Building Fibreglass Hatch - Need advice on material selection and layup

Hello,

I have a Kirby 25 Sailboat that was recently shipped to me. During the shipment the companionway hatch came loose and was lost on the road.

I would like to make a new fibreglass hatch. I have access to a fibreglass hatch from a second boat and thought that I could use this one as a plug to make a female mold.

My plan of attack was to take the hatch off the second boat and fix any imperfections in the finish, coat it with mold release wax, coverall film, and then lay up the materials for the mold construction.

I do have some experience with polyester resins performing small repairs to dinghies etc. but I have never done a “new build” or played with any products other than the general hardware store variety. The only larger scale (for me!) work I have done with fibreglass has been wetting out cloth with epoxy on 16' - 22' canoes and rowing shells.

What I am hoping to get a bit of help with from you guys is some advice on layup schedules, material and cloth weight suggestions.

I know that there are probably easier methods to build a one off hatch but I thought this would be a good opportunity to learn a bit about molding on a small scale and maybe even try some vacuum baging.

The hatch has rough overall dimensions of 36” x 27”. It is of very simple design and closely resembles a box lid with a 2” lip on three of the four edges and hinge points on the fourth. When I look at the thickness of the original hatch’s layup the thickest point on the one lip is ¼”. The outside finish of the part is smooth gel coat and the inside finish is chopped glass. It also looks like the factory added a piece of core material I’m guessing about ¼” thick (30” x 20”) in the middle of the hatch.

I thought for the mold I would brush on tooling gel let it cure then add two layers of .5 oz veil chop, let things cure then, two layers of 1.5 oz chop (Mat), let things cure then add a final layer of 18 oz stitch mat.

I chose the above materials and process based on the materials available to me locally at this time and articles I have read online from others making small molds. I can order online with the best of them though so I'm open to all suggestions.

Where I am drawing a complete loss is what to use as a layup schedule for my finished part. I have access to ¼” Balsa Core. I want to brush the gel coat on to the mold and do a hand layup to avoid the necessity for buying a spray gun. If I use vacuum bagging would I be able to do such a small project in a single layup?

Thanks for your help!

 

Set up two sawhorses four feet apart.
Lay three 2 x 4s on them.
Lay a 3/4" melamine board on that.
Random orbit with the finest grit you can find an area the size of your cover.
Cut four 4" strips from one end.
Hot glue them to the melamine board in the shape of your hatch cover. Be precise. Be neat with the glue.
Wax. Any wax - Johnson floor wax
Precisely radius with modeling clay, having taped where it will not be radiused.
Then remove tape and be more precise.
Layup, set balsa into wet matt to bind to top layup. Mix Cabosil and resin for thixotropic putty to fill any small voids/ make radius your glass will lay around.
Lay up inside.
Gelcoat the inside, too. Take out of mold, sand imperfections, rub out.
Very simple in theory, difficult to do without messing up gelcoat. Any kind of nonskid and the job gets more interesting.
Good luck.