Performance Drop Off Due To Slime??

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ianphillips

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How many knots/revs might it be considered reasonable to lose due to three months growth on the hull of an outboard driven Sportsboat (23ft). We seem to have lost 800 rpm and about 8 knots, which dealer says is normal - although I am not so sure. The anti-foul is discoloured but does not feel particularly slimey but is very slighly gritty to the touch. Acceleration is still good and planing speed has not risen, same gear on board etc, so I suspect something else may be amiss.

Before I pay out for a lift/scrub, would like other opinions.

Cheers
 
Have you checked the props and out drives

they get slimy too, don't worry, thats what the problem is, jump in and give it all a scrub or its lift out time again
 
Re: Have you checked the props and out drives

Sounds about right to me. Slime slows, even a nick in the prop can cause you to slow. This is why out and out racers polish their bums and have chromed or stainless props.
 
Re: Have you checked the props and out drives

Outboard is tilted clear, so leg and prop are like new.

I appreciate slime has a big effect. But hull was freshly anti-fouled in October and was pressure washed in Feb during a few days ashore - hardly any growth at that time. I have never experienced such a drop in performance in just three months, particularly when it has been so cold and considering the boat is used at least once a week.

My experience of previous boats has been that slime affects acceleration before knocking top speed - but may be I have just been lucky??

I guess I am going to have to get a scrub to find out!!!

Thanks
Ian
 
Re: Have you checked the props and out drives

blimey, with clean props and no rudders there must be more than a bit of slime - esp if the clean was in october. It doen't sound too normal to me. However, with a smaller boat the actual water conditions are more critical praps? And how manyon board, water tanks etc etc. Heyho, praps scrub and try again but i wd want think there must be summink else? Let us know...
 
Re: Have you checked the props and out drives

Why are you assuming it's slime that's causing the lower achievable revs?
Could it be the motor that's not pulling full revs. Perhaps the mixture's weak (air leak?)or something else.
 
Re: Have you checked the props and out drives

It's the slime - sigh! Why look for alternatives when the answer is blatantly obvious.
 
Re: Have you checked the props and out drives

I am sitting on the fence with this one, but maybe leaning on the "it's something else" side!
It does seem to be a dramatic loss of performance if it is just the slime from a relatively short period of time.
 
When will you high speed freaks realise;; dirty bottem means less speed.
and before you all knock me, I have spent a lot of time on fast power boats. i just like to relax now on comfy slow cruising /forums/images/graemlins/grin.gif
 
Yes, but he does say the bottom is discoloured but not particularly slimy. So no summer growth of inches of weed round waterline etc - this is winter growth in cold water. Just a tiny amount of slime. That shouldn't usually mean a drop in speed or of revs of that amount.
 
I'm with tcm / brendan - if it's discoloured antifouling type slime you aren't going to have lost all that speed / revs (although you don't tell us the actual speed; if you are playing up at 50knots then it's possible.........)

I am in the camp that say's barnacles; either a fine covering in the early stages of a few developed clusters lurking somewhere. Even a few will have this effect - in fact a few clusters would be my guess. If a fine carpet of spores just developing you would expect to see the effect of the drag even at lower speeds including the hole shot etc.

Of course if you idea of slime is ribbon weed 3 inches long then that would do it too - but as it need light any weed growth is unlikely to still be in the water when you are up and running!
 
As a matter of interest, what top speed, and what speed now, and what HP is the outboard.

If you are not particularly highly powered in first place, slime could cause a significant drop off in perfomance compared to a high powered inboard.
 
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