Lee wants a new trimaran design...

[Lee.007]

Re: Lee wants a new trimaran design...

You've not been to Lowes lately, have you?

Oops, I stand corrected. I was looking at the 2 foot x 4 foot sheets of luan on their website without realizing it was not 4 x 8 sheets.

Well, for that price, I could buy two cedar 2 x 4 's at $19.48 each and make 3/16 strips out them. Subtracting the blade kerf, one board gives me 14 strips, multiplied by 2 inches wide (rough sawn is actually 2 inches wide) and laid side by side will make a 96" x 28" panel. Do that twice and I have more than a 4'x8' panel for less than same price of a nice sheet of 1/4" maple plywood.

[Lee.007]

Re: Lee wants a new trimaran design...

I am still contemplating prices here. Lowes has SPF 2x4's pretty close to pre-covid prices now. Has anybody ever built a boat out of just straight Spruce / Pine / Fir wood? I am curious about the weight comparisons. From what I can see just poking around on google, some sites say pine is the same as cedar, some say more. From my experience I know cedar is much easier to bend and work with the pine. Just curious if anyone else had an opinion?

[Tomcat]

Re: Lee wants a new trimaran design...

Normally the SPF we get is black spruce, which in old books was said to be similar to sitka, which in 2x form it is not. When you find nice stuff it is pretty good. Often strips cut from wider boards have better grade and yield. Normally it would weigh a lot more than cedar. But you never want to bank on weight, you have to do some tests.

[Lee.007]

Re: Lee wants a new trimaran design...

Yeah I agree on not banking on weight, especially for wood bought at the big boxes. But every cedar piece I have bought has been pretty lightweight. The others can be heavy as lead, especially the ones that still have a lot of moisture. I have bought 2x4's that are downright wet from the big boxes. I have a whole lot of "western red" cedar from a stack that my father-in-law gave me. I think I will just have to mill it up into strips and see how much I can get out of it before I start buying lumber.

I purchased the Slingshot 19 plans and downloaded the pdf's from Duckworks today. They did a good job drawing it up. Lots of full view drawings. Only complaint I have is that they are all on 8 1/2 x 11 pages, but I guess I can blow them up at office max if I want. Can't wait to start sawing boards and slinging epoxy!! My son still has his jeep in the garage, so I am going to just mill up strips, make some framing parts, then when he finally gets the jeep done I will be ready to put it all together and lay down some glass and epoxy.

[Tomcat]

Re: Lee wants a new trimaran design...

Sounds like fun. I made my trimaran out of doorskins. 30 years later it is still fine. May not have been the waterproof glue kind. Doesn't seem to have mattered.

[Tomcat]

Re: Lee wants a new trimaran design...

Stressform/plywood, is a simple method of making a P and S panel, and stitching them together along the keel line, then folding them up until they pop into a perfect looking multihull. Ideal for floats, main hulls can be made the same way, but for racy boats, or simply lengthened a little for less racy boats. Fastest, cheapest, highest performing multihull hull, you can make. I made my 24 footer for 3500 Canadian about 30 years ago, and I think one could come close to the same money today. Mainly because the cost of epoxy and glass have up till now, fallen a lot. I have more sources for wood, so I am probably not that far off there either. But even at the doubled price for plywood, tripled at times over the last few years, It only contributes so much to the overall cost of the boat.

[Lee.007]

Re: Lee wants a new trimaran design...

May not have been the waterproof glue kind. Doesn't seem to have mattered.

I think that is true as long as it is well covered with epoxy. On my current little kayak trimaran, I really laid the epoxy on thick on the plywood case for the kick up rudder, and it is definitely not waterproof or even pressure treated. Not a bit of delamination after a year and a half now. The partner however, I didn't lay it on as thick and it is starting to de-laminate.

