20' Pontoon with 60HP Johnson 3 cylinder 2 stroke

[wfburton159]

I have a 20' pontoon with 1996 Johnson 60 HP three cylinder two stroke on it. Last year was my first year with this boat and it ran quite rough. So this year i have been working on tuning it up. It is now running well and i was finally able to get a tach on it because i could tell it wasn't getting to the recommended WOT RPM's. Well I was right. I was finally able to test the boat out with my tach installed and the load that I normally have. WOT and full speed it would only get to 4300 RPM's. The top speed is usually a little over 21 MPH. The prop that is installed is a 13 3/4" x 15 pitch. I was thinking of going with a 9 pitch prop to get the WOT RPM towards the recommended 5500 RPM. Any suggestions? To me the 15 seems like way too much prop.

 

[steelespike]

15 is way too much prop.I'm thinking perhaps a 11" would be closer to what you need.
Your at 21 mph now.Is that by gps?If you want to maintain speed you need to be conservative in your prop selection.

 

[lmuss53]

I would make sure the tach is set to the right pulse setting, and that you don't still have some engine issues.

The 15 is not really out of line for that boat with that motor.I had a 3 cylinder 75 on a 20 foot Tracker pontoon and ran 15 p props the entire time, Top speed was 23 or 24 with rpm of 5300.

On my current 20 foot pontoon with a 55 Evenrude I alternate between a 13 or 15 depending on what I'm doing. Top speed is about 18 to 20 with rpm's at 5500, I recently installed a newer 50 hp Merc 3 cylinder and have 13 and 15 pitch props to try on that.

I try to prop my boats so they get up and going quickly with an average load., I want the rpm in the high side of the recommended range at WOT and speed whatever that may be is the least important part of the equation.

The 15 is close and the 21 mph is another indicator of that, If everything is right with the motor try a 13 or 11, the 9 is a work boat prop and is way too low for your pontoon.

 

[wfburton159]

Well thanks for the recommendations. I have to verify if the timing advance is working correctly but i do trust this tach. I can tell that the motor isn't opening up all the way. I don't care about top end speed as much as I want to get the WOT RPM within spec. Something might still be wrong with the motor performance as even with this 15 pitch prop the acceleration is pretty good. The throttle is opening all the way so it's not that. It might be the timing advance. Oh and the 21 MPH is by GPS.

 

[Sea Rider]

If rule of thumb + 200 wot revs per one less pitch applies on your boat, you should go down at least 6 pitches to a niner, but that rule is unpredictable as have seen that much gained rpm only on very heavy boats, more on medium and much more on light ones. Ideal is to dial a prop that revs around max wot revs with current load. To rev around max 5500 wot rpm will need to know how much wot rpm is gained going one less in pitch. Six less is an exaggeration, probably 3 less will work well ? The only way to know is under a water trial.

Happy Boating

 

[wfburton159]

I wish I knew someone that had at least one prop that I could try without having to buy one for the test. I don't have a spare so I do need a second prop but I would like to see an 11 perform.

 

[Sea Rider]

As an example, needed + 200 wot revs to be at max required 5800 rpm when solo boating lightly loaded, went one less pitch from 9 to an 8 as per rule of thumb, oh boy that formula blew my wot revs up by 500. Jhonson props or other compatible brands are available in 1 or 2 increment/decrement prop pitches ? Personally I'm not interested to achievet the max top speed, as this will oppose nice hole shot which is much preffered specially when more loaded. Having nice hole shot with slight less top end speed is nothing that will take your sleep away.

Check a prop shop if they can lend you an 11 for testing, could be an excellent starter prop, but that is not known.

Happy Boating

 

[wfburton159]

I will call a place tomorrow to see if he has any loner props. I don't care about top speed. I want it to run at the correct RPM at WOT

 

[Sea Rider]

Wot has min and max rpm range that must be tached, OB should referably run at or near max wot range with current load or as you like boating for combo's best water performance along geting full horses out of that OB.

Happy Boating

 

[wfburton159]

Wot has min and max rpm range that must be tached, OB should referably run at or near max wot range with current load or as you like boating for combo's best water performance along geting full horses out of that OB.

Happy Boating

This is why I am trying to find a different prop. The full throttle operating range of my engine is 5000-6000 RPM. My last test was with the normal load I will have an I could only get to 4300 RPM. I did call a local marine shop today and he said he has a full wall of used props. Said he must have 75 or so of them. So i will swing in there to see if he has an 11 pitch for me.

 

[wfburton159]

I installed a 11 pitch Silas three blade prop. Into the wind and loaded up we got just under 19 mph and running at 5200 rpm. I am happy with that.

 

[wfburton159]

On the way back with the wind we were at 21 mph and 5800 rpm. Life is good. Boat felt much better.

 

[lmuss53]

Beautiful, now that 60 can breathe, she is much happier too.

You will find the boat more maneuverable at low speeds now too

 

[wfburton159]

The boat did feel great now. I adjusted the trim up stop as well so that the motor doesn't hit the back of the seat frame. Now to repair the damage to the motor cover from hitting the seat frame from the previous owner. I also ordered a trim gauge for it to install this weekend. My wife should be able to operate it much easier if she can see where the motor is at.