Noob needs prop advice

[malibuskier2003]

All,
I have a 56' houseboat and I need to replace the prop. Here is what I know (not very much):
The current prop is 14x11 - 13 spline.
From what I can figure I have a OMC stringer 400 2.5L but I can't confirm that due to lack of model number.
The boat is from 1982 and I think the out drive is a Frankenstein of parts.

Here is where the issue comes in. I currently have a 3 blade prop and would like to put a 4 blade on for better low speed maneuvering. However, I can't seem to find a 4 blade 14x11 configuration. My question is, would I be better staying with a 14x11 3 blade or moving to say a 14x13 4 blade? Top speed is meaningless to me as we never really get going very fast. I run the boat at roughly 2,800 - 3,200 RPM and I'm guessing we don't even get to 20mph.

Any help would really be appreciated.

Dave

 

[steelespike]

Re: Noob needs prop advice

I would wonder if a 14 X 11 is a low enough pitch.We need your wot rpm.Under the circumstances I don't think the gps speed is needed
though it is possible the right prop might make more speed on less fuel.Another words not necessarily more speed but less fuel for the same speed.
If the 11" is too much your slip numbers may be too high causing poor speed to rpm numbers.
You may be lugging your motor, over time could cause premature repair problems.
A lower pitch might also improve handling slightly.A cupped 3 blade may improve handling as well.

 

[dazk14]

Re: Noob needs prop advice

A 56' houseboat doing nearly 20MPH???

 

[malibuskier2003]

Re: Noob needs prop advice

High (& bad) guess. 12mph is probably more realistic and that's max speed. I only cruise around 8mph which is why I have no clue of what the WOT speed is.....

Dave

 

[steelespike]

Re: Noob needs prop advice

Take her for a joy ride and get us the wot rpm and gps speed. I don't think it will necessarily go faster but may go farther on a
gallon.

 

[dazk14]

Re: Noob needs prop advice

I think this will fall into the situation that sailboats with kickers run into.

Most do not prop the outboard for full throttle rpm and are very happy with the results of "Too" high a pitch.

They hit hull speed fairly quickly and enjoy the quieter operation of half-ish throttle.

Dock handling does suffer.

Obviously, Steelespike has made the prudent request.

My guess will be 7mph half throttle, 8mph full throttle.LOL

If needed...To drop the pitch on the Amita4, you can grind off the trailing edge of the cup. You can also have a prop dropped ~2" in pitch by a prop shop. Total combined cost would be less than $200 and help handling at the dock.

 

[steelespike]

Re: Noob needs prop advice

The wot test will help identify how well matched the prop is.I too am not concerned with top speed but trying to improve speed at a more economical throttle setting.Probably call it prop efficiency.