Propeller - 3 blade or 4 blade ?

[spongy]

Hi,

Im just after some advice on propeller choice.

I need to replace my current prop. Set up as follows;

- 4.8m glass cuddy boat

- Yamaha 70hp 2 stroke (about 13 years old).

- WOT runs at about 5000rpm

- Current propeller: TurningPoint Alloy 13.5" x 15Pitch 3 blade

Im after excellent fuel economy and good hole shot and acceleration.

Don't care too much about top end speed, as I spend most of the time cruising at low to medium speeds up to around 25knots.

Im guessing a new stainless steel 3 blade 15" pitch prop, will provide slightly better performance.

Will going to a 4 blade with the same 15" pitch give me any additional benefits? Or will it just drop my WOT rpm too low?

Cheers,

[JohnDory]

Hi there

I'm not the right person to answer your question but I wanted to know an answer.

I did a search on the WWW and found this tec page that may interest you.

Boat Propeller Advice and Tips

Follow This Link

I think it answers your Q well

Hope this helps you make a good choice.

JD

[spongy]

Hi there

I'm not the right person to answer your question but I wanted to know an answer.

I did a search on the WWW and found this tec page that may interest you.

Boat Propeller Advice and Tips

Follow This Link

I think it answers your Q well

Hope this helps you make a good choice.

JD

Thanks for the reply.

Yes I kind of knew the benefits of the 4 blade.

Would I see those benefits in the real world, and would the 4 blade put too much extra load on the 70hp 2stroke, which already has its work cut out for it? I would imagine it would knock off a few more RPMs at WOT. The 70hp is probably a touch too small as it is. I don't want to unnecessarily sap more power by using a 4 blade, if it doesn't return any real benefits.

[boattart]

I recently switched my props for 4 blade and the improvement was sensational. Boat is over 3 ton with twin 150 verados so obviously a different situation but if you want to send me a PM I'll give you details of who I dealt with. There service was great and they offered to switch them again if they didn't improve performance.

[Bleeding Green]

Mate I think I have the same motor as you but my boat is lighter. I was having cavitation problems with the stock prop so was looking for a solution. I went with a 3 blade stainless as someone in the know told me the 4 blade was bs. I guess you'll get different opinions where ever you ask.

I don't think I lost any rpm, I may have gained a few knots but the improvements have been great. Cavitation is almost 100% gone and the boat is quicker out of the hole. Cpany I dealt with also offer free exchange if your not happy, or trade in if you chance your donk.

Edited October 24, 2012 by Alfa-Rosa

[Geoff]

Spongy I have a 70 Yammie , similar age to yours. The motor came with a 13" prop.

During the test run at hand over there was noticable slippage ( cavitation) with the 13" regardless of the trim setting.

The dealer fitted a standard 15" Yammie prop & problem solved.

Like you , was not all that interested in WOT rev's as I rarely go over 4300 but if pushed the motor will spin to 5300/5400rpm.

Geoff

[spongy]

Thanks for your replies.

I decided on the 3 blade 15 pitch.

[spongy]

For those who are interested, I got the Solas New Saturn 15 pitch SS 3 blade prop.

Definite improvement from the old prop. Pretty much better everything.

- Smoother

- Better hole shot

- Better fuel economy

- Slightly higher top end speed

- WOT RPM is now 5550rpm

Im thinking I could have gone the 4 blade, as my concern was that my WOT RPM would drop to low with the 4 blade, but I reckon it would drop by a couple of hundred RPM only, which is still ok.