Gyro stabilizers

if your pressure stays at 1200 psi you have a variable volume pump. the math still works. with a fixed displacement pump working in standby the oil flows through a control valve and back to tank at low pressure ( 6 gpm x 20 psi / 1714 = .07 hp). with a variable displacement pressure compensated pump in standby you have high pressure a zero flow
( 0 gpm x 1200 psi / 1714 = .7 hp). they now use load sense pumps that in standby give you zero flow at 200 psi ( 0 gpm x 200 psi / 1714 = .11 hp.). The fixed pump has the lowest horsepower draw in standby, the highest horsepower draw when working. the variable pressure compensated pump has higher in standby but better in working mode. The loadsense pump gives the best all around; very low in standby and extremely low when working.
Almost all new construction machines today use loadsense. It's all about fuel savings. Your Vickers pump is probably a PVB6 series.
My company is the Eaton Vickers distributor for the east coast.
John
MS390

johnma said:

if your pressure stays at 1200 psi you have a variable volume pump. the math still works. with a fixed displacement pump working in standby the oil flows through a control valve and back to tank at low pressure ( 6 gpm x 20 psi / 1714 = .07 hp). with a variable displacement pressure compensated pump in standby you have high pressure a zero flow ( 0 gpm x 1200 psi / 1714 = .7 hp). they now use load sense pumps that in standby give you zero flow at 200 psi ( 0 gpm x 200 psi / 1714 = .11 hp.). The fixed pump has the lowest horsepower draw in standby, the highest horsepower draw when working. the variable pressure compensated pump has higher in standby but better in working mode. The loadsense pump gives the best all around; very low in standby and extremely low when working. Almost all new construction machines today use loadsense. It's all about fuel savings. Your Vickers pump is probably a PVB6 series. My company is the Eaton Vickers distributor for the east coast. John MS390

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Smaller ABT systems use a fixed displacement pump as you describe. But the only time pressure is relieved is when they are turned off. Otherwise pressure and flow are maintained by way of a regulator relief valve. So even if the fin isn't moving you are consuming full power. Its not ideal, but the power draw is small in the grand scheme of things.

The bigger systems use variable displacement pump which maintain pressure, but regulate it by controlling flow. The result is engine load that mostly tracks the actual consumed power by the fins. Its more expensive, but definitely a better setup.

sunchaser said:

How are the hydraulics set up to operate when the main is at idle when you are docking? A Nordhavn I was looking at recently got around this by operating hydraulic thrusters off the genset PTO when docking.

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They work pretty much as others have described for other boats. There is a pump off the main engine trans that operates the stabilizers while underway, and the thrusters and windlass while docking/anchoring. But as noted, at idle the main engine pump can only do so much. It basically can operate and one device including a single thruster up to full power, or close to full power. But if you run both thrusters the available power is split between them and they operate at reduced power.

The gap if filled with a second pump run either off the wing engine or gen set. Most Nordhavns run the pump off the wing engine. Its a great way to be sure it gets exercised. Mine runs off the genset, but the decision was totally driven by the stabilization at rest feature which of course needs power while at anchor. It makes much more sense therefor to run off the gen rather than the wing. The gen is quieter, is useful to run for other reasons, and is better loaded than the wing which would be running at very light load with just hydraulics under power.

Even bigger boats with 24x7 genset power will often power the hydraulics via a 3-phase electric powered hydraulic pump.

twistedtree said:

Mine runs off the genset, but the decision was totally driven by the stabilization at rest feature which of course needs power while at anchor. It makes much more sense therefor to run off the gen rather than the wing. The gen is quieter, is useful to run for other reasons, and is better loaded than the wing which would be running at very light load with just hydraulics under power. .

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Back on point ------

Given you will run your genset at rest if needed and the N60 has the space in the very large lazarette for a Gyro setup, what were the tradeoffs in your decision comparing ABT & STAR to Gyro stabilization?

