Saturday, 20. August 2005
COMPARING B&Q V SOEBO V IDEC
ALL ABOUT LENGTH? NOT NECESSARILY?
Aside from Ellen?s B&Q, Thomas Coville and his ORMA 60ft trimaran Sodebo are also on standby ready to make an attempt on Francis Joyon?s solo west to east transatlantic record. Three trimarans all looking to better the time for the same single-handed passage between New York and the Lizard within one year is unprecedented, especially since all three craft may be trimarans but are otherwise very different.
In terms of overall length. for example. Ellen?s 75ft B&Q lies mid-way between Joyon?s 90ft long IDEC and the 60ft Sodebo.
Under normal theory of single-hulled yacht design the longer a boat is, the faster it goes. However this is less true of multihulls and far from true when boats are sailed single-handed. For example, IDEC may be the biggest of the three but she also has the largest sails and so would be the hardest for her single-handed skipper to handle, evening out her performance against her smaller rivals.
Multihulls generally also perform at their optimum in strong winds with the wind just aft of the beam. But again this is also not completely true of the three transatlantic trimarans.
B&Q co-designer Nigel Irens, who has also been responsible for creating several 60ft trimarans like Sodebo, says that their performance under sail is heavily sea state-dependent. The 60 footers that have got 24-hour records have always got them on a rising wind before there is any sea, he says. Lighter and more powerful for her length and weight, a 60ft trimaran is likely to perform best on a crossing when conditions are moderate, perhaps 18-20 knots and the flatter the sea is so much the better. In lighter conditions and a smaller sea state, Irens says Sodebo would be much the fastest of the three due to her having more sail area (power) for her length and weight and more beam (width) relative to her length.
In contrast B&Q is not so powerful and prefers brisker conditions. B&Q was designed for the Southern Ocean, so Ellen would be looking for more wind than Sodebo, says Irens. Built for the Southern Ocean, B&Q has large freeboard (height) in her bows and her centre of effort (the fore and aft position of her rig), well aft compared to both IDEC and Sodebo, gives Ellen the ability to push B&Q harder in stronger winds with reduced risk of capsizing. For example, she is able to carry her large reaching sails like the gennaker in more wind than either of her rivals.
Generally speaking a larger boat will find waves relatively smaller and therefore can be pushed harder than a smaller boat when the sea gets up, but again this relationship isn?t uniform. The same features of B&Q that allow Ellen to push the boat in stronger winds than her rivals, also works to her advantage in large seas. By way of comparison, Irens says that if a 60ft trimaran is a Formula 1 car, B&Q is more akin to an off-road vehicle.
Her optimisation for the Southern Ocean also makes B&Q more suited for sailing with the wind further aft of the beam than her rivals. Ellen?s boat is optimised for off the wind sailing, where IDEC is not because her weight is further forward, explains Irens. That was consistent when we designed the boat with the use of the boat as a record beater, because going upwind is not something you?d do very often and you won?t go upwind in this record because you?d be way off the pace if you did.
To summarise - in terms of sea state all three boats go best when the sea is flat, but B&Q would be best of the three in waves. Taking sea state out of the equation, the optimum conditions for IDEC were around 25 knots from just aft of the beam, whereas they would be 15-20 knots on the beam for the 60ft trimaran while B&Q performs best in 30 knots 120-130 degrees off the bow. It is no coincidence that both B&Q and and IDEC have scored their best 24 hour runs (526 in the case of B&Q, 543 in the case of IDEC) in these conditions.
The upshot of this is that in New York at present Ellen and Sodebo?s skipper Thomas Coville will be looking for very different conditions for their passages across the Atlantic but may not have the luxury of this choice as looking for a low pressure system to propel them at speed across the Atlantic can prove to be an allusive business (see feature entitled Transatlantic Course and Weather in this section).
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