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Author Topic: Stability - how to avoid rolling upside down  (Read 2262 times)

Colin Bishop

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Re: Stability - how to avoid rolling upside down
« Reply #25 on: September 27, 2019, 10:15:33 AM »

The MM article is interesting as the anti rolling tanks fitted to full size vessels in the 1930s rarely worked and were soon taken out of use. I believe that the main problem was that sufficient volume of water couldn't be transferred across the beam of the vessel quickly enough to counteract the rolling. In a model this would be less of an issue and perhaps one instance where scaling down actually improves things over full size practice.

Colin
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Jerry C

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Re: Stability - how to avoid rolling upside down
« Reply #26 on: September 27, 2019, 04:10:17 PM »

Iíve sailed in a car carrier with anti roll (flume) tanks which worked well. Also sailed in ships with active wing type which also did the job however to a seaman they take some getting used to due to ship not doing what one expects.
Jerry.

Colin Bishop

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Re: Stability - how to avoid rolling upside down
« Reply #27 on: September 27, 2019, 04:49:49 PM »

Quote
Iíve sailed in a car carrier with anti roll (flume) tanks which worked well. Also sailed in ships with active wing type which also did the job however to a seaman they take some getting used to due to ship not doing what one expects.

I assume that there were some sophisticated control arrangements for moving the water around - something the 1930s ships which tried the idea did not have. They were tried in large passenger liners but after WW2 stabilisers seem to have become the favoured way of reducing rolling.

I was interested to hear that they are still used in modern vessels though, you learn something new every day!

Colin
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Jerry C

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Re: Stability - how to avoid rolling upside down
« Reply #28 on: September 27, 2019, 05:27:32 PM »

https://www.hoppe-marine.com/solutions/flume-roll-damping Thereís a lot of drag with active foil type and very complex plus the need to house them for berthing. No moving parts with flume tanks just varying quantity to fine tune.
Jerry.

Colin Bishop

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Re: Stability - how to avoid rolling upside down
« Reply #29 on: September 27, 2019, 05:28:58 PM »

Thanks for that Jerry.Colin
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Jerry C

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Re: Stability - how to avoid rolling upside down
« Reply #30 on: September 27, 2019, 05:44:26 PM »

Colin, there was a story doing the rounds that a Type 42 Destroyer at the Spithead Review was ordered by Her Maj to ďRoll your ship CaptainĒ. Apparently the foils can be operated manually.
Jerry.

Colin Bishop

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Re: Stability - how to avoid rolling upside down
« Reply #31 on: September 27, 2019, 06:09:34 PM »

Oh yes, fin stabilisers can be operated manually and I have read that they are often used during sea trials to initiate a roll as part of the stability tests.

Obviously it only works when the ship is making a reasonable speed.

Colin
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Jerry C

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Re: Stability - how to avoid rolling upside down
« Reply #32 on: September 27, 2019, 06:12:33 PM »

And thatís another plus for flume tanks they work when hove to and at anchor
Jerry.

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Re: Stability - how to avoid rolling upside down
« Reply #33 on: September 28, 2019, 09:14:33 AM »

Has anybody tried an active/dynamic stability system in their model boat - if so what did you do and what were the results?

I have had 2 stabilisation ideas on my project list for a while - one has a higher chance than "even" of working but as with all experiments time will tell...

C-3PO
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Colin Bishop

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Re: Stability - how to avoid rolling upside down
« Reply #34 on: September 28, 2019, 09:30:03 AM »

Quote
Has anybody tried an active/dynamic stability system in their model boat - if so what did you do and what were the results?

You could try scaling one of these installations down...

Colin

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C-3PO

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Re: Stability - how to avoid rolling upside down
« Reply #35 on: September 28, 2019, 09:48:47 AM »

Hi Colin,

An active Gyro is one of the easier options and one on the things on my project list that I have got to quite an advanced stage - I intend to test it in a boat in the next few weeks rather than in the bath tub - I expect results to be remarkable as early experiments have been really promising!!

I just need to scale up my solution, then break it down to the most simple cost effective one as right now the cost is approx £200 a pop!

