Channelling?????????

[garys]

At the outset I have to say this site is a great way to learn things. The topics are all relevant to a new "boatie" like myself and I have learned heaps.

Recently I was out on a dam pulling a child on a tube. From memory I think I had gone down a straight and was turning to make a return run when the boat seemed to lose pulling power in the water, the motor seemed to rev more, and seemed to spray water upward into the air. It was as if the propellor was not pulling through the water.

Has anyone had a similiar experience.

When I spoke to a guy who I think worked for an "Australian Boating College" he said it sounded like the propellor may have been surrounded by air locked under the surface of the water and referred to this as "Channelling".

I must admit I felt that something really bad had happened to the propellor and felt like the prop itself had become free from the shaft.

Thanks for any help

Gary S

[finga64]

cavitation is another name. And yes it seems as though something bad is going to happen.
It can be resolved in most cases but if it only happens occassionally just throttle back until the prop starts working again and then put the power back down again.
Not too serious a problem going around dams but if it happens all the time and you cross any bars then it's a huge problem. Crossing bars is when you don't need that lose of power and lack of control.

[Moffy]

any chance you had picked up a bit of wood on the front of the skeg for a bit - that could cause that problem - i.e if a smallish log gets trapped on the front of the motor, the wood creates a big air bubble and then the cavitation.

[caloundra]

agree with finga

cavitation

[basserman]

true name is ventaliation
just air getting sucked down to the prop when the motor is either trimed to high or turning too sharp and too fast
as the other said no big drama just back of for a second and go again ;D

[SWFISHER]

CAVITATION BOYS, HENCE THE CAVITATION PLATE ON ALL OUTBOARDS, THIS PLATE IS MENT TO BE AT THE CORRECT HEIGHT TO YOUR BOAT TO ELIMINATE WHAT WE CALL CAVITATION. CHEERS KEV

[NQCairns]

Not that it really matters but the miss-termed cavitation plate is correctly termed the ventilation plate. So the poster experienced ventilation, ventilation is any atmospheric air also atmospheric air from the combustion process, cavitiation is micro bubbles formed on the surface of the prop due to pressure.

I suspect channeling is when in a turn a strake causes a dip in the water, deep enough to reach the prop before i stabilises with the normal water height.
If it did it one way but not the other I would be looking also at anything in the water like a transducer or water pickup as well as the strakes.nq

[garys]

Many Many thanks fellows...............The first time it happened it realy worried me. Th eboat was new. I was new to boating. I had no idea what was happening and obviously thought the worst.

Once again, your experience has helped me enormously. This is a great site to learn valuable aspects of boating and the willingness to pass on advice is tremendous.

Thanks

Gary S

[mini696]

Slow down... ;)

[joeT]

I used to have this problem with my old 3.7 tinny. Turned out the problem was I had the motor trimmed up to much, and when I trimmed it down it was much better.