stabilizer systems and seakeaping

[NBs]

Hi

I was thinking of the "londonrascal" rough sea trip discussion that it would be interesting to discuss this topic on your own subject.

I think it would be good to discuss the stabilizers, they are good additions to comfort and help keep you apart from the sea sick when you are in motion.

Stabilizing systems give the impression of increased stability, but the static and dynamic stability of the boat does not change, the boat crashes at the same °angle regardless of stabilizers, they only work to reduce the roll.

The roll can also be reduced by swapping a bit of direction and it is just pitiful not dangerous, hardly any sailor will withstand that roll on what the boat, so guide the better direction automatically.

NBs

 

[benjenbav]

I have been very impressed with stabilisation, but only experienced it (in leisure boats) in benign conditions.

One question I have is whether stabs operate in a similar manner to the typical performance electronics on a sports car: brilliant up to a point, but with a tendency to lull you into the sort of false sense of security that sees you joining the scenery when you push it to 10/10ths.

In a boating context, could this mean that you might take a stabilised boat into conditions that you would run away from without stabs and then find that you were 'in too deep'?

 

[rubberduck]

For me its about added comfort, not a tool to go out in a F8 which I would never do, anything above 5 I will be tied up, there is enough stress in life without looking for it during leisure time.

 

[MapisM]

In a boating context, could this mean that you might take a stabilised boat into conditions that you would run away from without stabs and then find that you were 'in too deep'?

No way. Hoping that stabilizers can make a boat safer is wishful thinking, and voluntarily affording sea conditions that would have been avoided without them is pure madness.
Rubberduck is spot on, comfort is what stabs are all about, BUT:
1) arguably, comfort is what the whole pleasure boating thing is all about, 'innit? :encouragement:
2) at sea, sh!t does happen, and since stabs are mostly fitted in slowish boats, escaping bad weather ain't always an option.
In 17 years with a stabilized and rather seaworthy trawler, I never, ever went out there unless the expected conditions were fairly acceptable.
But in at least a couple of occasions, I had to withstand some unpredicted and very bad rock 'n roll which I would have happily avoided.
And while in a "normally" rough sea the difference that stabs can make is like day and night, in extreme conditions it's more appropriate to say that the difference becomes like day and... nightmare! :ambivalence:

 

[BartW]

No, we don't plan our trips in sea conditions that are not safe,
BUT,
on quite a few occasions we left the harbour while the swell was still strong, but decreasing (prediction)
so we could go ahead with our trip while without stabs this wouldn't have been possible, '(very uncomforteable)
I remember at least 3 occasions, that we had to re-arrange our planning / commitments / flight tickets,..,
if we didn't have stabs,

I also remember quite a few occasions when unexpected swell on beam would have made a trip extremely uncomforteable,
and occasions that the stabs brought us home in comfort, in unexpeted bad weather

but I remember aswell 2 or 3 occasions from before we had stabs, that were like a nightmare ;-)

I can assure you that stabs have a huge influence on comfort on the boat, at anker aswell during navigation,
not only in the extreme circ's here above in this post

 

[Portofino]

they are good additions to comfort and help keep you apart from the sea sick when you are in motion .

NBs

You are making an assumption, it depends on your threshold to seasickness .
It’s a bit like snow boarding or tightrope balancing - you can all train to do it - just takes time .
1 week with me in the alps and I will have you going down a 1/2 pipe doing tricks by Friday .

Once you can ride a bike , it’s time to ride without the stabilisation, just takes time n practice .

Going out to sea and NOT suffering seasickness is trainable if you have the time .

If you ( or crew ) have a low tolerance to boat motion then agree stabs are a great addition to comfort no doubts .

But it no benefit to folks that do NOW - NOT - ( they once did btw you are not born with sealegs ) suffer any nauseating symptoms .
For those folks - what problem are trying to solve by chucking £70-100K @ the boat ?

Like air suspension or massage seats in the car world , nice and add to the “ comfort of a “SMALL boat .
Stabilisation is a comfort addition ,but the similarities end at the cost .

While the former is a few thousand the latter is several tens or indeed over a hundreds thousand of any strong currency .

The slower the boat the more potential benefit if fitted , as without stabs they tend to create a more nauseating ride lifted and dropped by the waves .

A fast planing boat kinda cuts through the “ lifting wave “ and crosses the deep troughs , the vertical lifts n drops seem to decrease as the speed increases

The less —- hmm how can I pit this ? It’s to do with weight distribution— arh — the “more tippy “the boat .
Boats with a higher centre of gravity will ride more nauseating then those with a lower CoG in the same sea

A combo of high CoG and inability to plane fast = a more nauseating ride in the same sea than a boat with a lower CoG and ability to have a wide range of planing speed s to call upon .

