Awb stability

[capnsensible]

Yeah, c’mon Cap’n can you organise a zoom call for us all; I have a ton of questions like “what does it feel like going from the surface to underwater and losing the motion suddenly” “do submariners get seasick” “how do you know you aren’t surfacing under a yacht”

Channel 5 Monday's 2100 has a two parter (I think) recently made on board a submarine. May answer some of your questions. ?

 

[johnalison]

Interesting figures for stability which any skipper should know for their vessel are:-

2) Angle of vanishing stability (i.e. the angle of heel after which you will continue to capsize rather than turn the right way up)

I'm sure that I should know this but I don't. I am also uncertain as to what the procedure is when I get to that point.

 

[penfold]

A submarine has to turn beam to sea to dive. A warning is given that the boat may roll heavily, and generally does. ?

The ballast tanks, filled with air on the surface need to be vented so they fill with water. They form the bow and the stern of most submarines. So it's easier to get them properly cleared of air and get that bow down angle......around ten degrees depending on the type....to dive under control. In calm seas it's not so bad, but in higher sea states in can be quite interesting and discovers anything not properly stowed. People, generally, don't like being fenders for mobile objects.?

Modern big boats need a good bit of propulsive power to drive them down too and you don't want to stick the stern out of the water.

It can be quite interesting at periscope depth for extended periods when Neptune is having a bad hair day too. ?

Don't understand any of that, at least as far as necessitating turning across swell for submerging; can you expand? Unless your vents are sufficiently sticky that the wobble is needed to shift them? Isn't that what your kingstons are for?

 

[Bajansailor]

What were you surveying? The tacos on board?

Yes the blue is a nice shade.

This was the annual flag state inspection for the Bahamas Registry.
The Covid procedures a year ago were very strict - apart from masks, we (I went with a couple of colleagues) had to wear blue plastic gowns and disposable shoe covers, and various areas of the ship (including the wheelhouse) were out of bounds to us. But we were taken on a video tour of these areas while we were in the conference room (which was our base for the day).
The ship was operating with a literally skeleton crew of only 80, and it was very quiet and empty. We were not allowed to go to the crew mess for lunch, but instead had very nice sandwiches (in lieu of tacos ) brought to the conference room.
They keep the air conditioning going in all parts of the ship, as if they didn't, it would rapidly get mildew and fungus.
And all of the toilets in all the passenger cabins and public areas are flushed once a week - it takes a small team a full day each week to do just this.

 

[MADRIGAL]

Fascin

Well that does stray a bit into if I told you I'd have to kill you territory. ??

It doesn't really matter what the sea state is......think oop north in winter, it can get bumpy. So as Ship Control, if the Captain wants to be at Periscope Depth for a variety of reasons, it was my job to make it so. To prevent the fin broaching (bad) so that someone might see you in high sea states required a 5h1t hot planes man and some, well actually a lot of mutual trust to catch the trim and not catch wrath of skipper. To prevent dipping the periscope under water (super bad) was even more sinful as you can't see things that may go bump.

Submarines do roll a lot under such conditions and can induce motion sickness in crew who are subject to the naval discipline act and generally get on with things despite feeling crap. Going deep again was a bit of a relief!

I had a ball. ???

Fascinating! Thanks for the insight.

 

[mjcoon]

The ship was operating with a literally skeleton crew of only 80, and it was very quiet and empty.

Sounds like a literal Ghost Ship!

 

[roblpm]

This was the annual flag state inspection for the Bahamas Registry.
The Covid procedures a year ago were very strict - apart from masks, we (I went with a couple of colleagues) had to wear blue plastic gowns and disposable shoe covers, and various areas of the ship (including the wheelhouse) were out of bounds to us. But we were taken on a video tour of these areas while we were in the conference room (which was our base for the day).
The ship was operating with a literally skeleton crew of only 80, and it was very quiet and empty. We were not allowed to go to the crew mess for lunch, but instead had very nice sandwiches (in lieu of tacos ) brought to the conference room.
They keep the air conditioning going in all parts of the ship, as if they didn't, it would rapidly get mildew and fungus.
And all of the toilets in all the passenger cabins and public areas are flushed once a week - it takes a small team a full day each week to do just this.

Wow. Sounds like an amazing experience!

 

[zoidberg]

Interesting figures for stability which any skipper should know for their vessel are:-
1) Down flooding angle (i.e. the maximum angle of heel before you are in deep dodo)
And the hatches and openings which need to be closed to ensure that you can get that far.
2) Angle of vanishing stability (i.e. the angle of heel after which you will continue to capsize rather than turn the right way up)
These figures are usually mentioned in the MCA stability book for the coded vessel.

Folks might care to ponder the consequences of adding lots of bits above the waterline, as most do.
I have the unusual opportunity to examine in detail two ORC Club Certificates for the same boat - one 'light' as the designer planned, and one 'heavy' with a reasonable collection of cruising add-ons.... such as roller-furling genoa, deck-mounted liferaft, stern gantry with bimini.

The 'light' boat had a calculated Limit of Positive Stability of 177.6/Stability Index of 181. The 'heavy' boat, an LPS of just 121.1 degrees/SI 126.4

The added gear had changed the long-keel 27' family cruiser from something that would most probably 'pop up' quickly after a big knockdown ( beam on to an 15-17' breaking sea ) to one that probably wouldn't.

Given that most added-on gear, including stores, radar and other safety gear, is usually stowed well above the initial Vertical CofG, that unhappy figure of just 121 degrees is likely reduced rather more in full cruising trim. e.g adding another stay with a furled solent jib on it and/or PV panels.

