Wakeboarding Prop 65hp Johnson

[Ozark Caveman]

Hello, Noob here. I have a 1972 electric shift 65 hp johnson with a 13x19 prop on it. It performs just fine with 2 to 3 passengers and a wakeboarder but if you go to the boats max capacity of 1300 pounds it wont pull the wakeboarder. I only need the boat to go 22 mph max but I don't want to exceed the max rpm of the motor (I don't know what the max rpm is). Can anyone recomend a good prop size to reach these goals? They have a 9" prop listed on the following link but I dunno if that would be to low pitched?

http://boatpropellers.iboats.com/Johnson/65_HP_(1972-1973)_Propellers/62/

 

[steelespike]

Re: Wakeboarding Prop 65hp Johnson

Welcome,We need more info.please read "read this first" at the top of the prop forum.
We need the present lightly loaded wot rpm and speed.You don't want a 9" prop.
Will it plane at 1300 lbs when not pulling?

 

[Ozark Caveman]

Re: Wakeboarding Prop 65hp Johnson

Welcome,We need more info.please read "read this first" at the top of the prop forum.
We need the present lightly loaded wot rpm and speed.You don't want a 9" prop.
Will it plane at 1300 lbs when not pulling?

Yes it planes but it takes for ever. I have to move people to the front of the boat to get it to plane

 

[Ozark Caveman]

Re: Wakeboarding Prop 65hp Johnson

The tach quit working so dunno the wot but it does about 30 to 32 mph with an average load at wot. The boat is a 1973 glastron v156.

 

[Ozark Caveman]

Re: Wakeboarding Prop 65hp Johnson

T looks like the max rpm is 5,000 according to this link.

http://boatspecs.iboats.com/Johnson__65ES72__65hp__1972/bpe/57e7580

 

[steelespike]

Re: Wakeboarding Prop 65hp Johnson

With a 19" prop the performance is probably about whats expected at 1300lbs worth of people.
Guessing the slip the calculator says your turning about 4700 at 32 mph.but the only numbers we can be sure of is the ratio and the pitch. Speed is probably close but??
You shouldn't make any prop changes without a tach A Tinytach is about $47 and will work on any motor.
If you go to a 17" pitch it should help your hole shot and could increase your rpm about 300 to 400.
If our figures are accurate that could put you at about 5100.Motor is rated for 4500 to 5500. Boat should feel peppier and stay on plane easier at reduced throttle.
is the anti vent plate(just above the prop) about even with the bottom of the boat?
Bottom clean and smooth?
Its important for the health of the motor that it can rev freely within its rated rpm.

 

[Ozark Caveman]

Re: Wakeboarding Prop 65hp Johnson

With a 19" prop the performance is probably about whats expected at 1300lbs worth of people.
Guessing the slip the calculator says your turning about 4700 at 32 mph.but the only numbers we can be sure of is the ratio and the pitch. Speed is probably close but??
You shouldn't make any prop changes without a tach A Tinytach is about $47 and will work on any motor.
If you go to a 17" pitch it should help your hole shot and could increase your rpm about 300 to 400.
If our figures are accurate that could put you at about 5100.Motor is rated for 4500 to 5500. Boat should feel peppier and stay on plane easier at reduced throttle.
is the anti vent plate(just above the prop) about even with the bottom of the boat?
Bottom clean and smooth?
Its important for the health of the motor that it can rev freely within its rated rpm.

Thanks for the help. I also wanted to add that I only need this boat to travel at 25 mph, no faster. I would like the engine to do 4500 rpm at 25 mph. Is that possible?

 

[steelespike]

Re: Wakeboarding Prop 65hp Johnson

For the health of the motor it needs to rev freely within its rpm range 4500 to 5500. Once you have it propped for close to 5500
with just you aboard . If you get us the numbers with a light load Including your required water sports speeds we can tell better about specific rpm. As rpm increases or decreases speed change is not linear as the prop slows slip goes up
as the boat slows more hull is in the water, and so on.If the boat is propped correctly you can run it at any rpm your want with the throttle. As I said a lighter pitch should improve performance. We are still guessing about results until we get some hard numbers.

 

[Texasmark]

Re: Wakeboarding Prop 65hp Johnson

Just as a point of reference, back in the day, when I had a lot of fishing buddies and water skiing buddies and their families, a 65 with a 19P prop was for a light boat. I know because a buddy had a kingfisher bass boat and 65 Johnny on it. I am guessing he did 35 or a tad over with just him in the boat. I had a 125 on an 18' Caravelle and my speedo was showing 39 at WOT with 3 in the boat and I could just barely leave him in the wake....Used to hack him off. Grin.

Agree with Spike on the tach and where you want to run your rpm's and the fact that you certainly don't want a 9P.....if you could find one. The tach will tell the story but if you are doing mediocre where you are, same style/material prop in 17 would probably work and a 15 would certainly work for you. With the 15 you will have to keep tabs on your rpm's when not waking and loaded. With the 15 you will have a stellar hole shot as compared to where you are and everyone can keep their seat!!!!!

Mark

 

[Ozark Caveman]

Re: Wakeboarding Prop 65hp Johnson

Just as a point of reference, back in the day, when I had a lot of fishing buddies and water skiing buddies and their families, a 65 with a 19P prop was for a light boat. I know because a buddy had a kingfisher bass boat and 65 Johnny on it. I am guessing he did 35 or a tad over with just him in the boat. I had a 125 on an 18' Caravelle and my speedo was showing 39 at WOT with 3 in the boat and I could just barely leave him in the wake....Used to hack him off. Grin.

Agree with Spike on the tach and where you want to run your rpm's and the fact that you certainly don't want a 9P.....if you could find one. The tach will tell the story but if you are doing mediocre where you are, same style/material prop in 17 would probably work and a 15 would certainly work for you. With the 15 you will have to keep tabs on your rpm's when not waking and loaded. With the 15 you will have a stellar hole shot as compared to where you are and everyone can keep their seat!!!!!

Mark

I'm thinking i'm gonna get a 15" prop and get my tach running again. Then I'll keep a close eye on the rpm.