So,s it’s not just a broad brush statement that the only way to reduce a nauseating ride is to go for a stabbed slow tippy boat ( high CoG ) .
It’s more like a slow high CoG boats produce a more nauseating ride tending to lead the owner down the stab path , bit chicken and egg which come 1st ? - if the users have a low threshold to seasickness and are unable ( for what ever reason ) do the sea time / miles to “ retrain “ some sealegs .

Personally , we have sealegs ( trained on a sail boats + Sunseeker sports cruiser ) and find if we go faster the ride stiffens up and flattens out, gets smoother —- not rocket science ——- if you can !

In a large powerfull open ( all eyes on the horizon )
Two controls already fitted to cure any perceived excessive rolling

1st the tabs - put them down
2nd the throttles — push them fwds ———— works every time .

Regarding going out - in what ,and planing re looking @ forecast etc - agree - that’s just normal common sense and decent passage planning .

 

[jfm]

Stabilisers (fins or gyros at rest, and only fins in bigger seas) are transformational as regards comfort. BUT in a big sea they only create serious comfort for about 200 degrees of the 360 - they don't stop pitching in a head sea.

I agree with BartW that they don't make you do BJB's 10/10ths in the car. The passengers get uncomfortable long before the situation gets dangerous, and the stabs can mostly remove the discomfort, that's all. That said, I undoubtedly go to sea in conditions that I wouldn't dream of in an unstabbed boat, due to comfort factors. I once left Antibes for Mahon 270nm in a massive beam sea and was fine, but could not have done it that without stabs. Coastguard called me (as they do on AIS-ed boats in France) and asked me if I was sure. The trip was great!

I disagree with Porto on 3 points:
1. Sure, you can train everyone on seasickness but that means you ca'nt invite guests who are not hard core boaters, which rather restricts your social life, so "training" doesn't beat stabilisation in most people's book. Furthermore, Porto's comments relate to an "uncatered" boat where you have sandwiches on arrival - if you have chef/someone cooking while you're underway to the anchorage you can't expect them to work if the boat is rolling
2. Porto talks of top heavy boats implying his very non top heavy Itama is ok. It is in some respects, but a factor with non top heaviness is that when you do roll naturally the roll period is incredibly short, which is way more uncomfortable than a long roll period. Stability is much more complex that just talking of top-heaviness, but let's not go off on a lot of physics and googling (please!)
3. Pushing the throttles does indeed make for lots of "dynamic stability" That makes the boat not roll relative to the water surface - it keeps the boat relative to the water surface. Therefore when you have got a big beam sea the boat will roll as the waves pass under it. There is no way that the hull "knows" what horizontal - ie level with the horizon - is. So the boat will roll. Not in the "pendulum" way it rolls at anchor according to its natural roll period, but in time with the waves. Stabilisers however keep you level to the horizon, always. So dynamic stability/throttles is good, but let's not over sell it.

I'd be pretty sure that anyone who has been on a stabbed boat and felt the difference when turning them on/off would be very convinced of the benefits, and then it is the job of the skipper not to do the 10/10ths thing. I agree 100% with BartW

 

[Forty_Two]

Stabs are marriage savers, worth every pound

When we moved our GB42 to the SoF in 2001 after 21 years on the UK South Coast, what struck us the most (literally) was the wash from passing 80 footers:encouragement:. So we spent the 20k for Wesmars, best thing we ever did. Now when folks pass us a couple of hundred feet away (for a laugh) we don't care as we just go up & down a bit.

Whilst if we do get caught out by weather it's unbelievably more comfortable. They work much much better than I had ever imagined. I first had the idea to install them when crossing Lyme bay on route westward in a horrible beam sea.

Of course we are a slow boat, 8 knots. When clean I can WOT at 10 & you can feel her stiffen up I can understand it's so not such an issue for faster boats.

Mrs 42 would not have a boat without, neither would I now.

Very traumatic cutting such big holes in a wooden hull, still got the cutouts in my workshop.

 

[MapisM]

let's not go off on a lot of physics and googling (please!)

Good thing that I wasn't drinking a coffee while reading this! .

 

[NBs]

Hi all,

Thanks for all the answers, they confirmed my understanding of stabilization devices.

They are certainly comfortable and use if you have them if you loose money it can be a nice accessory for your boat. If you have a seaworthy boat you will surely also run without stabilizers either rock n roll or add gas and stabilize dynamically.

