Prop size

[Turn4fun]

I just picked up a 70 hp evinrude 2 stroke that I want to use on a 1991 20' sweetwater pontoon. The motor was originally on an old runabout so I am concerned that the prop may be wrong for my toon. I know how to calculate pitch change based on WOT RPM, but my boat does not have a tach so I'm looking for some advice on prop sizes. My motor currently has a stainless 13 1/2 x 15 prop. I have not had a chance to try it on my boat yet and won't for a while. Does this seem like too much pitch for my toon and if so how much?

 

[Jeep Man]

Re: Prop size

I just picked up a 70 hp evinrude 2 stroke that I want to use on a 1991 20' sweetwater pontoon. The motor was originally on an old runabout so I am concerned that the prop may be wrong for my toon. I know how to calculate pitch change based on WOT RPM, but my boat does not have a tach so I'm looking for some advice on prop sizes. My motor currently has a stainless 13 1/2 x 15 prop. I have not had a chance to try it on my boat yet and won't for a while. Does this seem like too much pitch for my toon and if so how much?

The bigger issue is the length. Most runabouts use a standard shaft (15"). Most pontoon boats need a long shaft (20"). What do you have?

 

[Turn4fun]

Re: Prop size

Dude, I'm not that clueless. Yes, it is a long shaft. My question is about pitch.

 

[Silvertip]

Re: Prop size

Try the 15 first but I'm guessing you will need to drop back to 13. But to dial this in your really need a tach. They can be had on E-bay used, or new old stock from Great Lakes Skipper or new Faria/Teleflex right here on iBoats. You might want to consider a pontoon specific prob which would be a four blade with uniform, rounded blades rather than a prop for a planing hull. Pontoon props provide much better thrust in reverse than standard props.

 

[trendsetter240]

Re: Prop size

As silvertip said, very difficult to pick a prop without RPM numbers.

However I happen to have a lot of experience with evinrude 70s (I've got 3 of them) and can pretty much guarentee that 15p will be too much prop for that boat.

A 13p 4blade solas amita would be about the max I'd put on that setup. A 12p or 11p might be what you really need but no way to tell without RPM numbers.

Just as a reference point for you my 1995 70hp will turn the solas 13p 4blade at 6600RPM on a 2000lb 17ft runabout.

 

[rickdb1boat]

Re: Prop size

I had a 1991 Sweetwater 2019 20'er with a 70 HP Evinrude at one time and I used an 11" pitch. Was just right. If I remember correctly, the boat was only rated for a 60 HP..

 

[Jeep Man]

Re: Prop size

Dude, I'm not that clueless. Yes, it is a long shaft. My question is about pitch.

Dude, no need to be rude. Just trying to help and covering the bases.

 

[Turn4fun]

Re: Prop size

Thank you all for the input, I really appreciate it. I was pretty sure 15 sounded like too much pitch. Rick, thanks for the response, glad to hear from someone who's had experience with pretty much the same setup. Mine is model 2022 F/C and the sticker says it 's rated for 75.

Jeep, didn't mean to sound rude, I know you were just trying to be helpful, just gets old when every time I ask a question on these forums the first person to respond never has an answer to the question asked but always gives an answer to a question that wasn't asked.

 

[flotebote24]

Re: Prop size

Hey I have a prop question for you if you can help. I have a 24' Harris Flotebote and a 1980 70hp Johnrude, I can not read the markings on the prop because its been on there so long and corroded. Can you give me a guess on what size prop will work for my combo. Sorry no tach either so this is one of those off the top of your head deals. I did lay the prop out and tried to measure the diameter and I think its approx 13 & 1/2" after turning it on paper and measuring the circle? If thats how to measure diameter? Any help would help.

Thanks
Gary B