3 blade SS to 4 blade SS Testing and results

[Bob_VT]

I have an 18' Fisher w/115 inline Mariner that had a 3 blade 19" SS prop. Top end was 40.5 MPH @ 5100. Hole shot good.

I was given a 4 blade to test and I was on a mission. Here are my results verified by GPS:

Test prop 18P 4 blade SS lot's of rake

1. Motor mounted on center hole Turned 5050 rpms touching 5100 (assuming the quicksilver tach is right) and 43.4 mph.

2. Motor raised to the max using the bottom hole looked real high. Went for top end and got to 44.5 (gps) and 5500 rpms for the first time and the steering was hard. It wanted to rip the wheel out of my hand and make a hard turn. (Water pump died but due to faulty impellar just a coincidence) Near impossible to turn left at WOT.

3. Motor in #2 hole one lower than last test with new water pump and very rough water (never have good water for testing) 5150-5200 rpm 43.8 mph with 12 psi of water pressure . . Better steering control can actually make left turns at speed. Holeshot still very respectable and the boat carried the bow out of the water. Gave me better mid range control and response for powering over waves.

So dropping 1" in pitch, adding a 4th blade and lowing the motor one hole resulted in:
Better control
3 MPH gain
50-100 RPM increase

All the tests done fully loaded, 2 people and gear and all in crappy rough water.

I did all these under the guidance of one of our respected long time members.

Bob

 

[Crownie2]

Re: 3 blade SS to 4 blade SS Testing and results

Great! Can you give us some more details about the two props tested?

So the motor was mounted lower for the 3 blade test?

I was just wondering how the 3 blade would perform at the same height as the final test...

Bob

 

[Dhadley]

Re: 3 blade SS to 4 blade SS Testing and results

Good, clear info Bob. I really like that you stuck to the normal load for testing even though the water conditions weren't the most comfortable.

Nice job!

 

[Bob_VT]

Re: 3 blade SS to 4 blade SS Testing and results

I did try the 3 blade at the higher level but the control was not there.

On moving the engine up and down I had some help..... Air tools and a forklift at work. Made very short work of the adjustments.

 

[Dhadley]

Re: 3 blade SS to 4 blade SS Testing and results

Bob, got a package from your neck o' the woods. Very nice, thanks!

You should offer that stuff to iboats to sell..........