Re: Prop Question
High rake props are used a lot on bass boats. High rake helps to lift the bow which, with the pad, help you to max out mph. Ported props were developed for heavy stern boats to improve hole shot. If a BB isn't stern heavy, I'd like to know what is.....an I/O with 2 people in the jump seats....Grin.
SS props have thin blades which take less power to twist through the water, hence more efficient design over other materials. They are usually the material that is used when designing high performance props.
150 engines run a low gear ratio like from 2:1 down to 1.68:1. That means the props spin up fast. This helps to reduce the pitch requirement for a given set of operating conditions.
Once the boat is up and on the pad, there is little water resistance so proportionally speaking the net hp required for a given mph is reduced. This allows a high pitched prop turning fast to get you those 65 mph numbers.
So if you want a Scientific Wild Arsed Guess (SWAG), get a high performance, ported, SS prop, with high rake, and 24P. Laser II is one such prop. The porting holes are large and can be plugged to suit. Reduce the size till you get the hole shot you want: Too large, engine revs too high in the hole and it takes a long time to get out. Right size = fast hole shot, engine revs but not excessively and locks up in 15 seconds or so once on plane with throttle firewalled. Trim to suit yourself during the hole and on the pad.
That's a lot of engine for that boat. I ran a 115 Merc tower (L6) with a 24P Laser (before the advent of the Laser II) on a Ranger 17 1/2 ft pad hull first outing after buying the boat and the dealer having decided what prop I was going to get I did a short burst to 55mph. The boat became unstable and also it was obvious that for that small of an engine 24 was too much pitch so I immediately got a shallower pitched Laser. For you it should work fine; again SWAG.
I will run over to the prop slip calculator and run some numbers and get back.
Edit: According to the
www.go-fast.com prop slip calculator and using an estimated 10% slip which is a reasonable guess you would get:
Gear box 2:1, 24P, 5600 rpm, 10% slip, 58mph.
Gear box 1.78:1, 24P, 5600 rpm, 10% slip, 65 mph.
The two variables are rpms and slip. Change either and you change your answer.
Mark
