: Tell me more about this.

The washers on the back side focus the magnetic forces on the front of the magnet. Don't fully understand the pysics behind it.

: 4mm space then between the magnets?

Probably more. I glassed the spacer with 3oz glass. 3oz glass on the lip, 5oz carbon fiber on the back side. The hope was for stiffness and protection for the magnets. The magnet/washer combo is about 3.5mm thick so there are 10 complete holes through the lip. On the hatch cover, I used a forstner bit to cut through 2 layers of ply. Scary, very very scary. Since my tool bin is thin, all I had was a drill, the bit, and a couple of beers. I managed not to go all the way through.

: How thick was your gasket originally? Ted Henry's (Holly's, actually) Silver
: used some soft 1/8" thick gasket material that compressed down to
: 1/16" or less and brought the magnetic fields in close proximity. He
: also had only half the magnet contact the hatch lip..I think Rob
: recommends this? You get an edge biting into the foam, and half the volume
: of foam to compress.

The hatch system is standard Pygmy. The neoprene gasket supplied was not nearly compliant enough to get the hatch flush with the deck. I had to experiment. Due to the extra thickness of the spacer, I ended up using 3/8 weatherstripping. This puts the front hatch just a little lower than the deck (less than 1/16). It seems watertight with the bungies installed. I didn't do the extra glass on the rear hatch, so the 3/8 thick gasket leaves the hatch 1/16 proud of the deck. Not too bad. Spare paddles and the like keep the exposed edge covered.

: I see that too. I'll have a provision in my deckline or for internal bungies
: to keep the hatch on while in rough water and gear in the compartments.

: How do you plan to do the retrofit? I'm thinking of retrofitting magnets into
: my Guillemot.

Since the rear deck on the Tern is fairly flat and the lips are installed, I'll just drill through 2 layers of ply and drop the magnets in with smutz. I may try to cover with glass for rust protection, may not. It all depends on time.

: Absolutely. I think the force varies with the square of the distance.

I try not to remember too much from my physics classes. Painful memories.

: Shawn

I have some pics at home I can email if you want to check out the spacing and the like.

Larry