Bogging, Daggerboards, Fairing

Dagger Sanded and Re Bogged

Posted by Paul

Last weekend I got up early (actually very early) to glass another layer onto the glassing I did the night before whilst it was still green. As a consequence I was home by lunch time and spent Sunday afternoon with Jo. She liked it! So the plan now is to start early Sunday mornings and still get 6 to 8 hours in and be home by early afternoon. This morning I started at 6 am and did 6 hours to be home by lunchtime.

The task today was to sand the original bog layer to get the board as close as possible to the correct shape then give it another go with a screed to get the lows filled and the shape exact. This is going to sound like waffle and it is but there is a reasoning behind it. Whilst I was sanding there is little to think about and your mind wanders and today I wandered back to my university philosophy lectures, Plato debated the merits of 3 professions, a doctor, a cook and a beautician. A doctor is only concerned with the health of the patient not if he looks better or worse just that he is better and prescribes accordingly, a cook is only concerned that the food tastes good and gives little or no thought to the health consequences of the food and the beautician cares only that the customer looks good and again gives little thought to whether the health is actually helped by their applications just that they look better as a consequence. When I faired the forebeam I was acting as a beautician in my motive but on the daggers I am more like the doctor in my actions even though the function was the same, sanding and shaping. With the forebeam (and most other fairing) the fairing is primarily cosmetic. With the dagger (and the rudder) the fairing is critical to the correct hydrodynamic performance. If the shape is out then the water flow over and around the board will not be correct which may affect performance.

I started by sanding with the rupes. It is a 450mm x 100mm orbital sander. You can move it along the job in the same way you would use a long board, at 45 degrees to the job pushing back as you go along, then you change and cross the other way (135 degrees). I use it to knock the highs down then once I get closer to fair I switch to the the manual long board. At half a meter the rupes isn’t long enough to ensure a fair job but it also is less likely to dig holes in your job, so although the purists will tell you that you cant use electric tools to fair, you can get away with them if you don’t use them to finish and leave enough bog that the long board will fair out any highs and lows.

When fairing the idea is to sand as much of the bog off as you can so you sand down the highs to meet the lows unless the glass below is exposed, you don’t want to sand through that. If you expose the glass in enough areas and still have low then you fill to the highs and sand again. It can be tempting to fill the lows without sanding down far but this adds weight and you want to avoid that. The temptation starts about 5 minutes after you start with the long board and continues until you finally cut through to glass and know that you cant sand much further. Once I had sanded far enough, I still had a few low spots surrounded by bog of the correct height so I knew the bog screed would fix that. There were also areas the length of the board that were low. When I back filled the spine with glue to the same height as the foam I used a straight edged trowel and of course the dagger is a constant curve so I know it would be a flat area and that the centre would need bog to return the curve.

dagger mold showing shapedagger mold showing shape 2

As part of the sanding process I continually referred to the female mold to see where the sanding was at, where the highs and lows were. After I had sanded as far as I thought was necessary I had intended to pull a screed of bog with the yellow tongue strip as it bends to form the shape the board should be when it occurred to me I already had a correctly shaped screed that would hold its shape no matter how much pressure I used to push it down and pull it along. I could put clear tape (so that the bog does not stick to it) over the mold and use that to pull the shape in the next bog layer.

dagger mold as screeddagger screeded

I pile bog onto the dagger and spread it out where I think the bog is still low, then once you pull the screed over it you immediately see if the area is still low because the screed does not touch the bog below wherever it is still too low and it pushes the excess bog wherever the low is filled to the height of the screed, often little or no bog is left in places which is fine so long as any holes or lows are filled. I use the scraper to continually redistribute the bog in front of the screed from areas that are full to areas still not filled and continually re-screeding until the lows are all filled and you see a consistent mark in the bog from the pulled screed. You can then see that the lows are all filled and that the next sanding should result in a fair surface and should sand out without too much sanding needed. I finished by over filling the edges so that when I next sand the board I can pretty much finish it and round the edges smooth.

If I get a chance I am keen to sand this dagger again tomorrow and if this bog is enough I can then use this board to make the cases off. The thickness of the highbuild and paint wont add much to the thickness (less than 1mm) but I will take that into account and build the cases with 4mm or 5mm clearance. I will close one case up over this dagger but will finish the other dagger and close its case with it in inside just to be absolutely sure, but I am fairly safe to make the halves using just the one dagger as they should both be very close to each other in size.

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