Galley hatch questions

[tinksdad]

I'm no there yet; but I'm getting closer.

I've noticed in the galleries that some people place their galley hatch spars parallel to the side walls and some place them perpendicular to the side walls. Will the direction make a difference to structural integrity, or is it just a personal preference? I would imagine that once it is skinned, it is not going to rack either way; but does it affect spring back?

Also, in the Gen Ben plans, it says to double up the spar at the roof edge to give something for the hurricane hinge to bite onto. It would make sense to me to do the same on the top edge of the hatch, for the same reason. Am I trying to overbuild??

[mikeschn]

You can double up the top spar on the hatch like I did on the Baja Benroy...

I don't think it's necessary though. I just went an looked at the hatch that I started for the ET. It's a single 3/4" thick spar, just like in the Gen Benroy plans.



Mike...

[madjack]

...we double the top rib...we also use horizontal spars as this helps eliminate the dreaded springback...the only way to go as far as I am concerned
madjack

[tinksdad]

MJ.... you are only a couple 300 miles away from me. Mike is a little farther. With all the advice the two of you have offered to my newbie questions, I am looking forward to meeting both of you someday!!!

[madjack]

...well, get that thing built and come on down to the LCGIII at the end of Oct...I can pretty well guarantee a good time!!!!!
madjack

[BrwBier]

We used no spars in the hatch, only a wooden perimeter frame, inner skin of 1/8 birch, two 1/2 layers of pink building foam and an outer skin of aluminum. Very light and no spring back or any other problems.
Brwbier

[mikeschn]

Hey tinksdad,

I am going to change my suggestion.

I was building my hatch today, and I noticed that doubling up on the top spar stiffened up the entire assembly quite a bit. So I am going to recommend that you double up the top spar.

I used three shorter pieces, and glued and screwed them to the top spar, capturing the middle ribs as you can see in this picture. I'll have to make that change in the Gen Benroy plans too!





Mike...

[madjack]

Mike, that is how we do it...................................................

[shoeman]

I just cut my notches yesterday and am starting to think about the hatch. First thing I noticed is that the cutouts that you use as a template are really springy and not going to necessarily give me the correct spar curve if I just lay them down and trace them. How do you deal with that??

Question two, since I plan on using only .040" AL for the main body skin, do I need a wood substrate on the hatch or can I go AL only with a stout rib and brace hatch frame?

This stuff keeps me up at night.
Geoff

[shoeman]

Anybody?? Come on... I know you're in there! My biggest concern is the spar cutting question, so if the other half about skinning scares you away just ignore. That's how I got through High School too.

[mikeschn]

When I built the 4x8 with aluminum skin, I used a wood substrate. It gave me something to attach the aluminum to, especially on the edges where the weatherstripping goes.

If you find that the cutouts are not holding their shape, then hold up a piece of plywood to the wall, and trace it. Add the thickness of the notch, and then cut, like I did in this photo... (only I didn't have to add the thickness of the notch, since I hadn't cut it yet. )



Mike...

I just cut my notches yesterday and am starting to think about the hatch. First thing I noticed is that the cutouts that you use as a template are really springy and not going to necessarily give me the correct spar curve if I just lay them down and trace them. How do you deal with that??

Question two, since I plan on using only .040" AL for the main body skin, do I need a wood substrate on the hatch or can I go AL only with a stout rib and brace hatch frame?

This stuff keeps me up at night.
Geoff

[shoeman]

Good idea, thanks Mike. I also had the thought after I last posted that I could use my full size template as a guide. So either way it's another problem solved!