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Old 01-27-2018, 08:55 PM   #41
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Originally Posted by Delfin View Post
I know that is what they say Jim, but it doesn't make much sense to me. For example, paravanes operate by directly creating drag - it is the whole principle of their operation. If paravanes create .5 knots cruise reduction with chains or cables attached in a KK42, plus a forward slopping dolphin being dragged through the water, then how does an active hydrodynamic fin create the same or more drag? Further, the most slipperly presentation of a hull in not when it is swaying from side to side, as it is more prone to do when rolling, nor when it is presenting greater wetted surface when heeled, but rather when it is upright.



With active fins, at least on Delfin with her hull shape, turning on the fins has zero impact on speed, or at least none that I can detect with GPS, so whatever drag there is comes from inefficiencies in the fin hydrodynamics, which don't intuitively seem like would be much.

My point was comparing the same hull and propulsion system, with and without active stabilizers, whether they are operating or not. I would concede that properly maintained active stabilizers are at least as good and probably better than paravanes, but the latter can be removed from the water and no longer contribute drag.

The problem with Delfin, unless you can do trials with the same hull and propulsion, with and without stabilization itís hard to determine the implications to performance (speed).
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Old 01-27-2018, 09:02 PM   #42
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I think up to 1/2kn loss by adding fins is about right. I can't give data because I changed engines and made other changes to my displacement # at the same time I added fins.

The fins probably have greater wetted surface area than paravanes, but a more efficient foil shape that will offset that increased area in terms of drag comparisons. And mine, like most, are not retractable so I cannot know my speed now without fins.

The point is, it's quite small. But the benefit is huge.
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Old 01-27-2018, 09:40 PM   #43
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The evidence for KK42’s suggests actively stabilized vessels loose about 0.5-1.0 kts at cruise rpm, as compared with unstabilized vessel
Exactly what evidence?

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turning on the fins has zero impact on speed, or at least none that I can detect with GPS
The true test would be your boat with no fins at all vs one with fins.
I agree with your observation about paravanes. Of course the nice thing about them is you can take them out of the water when conditions are calm.
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Old 01-27-2018, 09:49 PM   #44
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Exactly what evidence?



The true test would be your boat with no fins at all vs one with fins.
I agree with your observation about paravanes. Of course the nice thing about them is you can take them out of the water when conditions are calm.
The problem with this analysis is that there are so many variables. Clearly, in smooth water Delfin would likely add some speed without the fins, but I doubt as much as a half knot although I can't quantify that. However, as soon as you introduce any kind of roll, the loss of hull efficiency without stabilization is a factor that has to be weighed against any increase in drag. One thing I can tell you is that if we are in rolling conditions, my SOG goes down if the fins are off, not up. Turn the fins on and the vessel stabilizers, moves through the water more upright and shows a very slight increase in speed of maybe .1 to .3 knots, but I won't pretend to be able to measure it with precision.

Just one man's opinion....
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Old 01-27-2018, 11:13 PM   #45
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The before and after on our Grand Banks was about 1/2 kt. Not enough to matter, and a very small price to pay for the benefit.
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Old 01-27-2018, 11:21 PM   #46
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The before and after on our Grand Banks was about 1/2 kt. Not enough to matter, and a very small price to pay for the benefit.
Again, I think the total cost is a function of hull form and wave action. I can imagine that a shallower hull might have different characteristics than one drawing 7 1/2'.
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Old 01-28-2018, 12:58 AM   #47
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My stabilizing sails typically add a half knot with wind on the beam.
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Old 01-28-2018, 01:20 AM   #48
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[QUOTE=caltexflanc;630981]Exactly what evidence?

The true test would be your boat with no fins at all vs one with fins.
I agree with your observation about paravanes./QUOTE]


Exactly that. There are enough examples of KK42ís with and without active stabilizers with Lehman 135ís. Those with the active stabilizers loose about half a knot or more. We talk to each other, you know ;-). One vessel I know travels at less than 7 kts with Wesmar stabilizers. We travel at 7.5 at cruising RPMs.

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Old 01-28-2018, 09:03 AM   #49
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Again, I think the total cost is a function of hull form and wave action. I can imagine that a shallower hull might have different characteristics than one drawing 7 1/2'.
That's entirely possible, but way beyond my knowledge to assess.
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Old 01-28-2018, 10:52 AM   #50
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I don't think this is correct, at least not the fin stabilizer part. We have about 25,000 miles on two different boats with ABT stabilizers and have never experienced anything by positive results in all seas, following included.
+1 to Twistedtree's comment. We have ABT Trac fin stabilizers and have found them to be very effective in all conditions. Using them is like hitting the button on stabilized binoculars. Night and day difference.

