My boat going slower and slower.

[hlb]

Yet the revs are still the same. Course, to make it more complicated, they have again slapped antifouling over the log, so only got GPS speed.

The anifoul is new, nothing else visably wrong, I used to be able to get 24 knots, even 25 once. Now I'm lucky to get 20.

Just how much difference does it make, to take all the antifouling off and start again. Theres ten years of say two coats a year down there.

Who's had it done and how much difference.

 

[rich]

When was the last time you got a van along side and empty the boat of all junk, and then only put back what you need, we did it to hermees last winter, It's bloody amazing what you collect over the years, /forums/images/graemlins/shocked.gif

 

[MapisM]

Mmm... just two coats of new a/f, and now getting 20kts at the same revs as when you got 24? Sounds like you've been cruising against a 4kts current!
Surely just the weight of two new coats alone can't make you loose 4 kts, and you would also loose revs if overloaded, anyway.
Re.the log, normally the wheel can be removed and cleaned from inside, also with the boat in the water. Is it hard to reach maybe?

 

[Bandit]

Did your log always agree with your GPS ?

Tide with and against boat ?

Was the log set to the GPS ?

 

[hlb]

No it's 20 coats of AF. I dont think it's anything to do with weight, just maybe unsmoothness.

Thanks for the reminder of removing from inside. I'll have a look.

 

[hlb]

Of course it did'nt. Point is, the log is the only real test of performance. Even when it was working last year, I was going slower. Not so worried about going slower, just that I'm using more fuel.


The question is. If I get all the antifouling taken off. Will it make a difference.

 

[EddieA]

Yes of course - by how much, I've no idea /forums/images/graemlins/tongue.gif

 

[omega2]

Overtime any boat will absorb water and get heavier, I know of a boat that that weighed in 3 tons heavier than original, it was left out the water for a year and lost nearly all that excess weight, it was then treated with gell shield and re anti fouled and performed as new, alas that was 10 years back she is now a bit slower again.

 

[carlton]

[ QUOTE ]

The question is. If I get all the antifouling taken off. Will it make a difference.

[/ QUOTE ]

Hmm. Tricky one. I had mine soda blasted recently. Took about six layers of antifoul off. Here's how it looked after the job.

I can't say it made much diference to speed/fuel consumption, perhaps a bit as the previously applied layers were a bit 'lumpy', but it has made subsequent anti fouling quicker and easier.

If - as you say - MF has somewhere approaching 15-20 layers of old antifoul on the hull then soda-blasting (or similar removal) might be worth a punt. Cost me about £250 or so I think. /forums/images/graemlins/confused.gif

Could be worth getting a compression test done on the lumps first though - prob'ly cheaper and worthwhile as a first check. I say this as my van (background of the picture, coincidentally) engine lost power recently and began slurping oil. But it still seemed to run like a good 'un.After a £1000 rebuild it's like new, but I hadn't noticed its gradual detorioration.

 

[hlb]

When I bought her, ten, eleven years ago, she had just had all the old antifouling stripped off. WE used to cruise at around 22 knots then, ok I was giving her a bit of stick, around 36,00 revs. These days I aim about 3,400 to 3500. But never see 20 knots on the screen as I would expect to.

The props are going round fast enough. The bottom is clean. Weight has never made any difference.

The only thing I can think of, is an unsmooth bottom due to to much paint.

 

[sarabande]

Did you have new props as a result of arguing with a sunken container ?

 

[hlb]

Nope props are fine. May be not as good as when they were new. about five years ago, but still look respectable.

 

[oceandrive]

You say your log is not working have you always compared this against GPS and tidal flow. MapisM could have a good point here. so maybe check out on GPS at slack tide. Also tanks full or empty and are the builges dry etc. have you got more canopies up bimini etc.

We have just scraped back a Cranchi 37' using draw scrapers which took two days. we tried a test area first on the stern just to see how hard the task would be, found that if you got the pressure right managed to scrape back eight coats of antifoul back i.e two coats per year since 2005. We then re primed and the aplied two cotes of Trilux ( International) boat back up to 38 knots against it's record speed of 39 knots with empty tanks. we also had a bimini up on the test. So very happy. also make sure that the underside of your tabs are clean I have found that many antifoul tabs and this can have quite an effect.

It is well worth also making sure that the underside of trim tabs are as smooth as possible also shafts, rudders and props. We tend to clean all off with acid and then a good rub with wet and dry followed with a good rub over with vassaline which seems to keep the nasties off until the season
starts and the boats are running regular. people say its a wives tale but if after launching you are just going back to the marina to moore up and not use the boat until the next sunny day then this can help keep things clean until you realy hit the RPM and wash it off.

 

[MapisM]

[ QUOTE ]
No it's 20 coats of AF. I dont think it's anything to do with weight, just maybe unsmoothness.

[/ QUOTE ]Whoops, I understood that you used to achieve 24kts just before the last coats of a/f.
If you meant that you lost those 4kts in a decade, well, that's not too bad... /forums/images/graemlins/wink.gif
But mind, almost 20% less speed at the same rpm is weird anyhow (unless you changed the props in the meantime, of course).
Weight or rough hull surface make no difference in this respect, it's always higher resistance, which is bound to reduce not only the top speed, but also the revs.

 

[Nick_H]

Same revs, less speed seems to suggest a change to the props, are they damaged, worn or eroded? Most other things, weight, fouling, built up a/f, etc would reduce revs as well as speed.

 

[mjf]

Yes I agree.

Same revs less speed indicate its a prop issue.

 

[hlb]

I would not be asking about the antifouling issue if I thought it was the props or a dirty bottom.

 

[MapisM]

Understood Haydn, but there are reasons to consider props, based on your initial input (lower speed, same revs).
Either that, or a difference between SOG and SOW, as I mentioned in my first reply.
I can't think of any other plausible reasons.
Aside from new gearboxes with a different ratio, maybe? /forums/images/graemlins/blush.gif

 

[hlb]

Well I have many times heard of folk having the antifouling removed, presumably theres a good reason for this. I'm asking folk that have had it done. Did it make a difference and how much.

 

[BartW]

[ QUOTE ]
Most other things, weight, fouling, built up a/f, etc would reduce revs as well as speed.

[/ QUOTE ]

Ususally I cruise around 3000 RPM,
When the boat was new, 3000 revs gave 27 kn.

Today while we have added many bits and pieces, radararch, etc.. and the boat is heavy loaded with people, etc.. I still cruise at 3000 rpm, but then cruising speed is reduced to 23-24kn

the hull doesn't have A/F, and still looks impeccable

max revs and max speed is reduced ofcause