Prop Size for 1988 88hp Johnson

[nastyquedawg]

I have a 17ft center console invader. I purchased the boat used and had a mechanic check it out and tune up the motor. He stated that it looked like the prop had been spun but it should not cause any problems. I took it on it's maiden voyage to today and was unable to achieve WOT at 5500 rpm. I made it to 4500 rpm.

If the prop has been spun would it cause it not to achieve WOT?

Or did the previous owner have the wrong prop?

Currently it has a 13 1/4 x 17 prop on it

 

[steelespike]

Re: Prop Size for 1988 88hp Johnson

A spun prop has nothing to do weith your problem.
I would say the 17" is in the ball park. I think something is up.I think the max rpm for the 88 is 5,500.You would have to drop to a 12" pitch to get there that's pontoon type pitch.The motor is either lacking power or the tach is off.
What speed did you make?how was the hole shot?

 

[nastyquedawg]

Re: Prop Size for 1988 88hp Johnson

Max speed was 30 mph, hole shot was good. Boat weighs 2100 lbs

 

[steelespike]

Re: Prop Size for 1988 88hp Johnson

Is 2100 dry boat weight or boat,motor gas and gear,etc?
It does appear your in the ball park for speed.
You probably need to go to a 15".It should put you at about 4,900.
If you don't have any venting(cavitation) problems you can probably raise the motor a hole or two vertically for a little more rpm and speed.A Turning Point prop should allow even more height.Make one change at a time.

 

[nastyquedawg]

Re: Prop Size for 1988 88hp Johnson

2100 is dry boat weight. I purchased a 13 3/4 x 15 prop and will try it out this week. Thanks for the feedback

 

[nastyquedawg]

Re: Prop Size for 1988 88hp Johnson

Tried the 15 pitch prop. Hole shot was a little better. I was able to get about 5300 rpm at WOT. Top speed about 32mph. Should I drop to the 13 pitch or stay with this one. What happens if I am unable to achieve 5500rpm. Does that have any negative impact to the motor.?

 

[jay_merrill]

Re: Prop Size for 1988 88hp Johnson

If you had the boat loaded as you normally use it, I would stay with that prop. If you were lightly loaded, I would go down in pitch 1 to 2".

At 200 rpm per inch as a general rule of thumb, a 13" prop will put your WOT rpm a bit over manufacturer recommendation if you use a WOT setting, but will give you more latitude in terms of loading. The drawback to this, however, will be increased fuel consumption and lower top speed.

A 14" prop, or a repitch on your prop to 14", will probably be just about right and will improve fuel consumption and top end just a bit.

 

[nastyquedawg]

Re: Prop Size for 1988 88hp Johnson

Finally got my prop repitched to 13.5. I asked the guy for 14 but also told him that I was getting about 5100 to 5200 rpms with a 15 and wanted to get my rpms up to 5500 to utlize the motors expected horsepower range. Thinking I could get a few mphs out of it. Anyway, tried this weekend and was not happy at all. The 13.5 pitch got my rpms to 5500 but I lost 3 mphs. I also added a stingray hydrofoil stabilizer XPI. I am not sure if that helped or hurt. The Hydrofoil was orginally purchased to stop the boat from porpoising and it did not stop it. I am tring to get the best performance out of this boat. I am thinking about getting the prop guy to repitch the prop back to 15. The boat actually weighs 2900lbs. I also have 2 trolling motor batteries under the center console and I weigh about 330lbs. I really would like to get this boat up to 35mph. Am I asking too much. Should I repitch to 14 or 15.