Need prop recomendation

[cobra1476]

Got a 17.5 Larson BR with a Volvo 3.0 cobra sx drive. Right now I have a 14.5X19. Top end is fine 37 to 40mph depending on the weight on board.

Pulled a tube once this summer w/ 1 person on it. the thing really struggled to get on plane. Once I got up to speed it was fine.

From what I have read switching to a 4blade would be my ticket to having more fun. Question is, how do I determine the right size?

Not really a speed freak so I don't mind loosing top end speed.

I have searched on Prop finders on the web with zero help.

Any recommendations would be appreciated!

 

[david2027]

Re: Need prop recomendation

You need to post your rpms at WOT before you will get much help

 

[Haffiman]

Re: Need prop recomendation

Quite often switching to 4-blade means 1" down in pitch in order to keep the same WOT rpm.
You may gain in planning and cruising speed, but most likely loose slightly in top end.

 

[cobra1476]

Re: Need prop recomendation

Quite often switching to 4-blade means 1" down in pitch in order to keep the same WOT rpm.
You may gain in planning and cruising speed, but most likely loose slightly in top end.

That's what I was looking for! So just get the same diameter and 1" down in pitch.

What exactly does diameter of the prop do?

 

[Robbabob]

Re: Need prop recomendation

That's what I was looking for! So just get the same diameter and 1" down in pitch.

What exactly does diameter of the prop do?

Diameter, pitch, aluminum, stainless, cupped... all variables to consider. Need the specifications on your WOT RPM to gain a better idea for giving advice.

The lower pitch will give you the better hole-shot you want, but watch your WOT rpm.

Good luck!

 

[cobra1476]

Re: Need prop recomendation

According to my volvo manual max rpm speed is 4600. I think I only touch 4000 to 4100 WOT with my current prop.

 

[Robbabob]

Re: Need prop recomendation

According to my volvo manual max rpm speed is 4600. I think I only touch 4000 to 4100 WOT with my current prop.

You would do well to drop the pitch by 2.5" with a 3-blade prop. Maybe go to the 4-blade with a 3" drop in pitch. Either will increase your hole-shot and should keep you from exceeding WOT.

If you have a place that will loan you a prop above, that would be best so you can feel the difference. If you're still not happy with the hole-shot, you could even drop another inch or more. ONLY IF YOU STAY MINDFUL OF YOUR RPM. You wouldn't want to blow your engine for the sake of a little extra fun

Good luck and happy boating!

 

[Haffiman]

Re: Need prop recomendation

One normally add dia to add blade area, however that demands more torque due to increased resistance in the water when rotating.
If keeping the pitch and changing dia 1" the rpm normally changes about 100 versus keeping the dia and change the pitch 1" gives about 200 in change.
Instead of adding dia one might add another blade to increase total blade area.

 

[sethjon]

Re: Need prop recomendation

Got a 17.5 Larson BR with a Volvo 3.0 cobra sx drive. Right now I have a 14.5X19. Top end is fine 37 to 40mph depending on the weight on board.

Pulled a tube once this summer w/ 1 person on it. the thing really struggled to get on plane. Once I got up to speed it was fine.

From what I have read switching to a 4blade would be my ticket to having more fun. Question is, how do I determine the right size?

Not really a speed freak so I don't mind loosing top end speed.

I have searched on Prop finders on the web with zero help.

Any recommendations would be appreciated!

You could drop in pitch 2" but in my opinion it would be as good and cheaper to have 2 people sit up front on take off.

 

[sethjon]

Re: Need prop recomendation

That's what I was looking for! So just get the same diameter and 1" down in pitch.

What exactly does diameter of the prop do?

1" is hardly noticeable.