stabilizer systems and seakeaping

[jfm]

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

Exactly! And, a long roll period boat is much more easily/effectively stabilised than a short roll period boat

 

[jfm]

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 .

I agree that it's less nauseating. But fact remains that if you are only "dynamically stabilised", while you get the important benefit of no pendulum-motion rolling, you unfortunately do not remain flat to the horizon and instead you remain flat to the sea surface. That must be so because your hull cannot know where the horizon is, whereas the inclinometers/accelerometers in a stabilisation system do. You cannot stand a full champagne glass beside you on the dashboard in your big troughs scenario (that being the ultimate test ).

One other point is that I think you speak as a helmsman Porto, and rather like in a very fast car the driver is less tuned into the horribleness of the motion. The passengers feel it much more. Especially the most important person on board, namely the chef with boiling pot of pasta.

 

[Portofino]

I agree that it's less nauseating. But fact remains that if you are only "dynamically stabilised", while you get the important benefit of no pendulum-motion rolling, you unfortunately do not remain flat to the horizon and instead you remain flat to the sea surface. That must be so because your hull cannot know where the horizon is, whereas the inclinometers/accelerometers in a stabilisation system do. You cannot stand a full champagne glass beside you on the dashboard in your big troughs scenario (that being the ultimate test ).

One other point is that I think you speak as a helmsman Porto, and rather like in a very fast car the driver is less tuned into the horribleness of the motion. The passengers feel it much more. Especially the most important person on board, namely the chef with boiling pot of pasta.

Agree

You can,t really do the galley in a fast planer in any other than a calm ish sea .
We have done in fair conditions s ,but it’s not dialled into a plan - cooking .

@anchor without stabs ( gyros ) there has been a few occasions where after a bit we have up anchored and moved cos of passing wakes / fetch rolling in etc ,
There’s allways a flat side to say Cap d Antibes or Cap Ferrat , it’s opersite the rolley side

As said stabs are a huge addition to comfort generally , and nice to have etc , but we have enough dynamic stability running on tap and seem to be able thus far live with the static stability.
Dogs not been sick —- yet ,so boat even passes the dog test

 

[jfm]

Agree

You can,t really do the galley in a fast planer in any other than a calm ish sea .
We have done in fair conditions s ,but it’s not dialled into a plan - cooking .

@anchor without stabs ( gyros ) there has been a few occasions where after a bit we have up anchored and moved cos of passing wakes / fetch rolling in etc ,
There’s allways a flat side to say Cap d Antibes or Cap Ferrat , it’s opersite the rolley side

As said stabs are a huge addition to comfort generally , and nice to have etc , but we have enough dynamic stability running on tap and seem to be able thus far live with the static stability.
Dogs not been sick —- yet ,so boat even passes the dog test

You've got the dog well trained Can (s)he snowboard too

 

[Boatbore]

I know that the subject of my rebuild, my sunseeker Superhawk 50, has already bought mirth to the good citizens of this forum....... but when I tell you I have included a seakeeper gyro as well, I can almost feel the tears streaming down your cheeks !

In practice, and Porto alludes to this above, beach hanging in the SoF very often involves nose to wind, but sadly beam to sea (which is not really sea..... it’s Porto and JFM and about 1000 others zooming past ) which often results in rose in the lap...... a terrible waste.

A friend of mine has a great big Magnum (I though it was 80ft but I’m told it’s actually a 70) with gyros and they have been very successful in reducing spillage....... on the sunseeker, the beam is very narrow but seakeeper reckon that the device will reduce 85% of roll worst case, and 95% best case....... tbh, I’d be chuffed with a lot less reduction than that.

But all of the above is based on sitting at anchor, not underway. And it has been interesting to learn that seakeeper also recommend running with the gyro on. And the reviews from similar long, thin, pointy boats in the USA that have fitted the stabiliser confirm that it has a surprisingly beneficial effect.

Of course it is possible to roll further than the gyros limit, at which point it ceases to be effective, but the smaller rolly moves are apparently reduced effectively and the boat for the most part runs flatter and with more stability.

Boat goes in the water next week for sea trials, I guess I will know more after that !

 

[Deleted User YDKXO]

I know that the subject of my rebuild, my sunseeker Superhawk 50, has already bought mirth to the good citizens of this forum....... but when I tell you I have included a seakeeper gyro as well, I can almost feel the tears streaming down your cheeks !

Not at all. Why? I put a gyro in my boat last year simply because I wanted a bit of peace at anchor in the SoF and jolly good at that it is too. Its just not so good at stabilising the boat underway and yes last season at least I did run it all the time underway. Maybe thats because my boat is relatively beamy and heavy for a planing boat of its size and if I was doing it again and planning to keep this boat for ever I'd go one size up on the gyro in an attempt to gain better stabilisation underway

 

[Portofino]

Yup Pampelonne can be very bumpy as you say from every 8ugger else bombing about .
Sounds good ,infact the whole boat imho .:encouragement:
What sort of genny have you got ? Just thinking of the drone .@ anchor .

