: Hi, Paul,
: I use Hypalon cloth as the hull, and use pleaster (w/PU coat) cloth as deck.
: But how to sew them together and waterproof?

The strongest type of seam is one called a "Flat fell seam" This is the type of seam used on tents, and also on denim pants ( blue jeans, Levi's, etc.)

To sew this seam you would first sew a straight seam on the seam line. With clothing fabrics you would leave 5/8th inch, or about 15 mm of extra cloth on the other side of the seam line. With heavier materials you may wish to leave 2 to 3 mm more fabric. After you sew the first seam, take a scissors and trim one of the layers of excess fabric in half. If your excess material was 15 mm wide, then trim one layer to make it 7 mm wide. Wrap the wider piece of excess material around the trimmed piece. This gives you a part that is three layers of cloth in thickness, with all of the rough edges wrapped inside. Sew this down flat onto your kayak skin with two parallel rows of stitches, spaced about4 mm from each side of the lump of folded fabric. You be sewing through 4 thicknesses of material.

: I would not like PVC because PVC feels freeze and very heavy.

It can be, but at the same time, if it has a strong layer of fabric reinforcing it, then it can be extremely durable at a reasonable price.

: Hypalon looks difficult to stick any material, would you please suggest some
: material for Hypalon's hole's seal?

Hypalon needs a special solvent. If youhave some hypalon liquid you can simply paint it on the seam. If you have purchased cloth that was already coated with the hypalon then you need to buy a special glue for the hypalon. The glue is basically the solvent for the hypalon with some hypalon disolved in it. When the solvent evaporates the dissolved hypalon remains, sealing your stitching.

I think that neoprene and hypalon are close enough that you can use a similar solvent for both. The reason I mention neoprene is that it is more commonly used. Wet suits used by skin and SCUBA divers are made of neoprene, and they frequently tear. Store that sell these items also usually carry small cans of repair "glue" for wet suits, which is really a neoprene solvent. If you can find a diver's supply store you should be able to get this at a reasonable price, and it should seal your seams nicely. I have only seen this material in black, so I hope you like black seams.

: Do you know what's method does Nautiraid use? Or Klepper use now? Or Fujita
: use?

Since Klepper attaches their waterproof hypalon hull to a cotton and hemp deck which is porous, I suspect they use either a standard polyester sewing thread, or a cotton/hemp thread like their decks. The hypalon hulls are rather thick and I suspect that after the needle passes through the material holds rather tightly to the thread that remains, with the thread sealing the hole lik a cork seals a bottle.

If your seam lines are going to be above the water line you may not need to seal them at all. Build the boat first and try it out. If you get a lot of leaking from the seam holes, then let the boat dry and cover the holes.

Someone suggested using contact cement. If you cut a strip of your wterproof fabric about 30 mm wide and coat it with contact cement on one side, you can put a 30 mm stripe of contact cement over your seam and portions of both the hull and deck. When the contact cement is no longer wet, you press the cloth strip firmly over the area you covered with cement and the fabric will stick permanently and neatly. The seam will be covered. You can do the same on the inside of your kayak skin if you wish, but it may not be necessary.

Hope this helps.

Where in China are you?

PGJ