First I would like to thank you all for the ninfo you provided.
It all makes sence and I also agree with your views.
The boat is in Greece. Hench is quite difficult to find the props (especially the 15 3/4 x15 Saltwater Series II which I have now ordered and is in the post) to test.
I decied for this prop 15 1/4 x 15 Series II because it was recommended to me by a good friend who is an engineer in the US who has spent hundered of thousands of hours with Yamaha engines, racing them, tuning and re-tuning them and upgrading them. Also after I gave all the data to Yamaha USA they recommended the 15 1/4 x15 Saltwater Series II
MAR.CO the builders recommend minimum 225 bhp 4 strokes with 15 1/4 x 17 Saltwater. I have discussed the issue of putting a 200VMax on the boat and after making a few calculations and taking in to consideration the different (I suppose gear ratio and torque of the 200VMax compared with the 225) they advised that it was an OK combination.
Is only that the engine does not pull the revs at WOT. The boat accelerates very well and comes to the plane very quickly even with 500ltrs ful, 100 ltrs of water and 8 people on board, it also pulls OK from the waves. However at WOT it does not give the appropriate revs (5000 max instead of 5500-6000 as recommended by Yamaha).
BTW this is a slow motion video clip when in a flat sea were going behind the wash of various crafts to see how the boat handles waves
In the real situation (we hit forse NNE 6 to 7) it coped more than well both boat and engine doing between 15 to 17 knots without any problem what so ever.
Click here to watch GATO DI MARE SLOW MOTION.wmv 4MB
The set up on the film is:
Gato Di Mare @ 4200 revs e 26 to 28knots
Trim @ 2.7
Power lift full up
300 ltrs fuel
100 ltrs water
Prop 15 1/4 x 17" Yamaha Saltwater Series II
Yamaha 200VMax XL 2-srokes
The consumtion I got for the boat during cruising it was also good (I think)
First fill ............................ 400 ltrs
First trip to Milos ................180 ltrs
2nd Trip to Milos................. 200 ltrs
plus another ...................... 200 ltrs
Trip to Poros 200 ltrs ............200 ltrs
Fill again ............................ 150 ltrs
Trip to Kithnos, Serifos, Sifnos 250 ltrs
Total 1580 ltrs plus 35ltrs of oil and done about 40 hours which averages at about 39.50 ltrs of fuel /hour at 25 knots average speed per hour is about 1.58 ltr/mile