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| Originally Posted by Jage Thanks Eric! That explains a lot. Would active/dynamic trim-tab stabilization system be the best way(effective) to stabilize these type of yachts? Suggesting that when conditions present themselves for high speed cruising the active trim tab system would not need to be activated, there by eliminating the drag issues. And of course during rougher conditions , the activation and increase in drag that may be caused by the active trim tab system would be perfectly acceptable if you can actually stabilize the roll in those rougher conditions?
Well I really like that style of yacht and certainly the speed aspects of those yachts but I remember the type of rolling we experienced in the Hatt 53 (realzing it is a different style hull and yacht) when the stabilizers were inoperable due to a stolen part. Generally speaking what is the roll like at anchorage in an "itallian/eurostyled yacht?" They tend to have a lower-profile (in regards to wind), usually a tad beamier(but maybe because of the protruding exhaust ducts), and deeper drafts than the old hatteras I have had experience in . Just trying to guage the differences.
Thanks again! This discussion is much appreciated.
Jage |
Active trim tab: You don't need one, generally. The helmsman sets the trim tab angle for the conditions at hand. For any given sea state and speed, you use the trim tab setting that will give you the best average speed and motions. They are NOT to be used actively because of the possibility of sending the boat out of control. Trim tabs are operated by joy stick or hand lever, and adjustments take mere seconds. If the motions or trim and roll of the vessel are too great and uncomfortable, then you have to slow down. It is the helmsman's and Captain's responsibility to operate the boat in a prudent manner for the conditions at hand. You cannot take the human out of the equation and expect all boat motions to be all automatic.
Rolling at anchor is a function of the swell, not the wind. The southern coast of California is particularly notorious for its uncomfortable Pacific swell. Some stabilizers have active control at anchor, but again, these are mostly for displacement and semi-displacement yachts. I believe there are also other manufacturers that make retractable stabilizers, but these are very expensive and their pockets into which they retract take up a pretty good portion of the interior. Therefore, they are best used on larger yachts. I don't know if you can get retractables with at-anchor stabilization.
Being a matter of the swell and not the wind that affects rolling at anchor, the shape of the hull, the width of the beam, the depth of the hull, and the height of the center of gravity all come into play. The narrower and deeper the hull, the softer the rolling motions, both at speed and at anchor. Shallower and wider hulls, such as you find in the go-fast Italian style boats, all behave more poorly with regard to rolling motions. The amount of roll is not necessarily so much, but the accelerations of roll are worse. It is the acceleration of starting and stopping on each roll cycle that is uncomfortable and leads to sea sickness. Amplitude (the angle of roLL) is not important. In general, the greater the roll angle, the slower the rolling speed and acceleration and the more comfortable the motion. The lesser the roll angle, the higher the rolling speed and acceleration, and the less comfortable the motion.
I have been in the Mediterranean but not the Adriatic. I did not think that the swell in the Med was very significant, so I don't think this should be a real major concern for that region. I defer to others who may have more experience.
Eric