Superstructure construction??

Good question. Has anybody heard of an aluminum or steel hull with composite superstructure?

Kelly Cook

Yes, there are boats built with all combinations, sometimes all three and also wood! Normally the heavier material in the hull for strength and stability.

Which brings us to the debate: Which is considered heavier, aluminum or composite?

Kelly

There are different aluminiums and different composites... it all depends of the yacht and the dimensioning.

Kelly I believe Princess Mariana has Steel hull and composite superstructure

Regards Ken

Indeed. In techmati's photograph the superstructure does not appear to have as glossy a finish as the paint on the hull -

http://www.yachtforums.com/forums/showpost.php?p=14563&postcount=4

I suppose that could be a tip-off?
Kelly

Princess Mariana was scheduled for a repaint in May this year and should be with a new full paintjob when these pictures were taken? Anyway, she was originally painted with Awlgrip and it is of course the same paint on her steel, aluminium and composite structures. It is the upper 2 1/2 floors that are built in fibreglass sandwich. A piece of 55m x 14m, weighing 60 tonnes, where a system of integrated steel rails are bolted to similar fittings welded to the steel hull.

So it's common practice to paint over the composite structures? Very interesting. On production boats they most always just depend on the pigment in the gelcoat for the color, no paint (except contrasting trim panels).

Kelly

I think all larger fiberglass yachts are painted, as well as some high end production boats. Hinckley use to have Awlgrip and also clearcoat on top, like all the metallic painted boats you see around today. There is metallic gelcoat, but it is not yet the same finish as when you spray it on top.

This may be a difference in perception between the European and US markets. Cobalt is a "high end" brand, no? Well one of their bragging points is that their colors are in the gelcoat, not painted. Over here painting on color, vs gelcoat, is considered a cheap solution. I'm not saying paint is all that bad an idea. I've seen some very attractive boats with paint. Just the market perception.

Kelly

The structures of production boats typically come out of the mold in one piece, allowing all the finish to be done in the mold. Larger parts and one off parts are usually assembled after being popped, requiring all the seams to be repaired and finished outside the mold. Also one off molds don't provide the mirror glaze that you can get from a production molds. So the whole boat ends up being painted or regelcoated. It's probably most often more economical to paint rather than gelcoat and the finish bill be much nicer and longer lasting.

Thanks Palmer. That would be a heck of a big mold for an entire superstructure wouldn't it?

Kelly

What most people tend to forget as being a primal difference between aluminum and composite is that composite allows more flex then aluminum. Though composite will dampen this flexing faster then aluminum.

From this you can conclude :
A racer/fast cruiser are most likely to use composite in order to obtain a very rigid platform that (just as aluminum) deforms under load, but will dampen this structural movement much faster and such will provide a harsh ride. (like the sport-suspension in a car).

A ocean-cruiser, will most likely use aluminum for exactly the opposite reasons.

Steel is very slow to dampen structural movements, but has other characteristics that make it a very good choice for hulls.

Obivously a top-noch luxury-performer will try to combine best of 2 worlds using an aluminum frame in a composite enclosure for the superstructure/hull.
This way, they can reduce costs and still provide a "stiff" hull with fast structural-movement dampening thanks to the composite pannels. Any serious yacht-builder most likely will have done some investigation into using these different characteristics to kill onboard noise and vibrations.

Volvo Ocean-Racers and the sorts care nothing about luxury-feeling and only require a very stiff hull that resists any movement/flexing to the maximum. Obvisouly a certain "flex" is built into the boat to avoid overstressing the hull and risk damage/breaking.

Likewise, the advantage of Carbon-masts over aluminum masts does not come from the potential weight-savings. The advantage here comes from the quicker response of carbon to wind-gusts and transfer the "captured" power in to forward thrust. An Aluminum mast will oscilate 3 times as long before being at "rest" again. A "big" loss in the super-competetive V60 and America's Cup worlds.