When is it time to scrape off antifoul ?

jointventureII · 9 May 2024

@DAW how has that stood up so far?

I have to say, I'm now up to 17 months without lifting mine, intending to lift in June having been launched Jan 23. I binbag the stern drive leg every time I've finished using the boat so that stays out of the sun but the actual hull is still clean ( 2 coats of Boero Altura 619, velux on the leg)

ChromeDome · 9 May 2024

Bouba said:
Ok...ten years...I can live with that

That's up to 9 years of wasted fuel, dragging a submerged giant beard around.

Daydream believer · 9 May 2024

ChromeDome said:
That's up to 9 years of wasted fuel, dragging a submerged giant beard around.

I know what you mean. Some wives say the same about their husbands

DavidJ · 9 May 2024

Unless you blast around a lot at 30 knots then soft (self eroding) antifoul works well and it’s easy to jet wash off every year.
This was my experience in my first ten years of S37 ownership
I changed marina and shipyard and even though I specified soft, they put hard antifoul on which I didn’t discover for years. After another decade it looked awful because hard leaves a lattice behind, I believe, which builds up.
So for 24 knot cruisers go “soft”

DAW · 9 May 2024

jointventureII said:
@DAW how has that stood up so far?

I have to say, I'm now up to 17 months without lifting mine, intending to lift in June having been launched Jan 23. I binbag the stern drive leg every time I've finished using the boat so that stays out of the sun but the actual hull is still clean ( 2 coats of Boero Altura 619, velux on the leg)

The boat is being lifted next week and this will be the second year, so new antifoul will be applied. When it was lifted last year after 12 months in the water, the bottom was relatively clean and the limited fouling that was present was easily washed off. With clean props and rudders, performance was completely normal. At the moment, there isn't much fouling at or below the waterline on the hull whereas the trim tabs, rudders, etc. all have a reasonable amount of build-up. So from my perspective, antifouling every two years seems to work in this area.

DAW · 9 May 2024

DavidJ said:
Unless you blast around a lot at 30 knots then soft (self eroding) antifoul works well and it’s easy to jet wash off every year.
This was my experience in my first ten years of S37 ownership
I changed marina and shipyard and even though I specified soft, they put hard antifoul on which I didn’t discover for years. After another decade it looked awful because hard leaves a lattice behind,I believe, which build up.
So for 24 knot cruisers go “soft”

I had always used soft antifoul on previous boats and when my current boat was delivered new I switched from hard to soft. However, we typically cruise at 20-25 knots and I found the performance was always marginal after 12 months of use with moderate growth occurring at or just below the waterline, particularly in areas exposed to the sun.

My local shipyard Monaco Marine recommend against soft antifoul for planing boats travelling at this speed. I also got sick of washing antifoul marks off paddle boards where they had bumped into the hull, and of people complaining that if they brush against the side of the boat when swimming they come away with black hands. I decided to switch back to hard antifoul and so far have no regrets. Performance has been good and even after two years in the water there is only limited evidence of fouling.

I know many people on here swear by soft anitfoul (I used to be one of them) ... I think both solutions can work equally well. It all depends on your cruising area, type of use, and annual maintenance routine.

DavidJ · 9 May 2024

DAW said:
I had always used soft antifoul on previous boats and when my current boat was delivered new I switched from hard to soft. However, we typically cruise at 20-25 knots and I found the performance was always marginal after 12 months of use with moderate growth occurring at or just below the waterline, particularly in areas exposed to the sun.

My local shipyard Monaco Marine recommend against soft antifoul for planing boats travelling at this speed. I also got sick of washing antifoul marks off paddle boards where they had bumped into the hull, and of people complaining that if they brush against the side of the boat when swimming they come away with black hands. I decided to switch back to hard antifoul and so far have no regrets. Performance has been good and even after two years in the water there is only limited evidence of fouling.

I know many people on here swear by soft anitfoul (I used to be one of them) ... I think both solutions can work equally well. It all depends on your cruising area, type of use, and annual maintenance routine.

