Volvo DP Prop Size

[olivergm]

Hi,

I own a '06 Fourwinns Vista 278 and have recently replaced the 8.1l VP engine with a 5.7l GXi VP engine. I have stuck with the original XDP-B 1.78:1 drive and F5 prop. During the sea trail the engine could only achieve 2200 rpm and the mechanic suggested it was because the prop was too big. This seems to make sense as the FW 5.7l option came with the F4 prop., although a 1.98:1 ratio. Can anyone suggest what prop size is best for the following combination:

28ft 7000Lbs Cruiser 5.7l GXi 320HP XDP-B 1.78:1 = prop size?

My concern is the 5.7l F4 combo uses a 1:98.1 ratio, not my 1.78:1 ratio....any help would be much appreciated!
Oliver

 

[steelespike]

Re: Volvo DP Prop Size

Are you able to tell us what pitch the F5 is? What was the speed at 2200?Did the boat plane?
I have a feeling it didn't plane which would account for the very low rpm. It might plane with a F4 but may be slugish
causing the motor to lugg. A F3 might be help though my limited erxperience they say that a missmatched ratio is diffucult to solve.
You would be better off slightly under propped than over propped.

 

[Maclin]

Re: Volvo DP Prop Size

The drive ratio is definitely the biggest factor in your boat's struggle to hit the rpm band.

My gut feeling is you will have to drop at least 2 series number down from the factory 5.7 spec, to an F2 which is the least pitch I think VP has available. Theoretically an F3 shows the same "numbers" in a prop calculator but I think the holeshot will be so bad you will not be able to get to plane. The 5.7 300hp has lot less torque down low and really needs the other drive ratio.

With VP duoprops, each of their numbers within a series seems to be about 2 pitch-inches apart. I have put in a link below to a simple prop calculator that may help you see the differences. Use 23 for an F5, 21 for an F4, etc. I would use 10% slip for the base.

I know it is expensive but with that size boat it may be necessary to change the ratio to get above trawler performance.


http://www.marksmarineinc.com/prop_calc.aspx

 

[Maclin]

Re: Volvo DP Prop Size

I have attached the Volvo prop guide, it may help some.

 

[Don S]

Re: Volvo DP Prop Size

If you are only getting 2200 rpm, you do not have a prop size problem. While the wrong drive will cost you some rpm, it's not going to drop 3000 rpm. I would guess the wrong ratio and prop would cost you 1000 rpm, but not 3000.
At 2200 rpm, it sounds like the engine is going into protection mode for some reason.

 

[olivergm]

Re: Volvo DP Prop Size

Thanks for all the responses.
No at 2200rpm she was not planing and unfortunately VP keep the DP prob pitch under wraps.
I'm waiting for a response for FW. Support from Volvo here in Singapore is none existent. Shocking considering they installed the engine. My search continues although I also suspect the engine management system may be involved. Volvo recon that's not the case.
I'm more interested on planing that top speed as the sea state here is pretty chopping considering all the passing ships...

 

[Don S]

Re: Volvo DP Prop Size

Rather Volvo supports it or not is nothing we can help you with, but the fact remains. If you have a sensor on the engine telling the ECM to limit the rpm, you can put on a F1 set of props and it's going to have the same WOT rpm. You have to fix the engine problem before you can adjust props.