Boating a boat has great differences in the acceleration of speed and depth, but it does not discuss it any more because "JMF" is the right physics for endless conversation, boats are different and endless variable parameters.

NBs

 

[jfm]

...if you loose money...

That's a whole different thread(!) and should be a whole new module in Deleted User's man maths degree course.

My previous boat, a 2010 Squadron 78 hull #70 was the first one built with fins, and the only one on the market with fins when I sold it @18 months old. The very first guy to see it bought it on the spot for a very full price and I'm as sure as can be that I got my £100k back, plus the sale was easy.

Nowadays lots of 20-24m boats have stabilisation. Here's a piece of data: Fairline recently stopped Sq78 production at (I think) hull #114 and of those 45 boats starting with #70 I think about 2/3rds had fins. One has gyros, and the others were bare. That gives you an idea of the proportion (I'd say 2/3rds +) of 24m boats now build with stabilisation ex factory.

So when selling I guess you still get a premium over unstabilised, but you are not the only seller, so perhaps the premium is less than when I sold my last boat. I would think it is pretty hard to sell an unstabilised boat if you're a seller into the "less than 6 years old" market.

But is a whole different discussion I guess.

 

[MrB]

That's a whole different thread(!) and should be a whole new module in Deleted User's man maths degree course.

My previous boat, a 2010 Squadron 78 hull #70 was the first one built with fins, and the only one on the market with fins when I sold it @18 months old. The very first guy to see it bought it on the spot for a very full price and I'm as sure as can be that I got my £100k back, plus the sale was easy.

Nowadays lots of 20-24m boats have stabilisation. Here's a piece of data: Fairline recently stopped Sq78 production at (I think) hull #114 and of those 45 boats starting with #70 I think about 2/3rds had fins. One has gyros, and the others were bare. That gives you an idea of the proportion (I'd say 2/3rds +) of 24m boats now build with stabilisation ex factory.

So when selling I guess you still get a premium over unstabilised, but you are not the only seller, so perhaps the premium is less than when I sold my last boat. I would think it is pretty hard to sell an unstabilised boat if you're a seller into the "less than 6 years old" market.

But is a whole different discussion I guess.

I read NBs's post as "If you have SPARE money they are a nice accessory to have " lol. Translation thing.

 

[NBs]

That's a whole different thread(!) and should be a whole new module in Deleted User's man maths degree course.

My previous boat, a 2010 Squadron 78 hull #70 was the first one built with fins, and the only one on the market with fins when I sold it @18 months old. The very first guy to see it bought it on the spot for a very full price and I'm as sure as can be that I got my £100k back, plus the sale was easy.

Nowadays lots of 20-24m boats have stabilisation. Here's a piece of data: Fairline recently stopped Sq78 production at (I think) hull #114 and of those 45 boats starting with #70 I think about 2/3rds had fins. One has gyros, and the others were bare. That gives you an idea of the proportion (I'd say 2/3rds +) of 24m boats now build with stabilisation ex factory.

So when selling I guess you still get a premium over unstabilised, but you are not the only seller, so perhaps the premium is less than when I sold my last boat. I would think it is pretty hard to sell an unstabilised boat if you're a seller into the "less than 6 years old" market.

But is a whole different discussion I guess.

Hi,

I looked at the narrow point of view with just my own boat sign. I know only one new NT 42 installed seakeaper, again at the seller's order on a shop boat and it did not reach any further orders to equip a boat gyro stabilizer because NT Hull's design and weight distribution has been well and is really stable. There is also a range of 40 "-54" on-board features and it's a small additional price on a new boat so I completely understand your point of view as you are letting Sunseeker and same type models and V-Hull boats at or below Hull speeds are easily rolled due to underwater design and 80 " the price stabilization system is such a small slice to increase the money to get some comfort.

NBs

MrB yes, you are right, my bad English

 

[MrB]

MrB yes, you are right, my bad English

Don't worry NBs, your English is absolutely fine :encouragement:

 

[Portofino]

Hi,

I looked at the narrow point of view with just my own boat sign. I know only one new NT 42 installed seakeaper, again at the seller's order on a shop boat and it did not reach any further orders to equip a boat gyro stabilizer because NT Hull's design and weight distribution has been well and is really stable. There is also a range of 40 "-54" on-board features and it's a small additional price on a new boat so I completely understand your point of view as you are letting Sunseeker and same type models and V-Hull boats at or below Hull speeds are easily rolled due to underwater design and 80 " the price stabilization system is such a small slice to increase the money to get some comfort.

