Copper epoxy antifoul, Port hull

So Close I Can Smell It

Posted by Paul

I have finished the port hull. All that is left is to turn it over. Actually I will sand the glass tapes on the inside of the hull so as to be sure that none of the helpers that help me turn it over doesn’t jag themselves on any sharp splinters. I have to do it sooner or later anyway (even though I eventually plan to laminex the internal walls that are not covered by cupboards etc so I don’t really need to fair the internal surfaces) and I have a week to get things sorted so that is going to keep me busy. I may even lightly sand the coppercoat. I cant believe I just said that. Who would have thought that I would want to sand anything after the last few weeks!

I have learnt my lesson and used “masking tape” to mask the copper epoxy line. Masking tape for masking, go figure!. First I marked the waterline in pencil using the 2000mm from the strongback measure on the outboard side and confirmed the line with a stringline then used the spirit level to be sure it was level. On the inboard side I used just the stringline as it is not possible to measure from the strongback.

I marked a line 60mm above (below on the upturned hull) the waterline with a marker pen (again a purposely named tool!). I chose 60mm simply because it is the width of my spirit level and that made it easier as I lined the top edge with the marked waterline and then marked the mask line with the other edge of the level whilst checking the spirit bubble to be sure. I had conflicting information on the correct distance above the waterline that an antifoul should go to. Some say 50mm some say 100mm, so in the end I figured anything in between would work.

I noticed after I had marked the inboard mask line from the stringline that it wasn’t completely straight all the way along. There was a slight upturn of the line about 3 meters from the stern. Don’t trust the stringline, as no matter how tight you make it, friction against the hull makes it possible for it to sit where ever it may be whether it is level or not and you must move it to where it should be after making it level and it is not fixed, you may move it again as you mark your line along the hull as I must have to end up with a kink in the marked line. So I made a quick adjustment of the tape and confirmed it was straight with the level, you can see it got to about 10mm out at the end. Over 12 meters the stringline only needs to be 1mm out at one end for it to be 50mm out at the other.

outboard masked for copper coatinboard masked for copper coat

After I masked the coppercoat line I taped the plastic to it using the clear sticky tape (I am addicted to the stuff, I just cant get off it…actually it is easy to use because it has a dispenser). I re used the plastic from the highbuild mask. (In places I still dripped epoxy on the hull but I will need to sand these areas again anyway so no harm done).

outboard skirtedinboard skirted

All of the prep work took about an hour. Now to the copper powder. The tub that it came in is a little smaller than a 20 litre tub, but when you open it you get a surprise. It is only filled about 50mm. I bought 9kgs, based on advise from Tom and Judy building Scrumble. They bought 10 kgs for a 44ft hull so I bought 10% less because MM is 40ft. I measured out 4.5 kgs (half for each hull) and then split off 1.5kgs in 3 500g lots. I figured on 3 coats per hull so 1.5kgs of copper powder per coat per hull and that is a total of 18kgs of copper epoxy resin on the boat (based on 50:50 copper to resin as per the ratio used by Scrumble).

9kgs of coppercopper powder

I figured on 3 lots of 10 pumps (from the West wall pump) of resin being enough to cover the under waterline area. I needed 5 lots of 10 pumps for the seal coat before the highbuild and that is about twice the area of the underwater area (this turned out to be exactly spot on). 10 pumps of the West wall pump is 490g of resin/hardener mix so 500g of copper powder equated equally enough to 50:50 by weight, which again is what Tom and Judy used. I used the battery drill (I killed the electric drill) with the mixer on it and about a minute of mixing before adding the powder and another minute after adding the powder. The first coat mixed and went on easily. It is a bit mottled but as with all first coats it will be covered and the mottle filled out on the second coat.

I got slightly different advise from ATL regarding the ideal copper epoxy mix. Their advise was to load up the resin as much as I could with copper as this is the active agent that stops marine growth and the more copper in the mix, the more working agent that is exposed which makes sense. They suggested that at around 70% mix ratio it would get too hard to mix. So I used their advise on the second coat and decided that if I put 1kg of powder in with 500g of resin that would equate to 66.6% copper and I could do away with the idea of 3 coats as I would achieve the same effect with 2 coats. (Remember the plan is to coat the hull with PureSeal anyway so this is like a last line of defence should it fail and a defensive base coat if the PureSeal barrier is broken.) I had a back up plan if the mix was too thick, I would simply pump in another 10 pumps to bring it back to 50% but I didn’t need to as it mixed and went on easily enough but the cordless was starting to struggle a bit under the weight.

copper 1st coat outboard sterncopper 1st coat outboard bowcopper 1st coat inboard bow

I had to literally wait for paint to dry before I could apply the second coat. I measured out the 3 1kg lots of powder then I split one of the lots down to 2 500g lots. I figured that I may not use quite as much on the second coat so rather than have leftovers I would make the last batch up in smaller lots, I could still mix it all up if my calculation was inaccurate but in the end I didn’t need the last lot so I can save that for touching up. That’s 500g of spare copper powder so theoretically I should also save the same on the second hull, meaning that I will only use 8kgs of the copper powder. I still have to apply some to the shaped bow when I attach them and I will probably need to do the inside of the dagger housing and the daggers and rudders so I may need that extra powder so I am pleased with the outcome. If there is still any left after all the rest of the jobs I may use up the last of it by putting another coat (using a brush) along what I call the slapping line, the area at the waterline that has the constant slapping of waves (mostly at anchor) as this may wear that area faster.

copper 2nd coat outboard sterncopper 2nd coat outboard bowcopper 2nd coat inboard stern

The thick second coat felt really heavy rolling on which was also due to the first coat still being a little tacky. On the first coat I used a medium roller but on the second coat I used a fine foam roller (which is why I correctly assumed I would use slightly less on the second coat). My arms were quite sore by the time I finished. With any luck this hull treatment along with the PureSeal will mean minimal underwater maintenance for about 10 years. My understanding is that just a gentle scrub is enough to remove the slight slime or growth that may start on the copper epoxy and PureSeal claim that the motion of sailing is enough to remove anything that may get a slight holding and even claim this is almost impossible.

Tomorrow I will remove the skirt, but there is not much else to do, so I can sleep in and watch the Sunday program I like to watch in bed with no feeling of guilt at all.

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