Prop for a 1996 75hp Force

[dadofemily]

I have a 1996 bayliner 16' bowrider with a 1996 force 75hp. I bought the boat last year and it came with a pretty beat up 3 blade 15 pitch prop. With the boat loaded with 5 people it would get to about 5700 RPM but never get on plane. The blades on this prop were pretty bent in different directions. I replaced it with a 4 blade 14 pitch prop. Unfortunately I was unable to test it with 5 people on board after getting the new prop, but with just two of us on the boat, WOT resulted in @4500 RPM and @42 MPH. I'm looking to get another 3 blade for this year. I want to make sure it will have no problem with 5 people on board getting on plane. Top speed is not too important to me. I think the engine should top out at around 5000RPM if propped right. So I need to increase RPM by about 500-600 RPM while losing one blade. Does nayone have experience with a boat like this?

Jeff

 

[jerryjerry05]

Send the old prop to a prop shop.
Most boat/marine sales have a drop off service.
They recondition the old to new specs.

Or try Michigan Propeller.
They have prop finder service.
Give them the specifications and they recommend a prop.

The 3 blade 15p sounds a bit small? if you can get 5700 with 5 people in the boat.
I'd guess you need a 17p or 19p

 

[VivaLaMigra]

Ummm...If that motor was turning 5700 RPM with FIVE people on board, I'm betting that "beat up" prop was slipping. You do know that Capri on which Bayliner put the 70/75 hp motor is spec'd at 1300 lbs, right? That's a LOT of passenger load to expect that motor to carry, presuming they're adults. Now, if they're 70 to 90 lb kids, maybe she can handle it. But not five adults.

 

[dadofemily]

Success! I decided to just stick with a 4 blade and got a Solas 4-blade 12 pitch. Took it out today for the first time of the year. WOT resulted in 5100 RPM and about 34MPH on the speedometer. I have no GPS speed. This was with 2 adults on board. We'll see what happens with more of a load.

 

[dadofemily]

4 adults today on the boat and performance changed very little. Right around 5000 at WOT and maybe 30-33 MPH as indicated on the panel speedo. Very pleased! I'm also inclined to agree with VIva that the original prop was probably slipping.

 

[roscoe]

Great.
Now buy yourself a spare prop to keep on board.

That motor really runs well at 5400-5600 rpm.
By the numbers you posted, you should easily be able to get a 14 pitch prop.

Maybe use the 14 pitch, and keep the 12 as your spare.

Glad you are up on plane.

 

[jerryjerry05]

Going up in pitch will drop your rpm's
Go down to an 11 and the rpm's should go up.
1 -2 people CG package 1/2 tank of fuel is the load to test with.
You should be running 52-5500 at wide open trimmed up.

Had 17p on my boat, wanted MORE!!
I changed to a 19p and got more.
2-3 mph more and fuel usage went up 15-20% MORE

 

[roscoe]

Oh man, I must have gotten too much sun yesterday.
Made me all kind of dyslectic .

Yes, get another prop with a a 10 or 11 pitch, as Jerryjerry said.

 

[dadofemily]

Good idea on getting a spare, but the plate on the motor lists max RPM at 5250. I stopped at Chris Carson marine over the winter and picked up some of his reed valves so the motor could probably handle more, but I talked with Chris for a while when I was there, he's a great guy and very informative. The impression I got from him is that it's important to have the WOT closely match what the manufacturer lists because the timing is advanced mechanically with throttle position. I told him how I was maxing out at 4400 with the higher pitch, and his suggestion was that this could really beat up the motor as the timing is now too advanced at any given throttle position. Made sense to me. If I prop for a higher RPM than specs, I would assume the timing would not be advanced enough at any given throttle position. This probably isn't as detrimental as too advanced but I would assume decreased performance.

BTW, the new reeds made a significant improvement in starting, acceleration and overall performance. I highly recommend them.