I want one system for underway and at rest, and picked ABT. I've had a great experience with them on my Grand Banks, so went with them again. With everything else hydraulic, it makes sense for the stabilization to be hydraulic as well. Plus I still don't want to have to run a generator for stabilization underway, so that further drove me towards a hydraulic approach.

When we built hulls 1 and 2 of our Northwest series, hull 1 had ABT stabilizers and hull 2 had none. Top speed was .5 knots greater with hull 2. ABT installations have been great with little or no issues. Hull 2's owner, however recently installed Keypower stabilizers and is very happy with them. We installed Keypower stabilizers and thruster on another boat we built in 2004 and the owner reports nothing other than routine maintenance and would buy Keypower again.

OkSkipper said:

When we built hulls 1 and 2 of our Northwest series, hull 1 had ABT stabilizers and hull 2 had none. Top speed was .5 knots greater with hull 2. ABT installations have been great with little or no issues. Hull 2's owner, however recently installed Keypower stabilizers and is very happy with them. We installed Keypower stabilizers and thruster on another boat we built in 2004 and the owner reports nothing other than routine maintenance and would buy Keypower again.

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Useful comparison, thank you Peter.

Do you think it possible that in a seaway, there would be improved tracking on the vessel with stabilizers that would offset the speed loss until more benign conditions? Don't know myself, but I have always wondered.

Delfin said:

Useful comparison, thank you Peter. Do you think it possible that in a seaway, there would be improved tracking on the vessel with stabilizers that would offset the speed loss until more benign conditions? Don't know myself, but I have always wondered.

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At the risk of being jumped on by all the experts here, I will break my rule and answer an excellent question; a question that will surely illicit a lot of comment from others.

Hulls will always track their straightest when they are sitting on their lines. As a hull rolls or heels, uneven lift is generated, causing the hull to steer. Now if the hull is rolling, the boat will wander in sync with the roll.

So now the question of roll period comes in. A snappy boat with a very short roll period will tend to not wander as much as a boat with a longer roll period as the hull will be returning to the level quicker, thus arresting the directional instability.

Boats with longer and deeper keels will tend to wander less than those with shorter keels or no keels as in the case of many planing hulls.

Boats with larger rudders will tend to wander less than those with smaller rudders.

So back to the original question; generally speaking, a boat with active fin stabilizers will tend to track straighter than one that is not stabilized, all other things being equal. BUT..........

A stabilized boat can also develop "stabilizer steer". If the stabilizers are installed in an improper position or at the wrong angle, they can cause the boat to steer as they actually are 2 more "rudders" on the boat. As the boat begins to roll, the stabilizers may more than offset the rudder and the boat wanders. Steve Seaton can tell you a story about a well known boat builder who didn't listen to him as to where the stabilizers should go The boat wandered terribly, and it was costly for them to move the stabilizer fins to where he said they should be in the first place.

Another issue is that some people like to run their stabilizers in the "zero heel" mode. If the boat does not tend to sit on its lines (athwartship), then forcing it to by using the zero heel mode will make it steer in the direction the stabilizers have moved to bring the boat back to level. I have experienced being underway in relatively calm seas, observing the stabilizers offset to one side (on the control panel) to counteract the heel and the rudder angle off in the opposite direction to keep the boat going straight. This definitely is increasing drag.

OkSkipper said:

So back to the original question; generally speaking, a boat with active fin stabilizers will tend to track straighter than one that is not stabilized, all other things being equal. BUT..........

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So, is it fair to say that a vessel that will track relatively easily natively (long keel, adequate rudder), will not suffer additional drag from fighting the action of the stabilizers, and where those stabilizers are optimally situated may decrease overall drag in lumpy conditions?

(Trying to pin you down here Peter.....)

Delfin said:

So, is it fair to say that a vessel that will track relatively easily natively (long keel, adequate rudder), will not suffer additional drag from fighting the action of the stabilizers, and where those stabilizers are optimally situated may decrease overall drag in lumpy conditions?

