Building Logs

Invisible extensions

Posted by Paul

Happy May Day to our Northern Hemisphere friends, or as it is more widely celebrated, workers day around the world. Ironically it is one of the things you never want to say into a radio mic on a boat. Nothing happy about that.

With the copper epoxy coating on the rudders and hull extensions the additions to the original shapes and sizes become invisible. There is little to no evidence (other than this blog) that the original shapes have changed at all.

To recap the final steps taken, I left off the last blog with most of the heavy sanding having been done. The bog sanding is far far harder work than the highbuild sanding is. First off the bog is much harder material than the solids in the highbuild and second the grade of paper is much finer on highbuild, starting with 120 grit and finishing with 240 grit (when sanding bog I use 40 grit first to remove most of the highs, then 80 grit, sometimes 120 grit to finish it) and each subsequent finer paper is much easier to push through, it takes off less material each stroke but as you get closer to fair (and closer to the underlying glass) you want to be taking less material off. But having said that, sanding anything upside down is still tiring and after a few hours of it my arms ache. You still have to push that sandpaper over the area and even if the resistance is less your arms above your head still feels every stroke. Regardless, I think it would be good preparation for a Mr Universe pose off. I again could barely lift my arms the next day but man was I ripped.

So sanding the highbuid before applying the copper epoxy was much easier than sanding the bog. Having said that, I also was nowhere near as fussy with the finish as I will have to be on the topsides, for 2 reasons, first none of the sanding will be visible (from above water anyway) and whilst fair is important hydro-dynamically, the kind of imperfections I am talking about are knicks, scratches, bumps etc that either wont be in the waterflow (most of the hull extension is actually above the waterline) or are so insignificant that they wont have any effects. For example, a scratch that is visible through paint will not be visible through copper epoxy coats (the copper epoxy will fill the scratch but self level on the surface) and even if it didnt it is so shallow that it wont matter. Remember, this is in areas that gets stuff growing on it, so a single barnacle will be 20 times more hydrodynamic in its effect than a scratch. And whilst I will want to keep growth off the hulls, its going to happen from time to time.

under the boat cleaned out

One area I was particularly slack on was the cove on the underside of the bottom step overhang. I could have done a much better job of fairing that and because it is above the antifoul line it will be painted. It is below the step which will be about 250mm above the water so you would have to be swimming to ever see it. But because it is above the copper I can give that another go over later. I probably will, but I get less fussy with each week that passes now. One of the good things about highbuild is you can fill holes with filler (bog) over it or apply new coats over it. So I figured I can always go back to these sections later, right now my impatience to move on to the next phase is too great. I also took a punt that I could fill a lot of the remaining imperfections with a thick coating of highbuild. I applied it with rollers (later I will probably spray it on, the advantage being speed, you can spray so much faster than rollers).

One of the great advantages of rollers is that you dont have to thin the highbuild down like you do when spraying, so it is a much thicker coat each time. I can really load it up with solids. Epoxy highbuild is a 2 part mix just like epoxy resin. Jotun is a 4:1 mix. When you fill a small pot with part A you have to give the drum a good stir because the solids fall to the bottom. So much so that you can lift lumps of solids with your stirrer. I ensure I get a good share of the solids when I am doing the places I know still have imperfections. For example, the underside of the bridgedeck was 80% flat panel so did not need much fairing at all so I was able to not worry about thick highbuid, so did not insist on a high solids count, but when fairing in the stiffeners with right angles, tapes and coves I loaded up the solids. So my hope with the large cove and underside of the step was that a thick highbuild coat would fair them out completely. (The other advantage of spraying highbuild on is that you get a much smoother finish, with a roller you get stipple that must be sanded out again, however a disadvantage of spraying is waste, I think you use about 20% more paint when spraying, lost in overspray which floats off in the air and lands on anything and everything around, so you have to cover everything nearby and must wear protective clothing and breathing gear.)

As with most fairing or bogging it is usually a multi step process. It took me 2 applications of highbuild. First session was 2 coats then a sand back the next day, then a second session of about 4 more coats put on over about 3 hours, with about a half hour gap to let each coat tack off. I ran out of mix on the first session and had a bit too much on the second so I ended up putting more on than I had intended, but I figured it would be better used than drying in the pot. So here are some of the after first coat images.

