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Old 02-24-2014, 02:33 PM   #61
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Northern Spy has a good point. 23 kN is only 5170 lbs force. This isn't a very high load.

As far as the loading on the stringers goes, it isn't a twisting load on the stringer. The primary loading is up on the stringer that the boat is rolling toward and down on the opposite stringer. This load is distributed into the skin and the frames over a large area so there shouldn't be an issue. That said, I would still hire a Naval Architect or a structural engineer to perform a loads analysis if only for peace of mind.

The infinite load life statement is a typical fatigue loading term that a structural engineer would understand. In high-cycle fatigue situations, materials performance is commonly characterized by an S-N curve, also known as a Wöhler curve where S stands for stress and N the number of cycles. In some materials, such as aluminum, the S-N curve intersects the zero stress axis. These materials are said to have a finite fatigue life. Some materials, such as steel, the S-N curve becomes horizontal at a stress value greater than zero. This stress value is defined as the infinite fatigue life stress. When the structural engineer selects the adhesive bond material he will use this infinite fatigue life allowable stress to determine the minimum bond surface area that is required. There will also be a factor of safety that is applied to account for possible voids in the adhesive bond.

The initial target market for Seakeeper was Sportfishing boats because fin stabilizers have higher drag loss at planning speed and Sportfishers spend more time drifting or at trolling speed (where gyro stabilizers work better than fin stabilizers). Now, having made significant inroads to the megayacht and sportfisher markets, Seakeeper is targeting trawler owners as potential users of its new gyro stabilization system. Read more: Seakeeper Gyro Stabilization for Trawlers | OceanLines

They are also experiencing success in the Naval market. Seakeeper Sets Standard for Stabilizing Naval Vessels. Read more: http://www.maritime-executive.com/ar...ls-2013-05-30/

Even though Seakeeper is new to the trawler market, they have delivered more than 1,300 gyro systems, and 374 were delivered in 2013, says Seakeeper’s Shep McKenney, who founded the company in 2003. I have yet to find a report of a Seakeeper failure.

“With every boat we draw now, we have to have a planned space for [a gyro stabilizer],” said designer Michael Peters, owner of Michael Peters Yacht Design in Sarasota, Fla. “Five years ago, we didn't even think about this. It’s a huge development. It’s becoming much more prevalent than we thought. We thought it was just for guys with larger boats and deep pockets, but with everything we design over 40 feet, the builder wants to know where the gyro is going.” Read more: VIDEO: Gyro stabilizers gain popularity | Trade Only Today
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Old 02-25-2014, 04:27 PM   #62
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MJM has recently announced that a Seakeeper Gyro will be Standard Equipment on the 50Z. MJM using Doug Zurn as the NA produces vessels with very good economy at + 25 knots and in the case of the 40, Ocean rated class A.
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Old 02-26-2014, 01:02 AM   #63
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MJM has recently announced that a Seakeeper Gyro will be Standard Equipment on the 50Z. MJM using Doug Zurn as the NA produces vessels with very good economy at + 25 knots and in the case of the 40, Ocean rated class A.
IMHO, Doug Zurn designs and MJM makes the highest tech boats in the market. Maybe not trawlers, but great design. 20-30 years from now they will be considered revolutionary.
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Old 02-26-2014, 01:25 AM   #64
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Here is another brand of gyro. Does anyone have one of these installed? Interesting size ranges and calculator on their website which I'm yet to play around with.
Sea Gyro International
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Old 02-26-2014, 05:44 AM   #65
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Here is another brand of gyro. Does anyone have one of these installed?
I have heard that they do not have one installed at the moment.

Their "operating manual" is a copy of the manual that came with a VFD they evidently bought to run the motor that spins the open air flywheel.

From what I know about gyrostabilizers, this one isn't quite ready for prime time.
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Old 09-16-2014, 11:57 PM   #66
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Not sure, but I can tell you that if I am cruising along and turn off the fins, the change in rpm is almost imperceptible and the speed doesn't change based on GPS readings to .1 knots. On that basis, I'm not sure they use much power under 'normal' conditions and have no effect on speed. I wouldn't be surprised if they actually, at least on Delfin, result in greater fuel economy since they keep her oriented in the water in a position with what I assume is the least resistance, and tracking a straighter line. Gyros need the same power regardless of the sea conditions, whereas active fins are variable depending on how hard they have to work.
The reason you are not noting a change in RPM is because propellor hp requirement drops off as a cube root function, ie at half engine speed the propellor requires 1/2 x 1/2 x1/2 = 1/8 the hp of full RPM. This simply means that other than at full throttle any additional hp required is generated almost instantly as the governor or electronics maintain engine speed.