Seakeeper gyros and active stabilized fins reduce roll. Not effective controlling pitch. What if a Seakeeper gyro is "mounted sideways" in a hull. Would it help with pitch? Maybe the pitch forces are too strong to be controlled compared to roll?
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Old 01-28-2018, 11:41 AM   #51
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+1 to Twistedtree's comment. We have ABT Trac fin stabilizers and have found them to be very effective in all conditions. Using them is like hitting the button on stabilized binoculars. Night and day difference.

Seakeeper gyros and active stabilized fins reduce roll. Not effective controlling pitch. What if a Seakeeper gyro is "mounted sideways" in a hull. Would it help with pitch? Maybe the pitch forces are too strong to be controlled compared to roll?
When I was researching Seakpeer a few months ago, I didn't read about anyone who had these mounted sideways to dampen pitch. I'll take a guess and say you are right regarding the potential pitch forces, but I don't know. It may also be that two systems (SKs mounted to control both) would have trouble working together in tandem to control the various motions. The Seakeeper brains may not be that evolved yet.
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Old 01-28-2018, 01:26 PM   #52
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+1 to Twistedtree's comment. We have ABT Trac fin stabilizers and have found them to be very effective in all conditions. Using them is like hitting the button on stabilized binoculars. Night and day difference.

Seakeeper gyros and active stabilized fins reduce roll. Not effective controlling pitch. What if a Seakeeper gyro is "mounted sideways" in a hull. Would it help with pitch? Maybe the pitch forces are too strong to be controlled compared to roll?
The Seakeeper gyro can operate in either orientation as the internal rate gyros only sense up/down movement and compensate accordingly. Theoretically they could be mounted sideways to dampen pitch forces. However, roll forces act along the longitudinal axis of the boat and the dampening effect is lateral (the shorter distance). Whereas pitching forces act on the lateral axis and dampen longitudinally, a longer distance. Longer distances mean a longer arm of momentum for the gyro and this would require a greater torque to dampen the pitching force. Greater torque equals larger gyro with a higher weight and cost. As an example, the Seakeeper 9 produces 9000 N-M-S of torque with a weight of 1200 pounds and eat. cost of $72,000, plus install. A Seakeeper 6 produces 6000 N-M-S of torque, weighs 800 lbs, and cost of $40,000, plus install.

Theoretically it is possible. But actually, it is impractical to do it. As an aside, there are several boats, to include the US Navy, that have more than one gyro installed, but these are all oriented to dampen more roll than a single gyro can handle.
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Old 01-28-2018, 03:01 PM   #53
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+1 to Twistedtree's comment. We have ABT Trac fin stabilizers and have found them to be very effective in all conditions. Using them is like hitting the button on stabilized binoculars. Night and day difference.

Seakeeper gyros and active stabilized fins reduce roll. Not effective controlling pitch. What if a Seakeeper gyro is "mounted sideways" in a hull. Would it help with pitch? Maybe the pitch forces are too strong to be controlled compared to roll?
If the bow of your boat was rising to climb the face of a large wave, would you want the gyro to hold it down and bury it into the face of the wave? The same in a following sea: I would want the stern to be able to lift to the overtaking waves, not be held down and pooped.
Conceptually, this is a bad idea.......
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Old 01-28-2018, 04:18 PM   #54
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Good points regarding roll vs. pitch control for SeaKeepers.

There are some good YT videos on the web showing multiple SK's controlling roll, especially on the big Sporty's.
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Old 01-28-2018, 07:08 PM   #55
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Flatten out pitch? You want your props out of the water? Think about it!

I see posts like these and wonder if some people have any concept as to how a boat moves in the water.
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Old 01-28-2018, 08:54 PM   #56
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Flatten out pitch? You want your props out of the water?
Agree, left my thinking cap off when I posted that response. Should have pondered more and held back on the keyboard. Can I go back in and delete?
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Old 01-28-2018, 09:03 PM   #57
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Agree, left my thinking cap off when I posted that response. Should have pondered more and held back on the keyboard. Can I go back in and delete?
Sure. I've learned a lot of things by starting off dumb... make that almost everything.. the key is to stop being dumb once you've learned, and can't say I've mastered that either!
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Old 01-28-2018, 09:32 PM   #58
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Bulbous bow fitted to your boat will dampen pitch, and have the added benefit of increasing LWL. Can be done cheaper than experimenting with a side mounted Seakeeper gyro.
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Old 02-11-2018, 11:07 AM   #59
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My boat came with paravane stabilizers. Stabilizers were not even on my radar as something I wanted in a boat, but after trying them, I would never consider another boat without some form of stabilization. We use them almost all the time. Even on calm summer days, as they make such a difference with wakes from other boats. About .5 knots seems about right for how much they slow us down, but it is more than worth it, they make boating so much more fun. We used them extensively at speeds as low as 1.5-2.5 knots last summer while trolling for King salmon off the Pacific coast of Vancouver Island last summer, and they were surprisingly effective even at those slow speeds. Some day I am going to get around to building some flopper stoppers to hang off the poles while at anchor. The fish do not have enough surface area to really do much while at anchor.
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