Good point about the “soft stuff” coming off onto swimmers, not one I had thought of. I think the question is about not which one (hard or soft) works best but about the build up over years of the hard stuff and when to go for a scrape off.

Portofino · 9 May 2024

Used hard AF most of the time .Once used a soft eroding but it washed off and in the end looked patchy .
Since we have been in Italy used the yard Amico , who know there onions and been very satisfied going back to hard.
This yr they suggested it doesn’t need a full lift and I go on to 2 yearly .Just get the diver to anode it and jet wash it .
The 2 yr thing seems what everyone else with planning boats does .
Tend to cruise near 30 knots .I maxed it last season at the end Sept and it reached 38 knots and 70 rpm over manufactures rated rpm @ WOT which tells me it’s correctly propped , motors are healthy and the AF regime works .

It’s not smooth .Never was when I acquired it back in 2014 .Thus because there’s no apparent drop in performance ( which Bouba is intimating if I I have understood his line of thrust ? ) I have nether bothered to strip it .

The difference might be it lifts up and out a lot above 24 knots reducing drag so any WL , the first few inches gets air not water .Wether Bouba s Semi D “ lifts “ enough, or doesn’t means perhaps at semi D or D a rough surface might be detrimental? But if he’s chugging along @ 8-12 knots on a single small engine I can’t see the cost benefit ratio , the € splashed out on a shell blast , re epoxy ( all blasting damages btw irrespective of media ….it just some are less invasive than others ) then fresh AF is gonna pay off in terms of fuel usage .

The science behind a smooth bottom is not that straightforward.Maybe in a yacht race down between 6-9 knots in light airs perhaps if you loose by 7 seconds you might regret not polishing the hull the day before .
But a planning boat not so sure .A semi D or D single engine low yearly hr then it’s waste of € stripping.

Portofino · 9 May 2024

Not the smoothest surface ( underwater exhaust area )

Any real or perceived drop off in performance is unremarkable.

Obviously if was a couple of hundred rpm under rated @ WOT and way off the test speeds then I would investigate if a strip and start again might be of benefit . But iam not it all appears spot on numbers wise .

jointventureII · 9 May 2024

I don't know how much truth there is in this, but I read an article once that stated a slightly rougher hull surface is preferential.

The example given was if you have 2 thick sheets of a plexiglass material, one lying on top of the other, they can be surprisingly difficult to slide apart. Whereas if one has a very slightly roughened surface, they slip apart much more easily, and that the same principle applies to boat hulls.

DAW · 9 May 2024

jointventureII said:
I don't know how much truth there is in this, but I read an article once that stated a slightly rougher hull surface is preferential.

The example given was if you have 2 thick sheets of a plexiglass material, one lying on top of the other, they can be surprisingly difficult to slide apart. Whereas if one has a very slightly roughened surface, they slip apart much more easily, and that the same principle applies to boat hulls.

I suspect if you live in area where you have lots of creatures attaching themselves to the hull, the analysis is different. However, here in the SoF the most I have seen on the hull in over 10 years of boating is a millimetre or two of slime and a few barnacles, easily removed by pressure washing. The new hard anti-fouling paints are designed to be slow release and last more than one year so why not take advantage of this.

Monaco Marine seem to agree with the article you found ... that on a planing boat slight surface roughness makes little or no difference to performance, and may even be advantageous. Therefore, hard antifoul, painting every 2 years and blasting when necessary (5-10 years) is their recommended approach. In contrast, for sailing yachts they recommend soft anti-foul and painting every year.

For me, it is the condition of the propellers, shafts and rudders that make the most difference to performance in the water and fuel economy. While Propspeed helps, I still struggle to get more than about 6 months without a noticeable drop in performance. I don't find cleaning by a diver in the water to be that effective. Therefore, annual lifts at the start of the season will continue for now.

