Prop Selection-gctid377849

I ended up with the 19 pitch and it is really good. dont notice much of a difference in the hole shot, but very smooth and top end is nice. 3500 rpm is 29 mph. Very happy.

Tried the 17s today. Not good. Jumped on plane, and to 4800 RPM with lots of throttle left over. Great time on plane, VERY fast, but no top speed. Maybe a combination of the diameter and the pitch. I will put the 19s on next weekend and see how they perform. These would be good props for altitude.

[itsabowtime2]

My WOT RPM's when I had the 14.5 x 17 (3) blade props was 4200.

With the 14.75 x 15 (4) blade props I get 4450.

So I dropped 2 pitch, increase 1/4 inch in diameter added a blade and gained 250 RPM's.

4200-4600 is spec for my engines.

I understand that completely, but the trim issue would be somewhat consistent between drives it it was in fact, an issue with all 4 blade props. I think it may be something about the composite Piranah props rather than a wider 4 blade issue. At least I hope.

[2850Bounty]

Dan, you cannot compare props for your Volvo drives with that of Mercruiser drives, or visa-versa........ Apples/Oranges.

All you can do is try these props.

Your target will be your WOT RPM as specified by Volvo Penta OEM.

If all of this falls within specs, and if your speed is satisfactory, ya got it!

.

itsabowtime2 wrote:
My wheels are 14.75 x 15. Merc drives however.

As far as trim, the results I get is with zero trim.

GREAT! That makes me feel MUCH better. Thanks!

itsabowtime2 wrote:
I would go with the 17 first. The 4th blade will lower your WOT RPM's by about 200. Dropping the pitch will compensate for that. You are also dropping in size by 1/2 inch, that will bump up the RPM's by about 50-100.

So will the diameter almost completely comensate for the 4th blade if I kept the 19 pitch? I want to try them both so bad just to see the difference, but dont want to flush $220 down the drain by not being able to return them. Grrr.

[itsabowtime2]

I would go with the 17 first. The 4th blade will lower your WOT RPM's by about 200. Dropping the pitch will compensate for that. You are also dropping in size by 1/2 inch, that will bump up the RPM's by about 50-100.

[itsabowtime2]

dpoelstra wrote:
And you? What about needing more power trim?

My wheels are 14.75 x 15. Merc drives however.

As far as trim, the results I get is with zero trim.

2850Bounty wrote:
14.5x19 and 14.5x17.

I'm not a prop expert, but I think that for your boat a 14.5" diameter prop, regardless of pitch or blade count, is too small in diameter.

.

Why is that? The reading I have done from multiple sources, including high performance shops is that diameter is much less of a performance issue than pitch, and a half inch one way or another will make no differnece, especially in a 4 blade prop. 4 blades are much more efficient with less slippage than 3 blades, that unless you are after VERY high speeds and high performance, a half inch in diameter is of little consequence.

I will be testing them this weekend, so we will see. May be a total ($450) failure. I would have stayed with the same diameter, but they were not available in the 15 inch in that line.

Wish me luck.

Still open to suggestins on which ones to try first.

[2850Bounty]

14.5x19 and 14.5x17.

I'm not a prop expert, but I think that for your boat a 14.5" diameter prop, regardless of pitch or blade count, is too small in diameter.

.

For anyone interested, Bayliner confirmed for me that the 1985 2850 Contessa Sunbridge, with twin VP 225/280 came with 15x19 3 blade props for sea level boats.

I have 14.5x19 and 14.5x17 4 Blade props ordered and comming. Which ones to try first? A high performance prop shop (Hill Marine) says not to dop down in pitch, but the common response it to drop pitch.

I am also worried because Piranah props says power trim is important with 4 blade props, and I don't have power trim.

Open to suggestions and experiences at this point, but once these props hit the water, they are not returnable (iboats.com).

I'll bet! Unfotrunately, well...you know... $$$$$$:sorrow:

[2850Bounty]

Dan, I think that you should try two sets of these! They cured my issue!

ok, I pulled the trigger and bought 4 blades. 17 pitch and 19 pitch (yes I bout FOUR props). Wish me luck. I am just hoping power trim is not needed and it just comes down to pitch selection. Most report going down in pitch, but on the Hill Marine website, which handles high quality and high performance props, they report this is not true. They recomend keeping the pitch the same. We will see.