Most seaworthy type of ship?

[jkh112]

wolfracesonic said:

MBBlat said:

Its not against physics - its all about the ships response to the sea, which in a storm is anything but flat.

A very stable ship will tend to stay perpendicular to the local sea surface, which means that on the side of the wave it can be at quite an angle to the vertical. A less stable ship (note not unstable) will not follow the sea quite so closely, thus have lower accelerations.. Add a bit of damping such as bilge keels to the equation and you can quite quickly reduce the amplitude as well.

If you still think that's counter-intuitive don't look up anti-roll tanks, http://en.wikipedia.org/wiki/Antiroll_Tanks as this uses the movement of water from side to side to counteract roll.

One example I worked on a while back, unmodified in beam seas the model tests (and reports from the full sized ship in question) showed roll amplitudes of 45degrees. Lowering the GM (ie reducing stability), increasing the size of the bilge tanks and putting in some anti-roll tanks and in the same beam seas the ship was just bobbing up and down with no roll.

That's me and RobDickinson put in our place then!

But how much of the reduced roll was from the effect of the anti-roll tanks rather than the reduction in GM? Normally a reduced metacentric height will cause an increase in roll amplitude, but with a reduction in acceleration. If the roll amplitudes of 45 degrees were reduced by your modifications then I suspect that was primarily due to the anti-roll tanks, the reduction in GM may also have helped if it shifted the roll response frequency of the vessel outside the frequency range of the waves being modelled.

[gwm]

A small ice breaker - you know it's tough and small so rides the waves more.

No way would I want to be on anything like a ULCC, guaranteed to break its back. You can feel those things flexing in a stiff breeze.

[PanzerCommander]

Easy, a submarine of some sort dive below the waves and ride it out. I believe it was on Das Boot where the captain quoted "The sea can't sink us, Hinrich. No ships are as safe as our U-boats".

Failing that one of those modern RNLI life boats; they seem rather good.

Edited by PanzerCommander on Monday 6th October 15:06

[prand]

All the RNLI boats (not ships tho) are supposed to be self righting. I'd feel pleased to be on one in a bit of chop.

Biggest one is the Severn class at 17m.

[wolfracesonic]

jkh112 said:

wolfracesonic said:

MBBlat said:

Its not against physics - its all about the ships response to the sea, which in a storm is anything but flat.

A very stable ship will tend to stay perpendicular to the local sea surface, which means that on the side of the wave it can be at quite an angle to the vertical. A less stable ship (note not unstable) will not follow the sea quite so closely, thus have lower accelerations.. Add a bit of damping such as bilge keels to the equation and you can quite quickly reduce the amplitude as well.

If you still think that's counter-intuitive don't look up anti-roll tanks, http://en.wikipedia.org/wiki/Antiroll_Tanks as this uses the movement of water from side to side to counteract roll.

One example I worked on a while back, unmodified in beam seas the model tests (and reports from the full sized ship in question) showed roll amplitudes of 45degrees. Lowering the GM (ie reducing stability), increasing the size of the bilge tanks and putting in some anti-roll tanks and in the same beam seas the ship was just bobbing up and down with no roll.

That's me and RobDickinson put in our place then!

But how much of the reduced roll was from the effect of the anti-roll tanks rather than the reduction in GM? Normally a reduced metacentric height will cause an increase in roll amplitude, but with a reduction in acceleration. If the roll amplitudes of 45 degrees were reduced by your modifications then I suspect that was primarily due to the anti-roll tanks, the reduction in GM may also have helped if it shifted the roll response frequency of the vessel outside the frequency range of the waves being modelled.

HaHa! Me and RobDickinson were right all along!

[Vipers]

prand said:

All the RNLI boats (not ships tho) are supposed to be self righting.

They are.

[prand]

Vipers said:

They are.

FFS, I flipping hate this place

I left in the "supposedly" because I knew some know-it-all tw*t who likes QI too much would come along say there was some renowned exception to the rule, yet instead some know-it-all tt comes along and does the complete opposite!

