Humphree stabilisation system?

[Cheery]

The patent won't be on the use of 24v per se; that isn't patentable

A former neighbour of ours was a computer programmer for a company developing mass spectrometers. He said, iirc, they were fined for using a particular voltage as it was copywrite protected. I obviously asked how the hell can you copywrite a voltage. As it was an American company I assume smart arse lawyers were involved. Ironically the company is now owned by the same people who employ my Dr. friend I mentioned above.

I'm still none the wiser years later (this was late 90s).

 

[jrudge]

Oi, that's what I argued with!

I think the 50% was me. I just assumed that drilling holes in the side and routing cables was simpler than cutting chunks of the boat away re a gyro ... clearly not!

 

[jfm]

Oi, that's what I argued with!

I think the 50% was me. I just assumed that drilling holes in the side and routing cables was simpler than cutting chunks of the boat away re a gyro ... clearly not!

Oops, sorry both, my mix up!

 

[Deleted User YDKXO]

Thanks to Mapism, jfm, Bart, Jtb and Pete for your inputs. First the flopper stopper remark was just a throwaway line; I wouldn't consider fitting them to my boat in a million years! My situation is that I keep toying with the idea of fitting some kind of stab system to my boat, hence my interest in the Humphree system, but at the same time I'm trying to be sensible about it. The cost for any stab system once you factor in fitting, VAT etc is very high and given the fact that I don't use my boat as much as some of you guys and, as ever, I don't know how long I'm going to keep it, I'm not sure I should spend the money. I'm not convinced I'd get back any of the cost come resale time either. FWIW intuitively I favour a gyro because I think I've got the perfect location for it and because I really want the stab for at rest or d speed operation. Ferrettis always have a vast void under the bathing platform which is nominally designed to store a jetski and my boat could easily take a Seakeeper 16 down there although as Mapism has pointed out, it can be a bit wet in this space and I'm not sure how that would affect the gyro's long term performance. FWIW when Ferretti fit their ARG gyro in a 630 like mine they put it in the engine bay

Anyway the thinking about it still goes on!

 

[petem]

Mike, I think you should save your money for your 'forever boat'.

 

[jfm]

I really want the stab for at rest or d speed operation.

First off mike, i think you are not realising that you want the stabilisation for all speeds. You will never want the thing turned off. It is just not true that P boats self stabilise at P speeds to a point where stabilisation is not of significant benefit. In a beam sea for example, they roll with the waves and stay flat to the water surface. Really, you want full stabilisation at all times if you're spending this sort of money.

Second, gyro is a great thing at rest but at d speeds a gyro will give up long before a fin. Once you get into big or even moderate seas at d speeds, each wave lasts a long time, especially say when it's a quartering sea. A gyro can only provide stabilisation torque for a short interval of time then it hits its stops. The big wave won't have finished doing its thing. A fin, in contrast, can provide an antiroll force all day long without ever hitting its stops because it has no stops. It can stay angled all day if your wave period is all day. The concept of "can only provide an anti roll torque for a limited time period" simply does not apply to fins. Now when you get to P speed it is a finer debate: the waves do their thing faster in some scenarios at least (eg quartering seas) and the gyro has benefit of no appendage drag.

My analysis is that gyro and fin are similar performers at rest but fins are better underway and if you are a 23knt cruiser the appendage drag isn't significant, so fins win everytime in my book for new build in a modest speed P boat (as opposed to a 40 knot Pershing). For retrofit, you have to consider the installation issues of course and that might dictate the fin or gyro answer

At first sight I wouldn't think the aft locker in many ferrettis incl your 630 is a great place for a gyro due to risk of water ingress, but come to think about it if you can somehow seal the lid reliably it should be ok, and provide for a low-cost installation. Go for it!

 

[vas]

At first sight I wouldn't think the aft locker in many ferrettis incl your 630 is a great place for a gyro due to risk of water ingress, but come to think about it if you can somehow seal the lid reliably it should be ok, and provide for a low-cost installation. Go for it!

slightly confused,

shouldn't gyro be placed closer to the COG of the boat compared to the rear end of it???
Am I missing something?

