Antifoul and the 1" gap around outleg

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sprocker

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I am just about to re-antifoul ready for launching this weekend. I have International Ultra for the bottom, and Trilux33 for the outdrive. (This is what was used on the boat by the previous owner).

Looking at how the boat was previously antifouled, a 30mm gap has been left around the outdrive, which is correct.

However, the 30mm gap has been coated with Trilux33. So in effect there is no 'gap', but the bottom antifoul (International Ultra) does not touch the outdrive.

Is this OK or should I remove the Trilux33 on the transome and create a 30mm 'gap' that is antifoul free.?
 
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My understanding is that the gap is required to keep copper rich bottom paint away from the aluminium out drive that would cause galvanic corrosion.. Since the Trilux33 is for the drive it wont have any copper and so won't a) harm the drive and b) complete the circuit between the copper rich bottom paint and the drive.. In my opinion having the Trilux33 in the 30mm gap would mean growth would be reduced in that area where raw gelcoat would just mean lots of growth that would be pretty stubborn to clean off later..

Of course I could be completely wrong but that's my theory.. ;)
 
wipe_out said:
My understanding is that the gap is required to keep copper rich bottom paint away from the aluminium out drive that would cause galvanic corrosion.. Since the Trilux33 is for the drive it wont have any copper and so won't a) harm the drive and b) complete the circuit between the copper rich bottom paint and the drive.. In my opinion having the Trilux33 in the 30mm gap would mean growth would be reduced in that area where raw gelcoat would just mean lots of growth that would be pretty stubborn to clean off later..

Of course I could be completely wrong but that's my theory.. ;)
Click to expand...

I think you are right :)
 
My boat always had the gap when I did it myself but the yard have just antifouled it for the first time (they were not supposed to but they took it upon themselves to do it), and they painted in the gap and quite a lot of the transom with tri33, with the hull antifoul only coming up to about a foot either side of each outdrive. Apparently that is "how we always do it", but then they also painted over the mercathodes on the basis that "they never work anyway" so I am not sure how much faith I put in their knowledge or abilities...

Anthony
 
Many thanks for your replies gents. It is as I suspected. Its shaping up to be a lovely day for lying on the stoney under a trailer antifouling......
 
Hi,

I just antifouled my boat and left the gap. In fact this was the first time we have antifouled the outdrives.
Trilux 33 does in fact contain copper 'COPPER AS METALLIC 8.83%' (from label).

I'm no expert on this at all but doesn't this mean that the Gap should be kept.
In addition any bare metal on the outdrives need to be primed - especially after sanding if the factory coat is removed.
If the outdrives are properly primed then presumably there is no risk anyway as the aluminium shouldn't be in contact (again don't rely on this - i'm just guessing :) )

Thanks
Simon
 
My understanding is that Trilux 33 uses Copper Thiocyanate, which is safe to use on metals/ outdrives etc as long as they are primed correctly.

Most bottom antifouls use Copper Oxide which is not safe on metals, hence the need for a gap to be left.

(I think.....)
 
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