Niaid Stabilizers

[Seabrooke]

G'day guys,

A quick question about stabiliser effectiveness.

I understand the surface area of the fins would make a significant difference but for an average installation, how effective are the fin stabilisers, say on a 53MY, at hull speed or lower.

Our plan (some time off yet, but lots of planning to be done) is to come to the US for a few years, buy a 53MY (most likely) or a 48 LRC and spend 2 or three years travelling America's Great Loop as well as a whole bunch more of the east coast and through the Caribbean.

Large parts of this will be at slow speeds, sometimes plodding along 6 or 7 knots and I have heard some opinions that the fin stabs often need more speed than that to be effective.

You blokes are the source of massive Hatt knowledge, so I figure you are also the best source for the right information.

 

[SeaEric]

Its all about the size of the fins. You go slow, you need bigger fins.

 

[jim rosenthal]

They are sort of like rudders; they depend on water flow over the fins to exert their effect on hull rolling. I would imagine that there is a minimum speed below which there isn't enough water flow to make them effective. And at higher speeds, the drag becomes a problem, decreasing cruise speed- but I don't know for certain. The most popular ones are Naiads- you might usefully ask Naiad for their opinion. I would be curious as to how they estimate the size fin required based on the expected cruise speed of the boat, and how much difference there is in fin area between a trawler, like the 48LRC, and a 53 MY.

Only you can decide whether you need them. I have only run one boat with them, which actually WAS a 53 MY, and it was interesting to say the least. My impression was that the rolling motion was translated by the stabilizers into yaw, which in turn required correction by me or the AP, but they really do keep the boat roll down a lot.

 

[Fanfare]

If starting with a new boat I would certainly investigate the new gyroscopic stabilizers. No external fins, no holes in the bottom or bearings to replace every two years. From what I have learned on this forum new Niads would cost about $50,000. While the gyros started out being very expensive there are now several manufacturers and the costs may have become more competitive. Best of all, these stabilizers work at anchor as well as under way. The biggest drawback seems to be their electrical draw on your generator, but I would expect that this is proportional to the amount of work they have to do. So perhaps less draw at a calm anchorage.

 

[Milacron]

If starting with a new boat I would certainly investigate the new gyroscopic stabilizers.

Or buy the below Hatteras and get them for free. I say free, as they probably add zero market value to that particular boat. He spent $175,000* on the pair of them but the prices have come down a lot just in the 3 years since they were installed.

http://www.yachtworld.com/boats/197...23461/Pensacola/FL/United-States#.VbT0vUWjVFA

Another disadvantage is the noise they make and the fact they don't react as soon as you turn them on...takes afew minutes to ramp up to full gyro rpm. If generator and air conditioning on, the noise is not noticable however. (except perhaps in the master stateroom where the pair reside under the bed !) Also have heard on trawler forums some say when conditions get really bad they can get "confused" to the point you have to turn them off !

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*He really did spend that much...I called Seakeeper to confirm. As an aside, having been aboard the boat, I find it hard to believe the remaining $425K the broker claims he spent on it. A pretty sloppy "restoration" IMHO... some cool gee whiz electronics but the woodwork and such is below par, engine rooms look abysmal. Outside appears much worse than photos in real life.

 

[jim rosenthal]

Yeah.... I think Rick, who started this thread, was talking about a smaller boat- maybe even an LRC. so although this boat does have Naiads, I don't think this was the model he was looking at.

 

[Seabrooke]

Yeah.... I think Rick, who started this thread, was talking about a smaller boat- maybe even an LRC. so although this boat does have Naiads, I don't think this was the model he was looking at.

Thanks Jim.

I'm trying to get a broad understanding of how. mainly in this case, the average 53 Hatt behaves at slow speeds with the typical (what I understand as 6 ft sq) fin stabilizers and how much difference a few knots can make.

 

[bobk]

Thanks Jim.

