New Prop or Smart Tabs?

[seedlings]

1979 15' Crestliner Muskie 550 Tri-Hull
1978 70hp Evinrude outboard

My goal is to keep the motor around 5500~5800 rpms WOT with people in the boat while pulling a tube.

Motor came with a 17 pitch prop. This prop is fine for two people cruising the lake, but hard to get out of the water with 3 people in the boat pulling the 4th on a tube, and maxes out at 4800 RPMs, which is too low. So I picked up a used 13 pitch prop and that is fantastic for getting the tube out of the water, but the RPMs can go over 6K, although I'm very conscious to keep it 5500~5800 which is about 80% throttle. BUT when someone else drives I get nervous they'll blow out the motor.

So... with $100 to spend... is it time to get the in-between 15 pitch prop or try smart tabs?

CHAD

 

[Faztbullet]

Re: New Prop or Smart Tabs?

Prop......

 

[steelespike]

Re: New Prop or Smart Tabs?

I think I would go with a 4 blade 15. It should give you almost the same hole shot with
better low to mid range all around performance.Usually improve handling at speed and at the dock.
You may lose a little top end.
Tabs in general whether active or passive can be very helpfull with hole shot and certain specific conditions but can cause wierd handling, excessive fuel use if poorly matched or used too agressively.I've seen a few tests where it was found that best economy was with the tabs retracted all the way when on plane.I should point out that fuel excesses are measured in tenths of a gallon so difficult to track without a flow meter.

 

[seedlings]

Re: New Prop or Smart Tabs?

I think I would go with a 4 blade 15. It should give you almost the same hole shot with
better low to mid range all around performance.Usually improve handling at speed and at the dock.
You may lose a little top end.
Tabs in general whether active or passive can be very helpfull with hole shot and certain specific conditions but can cause wierd handling, excessive fuel use if poorly matched or used too agressively.I've seen a few tests where it was found that best economy was with the tabs retracted all the way when on plane.I should point out that fuel excesses are measured in tenths of a gallon so difficult to track without a flow meter.

The 4 vs 3 blade iboats help article says, "When switching from 3 to 4-blades, generally a 1" pitch decrease is required." So do you recommend looking for a 4-blade that is 14" pitch or 15" pitch?

CHAD

 

[steelespike]

Re: New Prop or Smart Tabs?

The 78 70hp is rated at 5,000 rpm 5800 may be a little high.
Your looking to reduce your rpm.I figure a 2" pitch change should get 300 to 400 rpm going to a 4 blade 50 to 100.At 6100(?) plus it appears you need 300- 400- rpm drop.
Keep in mind prop change results are approximate under the best of circumstances.

 

[seedlings]

Re: New Prop or Smart Tabs?

Picked up a 4 blade 15P COMPROP for $75 at Midwest Propeller. 5500 on the nose WOT @ 29mph gps. Thanks everyone.

CHAD