Building Logs

Roofing around

Posted by Paul

Many years ago I made a mistake when fitting the roof that I have documented before. But before I go into that again, lets go back a bit further. The boat I am building is a kit, that is, most panels came pre-cut out of flat panels. The parts that did not were the highly curved parts or more accurately the compound curved parts – the hull to deck panels, the inboard bow tops forward of the cabin turret that the trampolines attach to and finally the roof (there is one more strip planked component, the forebeam). Compound curve means the curve is in more than one direction. For example the underside of the bridgedeck curves up in just one direction, fore and aft and this is made using kerfs. The decks, roof and forebeam not only curve left to right (and back in some cases) but front to back and were made using a method called strip planking. You rip full length panels (in my case a combination of duflex and duracore – duracore is balsa core pine veneer panel that then gets glassed once the panel is glued, I only used duflex because I had run out of duracore) down into 30mm-50mm wide strips and bend them around molds, some temporary but the others being the bulkheads. Being narrow they are flexible enough to bend around the curve shape and each one is glued to the next so that they can be glued around a bend/curve the other way to the length, giving the compound shape required. Once the glue is set they can be ground or sanded to a more round shape and then glassed inside and out so they hold the curve in each direction. I did a fairly good job on the first one I did, the forebeam and seemed to get progressively worse as I went. The roof was the last one I did and to be frank, I made a bit of a mess off it. Without going into too much detail, I made them under the bridgedeck under the boat in not ideal circumstances, and then to top it off, I went ahead and fitted it incorrectly as well. I have a theory on why my forebeam turned out so well and the others progressively worse.

First the forebeam is strip planked out of western red cedar strips. This means that once the shape is glued the cedar can be ground and sanded into a very smooth and well curved shape before glassing. The rest of the strip planking in duracore cannot be so easily ground down. Grind too far (2mm) and you remove the pine veneer and are at raw balsa. Also I made some modifications to my aft bulkhead (raised 120mm to allow outboard more height under steps) and this meant the strip planking at the aft of the boat is more severely bent which resulted in some deformity that I will need to fair out, the strip planking around the tramps I did ok on, and finally the roof, I did under the boat, that was the first mistake, cramped and poor light, but the real roof issues are more related to misfitting it. Anyway, what’s done is done, now to fix it. Thats the great thing about these boats, dummies like me can build them (eventually!) and fix the amateur mistakes to a semi pro finish. Some even achieve full pro finish status.

Fortunately for anyone contemplating building a kit boat, strip planking seems to have been eliminated with most designs now employing a roof and side deck design that does not need it. Here is how nearly all designers have solved the roof design, it curves fore to aft but not side to side, and the cabin sides curve fore and aft also, as you can see in the following Schionning pictures of their latest 12 meter design. Unfortunately for me, I was a little ahead of this much easier design aspect. Never mind.

new-roof-style (1) 041200ARROWRenderv340_srcset-large

There seems to be a saying in boatbuilding that there isnt much that a bit of bog cant hide. All of my roof issues are purely cosmetic, but to most eyes, even untrained ones, it was a bit of a mess that needed fixing. So I have set about fixing it as a bit of a test for myself. The roof is by far the most in need of bog (and quite a bit of it) in order to clean it up. There is another crude saying in boatbuilding, that fairing is “polishing the turd”. My roof needs a fair bit of polishing. And because the fairing has loomed large in my fears for some time I figured if I can fix the roof then the rest of the boat should be much easier for me to contemplate if not complete.