(Trying to pin you down here Peter.....)

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I think a few years back someone posted some real world numbers that their economy increased with use of the fins due to the boat riding on it's lines better.

However, like many performance discussions on TF...SO many variables come into play, to measure performance between 2 boats that aren't exactly alike ....as you change the equation...you really can't predict exactly what YOUR boat may do.... but if I were to bet...the drag caused by fins could easily be nullified by smoothing out the ride and eliminating forces that Peter described.

Delfin said:

(Trying to pin you down here Peter.....)

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My former JV partner is a brilliant aeronautical engineer. During our association, we had many discussions where he would complain about the relative lack of engineering standards available with respect to naval architecture vs. what is available in aeronautical engineering. How data collected from tank testing paled in comparison to that of wind tunnel testing. There were just too many variables in hydro dynamics to nail down an absolute standard for many important design elements. Each new design is compared to previous designs.......not to an absolute standard. He finally retreated back to aircraft design.

So.....in answer to your question, you can't pin me down because in order for me to prove one argument over another, I need a way to measure and compare under equal conditions. And that is not possible. (me tap dancing)

OkSkipper said:

My former JV partner is a brilliant aeronautical engineer. During our association, we had many discussions where he would complain about the relative lack of engineering standards available with respect to naval architecture vs. what is available in aeronautical engineering. How data collected from tank testing paled in comparison to that of wind tunnel testing. There were just too many variables in hydro dynamics to nail down an absolute standard for many important design elements. Each new design is compared to previous designs.......not to an absolute standard. He finally retreated back to aircraft design.

So.....in answer to your question, you can't pin me down because in order for me to prove one argument over another, I need a way to measure and compare under equal conditions. And that is not possible. (me tap dancing)

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Retreating into Godel's Uncertainty theorem, eh?

Permission to treat the witness as hostile, your honor.

Yes........retreating in Godel's theorem (thank you Wikipedia). But not hostile at all. Just can't prove nuthin' to no one........no how. And I would be a fool to try. And besides.....I am entitled to my opinions......no matter how wrong they may be.

This is probably apropos of nothing, but the earlier discussion of gyros running amuck reminded me of this picture of the Tennessee Valley Authority's Ocoee #2 hydroelectric powerhouse. I used to work for TVA but can't remember if it was a governor overspeed failure or if they tried to synchronize the unit to the grid out of phase. Whatever they did, the massive rotor and turbine shaft exited the building. Witnesses when this happened in the 1940's said it went partway up the side of the Ocoee gorge before finally coming to rest. Not sure I'd ever be able to get that image out of my head if I had a gyro on board.

I'd never fly an airliner if I thought I was going back to 1940's tech and maintenance...seriously?

I would think a bazillion law suits since the 40's would have wised up most companies and engineering standards for failures.

some years back there was talk of utilizing the existing large rudders on some trawlers to offset roll.

I believe the idea was to get some sort of roll input device to fire off a big fast hydraulic pump to 'whip' the rudder to compensate for the roll from a wave.

I don't remember this idea happening for our size boats, but think some larger ships may utilize this type of roll dampening.

psneeld said:

I'd never fly an airliner if I thought I was going back to 1940's tech and maintenance...seriously?

I would think a bazillion law suits since the 40's would have wised up most companies and engineering standards for failures.

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You'd think so, wouldn't you? Seriously!

One concern I haven't ever head addressed, probably because it isn't one, is the need for the hull to be able to withstand the torque loads involved. From one Gyro manufacturer website:

The gyro foundation saddle beams should be attached to stringers using an adhesive bonding agent. The stringers and bonding agent must be capable of reliably and effectively transmitting the gyro's torques to the hull structure through an infinite number of fully reversing load cycles.

An infinite number of reversing load cycles sounds like rather a lot of them, and I just wonder about fatigue being an issue at some point. Probably not a problem, but just curious.