Portofino · 9 May 2024

jointventureII said:
I don't know how much truth there is in this, but I read an article once that stated a slightly rougher hull surface is preferential.

The example given was if you have 2 thick sheets of a plexiglass material, one lying on top of the other, they can be surprisingly difficult to slide apart. Whereas if one has a very slightly roughened surface, they slip apart much more easily, and that the same principle applies to boat hulls.

Yup .
Think golf balls dimples .
Contradictory one can’t argue for a super smooth surface ( ok it’s air less dense ) which a golf ball certainly isn’t- and then transcribe that principle to denser water forgetting the dimples .

As I said my dog rough multi years hard surface seems have no noticeable detriment .

I think with yachting / sail boats under 10 knots or so in a tight race ( as well as other multi variables ) then sure a super smooth bottom might be beneficial.This is a mobo forum .

I came from yacht racing to mobo ing btw .So I can where the smooth polished psychi comes from .

Not wanting to dive down another rabbit hole folks remember the strakes or indeed steps on some hulls ….Some more pronounced then others Inc Bertram’s btw ....@ P speed ( not D or semi d Boubas boat ) air is introduced under the hull .A rougher source might create micro vortices .This will reduce the surface contact area of the denser draggy water when totted up .By way of example your lung alveola the micro structures that transfer oxygen into your blood ….if extended and spread out have the surface area of a tennis court .

So think of the air bubbles / gasses interacting with that scabby surface on the pic i illustrated ^ .Air drawn i n from the strakes and the speed 26- 30 knots or so .If the air separates the hull from water then drag is reduced .A super smooth surface might not achieve the same sepertion levels as a micro dimpled . = your point / observation .
Also ( sorry folks for bring ing Itama in ) the underwater exhaust air ate the posterior sections at the stern .Engines are mid mounted so a lot of area distal is air ated .Adds up drag reducing .

Bandit · 9 May 2024

If the antifouling is peeling off in patches this is down to poor hull preparation in the first place perhaps lack of a tie coat or further down the line incompatible antifouling coats. It should not be a problem after 8 years.

If it can be easily scraped off that is an option or slurry blast and Gelshield, hard racing af or self polishing af thereafter.

I had my boat at 16 years old slurry blasted then 5 coats of Gelshield AB 2 coats of hard racing thereafter I have used self polishing. After slurry blasting you can Apply copper coat with out without Gelshield first.

In the UK with the cost of fuel and a mobo in the water 11 months of the year there is a sensible business case for a mid season hoist and pressure wash.

In the Med possibly two hoist and pressure wash on top of annual service hoist pressure wash and re antifouling.

In Uk waters 12 months in the water without a pressure wash fuel consumption goes up by about 25%

Chiara’s slave · 10 May 2024

Portofino said:
Yup .
Think golf balls dimples .
Contradictory one can’t argue for a super smooth surface ( ok it’s air less dense ) which a golf ball certainly isn’t- and then transcribe that principle to denser water forgetting the dimples .

As I said my dog rough multi years hard surface seems have no noticeable detriment .

I think with yachting / sail boats under 10 knots or so in a tight race ( as well as other multi variables ) then sure a super smooth bottom might be beneficial.This is a mobo forum .

I came from yacht racing to mobo ing btw .So I can where the smooth polished psychi comes from .

Not wanting to dive down another rabbit hole folks remember the strakes or indeed steps on some hulls ….Some more pronounced then others Inc Bertram’s btw ....@ P speed ( not D or semi d Boubas boat ) air is introduced under the hull .A rougher source might create micro vortices .This will reduce the surface contact area of the denser draggy water when totted up .By way of example your lung alveola the micro structures that transfer oxygen into your blood ….if extended and spread out have the surface area of a tennis court .

So think of the air bubbles / gasses interacting with that scabby surface on the pic i illustrated ^ .Air drawn i n from the strakes and the speed 26- 30 knots or so .If the air separates the hull from water then drag is reduced .A super smooth surface might not achieve the same sepertion levels as a micro dimpled . = your point / observation .
Also ( sorry folks for bring ing Itama in ) the underwater exhaust air ate the posterior sections at the stern .Engines are mid mounted so a lot of area distal is air ated .Adds up drag reducing .

