Build doghouse over engine

[jy2glasplyer]

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

[mudman]

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

[apex1]

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

[alan white]

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.

[fasteddy106]

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.

[apex1]

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.

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

[dockdave]

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.

[jy2glasplyer]

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

[mark775]

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).

[jy2glasplyer]

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.

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.

[jy2glasplyer]

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).

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

[jy2glasplyer]

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.

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!

[Rangerspeedboat]

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.

[Village_Idiot]

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.

[Carlo]

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!

[mark775]

3/4" Airex rigid foam I believe is distributed by Baltek, an Alcan company (I get a lot of balsa from Baltek and they are very helpful if you want to call and ask questions). The foam will route neat as can be but you must wear lung protection. I didn't look where you are from but someone there sells Systems Three or West Systems epoxy. Systems Three gives free "how to" books on epoxy.
BTI is for "Brunswick Technologies", the people who build sporting equipment and Bayliners.They developed a material that combines mat and unidirectional fibers and is wonderful to work with if you take your time, read, cut material with a fabric cutter on a flat surface, wet out material on a piece of cardboard, wear hand, eye and lung protection. It has revolutionized lay-up and projects like what you are doing. There are many companies producing it now and comes under many names - ask for "combination cloth" and most boat places will help. One layer of 17oz stuff will be hell-for-stout. Two would be bullet-proof. You might find 24 or 32 oz material but for you doing this, I'd stick with no more than 24. Putty can be hand mixed but better to just buy epoxy fairing putty for your project. The reason you route the corners (1/2", or more, quarter round) is so the glass will make the radius without forming a line bubble and it will look very nice. Make the box like this and the fat lady can't break it trying... Don't hurry, don't short-cut and it will end up cheap, strong, good looking, light and increase the value of your boat. Also, you don't even have to measure anything - just start gluin' and trim off after. Liquid nails sound insulation made for this with no gaps on the inside and you'll love the finished product. Good luck

[mark775]

Oh, and don't use just any foam. There are reasons I won't go into now but don't try to save money or time on the foam. Somebody near you has some. I saw that you are from LaConner - Cap Sante Marie will probably sell you what you need. Stellar people.

[jy2glasplyer]

Pics below show the completed 3/8 ply rabbeted 2x2 fir constructed box for my doghouse (engine cover). It has been glued and screwed and has support 2x2's to allow someone to sit on the doghouse (i think) if necessary.

Several questions...and hopefully some of you won't tell me to trash this job (took many more hours to do than i thought it would) and get marine ply or ac ply. The ply was $8.50 at Lowe's but has many knot holes (not ac but must be dd, if there is such a thing!) Anyway...this is what a local has suggested i do...

step 1) generously apply Smith 105 or 'Restore' to the out and inside and ends of the box to thoroughly waterproof the ply and 2x2's. Keep applying until the wood soaks all it can soak.

step 2) make a putty of epoxy and sawdust (1:1 hardner) to fill all the exterior cracks and knotholes.

step 3) sand all exterior surfaces to a smooth finish (not 220 or anything like that)

step 4) apply an epoxy to the finished surface, glass (1.5 oz) and epoxy over the exterior surfaces and ends;

step 5) complete the glass/expoxy finish.

Questions: does this make sense to you experts out there? I cannot seem to find 'Smith 105'...apparently it is quite different than the west 105. Also, if I am going to finish the 'box' to such a smooth condition. Is there a paint or some other surface i could apply to the 'box' that would be adequate?

As you can tell...i am a newbie...and would really appreciate some input so i don't totally screw this up and can have a doghouse (i don't have to live in) and that will last me as long as this glasply.

Thanks

[mark775]

You're gonna have a lot more money in the epoxy and fabric than what you have spent thus far. It needs more radius if you are going to wrap the corners. Certainly, places where the plywood's void repairs are probably falling out of that stuff need to be filled. It looks like it has a hatch and cover - how are you going to address glassing that? I would consider just sealing this and plan on building new later. Write back in six years... good luck