V.

 

[jfm]

slightly confused,

shouldn't gyro be placed closer to the COG of the boat compared to the rear end of it???
Am I missing something?

V.

Vas, the gyro applies a torque along the boat's roll axis. It makes no difference on that score whether it is in the bow, stern or midships. Pearl 75 has them in the bow, btw

Of course the dead weight of the gyro might be relevant to boat trim, but that's nothing to do with anti-roll

 

[Deleted User YDKXO]

slightly confused,

shouldn't gyro be placed closer to the COG of the boat compared to the rear end of it???
Am I missing something?

V.

From the Seakeeper website

Where does the gyro have to be located in the boat?
From a theoretical perspective, the Gyro Stabilizer can be located anywhere in the boat hull. From a practical perspective, Seakeeper strongly recommends that the Gyro Stabilizer be installed aft of amidships to minimize vertical accelerations due to wave impacts.

In fact I've been told as far aft as possible

 

[Deleted User YDKXO]

First off mike, i think you are not realising that you want the stabilisation for all speeds. You will never want the thing turned off. It is just not true that P boats self stabilise at P speeds to a point where stabilisation is not of significant benefit. In a beam sea for example, they roll with the waves and stay flat to the water surface. Really, you want full stabilisation at all times if you're spending this sort of money.

Second, gyro is a great thing at rest but at d speeds a gyro will give up long before a fin. Once you get into big or even moderate seas at d speeds, each wave lasts a long time, especially say when it's a quartering sea. A gyro can only provide stabilisation torque for a short interval of time then it hits its stops. The big wave won't have finished doing its thing. A fin, in contrast, can provide an antiroll force all day long without ever hitting its stops because it has no stops. It can stay angled all day if your wave period is all day. The concept of "can only provide an anti roll torque for a limited time period" simply does not apply to fins. Now when you get to P speed it is a finer debate: the waves do their thing faster in some scenarios at least (eg quartering seas) and the gyro has benefit of no appendage drag.

My analysis is that gyro and fin are similar performers at rest but fins are better underway and if you are a 23knt cruiser the appendage drag isn't significant, so fins win everytime in my book for new build in a modest speed P boat (as opposed to a 40 knot Pershing). For retrofit, you have to consider the installation issues of course and that might dictate the fin or gyro answer

At first sight I wouldn't think the aft locker in many ferrettis incl your 630 is a great place for a gyro due to risk of water ingress, but come to think about it if you can somehow seal the lid reliably it should be ok, and provide for a low-cost installation. Go for it!

Thanks jfm. Fair comment as ever

 

[Nick_H]

From the Seakeeper website

Where does the gyro have to be located in the boat?
From a theoretical perspective, the Gyro Stabilizer can be located anywhere in the boat hull. From a practical perspective, Seakeeper strongly recommends that the Gyro Stabilizer be installed aft of amidships to minimize vertical accelerations due to wave impacts.

In fact I've been told as far aft as possible

One gyro owner who had it installed right at the stern thinks it affects manoeuvring at idle speeds. It seems odd, but he's an experienced owner and says it happens consistently. He's taken to switching it off as they come into port.

I've not noticed anything similar with mine mounted a couple of meters further forward

Have you spoken to Seakeeper about the results you'd achieve with a model 9? My gut feel is it would still have a big effect, as a model 8 with 15% less angular momentum worked well on a 36 tonne Squadron 65. Also worth a pm to A&K to see what kind of deal they negotiated for theirs.

 

[MapisM]

Why would you choose gyros btw?

As BartW already said, but not only.
Travelling ATM, and I hate typing on a mobile, but will revert ASAP.

Ok, back home now, so I can elaborate a bit, enjoying the luxury of a decent keyboard.

Drag has already been mentioned and is pretty obvious, but we must also bear in mind that its relation with speed is exponential, not linear: the higher drag associated with a 5 knots speed increase is neither here nor there when going from 5 to 10, while it begins to be relevant from 10 to 15, much more so from 15 to 20, and so forth.
So, putting inside a boat huge engines, good enough for 30+ knots cruising speed, and then stick some big fins on her bottom, well, that doesn't sound like a brilliant idea to me, to start with.

