Antifoul

Dockhead

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My boat, based on the upper reach of the Hamble, has been in the water continuously for going on two years now. I lift and scrub her approximately once in four months, which is the maximum life of the anodes. Her bottom has never looked all that bad, but the speed difference from four months of growth to freshly scrubbed is amazing, so I would be loath to scrub less often than that, even if my anodes lasted longer.

When I bought her, the bottom had just been done with some kind of eroding antifoul. I think the bottom might have been blasted off beforehand, because the bottom was very smooth and nice looking -- much better than the bottom of my old boat ever looked.

Now after five lifts & scrubs the antifoul still looks very good, very smooth, without any flaking or thin spots whatsoever. In fact I can't tell any difference in the appearance of the antifoul from two years ago when I bought the boat. Except the lead keel, where bits of antifoul are coming off, especially the leading edge, same with the bronze skeg.

Here is my question: It seems to me that it's simply about time to antifoul the boat. The previous boat lived in Florida and I would never dream of going two years without fresh antifoul. But these waters are different, with different growth, and much less problem with barnacles. If the antifoul looks so good, maybe I should let it go for a while longer? Maybe it's even harmful to build up unnecessary thickness? Maybe I should just sand and prime the keel where the lead is showing through, and antifoul that? Instead of the whole bottom.

What do you guys think?

I was just about to order 17.5 litres of Jotun Sea Queen, when I thought it might be wise to solicit some advice.
 

Playtime

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Maybe I should just sand and prime the keel where the lead is showing through, and antifoul that? Instead of the whole bottom.

What do you guys think?

I was just about to order 17.5 litres of Jotun Sea Queen, when I thought it might be wise to solicit some advice.

What sort of growth are you getting between scrubs? Is it any worse now than it was 2 years ago? Does the boat have the same usage pattern as it did 2 years ago?

If the antifoul seems to be as effective as it was previously, then I would just do as you suggest i.e. patch the keel and leave the rest.

If the antifoul seems less effective now, then maybe it is time to refresh it.

It might also be worth investigating why anodes are only lasting 4 months. Do you suspect a problem or is this 'normal' on your type of boat/set up?
 

Dockhead

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What sort of growth are you getting between scrubs? Is it any worse now than it was 2 years ago? Does the boat have the same usage pattern as it did 2 years ago?

If the antifoul seems to be as effective as it was previously, then I would just do as you suggest i.e. patch the keel and leave the rest.

If the antifoul seems less effective now, then maybe it is time to refresh it.

It might also be worth investigating why anodes are only lasting 4 months. Do you suspect a problem or is this 'normal' on your type of boat/set up?

Hi -- thanks for that. To start with the last question -- I don't know. I've been in a marina which might be hot, connected to shore power. I installed a Victron isolation transformer which I thought would help, but it did not. It is possible that I have some electrical leakage from the bilge pump -- on my list. It seems to me excessive anode consumption but on the other hand many of my neighbors have the same regime.

As to growth -- likewise, I can't tell. I've only had one summer with the boat. Obviously the growth is much faster in the summer. The last time I scrubbed, in December, four months after a scrub at the end of July, the growth was very light -- just a bit of slime. Nevertheless, taking off that slime made a big difference in performance.
 

VicS

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Hi -- thanks for that. To start with the last question -- I don't know. I've been in a marina which might be hot, connected to shore power. I installed a Victron isolation transformer which I thought would help, but it did not. It is possible that I have some electrical leakage from the bilge pump -- on my list. It seems to me excessive anode consumption but on the other hand many of my neighbors have the same regime.

I think I would check that there is no continuity between the incoming shore-power earth and the boats own internal earth/DC negative/anodes system.

The shore-side earth should come no further than the transformer ( if even that far)

One conductor of the transformer secondary winding output should be bonded to the vessel's earth an DC negative to create a "neutral" and the safety earth for the onboard installation.

If you have scrubbed an eroding antifouling 5 times then I should think it is getting a bit thin and fast approaching the time to re-apply.
 

Dockhead

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Thanks for all that good advice!

The isolation transformer was professionally installed and correctly; I checked. Next thing I will check is the bilge pump, which is a common source of stray currents.

Concerning anti-fouling, I have one more question, a rather banal one, to which I know there is no clear answer, but still --

I can get Blakes Hempel Cruising Performance antifoul for 40 squids per 2.5 from one of the more aggressive online chandleries -- special offer. The same cost per litre as Jotun Sea Queen from Shepherd. I've heard a lot of praise for both Jotun and Shepherds. Does anyone have any thoughts on the choice between these for a boat based up the Hamble (so somewhat brackish)?
 
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