Stabilizers on planing yachts?

Are you thinking of trimtabs? This is anyway what some planing yachts have, especially if they have a deep V hull. Traditional stabilizers are more effective on certain semi planing hulls in speeds below 20 knots.

The most obvious reason that you don't see stabilizers on planing yachts is that the loads on the blades and their stocks would be way too high at higher speeds. You would not be able to build the stabilizers strong enough to handle the loads. Also, the blades would cause a lot of drag at higher speeds and therefore they would reduce speed considerably. I am talking probably a few knots here, which is a lot.

Control is another matter. Stabilizers get their power from the speed of the water going over them (actually, the load is a function of speed squared) and the angle of attack of the blades to the flow. The faster the boat goes, the less angle of attack is required to obtain any given amount of lift. So as the boat goes faster and faster, the angle of attack gets tiny, and very small shifts of angle of attack can cause enormous amounts of heeling force. You don't want that at high speed. It would be too difficult to contol the proper angle of attack at high speeds, I believe. The alternative to this is to design very small stabilizers (small planform area) to do the job, but then they would be worthless at lower speeds. And you still have a control and drag problem.

A planing boat achieves a lot of dynamic stability from the hydrodynamics of a well designed bottom. You should not need stabilizers to adjust the roll or trim of such a vessel. That is usually handled sufficiently well by the trim tabs. Stabilizers are intended primarily for displacement and semi-displacement vessels where the speeds and loads are relatively low and easy to design and build to.

dear jade,

although eric has replied to your enquiry quite extensively, there is still a point which i feel needs clarification. that is, what happens when planning boats are not able to go up the plane due high seas.

there is a simple answer, it is a very uncomfortable passage, if not dangerous. the boat becomes very unstable, it is like a a bath tub on the water. however, when you can go up to planning speed she is much more stable than displacement boats without stabilizers. so, you watch out the weather and if it gets bad you use your speed to run away to a secluded place. in fact a boat with planning hull is a coastal boat, in line with the italian way of using them.

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.

I must agree, if you think you are going to get a smooth ride in rough seas at speeds over 25 knots, you better learn how to drive a boat. I would never trust any automatic stabilizing system under such conditions.

Zero speed stabilizers is another thing and could be nice at times.

Yes, there are some systems, like the Ferretti gyro that should prevent rolling at any speed. But I have no personal experience of it. I have of others but I am not impressed of systems that makes the boat move unnatural so you get dizzy or seasick instead. Small boats, say under 100 feet, will always move with the sea and the best is to move along for a while until you don´t feel it any longer...

A short answer is; Different.

The latest 53:s with more power and prop tunnels would probably compare to some of the more heavy eurostyle yachts. But the remaining are a broad variety of seakeeping and ride, from the best to the worst...

At what speed were you running this Hatteras?

I am afraid that you can not compare this to the boats you are mentioning, it would rather be an older Pisa, like the Pegasus then.

Also some older Bagliettos or Admirals. The newer models are behaving different, not always better, especially not in speeds between 15 and 20 knots where they can be pretty wet!

But this is nothing that would change with stabilizers, it is rather the hull shape and the fact they are loaded with too much equipment...

If you go at their cruising speed, say 22-26 knots, they are pretty OK as long as the weather conditions allow them. I was just giving the example that going down to 15 knots as your Hatteras, will not compare right.