a question on anti fouling (maybe not what you're thinking)

jon and michie

jon and michie

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I was pondering this the other day and I am intrigued to find out.
Say the boat has had 2 coats anti foul applied each season or 2 for a few years and is still in good condition i.e not flaking away and hasn't been taken back to the gel coat - would this make the boat heavier ?
2 tins of 2.5l antifoul does have a bit of weight to it and also if the a A/F is in good condition how would you know when it needs to be taken back to gelcoat for a fresh coating ???
Jon
 
I don't think people generally are concerned about the weight of the paint left on the boat. Considering that most a/f paint is self ablating. So comes off with use and with scrubbing. What happens more often is that the paint builds up to a thickness and then flakes off or leaves a step where it ends at the water line. In other words it gets rough so more paint is needed to fill the bumps and of course more friction in water. For me I know A/f is getting old when weed grows more quickly. This then requires in water scrubbing more frequently so paint is largely removed by scrubbing. But then water is warm so weed grows quickly (like over a week it is noticeable) but warm enough top make swim scrubbing pleasant. So in answer to your question. Trust me you will know when you need to scrape it off. ol'will
 
In theory it will, but fill your tanks with water or food and the same thing happens.

Prior to getting copper coated the hull looked like the surface of the moon; that had more of an impact on speed than the mass of the antifoul.

After 24 months I was lifted and the slime that was present, COVID prevented use, was jet washed off in 20 minutes. I have no plans to ever going back to traditional antifoul again.
 
If you get pressure washed and it looks sound then one coat should enough. You’ll know when it needs taking back - it will become uneven and start flaking. Weight is irrelevant compared to fuel, water, people and personal gear.
 
I've stripped a few boats to gel coat. The shavings, swept up, don't weigh a lot.
But when it gets so thick it takes on a rippled surface it must be slowing you down.
 
Much of the weight of the tin is solvent when will be released, and eroding fouling don’t leave a lot be the end of the season.
 
Blueboatman said:
You do put it on with diagonal strokes from the bow down, don’t you ?
To create lift and go faster and negate the added mass of the paint itself

(Early April is a good time)
Click to expand...
Also------Because antifouling paint is applied to areas below the waterline it will weigh a lot less than paint applied on the topsides or deck so not worth the worry. Its a little heavier in fresh water of course so best put it on thinly there.
 
The Reynolds number of things in water is rather different to the Reynolds number of things in air; dimples might work in water but their size and placement will be nothing like golf balls.
 
It's a big deal on aircraft, especially large aircraft but even light aircraft and gliders need to be reweighed after painting. On a light displacement racing boat they might worry about it and I guarantee it's a factor on America's Cup boats but, for any vaguely normal craft, it's exactly as William_H and others have said.

Painting an airplane: Why every layer counts
 
penfold said:
The Reynolds number of things in water is rather different to the Reynolds number of things in air; dimples might work in water but their size and placement will be nothing like golf balls.
Click to expand...

Eggsactly. The biggest factor with the golf ball dimples is the boundary layer and the boundary layer is totally different for a boat in water - much, much smaller owning to the higher viscosity and especially the density of the water. With a golf ball the dimples create a very thick boundary layer that gets dragged out into a teardrop shape behind the ball making it a lot more efficient aerodynamically. If you can get some spin on the ball then the Magnus effect will kick in (Magus Effect basically a rotating sphere or cylinder will generate lift) and things start getting really whizzy. The dimples will magnify the Magnus Effect whilst still reducing drag.

Dolphins and sharks apparently have trick skin that significantly reduces their drag and every so often someone claims to have replicated this with a magic coating or something - not sure how exactly they work but it's a similar concept of boundary layer manipulation I believe.
 
One of the supposed benefits of the silicone coatings is that being slippery they are more effective.

I have never seen any data to support the idea. It sounds good but.....

When we raced our X-99 initially we used Micron Extra but with enhanced boatyard facilities we could dry sail. We stripped al the AF off and sanded down the gelcoat, removed any blemishes. We were CHS Champions 2 years in a row - whether the attention to hull detail (or a general philosophy of an attention to detail) contributed - don't know

Jonathan
 
I offer “Dimple”, the golf ball shaped boat that rides over the waves on hydrofoils

Prob wouldn’t use antifouling at all
Think of the savings!
Dimples, simples
 
Neeves said:
One of the supposed benefits of the silicone coatings is that being slippery they are more effective.

I have never seen any data to support the idea. It sounds good but.....

When we raced our X-99 initially we used Micron Extra but with enhanced boatyard facilities we could dry sail. We stripped al the AF off and sanded down the gelcoat, removed any blemishes. We were CHS Champions 2 years in a row - whether the attention to hull detail (or a general philosophy of an attention to detail) contributed - don't know

Jonathan
Click to expand...
The first thing that happens when my boat fouls is that it goes slimy. By all rights, this should make the boat go faster but it certainly doesn’t, something that I think the sea gods should have sorted out properly in the first place.
 
I imagine dry antifoul is less dense than seawater, so your boat will be heavier but actually float higher!

Dimples are irrelevant for a displacement hull because there is no flow separation.
 
I'm just guessing, something of which I would criticise others :). Don't guess!

AF less dense than seawater? - have you ever picked up a drum of AF? Even if apply it with 50% porosity it will still be more dense than seawater

If it is a hard antifouling the coating will slowly accumulate and because it is part based on copper compounds the weight will increase with additional coatings. One reason to use an ablative coating. Suspect it will become flaky before the actual weight becomes an issue but the flaking will allow the hull to become rough, not fair, and the rough surface might reduce boat speed more than the increase in weight. When it starts to flake you will need to introduce some remedial work as increased coats of AF will simply accelerate the flaking - so maybe its self healing, when the thickness becomes a problem it flakes and you need to put in some elbow power.

I find it difficult to believe you will notice any difference as during the time your AF coating thickens and becomes rough and heavy your sails will become more baggy, one (I) will become old and less attentive - its a slippery slope. :(

The same will be true of ablative paints as even after power washing there is always AF left on the hull - it is never washed backed to gelcoat, or primer. But the process will be slower (allowing the owner to age more slowly :) ) - not sure about the sails ageing.

Take care, stay safe

Jonathan
 
grumpy_o_g said:
It's a big deal on aircraft, especially large aircraft but even light aircraft and gliders need to be reweighed after painting. On a light displacement racing boat they might worry about it and I guarantee it's a factor on America's Cup boats but, for any vaguely normal craft, it's exactly as William_H and others have said.

Painting an airplane: Why every layer counts
Click to expand...
Boats on which this is a consideration are generally dry-sailed anyhow, so no antifouling is used.
 
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