Where’s it gonna fit and how many extra kg,s ?

Great project

 

[markc]

Reprising the Air Suspension comparisons, I just got my Porsche back today having paid £2600 to fix the air suspension. That's an option I'm unlikely to tick again! Quite fancy a gyro for wine spill reduction at anchor

 

[MJGH]

What sort of genny have you got ? Just thinking of the drone .@ anchor .

Oh god be careful about saying too much as someone likes to shoot drones!http://www.ybw.com/forums/images/smilies/smile.png

 

[MapisM]

All well and good, but since nobody can tell that I'm biased AGAINST stabilizers...
...On a triple Trimax surface drives boat? Over my dead body!
You were doing well by chucking the heavy passerelle overboard, just be consistent and throw away also the genset, the liferaft and anything else heavy and useless, while you are at that.
Your boat is specifically built to upset Itama owners by running circles around them D), and you want to ballast her?
Next thing you will tell us that you are detuning her Yanmars for durability...

 

[jfm]

Yup, ditto, no mirth here Bb; you have made an excellent choice and you'll love it. Yes, run it underway- it will be useful especially in moderate seas.

 

[benjenbav]

Probably need to run SK underway to spool up in order to be useful for stabilising that first cocktail when you anchor.

Which is the one that really counts, of course. :encouragement:

 

[petem]

I know that the subject of my rebuild, my sunseeker Superhawk 50, has already bought mirth to the good citizens of this forum....... but when I tell you I have included a seakeeper gyro as well, I can almost feel the tears streaming down your cheeks !

On the contrary, I'm liking your Squeaker posts. I think the repaint is a bit sacrilege but otherwise it's great that you're enhancing the boat. I'm sure Robert Braithwaite would approve. We do need more pics though.

 

[Boatbore]

Porto, I have fitted the small Fisher panda 3.5 kw single cylinder generators. This is approx 80kg, and replaces the old ONan 4 kw that weighed 200kg. (If anyone wants it, they can pretty much have it. It works but needs some love). But my stabiliser is DC, and runs off a big battery bank. The generator kicks in automatically when the battery discharges to a certain degree...... calculated to be 3 to 4 hours after the engines switch off (3 engines = 3 big alternators so we make lots of battery juice as we go). On top of that the generator is incredibly quiet and you can talk over it even in the engine room. From outside it’s barely detectable.

 

[Boatbore]

Mapis. I knew that someone was going to agree that I must be mad ! I am concluding the same myself. In practice I removed 100 kg of passarelle from the very back of the boat, and another 200kg of generator, also in the bathing platform. I then added 250 kg of seakeeper, but amidships. The SK is more or less underneath the drivers seat in the only decent locker that the boat has. I probably added a small amount of weight with an extra battery or so, but also quite far forward ........ so all in I am probably not far off the original weight, maybe 50 kg lighter or so, but it’s 15 feet further forward and no longer hanging over the trimax drives.

 

[Boatbore]

Reprising the Air Suspension comparisons, I just got my Porsche back today having paid £2600 to fix the air suspension. That's an option I'm unlikely to tick again! Quite fancy a gyro for wine spill reduction at anchor

Anything that costs £2600 would be at the absolute bargain end of the scale on my particular project !!!!

 

[Boatbore]

On the contrary, I'm liking your Squeaker posts. I think the repaint is a bit sacrilege but otherwise it's great that you're enhancing the boat. I'm sure Robert Braithwaite would approve. We do need more pics though.

I know what you mean about the paint, but I think you’ll like it when it’s done. If you think the paint is sacrilege....wait until you see the new interior !

 

[Boatbore]

All, thanks for the supportive messages....... I was only making fun of myself because you’d have to be a bit deranged to take a 15 year old boat and then spend enough that the total spend would have bought a brand new 40 footer !

For me, there is a great satisfaction in identifying exactly how I want to use my boat and then finding the boat that can most easily deliver tha once tweaked. That brand new 40 footer whilst lovely, wouldn’t do 50 knots, wouldn’t be stabilised and wouldn’t suit me as well !

 

[markc]

Anything that costs £2600 would be at the absolute bargain end of the scale on my particular project !!!!

Ahh, sorry Boatbore that was just me referencing an earlier thread where stabs were compared to choosing air suspension in a car. Obviously one of the many man maths benefits of our boating is to make our motoring appear cheap!

 

[Boatbore]

You were doing well by chucking the heavy passerelle overboard, just be consistent and throw away also the genset, the liferaft and anything else heavy and useless, while you are at that. :

Can’t resist making a joke about Mrs BB not wanting to be left behind.......