fiberglass and ply hardtop build question...

just a small project compared to what looks like goes on here...so, just tired of getting wet in my rag top, metal 22 footer. Wanting to build from 1/4 ply ang glass a hard top (soft sides with plexi windows above the factroy wind sreens). is using woven roving underneath and a a coat or two of much lighter glass on top sufficient for a 16 lb radar dome and some rods near the back? might even frame 2 10x10 inch hatches.
I plan on mounting atop 2 inch aluminum tubes. 2 in back 1 in the center up front with 2 one inch tubes on either side up front also. top will measure about 7ft by 7ft.
Plan on using some 1x2 inch pine wrapped in glass for upper winsheild frame and side curtain mounts.

 

The plywood alone will easily handle the loads you're expecting. Rather then go crazy with goo and fabrics, just simply sheath with a light weight cloth (not roving) and call it a day.

The usual course is to make a perimeter frame of 1x2's, maybe rabbited to hide the end grain, then some more 1x2's for curved beams, say of 16" or 24" centers. This will get it done as far as strength is concerned. The sheathing (4 to 8 ounce cloth) is just to water proof and add some abrasion resistance. Epoxy is the normal recommendation for novices, as it's easier to get good results and more importantly is actually waterproof, whereas polyester (boat resin) isn't.

You don't even have to wrap the 1x2's with 'glass, just epoxy coat them, then paint, varnish or clear polyurethane to suit.

If you want to get fancy, you can use aluminum or stainless tubing for the beams and/or perimeter frames. You'll have to do something about the plywood end grain, but it could work too. The last one I built like this, used aluminum angle stock and some square tube. It looked like the rest of the boat this way, which is why I chose this route.

 

It might be obvious but throw some camber in that top, it'll make it stiffer and ensure water drains.

 

Thanks...i think i will rely more on the ply then. ill put a up a pic or two when ready to build.

 

I would do two or three coats of epoxy simply to build up area a little. First a clear liquid area for penetration, wait a few hours then a layer with filler powder or or old sanding dust to thicken middle coat. After it dries, sand then paint it. This should last almost forever if you do it all the way around.

 

I don't like the sanding dust idea very much is this application unless you have had a bit of experience with making your own formulas on other projects. It can be done, but you need something like real wood flour. Softwood stuff from a sixty grit palm sander isn't going to cut it. I've been saving bags of dust for 30 years. Last move I tossed about a hundred of them in the trash. Experiment with smaller projects. Now if you really want a nonskid, nonglare finish on top- beltsander crumbs work well.....

wood dust doesn't make a very good thickening agent for epoxy. I tends to make runs and curtains more prevalent on something like a cambered roof. There are very good thixotropes available at reasonable cost.

 

I don't know what all this talk about home made thickening brews is all about. It's certainly not necessary and complicates the tasks considerably. Textured finishes are easy enough to make, in one of several conventional ways, and I'm not sure if it's at all advisable on this particular project. This is a light weight dodger, not a dance floor.

Wood flour is a good thickener, though you'll need to control viscosity with silica on vertical and overhead surfaces. Wood dust from a sander just doesn't work well as a filler, the particulates are too big and tend to clump too. If you want a texture embalmed in epoxy, you're much better off with a "sized particulate", such as that available from nearly every paint manufacture or paint store. I'm fond of the polyurethane beads, which is a common material used in texture granules. These can be had in several sizes and a few different types (smooth, rough, etc.). They sand well, finish well, distribute well and generally are far superior to sand, ground up organic stuff like nuts or sea shells.

 

OK, a dodger thats what this is thing called. Correct, in that I dont want heavy weight. Yes, that I need some strength for a small rdome and some rods and maybe an anttanae.
I think the "not so smooth" look is what im after as well. I may accomplich this with sometnihg as easy as a dry paint roller over the top when the final coat is tacky. Then paint white.
As far as the top being flat...that wouldnt be bad for me in the looks department but if it need to be angled for strength then Ill have t rethink construction.
Water run off isnt a huge concern because this boat lives inside except for fishing excursions and occasionall over nights.
My challenge with a cambered roof is how to angle my attach points to my uprights (round aluminum 2 inchers with schedule 40 aluminum tubes straight down to the gunwhales).
The edges will have down angles on it for drip eges and looks with soft windows snapped up underneath.
Yes. purlans will be used (1x2's of wood, especially at sun/vent hatch point if any).
Im planning a 7x7 which will start as 2 4x8 of light 1/4 ply with an over lap down the seam on top about 18 inches wide running for and aft. That will give a slight illusion of a camber...?
Reinforcements on the uotside top where I will bolt through the tubes. (beautyy nuts on top).

thanks again for all the info. I would not use wood dust. If any thickener is used it wood most likely be micro-ballon type glass. (im a big model builder /flyer as wellas a pilot of full size planes).

Cheers!
please comment on construction...

 

Camber would be the way to go, and just do a small template developement for your connections from the deck to the uprights.

Good luck

 

When I said filler, I never meant wood filler. I used talc, cabosil or fibers, or sanding dust from sanding epoxy that I always keep for this. I only said to use filler to thicken it to provide some abrasion protection.

 

Gotcha...thanks for the posts.

 

You really should make it cambered, it will be stronger and better looking. If you're worried about your support legs, just make up wedges, if you need to make them fit.
Sounds like some are suggesting you just coat the ply with resin, I'd encourage you to also do a layer of fiberglass cloth, it will make it much more durable. And if you are using fir ply and just resin coat the grain will eventually show through.
If you want a hard filler that you don't intend to sand use West 406 Colloidal Silica. If you want a filler that you intend to sand use West 407 Low Density filler, it's microballoons with a little 406 in it so it doesn't sag.
I wouldn't think you'd be walking around on this top so why bother non-skidding it?

 

ok...I will put a little curve in it. for sure I will not be walking on this thing. and I did plan to use the glass cloth. I just didnt know what type weight. I bought some woven roving and wow...way to coarse.
I guess if the strength will be in the stucture ill just use cloth enough to hold the resin. Would you suggest the oz weight of glass? I dont want to see the weave after im done. I also dont want to put alot time/$$ into fillers and smoothers.

 

yeah, I never stated non-skid. it would have only been for an intentional orange peel finish... to hide any imperfections im my handy work.

 

I would use 24 oz roving, It is thick in one shot, then second coat gives you final finish.