C-3PO
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derekwarner

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Re: Stability - how to avoid rolling upside down
« Reply #36 on: September 28, 2019, 10:37:13 AM »

I thought that even Jewels Verne understood engineering design dictated one element for Port & the second element for Stdb


Or mirror reversed components ....for balance  O0 

These look like giant oily water/fuel centrifuges with plastic bowls 
{-)


Derek
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Derek Warner

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Colin Bishop

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Re: Stability - how to avoid rolling upside down
« Reply #37 on: September 28, 2019, 11:13:05 AM »

I don't think it's anything to do with port or staboard Derek. More a question of the flywheels being massive enough to exert a direct leverage on the structure of the ship. The flywheels in the Conte de Savoia weighed 175 tons each and she had three of them. The effect of the gyroscopes was purely mechanical so they had to be heavy.

However in a drone, the gyroscope can be small and lightweight because it only has to provide signals to the speed controllers of the electric motors.

Colin

PS: Jewels Verne? Your auto correct needs educating.
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warspite

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Re: Stability - how to avoid rolling upside down
« Reply #38 on: September 28, 2019, 11:47:39 AM »

The Mersk ship 'Starfish' has a flood tank above the bridge to counter roll - according to the biggest ship builders series on Quest.


Jewels HA HA HA {-)  what a diamond
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derekwarner

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Re: Stability - how to avoid rolling upside down
« Reply #39 on: September 28, 2019, 12:16:33 PM »

Colin...........one of the problems with Google or Wiki.......is who checks the checker? ..............

The images you presented are not real or scale........

Your comment of port nor stdb >>:-(  [in the context] is speculative, inconclusive and certainly not necessarily correct

Have you actually seen examples of giant oily water/fuel centrifuges with glass bowls?

There are no massive flywheels shown.........just far distant thoughts from a mind many nautical light years %%  from reality 

Derek
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Derek Warner

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Colin Bishop

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Re: Stability - how to avoid rolling upside down
« Reply #40 on: September 28, 2019, 01:21:40 PM »

Sorry Derek, but you know not whereof you speak!

Those two images were taken by little 'ole me at the wonderful Ocean Liner Exhibition held last year at London's Victoria and Albert Museum.

https://www.vam.ac.uk/exhibitions/ocean-liners-speed-style

They are of a cutaway sectional model of the Italian liner Conte De Savoia loaned to the exhibition from the Paolo Piccione collection.

They were described in 'Shipping Wonders of the World' which details the gyroscope installations here:

https://www.shippingwondersoftheworld.com/rex.html

'Nuff said?  %)

Colin


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derekwarner

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Re: Stability - how to avoid rolling upside down
« Reply #41 on: September 28, 2019, 11:03:14 PM »

Well I'll eat my hat  :embarrassed:  ...apologies Colin.........[wonder if Tomato or BBQ sauce will taste betta?]  :-X


Those large cylinderical + pointy ended drums are Gyroscopes..........still bet there is an error in the model as the two elements are off axis  <*<  within the vessel

NB.....the image from your posting is I suspect one unit as being manufactured [& tested] in the Vickers-Armstrong British workshops

Derek

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Derek Warner

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Colin Bishop

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Re: Stability - how to avoid rolling upside down
« Reply #42 on: September 28, 2019, 11:17:15 PM »

Don't choke on the corks Derek.


Colin
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derekwarner

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Re: Stability - how to avoid rolling upside down
« Reply #43 on: September 29, 2019, 12:05:34 AM »


So whilst eating my Akubra Hat for breakie   {-)  .....& to better understand from Collins postings, I found and watched this amazing Video on the Sperry Stability Gyroscope as fitted to early steam and warships.........symmetry of axis is a constant thought

yum yum....& well worth watching


https://www.youtube.com/watch?v=De8c15TFoPk


It is a little unclear, however the three Stability Gyroscopes as manufactured by Vickers-Armstrong in Britian for the Italian Liner Conte De Savoia were actually built under Licence to the American Sperry Conglomerate...[I use this term as at one stage, Vickers in the US were Sperry-Vickers-Sperry Rand]


Derek
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NickelBelter

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Re: Stability - how to avoid rolling upside down
« Reply #44 on: October 01, 2019, 01:18:19 PM »

Has anybody tried an active/dynamic stability system in their model boat - if so what did you do and what were the results?

