Build doghouse over engine

Have a 21' 1975 Glasply with a 302 mercruiser and have been getting her ready for fishing up here in the Northwest. The old engine doghouse (cover) was rotten and in bad shape so 'deep sixed' it. Now have to replace. Would like to look at a fiberglass (light weight) cover. The old one must have weighed 75 lbs and was a 'back breaker' the lift off. Any thoughts?

Thought i might manufacture one...use a heat shield material back with insulation formed to fit the engine compartment...then have rhinoliner spray it. Would that work? Otherwise...haven't used fiberglass before...just mold the outside with fiberglass. Would that hold? Could we put weight on it i.e. if someone sat on the cover?

Just rambling...would appreciate some of this forums experience in building a engine cover (doghouse). i'm an old medic that rode carriers and repair ships during the 70's...that's the experience i offer...i'm a little mechanically challenged...but appreciate the help!

You can see the old doghouse in the pics. It 'was' about 32" x 32" by 24"H. Going to keep the same 32" x 32" but want to reduce the H to 18". It will restrict the air flow some but still appears to be ample flow aft to the transom.

Thanks for the help

 

If you go fiberglass, then use wood covered in fiberglass. If it were me, I'd go Aluminum.

 

Muddy, Al is one of the best heat conductors we have! I would rethink that! And what should be difficult in making the same house in ply Epoxy? I´m sure, PAR will chime in here sooner or later and tell us his point of view.

Regards
Richard

 

You could make a mold but it would be quicker to build a plywood box and then lay glass/epoxy on it.
You will need solid wood corners to get a soft radius. The corners can be any suitable wood with about a 1 1/2" square section, then radiused outside and a 45 degree angle inside. The plywood (3/8") can be set into a rabbet cut into the corner pieces. Then glass the ouitside with epoxy and glass the inside corners and coat the inside with epoxy.
Short of making a mold, this will work best. You can buy insulation and cement it to the inside, though a mechanical means of holding it will be more secure. You could run steel banding across the insulation and screw it to the frames.

 

I made one for my old 23ft Winner out of plywood covered with 2oz fiberglass cloth. then painted it. On the inside I used sound dampening foam insulation from HD. Weighs less that the old one and is multifunctional because the top is flat with a raised mahogony lip around it.

 

Naahh, thats to simple to be good.
I would make it about that way though.
R
R

 

head down to the depot, grab 2- 4'x8' sheets of laminated chip board, cut to shape. Build box (dog house), radius corners with clay, spray with gel, lay glass, core with whatervr, glass again. Let cure, dismantle mold panels, trim part . You should be able to get that part down to 50 lb.

 

You guys are great! Sounds like a great idea. The 3/8" ply would be a lot lighter than the old 5/8" ply on the 'deep sixed' doghouse. The glass would give it strength (without a lot of weight) and durability as well as waterproof it. Did i miss something?

Not quite sure how i would use aluminum. Guess go to a metal shop and have them fabricate to the dimensions of the old doghouse. Would i cover or insulate it with some other material? Also sounds like a good idea. Give me some information on the aluminum doghouse.

Thanks again

 

NO, No, nope. Hot glue foam together, right in place, in the shape you need. Off the boat, Router radius the corners, epoxy and BTI, putty smooth with lightweight fairing putty, then paint (don't even need paint if it's getting the vinyl treatment), then insulate. Easiest thing you ever did, and you'll be able to lift it with your tongue (it'll be light).

 

Alan...am really new at glassing. Have the 3/8in ply and 1 1/2 corner pieces and am ready to constuct. Not quite understanding the epoxy. Do i apply just epoxy to ply on the outside? Or do i glass and apply epoxy over the glass on the outside? Sorry to be so uniformed about glass...are you suggesting i glass just the rabbeted corners...and epoxy the rest? Help.

 

Foam and putty doghouse

Mark...now this is what i am talking about! Already bought the ply and wood but am interested in hot gluing foam in place. What kind of foam? The rigid insulation foam you can buy at Home Depot? it comes in widths of 3/4 up to 2 in. Really like the concept. If i router radius that stuff it comes apart???No??? Do you have another foam you are suggesting?

You mention epoxy and BTI then putty smooth with fairing putty. Again, new to glassing. Just put expoxy over the foam??? No glass...then putty. What is BTI (you can tell i am a newbie)? i am an old retired salt (21 yrs Navy) but just know nothing about glassing....or fairing putty. help

 

Lights are coming on...seems all of you experts are suggesting one of two methods...1) build a doghouse out of ply and 1 1/2 corners (radiused..for safety???) and glass it...for use as a ply/glass doghouse or 2) build a form out of foam or any rigid material, glass it, remove the panels and have a fiberglass molded doghouse. Duh???

Would the fiberglass molded doghouse have the strength of the ply glassed doghouse? I want to build the lightest, strongest doghouse...in case someone falls on it or???

In the case of a fiberglass (only) formed doghouse...would i have to insulated it for noise or heat? help.

Again all thanks for your help!

 

Have a frame built out of built out of 1X4s then cover it in 1/4" ply. Fiber glass it to make it water proof. I think that would be light with out being weak.

 

As long as we're at it, just find a cardboard box of the appropriate size, then 'glass it with heavy cloth. Add 2x2's where appropriate if extra strength is desired.

 

Heavy construction is a good thing if your goal is sound dampening. You didn't mention this in your original post but I thought it would be a good idea to remind you in case you forgot. The lighter construction will be noisier and if someone wants to sit on it or accidentally get thrown against it, it might not stand up to loads.

If you want to really dampen the sound after the box is built, run the engine at the most frequently used RPM with the cover on. Toss a bit of sand on the cover and watch how it migrates over the structure. It will collect at the "nodes" of the vibrations. Put stiffeners halfway between the nodes and that will kill alot of the resonance of the structure.

First post for me!