Prop Help
 

I have a 1986 V-20 Fisherman. It was originally equipped with an OMC Seadrive. A previous owner removed the powerhead and lower unit but retained the bracket and tilting mechanism. A tapered wedge was then fabricated out of what appears to be marine grade plywood & fiberglass. This serves as the mounting plate for a 2003 Johnson 115 HP 4 Stroke. the best I can figure the anti ventilation plate is 2-3 inches above the keel. My WOT is about 5700 rpm and max speed is 31-32 MPH by GPS. The only markings on the prop look to be 21R. I measured the dia. at 13". Any ideas on how to increase top end and have a cruising speed around 30 MPH would be a big help. As a side note this fall I am removing the OMC stuff and will be installing an aluminum bracket that will move the motor back about 4 inches and maintaining the 2-3 inches above the keel.Attachment 6635

Most v's only hit 28 or so wide open with a 115hp, I would say you're propped pretty good, and should consider yourself lucky to break 30 at full throttle. You can try a 4 blade prop, nut with a 115, you need to be shooting for a 22 mph or so cruise speed.

I'm with Ferm, sounds like you're set up about as good as you could expect to be.

ANYTHING in the 30's is crazy fast for a 115 engine.

Engine up high as it is likely accounts for your higher top speed - that's fast.

Want to go faster ? Likely only downhill ( such as Niagra Falls) or bigger motor !