What prop do you think I should start out with?

[des3m8]

Hello I'm picking up a new to me 2001 Johnson 90hp outboard motor today. It's going on my 15f glastron gx-150, heres a link to a pic with some specs.

http://www.classicglastron.com/81gl-gx150.html

I can tell you that the old motor was a '81 Johnson 75hp and it used a 13.25 x 17 prop if that helps with the new size.

I can't give you much more detail than that right now, so thanks for your help if you can.

 

[Texasmark]

Re: What prop do you think I should start out with?

I can tell you that the old motor was a '81 Johnson 75hp and it used a 13.25 x 17 prop if that helps with the new size.

Well you are now prop rated, (+ 10-15% hp increase) and your engine hp is 90 not 75 for at least another 20%. Soooo for 30 to 35% additional whoopie, a 21P of 13+ diameter wouldn't be out of line for a conservative number if your current engine runs the same gearbox ratio and all. Take this to the OMC section and ask the question.

Mark

 

[steelespike]

Re: What prop do you think I should start out with?

I was thinking a 19 because I like to start out light. But that little rascal is pretty light and appears fast so maybe the 21 is closer to what it needs.

 

[des3m8]

Re: What prop do you think I should start out with?

well he gave me the biggest prop he had on hand which was a 13.25 x 17, i already know it's too small so i'm going to take her for a test run and watch my rpms, i'm sure i'll be taking a trip somewhere to buy a larger one..

 

[etracer68]

Re: What prop do you think I should start out with?

The 17 might be good, but I would guess 19 with that boat, depends what wot is at your normal load.

Why the trip? Here at IBoats, the prop will be at your door in 4 days, and I bet the price is better.

 

[des3m8]

Re: What prop do you think I should start out with?

He even said he wishes he had a 19 to start out with. But if all goes well I should have a test run tomorrow and ill let you know. I have to figure out some
of the wires on the harness first Haha


I say make a trip but I'm surrounded by lakes there are shops everywhere so its not very far and while I agree the prices for new are better here, I can get a used one at one of the local prop shops for half price. If I'm lucky they might even trade me straight up.

 

[Texasmark]

Re: What prop do you think I should start out with?

He even said he wishes he had a 19 to start out with. But if all goes well I should have a test run tomorrow and ill let you know. I have to figure out some
of the wires on the harness first Haha


I say make a trip but I'm surrounded by lakes there are shops everywhere so its not very far and while I agree the prices for new are better here, I can get a used one at one of the local prop shops for half price. If I'm lucky they might even trade me straight up.

Make sure they guarantee the trade to be in working order. I traded once and the prop I got had the insert I guess improperly installed as the prop wobbled as you rotated it and in running it the thing vibrated terribly. I took it back and got my old prop back.

Mark

 

[des3m8]

Re: What prop do you think I should start out with?

I will thanks for the advice.

 

[des3m8]

Re: What prop do you think I should start out with?

so I finally got out on the water and the results were not what I expected. With the current 13.25 x 17 prop at wot I was getting 5200rpm. I was told by the shop where I got it that 5500rpm - 6000rpm was the wot range. Do you think I should try a different prop to achieve this range or not?

Also I have a 13.75 x 15 prop I could try...

 

[Texasmark]

Re: What prop do you think I should start out with?

so I finally got out on the water and the results were not what I expected. With the current 13.25 x 17 prop at wot I was getting 5200rpm. I was told by the shop where I got it that 5500rpm - 6000rpm was the wot range. Do you think I should try a different prop to achieve this range or not?

Also I have a 13.75 x 15 prop I could try...

Certainly. If everything is identical other than dia and pitch, it should solve your rpm expectations.

Mark