Prop Advice - 3 or 4 blade and what pitch?

[Toronto boater]

I thought I would re-post this as I got very few replies the first time I tried last fall. Further help would be much appreciated

I have a 19.5 foot Sunbird Corsair Cuddy with an OMC 4.3L Cobra I/O engine.
With two passengers, and mimimal load, I get the following stats from the 17" pitch, aluminum Solas, 3 blade propeller:

wide open throttle (trimmed up): 4500 RPMs at 41 mph
3000 RPMs (trimmed down): 26 mph
coming off plane at about 21-22 mph

With a couple more passengers on board it is really slow out of the hole and doesn't hold plane well at lower speeds. I want to increase the performance to get better hole shot and handling at lower speeds. I am willing to sacrifice a couple of mph at the top end. I am an avid slalom waterskiier.

Any suggestions as to whether a 3 or 4 blade propeller is best?
If so, at what pitch?
Any suggestions as to make/model?
Note that I tried a 21 inch 3 blade pitch propeller and the hole shot was just awful so I switched to the 17 inch.

Any thoughts would be appreciated.
Thanks.

 

[Dhadley]

Re: Prop Advice - 3 or 4 blade and what pitch?

There are props, in 3 and 4 blade, made specifically for stern drives. A typical stern drive prop is usually deeper in the water compared to an outboard. And it's not likely you'll be raising the X dimension. For a 4 blade in the Stiletto line you'd be looking at the Bay Pro II series most likely. The folks here at Iboats can probably help you out with that. Or just let me know.

 

[Tail_Gunner]

Re: Prop Advice - 3 or 4 blade and what pitch?

Let's take you thourgh the step's
3 blade alum 17@ 4500
15p 3bl alum should get 4900
16p 4bl alum should get 4700
now drop 200 for ss in the above
You have some kind of problem..4800 should be your target rpm
If you dont think so post the year of your boat

 

[dan t.]

Re: Prop Advice - 3 or 4 blade and what pitch?

all I can speak from is my own experiance,I was running a 16x16 wide blade,3 blade and wanted a better hole shot, after doing a lot of research I decided on a 15x16 4 blade. bad mistake, I lost in all catigories, there it sits on the shelf with 1/2 hour of use. the real cure, add some cup

 

[Tail_Gunner]

Re: Prop Advice - 3 or 4 blade and what pitch?

all I can speak from is my own experiance,I was running a 16x16 wide blade,3 blade and wanted a better hole shot, after doing a lot of research I decided on a 15x16 4 blade. bad mistake, I lost in all catigories, there it sits on the shelf with 1/2 hour of use. the real cure, add some cup

Dia has little effect on pitch...you just went from one 16 to another....actually you more than probably lost rpm by adding a blade..Boats are not cars nor truck's Pitch is what pushes you or pulls..

 

[dan t.]

Re: Prop Advice - 3 or 4 blade and what pitch?

problem wasnt wot rpm it was slippage out of the hole, 4 blade cost speed at same rpm and poor hole shot, like I said , cured the problem by adding cup

 

[Tail_Gunner]

Re: Prop Advice - 3 or 4 blade and what pitch?

Agreed right now i would like to hear if his motor is in good running condition and his tach is fairly accurate. It looks like a 15p ss is the right pitch in a stilletto plenty of cupping on that prop. Lets see where the thread goes

 

[Toronto boater]

Re: Prop Advice - 3 or 4 blade and what pitch?

Thanks for the replies. I just bought the boat last year - am a newbie so forgive the lack of knowledge. The engine is in reasonably good shape, and am not sure if the tach is perfectly accurate (how would I know?). The engine is a 1991 OMC 4.3 I/O.

Not sure if I understand the advice fully - are you recomending a 4 blade over a 3 blade for my purposes? I plan to buy aluminum due to cost.

As for pitch, are you reccommending 15 or 16?

Thanks to all for your advice.

 

[Tail_Gunner]

Re: Prop Advice - 3 or 4 blade and what pitch?

1. http://boatpropellers.iboats.com/OM...17907/?**********=984354873&*******=132159763

That is a 3 blade that is a outstanding prop for grip it would be a first choice for me it should take your rpm's to 4700 a better place to be for that engine and a far better hole shot.

2. http://boatpropellers.iboats.com/OM...20458/?**********=984354873&*******=132159763

http://forums.iboats.com/showthread.php?t=248765&highlight=solas+rubex

Walleyehed has highly recommended that prop in some of posting's and should take the boat to 4800 again a better overall gearing for the boat's effeciency. Yes a 4 blade should give you more lift and lower planing speeds..but note that stilletto above for the money will more than probably outperform that 4 blade alum.

Just be sure of the below info...is that your drive info

OMC Sterndrive Model 800, King Cobra, Cobra 4.3 L (15 Tooth Spline) (1991 - 1994)OMC Sterndrive Model 800, King Cobra, Cobra 4.3 L (15 Tooth Spline) (1991 - 1994)

 

[Toronto boater]

Re: Prop Advice - 3 or 4 blade and what pitch?

Thanks for the info. So 15" pitch on four blade aluminum, or a 3 blade stainless is what you're suggesting - appreciate the advice.