Which of these 3 is best for me?

[SleekCraft85]

My boat is a 21" SleekCraft Diplomat powered by a 260hp volvo penta (optimal rpm range i believe is 4000-4400 as per manual) i normally go out with 4-6 ppl on board and i tend to cruise at around 2200 rpm. i would like a well balanced prop without sacrificing fuel economy, hole shot, or top speed).

At the moment i have the following 2 props:

OEM "elephant ear" 15 X 19 prop (max rpm 4000-4200 max speed 42-45)
Michigan 14 3/8 x 23 prop (max rpm 3800ish max speed havent clocked it on gps but i assume is in the upper 30s)

and i am considering purchasing the following 4 blade (14 1/4 x 19)
Solas Amita Aluminum Boat Propeller #8814-143-19 for Volvo Penta Sterndrive Aquamatic 275 Long Hub 110 - 260 HP - iboats

of the 2 i currently have which is better for what? is the 3800 max rpm on the 2nd prop putting too much load on engine?

and would my current setup benefit from the 4 blade? (if so, know of any discount codes i could use for check out? lol)

thanks

 

[QC]

Re: Which of these 3 is best for me?

Seems like you have a good balance with the 19, but hard to tell from the info. What is the existing 19 doing that you'd like to improve. I am concerned a 4 blade could bring your RPM below acceptable based on the good numbers from your existing 3 blade.

of the 2 i currently have which is better for what? is the 3800 max rpm on the 2nd prop putting too much load on engine?

The 19 is right and the 23 is wrong. Yes, the 23 could damage the engine. WOT RPM range determines everything. If the RPM is under there is risk of damage for sure.

 

[SleekCraft85]

Re: Which of these 3 is best for me?

Seems like you have a good balance with the 19, but hard to tell from the info. What is the existing 19 doing that you'd like to improve. I am concerned a 4 blade could bring your RPM below acceptable based on the good numbers from your existing 3 blade.

The 19 is right and the 23 is wrong. Yes, the 23 could damage the engine. WOT RPM range determines everything. If the RPM is under there is risk of damage for sure.

Thats what I suspected with the 23. When running it at lower rpms am I still risking damage? Is it more fuel efficient?


I'm considering the four blade because I hear from everyone performs better than the three blade in all aspects. is there any size 4 that you would recommend?

 

[steelespike]

Re: Which of these 3 is best for me?

Is the 4000 to 4200 with your normal 4 to ppl aboard. My very limited Volvo info indicates 4800 rpm max. for a 260 hp SX.
1.43 ratio. It didn't have a minimum rpm but usually around 400 less.
If a motor is over propped it is over propped throughout its rpm range like going uphill in over drive all the time.
The 4 does usually perform better in the low to mid range speeds, usually wot is a little slower.
It is suggested to drop one inch in pitch when going to a 4 blade.
The best practical cruising speed can be from just on plane up to 500 or a 1000 rpm higher.

 

[QC]

Re: Which of these 3 is best for me?

When running it at lower rpms am I still risking damage? Is it more fuel efficient?

Theoretically it would be more fuel efficient, butttt, the damage risk outweighs any advantage. ALWAYS prop within the recommended WOT range with a typical load. It is the best overall compromise of hole shot, top speed, fuel AND engine life/damage risk.

 

[SleekCraft85]

Re: Which of these 3 is best for me?

Theoretically it would be more fuel efficient, butttt, the damage risk outweighs any advantage. ALWAYS prop within the recommended WOT range with a typical load. It is the best overall compromise of hole shot, top speed, fuel AND engine life/damage risk.

i guess il just run the elephant ears. was hoping someone could give me a suggestion for a safe sized 4 blade prop

 

[QC]

Re: Which of these 3 is best for me?

was hoping someone could give me a suggestion for a safe sized 4 blade prop

I think we did. steelespike sort of suggests an 18 inch 4 blade based on your existing numbers. Take a reread of post #4 and combine that with what you do know about your 19. Good luck!!

 

[SleekCraft85]

Re: Which of these 3 is best for me?

I think we did. steelespike sort of suggests an 18 inch 4 blade based on your existing numbers. Take a reread of post #4 and combine that with what you do know about your 19. Good luck!!

thanks didnt catch that. from the looks of things solas doesnt make a 4 blade 18 pitch prop would 17 be too little?

 

[QC]

Re: Which of these 3 is best for me?

If your tach is right, and the WOT RPM range is right, and the existing prop is perfect, then she won't pull a 19, and I am concerned a 17 is too little. However, I am not convinced about the existing prop, so maybe on the 19. That's the deal with props. You can only know once you install and run it. Just the way it is . . .

 

[steelespike]

Re: Which of these 3 is best for me?

Double check your wot rpm range in the manual.
Is your 4000 to 4200 with 4 aboard?
What is the speed at 2200?
If you pin down your speed with a gps it will help also see if you can come up with a single rpm is it 4000 or 4200?
Theoretically a 18" 4 blade would run at about the same rpm as the 19.
A 17 should add 150 to 200 rpm. more.
As QC suggests these figures aren't carved in stone.

 

[SleekCraft85]

Re: Which of these 3 is best for me?

So i took the boat out on monday and with ~900 lbs of ppl on board + ~220 lbs of fuel, ~10-15mph of head wind (minor chop) i topped out at 40mph (gps) @ 3900-4000 rpm (needle refused to pass 4000) rpm with my 15*19 elephant ear prop.

If i were to run a 4 blade 19" prop my rmps would drop more (will my speed drop too?)

 

[QC]

Re: Which of these 3 is best for me?

If i were to run a 4 blade 19" prop my rmps would drop more (will my speed drop too?)

Theoretically, yes. However, I am still not convinced the existing prop is all that great. You need a prop shop that will allow a try and swap type buying arrangement. I am sure where you live this kind of deal is quite common. Make some calls, and tell them what you have told us. If they contradict our info much I would suggest you think hard before using that one. Not that we are perfect, but we have hashed this one pretty good, plus 100s of others. If they say something like "our 4 blade 19 will be fine as is, don't worry." Then I would be suspicious. If they say "yeah, we understand, hard to nail down without a test." Then I would trust them more.

 

[SleekCraft85]

Re: Which of these 3 is best for me?

Theoretically, yes. However, I am still not convinced the existing prop is all that great. You need a prop shop that will allow a try and swap type buying arrangement. I am sure where you live this kind of deal is quite common. Make some calls, and tell them what you have told us. If they contradict our info much I would suggest you think hard before using that one. Not that we are perfect, but we have hashed this one pretty good, plus 100s of others. If they say something like "our 4 blade 19 will be fine as is, don't worry." Then I would be suspicious. If they say "yeah, we understand, hard to nail down without a test." Then I would trust them more.

Thanks for the input. locally i found a few prop repair shops and volvo penta props are not that common. im also scared of borrowing one and scuffing it up so i jumped the gun and went with the 4 blade 14.5x17 (ordered from iboats a few mins ago) since i was stuck at 4000 n not hitting the max 4,400 rpm (just confirmed in manual) with the 19 pitch prop and 4 blades was going to bring me down even more.

 

[QC]

Re: Which of these 3 is best for me?

Without a loaner program, that's what I woulda done. Please post back results