starboard step underside 2nd highbuild starboard step underside 2nd highbuild 1

You can see some of the lines, scratches, etc in the coves above, still visible after the first 2 coats of highbuild on the starboard hull. The light gives an excellent indication of the areas that are now fair and those still needing to be faired. Even more so when the paint is wet as it glistens more. Highbuild usually dries to a matt finish if only applied in a thin coat, however, when applied really thick it dries glossy. I am using the highbuild for 2 purposes, firstly to fair out fine scratches and hollows but also, and especially so below the waterline that will not be readily visible, as a seal coat. Apparently epoxy is not 100% waterproof, maybe 99%, and bog or filler certainly not so a seal coat is always recommended below the waterline.

port step underside 2nd highbuild 1 port step underside 2nd highbuild

Fairing is a matter of degrees. Above water it is almost totally cosmetic. (I say almost because scratches, holes etc make it harder to achieve a paint barrier coat that has no places for that barrier to be broken, so the fairer and smoother the surface the more complete the barrier the paint is able to achieve, that barrier being against water and UV light from being able to effect the structural properties of the material used to build from.) I like to both see and feel for imperfections. So the surface needs to not only look smooth but feel smooth and be fair, that is, a constant line whether curved or flat, from one area to another. After sanding the first coat down again, I gave the surfaces another blow down. Fairing is never fair until after a blow down. What happens is that the fine dust created by sanding fills all of then tiny holes, scratches and voids giving the impression of fair and clear of imperfection. When high pressure air flow is applied many of the imperfections you thought were gone re-appear. Some are huge or become huge when you fix them properly by picking away until solid voidless surface is all that is left. If you leave a void under surface glass it will eventually weaken and the top layer will collapse so you must remove that loose top layer (with the void below) and refill it.

starboard step underside hole to fill 1 starboard step underside hole to fill 2

The above canyon started with just a small movement in the surface glass when the blower ran over it. I had to pick away and open the hole up to ensure it was properly filled. You can see the glass layer below so it gives an idea of how thick the bog is in some places, that is about 1mm. You can also see glass on the surface only 20mm or so away and another surface of glass about 100mm away. So what probably happened was an air bubble under the topmost layer of glass, that when the top layer became thinned by sanding ended up being loose when the air ran over it resulting in a hole with a fair bogged surface all around it. The holes and scratches still visible after the first highbuld sand should really be spot filled but I am hoping that another thick layer of highbuild might fill them suitably that when the epoxy layers go on they will be almost invisible and the copper epoxy will take care of making them completely invisible.

The thick coat of highbuild did indeed fill a lot of the imperfections I decided against spot filling with epoxy filler. There are just a few left now and I will fill the ones above the copper epoxy line. The highbuild finish below is not wet, its after it has dried, so it dries glossy when applied thick.

port step underside 2nd highbuild 3 hulls and rudders highbuild second coat

In some places the finish is top coat finish, which if course it should be I guess, the sanded highbuild is the last finish before topcoat and topcoat is thin so takes the exact finish of that below it. On the top of the step, the finish will not be topcoat but non slip, so there is no need to be as fair as it would be with gloss top coat. Non slip is much thicker than topcoat and is filled with lumps of whatever the media used (usually sand or glass beads) to make it grip, and that hides a multitude of sins.

port hull 2nd highbuild starboard bottom step top

port hull and rudder highbuild 2nd coat 2 starboard hull and rudder highbuild 2nd coat

I did make one mistake when highbuilding the rudders. I made the mistake of using the same paint tray as used the day before, without peeling the dry paint off. I didnt realise the next days paint would “melt” the previous days, thinking instead that it would just dry on when used up. But instead, that semi melted paint came off the tray in flecks, some quite large, when I rolled the roller in the final couple of times to get the last bits of paint from the tray onto the rudders. This deposited the flecks all over the rudder surface, then to compound an already silly mistake, I tried to get the flecks off again instead of just letting them dry and sanding them out. The resulting “repair” made it much worse. These will sand and refill (and sand again) out but it just adds work to an otherwise satisfying days work, and it happened in what would have been the last 5 minutes trying to make use of the last of the highbuild in the pot rather than just throwing it out. The rudders looked fantastic with thick glossy paint on before I applied that final adulterated coat. Nevermind. As you can see from the pics on the second row below and then of the copper coated pics, it all worked out in the end.

