Custom build engine cover.

[FrankenCub]

I just picked up a really solid 1979 Thompson Sidewinder 16 for a play toy for my wife and I. It has the Mercruiser 470 I/O and is completely missing the engine cover. Problem I'm having is finding pictures of how they were originally. Most Sidewinders were either jet drive or outboard. The few I've found with I/O, there isn't any detailed pictures of the interior or have the Photobucket watermarks and you can't see any detail. And the covers for the jet drive Sidewinders were different than the I/O. Engine size being one, and the I/O version had a "hood scoop" built into them.

What I was thinking of doing is making one with a glassed foam core. I figured I can glue foam boards together and sand to shape a lot easier than it would to make a shaped wood cover.
Is there a certain type of foam that is resin safe, and would bond well to fiberglass?

I really don't know any other way to go about this. I'm sure I'd never find the correct cover anywhere. At least here in NY.

 

[Scott Danforth]

they make polyurethane foam boards made for fiberglassing. check with your fiberglass supply hous.

 

[FrankenCub]

That stuff looks pretty pricey from the sites I seen. Might be better off gluing 2x4s inside all seams of the plywood then shape the corners off till I get nice curves. Was hoping to save weight but I dont think it's worth the cost.

 

[Scott Danforth]

everything boat worthy is costly.

a 4x8 sheet of foam 1/2" thick is only $23
a 4x8 sheet of foam 1-1/2" thick is only $63

so you are right, it will cost you about $10 more to use foam core vs plywood and 2x4's. however your plywood and 2x4 engine cover with a bunch of fiberglass, fairing and gell will be about 150-175# compared to the 50-60# of the foam/fiberglass version.

 

[Reserector_]

If I understand correctly, epoxy resin can be used on foam.
I saw a YouTube vid of a guy who tested exterior latex paint over the foam and polyester resin over that. He had to go with two or three coats, but it worked.
Also check out "poor man's fiberglass" The key is not the fabric so much as the inexpensive wood glue that is used in place of poly resin. I saw a teardrop camping trailer in person made with canvas, glue and paint, directly over foam board and it was impressive.

Options to ponder if nothing else.

 

[AShipShow]

You can also use polyisocyanurate foam from the big box stores... they have a foil face on one side tho that you have to peel off... that's what I used for my stiffening ribs for my floor.

 

[Scott Danforth]

I used to make speaker boxes using old tee shirts stretched over a simple form

one coat of resin made it strong enough to then lay the cloth layers

 

[FrankenCub]

everything boat worthy is costly.

a 4x8 sheet of foam 1/2" thick is only $23
a 4x8 sheet of foam 1-1/2" thick is only $63

so you are right, it will cost you about $10 more to use foam core vs plywood and 2x4's. however your plywood and 2x4 engine cover with a bunch of fiberglass, fairing and gell will be about 150-175# compared to the 50-60# of the foam/fiberglass version.

I must have been looking at the wrong stuff. What I was looking at was easily 3 times more costly. I wouldn't have a problem at $23 a sheet. I think it was more like $60 something a sheet.

I did see somewhere about using XPS foam sheets from Lowes, and I'm pretty sure it was a foam safe epoxy resin used with it. I'd much rather go this way to save weight. I'm thinking of swapping the engine/drive out for something more readily available so weight will be a concern.

 

[FrankenCub]

If I understand correctly, epoxy resin can be used on foam.
I saw a YouTube vid of a guy who tested exterior latex paint over the foam and polyester resin over that. He had to go with two or three coats, but it worked.
Also check out "poor man's fiberglass" The key is not the fabric so much as the inexpensive wood glue that is used in place of poly resin. I saw a teardrop camping trailer in person made with canvas, glue and paint, directly over foam board and it was impressive.

Options to ponder if nothing else.

I seen that too. I'd be kinda concerned about the latex separating from the foam, then the glass being loose from the form. I'd think the heat from the engine would soften the latex leading to problems later on.

I think I'll look into the foam safe epoxy resin I seen talked about.

 

[FrankenCub]

You can also use polyisocyanurate foam from the big box stores... they have a foil face on one side tho that you have to peel off... that's what I used for my stiffening ribs for my floor.

What resin did you use over it?
I wonder if that's the same foam they are stripping off commercial buildings when they rebuild the roofs. Sometimes has a foil face, sometimes more of a fabric like face. And usually really cheap.

 

[Scott Danforth]

it takes about 3 hours to peal the foil off the sheets because it tears when trying to pull the foil off. works with poly. went that route 8 years ago for my cooler builds. however the cost per sheet is the same as the correct stuff if you have access to it.

 

[Reserector_]

I used to build model aircraft. Epoxy over foam (including styrofoam) was common, although I never did it myself. I was a film-over-wood guy back then.
But anyway, YouTube some foam core wing vids.
Pretty sure that if you use epoxy, you can use any foam you want. I totally agree with you there.
Most foams are easily cut with a nichrome wire (home made) cutter. Some sand better than others. Model airplane construction would be the entrance to that internet rabbit hole.

 

[Scott Danforth]

as far as I know, the nose cone, part of the prop and part of the motor from my first model air plane is still embedded in the roof of the school that was across the street from my first house.....rrrrrrrrrrrrrr......rrrrrrr.......thwack....:facepalm:

 

[froggy1150]

My first rc airplane...... 10 seconds up, 4 seconds down and it looked exactly like that beastie boys album. lane:

 

[FrankenCub]

I must not be finding the same info you are Scott lol. The structural foam I've found for marine use has been like $67 for 1/2", and I dont think they were 4x8 sheets. No biggie. I forgot i have a couple pieces of the structural roofing foam in storage, has a fiber like skin to it. Stuck on really good. I bet epoxy would bite to that like no tomorrow. I'll have to get some resin and test it some. If it works out I'll buy a couple more sheets to work with. The stuff only cost me $15 a 4x8 sheet and its 2" thick.

You know, it's funny you guys should mention rc aircraft. Dummy me should have thought about that. I've built a few rc planes but only one in foam, it was a box plane though. DCH-2 Beaver. The others were balsa.
A guy I know was showing off for a group of people watching, diving under power lines and around plles. Well last pass he didnt quite leave enough room. Dead nutz into an electric pole. Spinner and engine stuck to the pole while everything blew to pieces. I used to look at that pole every so often when I drove by and for at least 5 years the engine was there lmao.

 

[Scott Danforth]

this is what I used as core for a few projects. I used 2# in 1/2" and 4# in 5/8"

https://fgci.com/item/124986/Poly-Foam-Sheet-02lb-0-5-/

https://fgci.com/item/134416/Poly-Foam-Sheet-04lb-0-625-/

the strength of your cover comes from the layup, not the core material. the core material is to add spacing between your fiberglass layers.

 

[AShipShow]

Scott is correct.. the foam is not supplying any strength, it's just a light weight space filler that wont rot...

 

[FrankenCub]

The price on that 1/2" isn't so bad, definitely cheaper than what I was finding. I think I'll try that roofing foam, especially seems I can get it in 2 and 3" thicknesses. That will give me more material to sand away on the corners to couture the shape more. It isn't going to supporting any weight, wont be having any seats back there either. Just going to have seats for my wife and I. Just a play toy for us