This is my first try at flush hatches. I understand that there is a spacer ring and a lip ring below it that the gasket will rest on. I've seen some people use two 1/8th inch spacers followed by the lip ring that has the smaller inner diameter for the gasket to rest on. I have plenty of 1/4" ply and was thinking of one ring of 1/4" for the spacer and one for the lip ring.
Can anyone guide me on what type of gasket material to use and what size it should be? How do you ensure waterproof attachment to the lip ring? Is the gasket material needing to be somehow resistant for the marine environment? I'm going to use bungee loops to hold the hatch down from the inside and am wondering what thickness the gasket material should be so the hatches wind up flush once the downward pressure from the bungee is applied?
Thanks in advance.
Gasket material choices
There's lots of variables on your gasket material and thickness and width.
Many people have used hardware store house door sealing gasket material with success. I have cut one piece gaskets from Yoga mats. And if you go on line there's lots of gasket materials.
How thick? depends on how much pressure you generate to pull the lid down. I understand you want flush hatches to be flush. Same thing applies to the width of your gaskets. I personally know that often a less-wide gasket will get crushed equally and create a better seal than a wide one that can cause weak spots. So, your thoughts of using an internal bungee arrangement is a player in your choices - how much down pressure you will have. If you email me I will send you the page from my manual showing my crank down flush hatches. jbabina at snet.net
Unfortunately there's no absolute solution on your question - it always takes some experimentation. But suggestions help.
Thank you Jay. Your suggestions are very helpful and the guidance that I should experiment is understood and appreciated. Thanks for the offer to share your crank down flush hatch design. I have your plans and am building your OI. I'm going with the internal bungees only for the aesthetics of not having a knob showing topside. I realize its a small point but the deck is looking so good, I just don't want to interrupt the visual flow. Thanks again.
After using the bungee system, which works, I have done a couple of sets of magnet hatches. I found that the hatch conformed more closely to the deck shape and stayed that way. The magnetic system is more secure and you don't lose space in the interior holds. I used fiberglass layups instead of wood rings but have seen both used with magnets. If you are installing a deck compass, then the magnets might not be for you.
Photo link as upload won't play well tonight. https://photos.app.goo.gl/avq2kbeubfsjpEmm9
Thank you Don
Thanks for sharing your experience. The magnetic approach looks interesting and I might try it on the next one. Thanks for the photo link, congrats on a nice build.