How much effect can fouling have?

[RobWard]

My boat - a Bav 30 - has suffered a marked decline in motoring performance, from a cruising speed of c. 6 kn to 4kn. (I can't really comment on sailing performance because we haven't been out enough to assess )

The engine has been thoroughly checked - fuel quality and lines, air filter, exhaust elbow, compression - all good. I'm now beginning to wonder whether a combination of foul bottom and prop (fixed 2 blade) could be the cause?

 

[NormanS]

Yes.

 

[MoodySabre]

I expect that it is the prop. A lot of barnacles will have a major affect, more than just weed on the hull.

 

[Refueler]

2kn reduction is quite a lot - but that of course depends on how the boat is powered ... small engine / prop - then fouling will take a large toll on performance, but if large engine / prop - then less % effect.

My 43hp Perkins powered 25ft motor sailer (4 tons) can do 9kts max ... heavily fouled she will drop to just over 8kts.
But my 2GM 23hp Yanmar powered 38ft racer (5 tons) - if she's fouled - I can expect a significantly greater loss of performance as the power combo just does not have the 'grunt' to suffer it.

 

[shanemax]

I expect that it is the prop. A lot of barnacles will have a major affect, more than just weed on t, probably the prop

 

[shanemax]

Couldn't agree more about the prop and barnacles.

 

[Snowgoose-1]

My 43hp Perkins powered 25ft motor sailer (4 tons) can do 9kts max ... heavily fouled she will drop to just over 8kts.

9 kts sounds rather a lot for a 25' motor sailer.

 

[Refueler]

9 kts sounds rather a lot for a 25' motor sailer.

Believe it ... I do not joke because it spends most of its time on a river with slow current ... I have had ample opportunity to prove that ...

Open invitation to come over to see for yourself (once keel repairs completed !)

The wake is humongous ... so only when no one else around ... and engine is way over prime running so plenty of black soot chucked out wehen throttle wide ...

She maintains 5kts on about 1/3rd cruise throttle.... which is my prime setting ... I can reliably set an ETA and adjust speed to make it - unless weather is really bad ... and I am not talking Chichester to Bembridge distances ... I'm talking 90nm and more ... Ventspils to Farosund as example .. Farosund to Swedish Islands etc.

Because boat is over-powered - I make sure I give engine a good 'thrashing' every now and then ... speed in the river is my good indicator.

 

[Neeves]

My boat - a Bav 30 - has suffered a marked decline in motoring performance, from a cruising speed of c. 6 kn to 4kn. (I can't really comment on sailing performance because we haven't been out enough to assess )

The engine has been thoroughly checked - fuel quality and lines, air filter, exhaust elbow, compression - all good. I'm now beginning to wonder whether a combination of foul bottom and prop (fixed 2 blade) could be the cause?

as posted, Yes

It actually does not matter whether it is the prop, prop and hull or hull as you need to lift power wash and treat. But a badly fouled prop, alone, could cause the reduction.

However its unlikely only the hull or prop are fouled and the other acceptable.

It will only get worse - bite the bullet..... now

Jonathan

 

[Daydream believer]

My new engine has more than enough grunt for my boat, but what now affects me most with it is fuel consumption.
When launched on 21 june this year I averaged 2.19 litres per hour running at 6.4 kts water speed in flat water over 110 miles. Last week in similar conditions I came from Dieppe -Dover - Bradwell & averaged 2.4 litres per hour at the same speed.
I put it down to the fact that I have coppercoat, which is next to useless.
In the past, when sailing I found that after a couple of months the silt that forms on the hull reduces sailing speed by at least .5 knt. If cruising to the channel islands & back I often resorted to motor sailing on the way back(which is where the Brunton prop comes into its own) due to weed after 4 months, if I could not get a mid season jetwash.

 

[Tranona]

My new engine has more than enough grunt for my boat, but what now affects me most with it is fuel consumption.
When launched on 21 june this year I averaged 2.19 litres per hour running at 6.4 kts water speed in flat water over 110 miles. Last week in similar conditions I came from Dieppe -Dover - Bradwell & averaged 2.4 litres per hour at the same speed.
I put it down to the fact that I have coppercoat, which is next to useless.
In the past, when sailing I found that after a couple of months the silt that forms on the hull reduces sailing speed by at least .5 knt. If cruising to the channel islands & back I often resorted to motor sailing on the way back(which is where the Brunton prop comes into its own) due to weed after 4 months, if I could not get a mid season jetwash.

Fuel consumption is nothing to do with the new engine per se - but the amount of power you are demanding from it. Consumption with the proper 20hp motor at 6.4 knots would be exactly the same, although the engine would be running about 300rpm higher. The increase because of the fouled bottom would also be the same. because you need the same extra power to overcome it.

 

[Stemar]

Believe it ... I do not joke because it spends most of its time on a river with slow current ... I have had ample opportunity to prove that ...

Open invitation to come over to see for yourself (once keel repairs completed !)

The wake is humongous ... so only when no one else around ... and engine is way over prime running so plenty of black soot chucked out wehen throttle wide ...

She maintains 5kts on about 1/3rd cruise throttle.... which is my prime setting ... I can reliably set an ETA and adjust speed to make it - unless weather is really bad ... and I am not talking Chichester to Bembridge distances ... I'm talking 90nm and more ... Ventspils to Farosund as example .. Farosund to Swedish Islands etc.