Something to think hard about when contemplating another passage across Biscay....

 

[zoidberg]

Readers might like me sharing one anecdote about 'Anti-submarine warfare' from the last days of our LRMP aircraft, the Shackleton. I had the pleasure of learning 'stuff' from some of their left-over specialists who operated the Nimrod Operational Conversion Unit ( OCU ) 'back in the day'.

Among other precocious questions, I asked them about the pair of 20mm cannons fitted in the nose...

"Wot they for?"

"Well", came the considered reply. "One of our tactics was to remain more-or-less overhead until the diesel sub really needed to surface. We'd spray a green dye on the sea surface over the general area we knew it to be in. At some point, the sub commander would want a sneaky-peek by periscope, to see if we were still hanging around, and he'd start to come up slowly - peering through his 'scope. The top lens would be coated with our green dye and so the sub commander would think he was still safe underwater, continue coming up.... and coming up..... and when he was 300 feet in the air, we'd shoot him down with our air-to-air cannons....."

 

[PeterV]

The main reason for turning a submarine beam on is because if facing into the waves the seas tend to ‘suck up’ the aft end of the submarine towards the surface, leading to difficulty diving and much more difficulty avoiding broaching at periscope depth. The effect is much more significant on a ‘bomber’ with a long flat after casing. As for rolling, I’ve been rolling 30 degrees either way at 300’ in a bad winter storm, I dread to think what it was like up top.

 

[capnsensible]

The main reason for turning a submarine beam on is because if facing into the waves the seas tend to ‘suck up’ the aft end of the submarine towards the surface, leading to difficulty diving and much more difficulty avoiding broaching at periscope depth. The effect is much more significant on a ‘bomber’ with a long flat after casing. As for rolling, I’ve been rolling 30 degrees either way at 300’ in a bad winter storm, I dread to think what it was like up top.

Flippin horrible. ?

 

[zoidberg]

As for rolling, I’ve been rolling 30 degrees either way at 300’ in a bad winter storm, I dread to think what it was like up top.

It's not nearly so bad at 30, 000 feet.

Just a little bit of 'yaw-roll coupling'... easily damped out by some gentle application of rudder. Doesn't even spill the coffee.....

 

[Bajansailor]

It's not nearly so bad at 30, 000 feet.

Just a little bit of 'yaw-roll coupling'... easily damped out by some gentle application of rudder. Doesn't even spill the coffee.....

Is this in the Marianas Trench?

 

[zoidberg]

Is this in the Marianas Trench?

As per #30 .... "The effect is much more significant on a ‘bomber’ ...... I’ve been rolling 30 degrees either way at 300’ in a bad winter storm, I dread to think what it was like up top."

'Up top' for me, in the bombers I used to operate, was well above the 'bad winter storms' - generally above 30,000 feet..... and smo-o-o-th.
'Way to go'....

 

[dunedin]

Interesting figures for stability which any skipper should know for their vessel are:-

2) Angle of vanishing stability (i.e. the angle of heel after which you will continue to capsize rather than turn the right way up)

Might be scary ro know the AVS for Roblpm's cruise ship.
As they get higher and higher to give more cabin balconies, and yet shallower to get into more harbours, the physics looks worrying

 

[zoidberg]

Remember 'Viking Sky'....?

 

[roblpm]

Remember 'Viking Sky'....?

Wow. Interesting reading. https://www.iims.org.uk/wp-content/...opulsion-and-near-grounding-of-viking-sky.pdf

Though sounds like operator error. I don't really understand it but apparently the sump oil tanks were not filled correctly and the bad weather meant not enough oil to the diesel generators so they all shut down.

Apparently within a few hundred metres of going around. Must have been pretty scary getting evacuated in the middle of the night by helicopter!

Also in the Wikipedia suggests they set off knowing storm force winds blowing.

So actually I'm not sure the avs was the concern! More people being careful?!!!

In whatever boat I eventually get I will have sat forecasts (from elons satellites.... ?) and will be a chicken sailor as far as possible! ?

 

[zoidberg]

So actually I'm not sure the avs was the concern!

Without electrical power, they don't have 'ships stability augmentation system'..... so Angle of Loll, LPS/AVS very much becomes relevant. But of primary concern were the storm-lashed reefs very close to leeward. Inspect the chart in the AIBN Interim Report.

 

[lustyd]

one 'light' as the designer planned, and one 'heavy' with a reasonable collection of cruising add-ons.... such as roller-furling genoa, deck-mounted liferaft, stern gantry with bimini.

Perhaps worth buying something designed by someone who plans for reasonable features. roller furling genoa is not a weird configuration and neither are liferaft or radar.
It's also reasonable to suggest that an extremely fast righting might cause more damage than a slower one to the meat based cargo inside so chasing "better" numbers is not necessarily the best approach. Lifeboat righting tests show how dangerous it can be to roll too fast.

 

[oldmanofthehills]

Perhaps worth buying something designed by someone who plans for reasonable features. roller furling genoa is not a weird configuration and neither are liferaft or radar.
It's also reasonable to suggest that an extremely fast righting might cause more damage than a slower one to the meat based cargo inside so chasing "better" numbers is not necessarily the best approach. Lifeboat righting tests show how dangerous it can be to roll too fast.

Our liferaft weighs much less than I do as does the deck stowed anchor, so I am given to wondering what on earth the destabilised 27footer had on deck to reduce stability that much.

We will continue reduce our CofG by storing bottles of beer and wine down down in the bilges.