What kind of prop do I need? here's my rpms..

[americands]

So I had a 4 blade SS that cost me $500ish which I sold to one of the guys here. I was having RPM problems which I fixed so I never had max rpm on it. Anyhow; I bought a Volvo Penta 3 Blade black aluminum 19pitch. My boat's speed is unknown (speeo broke). But my RPM is going to 4800-5000 at wot, so I've been throttling back. The PDF file here states a 4400-4800rpm for the GS models.

1. Would I get like a 21 pitch 3 blade, or a 17 pitch 3 blade?

2. When I change to the recommended pitch in # 1, will my boat go faster or slower?

thanks

 

[Maclin]

Re: What kind of prop do I need? here's my rpms..

If your tach is accurate then the 21 pitch is what you need.

With the 21 pitch the actual boat speed (assuming no prop slip) would be slightly higher at any given RPM when compared to the 19 pitch.

 

[steelespike]

Re: What kind of prop do I need? here's my rpms..

It would help to know what size boat and your horsepower or displacement.
If your running a 3.0 a 21 might really sap your power.
With the rpm so close to right I wouldn't make any prop change until you get the speed to go along with the rpm.
A gps for speed works really well.Some cells have a gps app.

 

[Maclin]

Re: What kind of prop do I need? here's my rpms..

Hi Steele, the OP had posted in the VP section about his boat recently so I already knew a little bit about his sitch. I will let him post more in regards to this, but he has a V8 in a 20-21 footer.

 

[Maclin]

Re: What kind of prop do I need? here's my rpms..

I think he went from a 2bbl to a 4bbl, and is in the process of re-tuning the boat now.

 

[americands]

Re: What kind of prop do I need? here's my rpms..

I think he went from a 2bbl to a 4bbl, and is in the process of re-tuning the boat now.

Correct, my boat is a 5.7GS Volvo Penta on a Caravelle Interceptor 212 (21'). It's a 4BL (the intake was a 4bl but someone had a corroded 2BL on there that I replaced). My boats now maxing RPM's and at WOT 5000rpms. So it's got a 19 pitch 3 blade aluminium on it, so I thought I had to go down (like 17), but I guess I'm to go up?

So at WOT on 5k rpm's, if I went to a 21 pitch 3 blade I should expect (1) more speed and (2) a lower rpm? Probably around 46-48?

thanks again guys

 

[Philster]

Re: What kind of prop do I need? here's my rpms..

Pretty much. Yes.

You gonna do stainless steel?

 

[steelespike]

Re: What kind of prop do I need? here's my rpms..

It helps to be well read. I don't get around enough I guess.