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.

Very good prices too.

Thanks GlassDave, compliment appreciated. I've read many of your threads and learned lots from them.

I'm pretty fast with Rhino, as I use it for the front end for most of my structural, lofting, hydrostatics and FEA programs. If anyone on here ever wants something modeled up, we can do that.

Okay so the basic structure of the hatch is built. I ended up going with a piece of 1/2 plywood with some 1x3 white oak bracing on the bottom. Now the next step is what to use for mat & resin? I would like to put only 1-2 layers of mat on the top side and then maybe 2-3 layers on the bottom tying all the supports into the plywood. The top side will be completely covered with an hatch pad so it doesn't need to be glass smooth, the bottom needs to look okay.

My thought is to use the 1708 mat as it comes highly recommended but not sure what I should use for a resin? Is there one that works particularly good with the biaxial mat?

Thanks
Jim

http://i69.photobucket.com/albums/i4...b/8beafbf2.jpg

ttt

I think Vinylester resin would be your best bet with the 1708, but for it to kick properrly it needs a work place temperature of atleast 70 degree's

Thanks!

I am building the hatch in a heated garage so keeping the building warm shouldn't be a problem. Have you used the vinylester resin before? How does it lay down? I need something that is going to give me the most rigidity when paired with the 1708. People will be walking, sitting on the hatch and I want to have very little flex!

Thanks
Jim

Like yourself, I decided to build my own engine hatch (see post #10) I'm no pro, but I was pleased with the results of 1708 & vinylester resin. The only difference was I used 1/2" balsa core. The only ply I used was around the perimeter for some bite............seal the plwood first with resin (let it soak in good with a roller) let it dry overnight. Rough it up with 60 grit before you put down 2 layers of 1708 ....top & bottom.

Sorry, missed your first post!

That hatch looks great! So you used 2 layers of 1708 on each side of that cover? Can you stand on it? How much does it flex?


I was thinking of going with the West system epoxy resin because it doesn't seem to be as sensitive to mild temperature variations during cure and isn't as toxic to work with. I also read that in the end it is stronger than a vinylester resin? It is a little more expensive than the vinylester resin but not too bad!

This is what I was looking at

http://www.jamestowndistributors.com...5+Epoxy+Resin#

Have any pics of the hatch installed that we can see? Trusting that the hatch in your posted pic is for your 3100 AO, what is the "dip" in the forward area of the hatch?

Yes 2 layers of 1708 top & bottom........remember, I course of1708 is conprised of 17oz. bi-axle & 8oz. Mat.....so, in actuality it's 8 total layers of glass used. I can stand on it and it doesn't flex.

I've used Epoxy & 17 oz. bi-axle to glass the hull & deck together. It is a stronger resin, better sealer for wood, has better temperture tolerance and better strenght ratio with less glass. It is expensive and you don't need 1708 .....17oz. bi-axle alone would work the best.

No harm in using the bi-axial mat with the resin though right?

I really want to make sure it is nice and strong!!!

Thanks
Jim

Jim,

For your hatch, the strongest application (I would use) is to match the best suggested glass with the proper resin. Hence, Epoxy resin/Bi-axle glass without mat....Vinylester resin/Bi-axle glass with mat.......I think these are the best combinations to use for laminating. Can you use epoxy & 1708?..........I think (like Dave said) in a pinch yes, but there's a definite reason to stick with the recomemded pairings......I remember something about the bindings in 1708 & using Epoxy isn't the best suited???........Dave???

Yep, you should try to avoid using any laminates with mat in an epoxy system. They tend to be very hard to balance properly and will be very resin rich which translates into heavier weaker lay ups. The stitched mat and bi ax is ok in a pinch but the raw chop strand mat cannot be used because of the binder, 1708's mat does not have a binder. For something like this I would probably use a vinylester it's gonna work faster and you don't really give up that much strength. Finishing epoxy is a Pain in the azz if your not bagging.

All my materials have arrived and all the prep work is done to the wood. The next step is to fiberglass it! Any final pointers??

