Boat Hatch Fail - Looking at Polycarbonate

After a test of my boat hatch this evening resulted in a complete flooding of my thankfully empty compartment I’m thinking of sacking it off and going with a polycarbonate cover and gasket.

What thickness of polycarbonate do people use and where can I get a good self adhesive gasket.

This was my hatch before it failed

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I went with 1/2inch thick sheet of polycarbonate bought at acme plastics. It is not too flexible and feels very solid. I am not afraid to step on it! IMG_20190728_202634|374x500

I used these rubber strips as a gasket and the compartment is fully waterproof. However, the “waterproof” hatch I bought isn’t so I will probably have to seal it with sillicone or find another solution. I also used screws with integrated o-ring so the water can’t get in through the screws. I hope this helps!

Edit: you can find self adhesive gaskets and my o-ring screws on McMaster Carr

1: I’m not convinced those nylon screws are pulling the hatch down tight enough to seal.
2: If the hatch is not perfectly level the seal on the lid will not work.
3: unless you used a sealant on those wires, water will creep up and through them.

I use an 8mm polycarbonate top. It works well but is a real pain and I have to take my E-drill with me to make it faster to foil.
There is pressure on the screws so I hope those nylon inserts are strong.

@RamsUK I see that the joint of your white trapdoor has a bad junction or water infiltration… have you thought about trying to install an additional EPDM flat seal on the outer periphery of your trapdoor where it has the screws? This would strengthen the waterproofness… and for my part I sealed the trapdoor on the board with Sika Marine.

Thanks for all the feedback and advice, I’m going to try and persevere with the hatch for easy access in the future. Jez has successfully managed to use a virtually identical one on one of his boards

I have identified my weak point, it’s essentially this gap where the cable glands are. For the first test I tried to waterproof this section just using the neoprene rubber. I should have probably used Silicon but it’s very hard to access the area.

I’m now considering filling this gap, making three holes for the wires and just filling them with silicon. Has anyone else done this?

Install the hatch and then pour silicone in to seal the gap. There are ways to thin silicone down.

Thanks Jez, good idea.

Has anyone got any experience of doing this or is there a liquid based Silicon that dries as a flexible solid?

Rumour has it you can mix thinners I to marine silicone. Maybe do a test on something first though

You could fill it with this silicone. Then you could use the rest to mold a good seal for your hatch.

Thanks Michion,

Once dry does it stick to surfaces like regular marine sealant?

No it doesnt bond to surfaces like marine sealants. A bit of surface tension but not much. It doesnt just fall out if thats what you mean.
In that gap you have on your board, it would fill the gap nicely and you would be able to remove it when needed.

I installed my hatch like this:
and i never had any leaks…
While you have the sealant out, just fill the bottom corner and sides of your wire passage and you should be ok. if you’re afraid it will fall in the gap, just tape if from behind.
Don’t use mold silicon though as it will fall off, it’s only usable as a compression seal.

Thank you @Mat I also put my hatch on the board with Sika Marine and no leaks, which worries me It’s the gasket on which the hood comes to press… how to strengthen its tightness?

Not sure if it will help, I used 10mm perspex. With a hand router I machined 3mm deep to create a lip that compress an EPDM foam seal. I can waterblast on it, sink the board not a drop of water

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I take note @Manufoil thank you😉