NBs

MrB yes, you are right, my bad English

Well put :encouragement:

You can get faster planing 24 M size like Pershing s , Rivas and there even a Itama 75 .
These rely on the dynamic stability, but I suspect the onwners buying decisions are from a different list from the FB / floating holiday home guys -
Interesting to see “ factory fit “ fins #stats on those eg a Riva 84 as a typical example to exclusively limited .

 

[jfm]

...only one new NT 42 installed seakeaper, again at the seller's order on a shop boat and it did not reach any further orders to equip a boat gyro stabilizer because NT Hull's design and weight distribution has been well and is really stable.

That is a fallacy - the sort of thing some salesmen say when they don't understand stuff. All boats of the type discussed here roll in a beam sea if not stabilised. It is theoretically possible to build one that doesn't, =an ultra SWATH boat that stands taller than the wave height, but that's an extreme solution not practical for us. If your NT42 sits level in a flat anchorage, then it MUST roll when a wave comes at its beam and lifts the side of the hull. In a rolly anchorage, it MUST roll in time with its roll period, because it is a pendulum (centre of buoyancy is not in same place as centre of gravity - that is a pendulum) and the arrival of a wave at the beam moves the centre of buoyancy towards the wave, which results in a torque applied to the hull. This is true for any non-SWATH boat. There is no getting away from the physics.

 

[MapisM]

That is a fallacy

Positively +1.
And just to reinforce if possible what jfm said, even SWATH vessels, whenever they should cruise in beam seas with waves much longer than the distance between their hulls (which is perfectly possible!), are also bound to "copy" the sea motion, hence roll - potentially even more than a stabilized monohull.

 

[Deleted User YDKXO]

I looked at the narrow point of view with just my own boat sign. I know only one new NT 42 installed seakeaper, again at the seller's order on a shop boat and it did not reach any further orders to equip a boat gyro stabilizer because NT Hull's design and weight distribution has been well and is really stable. h

That has probably far more to do with the fact that gyro stabs work very well at zero speed and increasingly less well as speed increases so if the NT42 owner was hoping the Seakeeper would reduce roll significantly at speed, he was probably disappointed. If you want stabilisation at any speed, then fins are the only way to go. However if stabilisation at anchor is your main aim then a gyro is a good choice

 

[Deleted User YDKXO]

2. Porto talks of top heavy boats implying his very non top heavy Itama is ok. It is in some respects, but a factor with non top heaviness is that when you do roll naturally the roll period is incredibly short, which is way more uncomfortable than a long roll period. Stability is much more complex that just talking of top-heaviness, but let's not go off on a lot of physics and googling (please!)

I dont want to get into a physics argument either mainly because I usually lose the argument! Just to say that Nordhavns, which are probably some of the most seaworthy production boats out there, generally have a lot of top hamper (check out the N55) but that is for a reason. They will tell you that they design their boats in that way so as to lengthen the roll period because, as you say, they believe a long roll period is more comfortable than a short one

 

[Portofino]

I dont want to get into a physics argument either mainly because I usually lose the argument! Just to say that Nordhavns, which are probably some of the most seaworthy production boats out there, generally have a lot of top hamper (check out the N55) but that is for a reason. They will tell you that they design their boats in that way so as to lengthen the roll period because, as you say, they believe a long roll period is more comfortable than a short one

But arn,t we back to causation and effect ?
Or in simplistic terms chicken and the egg ?
Reason i drop this in is that in the original thread , that this thread is a side shoot - LRs Del trip , MapishM said stabs were 100 % factory fit on long range ocean stuff that folks spends weeks bobing about on - or try not to — bob about - as they plod on @6 /8 knots or what ever siping fuel ,staring at a blank view !

You don,t see any short snap role periods btw when bombing along in a fast planer cos the “ dynamic stability “ takes over .

Regarding JFM,s 3 point above ( somewhere? )
In a big beam sea ,and linking to Robins point on his thread of not seeing out properly ,if the boat heeled over etc - we have speeded up to go a fast as I dare and actually sat either in the trough on with skill at the helm sat it on top of the crest .
I,am talking when we disappear waaay below the crests when in a trough .So deep ,or so high the swell we are invisible to others .
Then bit like going up / down a steep hill in a car turn — up / down and put the boat where we want .
Don,t like spending too much time in a huge trough in a beam sea @30 knots + cos obviously you can’t see who’s about coming from port or stb ,
buts it not nauseating riding up or down a hill that’s the point .