Chances are that all the boats will then be 44 feet - probably a class regatta. A 44 foot boat would have a mast height of about 40+/- feet. Americas Cup boats are about 44 feet in length and have 120 -130 foot masts. So, going with a 40 +/- foot mast, so as to be able to get some of the shots in with the full boat.... (
http://www.tawbaware.com/maxlyons/calc.htm using the Dimensional Field of View Calculator)
@100 feet away - what amount of area will the lens provide you....
50mm - 48' x 32'
100mm - 24' x 16'
200mm - 12' x 8'
300mm - 8' x 5'
@200 feet away - what amount of area will the lens provide you....
50mm - 96' x 64'
100mm - 48' x 32'
200mm - 24' x 16'
300mm - 16' x 10'
So depending on how close you get you may need a wider lens at times. I think that the 100-300 is a good choice for the distances, for a majority of the time. I also think that the 18-55 would work very well for the closer in shots. Since the race is moving quite quickly, and if you are near one of the turns, you will probably be using the telephoto 90% of the time and the 18-55 the other 10% when the boats are closer in. I would also shoot in bursts of 3 to 5 frames, which would burn through SD cards pretty quickly. I can see you coming home with easily 1000 images, maybe 2 to 3 depending upon your proximity to the "action". Ask for a layout of the course, and where the judges boat will be (at various times). I would think that your best shots would be at the race start, the end at the finish line, and if the judges boat goes to one of the turning points.
Given that you are going to be bouncing around in the boat, 2 bodies should work out very well - no lens changes.
The other thing to consider, is to get shots of the various boat crews - "at work".