Prop

[raven1978]

Well, I took my prop off and took it to a shop and found out that i have a 14x17 LH prop. My current setup for those that dont know, is a 4 cyl 117 hp motor with the 270 O/D with gear ratio 0f 2.15:1. I can hit my max rpm no probs with myself and the admiral, which puts me at 35 mph (which seems pretty good to me). My cruise speed at 4400 rpm is around the 25 mph ish range. Can I or should I re-prop to gain a few mph at cruise range ? I never run at max rpm but wouldn't mind a few more mph at cruise. What does everyone think ? If re-propping is possible for what i would like, what would you recommend? Boat is a 2150 ciera sunbridge with approx 3200# displacement.

 

[steelespike]

Re: Prop

It would help to know your wot rpm and speed. It will tell us if your information is correct and the boat is performing as it should.
32 seems very good,is it by gps? Is your 4400 cruise your minimum before it drops off plane?

 

[raven1978]

Re: Prop

It would help to know your wot rpm and speed. It will tell us if your information is correct and the boat is performing as it should.
32 seems very good,is it by gps? Is your 4400 cruise your minimum before it drops off plane?

WOT RPM is 5000 and yes, 35 is gps'd

As for 4400 being the plane drop off, dont remember but dont think so, (new to me boat used 2x last year). IMO, the engine performs well for the size of it and the boat, i use the trim tabs to help plane out, just wondering if i get get a few more MPH at the same rpm. What would, or what do you THINK would happen if it wen to a 15x17 prop? I understand that the pitch affects the rpm, pitch goes up, rpm goes down and vise versa. But what about diameter? Oh and the 4400 rpm is where i cruise only because i figure it puts me at a decent mph. Fuel consumption isnt an issue as this engine sips the fuel

 

[steelespike]

Re: Prop

Your setup is working really well. only something like 7% slip. Excellent for a large underpowered boat.
Diameter has little affect on performance.It's likely the increase in diameter would lower rpm if anything.
There is the possibility it could improve slip but according to your numbers it couldn't amount to much.
Retracting your tabs all the way might add a little speed and save fuel though probably a tiny amount.
I think you can change over to right hand rotation;it will probably give you a broader choice of props at lower prices.

 

[raven1978]

Re: Prop

Thanks for your help/input steelespike, i do appreciate it. I thought the same thing about the performance of my boat with this lil motor. Was curious but i guess i will make do with what i have. Will try the suggestion about the tabs once i splash it this year. But since you mention it, how do i go from a LH to RH prop? Im a wee bit confused now lol

 

[steelespike]

Re: Prop

I'm not acquainted with the Volvo outdrives but If it is possible on the 270 It is a relatively simple procedure.
They can probably tell you over at the Volvo I/O section.Tell them I suggested it as it is a Volvo specific question
and kind of like a repair.