The basic headsail configuration can be devided into three main categories :

Spinnakers
Gennakers (often called spinnakers by catsailors)
Reachers (hooters, screachers, code 1's)

I think Bills use of the words "Spinnaker" and "Gennaker" refer respectively to Gennakers and Reachers. Don't be confused by this.

A spinnaker is often a symmetrically cut headsail that derives its power from beyond a big drag in an airflow coming from behind.

A gennaker is an asymmetrically cut headsail with a loose luff ; . It acts like a wing and produce drive by creating lift from a airflow that comes from abeam or even forward of the boat.

A reacher is also an asymmetrically cut head but differs from the gennaker by having a straight luff (considerable tension). It closely resembles a very big jib with a very full cut. It is also far more triagular in shape than a gennaker.

I hope this helps

To answer your direct questions :

Rules of thumb for a gennaker (Bills Spinnaker)

-1- don't place the spi head gate past the hound by more than 60 % of the mast length above the hounds. Example hounds at 6 mtr. mast total = 8.5 mtr ; mast length above hounds = 8.5 -6 = 2.4 mtr. 60 % of this = 2.5 * 0.6 = 1.5 mtr. So spi gate will at 6 + 1.5 = 7.5 from the mast base.

I know the Supercat masts are relatively strong and stiff on the SC15 so you could get away with a mast gate higher than this. But bear in mind that the loads increase by the 3rd power (stronger than quadratic) when you move the spi gate up.

-2- pole length = about 0,80 mtr + sq root (Width boats)^2 + (length boat/2)^2 = for you about 3.35 mtr = 11 foot.

You bows go deep so you should fear lee helm to much so I would do 11 foot. On boat with leehelm problems I would choose 10 ft over 11 foot.

-3- Spi size; this is more determine by the triangle that goes from "tip of pole to ratchet block on side stay to spi gate on mast" THEN on the desire to have a particular size. The lengths of the legs of this triangle combined with the modern developped optimal shape determine the size of spi you can have. Don't delude yourself that more spi area is better. I the class I'm involved in we find that a good shape and balance between luff length and area is more important than overall size. A recent example is in the Mosquito class (A sligtly smaller cat than the F16's) were they are seeing signs that a 15 sq. mtr spi (161 sq. ft) is faster than a 17 sq.mtr. spi (183 sq .ft) which share the same luff length.

In your case I expect that somewhere around 15 sq. mtr. is optimal, given the dimensions of your hull and mast. Both your hulls and mast are 15/16 = 93,8 % is about 26/28 = 92.8 %. So your spi foot will be about 93 % of those of the 16's and your height will be about 93 % as well, with this you expected area will become 17,5 sq.mtr. * 93 % * 93 % = about 15.1 sq. mtr. = 163 sq. ft. THIS IS JUST A NUMBER TO GIVE YOU A FEEL OF WHAT YOU CAN EXPECT NOT AN ADVICED AREA, because you must let a good sailmaker decide what he can put in there in a optimal way.

-4- Homebuilding ? Yes, do that most definately; saves you heaps of money. Only think you can't make yourself is the spi sail itself. That takes to much experience.

Go to http:\\www.geocities.com\kustzeilen\ to download a document on how to make your own spi setup.

Have fun

Wouter