Trimaran - Especially Searunner - Owners

[gruffa]

Oh, interesting.
I think the ad said it was built with epoxy.
It's tempting.
But I already have a boat...

[longjonsilver]

Originally Posted by w32honu

There is a beautiful custom Marples 40 foot "Fast Cruiser" trimaran for sale.

The specifications on Yachtworld for the CC40FC say bridge clearance is 47' (air draft?), but the specs for the CC40M on Marples site say the bridge clearance is 53'. A 6' difference is significant. i've heard about boat designs having a tall rig, but a short rig???

Any idears? honu, do you know?

[Randy]

Originally Posted by longjonsilver

The specifications on Yachtworld for the CC40FC say bridge clearance is 47' (air draft?), but the specs for the CC40M on Marples site say the bridge clearance is 53'. A 6' difference is significant. i've heard about boat designs having a tall rig, but a short rig???



Any idears? honu, do you know?

I wouldn't have much confidence in Yachtworld stats.

[md7a]

My winter project is to build a new ama for by A-frame 31, and I'm looking for tips.
Pineapple Express was started in about 1969, and the ama's were built with polyester resin, fir, and a mix of steel staples and copper ring-shanks. A couple of years ago I had storm damage at the dock, and had a pro do a near-complete rebuilt of my starboard ama with real marine ply, stitch-and-glue. The difference is amazing - the rebuilt ama has about 7% lower humidity than the other one, which is pretty important here in the pacific northwest winters.
So I'm pulling out my plans and borrowing some shop space. I have a good set of plans from John, plus the Construction manual, and a pretty good set of tools from almost 20 years of dealing with Searunner repairs.

Can any of you help with the following, or with other things I haven't thought of yet?

1. What kind of plywood? Meranti? Sapele? Ceiba? Fir?
2. How many sheets do I need? How many mistakes (spoiled sheets) should I expect?
3. What do y'all think of stitch-and-glue vs nails or screws?
4. How long does it take to build your first ama?

[Randy]

Stitch and glue won't replace the need for fastening the plywood panels to the stringers. S&G is used to fasten adjacent panels.
For plywood type I would use the same that was used for your study ama to balance the weight. It seems to me that if you used saplele, the port ama would be a fair amount lighter than stbd.
Best of luck with your project! Please keep us updated.

[Cavalier MK2]

You can get Marine fir at Hardell on the West side of oly, it is great but pricey. Meranti is about the same weight as fir and similar rot resistant. Okoume is light but needs careful coating as it isn't rot resistant. For Meranti you might try Architectural Woods in Tacoma as a alternative to Eden Saw. Bronze ring shank nails can be had at Tacoma Screw on Martin Way.
I'd build stringer and frame and then stitch and glue the seams. I don't think you'll have waste, I like to draw panel patterns at 1" per foot scale and move them around a 8x4 inch rectangle to maximize material use

[Buzzman]

Avoid leaving steel or even S/S fasteners in the plywood or timber. While Randy is correct - you can't stitch and glue the ply initially - this is the beauty of this methodology.
Literally you 'stitch' it together, then 'glue' it. And reinfoice the joins with fibreglass tape.
The stitches can be either cable ties (zip ties) or wire, twisted to tie off.
Some builders use copper wire, fold the twisted bit flat, and simply glue and tape OVER the 'stitches', but this makes for a rough 'finish'.
Another way to do it is to use a strongback with 'frames' (like bulkheads) and actually screw the ply planks/boards to the 'frames' with a plastic or nylon packing piece under it. You can do this with nails as well, and the plastic piece enables the nail to be removed, but also prevents epoxy glueing to the fastener...
In either case, once the 'stitches' are in place, and the hull shaped properly (i.e. don't let it 'rick' out of shape) then you tape over the join between the ties. Once glue dries, remove ties and tape of the whole length of the seam/join.
For a Searunner ama I'd recommend using the frames/strongback method so as to keep the ama plumb, level, true and properly shaped as per the plans.
I'd imagine the plans include bulkheads, so use those as the frames, but only use temporary fastenings when fixing the ply down to the frames, and remove them after the initial glueing/taping.

[Cavalier MK2]

I've actually been wondering about the repaired ama. Were stringers used and if not was thicker ply substituted? If so you might consider making a set of amas if weight and shape between the 2 is a consideration.

