Propsize. V drive angle.

Hello..

We are planning to install a Volvo Penta D9 whit a V-drive.. The boat is in alu that was 12*4m, 6.8 metric tonnes .. It will be made a bit longer to go from two small stearndrives (105 hp) to bigger engine whit V-drive.. The weight will go up to about 9t. The boat has a V bottom that goes to flat out towards the sides and a hard chine , if that makes sens..

The speed we want to be most efficient in is 20 - 22knots.. We think we need to use about 300-350 hp to do that.

So in regards to this. What diameter do U mean a prop for this speed/hp should have ? There are endless configurations i sure. The limits ore the max propsize diameter whit 15% clearens is something like this:
14 deg shaft/ 140 cm propp
12 deg shaft/ 110 cm propp
10 deg shaft/ 90 cm propp
8 deg shaft/ 70 cm propp

Noting of the driveline is bought yet.. And we are willing to pay a bit more for bigger gearbox that might be needed for a lower prop rpm for exampel. The propp should be a fixed one..

Any thought , general ides , ruff estimats are welcome..

Thanks

 

Hello Johan,

Your data (Vbottom, LOA, Displacement) are scarsecely sufficient to replay as following.
2 x 225 HP (300 kg eachone)+ stern drive are sufficient to run 22 kts about.
2 x 250 HP (300 kg eachone)+ stern drive are sufficient to run 24 kts about.
+12% speed with nozzle around the props.
Cruising speed -20% about.