what prop size

[grahamd7504]

hi , i have a yam f80 2004 on a 650 kg fishing boat (semi planning hull) what prop would you recommend? i have tried a 17x13 revs at 6000 rpm 28 knotts and 19x13 5600 rpm @ 31 knotts and a 21x12 5/8 5200 rpm and 32 knotts with 2 adults on board , yet a yamaha book i have lists a 23x13 ???? any help would be appreciated Graham uk.

[boats.net]

The F80 rpm range is 5000-6000 rpm's, a larger pitch prop would drop you below that range and not recommended.

[grahamd7504]

what prop

thanks, might try the 19 again although i am in the rev range allbeit the lower end thanks G..