Long term readers might recall that it took over a year to discover I had even made a mistake and there was a positive consequence of that mistake, one that in retrospect, given the choice to remake that mistake or not, knowing how difficult the fix was, I would still make. When I lifted the roof (along with about 5 friends) onto the boat and I then adjusted its position before glassing it to the main bulkhead, then fitting the wrap around panels which became windows etc. It was in that fitting that I made a minor mistake, minor in terms of structure, in fact there is no structural issue except perhaps a minimal amount of increased windage but as I have explained, this would be impossible to measure. Externally my roof is the same height as everybody elses, as this is dictated by the bulkhead it fits to, mine is just the same height to the front instead of sloping down 100mm before it meets the front window panel. But cosmetically I had a fairly big issue to resolve. The problem occurred because, instead of following the plans, which instructed a specific distance from the leading edge of the roof to the main bulkhead, I adjusted the roof forward or aft until the front window panel fitted the space perfectly and the top of the roof was level with a spirit level. This I thought would be correct. Turns out not. The roof is designed to slope down sightly from aft forward. And when I later discovered the actual fitting instructions in the plans and measured that leading edge to bulkhead I am about 40mm too far forward with the roof. Doesnt seem like much, and having the extra 100mm head room in the front of the saloon is great, many people have commented how much bigger my living space is than other 40ft boats, even one friend building the same boat (standard rig though) commented that my boat seemed bigger inside than his, so I was pretty happy with my fortunate mistake. I think the internal volume is exaggerated by the slightly raised roof giving the perception of being bigger than it is, perhaps this is why high ceilings are fitted in mansions!

That is, until I also noticed that I had fairly noticeable hollows on the front corners of the roof and had a pronounced “brow”. The reason is that the designer would have had the molds of the roof at such an angle that the transition from wrap around flat front panel to curved roof panel would meet at the same angle, so there would be no perceptible change from one to the other until the curve built into the roof started, but because the roof is not in the exact position as per the design specs the angle is slightly changed from flat meeting to a corner. The sides always had a corner designed in, so I dont have an issue past 90 degrees on each side. So as designed and the way everyone else building this design correctly would have,  is a smooth transition from flat front panel to curved panel. Mine had a pronounced corner, that is, an abrupt change in direction rather than a smooth gradual change. Its not much but enough to cause that visible “brow”. This is what I now have to fill above to return a curve to remove those corners and return volume to the roof where the hollow caused by the change of direction is.

One thing I have learned recently and perhaps would have been better to know from the get go, a uniform flexible batten when bent around a curve will instantly form to the correct curve, instantly revealing any highs or lows that will need fairing out. I dont have a very good eye for this aspect of the work, and the batten method is like putting on glasses. Your vision is instantly improved.

I once was told you have 2 choices with things like that, hide it or feature it. I asked a few friends, some liked the brow, most didnt and neither did I. So I decided to try to hide it.

And I have become a bit stuck on the outboard well for a while so I decided to dip my toe in on the massive and somewhat daunting project that fairing this boat will be but seeing if I can repair and fair the roof being a big test and if I can successfully complete it, that will ease my mind somewhat for the task of fairing the rest of it.

In the first pic below, you can clearly see the “brow”. It runs along the sides at the correct height above the windows and level and is supposed to be there along the sides because the sides are flat then the roof starts on a corner angle on purpose and curves as you can see from the cockpit looking forward in the next 2 pics. I know this is the actual design because that shape was in the bulkhead. But instead of remaining level as it goes around the corner from the side to the front it angles upwards because I have the roof running level and not sloping down as it was designed to be. Had I had it slope down correctly and that line was level as it rounds to the front then back around the other side I would not have a brow at all, and not have hollows to fill above it and the lines around the boat would be level all the way and would look normal. Another thing you can see in that first pic is the “frame” around each window that protrudes above the outer fibreglass skin by 5mm, this will come in very handy when I fill the hollows and so too will the protruding hatch frames, they also draw the eye away and help to hide the inconsistencies. The next image shows the depth of the hollow, under the middle of the batten its about 25mm, and just out of shot below to the left is the brow that the batten is sitting on, so this is a high, leaving the hollow until the batten meets the top of the roof so everything beneath the batten is now a visible hollow that needs to be filled if I am to make this problem disappear with bog. In places the hollow is 25mm deep! I have been a bit concerned about bogging that deep and thought about a solution, I have very flexible thin polycore that I was going to use to make wall linings because it is so flexible. I can use that to fill some of the deeper areas (about half a sq meter each side) to reduce the depth of the bog, then bog over the top and you could never know it was in there. In a couple of the deepest points I ended up putting 2 layers of polycore down.


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