Roll Stabilization

Stability for Cruising Power Craft

Oh, how our boats grow!

I mght suggest you contact Dave Gerr and Steve Dashew, both who are designing 'cruising power craft'. Don't recall what they are using.
Opps, just found this http://www.setsail.com/dashew/stabilizing_gear.html

An excerpt from that ProBoat article, "One reason sails work well is the fluid dynamic forces go up with the square of the speed (ed:rolling speed). the portion of the sail near the top of the mast is traveling through the air very fast due to the long distance from the roll center (roughly the waterline), so the forces generated by it are large"

 

Need for Roll Stabilization

We don't see that many photos of 'salty old vessels' in their element. Here's one experiencing problems with its power supply to its stabilizing system.

Sure makes one believe in having a back-up system that's not dependant on an active power supply.

...and this isn't even a BIG sea

 

Brian;

Yes, boats have been known to grow when you add water. In my case the Admirable is scared of small boats and she is happy every time it grows (maybe I should rephrase that?. I think we are close to the limits for transportability without an escort vehicle, which is where the transport cost start to escalate.

Most stabilization systems are powered off 3 phase AC power, so you need the main engine for propulsion and the generator for stabilization.

Portager will power the stabilizer electrical systems off the battery bank. The hydraulics will be powered by pumps on a PTO on both the main and auxiliary engines, so if I have either engine I should have propulsion and stabilization. If the hydraulic or electrical systems fails, the paravanes are the backup stabilizers.

Regards;
Mike Schooley

 

Brian and Portager. I see that old salt leaning. Why is not, a manual hand crank irreverseable worm drive provided to return it to at least a neutral position? That is suicidal in bad weather. Does the manufacturer show them their boat in that condition after installation? We simply do not have enough USCG rescue boats to run down all these boats with gadgets in them.

 

That is the most powerful stabiliser system I have ever seen. Usually stabilisers are sized to give the vessel a theoretical ability to have a static heel of between 3 and 5 degrees (in other words if both fins go hard over in opposit directions then the vessel will be suject to a constant heeling moment which is proportional to the square of the speed - so if your control system fails in this dramatic fashion then to return upright you simply stop.) The systems I have seen have a mechanical locking device to move and hold the fins at zero degrees in the absense of hydrualic power, which for small yachts is typically taken from a PTO rather than a 3 phase electrical power unit as is common on very large yachts and ships.

Looks to me like this vessel was performing a roll test, or someone fitted the stabiliser roll sensor back to front which produces a similar effect.

Of course you do have some redundancy with a fin system. You can always hydraulically isolate a problem fin and continue operating on the other.

Cheers

David

 

Powered Stabilizers

Actually this photo came from a relatively new magazine "Power Cruising", and was reporting on the Atlantic Rally sponsored by Nordhavn this past summer. This vessel lost electrical power to her Naiad stabilizers.
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An excerpt: "Mather worked his way to the sea strainer for the primary bilge pump. He removed it and handed it to Sue. As she began cleaning it, she noticed the blockage was odd. Most of the material looked strangely familiar. Then the realization struck: It was shavings and dust from the boat’s manufacture. As Mather worked through the lazarette, the Spencers pieced together the events.
When Uno Mas went over, her port side was momentarily submerged. Seawater forced its way aboard via the engine-room vents, through the lazarette vents on the outside of the hull (which had been plugged with sponges for the passage), and past the lazarette’s hatch gasket in the cockpit floor. The water pushed into tiny spaces never before accessed, collecting construction shavings from the far reaches of the bilge. The primary bilge pump simply couldn’t handle the load. Salt water filled the bilge up to the engine’s oil pan. The high-water alarm sounded, and the large-capacity emergency pump started throwing water overboard. With the primary pump working again, Mather moved farther into the storage space, where he found the inverter fried completely black from its saltwater bath. There was no fire. Relief.
The cooked inverter explained the last part of the mystery. The part’s failure meant no power was getting to the cooling pump for the Naiad stabilizers, which promptly shut down.
Problems Solved — Not
Uno Mas was not sinking, and she was not on fire. But without stabilizers in a brutal, heamy sea, The Fearless 40 was more than just uncomfortable; she was downright dangerous. John had the ship aimed into the oncoming wind and waves to minimize the battering while they assessed the emergencies at hand, but that had put them off course. Any farther afield and Uno Mas wouldn’t have enough fuel to make the remaining distance to the Azores. Getting on course without stabilizers put her at the mercy of a savage sea.
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If I were to consider electrical drives for stabilizers, I might have a look at the 'new generation' DC motors, and in fact the whole systems approach of smaller 'DC' generators and motors discussed in the Dec/Jan issue of Professional Boatbuilder magazine under an article entitled "Diesel-Electric Technology". Lots of good material to think about.