But the hull size/displacement/shape also matter a lot.
Actually, what really matters is the roll period (RP for short), which mostly depends on the metacentric height, but let's leave that complication aside.
We can consider size, weight and shape instead, because they are among the most intuitive components eventually affecting the RP.
Now, for any given length, P hulls are lighter, have less draught and ultimately a shorter/snappier RP, when compared to D hulls.
And these are the conditions where gyros are more effective - or to put it another way, their physical limitations are less relevant.

But of course, there isn't such thing as a clear-cut RP limit above which the advantages of fins prevail over gyros - also because at least to some extent that's a matter of personal preference.
'Fiuaskme, while fins make perfect sense also for smallish D hulls, and indeed there are 40' trawlers with fin stabs, it would take a pretty substantial P hull (surely not smaller than 70' or so) to make me prefer fins over gyros.
Then again, if anyone is thinking to use a 50' P boat capable of 35 knots mostly for pootling, possibly also in heavy seas and with long swells, well, fin stabs would work better than gyros.
I'd rather question the overall boat choice than the type of stabs in this case - horses for courses springs to mind - but that's another matter.

Re. a potential gyro placement on your boat, as much as I can see the appeal of using the otherwise wasted space under the swim platform, fwiw I'm not sure I'd fancy the idea of putting there such an expensive bit of kit.
No matter how well you could seal it, it's bound to be always a very salty/humid environment...
...otoh, I can't think of where Ferretti stick their OEM gyro in the e/r - Either I don't remember your e/r spaces very well, or it must be pretty small!

 

[jfm]

we must also bear in mind that its relation with speed is exponential, not linear: the higher drag associated with a 5 knots speed increase is neither here nor there when going from 5 to 10, while it begins to be relevant from 10 to 15, much more so from 15 to 20, and so forth.
So, putting inside a boat huge engines, good enough for 30+ knots cruising speed, and then stick some big fins on her bottom, well, that doesn't sound like a brilliant idea to me, to start with.

Yes mathematically, but you ignore the fact that the absolute drag levels are small. I mean, you could apply your analysis above to a seacock or a depth transducer, whose drag also increase much more from 15-->20 than from 5-->10, but the absolute size of the drag is tiny, even at 100 knots. And so it is with fins: the drag of fins is very small compared with the drag of the hull itself. The data shows that a pair of 1msq fins requires about 100bhp at 25 knots, compared with say 2500hp for the hull. 100hp or 4% is not a completely trivial amount, but it's not enough to compromise your comfort and stability for, in my book

Then at higher speeds you get a bit of lift from fins which reduces hull drag. I believe that Sunseeker/Princess/Fairline all report that there is no difference between top speed of finned boats compared with the identical model fin-less

So I don't think that, even allowing for the exponential relationship, drag values are significant at say 25 knot cruising.

 

[MapisM]

Then at higher speeds you get a bit of lift from fins which reduces hull drag.

Well, I for one but don't buy that. Why not stick fixed moulded fins on every hull, if it were that easy?
Btw, funny that you should mention 100 knots, because many years ago, Buzzi chief mechanic told me of something that allowed them to gain 2 to 3 knots, exactly at that speed.
Those things were two 30mm bolt heads, facing the lower side of their surface transmission (hence touching the water).
They reversed the installation, leaving the bolt heads on the upper side, and that was the result.
At that speed, I honestly doubt that some plastic fins wouldn't fall apart completely.

PS: coming to think of it, does a Sq78 really demand 2600hp @ 25kts?
Which sort of rpm and load do you see at that speed?
Sounds like a helluva lot of power to me, that would only make sense if you'd be pretty near to WOT.