The glassing starts tomorrow! :drink:

http://i69.photobucket.com/albums/i4...b/69dc0e3b.jpg
http://i69.photobucket.com/albums/i4...b/eca576d0.jpg
http://i69.photobucket.com/albums/i4...b/29f1c6c2.jpg

Top side is done! Tonight or tomorrow I will do the bottom. It was tricky to get the glass to wrap around the edge of the board and stick to the bottom. I had resin running down my arms from working upside down! What a mess but I am happy with the results so far!

http://i69.photobucket.com/albums/i4...b/acedafec.jpg
http://i69.photobucket.com/albums/i4...b/d0593cfe.jpg

Ready for some more resin!

http://i69.photobucket.com/albums/i4...b/b2affee7.jpg
http://i69.photobucket.com/albums/i4...b/fee5d75c.jpg

Jim,

Why does the box frame (you built on top of ply sheet) not extend out to the corners of the plywood?...........Also, if you haven't already, fillet all the corners with a hull & deck putty. 1708 doesn't like sharp bends..........looks like you making good progress......nice job!

Thanks for the compliment! It is all glassed (finished it Friday afternoon)

The 1708 did very well in the tight corners. It helped to have the right rollers. I bought the corner roller and the small roller used to remove air bubbles. Huge difference!!

We tested the strength today. Had it supported just along the two edges and had me and my buddy (close to 400lbs) stand on the cover and it didn't move at all!

The reason the box doesn't go out to the edge of the plywood is because of interference with the manifold risers. The vertical box will land just to the inside of the outside risers directly over the valve covers. (see picture below)

My next question is what do I paint it with? Top side is not that important because it will be totally covered with a hatch pad but the bottom side needs to look good! I am thinking either awlgrip or actual gelcoat!

Any thoughts??

http://i69.photobucket.com/albums/i4...b/5fb969b6.png

Looking good! What are you going to use for the hatch ram? and where do you plan on placing it? If you need some pics I have some for ram placement if you use a single ram in the middle. We have pretty much the same setup.

Thanks man!

I have spent many hours in my CAD software playing with different ram mounting options. I have settled on mounting it on the center stringer right between the engines. I am going to push on the cover were the recess is on the center support beam. You can see it in one of the earlier posts and in the CAD renderings. Where are you pushing yours from?

http://i69.photobucket.com/albums/i4...rab/hatch1.jpg
http://i69.photobucket.com/albums/i4...rab/hatch2.jpg

I am pushing from the wall behind the seat in front of my engines. I don't have any room between the exhaust to fit anything between them. These are the only pics I have on my computer. I will be out at the shop tomorrow and can get better pics. The white box in the first pic is where the ram mounts.

Did you build that one piece hatch or did the panther come with it?

Do you know the open and closed dimensions of the ram?

My boat came with the hatch.
Fully extended the ram is 42" from center of the holes and retracted it is 24.5". Here is a new pic from today.

Hope you don't mind me asking why you want to go from two to one hatch?

I always liked the twin hatches and how it makes it easy to get to things in the back of the engine bays, just wondering why you are changing.

Great question! There are definitely pros and cons to either design. Most of my decision to go with a single hatch was purely esthetics!

I want a single hatch pad with the scarab beetle embroidered on it and didn't want a seam down the middle.

I want to install mirrors on the bottom side of the hatch to showcase the power plants.

I want to clean up the looks in general.

The current hatches were water logged anyway so it was time for a change.

You bring up some good points about getting to the back of the engines to work on them but I built a board that I use when I need to do this that lays over the top of the engine and allows me to access the transmission area.

If it turns out that I hate the single hatch then I will make new double hatches next winter! It has been a fun project making this one!!

Got you,

The beetle should look cool !

Hinges
 

Has anybody ever played with the idea of hinging a single cover on both ends, and depending on which set of hinges are in, being able to lift the cover from either the front or the back. Seems I'm always taking my entire cover off to get to something in the rear of the boat.