Trimaran motions in wavesFor a better understanding of the naval terms used in the following, such as “rolling”, “pitching” or “yawing”, please refer to the chapter in the annex entitled “Types of vessel motion in waves” *. In the following, we compare the trimaran with a single-hull ship of a conventional design having the same water displacement.
Let’s first look at linear motion and in particular at acceleration, both in the positive (acceleration) and negative (deceleration) sense. The trimaran is slowed down less when it encounters a wave, since the floats react more quickly due to their smaller mass. The wave lifts the bow of the float and it slides over the wave. In contrast, the bow of a conventional vessel drives more deeply into a wave. Positive acceleration is not relevant for safety and thus we will not go into this issue any further here. Upward and downward linear motion reaches a maximum when waves are of such a size that the _____________________________
*At present, only the German version of the annex is available
|vessel fits completely on the crest and in
the trough of a wave. With its broader but shorter
shape, our trimaran is susceptible to more extreme
upward and downward motion when travelling transverse to
wave fronts. The reverse is true when pursuing a course
parallel to the wave front. In this case wave crests could
be broad enough for a conventional vessel to be lifted to
the top of them, while the floats of the trimaran, being
broader, would still be on either side of the wave crest
while the main hull is lifted less.
Pitching, a type of circular motion, generally begins when a vessel holds a course transverse to the wave front and the wave is at least as long as the ship. With its broader basic shape, the Eco-Trimaran is shorter than a conventional ship and would thus be more susceptible to pitching. Slamming, a special, particularly unpleasant form of pitching, is as likely to occur with individual floats of the trimaran to the same degree as with conventional vessels. Yet this motion is hardly transferred at all to the horizontal axes of the trimaran and thus not to
|its main hull.
Rolling, which mostly occurs when holding a course at a sharp angle to the wave front, is not as pronounced with a trimaran, since it is better supported at the sides by the two rear floats.
Heeling a type of motion related to rolling, occurs in crosswinds and can in extreme cases lead to capsizing. There is less risk of this with the trimaran, due to its shallower and broader design, than with a conventional vessel.
The amount of yawing is difficult to predict for a trimaran, but this movement is not relevant for safety. Yawing makes it harder to hold course, but, in an age of satellite navigation, this is hardly an issue any more.
In summary we may conclude that, to the extent that vessel safety depends on its motion in rough seas, the Eco-Trimaran can on the whole be judged safer than a conventional vessel with the same water displacement.
With respect to the particular kinds of motion relevant to safety, such as slamming, rolling and heeling, the Eco-Trimaran must clearly be judged superior.
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