Builders' Forum Archives
turning a trimaran
Posted by Howard on Feb 26, 2005
as a general rule, catamarans and trimarans are relatively difficult to turn through the wind with a tack (the bow moving through the eye of the wind)and the easier way to turn through the wind with a gybe(the stern of the boat passing through the eye of the wind).
i point this out becuase in addition to correctly sizing your rudder, technique is pretty important as well. there are just some manuevers that will not work, no matter the size of the rudder, becuase of the basic physics of driving a hull through the water.
in lumpy/windy seas you may find it all but impossible to tack a trimaran but a gybe would be pretty easy. in order to prevent burying the bow, the maneuver should be timed to execute going up the face of a swell (while the rudder is still submerged) so that you can bear off (head up towards the wind slightly) as you go into the trough of the next wave to avoid burying the bow.
my other sense, is that the sail will have relatively little to do with burying the bow....the trimaran sails are relatively small and set low to the boat. the bigger cause of burying the bow is probably the buoyancy of the rear of the boat on the back face of a wave driving the bow into the front of the next wave. this phenomenon is also very much a function of the length of the boat relative to the wavelength of the swells. when the two coincide...it can get pretty ugly.
however, there are techniques to change this relationship of boat length to wavelength...so that is why you will see good sailors doing "S" turns as they drive through waves which effectively increases the wave length and prevents the bow from burying into the oncoming wave form.
hope this helps
In Response to: Sailrig on the "old" WR18 by Petewp on Feb 24, 2005