Slightly OT: Why aren't sailing trimarans...built past a certain size?

[camerashy]

Apologies for the silly question...but.


Why aren't sailing trimarans built over a certain size? e.g. past Geronimo's 110ft? Why are the superyachts like Maltese Falcon and Mirabella monohulls?


I'm sure theres an obvious answer like 'its not particually luxurious and cramped hulls etc' but are there any actual structural/engineering reasons none have been constructed over a certain size?

Thanks in advance. Just a query that's been bugging me for a very long time!

[BWD]

...I think in the 60-100 foot range as in hydroptere, geronimo, etc, they are already pushing state of the art. (ie large parts of Hydroptere were built built by parts of airbus consortium -probably few others up to it).
And panamax beam still only 33.53m . For the same money you could get airbus to build you something that went 400 knots faster and was easier to park.
So naturally, someone will do it sooner or later!

[marshmat]

Canal limits are one thing. Once your beam gets up over 20 m you start running into problems when you have to move it around. It just won't fit in the locks.
The structural requirements of a tri that size would be horrendous. Try putting a 200-ton boat on the end of a 10-metre stick and you've got twenty million newton-metres of bending moment trying to tear the thing apart before it even starts to move. It ain't easy to stay lightweight under that kind of stress.

[kach22i]

Originally Posted by marshmat

Canal limits are one thing. Once your beam gets up over 20 m you start running into problems when you have to move it around. It just won't fit in the locks.
The structural requirements of a tri that size would be horrendous. Try putting a 200-ton boat on the end of a 10-metre stick and you've got twenty million newton-metres of bending moment trying to tear the thing apart before it even starts to move. It ain't easy to stay lightweight under that kind of stress.

I just read something akin to this. Ship hulls not being able to come out of the water without engineered supports because they cannot hold their own weight (the water does and evenly too).

[charmc]

Basically, it's a matter of cost vs return. Stress loads increase exponentially with size. The main purpose of most sailing multihulls is speed, which also increases stress loads, with the added requirement of minimal weight. Add in the fact that multihulls operate at high speeds with one hull out of the water sometimes, which creates even higher (and different) stress loads, and the strength/lightness requirement can get pretty high, which means ever more costly materials and construction methods, etc. etc. There isn't the direct correlation between waterline length and speed, either, as there is in pure displacement hulls.

Given enough money, it should be possible to build a 200' multihull, but given the huge cost and marginal increase in speed, the question, at least for now, remains, IMHO, "Why?".

[tspeer]

Both cats and tri's were considered for The Race, and cats generally won out as being the better choice in that size range and for the sailing conditions of that race. It's a matter of balancing stability and wetted area, not to mention cost.

At the opposite end of the scale, you can get more usable living space in a trimaran than a cat up to around 35 ft (+-5 ft). Above 40 ft, a cat is the better choice for a cruiser in terms of living space for the money.

The really big monohulls are monohulls because the ower likes monohulls. Clearly, if speed was the only criterion, they'd have built multihulls. A monohull has a lot more load-carrying ability for the same size than does a multihull and is viewed as more of a proper yacht in their social circles. "Every design is a compromise between performance, comfort or economy - pick any two" (Dick Newick) is just as applicable at the biggest sizes as it is on the smallest.