Because boat is over-powered - I make sure I give engine a good 'thrashing' every now and then ... speed in the river is my good indicator.

I can believe that. I had 28hp in a Snapdragon 24 and, with a clean bottom, I could do just over 7 knots, a good knot over hull speed. Like Refueler, I had to give it an Italian tuneup every now and again.

As for fouling, when I bought her, the same boat had a very tired 8hp engine that would manage 2knots. Any more and she left a smokescreen like a destroyer on the Murmansk run. After the first winter on her mooring, I barely had steerage way going to the grid to scrub off. I don't know what antifoul they used, but I think it said Growmore on the tin.

 

[Boathook]

A member on here had the same problem a few weeks back. It turned out a few barnacles on the keel leading edges knocked the speed by quite a few knots.

 

[Daydream believer]

Fuel consumption is nothing to do with the new engine per se - but the amount of power you are demanding from it. Consumption with the proper 20hp motor at 6.4 knots would be exactly the same, although the engine would be running about 300rpm higher. The increase because of the fouled bottom would also be the same. because you need the same extra power to overcome it.

What I was trying to demonstrate was the effect that weed growth has on fuel consumption, as well as the affect on speed mentioned above
The 20Hp motor would not push the boat at 6.4 kts if badly fouled like it is now, so a direct comparison at 6.4 kts would not be possible.
I am able to make that comparison now I have an engine capable of delivering the power needed, rather than the under powered 20Hp one.

 

[jac]

Short answer yes.

I was talking to a surveyor last year about some bad rust that was coming through the copper coat on the keel and he mentioned it would affect speed. When challenged on how much, he said that in his experience thatcould lead to 0.5 to 1 knot reduction in speed. If some bubbling rust could that then a shed load of barnacles and weed will do lots more

 

[fredrussell]

I’ve spent the last year complaining that boats that shouldn’t be faster than my boat kept overtaking me under sail. Had the antifoul and prop clean done a week or two ago (after two years in water) and I’m blasting past all the boats now. Coppercoat next year then.

 

[Refueler]

Any fouling will affect hull through water speed ... so we have to be careful to only be referencing STW ....

Comment about fuel consumption - of course consumption increases as fouling takes effect - if we push to drive at same STW ... basically throttle is that bit more open ... its like climbing a hill in the car vs on the flat ...

Coppercoat .... mmmmm seen many a slimy dirty bottom with it ...

 

[dunedin]

My new engine has more than enough grunt for my boat, but what now affects me most with it is fuel consumption.
When launched on 21 june this year I averaged 2.19 litres per hour running at 6.4 kts water speed in flat water over 110 miles. Last week in similar conditions I came from Dieppe -Dover - Bradwell & averaged 2.4 litres per hour at the same speed.
I put it down to the fact that I have coppercoat, which is next to useless.
In the past, when sailing I found that after a couple of months the silt that forms on the hull reduces sailing speed by at least .5 knt. If cruising to the channel islands & back I often resorted to motor sailing on the way back(which is where the Brunton prop comes into its own) due to weed after 4 months, if I could not get a mid season jetwash.

But if you motored at 5.5knots the reduction in fuel used would probably be quite dramatic.
Lots of data on power needed by speed, partly driven (!) by the trends to electric propulsion who measured this. Most e-propulsion boats often motor at 4 knots to improve range dramatically, but suspect 5.5knots might be a sweet spot for your size.

 

[Daydream believer]

But if you motored at 5.5knots the reduction in fuel used would probably be quite dramatic.
Lots of data on power needed by speed, partly driven (!) by the trends to electric propulsion who measured this. Most e-propulsion boats often motor at 4 knots to improve range dramatically, but suspect 5.5knots might be a sweet spot for your size.

Would not have helped much when on passage a couple of weeks ago between Dunkirk & Boulogne when I caught an adverse tide ( running at something like 2.8kts for quite a while) & head wind & severe chop rounding Cap Griz Nez
The data figures tend not to take into account the extra time taken especially when motoring against a foul tide. That soon eats up any fuel saving
But the point of my post was not about this thread drift but just to point out that fouling also affects fuel consumption.

 

[Daydream believer]

Coppercoat .... mmmmm seen many a slimy dirty bottom with it ...

Big thread drift here
The only benefit of Coppercoat is not having to get under the boat sanding down old A/F every year
In my mind that is a big plus
Also there is the ever rising cost of the A/F paint. Not to forget the ancilliaries , such as rollers, thinners, wipes, gloves, masks, overalls etc.
What one does have to do, after the launch at the start of the season, is budget for a mid season scrub.
I have spoken to a number of staff in St Helier, Burnham, Inverness, Dover & Shotley, who all say that Copper coat is no better- in some cases worse- than ordinary antifoul paint. None of them has said that it actually works as claimed. I have spoken to owners who are happy, but generally their form of "happy" is a thick film of speed reducing scum, all over the hull & long weed at the waterline. I have spoken to owners who are very disappointed I currently have long furry growth 50mm plus long, well below the waterline. I am far from impressed & if I had been able to continue my holiday, I would have had the hull jetwashed in Cherbourg.