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Lengthwise distribution of vertical accelerations
Designing yachts for a comfortable sailing experience
It is important to understand that discomfort due to ship motions originates from both horizontal and vertical accelerations. On- board a ship, vertical accelerations are in- troduced by the heave and pitch motion, while the horizontal accelerations come from surge and roll.
Since roll is lightly damped, devices that in- crease this damping – such as bilge keels, U-shape anti roll tanks and (zero speed) fins and maglift - can decrease horizontal accel- erations significantly. However, reducing the more influential vertical accelerations is difficult. The heave motion is only de- creased by reducing the water plane area, whereas pitch is best decreased by length- ening the ship.
There is no doubt that some hull shapes help increase comfort when compared to others. The location where people are situ- ated on board the ship also matters. At around a third from the aft at the level of the waterline at mid ship, the comfort levels
are at their best, while up high at the bow, the comfort is lowest.
To improve the comfort of a yacht it is im- portant to consider the issue at an early stage of the design process. If this is taken into account early enough, it might still be possible to fit a U-tank or modify the hull in such a way that the pitch and roll motions are reduced. The layout of the interior may not be permanently fixed as yet so it might be worth considering moving the owner’s cabin to a more comfortable location.
MARIN’s model basins can help owners in assessing and improving the comfort of their yachts. The earlier MARIN is involved in the design process, the more can be done to make the yacht as comfortable as possible. Contact: Michiel Gunsing,
m.gunsing@
marin.nl
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