Note unlike petrol engines your throttle actually controls a governor (or electronic device) which sets a constant engine speed by adjusting the fuel delivery to the engine. This is why with diesels when you climb that wave the engine does not slow down and again when going down the wave face (normally) the engine does not speed up.
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Old 09-19-2014, 12:18 AM   #67
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I have heard that they do not have one installed at the moment.

Their "operating manual" is a copy of the manual that came with a VFD they evidently bought to run the motor that spins the open air flywheel.

From what I know about gyrostabilizers, this one isn't quite ready for prime time.
I have a SeaGyro installed in my 1986 46' Jefferson Sundeck.

It's been installed since 2011 and served us for 3 winters in the Bahamas and has currently carried us to Grenada.

I know the designer/builder, how incredibly efficient it is, and that it is virtually maintainence free.

We have traveled thousands of miles on "Just Cause" will our SeaGyro active, and would NEVER travel without it.... In other words, it IS ready for prime time.

No regrets on this one.
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Old 09-19-2014, 10:52 AM   #68
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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.
I am pretty sure that is wrong. If the pressure is not relieved (for example, by doing the work of moving a cylinder), once the pressure is built only negligible power is necessary to maintain that pressure. Much like an electric centrifugal pump connected to a hose lifting water and with a valve on the end of the hose. While the valve is open the pump is doing the work of lifting water and electric consumption is high. As the valve is closed, the quantity of water lifted is reduced (ie, less work is done) and the electrical consumption goes down.
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Old 09-19-2014, 01:43 PM   #69
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I have a SeaGyro installed in my 1986 46' Jefferson Sundeck.

It's been installed since 2011 and served us for 3 winters in the Bahamas and has currently carried us to Grenada.

I know the designer/builder, how incredibly efficient it is, and that it is virtually maintainence free.

We have traveled thousands of miles on "Just Cause" will our SeaGyro active, and would NEVER travel without it.... In other words, it IS ready for prime time.

No regrets on this one.
Interesting. What model SeaGyro do you have?
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Old 09-19-2014, 02:35 PM   #70
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Have you considered electric stabilisers. They are very easy to squeeze into small spaces and use very little power.

A Member of the MBM forum fitted these to his boat and is very pleased. They work in the star mode too, 'swimming' to keep the boat level when it's at anchor.

CMC Marine: Electrical fin stabiliser for superyachts - YouTube
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Old 09-19-2014, 03:32 PM   #71
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Have you considered electric stabilisers. They are very easy to squeeze into small spaces and use very little power.

A Member of the MBM forum fitted these to his boat and is very pleased. They work in the star mode too, 'swimming' to keep the boat level when it's at anchor.

CMC Marine: Electrical fin stabiliser for superyachts - YouTube
I like the concept of electrical stabilizers. Perhaps these folks have overcome the challenges and have a product that will work, and be reliable, and hopefully at a decent price.
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Old 09-19-2014, 08:11 PM   #72
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I like the concept of electrical stabilizers. Perhaps these folks have overcome the challenges and have a product that will work, and be reliable, and hopefully at a decent price.
CMC Marine: Electrical fin stabiliser for superyachts - YouTube

These do look interesting. Of course the control box smarts will be the telling aspect. Do they have accelerometers in it like Naiad (and others)?
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Old 09-20-2014, 06:22 AM   #73
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CMC Marine: Electrical fin stabiliser for superyachts - YouTube

These do look interesting. Of course the control box smarts will be the telling aspect. Do they have accelerometers in it like Naiad (and others)?
Here's some more info : Stabilizers for Blue Angel, engineering question
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Old 09-21-2014, 01:08 AM   #74
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I am pretty sure that is wrong. If the pressure is not relieved (for example, by doing the work of moving a cylinder), once the pressure is built only negligible power is necessary to maintain that pressure. Much like an electric centrifugal pump connected to a hose lifting water and with a valve on the end of the hose. While the valve is open the pump is doing the work of lifting water and electric consumption is high. As the valve is closed, the quantity of water lifted is reduced (ie, less work is done) and the electrical consumption goes down.
I guess it depends on the specifics of the system. On the Grand Banks with a fixed displacement pump, it is always moving oil, either through the relief valve or through one of the cylinders. And it does so maintaining approximately 1500 PSI the whole time. So I'm pretty sure that's the same power consumption all the time.

My Nordhavn, on the other hand (but still an ABT system) uses a variable displacement pump, so pressure is regulated by changing the displacement of the pump. When no fin movement is called for, the pump can maintain pressure with near zero displacement with near zero oil movement, so power consumption is reduced accordingly. But of course it's a much more expensive system.

I'm not sure about your water pump example. Wouldn't the pump still be churning the water and generating heat with the flow shut off?
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Old 09-22-2014, 10:57 PM   #75
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Interesting. What model SeaGyro do you have?
I have the GT3K, currently discontinued and replaced by a newer model (SG series).
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