Oddly, though, my sailboat can touch 20kn in favourable conditions, but you’d be lucky to see over 14 unless the bottom is utterly perfect. It’s glass-smooth, coppercoat, and scrubbed by hand every week in the sailing season and before any race. Any trace of slime, you can feel in the tiller, the turbulence causes it to vibrate. It is equally true in the low speed ranges, this all pales into insignificance compared to what we do to race prep an XOD, small classic keelboat. The air bubble theory holds no water with me.

Portofino · 10 May 2024

Chiara’s slave said:
Oddly, though, my sailboat can touch 20kn in favourable conditions, but you’d be lucky to see over 14 unless the bottom is utterly perfect. It’s glass-smooth, coppercoat, and scrubbed by hand every week in the sailing season and before any race. Any trace of slime, you can feel in the tiller, the turbulence causes it to vibrate. It is equally true in the low speed ranges, this all pales into insignificance compared to what we do to race prep an XOD, small classic keelboat. The air bubble theory holds no water with me.

You haven’t got strakes or steps in the hull . It’s not odd at all your sail boat needs a super smooth bottom to stay race competitive .

You have fallen into the sail boat psychi mentality.So did I until I found I was reaching all the numbers in my mobo boat which hasn’t got a smooth surface.The rpm @ wot exceeding manufacturers rating and simultaneously reaching new boat speed . Load syncing at 100 % which I can access .Fuel burn data all syncing etc .

If it the rough surface was detrimental then the drag would inhibit it reaching rate rpm and it would be overloaded .
Fuel burn would peek out at lower rpms and speed

I used 10 knots as a indicative slow speed . To define out D and semi D mobos from higher speed planing ,Dimpled golf balls we can agree when whacked with a club are high speed balls say compared with a cricket ball being thrown 11 yards ?
The differential speed with mobos boats may well be higher whereby a rough surface benefits .No benefit having a rough surface as I said in a sail boat indeed you can loose races with less than super smooth bottoms we are agreeing and I said that earlier.

With Bouba it’s wether the cost benefit ratio of his semi D , though he mostly proceeds at D speed with a single engine , to be fair not very far .Latest post “ @ anchor “ is a handful of miles from his marina base …..is worth the effort and tiny risk of media blasting and re epoxying etc etc .Assuming its gen clean fresh AF or scrubbed if on hard 2 yearly regime .
He will have to work out his €1.93 diesel per L , any saving from a super smooth new smooth surface against the €5 K upwards …with lift and yard somewhere between €5- €10 K in the SoF for a total strip and start again by professionals
Then there’s the usual seasonal growth so any marginal benefit migh be neutralised by mid July any how by a film .A film he hasn’t got the 30 + knot capability to wash off .Better in waves btw

- for those that can ….nuff said

.Don’t ask me how I know that .

Bouba · 10 May 2024

Portofino said:
You haven’t got strakes or steps in the hull . It’s not odd at all your sail boat needs a super smooth bottom to stay race competitive .

You have fallen into the sail boat psychi mentality.So did I until I found I was reaching all the numbers in my mobo boat which hasn’t got a smooth surface.The rpm @ wot exceeding manufacturers rating and simultaneously reaching new boat speed . Load syncing at 100 % which I can access .Fuel burn data all syncing etc .

If it the rough surface was detrimental then the drag would inhibit it reaching rate rpm and it would be overloaded .
Fuel burn would peek out at lower rpms and speed

I used 10 knots as a indicative slow speed . To define out D and semi D mobos from higher speed planing ,Dimpled golf balls we can agree when whacked with a club are high speed balls say compared with a cricket ball being thrown 11 yards ?
The differential speed with mobos boats may well be higher whereby a rough surface benefits .No benefit having a rough surface as I said in a sail boat indeed you can loose races with less than super smooth bottoms we are agreeing and I said that earlier.

