Change of Propller

[ivorlm]

I own a Larson 235Hampton 1999 powered by a Volvo penta 4.3L GL PWTR. The propeller installed on the Volvo Penta outdrive is an aluminium prop 15 x 17. The WOT of the engine is 4200 to 4650. When flat out, the revs hit 4750. I would like to change prop to hopefully increase some speed. I am interested in the volvo stainless steel prop 14.75 x 19. I however need some guidance if this would be a good choice or not. Would I see a change in performance by changing from aluminium to stainless steel?

Guidance will be greatly appreciated.

Thanks

Ivor

 

[Dhadley]

Re: Change of Propller

A lot depends on which aluminum prop you have now but in theory a 19" ss prop will have a bit less slip so you should be able to pull the rpm down a shade and gain some speed. Again it depends on which style 19" ss prop you choose.

 

[ivorlm]

Re: Change of Propller



I have attached a photo of the propller I have - based on the information I provided, is the change from an aluminium to stainless steel prop recommendable?


Regards

Ivor

 

[steelespike]

Re: Change of Propller

Is it 190 or 205hp?
what is the present speed/rpm? By gps?
My limited info indicates some 190s are 4600 some 4800 the 205s seem to be 4800.

 

[ivorlm]

Re: Change of Propller

It is a volvo 190hp 4.3gl. The WOT is 4200-4600. Maximum speed is just about 30 kt on gps. When flat out, it would do 4750.

 

[steelespike]

Re: Change of Propller

Your slip seems high at 24% According to my figures if your slip was 12% the your 17" prop speed would be about 40mph, I feel that a 19 might take too much off the rpm and slow your hole shot. Dhadley may be able to suggest a particular ss prop to help your speed and have some thoughts on the 19" prop.
I have your dry weight at about 4000 lbs.

 

[TilliamWe]

Re: Change of Propller

Your slip seems high at 24% According to my figures if your slip was 12% the your 17" prop speed would be about 40mph...

He stated his speed was 30 knots. So that would be about 37.5 mph. What's his slip then?

 

[steelespike]

Re: Change of Propller

My kts to mph chart indicates 34.6 mph thats what I used to figure slip.
37.5 mph would be a little over 18%.slip. I think still too high.

 

[ivorlm]

Re: Change of Propller

the boat is approximately 2 tons, that is, 4,400 lbs. What slip should I ideally have? If you think perhaps a 19" ss prop will drop my revs too much, then how about perhaps remaining with same prop dimensions? From what I read, there is quite a difference between aluminium and ss props, when comparing the two props with the same dimensions.

 

[steelespike]

Re: Change of Propller

If the boat is intended to plane 24% is excessive I could be wrong but I don't think it should exceed 12%.I've seen hard to push pontoons at something like 8%.
Changing to stainless can be pretty unpredictable but with 24% slip it would seem
it would be hard to do worse.Maybe we can get Dhadley to comment. He likely will have some specific suggestions.With a 4400 lb boat I think a prop with stern lift may improve things.

 

[ivorlm]

Re: Change of Propller

What do you mean a prop with a stern lift? (sorry but my knowledge on props is rather limited) The boat is a day cruiser. it is a larson 235 hampton 1999

Going back to Dhadley's first comment...I would like to install the volvo penta ss prop, so style whise, I am presuming, it would be pretty much like what I have....

 

[steelespike]

Re: Change of Propller

Unfortunately I can't speak specifically to what design produces stern lift but it involves cup and blade design.Volvo may be able to make some suggestions.
Typically a 2" pitch increase would lower rpm 300 to 400.
One of the unpredictable things is the ss prop may improve the planing attitude and thus increase speed and reduce rpm less. Your dealer may let you try props till you find the best one.Usually requires a deposit and the purchase of a prop in the end.
I think it should be fairly easy to find a prop that performs better than your present one.