 

[jfm]

OK, but there's no need to buy it because it was a marginal point away. Let's assume I'm wrong on it; fact remains that the drag of a pair of 1m sq fins at 25 knots is around 100bhp, when the hull itself is taking 2500hp. A pair of 0.6m sq like Bart's will take less*. Each to their own, but that's a pretty marginal difference in my book, compared with comfortable cruising/less seasickness, no spillage of G+T
(*I'm happy to be corrected but I seem to remember BartW reported there was no meaningful difference in WOT top speed of BA before and after his fin installation. That was an AOTBE scenario. Ergo his fins cannot be creating meaningful drag even at P speed.)

 

[MapisM]

a pretty marginal difference in my book, compared with comfortable cruising/less seasickness

Agreed, if we were comparing fin stabbed cruising with non-stabbed cruising. But it's not like gyros don't do anything!
Yes, there are conditions where fins are better and I already conceded that, but in my experience most P boats (or any pleasure boat, for that matter!) are rather tied to the dock anyway, in F7+ seas.

Sorry, I suppose I added the PS to my previous post while you were replying....

 

[jfm]

Agreed, if we were comparing fin stabbed cruising with non-stabbed cruising. But it's not like gyros don't do anything!
Yes, there are conditions where fins are better and I already conceded that, but in my experience most P boats (or any pleasure boat, for that matter!) are rather tied to the dock anyway, in F7+ seas.

Sorry, I suppose I added the PS to my previous post while you were replying....

Hmm yep actually i agree, if we accept your premise. I mean, if we assume that P boats only go out on modest seas, and so not spilling G+T is truly the main concern, not surviving Perfect Storms, then yes a gyro is arguably the better choice (ignoring things like loss of interior space, which is an each-to-their-own thing so let's ignore it). But in my defence I was working on the basis that P boats do go out in quite big seas!:encouragement:

Regarding the PS, I was using very ballpark numbers. I don't know the exact bhp at 25 knots. Obviously it is 3244hp (less internal losses) at 32 knots. I need to look again but iirc it's around 2000hp (65% load) at my usual 22 knots cruise). BTW, the difference between full fuel and 1/4 fuel is more drag than the fins. It adds a litre per mile of fuel burn at P speeds. Which is why I try to drive round on ~empty tanks for local cruising!

 

[BartW]

Then at higher speeds you get a bit of lift from fins which reduces hull drag. I believe that Sunseeker/Princess/Fairline all report that there is no difference between top speed of finned boats compared with the identical model fin-less

I can not believe that the lift from the stabs can create less drag, at least not on my setup,
we have calibrated the zero position of the fins so that they have minimum drag when free floating, (at D and P speed)
that was 3 or 4 degrees out off the central ax-line of the boat iirc.

AFAIK, That reason that boat or stab manufacturers claim that there is no loss of speed with stabbed boats, is that the boat rides more smooth and straight from point a to b,
A non stabbed boat will dig in to waves, or has to cope with the movements of waves where as a non stabbed boat ploughs smooth through the waves, going much more straight.
I have no real evidence of that, but having much experience how smooth the stabbed boat ploughs through waves, I have the subjective feeling that this claim could be correct.

 

[piratos]

LOL, much less of course, but I'm not sure that the spreaders - without which they are practically useless - would fit with the sleek profile of a Ferretti...
...not to mention the deployment procedure, compared to just pushing one button - see below.
Re. your previous question on the damping percentages, forget them. Totally meaningless numbers, marketing BS at its best.
The simple truth is that all systems work very well, and the difference any of them can make to the comfort of a monohull mobo is like day and night.
If you should consider retrofitting a stab system to your boat, in terms of effectiveness you can't go wrong with any of them.
But fwiw, in a 20m P boat capable of 35knots, I'd choose gyros in a heartbeat.

Hello,
Flopper Stoppers are only for anchoring, underway Paravanes and as you say not really suitable for a Planning boat...

In the whole discussion about stabilizers it is in the end a question whether its worth the cost. Do you want to eliminate roll, or are you happy to reduce.

The cost to reduce roll at anchor with Flopper Stoppers are mininal, so are the use of tanks....: https://www.youtube.com/watch?v=dtEJamVv05M
(and yes I realize that is only ONE of many alternatives)

 

[jfm]

Bart, have you experienced any meaningful loss of top speed, or increase in fuel burn, since fitting the stabs to BA?