: for Myself Im looking at doing a Nikumi 18 or 19 expanded a bit for
: larger feet (size 12).

Of course all you need to modify is the deck height. That is pretty simple. Just raise the fore deck an inch or two at the front of the cockpit.

: Nylon: easy sewing ( one problem cant get good oil based finishes
: in NY state)

Really? I'd not heard of this problem before. Is there some law against oil based finishes in NY? Do they forbid mail-order purchases, too?

: Vinyl Looks great pretty durable (clear Not too durable I hear ?? )
: Vinyl seems labor intensive due to all the prep work and glueing
: compared to sewing.

You can sew vinyl if you like. The fabric-reinforced types are used as truck tarps, and all those tarps are sewn. Sewing may be stronger than gluing or heat sealing. I'd suggest using a needle with a triangular cross-section such as the needles used for sewing leather.

Your stitching will be above the waterline so you don't really need to seal the needle holes, but if you want to then you can put a drop of vinyl cement over each hole or you can glue a strip of material over the seam. This would disguise a wiggly seam line and adds some reinforcement and protection to the stitches, too.

Clear vinyl is commonly sewn to "sunbrella" fabrics used for making the tops and covers for motorboats. They use the vinyl for windows. The clear vinyl is frequently sold with upholstery fabrics. I think this may be because it used to be the fashion to have vinyl covers on your sofas and chairs to protect them.

Sewing does put a lot of holes in the vinyl, so when it dies it will likely be from a seam failure--so let the seams be your barometer in forecasting when it is time to reskin.

Gluing a 2" wide strip of additional material over the sewn seam reinforces the area and probably makes that area stronger than adjoining material.

Vinyl has 2 big advantages going for it: since it doesn't need to be coated with a paint or varnish you save on the time of applying the finish, and you save on the fumes from the drying finish.
For a winter project it can spare you from paint/varnish fumes. You won't need to wait for a warm day to take the boats outside to paint them.

Are you using aluminum or wood for your frame? If the gunwales are wood you can staple the fabric to the frame. No gluing or sewing. If you go with a non-folding aluminum frame and screw a wood strip onto the length of the gunwales, and along the bow and stern frames, you can drive staples into the wood. Stainless steel or monel staples won't rust out easily. Copper (and brass and bronze) tacks are also available

You didn't mention cotton fabric. It is a serious contender. #10 duck (please, it is about 15 ounces per square yard and not to be confused with 10 ounce duck) is very tough stuff. #8 duck is even heavier. You can get the stuff from art-supply stores, so it should be easy to source locally--or get it by mail order. Price is good, durability is good. Cotton is more resistant to UV damage than nylon. It can be shrunk with water and heat. It takes paints and varnishes well. I suggest adding an anti-mildew additive to the paint. This is available at paint stores.

You also forgot fiberglass fabric. You don't need to coat woven fiberglass with a rigid plastic resin. Use one of the coating materials you might use on canvas, nylon, or poly. 12 ounce or 18 ounce woven fiberglass fabric is really tough stuff, and the price isn't too bad.

Spectra and kevlar fabrics are available, too.

PGJ