Need Prop for Small Aluminum Boat...

[frustratedboater]

Gentleman,
I need to select a prop for my duck boat and need some advice. My set up is: 12' LOWE flat bottom boat, 1996 4-stroke Honda 15hp-Long shaft (I built a jack plate for it), it has a 14-1/4" x 8, 4-blade prop. I'd like to get some more top end and it seems to hit the WOT and I usually back it off when cruising...

Given the size of the motor and the set up, I can't provide you with RPM, as I have no tach, or the weight, but I'd say it is medium-weighted with everything in it and will usually have two people. It doesn't have any hole shot, but it will plane off with my son in the bow and goes fairly well and feels like it is winding out, so I usually back off and move to a more "comfortable sounding" speed, which is a bout 3/4 throttle.

I was thinking about a 10 or an 11 pitch... Any recommendations given my basic info?

 

[steelespike]

Your numbers are odd. Prop size is written Diameter X pitch.
Typical diameter is about 9" the largest pitch listed here is a 12".
We really can't do much without your present lightly loaded rpm and gps speed.
It's critical that the motor can operate within its rated wot rpm.
Once established you can operate at whatever speed you prefer.
Prop selection would be based on the typical load and activities.
An induction tach will get you the rpm.
A careful wot lightly loaded gps speed will get us some idea of the setup.
If it really is a 14 1/4 pitch its amazing it could plane.
​

 

[frustratedboater]

No Title

I think I meant to say that my current prop dimensions are 9-1/4" diameter and my present pitch is an 4-blade 8 pitch. Generally my load on this boat is fairly light and was wondering if an 11 pitch would be too drastic, or not plane off. Should I stick to a 10? I went out hunting today and it definitely sounds like it is screaming if I opened it up... With a 15hp, it is not moving very fast. I have attached a picture of my boat just to get a feel of my setup. The boat is light and usually will have 1 adult and a child in it. I am not sure I can put a tach on it to get readings, as I do not have one. By chance, is there an 'app' that I could use to get my speed at least? Thanks for your time.

 

[steelespike]

A 8" is definitely too light. For about $40 you could get a induction tach that will work on a number of motors.
Most cell phones have a gps app.For the health of your motor you rally need to be able to check your rpm and speed.
The 8" prop should have come against the rev limiter.Did you feel that?At 6200 rpm 8" prop. speed would be about 18, brisk but not fast.
The motor needs to operate within its rated wot rpm range.5000 - 6200. I feel the 10" is the better bet because it's not likely to lug the motor and if it revs too much
you simply throttle back a little. If an 11 is too much you shouldn't use it for an extended time.
We could estimate the rpm by the prop size and lightly loaded wot speed.

 

[Sea Rider]

Get yourself an induction Hardline hour/tach ot Tiny Tach with programmable fire order sequence from Amazon, follow instalation procedures which are piece of cake. Check current prop at wot to see at which rpm does the rev limter kicks in if you know OB has one. Can maximize a larger pitch to lower rpm so rev limiter doesn't kick in before reaching wot, will have more rpm available at extreme of throttle. It's better and healthier for OB to know wot rpm as opposed to gps speed which varies depending on pitch.

Happy Boating