30hp johnson slippage

[onceagain_04]

i posted last week about my 1997 seanymph and greatly appriciate all the responses that cured some of the problem
next problem is, after half to almost 3/4 throttle, seems to slip, the prop is brand new, and there is no shear pin in the shaft, bottom end is beautiful, but once up to 10-14mph on gps slips unless i feather it......hole shot wide open slips or feels like it, but will eventually get up and plane

 

[onceagain_04]

Re: 30hp johnson slippage

just reading thru the owners manual for the motor for the 50th time, and realized the correct pitch for the prop is supposed to be a 15, and i have a 13 on it, would this cause the problem?

 

[beau123]

Re: 30hp johnson slippage

Not to sure if that would cause the problem you are describing. I am having a very similar problem with a 1989 40 hp Johnson, an outboard mechanic told me that the motor was sitting to low in the water, and that I may need to adjust it up a bolt hole or two. Also you may want to do a search in the threads for this type of problem, I remember reading one similar to this a while back.

 

[wbeaton]

Re: 30hp johnson slippage

Sounds like ventilation (cavitation).

Prop shouldn't be the problem. There are lots of different styles and choices of props for that motor. The 15" is likely just the stock "all purpose" prop. I have a cupped 11" on my 1988 Johnson 30 hp.

 

[F_R]

Re: 30hp johnson slippage

Normally, I would say it's the prop hub slipping, but that is kind of ruled out with the new prop. So-o-o-o, the next guess is cavitation or ventilation. No real point in getting into the difference, both amount to air getting into the prop stream. Usual causes are motor too high on transom, or something creating a disturbance ahead of the prop, such as seaweed on the motor or gunk on the bottom of the boat.

I'm assuming it isn't making any horrible noises or grinding sounds, is it?

 

[clint]

30hp johnson slippage

Cavitation or Ventilation,,Good Luck!
Clint

 

[mikesea]

Re: 30hp johnson slippage

I would start by experimenting with the adjustment pin for hieght.I would go down a hole first.Are you sure the hight of the transom and the eng shaft is right?distance from the top of transom to bottom of hull should be about the same as engine bracket that sits on transom to cavitation plate on lower unit,give or take 2 inches

 

[onceagain_04]

Re: 30hp johnson slippage

cavatation plate/ antiventilation plate was recently adjusted up one inch now even with the transom, same issue, me in the boat hit 26 on gps, two ppl, takes forever to plane, babying the throttle after half, taggin 13ish and eventually 21, light gear and just 2 ppl....tack is in the mail

 

[wbeaton]

Re: 30hp johnson slippage

You should be an inch lower. Did the problem start after the adjustment was made?