problems

[qwackhead]

I have a 01 30hp johnson it has a 13 pitch prop its on a 15X48 aluminum boat i have a cmc tilt and trim it seems that my boat is cavitating i have the cavitation plate about even with the bottom of the boat cmc recomends 3in above the bottom if i do that i know ill have problems this weekend i had 3 people in the boat along with all our junk had trouble getting the boat to plane out even had the two guys slide to the front to get it to set down then the motor would sound like it was cavitating maybe the hub is spun but it will pull good then it starts standing the front up and it just blows out any suggestions would be appreciated.

 

[psteurer]

Re: problems

I presume a 15x48 aluminum boat is the type that is 15 feet long by 48 inches wide. If that is correct, a 30 hp is good fit for that boat and a 13 inch pitch is probably the standard prop that came with the motor. The cavitation plate is okay even with the boat keel but can be up an inch or so.

Has this problem just started or something that has existed every since you owned the boat? Your problem could be prop related like a spun hub. You can test for a spun hub by scribing a line across the interior part of the prop that connects to the prop shaft. Give the boat a run and then see if the line still lines up. If it does not line up, your prop hub is spinning and the prop needs to be replaced or repaired.

Three people in a boat this size along with you is a big load. Does the problem also occur with just you in the boat?

 

[steelespike]

Re: problems

If this is a new development I would suspect a spun hub as suggested.
I assume it is a Jon boat.Being a flat bottom should help it get up betrter than
a rounded bottom.
If the boat was wider 54 or 60" it would plane easier.

 

[qwackhead]

Re: problems

after a little inspection today the prop is shiney behind the splined washer so i think my hub has spun i plan on marking it and running it tomorrow. the boat is rated for 4persons and yes it is a flat bottom john boat i was hitting the rev limiter from time to time with one or two people in the boat am thinking of trying a 14pitch prop to get a little more speed. what kind of stainless prop do you all recomend i have a solas and this is the second time i have spun the hub if that is my problem we are restricted to 25hp but mine has 30hp carb on it tying to stay up with the 3cyl tohatsu's and yamaha's

 

[psteurer]

Re: problems

If you are wanting a detailed recommendation on a prop, I would recommend that this post be moved to the prop forum. You will not get much help in this forum though unless you have a tachometer that will give you your WOT rpms. Going to a 14 inch prop will lower your rpms by about 200 or so and should increase your speed a bit. If you are hitting your rev limiter, you really need more pitch to prevent damage to your engine.

 

[qwackhead]

Re: problems

checked prop today its not spun the boat seemed to do fine today dont know what the problem was the other day. but i did notice today i seem to be running on one cylinder for a bit then after bout two or three seconds it will pick the other one up so i checked the compression it is 115 on both cyl. is that about right. the boat porpused bad with me alone in it have to trim down to keep it from doing it like almost neg trim. may try raising the motor like cmc says it just goes aginst what my gut tells me i think its gonna cavitate bad.

 

[psteurer]

Re: problems

115 psi compression on both cylinders is great for that motor.

You seem to have multiple problems going on. Running on one cylinder could be an electrical problem. Could be as simple as a spark plug. It could also be a bad coil.

I am not an expert on CMC tilt/trims. But if this after market tilt trim you put on extends the motor out past the transom (say six inches or so), I understand that you should install the motor so that the cavitation plate is a few inches above the keel. I have seen flats boats with this type of arrangement. Something to do with the motor being away from the turbulence caused by the bottom of the boat.

You could still have a prop problem even though it is not spun. Check the blades to see if they are damaged or out of balance. There are all kinds of aftermarket props that I do not know enough about. I do know that even though these props may have the same pitch and diameter, there are all kinds of designs such as cupping and raking which are used upon different types of boats.