom.  Paint with acrylic roof paint.

Mark

Hi,

Have you bought Gary Dierking book yet?

Building Outrigger Sailing Canoes

A must if you want to build small proa in plywood.

Cheers,

Laurent

Gary’s book is a very good resource, and there are a few boats that have already been built in the size range you are looking at. Most of these use 1/4” plywood. Some have frames (JZero) and some are stitch-and-glue (Madness).

Mark - 26 May 2013 04:02 AM

For a quick and cheap first boat, no epoxy.  Polyurethane glue stringers,  resin /tape chines, perhaps sheath bottom.  Paint with acrylic roof paint.

The difference in cost of polyester vrs epoxy - minimal
The difference in performance - enormous

For prejoining side panels, fiberglass tape butt scarf is pretty easy (requires epoxy)

For paint, porch enamel provides a lot of bang for the buck.
Water base for ease of use
Oil base is a little tougher and holds up a little better in my experience.

cheers,
Skip

It is very easy to be very efficient with epoxy. I decant small amounts into small jam jars with lids. I then use syringes to measure very small amounts, I keep the resin and catalyst in separate little trays so the don’t get contaminated. I never clean anything, I use re-used disposable yogurt pots etc. I have never had any epoxy failures, or thrown epoxy away.

Tink

Burt Rutan (the Spaceship One guy, among other things) has an excellent book on moldless composite construction (basically machined foam with fiber/epoxy skin).  Gary Dierking recommended it and I bought it on Amazon.

In there he shows an epoxy balance scale.  You divide a See-saw type of scale to represent the proportion of your epoxy and hardener.  Then you pour as much epoxy as you think you need in the epoxy cup.  Then you add hardener to the hardener cup until it goes into balance.  You get a perfect mix, and you pour based on your intuition.

Pretty clever!

You divide a See-saw type of scale to represent the proportion of your epoxy and hardener.  Then you pour as much epoxy as you think you need in the epoxy cup.  Then you add hardener to the hardener cup until it goes into balance.  You get a perfect mix, and you pour based on your intuition.

7

I like this. A very simple way of getting the right amount. I always use a digital scale, but since i find it difficult to pour the right amount out of a 2 gallon jar I need a calculator to recalculate the correct amounts every time I try to mix a batch..

Thanks for a great idea.

Regarding scantings I want to say it is more of a matter how you are going to use your boat. I you want to build a pure racer that never will see a terrifying breaking 40 foot growler in the north atlantic, you can build a 40 foot proa out of 1/4 inch plywood. If you want to sail around the world, through the Strait of Magellan and cross the atlantic in mid hurrican season you might want 2 inch plywood and some beefy stringers, watertight compartments and really overbuilt and watertight hatches in your 40 foot proa.

Cheers,
Johannes

Johannes, dont forget that increased weight leads to increased loads, and possible worse sea going capabilety (not talking about speed). Heavier is not allways safer.

Kind regards
Garg

Johannes, dont forget that increased weight leads to increased loads, and possible worse sea going capabilety

Plywood, epoxy and fiberglass adds more strength then weight. Try lifting a 1 cm wide strip of 4 mm plywood 244 cm long by one of its ends, and compare with a 10 cm wide strip of 2 inch plywood. The thin plywood will bend a lot and probably break with a fast twitch from your hand.

The sea going capability comes more from the shape of the hulls, size and placement of the rig and sails and weight distribution, then absolut weight.
I would rather sail a Colin Archer then a Melges 24 around cape horn, as the Melges 24 would probably break apart and/or turn turtle and sink.

I think the idea of worse seagoing capability comes from multihulls that where designed to be light, but where loaded down with gear, food, water and because of this behaved badly.

A multihull can be as heavy as a monohull and still be nice to sail - if designed for heavy displacement.
It is all about what they are designed for.