I have had 2 stabilisation ideas on my project list for a while - one has a higher chance than "even" of working but as with all experiments time will tell...

C-3PO

I had a large freighter model with an open ballast tank running the length of the cargo hold.  It did lessen the pitching and rolling a bit to have the water sloshing around with the delay, but I can't say how much was due to that and how much was due to it being a whole six foot long and h e a v y!
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GG

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Re: Stability - how to avoid rolling upside down
« Reply #45 on: April 29, 2020, 04:15:17 PM »

Keeping myself occupied whilst sitting out the virus problem, I started to go through my filing cabinets.  Boy! did I find a lot of stuff that had been forgotten about, rightly so in many cases but a few forgotten "gems" have been found.


One item relevant to the subject of model stability was an OHP (OverHead Projector - from the days before "Powerpoint" and computers)  transparency.  It had been used many years ago when giving a talk at a club meeting.  It brought back memories, including having to lug the monstrous OHP to the meeting room, and I felt it might be a handy addition to this thread.


It concerns the "Righting Lever" often abbreviated to "GZ" and how vessels behave when rolling over.  Using a modified diagram from the beginning of this thread, it shows the two forces acting on a heeled hull.  These being the Weight force, acting vertically downwards from the Center of Gravity and the Buoyancy force acting vertically upwards from the Center of the Immersed Hull Volume.


When the hull is at rest, these two forces would be in line and balance each other out.  When heeled to one side their Lines of Action move apart but are still parallel.  Provided the Center of Buoyancy moves further to the heeled side of the hull than the Center of Gravity does, then a "Couple" (the term for a pair of parallel forces that do not act along the same line) is created that will try to counter the heeling action.  In this case the the perpendicular separation of the two lines of action is called the "Righting Lever" (GZ) and can be used to describe how powerfully the forces act to return the hull to the upright position.


As you might expect, as the angle of heel starts to increase the value of GZ also increases.  But, the second diagram shows that there is a limit to how far you can go.  When the listing angle exceed a certain value then the Buoyancy force can start to move inwards and the value of GZ decreases.  Heeling further makes things worse until the two lines of action swap sides and the model capsizes.  This point being termed, quite appropriately, the "Vanishing Angle".


What does this mean for us modelers?  Not sure about you but I like to have no doubts about my models stability so my standard test is to push the completed model down on one side until the edge of the hull is at the waters surface.  If, when released from this position, the model springs smartly back upright and returns, maybe after a few oscillation, to the original state, I'm happy.  Should the model ever be caught out by rough conditions, then even the sight of it rolling with water at the edge of the deck isn't a worry as it should still be in its "Range of Stability".


To be honest, most of my models have such low Centers of Gravity (build light but strong especially any superstructure who's function is usually only to look pretty and keep the water out and put dense ballast as low as possible inside the hull) that they can roll on their "beam ends" (90 degrees to upright) and still know which way is up!
Glynn Guest
P.S. Left the OHP transparency in it's original had drawn form to remind me of the life before computers and drawing programs!




 
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Martin [Admin]

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Re: Stability - how to avoid rolling upside down
« Reply #46 on: April 30, 2020, 02:58:01 PM »


 Remember this article Glynn?



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Tug Fanatic

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Re: Stability - how to avoid rolling upside down
« Reply #47 on: April 30, 2020, 03:32:21 PM »


 Remember this article Glynn?



Does the remainder of the article say anything interesting?
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Martin [Admin]

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Re: Stability - how to avoid rolling upside down
« Reply #48 on: April 30, 2020, 03:41:14 PM »

 

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GG

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Re: Stability - how to avoid rolling upside down
« Reply #49 on: April 30, 2020, 05:41:21 PM »

Yes Martin,  it's the same one you posted on this thread back in 27 Sept 2019.


Glynn Guest
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