Opinions on going to 4 blade props from 3 blade?

[jonsm114]

Need opinions. I am told 4 blade props are better for idle maneuvers and top speed? Is there an advantage?

Also when going to 4 blade, how or does the diameter and pitch change?

Thanks,

Jon

400 Express Cruiser

 

[dpmulvey]

A well tuned to your boat (Propscan or Hale) 3 blade will perform as well as a 4 blade underway and because you are swinging less unsprung weight, and may yield a slight improvement in fuel economy. Around the dock, 4 blades are better.

As as to top speed, no, the extra blade creates drag. However, how much time do you spend at top speed. What you will gain is the ability to stay on plane at a lower RPM and a lower speed and likely a lower GPH burn.

As as to the diameter and pitch change, that's best left to the real pros. Props, shy of controllable pitch, are a compromise and even controllable pitch is a compromise, just a lesser one. Beyond pitch and diameter is hull clearance, cup, boat weight,LOA, LWL, max RPM of the engine and transmission, etc,etc,etc.......

I learned all this from Wildcat Propellers in Chesapeake, VA. I have no affiliated with them. I just a satisfied customer.

 

[h_gerry]

Jon,
i have an older version of your boat and asked the owner of a prop shop I trust the same question. He told me the change was not worthwhile. He felt that, on my boat (carberated 7.4s), any difference in low end torque/maneuverability, mid range cruise efficiency would be negligible. You generally will lose top speed on th switch to 4 blades. I had my 3 blades tuned and was perfectly content.

 

[alwhite00]

See below - Obviously a smaller boat but it was like a different boat with the change.

 

[fwebster]

Changing props is always a complicated issue. 4 bladed props do have more drag, but they also have less slippage because the pitch is lower. We boat in shallow water with a sandy bottom and most everyone who parks a boat on the sand and has to replace props does it with 4 bladed ones. The net effect is nearly always better handling around the dock, smoother running, quicker time to plane, better efficiency or fuel burn in the mid range where you cruise, but negligible performance and efficiency gains at top end RPM settings.

If you had to replace your props anyway, I'd certainly do it with 4 bladed ones, but unless you are changing props for other reasons, I wouldn't spend the money.

 

[Gary B]

We had a 1998 400EC that was repower end with 8.1's. We used the original 3 blade props for the first season after the repower and the second season on the new 8.1's we put on acme variable pitch three blade props and the difference was night and day- faster out of the hole, better cruise, better fuel economy, better slow speed manuevering and high speed turning. It was well worth the expense.

 

[Polarbob]

I have a 440 Sundancer with Cat 3208 / 375 HP. I put on 4 Blade props about 7 years ago. Love them. Better in the harbor and much better reverse. I have always used prop scan and have always tuned my props. I have put on over 3000 hours and think my boat is as fast or faster than any 440 around too. I have VC on the hull.