I also took note of this description, " engine-room vents, through the lazarette vents on the outside of the hull (which had been plugged with sponges for the passage)". How do the engines breath properly in this situation. I once had one turbo charger fail on a Chris Craft with a couple of big Cat diesels. The exhast gases leaking from the failed turbo quickly filled up the engine room and clogged the too small inlet air vents, which promptly shut down the other engine for lack of good air. Took some time to get the mess cleaned up enough to get back under power. Luck would it the seas were calm out in the Gulf Stream. Sure would not have been pleasant in a northerly.

This reported incident was a serious situation which could have resulted in abandoning the ship for many owners....just another reason I like the concept of motorsailers over trawlers for REAL ocean going boats.

And I'm always amazed by the descriptions of sea state. They call this a 10 to 12 sea. Doesn't look like that to me in the photo....maybe that's the top of the crest to the bottom of the trough, but technically that's twice the average wave height...so wouldn't this be a 5-6 foot sea. terrible to lose your ship in that sea state.

 

If the boat has not been built yet, would a retractable fin like a centerboard, daggerboard, bilge boards, or leeboards be an option? If you are going to use in blue water and draft is not an issue, a deep fin would keep drag low for the amount of roll damping you would get. Also, could be retracted when not needed.

Simple operation, low cost, low risk, high benefit/cost.

 

I think what your suggest could be accomplished by locking the roll stabilizer fins at the zero deflection angle without increasing draft, however static fins are far less effective than actively actuating the fins to produce lift forces to counter the induced roll torque.

Draft is important, even on a blue water boat, because once you cross the ocean you still need to be able to get into port and access coastal anchorages. In the case of Portager, draft is very important because it increases the height on the trailer.

Regards;
Mike Schooley

 

Old salt, UNO MAS, is so bad, I don't know who to blame more. They were playing Russian Roulette, without being told. Sad, very, very, sad. That is ocean cruising, to the Azores? I have heard enough Gross negeligence by every body who designs, builds, retrofits and then owners who think they can afford to buy experience with money to enjoy the boat . No one is in charge of the boating industry. It is a joke compared to cars or aircraft. Good bye.

 

"No one is in charge of the boating industry."

Thank GOD "no one is in charge", as there can be advances and progress that is unavilable in the auto or aircraft industries.

Sure they create yet less efficent engines sfor the Smog Police , but what real advances have they has in the past 30 years?

At least in boats folks can experiment with advanced concepts like foils , or retro concepts like long skinney 1920's style Commuters with out pleasing some dead brained burocracy "Design & Materials Revew Board".

FAST FRED

 

One method of roll stabilization I have contemplated ,
but never seen in practice could be a center board with a wider than usual box.

If the board could be "steered" as a rudder , to damp the roll.

Advantage , in power failure it could be locked ahead or lifted , but when working should provide roll stability (if large enough) with out the danger of protruding wings sticking out .Going aground or a submerged log would be painless.


If balanced (pivot located aft of leading edge ) the force required should be quite small , so backup mechanicals could be cheap enough to carry complete spairs.

FAST FRED

 

Dear all,

I am currently doing some research in active fin stabilizers for zero speed. I am using a 33 m power boat and a variety of cfd programs to simulate the roll motion. I am currently at the stage where i need to choose reasonable fin dimensions for this particular yacht and then i will need to implement the damping produced by the fins on the overall roll motion. If anybody has any suggestions to my current stage i will be great ful to hear them.
Thanks, Ivan

 

but I’ll also have paravanes onboard for stabilization at anchor. I decided against paravanes because there have been a few mishaps retrieving them while underway.


I just read somewhere about the different methods of stabilization and one of the big drawbacks to paravanes is if one of them quits working due to being tangled up or lost (broken cable), in certain conditions the other can keep going deeper and deeper resulting in capsize.

 

Centerboard, daggerboard, bilgeboards can be easily retracted. Powered roll stabilization devices are inherently complex, and require a fair amount of maintenance.

 

SamSam

The incidence of paravanes fouling and/or failing while underway is very low if the equipment is properly maintained, however it is much low while at anchor. In addition retrieving paravanes while at rest is much easier that while underway.

As far as I know active stabilizers are the most effective means of stabilizing while underway and second place is far behind. However, active stabilization does not work without forward motion. While at anchor paravanes are the most effective although a steadying sail may be a close second.

Regards;
Mike Schooley