Cheers,
Johannes

For a 24’ deep vee or sharpie proa:

Main hull
3/8” ply sheathing
3/8” frames 16” to 18” apart with 1-1/2"x1-1/2” softwood cleats
You can use polyurethane on interior joints (PL Premium)
Heavy glass tape / epoxy on all the corners (as heavy as will make the bend, 12oz?)
Glass and epoxy sheathing, this should be fairly light, 6oz or less
You will want to beef up attachment points.
You will need to add cleats in areas where people stand
Add a weather sponson

Outrigger hull
1/4” ply, otherwise same as above

Beams
I don’t know
Probably plywood box beams, 3/8” ply, and the size around 12” to 14” square, built as above

FWIW if and when Nomad gets built (26-27’ trailerable cruising proa)
Hull bottom 9mm meranti
Hull sides 24” deep 6mm okume with a continuous stringer inside at about 8” from bottom 6mm bulkheads at end of bunk flats plus fairly stout laminated ring frames near center of boat,
Most everything else 6mm okume.
Probably 12 oz biaxial on outside to just above wl. 6oz biaxial tape on virtually all joints otherwise 6” wide inside hull and stems of float, 3” wide elsewhere.

Longitudinal pieces cut from 24’ lvl beam, also makes the birdmouth masts.

Predecessor P52 was built from 5.2mm underlay ply (3/4” t&g bottom) to the same basic configuration. Only failures in several 100 miles of journeying were associated with a swing wing system no longer used and a broken mast in trying conditions.

P52’s telescoping beams were select 1x4 top and bottom caps with 5.2mm webs.

cheers,
Skip

I’m interested on your use of the lvl beam.

Besides not having to scarf it, what do you like about it?  Aren’t they super dense?  How would you compare that material to clear doug fir?

thanks,
chris

skyl4rk - 28 May 2013 01:38 PM

For a 24’ deep vee or sharpie proa:

Main hull
3/8” ply sheathing
3/8” frames 16” to 18” apart with 1-1/2"x1-1/2” softwood cleats
You can use polyurethane on interior joints (PL Premium)
Heavy glass tape / epoxy on all the corners (as heavy as will make the bend, 12oz?)
Glass and epoxy sheathing, this should be fairly light, 6oz or less
You will want to beef up attachment points.
You will need to add cleats in areas where people stand
Add a weather sponson

Outrigger hull
1/4” ply, otherwise same as above

Beams
I don’t know
Probably plywood box beams, 3/8” ply, and the size around 12” to 14” square, built as above

I would think that quality 1/4” ply would be strong enough when the fiberglass sheathing is added. That sheathing could easily add the additional 1/8”. This is especially true if the sheathing is S-glass instead of E-glass. For more information regarding the difference, see: http://www.swaylocks.com/node/1009239

Perhaps a compromise of 3/8” to the waterline or flair/chine and 1/4” above that. Foam decks where possible would increase stiffness without increasing weight or requiring bracing.

For beams, I had been imagining a system where the beams bolted onto either end of the cabin and pod, which turns out is exactly how Madness is arranged. I am wondering if the beams could be carved out of solid foam and then sheathed. To do this I was imagining laminating the blue foam from Home Depot as Smoot did with his 24’ trimaran. However, this application for the foam in his tri doesn’t have any flexural stress placed on it. Some testing is in order.

Luomanen - 29 May 2013 09:19 AM

I’m interested on your use of the lvl beam.

Besides not having to scarf it, what do you like about it?  Aren’t they super dense?  How would you compare that material to clear doug fir?

thanks,
chris

Finding nice clear lumber is a challenge and when and if you find it, pretty pricey. LVL sets a fairly high minimum standard for strength and stiffness in the higher grades and you can cut it to an appropriate size for your use. one 24’ X 14” LVL should get all the non ply pieces for what I’ve in mind for a hundred bucks and change. I’d still have the coaming and ring frames laminated from clear stuff, everything else is gonna be painted.

No idea about the fir, not much available in SE Texas, LVL probably a little denser, the draw is having a relatively consistent cost effective material, consider it a linear plywood.

Cheers,
Skip

OK, I’ll play the dumb ass…

What does “LVL” stand for?

Thanks,

Laurent

Laurent - 30 May 2013 06:28 PM

OK, I’ll play the dumb ass…

What does “LVL” stand for?

Thanks,

Laurent

Laminated veneer lumber, a lot like a one way plywood, comes typically in 1-3/4” and 3-1/2” thicknesses by a multitude of depths to 16” or more. Usually available up to 40 feet long I think, in several grades topping out at 2.1 msi stiffness.

To cross thread a little like another forum 😉 Really miss you man, proadom in Texas has taken a real hit. Also tonight youngest granddaughter gave her middle school music teacher a music stand with some of your cypress in it, beautiful as usual.

Cheers,
Skip