Delfin-I have had the same question. Reading that the saddle is attached to stringers with an "adhesive bonding agent" doesn't ease my concerns. I have wondered about the directional forces on the stringers from a gyro, i.e lateral or angular forces where stringers are primarily designed to absorb longitudinal forces. Have gyros been around long enough to see if there are any issues created where the hull and stringer come together?

This probably isn't a whole lot different from the forces generated by fins, with similar structural reinforcement required - or at least analysis required.

Gyro Stabilizers & Nordhavn

Last year when we considered building N3 I spoke with the west coast sales representative about being the first Nordhavn with a Gyro system. To make a long story short the promises made were not kept (representative over stepped his authority). Even if the arrangement would have worked out I'm not sure we would have proceeded in part to the proven track record of Trac Stabilizers and having to run the generator full time. If we built another new boat I would likely go with Trac stabilization again.

John T.
N3522
La Tempestad

twistedtree said:

This probably isn't a whole lot different from the forces generated by fins, with similar structural reinforcement required - or at least analysis required.

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Maybe, but I'm not so sure. First of all, the loads of fins on a particular place on hull is 1/2 because there are two of them. Second, the fins act in water, where the load is spread over the entire fin. With a gyro, all of the force of correction is placed directly on a relatively small part of the hull. You might be right, but I can't quite visualize it.

Delfin-i think how the forces are placed on the hull are entirely different. The "collar" or the part actually attached to the hull is backed by a good sixed backing plate directly on the hull, not on a stringer. The force acts on the hull itself and is spread out over a decent sized area. If I understand the installation of the gyros correctly, they attach to the stringer itself and impart the force against the stringer. My question still is where the force acting on the stringer is lateral and angular, is there a danger of the stringer-hull joint cracking or separating?

THD said:

My question still is where the force acting on the stringer is lateral and angular, is there a danger of the stringer-hull joint cracking or separating?

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On a new build the NA and builders should be able to get this right. A lot of the points made on structural integrity for gyros could easily apply to poor designs and or applications for rudders, engines, passive stabilizers or anchor rode connections.

Similar discussions were common a few years ago when pod drives were in their infancy and long before that stern drives. New concepts always have their doubters, in the case of gyros I am one but not for being (un)able to design a suitable structure.

For new builds such as a Fleming, OA, Westport or Marlow gyros seem worth a look. Hull appendages create external strike potential and the fewer the better IMHO. I was reviewing a large vessel recently that had 30ft2 stabilizers, the thought of one of those striking a log or container in the open ocean is not pleasant.

It would be great to hear from someone first hand who has a gyro in their boat. I'd love to hear how they actually perform. We have a bunch of people here with fin systems, but it appears nobody with a gyro?

twistedtree said:

It would be great to hear from someone first hand who has a gyro in their boat. I'd love to hear how they actually perform. We have a bunch of people here with fin systems, but it appears nobody with a gyro?

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Yes, and a visit to Seakeepers website is worthwhile too. It is surprising how many builders appear to be on board.

I have talked with two guys who have them on their big sport fishing boats, which I believe was Seakeepers original target market. Both were installed as part of the original build as I recall. They both loved it, the primary purpose being stability while on the drift or slow trolling speeds ( it is very rare to see fin stabilizers on a sport fisher).

As far as the loads go, when I looked at sea keepers web site days ago there was technical info that showed the largest load in the worst sea state of 23 kN in the z axis. All the the other loads were in the teens. Not near as much as I had expected.

On a dying cell phone on a particularly boring ferry ride so not able to link right now. I'm sure the OP, RickB has already read it though.

twistedtree said:

It would be great to hear from someone first hand who has a gyro in their boat. I'd love to hear how they actually perform. We have a bunch of people here with fin systems, but it appears nobody with a gyro?

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People with gyros don't need no stinkin trawler forum

Wxx3 said:

People with gyros don't need no stinkin trawler forum

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Sometimes an eye opener is a good thing. There are some on this forum who still feel the best head is a bucket. :lol: