Prop Replacement on 75 HP Evinrude (spun hub)

[k4tdo]

Hello all, I?m Fishing for suggestions for a replacement Prop. for my 1991 Glaspost Fish and Ski. I am running a 1976 Evinrude 75 HP with manual Tilt. The boat is about 16.5 feet long and I have no idea how much she weighs. My current prop is a 13X19 Aluminum. I have spun the Hub on this prop and need to replace it.
Performance wise with one person on the boat runs great, Make WOT at 5200-5400 RPM which is within Factory Specs and runs about 30 MPH with GPS. With 2 persons it take a little longer to plain out. Well it seams like 30 seconds, but never timed it. With 4 people...taking the kids fishing, it taker for ever to plain out. Once pained it runs fine and make WOT and decent speed.
I hardly ever have just one person onboard. I don?t mind sacrificing some top end speed for a quicker plain. with a heavy load.
Suggestions?
Thanks Tim

 

[oldslowandugly]

Re: Prop Replacement on 75 HP Evinrude (spun hub)

I'm the last person that should be advising on props. BUT, if it was my boat I would be dropping at least 2" of pitch just because with you alone it's not revving higher than 5400 rpm. That and the fact that even one passenger is slowing you down.

 

[steelespike]

Re: Prop Replacement on 75 HP Evinrude (spun hub)

I don't think your numbers add up.Based on the numbers you gave your slip is about 42% not likely. I think your tach is reading high.
or speedo is low. more to come.

 

[steelespike]

Re: Prop Replacement on 75 HP Evinrude (spun hub)

I don't think your tach is accurate I think it is reading high.
With a 19" prop I think you have the 2.42 gears 30 at 5400 gives you a 25% slip not likely.
Typical slip is around 10% giving a speed of 36. at 5400 We know your 30 is accurate so check the tach.
Perhaps you can borrow a shop tach or get a Tinytach to verify your tach.
Once we get an accurate rpm it may be possible to go to a 17" pitch and get more hole shot.

 

[k4tdo]

Re: Prop Replacement on 75 HP Evinrude (spun hub)

I can't to anymore spped or RPM tests till I replace my Spun Prop. It slips at 3000 RPM like it's out of gear. It may be possible the Tach is not correct. This is NOT the original Motor on this boat, just the one that was on it when i bought it. There is not a marine shop within 100 Miles of me, so parts ect are very hard to come by. I need to order a new prop and was just looking for suggestions.
Thanks Tim

 

[steelespike]

Re: Prop Replacement on 75 HP Evinrude (spun hub)

Based on your description and the 19" prop I think a 17 will give you more pep and with a little luck about the same speed.
Just keep in mind prop selection is a bit of a gamble with the best info so a shot in the dark is a ??

 

[k4tdo]

Re: Prop Replacement on 75 HP Evinrude (spun hub)

I was thinking 1 17 Pitch would give a better hole shot and get the boat up on plain a little faster, especially with myself and the Kids or wife and a Kid or 2. Unfortunately none of us are small skinny folk..:>) Thanks for the input I really appreciate it. I have ebayed a Tiny Tach and should have it by next week. When I order my new Prop I'll do some comparison testing and see if I can calibrate my Tach for a better reading. The old boat starts first turn of the key every time and runs out good. Well till I spun the prop.
Now is my current Prop worth having rebuilt to keep as a spare? A new aluminum Prop is about 105.00 +-.

Tim

 

[BonairII]

Re: Prop Replacement on 75 HP Evinrude (spun hub)

I'm running a 17p prop on my '77 75hp evinrude. 35mph @5800 rpm (2 passengers, 12 gals fuel, 2 batteries) I've been toying with the idea of going to a 19p, but my aluminum boat is probably much lighter than your boat.

You are in the bottom end of the rpm range for your motor with the 19p. Def go down to a 17p at the very least. If it's taking a bit of time to get on plane with 2 passengers then you are probably taxing the motor quite a bit getting up to speed.