I have a 20' toon with a 50 hp 2 stroke Johnson, circa 1998 on both. I have been having cavitation problems for quite some time. Finally changed my prop to 13 X 11. Took the boat out to test it and ran perfect for about an hour. Was ready to kiss a pig I was so happy. Then, it started cavitating again. I am at a loss. Why would it run perfect for an hour, then not? Anybody have a suggestion? Motor is down all the way.
It would seem to me that if it ran good for an hour, it should run good all day unless other parameters changed.
My best guess is that perhaps some weight was shifted forward such as a passenger moving up front.
I don't think that an hours fuel usage would have shifted the weight much.
If you really have a cavitation problem, then you must continue to experiment with prop sizes and weight distribution. If you have a ventilation problem then you must lower the motor more or shift more weight to the stern.
It has a short shank. Have tried many things, weight in back, front under over. Ran with bimini up and down. Tried tilting motor to different angles. I do not think that the small use of gas during that hour would have anything to do with it but maybe. Going to take it out again this morning.
In almost all cases, pontoon boats need a long shaft motor. I had a short shaft on my old boat, and the only way it wouldn't cavitate was to have it tilted all the way down, virtually under the boat, resulting in poor speed and poor performance. Unfortunately, my only suggestions are to have your bottom end replaced with a long shaft if possible, or sell the motor and but a long shaft version.
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I've fished for half of my life, the rest I just wasted.
I have the same problem - have a 2008 21' Sun Tracker and am so frustrated with it I am very tempted to sell it. Love the boat, but can't stand going 8 mph.
I have ordered a different prop and am going to try that. I have a 50 hp 2 stroke, and understand that a bigger motor would help (longer bottom, bigger prop), but I hate to spend more than the $15k I just did to buy the thing.
We are to the point that I refuse to take friends out w/us because of making everybody sit in the back or go 5 mph, but being able to take friends out was the main reason we bought the thing.
Have a 20' Starcraft with a 40 Merc. Having similar issues as others. I believe my problem is ventilation not cavitation. The engine is not mounted all the way down on the transom....one more hole is available to lower it down. Hopefully this weekend I will pull it out and lower the engine down and see if that solves my problem.
Mine does it no matter what - the motor is as low as it can go, and when trimmed all the way down, unless I've got 70% of the weight in the back of the boat, it does it. Not sure if it is cavitation or ventilation but can tell you it is frustration. And to add insult to injury, the guy at the local prop shop suggested drilling holes in it, which I then paid him to do, which only made the problem worse. So much for "expert advice"...
So, a new prop came today and we'll see how that works. My old prop was a three blade with no cupping. The new one is four blades with cupping - can't be any worse than it was, can it?
I really do thank you people for your replies to my toon problem. The mystifying part is that it ran beautiful for an hour before the cavitation problem started up again after I replaced the prop with a 13/11. I just took it out again and it started cavitating right away. Had to run at low throttle for it to get anywhere. If it had not run for an hour like it should, I would then take some of these suggestions. I put gas in it and shifted weight to rear and that did not help. I know that it is very frustrating to you as it is for me but I still have the problem and really not solution other that get a long shaft. This is a Godfrey Party Kraft set up as fishing boat from the factory, 1998 vintage and the motor came with it and is a 1998 johnson 50hp 2 stroke. I am still looking for a solution.
Last edited by Costly Affair : July 11th, 2009 at 12:24 PM.
Reason: Adding information
I really do thank you people for your replies to my toon problem. The mystifying part is that it ran beautiful for an hour before the cavitation problem started up again after I replaced the prop with a 13/11. I just took it out again and it started cavitating right away. Had to run at low throttle for it to get anywhere. If it had not run for an hour like it should, I would then take some of these suggestions. I put gas in it and shifted weight to rear and that did not help. I know that it is very frustrating to you as it is for me but I still have the problem and really not solution other that get a long shaft. This is a Godfrey Party Kraft set up as fishing boat from the factory, 1998 vintage and the motor came with it and is a 1998 johnson 50hp 2 stroke. I am still looking for a solution.
Because long shaft motors are not used on as many boats as a short shaft, often someone who has one for sale is more than willing to trade for a short shaft. Another possibility is to convert it from short to long by changing out the bottom end. Keep an eye for one with low compression or a blown head, selling for cheap. This way you keep the motor you know.
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I've fished for half of my life, the rest I just wasted.
Yesterday we lowered the motor one notch down. We took the boat out and again, it ran ok for a half an hour, then started the cavitating again. While out there, we re-distributed weight all around the boat and it made no difference. I am using the boat in Sarasota Bay, relatively smooth salt water.
I have now sent an email off to Godfrey Marine to see if they have any answers. Very, very frustrating. And again, thanks for the comments.
Last edited by Costly Affair : July 14th, 2009 at 08:59 AM.
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