With Bouba it’s wether the cost benefit ratio of his semi D , though he mostly proceeds at D speed with a single engine , to be fair not very far .Latest post “ @ anchor “ is a handful of miles from his marina base …..is worth the effort and tiny risk of media blasting and re epoxying etc etc .Assuming its gen clean fresh AF or scrubbed if on hard 2 yearly regime .
He will have to work out his €1.93 diesel per L , any saving from a super smooth new smooth surface against the €5 K upwards …with lift and yard somewhere between €5- €10 K in the SoF for a total strip and start again by professionals
Then there’s the usual seasonal growth so any marginal benefit migh be neutralised by mid July any how by a film .A film he hasn’t got the 30 + knot capability to wash off .Better in waves btw - for those that can ….nuff said .Don’t ask me how I know that .

I didn’t realise that it would be that expensive

you are right, it would take me twenty years to recoup that in fuel savings
I think I will just get the yard to slap another coat on

jointventureII · 10 May 2024

DAW said:
For me, it is the condition of the propellers, shafts and rudders that make the most difference to performance in the water and fuel economy. While Propspeed helps, I still struggle to get more than about 6 months without a noticeable drop in performance. I don't find cleaning by a diver in the water to be that effective. Therefore, annual lifts at the start of the season will continue for now.

By miles, even more so with surface drives, being exposed to sunlight makes this a nightmare

The hull of the Pershing 108 (work boat) can be quite fouled but as long as the props are clean, we're fine.

However, as an example, last summer we dived to clean the props ourselves. Immediate tests after, cruise speed reached for normal revs.

6 days (!!!) later we'd lost 1-1.5 knots on cruise speed.

Stopped in a bay to clean them again and straight back up to normal cruise speed.

Chris H · 10 May 2024

jointventureII said:
By miles, even more so with surface drives, being exposed to sunlight makes this a nightmare

The hull of the Pershing 108 (work boat) can be quite fouled but as long as the props are clean, we're fine.

However, as an example, last summer we dived to clean the props ourselves. Immediate tests after, cruise speed reached for normal revs.

6 days (!!!) later we'd lost 1-1.5 knots on cruise speed.

Stopped in a bay to clean them again and straight back up to normal cruise speed.

In the summer I used to clean the surface drives every two weeks, with prop speed it’s been much better and I’ve only had to clean a few crustaceans off once.

DAW · 10 May 2024

Chris H said:
In the summer I used to clean the surface drives every two weeks, with prop speed it’s been much better and I’ve only had to clean a few crustaceans off once.

Propspeed has also worked very well for me. In the past I would lose perhaps 3-4 knots of top speed and see the consumption increase by 10-15% from June to September, with a further 1-2 knot / +5% deterioration over the winter months. With Propspeed applied I'm experiencing almost no loss of performance during the summer months and only 5-10% over the full year. It's expensive to apply, but definitely worth it when you factor in the better performance and lower fuel consumption.

Zing · 10 May 2024

Chiara’s slave said:
Oddly, though, my sailboat can touch 20kn in favourable conditions, but you’d be lucky to see over 14 unless the bottom is utterly perfect. It’s glass-smooth, coppercoat, and scrubbed by hand every week in the sailing season and before any race. Any trace of slime, you can feel in the tiller, the turbulence causes it to vibrate. It is equally true in the low speed ranges, this all pales into insignificance compared to what we do to race prep an XOD, small classic keelboat. The air bubble theory holds no water with me.

Curious to know how you do it. Do you scrub with a stiff brush or with green scourers or other?

How much does a little slime slow you?

When is it time to scrape off antifoul ?

Active member

Well-known member

Well-known member

Well-known member

Active member

Active member

Well-known member

Well-known member

Well-known member

Active member

Active member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Active member

Active member

Active member

Well-known member

Other threads that may be of interest

Share this page