I am almost ready to cut my hatches. I am going to use magnets. What strength, size and thickness magnets would you use on your next build. How close together do you place them. Are you happy with what you did. It looks like it would be possible to make them to strong. Has anyone done that?

Hi Thor,
I just finished my Night Heron and built some magnetic hatches. I used rare earth magnets from lee valley (http://www.leevalley.com/US/wood/page.aspx?cat=1,42363,42348&p=32065), 1/2" diameter and 1/8" thick.
My hatches are about 45x30cm in Size and I used 7 pairs. If you have a very close fit that's almost too much force but if you add a tiny sealant lip (I'm trying out Sugru for that) it should be just right.
The way I did it was a little complicated and I would recommend the following (that's how I will do it on my next build in a few weeks).
- Cut hatch
- round over edges a little, seal with epoxy.
- Drill holes in hatch for magnets, epoxy in place and protect with a thin layer of glass (don't use carbon directly on magnets, it supposedly corrodes!)
- Tape hatch flush into deck, also add tape on the inside! Make sure it's exactly in the right position (this might take a while)
- Cover inside lamination area with PVA, plastic foil, tape or whatever you use to inhibit bonding to the deck and laminate the inside lip (no precision needed as you will remove the laminate for trimming and sanding = a lot less work):
I did one layer of glass, then snapped the magnets in place, added some thickened epoxy putty around the magnets (this is important) and then another layer of glass and one layer of carbon.
- Once semi-cured you can remove the laminate, trim it, remove the tape on the inside of the deck and glue it onto the deck while the hatch is still taped in place (the magnets will locate it back in its original position). pay attention not to glue the hatch on ;-)
- remove the hatch tape and add some sealant (the thinner the sealant lip the better the seal)

one more thing: if you make sure the poles of the magnets are all in the same orientation, they will hold the hatch on the side while loading/unloading. Not important but might be useful.

hope this will help!
Matt