The only think I think I would worry about with the luan doorskins is voids. I don't know what the specs are for luan, but I don't think it is "cabinet grade". It would be just my luck to catch a sharp rock or stick at just the right angle on that one spot on my hull that had a void.

[Lee.007]

Re: Lee wants a new trimaran design...

After reading the construction manual and carefully going over the drawings, I have realized there are a lot of things missing in the Slingshot 19 package. If anybody has built one of these before, please chime in and answer these questions:

1. What are the dimensions of the shear clamps? I cant find a thickness or width anywhere in the drawings. Looks like 1" x .5", but I am not sure.
2. Frank talks about using bondo to fair the hull. Uh, no. Since I am going to do a strip build and bright finish, that's not happening. Has anybody ever built a wooden boat and used bondo?
3. Frank also says he used PL Premium construction adhesive. Has anybody done this before and how did it last compared to thickened epoxy?
4. Frank only fiberglassed & epoxied the floor of the inside of the boat, not the sides. I think I should glass and epoxy all exposed wood, within reason. Am I crazy for thinking that is the way to go?
5. What are the length dimensions of the cross pieces? There are NO drawings of the cross pieces themselves, only a mention that they are 1"thick x 2"wide in photo 53. I may have to SWAG these i guess.
6. Frank used two layers of 6oz cloth on the hull exterior. Does anyone think it really needs 2 layers of 6oz? I was thinking one layer of 6oz, or 2 layers of 4oz at the most.
7. What is the width and thickness of the frame pieces attached to the stern face of the ama bulkheads? There is no length dimension either, but I can figure that from the bulkhead dimensions.
8. Do I need to follow Frank's rudder / leeboard profiles or can I pick my favorite NACA foil profile and use it? I don't think it really matters, I have seen some rudders that just cut a 45deg bevel on the leading and trailing edges and call it good. But I want the boat to be as fast and as efficient as possible.
9. Are the rudder control lines terminated at the pedals, or do they go through the bulkhead, pass through a pulley, and then return back out??

Call me picky, but I spent 12 years as an electro-mechanical design engineer and if the machinists had to shut down a mill and waste time to come to my office and ask for a missing dimension on my drawings, my boss would lose his mind. I really expected more from a set of drawings that cost $119. Matter of fact, the free Drifter 16 drawings were more detailed than these. I am still going to build it though, because I like the hull design already being big enough for two people and camping gear. We will see how it goes!

[mattglynn]

Re: Lee wants a new trimaran design...

Most of your questions should really be put to the designer, most of the time paying for plans includes the ability to email the designer questions. It looks like his email is on the duckworks page.

2. On plywood/fiberglass/epoxy boats a lot of people use fairing compound aka bondo to fair in the fiberglass cloth edges before painting. For example when the deck cloth is wrapped down onto the hull.

3. My faher-in-law has experimented with PL premium extensively for the past ten years or so on boats that live in the water in the south Florida sun. It works surprisingly well as long as you have good clamping pressure, however it doesn't seem to work on treated lumber.

8. You can use whatever profile you like, however I'm not sure if there is any difference in optimum profile between a daggerboard and leeboard, thats a question for a more knowledgeable person.

[upchurchmr]

Re: Lee wants a new trimaran design...

Per my understanding, Bondo and fairing compound should not be considered the same thing.
And I wouldn't use Bondo on a boat.
Bondo is a trade name for a specific product used on cars.
IMHO - well, not so humble.

[mattglynn]

Re: Lee wants a new trimaran design...

Yeah I should have been more clear, the concept is the same between an automotive fairing compound and a marine fairing fairing compound but their composition is different. I have heard about people using Bondo brand filler on small boats but have no idea how successful it was

[Lee.007]

Re: Lee wants a new trimaran design...

Most of your questions should really be put to the designer, most of the time paying for plans includes the ability to email the designer questions. It looks like his email is on the duckworks page.

