boat wont plane

[kieronriley]

hi I have a Shetland 18 foot with a 70 h/p evinrude engine . I went out on Wednesday with two passengers and the boat would not go on the plane, now last time out I was on my own and there was not a problem but this time just as the boat should have gone up on the plane the engine just dropped revs and I had to throttle down and then back up to get going again ,has anyone any ide a what the problem may be.
oh and its been in the water for about five months without anti foul,dont know if that would make this happen. Thanks Kieron

 

[Nick_H]

oh and its been in the water for about five months without anti foul,dont know if that would make this happen. Thanks Kieron

It would explain why the boat couldn't get on the plane, but not why the rpm suddenly dropped. Have you checked the fuel filter, and is the fuel new this year? Did they definitely drop, or did the boat just seem to lose power? If the latter, it could be prop ventilation, which would explain why you needed to throttle back. If you had the two passengers up front to try and get the bow down, that could contribute to a problem with ventilation. It's usually pretty obvious when this happens though, as the engine screams at high rpm.

I'd check the fuel filter first and get the hull cleaned, after 5 months with no antifoul it could look like a crusty carpet underneath.

 

[runningman]

Definitely sounds like a fuel problem to me. How old is the petrol? I had a similar problem once with an outboard and petrol of an unknown age although at least a year old. New fuel cured it.

 

[CLB]

Don't know where you are but down here, three months in the summer without anti foul is enough to stop a boat planing. I would suspect this is at the very least a contributary factor. This, plus the extra weight of a couple more crew and a possible fuel issue and you have a perfect combination to stop a boat getting up on the plane.

 

[Sneds]

Not much to add to what has already been said, jet wash the bottom of the boat, replace the old petrol and put in a new fuel filter
Should sort it.

 

[kieronriley]

hi thanks very much for your advice, the fuel was new that day so I will check the fuel filter and clean her bum and then try again, once again thanks. Kieron