[md7a]

Originally Posted by Cavalier MK2

I've actually been wondering about the repaired ama. Were stringers used and if not was thicker ply substituted? If so you might consider making a set of amas if weight and shape between the 2 is a consideration.

Yes, the repaired ama was done to plans, with stringers, butt blocks and standard skins of meranti. MacKenzie Devin did the work and it's lovely.

I think I'll stick with the Searunner method and ring-shank nails now that Cavalier has pointed me to a good source.

[Cavalier MK2]

Well that's good, on the repair. I'm too busy to know the local boatbuilder scene, nice to know there is one, I do my own whittling when I can steal the time.
So at a quick glance it looks like 2 sheets of 1/2 inch on the frames and something between 8 and 12 sheets of 1/4 for the skins. I forget what the deck takes but probably a couple sheets of 3/8s? If you want to practice run off plan sheet 1 and cut out the ama frames on light cardboard or thin birch from the hobby shop, set them up and use pizza boxes or balsa for the skin patterns to see what you can layout on the full size sheets to avoid waste.. Draw a 8 x4 rectangle to the frame scale and play with the puzzle. It isn't really as silly as it sounds with the price of ply, 1/4 inch can be $100 a sheet these days.

[Cavalier MK2]

Make sure you don't use hemlock for the stringers or frames, not rot resistant at all. You can sometimes find decent grain in the Doug Fir 2x stacks at Lowe's for recutting if you want to skip premium pricing.

[Buzzman]

Originally Posted by md7a

I think I'll stick with the Searunner method and ring-shank nails now that Cavalier has pointed me to a good source.

Ring shank nails are old tech. They were recommended for Searunner (and other ply panelled tris) in the early years becasuse they were the 'best tech' of THAT time.


This is no longer the case.


The common modern practice is to use either screws or flat-heated plain shank nails driven through a strip of nylon webbing for ease of later removal.


The nails only hold the timbers together while the epoxy glue dries.


There is absolutely NO need for nails to remain as fasteners, and they will always be a 'risk' for rust and 'nail spalling' if the slightest bit of moisture gets into them.


If using bronze ring nails this is not an issue. But they are not cheap.

Far better to simply screw the ply panels onto the stringers and frames, tab with glass and epoxy on the inside, then remove the screws and tape and epoxy the exterior joins.

Hull will be probably be stronger using this method, even if you only fillet the inside joins and frames and don't tab them as well.

But definitely tape the outside at least.

[Cavalier MK2]

I like bronze ring nails, incredible mechanical holding power deep into the wood, not just the surface fibers like epoxy. Plus..... Call me lazy but I like skipping those extra pulling and filling steps ha ha.

[Cavalier MK2]

I noticed I gave the ama skin estimate for the set. One ama would be about 4 sheets of 1/4". Both for and Meranti come in at about 36 pounds per cubic foot density.

[catsketcher]

Douglas fir for the stringers and ply sounds good. The rot resistance is mollified by epoxying the entire interior with three rolled coats of clear epoxy after construction. In Australia I would probably use slightly larger cedar than specced for Douglas fir for the stringers and Hoop Pine for the ply.

I would most strongly not recommend any nails. For one nails are a place where you can get a sort of galvanic corrosion with timber. You can sometimes see this with old flooring, the wood around the nail turns black. Secondly, there is no need to have point loadings of "strength" when you can have much wider high shear strength epoxy glue over all the stringers. Point loads are bad conmpared to beautiful wide glued surfaces. There have been no modern boats using ply in the last 30 years that put potential issues into a composite boat if not absolutely required. Also, the buggers eventually show up in your finish. Even under 6 oz sheathing cloth and filler, the differences in expansion co-efficients will mean that one day, when the sun is low, you could see all the nails in a row along the boat. Plus, they are bad for lightweight boatbuilding. You never want to hammer into light timber unless you have someone inside with a weight - a dolly. The light timber just bangs around.

BUT

With a cheap 500 pack of drywall or chipboard screws you can gently screw in the ply onto the stringers. Set the torque so that it stops with the head bitten into the surface and the job is easy. I reckon I could plank up the sides of a Searunner 31 ama in a morning. Nice fun job with screws. Then the next day out the come and you then get to put a lovely EPOXY fastener in there. Push the filler in the side of the screw hole. Will take about an hour I reckon. Then a quick sand and you are ready for glassing.