Yup, I did that. No response. So then I emailed Duckworks. They sent him an email and said that he should respond, since he still recieves their payments. So 3 days later he responded to them. He was extremely rude, and all of his answers were mostly, "Anybody that reads the drawings and the construction manual should know the answers to those questions." So, I re-read the manuals 2 more times thinking I had missed something. No, I had not missed anything, and in fact I found more missing dimensions.

Even though I bought the plans, I think I am going to do a kit-bash of the Drifter 16 and the Slingshot 19. Combine what I like most about each design, and then build it using the construction method of the Drifter. I think the Drifter drawings, even though they are hand drawn, are far superior and easier to understand than the Slingshot drawings.

As I go along, I am going to make drawing adjustments. And heck, I just might create a nice cad package with complete detail drawings like I used to do when I was a design engineer and sell it on Duckworks.

[Michael K.]

Re: Lee wants a new trimaran design...

There is a Slingshot on eBay. Think of all the time and effort you'd save, even if it required a trip to Michigan.

[Lee.007]

Re: Lee wants a new trimaran design...

Hi Michael,

I looked that one up. It is a 16 footer. I am looking for an 18 to 20 footer, and I have plenty of cedar now to build one. I really do want to build one out of cedar and do a bright finish. Many of my Army friends have shown pictures of my boat to some colonels and generals and there is apparently an interest in hand made "craftsmanship" type boats. I figured I would build another one for me, and then start building some to sell as a retirement income when I retire in a few years.

Thanks for the suggestion though. The current bid is only $102, and even with the $300 boat angel document fee the trailer is easily worth that. If it was down here in the CSRA in Georgia, I would drive over and offer the guy 200(+the boat angel fee) right now. That trailer looks nice. The only thing I would be worried about is a mast and sails. I didn't see any in the photos and there was no mention of them that I could find in the description.

[Lee.007]

Re: Lee wants a new trimaran design...

Alright everybody,

Yesterday I ripped up all the cedar from the last batch my father in-law gave me into 1" x 1/4" strips, and according to my board feet calculations, I should have enough to do another trimaran, either the Slingshot or the Drifter. I still have almost the same amount on my racks in my garage that I didn't use from last time. So I am sitting on much more cedar than I originally thought. So the kit bash begins. I think I am going to call this new boat a "DRIFT SHOT". Catchy, eh?

I think I am going to build the Slingshot 19, but make bulkhead forms and stringers like the Drifter has. I want to have a skeleton under the skin. With 1/4" strips, and a solid frame underneath, this baby ought to be rock solid and last me a good while. It will make it slightly heavier, but since I am using cedar for 90% of the construction I'm not worried about that. I think I will make panels from strips, cut the hull pieces out of the panels, fiberglass / epoxy the insides of the panels, lay them up on the skeleton, and then fiberglass the outside. I like the hull profile design with the 3 planes (sides, bilges, bottoms) of the Slingshot better than the flat bottom Drifter, but I like the construction method of the Drifter better.

I also like the laminated akas on the Drifter better than the aluminum pipe akas on the Slingshot. I think they give a wooden boat a better "craftsman" feel. I may have mentioned once before doing birdsmouth akas, which Duckworks said would work just fine, but I am maybe thinking about laminated wood akas now. Much easier to make, and I can build the housing for the folding system like the Slingshot has whether they are laminated or birdsmouth beams.

The Leeboards and rudder I am boing to make the same way I did last time, laminating 1" or 3/4" thick pieces together opposing each other's grain to avoid cupping, and use a NACA foil like I did last time.

The mast is going to be tricky. Slingshot plans call for a 23 foot mast. Pulling this behind my truck on the trailer I currently have will be impossible. Anybody got any good designs you can point me to for a sturdy folding birdsmouth mast system?

So here we go. I am drawing up some form / bulkheads based off inferred dimensions from the Slingshot plans, and will soon be building the frame. I plan to be finished by summer, so I can get on the water with it within 8 to 12 months. Wish me luck!!