Prop

[Sherry]

Hi All,

I repowered my Allmand 35' with Beta 25 and replaced shaft (same size..1") and prop. I had a two blade 17" and went to recommended 14.9 3 blade. Now I'm getting 1-2knts slower speed.

My old engine was a M25 Universal 21 hp. My Beta 25 is 25 hp.

I've called two different prop places and spoken w Beta. Beta says what I have is correct. Prop guy says I need 16" 3 blade. Prop guy I purchased it from said 15" 3 blade then said 14".

Any suggestions?

Hate to think I went with more hp and got slower speed in return :(

Thanks!
Sherry Raintree

[Bill Cornpropst]

Sherry,
Check out West by North Campbell Sailer Prop.
http://www.westbynorth.com/CampbellSailer.aspx They have a list of
parameters that you fill in and then they tell you what size prop you
need. I can't remember what size my Campbell Sailer is, but I think it
is a 14" on my Westerbeke W27 which produces 3000 RPM. I remember that
after I first installed it, I had to have the pitch changed slightly to
get the RPMs and speed .

How many RPMs are you getting? Are you measuring speed thru the water or
speed over ground?

Bill

[Sherry]

Thanks Bill!

Today...
No load 3700 rpm
Full load 3400 rpm

Specs are for max rpm 3600, cruising rpm 2600.

The gauge was off by 150 (gauge showing more) when tested at sea trial. I'm having retest done this morning.

I was able to get 7.2 knt this morning full throttle. This is using handheld gps...so over ground?

Thanks for the link. Will do.

Sherry Raintree

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[Dave_E]

If your getting 7.2 GPS full throtle, what are you getting at cruise RPM? My guess is you had following tides to get that GPS reading. 7.2 is hull speed, I don't think that motor will push this heavy boat to hull speed. My 24 hp at max RPM with no tidal influence will only get me to 6. With this hull you get to a point of diminished returns. If you could put a 35 hp engine in the boat, you might see just a tiny increase in boat speed. This hull and her weight are only going to go so fast. If your reading a water speed gauge, do a calibration.

[Sam Scudder]

It depends on your transmission ratios. Do you know which transmission and which ratio you have? If you said you now have a 14 inch diameter by 9 inch pitch I'm guessing you have to much pitch, probably about 7 1/2 to 8 is the correct pitch. A prop shop can repitch it for you for less than $50. Of course you got to get the prop off the boat and take it to them.

Sam Scudder