[matchmaker]

prand said:

Vipers said:

They are.

FFS, I flipping hate this place

I left in the "supposedly" because I knew some know-it-all tw*t who likes QI too much would come along say there was some renowned exception to the rule, yet instead some know-it-all tt comes along and does the complete opposite!

All RNLI all-weather lifeboats are self-righting and have been so for many years. A Severn has 2 V12 Cats with 2100bhp in a boat that weighs 45 tonnes. Another attribute is that they are highly manoeuvrable.

Edited by matchmaker on Monday 6th October 17:16

[onesickpuppy]

Efbe said:

Harland and Wolff Olympic-class are unsinkable tbh

[prand]

matchmaker said:

All RNLI all-weather lifeboats are self-righting and have been so for many years. A Severn has 2 V12 Cats with 2100bhp in a boat that weighs 45 tonnes. Another attribute is that they are highly manoeuvrable.

Edited by matchmaker on Monday 6th October 17:16

Ha, funny you should say that, I was in Bridport earlier this summer watching the RNLI and Costguard doing a demo off West Bay. They had a Severn Class in from Weymouth but they were making quite a meal of mooring up on the quayside in the harbour afterwards. The harbour master (not sure if he was having a dig or anything) said over the tannoy that they couldn't manoeuvre so easily as their bow thrusters were broken!

[XJSJohn]

these bad boys are pretty handy

[Mabbs9]

doogz said:

Most modern naval ships are pretty much bombproof (literally) compared to merchant/cruise/ferry/other things made of tinfoil.

My Bro was on a destroyer in the North Atlantic. The storm was bad enough to break off the hangar door. Waves were breaking over the bridge.

[matchmaker]

I'm old school - I was crew on an Arun which had none of these new-fangled gadgets!

[Efbe]

onesickpuppy said:

Efbe said:

Harland and Wolff Olympic-class are unsinkable tbh

glad someone did, assumed it was either wasted, or a dust gathering joke.

prob the latter really.

[Vipers]

prand said:

Vipers said:

They are.

FFS, I flipping hate this place

I left in the "supposedly" because I knew some know-it-all tw*t who likes QI too much would come along say there was some renowned exception to the rule, yet instead some know-it-all tt comes along and does the complete opposite!

I shall have to clean my crystal ball. And when I find that tt I will deck him.

[mickrick]

My armchair, in front of the log burner. Single malt, Patrick O'Brian, and my Missus occasionally splashing a bit of water on my face for authenticity.

[DJFish]

That reminds me of the best sea sickness cure I ever heard of which was to "go for a quiet sit down under a large tree"

[anonymous-user]

matchmaker said:

All RNLI all-weather lifeboats are self-righting and have been so for many years. A Severn has 2 V12 Cats with 2100bhp in a boat that weighs 45 tonnes. Another attribute is that they are highly manoeuvrable.

They also have that most useful of accessories, vertically compliant damped cabin seating to take the sting off those big "into sea" landings at high speed when you are using your V12s....... ;-)

[Vipers]

Max_Torque said:

matchmaker said:

All RNLI all-weather lifeboats are self-righting and have been so for many years. A Severn has 2 V12 Cats with 2100bhp in a boat that weighs 45 tonnes. Another attribute is that they are highly manoeuvrable.

They also have that most useful of accessories, vertically compliant damped cabin seating to take the sting off those big "into sea" landings at high speed when you are using your V12s....... ;-)

I remember in the navy being standby diver when John Noaks (Blue Peter team) was strapped into the cox's seat, and two hawsers run under a new lifeboat, and attached to the bollards the other side.

A crane slowly pulled the boat upside down, and of course it righted itself.

This was on the IOW somewhere, Valerie Singleton was there as well. I was a bit shocked bearing in mind you associate these two with a kids programme, when John said something to Valerie, and she said "John, you are a fking wker"

This would have been early 70's.

[maffski]

Does Flip count?