Prop advise needed

[Aviator5]

Hi all.
Here is the deal. I have 16 x 14" 3 blade aluminum props on my boat, which is Wellcraft Monte Carlo. Twin 4.3 L 205s. WOT rpms go over 5000 (5100-5200). So obviously I'm underpropped. I'd like to buy Solas 4 blade aluminum props. Any suggestions on the size and pitch that I should start with? I'd like to keep my WOT rpms somewhere close to lower limit (4400).
Thanks in advance.

 

[SparkieBoat]

Re: Prop advise needed

you will drop about 200 rpms per pitch you go up, you will drop about 200 RPMs just by going to a 4 blade prop. so the math adds up to a 4 blade 19 pitch prop. but an 18 will keep you some hole shot and should put you in the 4500 +/- range.

 

[Aviator5]

Re: Prop advise needed

Thanks Sparkie.
Is that calcullation considering that 4 bladed props are smaller in diameter too (14.5")?

 

[steelespike]

Re: Prop advise needed

Your not doing your motors any favor propping near the bottom of your rpm range.
The closer you are to the bottom the more its like struggling up hill in overdrive with youre car.Prop near the top of the range lightly loaded. Then throttle back if you want to run a lower rpm.The boat will perform better and should get slightly better mileage.

 

[Bondo]

Re: Prop advise needed

Thanks Sparkie.
Is that calcullation considering that 4 bladed props are smaller in diameter too (14.5")?

Ayuh,... Diameter is reasonably irrelevant,...

Ya buy props by Pitch...
The prop designer takes care of diameter...

 

[SparkieBoat]

Re: Prop advise needed

Your not doing your motors any favor propping near the bottom of your rpm range.
The closer you are to the bottom the more its like struggling up hill in overdrive with youre car.Prop near the top of the range lightly loaded. Then throttle back if you want to run a lower rpm.The boat will perform better and should get slightly better mileage.

I think his range is around 4200-4700, just a guess though. that is why I suggested a 18 pitch prop, a 17 would not be out of the question either, depending on exactly what the recommended range is for his motor. most inboards that I have seen prop for around 4500.

 

[craze1cars]

Re: Prop advise needed

OP says his lower limit is 4,400 on a 4.3, so that means the upper limit is 4,800. I am quite certain these 4.3 motors have a 4,400 to 4,800 range on them.

That said, I'm with Steelspike, and I disagree with targeting 4,400 if that's the minimum. Aviator5, why are you choosing to target 4,400? What is your performance objective in doing so? Be aware that holeshot would really suffer if you were do this, and it would add some added load/strain to the entire engine/powertrain in many conditions.

Frankly I think a 16 or maybe a 17 in a 4 blade would be a good choice. A 16 will probably bring your RPMS down to about 4,800...which is where I feel they should be. And a 17 might drop them down to 4,600-ish.

And as stated, an 18 might get you to your 4,400 target. But I really do think that target may be misguided....

 

[Aviator5]

Re: Prop advise needed

Thank you, guys.
I've ordered Solas 14.5 x 17"(they don't have 18"), hopefully will try them out this weekend.

 

[SparkieBoat]

Re: Prop advise needed

I think you made a good choice considering the recommended RPM range, 4700-4800 should be perfect.

 

[Aviator5]

Re: Prop advise needed

OK, tried it out this morning. 4500 WOT, hole shot is about 2 boat lengths, will plain at 17 mph at 3200. And much more qiet than before. And a'm a happy camper now.

 

[SparkieBoat]

Re: Prop advise needed

I am glad it worked out good for you, a set of trim tabs will give you an even quicker plane and it will stay on a plane at lower RPMs. but if your happy stay with what you got. that 17 4 blade lowered the RPMs much more than I thought it would. Craze was dead on with his numbers.