Building a new engine hatch - any pointers?
 

Plan to build a new engine hatch for my scarab to replace the dual hatches. The new hatch will be one piece and hinged at the rear.

I plan to make it out of marine grade plywood and then glass the whole thing. Do you think I can get away with 1/2" plywood? What kind of bracing would I need on the bottom to keep it from flexing. The cover will have a finished size of 48"x73"

Any pointers would be appreciated.

Here is what it has for hatches now... http://i69.photobucket.com/albums/i4...b/40f7b30e.png

Here is what I did with mine.

1/2" ply should will be fine. It's just a core when you are all done glassing.

My hatch uses a single telescopic ram for opening, so I built in a 2x6 down the centerline to carry the load, and stiffen the middle of the hatch. That leaves fairly small panels left in front of the scoops, so I didn't reinforce further. I have some carbon in mine, and it is quite stiff to walk on, more so than most old school boat decks, anyway.

Get your plywood shaped out. I use furring strips or 2x2's at the edges, and screw the plywood to them. I was going to round off the corners, so that gave me enough meat to do that; just pay attention to where you are putting the screws. I ripped some of them to triangles so that it would make a good inside corner for the glass.

If you have to match the contour of a curved deck, what I did was take a 2x1, and a 2x4. Cut small pieces of 2x1, and screw them to the 2x4 every couple of feet. Lay the 2x1 down on the deck, then screw them to the standoffs from the 2x4, and you can make a decent template.

I designed mine up in Rhino and unrolled the surfaces, then made paper templates and cut the plywood from them. If you have a simpler shape, you can wing it.
Most guys on here will recommend using PPG urethane. I used Interlux perfection, rolled and tipped. Mine is probably "yacht quality" and not bling speedboat quality, but I didn't want it to come out too nice, or else it wouldn't match the rest of the boat at all...

I should point out that while I know all the mechanics of fiberglass and composite design, I'm by no means a fabricator of any caliber, just enough DIY to be dangerous, but thought I'd share. There is plenty of body filler in there...

use foam board . check out these vents http://www.ebay.com/itm/220763874211...84.m1423.l2649

That's pretty cool, I get a kick out seeing advanced do it youselfers think outside the box. I have been palying with Rhino for a couple years and that's a good way to use the program to your advantage by rolling out the surfaces. Nice work

Nicely done! I think it looks mean with those scoops!

Mine is definitely gonna be basic. Just a flat lid with some ribbing on the underside for structure! The top side will be covered with a hatch pad. I thought about a couple low profile pro stock hood scoops on it but again it will take away from the ability to use it as a sun pad

The industrial designers at my work have rhino but I haven't had the pleasure of using it. I do all my design in Unigraphics NX.

I will post some pics of the design and maybe you guys can give me some pointers on structural supports.

So you think 1/2" ply should be enough with the right bracing?

Thanks
Jim

I had one made out of foam, only weighed like 70lbs. I could jump on it and it doesnt flex at all, very strong.

Rottiguy, who made yours? Looks great and light weight

David at Joker power boats. I think we are going to try some carbon fiber ones for my Spectre. Seems like every boat I have the motors dont fit

How is the pricing?

You don't need anything as heavy as plywood. I used 1/2" Balsa end grain for the core in my engine hatch. Once you sandwich the core with 1708 fiberglass it'll be just as strong but lighter.