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Monday, August 6, 2012

Glossed

The process and resin we are using for our Katana Marblehead are optimised to obtain the best ratio of resin to reinforcement fibres.
In practice this means minimising the amount of resin that cures around the fibres which are themselves a fixed quantity determined by the weight and number of layers of carbon fabric put into the moulds.


The hull and deck skins are vacuum bagged to draw out entrapped air and any resin that is not closely in contact with the fibres.
The upside is a stiffer laminate because the matrix is effectively more tightly packed with reinforcement.


It also means that the fibres appear extremely close to the surface of the finished material simply because there is no surplus thickness of transparent resin to give the visual effect of 'wetness'.
This is what modern composite parts look like. It is a sort of satin finish with perhaps a utiliterian or militaristic 'stealth' quality to the surface finish.
It is interesting that the actual surface is smooth and glossy, replicating the mould surface which in this case is CNC milled then polished to a high gloss and waxed. However the gloss has no 'depth' because the fibres are densely packed microns below the outer surface.


For those who prefer the 'old fashioned' glossy look showing off the fibres encased in an amber like transparent glossy surface, we offer the no cost option of a tough polyurithane varnish which is applied by specialists at YachtMod.
The aesthetic coating is kept as thin as possible thus minimising the associated weight penalty.


As always, the choice is up to the individual. Some prefer one look and some the other. Some want to save every last gram and others are willing to sacrifice a tiny sliver of weight for the sake of beauty. It must be said that the difference in performance is too small to measure so either option should be competitive.


The varnished option offers the possibility to wet sand the boat periodically which is considered good practice by most skippers. Cutting the surface back with 1200 or 2000 grit paper can get rid of any scratches that may accumulate with use and decontaminates the surface from any dirt or oil.
If done correctly it leaves a low sheen (yet another look) that allows water to form a thin coating over the surface without beading.
There is an argument that this characteristic prevents air bubbles from sticking to the surface and acting as trip-turbulators thus possibly delaying the transition from laminar to turbulent flow until somewhere further aft.


However if conditions are sufficiently rough to cause enough pitching to introduce air onto surfaces below the waterline, then the oncoming flow will be turbulent anyway.
Specific tests on this aspect of boundary layer behaviour are few and in my opinion inconclusive.
As long as the surface is smooth and free of contaminants such as road film or dust, drag will be close enough to the practical minimum.


Volume distribution, foil shape, rig positioning, weight distribution, stability and sail trim have effects greater by orders of magnitude.
In a tight class sailing skill will be the key.
The design that best complements the class rule and can be sailed fast with greatest ease will give the sailor the winning edge.


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