JEM Watercraft

I have found that in rough conditions my bow hatch and even my hobie 'twist n seal' hatch are not water tight. I will probably just order a new seal for the Hobie one, I bought it second hand and it might just be worn, but the forward top hatch is the worry.

What is the best method to seal a cut-out ply hatch cover? At the moment I have closed-cell foam strip on the hatch lip, but that's all. The hatch just sits flush on that. I always knew I would need to improve on this, but until my last trip out today I haven't been in rough conditions so it got put on the back burner. But today I was out in rough sea and the waves washing over the foredeck ended up half filling my bow section.

The crossed bungies most likely do not apply enough downward force to get a good seal for the conditions you encountered. Especially when the hatch/deck is flat and the hatch is flush. You could put some blocks or dowels under the bungie where it is over the hatch to help increase the downward force. A stretched bungie will always stretch a little more. A bungie stretched horizontally doesn't apply much downward force.
Or you could go this route. Picture stolen from Roger's S&G build, but also shows the idea of the block/dowels, with the flat deck/hatch you would probably need them with the strap method also. But you can get the straps a lot tighter than you could get the bungies.


DM

I had to use the dowels to get extra pressure too. Then I switched to plastic hatches.

The rear hatch on my Laker keeps water out quite well. I used the concealed bungee method of holding it down and also put a ridge around the hatch where it seats on the seal. This was done by epoxying some thin cord in place then applying a few more coats to make it level, much like filling the weave when glassing. The ridge digs into the rubber seal and compensates for any minor ups and downs in the surfaces.

The hatch on my Northwind pictured above seals pretty well with no leakage under normal use. It does let in a little bit of water when hosing down with a garden hose, but that is to be expected. For a flat hatch I would have to agree with OnkaBob however. The concealled bungees pulling down on the cover would apply much greater force and I reckon would more effective. Failing that, the choice would be some kind of mechanical latchs or else glueing the lid down and fitting a plastic hatch in it.

Cheers Roger

I run all kinds of water and have been happy with my hatches and the water seal on them. I had no luck with the closed cell foam ,it leaked, I use a rubber seal like you use around doors to seal them and have had good luck with it.
I use the soft pad eyes like these
viewtopic.php?f=7&t=3723
and the rubber seal no blocks and it seems to work.
Ron

Like Ron I used the soft pad eyes and am going to use the softer weather strip.I find the closed cell foam does not compress.When I made the hatch I used the piece that was cut out as the inner and the outer one was 1/2 " larger so the inner one sat into the opening then with the seal around the lip should be no problem

here is the hatch strapped down

I have decided on a composite solution, by applying an additional layer of neoprene rubber foam on the lid, raising the profile and allowing the bungee cord to apply more pressure. I also notice that the middle front and especially rear of the hatch are the least effective seals, so I will add half-dowell ridges about 1/3 and 2/3 allong the length of the hatch. And finally, I will fit an angled splash diverter in front of the hatch to intercept and divert broaching wave splash away from the hatch.

I think that will work. If not I will gaffer tape the hatch down before heading out in rough weather. I never access the hatch when out on the water unless it is very calm anyway.

Because I sail my Sabalo, I love going out in 15-20 knot winds, but the odd broaching wave leads to almost filling my bow section after an hour or so which makes it heavier and easier to nosedive. When I fix that I will be much more sea worthy when sailing.

Steve, I'm not so sure about the extra layer of neoprene doing the trick - even with extra pressure. The trouble with hatches is there is a lot of area to press down on and if the seal material is not very soft you need heaps of force to create enough pressure to make it work.

I've just been out to the shed and checked the stuff I used - it's called Moroday Multiseal, 4.8mm thick by 9mm wide and self adhesive. It's a very soft closed cell foam strip and should be widely available (bought mine at the big green shed on Beach Rd Noarlunga )

Admittedly the duct tape will do the trick but I think a Jem craft deserves something a little more elegant .

Another thing - if you want to get away from using bungee there is a place at Edwardstown called C-Pol that sells a good range of rare earth magnets. Not for everybody but another option with parts locally available.

You're welcome to have a close look at my hatches if interested.