I'm trying to get a broad understanding of how. mainly in this case, the average 53 Hatt behaves at slow speeds with the typical (what I understand as 6 ft sq) fin stabilizers and how much difference a few knots can make.

Rick,

My 48MY has small fins. I suspect they were sized for use on plane, but we run her at 8 knots (mostly AICW). There are times where the boat can get rolly and we find a large improvement by just bumping it up to 9-10 knots.

Bobk

 

[GJH]

The Naiad manual had a few pages and graphs specifying recommended fin and system sizes for various sized boats and speeds.

I will tell you they help mitigate roll at virtually all speeds. We could tell when they were not on. Our fins were theoretically smallish for the speeds we liked to travel (8 knots +/-) but mde the difference between a rocky ride and a relatively smooth one. I think some may perceive that they add to yaw, but what happens is that with roll out of the equation, yaw and pitch become more noticeable, but not more severe. In certain seas, say very steep following seas on the quarter, the combination of yaw and pitch can induce some to think the stabs aren't on. Switching them off for a minute soon dissuades the doubters from that thought. By the way, if you have them, they should always be on, whether "needed" or not, and centered when doing close quarters maneuvers, especially backing down.

 

[dastahl]

You should also take into consideration hull type. The 53 motor yacht has a planning hull and thus a short roll. The LRCs have displacement hulls which creates a slower roll. I think the stabilizers have to work harder and faster to stop the shorter roll. You can check with Niaid. Part of the slower roll is due to the heavier hulls of the LRC. So they may even out. The slower roll of the LRC is a selling point. If you have to go slow at least go comfortably. Its a big difference at slow speeds and rough seas.

My 58 LRC had 6 foot square Niaids which I replaced with 11 SqFt fins before I ever used the little ones. I sold them covering about 20% of the cost of the new ones. They work just fine but I had no experience with the smaller ones. My friends tell me its much better.

Skooch
Wye River MD

 

[Seabrooke]

Thanks guys, great info.

It sounds like the larger the better with regard to fin size for slow speeds.

I recall VIVIDLY the difference between two Frigates I served on back in the 80's. Same class of ship, one with Stabs and one without. They were very effective as soon as the vessel was moving but the fins were quite large. Sailing "in company" on a wild day, HMAS Sydney (no stabs) was rolling to about 35 degrees whilst on HMAS Darwin we were rolling to about 12 - 13 degrees. Two weeks later I was notified of a posting change to HMAS Sydney.......

Back to thinking about small ships.......

I'd like to get a 48 LRC for the two or three years we will be cruising the US and Caribbean but the difference in fuel usage between that and a 53 Classic MY (mostly at slow speed regardless of what we buy) could easily be outweighed by the difference in purchase price for a good boat.

I'll be calculating the expected total costs for the two or three years and of course the resale potential and value of both types of boat if we choose to sell it before we come back. "The Admiral" seems to think this would be the plan. I'm thinking that we should have it transported across the Atlantic and explore the Mediterranean and Southern Europe or at least have it transported back to Australia.

I suppose if we went for the LRC we could take another year and island hop our way (with extra fuel bags) back to Australia.

The stabilizers would be absolutely vital for an adventure like that!!

 

[Nonchalant1]

W ehad a 53MY without stabilizers and I added Naiad stabilizers, with a little larger of two standard fin sizes for that boat and the new digital controls. They were fantastic. Cost $43K in 2005 and well worth it. We did the Great Loop in the boat (6,000 mile cruise) with much of it at 7 to 9 knots in the rivers and going slow to save fuel. The stabs work excellent at 9.1 knots hull speed, but less effective at 7 knots, although they still work. On a 53MY cruising at hull speed is the best speed for the difference between fuel efficiency and getting somewhere in a reasonable time. It is true that the stabilizers change roll into yaw so the boat makes small left/right turns as the fins work, however, I didn't correct for it because with waves it self corrects on the back side of the wave and with autopilot the pilot never had to correct for it either, for the same reason. In waves, the boat makes little turns left then right along the straight line heading.