port rudder 2nd highbuild rudder highbuild rudder highbuild mess up

rudder highbuild final sanded highbuild rudder run repaired

With the prep work done (lots of sanding) and ready for the copper coating I masked up ready for the coating. I took the chance to correct an earlier mistake. When I first copper coated the hulls I marked the copper line to be about 60mm above the actual dwl (design water line), for no other reason than 60mm is the height of my spirit level so I could mark the copper line off the string line (which was set to dwl) off the top of the level using the spirit guides as a double check I was maintaining level as I moved along the hull marking it. Most builders make their anti foul line go past water line between 50mm and 100mm so 60mm worked for me. But when I got to the stern I changed from level to waterline to inclining a line for the last meter so that it mirrored the rocker of the stern. Many builders do this, I dont know why, perhaps its because the rocker causes the hull to be immersed long enough for life to grow above dwl. But it doesnt look right. Many people, in particular professional boat builders asked me why I did this as it was not “normal” practice. For a while I hung on to the idea, because what is “normal”? But with the hulls extended, the copper line (some call it the bootstrap line) if extended “normally” at 60mm above dwl comes out at exactly the point where the hull ends, so it made sense to revert to a more “normal” anti foul line. The small area of copper above the new “bootstrap” line will be faired out and painted over when the boat is painted. Looks better I think.

The thick highbuild coat took a couple of days to dry enough to sand. When sanding it, I was mostly sanding down runs, and to take the shine off ready for the copper coat. It took me about 2 hours to get the final sand done. On the rudder with the massive run I created trying to remove a tiny fleck of dry highbuild, I had previously filled the area round the run with a mixture of highbuild with some Q-cell mixed in to thicken it into a paste which I applied a couple of hours later once the initial coat had tacked off enough not to scrape when I applied the fill mix. When sanded a couple of days later (the same day as I applied the epoxy) the run and hollow disappeared. A blow off and wipe down (just with water on a cloth) and I was ready to apply the copper epoxy coats.

new waterline copper epoxy line hull extension masked for copper epoxy

port rudder copper epoxy 2nd coat port rudder copper epoxy 1st coat

starboard rudder copper epoxy first coat port stern copper finished

port stern copper finished 1 port stern copper finished 3

runs in copper coat port stern copper finished 2

The first coat of copper epoxy, as it was with the hulls was thin, speckled and was a brighter red, then as the second coat went on it filled out the motley initial finish to a thicker and chocolaty finish. The coat will eventually brown further as it oxidises and will match the color of the existing copper coat. This oxidising occurs in the water too and results in the copper losing its repellent nature so every now and that (and initially just prior to launch) you need to sand the top layer off to reveal new copper particles that renew the repellent nature of the finish. I got some runs in the finish, this will come out when I sand it in preparation for launch, maybe take the tops off with a chisel first to reduce the work.

On the hulls I originally only put 2 coats of 66.6 percent copper (copper at 2 parts by weight, mixed epoxy 1 part). I made up the same percentage mix for the rudders, 200 grams copper powder 100 grams mixed epoxy (so about 85 grams epoxy 17 grams hardener) and this was enough for a coat to one hull and rudder. So in the end, 2 coats for each hull and rudder came to 800 grams, leaving me enough to coat the bottom 1/3 of the daggers when they are ready to go on (I still have a little more fairing to do on them and will do them when I paint the boat). I used 8 kgs of copper powder on the hulls proper and 800g on the rudders and hull extensions. That small area does not seem like 10% of the rest of the boat but I guess the surface area of the rudders both sides is quite large and stretched out it would be. Its a bit deceiving, but all underwater surfaces have the same treatment. Each coat took about an hour to apply to all the various surfaces (2 rudders, 2 hulls) and then about 2 hours of tack off time, then another coat which only took about 40 minutes to apply second coat.

The final step before lowering the boat back down is fitting the stainless steel tiller collar. With the rudders lifted up hard against the thrust plates I slid the tillers on and marked out the 4 positions of the drill hole (2 holes, 4 openings when those 2 holes are all the way through the shaft). The next and more difficult task is to figure out how to drill holes through the shaft and coming out exactly at the mark on the other side. Not as easy as it sounds. Remember, out just a smidge on any of the 360 degree plane and it will miss the mark on the other side and might not clear the stainless collar on the other side. To be absolutely sure I will have to drill the bolt holes through the collar and just hope it comes out the other side at the bolt hole.

Being attached to a massive rudder blade makes a drill press a difficult proposition. So drilled by a hand drill is going to have to be method. In the end, slightly oversize drilling and half way through from each side was deemed the best likelihood of success. I wanted the holes to be a snug fit, but could not risk the bolt not going all the way through both sides of the tiller. So with the help of the engineering department (Terry and Ray) I will have one of them tell me the drill is square left to right and the other front to back and I will drill half way through from one side, turn the rudder over and drilled the other half through until the holes met up.

Hopefully in the next blog the boat will be lowered back down and I can get on with finishing the outboard well so that the rear steps can finally go in. Here it is already May and I still dont have them in. I had hoped they would be in by the end of March. Its amazing where the time goes.

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