Hull boat design practice poor man's composite idea

Great accommodations is vague.
A relatively light displacement speed boat with modest power could be tested somewhat safely with quite a bit simpler and weaker setup than higher power planing vessel that can take some chop.

Xps insulation foam and hot wire cutting can work but has own issues. Polyester is out of question. I would not try anything too substantial.

Remember that typically hull is 30% of the cost of the whole build. Using real plans by experienced designer is smarter choice.

 

I have plenty of plans just none what I want, small cats are funny everyone wants to draw plans for fast cats but I don't want a fast one I picked a catamaran for it's stability, it's ride, it's look. I'm good I am using multiple people and plans from professionals to base my concept on. Besides will be in 4' water and going slow,, thanks

 

This is so very true ! You won't be left to pick up the pieces, the pieces will pick you up.

 

I will test and retest before the mock up so odds will be good it lasts long enough to get info I need. I can get part of it before it touches water how the interior /exterior layout feels and looks. Can change it around. this has value in multiple ways. Who knows maybe thrifty professional designers are rooting me on. It's expensive to build a boat the first time out to learn it's qualities. Evolution not Revolution here guys.

 

Likeboats having fun is good and I am not opposing it. Just making a point that in many ways what you are planing to do is not smart. If the fun over weighs the cons then you are good.

It really would help helping you if you defined the boat more accurately. Now you are dropping info in tiny bits. 24' cat that is not fast and has low draft and large accomodations - that is what I have gathered but I would suggest more accurate definitions and more numbers.

As its a slow boat I think you could just glue and screw xps to wood frame (2 by 4"). The foam can be glyed with cheap pva glue. Wire cut it, sand it and glue (water and pva) cotton sheets for slughtly more abrasive resistant surface. Forget real composites for now. Paint with something that doesn'r melt the xps.

 

Xps is the pink and blue foam in original post. Pva is Elmer's I have learned a new appreciation for it in boat building but looking for multi purpose stronger bond check out foam wars video on YouTube
I am building a slow boat but not a heavy one. To maximize accommodations in a small foam cat it has to be built light and strong so as much strength in the shell as possible.
Glidden gripper doesn't melt the foam and is a next generation primer/glue,composite the stuff might actually last a couple summers if pulled out of the water in my eyes for cheap it even sticks great to prepped recycled plastic twin walled cardboard.. so I might have Same Weight as foam/basalt fiberglass carbon fiber honeycomb build on final build or something less expensive but exciting to work with. Some guys like me like working with their hands and remember we were the generation that lived through lawn darts..we will be careful.

Anything cheaper/stronger that will stick to foam,sandable, make a good composite can use corrugated twin walled plastic sheeting with and take a polyurea,or cheap epoxy exterior???

I would like to keep my design private I don't ask every designer I make friends with to put there plans online for everyone to take. Meeting the mock up goals is no small task let's focus on that.

 

IMHO you are going the wrong way. If you want cheap and light and xps you must use epoxy and fiberglass cloth. The cheapest epoxy you can find that still is 100% solids (even flooring epoxy) and the cheapest chinese fiberglass cloth will deliver. Strip plank with 1/2" XPS, 200gr/m2 fiberglass cloth and epoxy either side will be ok for a low stress mockup.
The other option would be to substitute wood for xps, SPF is fine, and laminate either with epoxy and cloth or with CSM and polyester. Wood with CSM and polyester would be the cheapest option.
Paint it with whatever is cheapest locally.

 

Ha ha,. No that wasn't the same one thanks for the laugh.

 

Ok Rumars this deserves a fair shot We should all go into this with a open mind and a tightly closed wallet and see where the facts lead us..
Will have to compare costs and goals with various methods then see which one is best fit..

 

I don't really think you have a choice. If you want to learn about foam boatbuilding you need to use resin and cloth. Painting primer on top of mesh will bring you nothing, not to mention that it's futile structurewise. So for cheapness you have a few choices:
1. you skimp on the foam. XPS is cheap but incompatible with polyester resin so you must use epoxy. Cheap 100% solids epoxy exists, you just have to find it.
2. you use polyester resin. This is very cheap but you must either use a more expensive foam (polyurethane for example) or use wood. Polyester resin also opens the door to using CSM wich is cheaper then cloth.
3. you try to skimp on resin and foam alike and use polyester on top of XPS. This means sealing the foam with PVA glue and paint. A good method for making a mold but inapropiate for anything more than a static display because the fiberglass skins will not be glued to the foam, so there is no strenght.

Let's consider the final boat for a moment. You want a light multihull so your options are limited in construction. Carbon/honeycomb is probably to limiting in shape and hard to do. Next in line for weight/strenght is carbon/foam. Doable at home but if puncture resistance is to be observed not considerably lighter then thin plywood and usually more expensive. Next would be strip plank/carbon-epoxy and strip plank/fiberglass-epoxy using a light wood as cedar. Last is foam/balsa with fiberglass-polyester. Cold molding is also possible but weight ranges with skill.

So what is the final construction gonna be? Are you going to make a mold from your mockup and infuse a carbon/fiberglas/foam/balsa sandwich? In this case any method for building the mockup is ok since learning infusion will be a separate thing. If you go stripplank wood then build the mockup stripplank SPF with cheap epoxy or polyester and cloth or CSM. If plywood then do a cheap ply mockup.

If it was me the mockup choice would be easy. Buy the cheapest softwood in my location, cut to 6-8mm strips, glass inside-out with polyester or the cheapest epoxy. Minimal fairing and a coat of paint. Bulkheads out of exterior ply. Furniture mockup out of whatever, thick cardboard, thin ply, OSB, EPS, XPS, anything goes since it's not structural and just has to represent space.

 

I concur with Rumors. The cheapest structure will be made of wood. If you want to try to save money you could only tape the seams with epoxy fiberglass. Chine logs and Tightbond III is cheaper yet but now there is skill level to consider. Skin on frame can be even cheaper but it requires both design and build skills.

Fiberglass on foam core comes in two varieties -high quality which is expensive, and complete garbage -which seems to what you are asking about.

Have you considered the fact that you will have to register the boat you are building? Imagine yourself next to you pile of glue and garbage explaining to the representative from the dept. of natural resources how it is as good as the production boats he is trained to expect.

 

Fair comparison will require facts,facts facts a spreadsheet ,numbers ,materials list, testing of different materials with posted results, compare real products and prices anyone can access.
so next question how do we make a spreadsheet to compare on here everyone can access and put their info in that doesn't require a degree from MIT to figure out how to use.

 

Ok we need fair and honest guidelines to compare everyone agrees.

I did check with DNR a in transit works for testing but need stickers on final build, They said private ponds you can do whatever you want but wear a life jacket.

 

I'm surprised the delete function works for any posts more than 24 hours old.
I'm out of this thread. Nothing to learn here.

 

There are polyester resins that work with EPS foam, there are also Polyester primers that can be used on EPS foam that act like a barrier between the EPS and normal polyester resin. It's commonly used on CNC cut EPS tooling (making plugs and shapes), the low cost and easy cutting of the EPS allow for very large shapes at a lower cost.

I'm not saying this is what he should do, just saying they are available.