Non-motoring > Cut and Shut - Nautical style Miscellaneous
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New Fri 31 Jan 14 16:04 
 Cut and Shut - Nautical style - Zero
www.bbc.co.uk/news/world-europe-25970361
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New Fri 31 Jan 14 16:27 
 Cut and Shut - Nautical style - Bromptonaut
Fairly common I think. Townsend Thoresen's Viking class (Viking Valiant etc) were 'jumboized' by a similar process in the eighties.
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New Fri 31 Jan 14 17:14 
 Cut and Shut - Nautical style - Cliff Pope
I think it's an ancient practice. Lots of famous 19th century racing yachts were lengthened, and someone I knew on the Broads in the 70s lengthened his traditional sailing cruiser by about 6 feet.
Apart from increasing accommodation, which is I imagine the reason in a cruise ship, an increased length allows a greater speed.
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New Fri 31 Jan 14 17:34 
 Cut and Shut - Nautical style - Duncan
> an>> increased length allows a greater speed.
>>

How does that work?
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New Fri 31 Jan 14 17:35 
 Cut and Shut - Nautical style - Crankcase
And what is the limit? There must be one or eventually you'd have a ship travelling at the speed of light.
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New Fri 31 Jan 14 17:44 
 Cut and Shut - Nautical style - commerdriver
>> And what is the limit? There must be one or eventually you'd have a ship
>> travelling at the speed of light.
>>
Surely the limits are the obvious ones of weight and power
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New Fri 31 Jan 14 17:47 
 Cut and Shut - Nautical style - henry k
>> >> And what is the limit? There must be one or eventually you'd have a ship
>> >> travelling at the speed of light.
>> >>
>> Surely the limits are the obvious ones of weight and power
>>
or they snap in two!
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New Fri 31 Jan 14 17:19 
 Cut and Shut - Nautical style - borasport
Glad to see Blohm und Voss have recovered their eye for symmetry, they took their eye off the ball in the past...

tinyurl.com/p3xxabr

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New Fri 31 Jan 14 17:44 
 Cut and Shut - Nautical style - bathtub tom
>> tinyurl.com/p3xxabr

They got it nearly right, it's RHD!
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New Fri 31 Jan 14 18:10 
 Cut and Shut - Nautical style - Fenlander
>>>increased length allows a greater speed. >>>How does that work?

The law dictating hull speed for a displacement type such as the ships concerned is that, given the power to drive them up to the maximum, the maximum speed in knots is approx 1.34 times the square root of the waterline length.

The physics behind this is that the boat as it nears this maximum creates a wave with a peak at the bow and the trough at the stern so driving it past this speed is like trying to go uphill. The stern drops, bow rises and you use a huge amount of fuel but go no faster.

Of course different rules apply to boats that will plane due to their hull shape that allows this.
Last edited by: Fenlander on Fri 31 Jan 14 at 18:10
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New Fri 31 Jan 14 18:47 
 Cut and Shut - Nautical style - Old Navy
It is certainly nothing new, a WW2 built submarine that I was in had been stretched to make room for an extra battery.
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New Fri 31 Jan 14 19:24 
 Cut and Shut - Nautical style - Fullchat
The Norland which sailed from Hull was lengthened by 20.5M in 1987

www.ferry-site.dk/ferry.php?id=7333822

Requisitioned to take the Paras to the Falklands.

www.hulldailymail.co.uk/pictures/Flashback-Hull-ferry-Norland-Falklands-War/pictures-18664962-detail/pictures.html#24

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New Fri 31 Jan 14 19:55 
 Cut and Shut - Nautical style - Armel Coussine
I'm not sure of the real fluid dynamics - perhaps even N_C isn't although he's just the man to track the equations down - but my understanding is that a longer shape of the same section, while it may have slightly more surface drag than a short one, has very little more, and can carry e.g. more sail or more engine/fuel than a short one and is therefore quite a lot more efficient.

I understand too that a slightly rough surface is more slippery, something to do with boundary layer so-called... shark skin is a good example but it works on aircraft too.
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New Fri 31 Jan 14 20:14 
 Cut and Shut - Nautical style - Slidingpillar
R101 was a cut and shut too!
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New Fri 31 Jan 14 20:21 
 Cut and Shut - Nautical style - Bromptonaut
>> R101 was a cut and shut too!

They had fun and games with R100 too. Nevile Shute's 'Slide Rule' gives a full account though he's writing from the Vickers' perspective and very sceptical about the 'state run' R101 project.
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New Fri 31 Jan 14 23:55 
 Cut and Shut - Nautical style - Armel Coussine
>> a slightly rough surface is more slippery, shark skin is a good example but it works on aircraft too.

Another thing I find mysterious is the fact that submarines can go faster totally immersed (not close enough to the surface to disturb it) than they can on the surface... it's counter-intuitive to an ignoramus. Doubtless the explanation has to do with bow wave generation absorbing energy in some way.

ON may be able to explain, but I understand his old workplace could do 40mph under water but only 30 on the surface (figures could well be out).
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New Sat 1 Feb 14 00:02 
 Cut and Shut - Nautical style - bathtub tom
>>Another thing I find mysterious is the fact that submarines can go faster totally immersed (not close enough to the surface to disturb it) than they can on the surface... it's counter-intuitive to an ignoramus. Doubtless the explanation has to do with bow wave generation absorbing energy in some way.

I recall seeing some explanation (it made sense at the time) of that underwater projection on the bows of modern ships, reducing energy.

A bit like wing-tip winglets on modern aircraft.
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New Sat 1 Feb 14 10:09 
 Cut and Shut - Nautical style - CGNorwich
Explanation courtesy of the US navy:

"A submarine's "tear drop" hull design allows it to slice cleanly through the ocean when there is water on all sides. When a "tear drop" hull submarine is on the surface, a great deal of energy is used to generate the bow wave and wake. That energy is then unavailable for propulsion. The hulls of older submarines, like the World War II vessels and the first nuclear-powered submarine, USS Nautilus, were designed with narrow bows to move faster on the surface than they did underwater."

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New Sat 1 Feb 14 10:29 
 Cut and Shut - Nautical style - Old Navy
>> ON may be able to explain, but I understand his old workplace could do 40mph
>> under water but only 30 on the surface (figures could well be out).
>>

Under water no comment, slower on the surface.

The first "fast" submarines with an efficient teardrop hull shape were the Albacore class diesels, built by the Americans. The first nuclear powered submarine was a tube shape with a sharp bow (USS Nautilus) the nuclear submarines that followed had an Albacore shape hull which had proved to be a success. The Albacore hull with its blunt bow, which is handy for mounting sonar sensors in, away from the propulsion machinery, and a pointed stern is basically a copy of a fish. This is now seen in the bulbous bow that many surface ships have.
Last edited by: Uncle Albert on Sat 1 Feb 14 at 10:30
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New Sat 1 Feb 14 12:34 
 Cut and Shut - Nautical style - four wheels good...
>>
>> I understand too that a slightly rough surface is more slippery, something to do with
>> boundary layer so-called... shark skin is a good example but it works on aircraft too.

We used to lightly sand-paper the hulls of racing dinghies for this reason.
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New Fri 31 Jan 14 21:09 
 Cut and Shut - Nautical style - MD
>> It is certainly nothing new, a WW2 built submarine that I was in had been
>> stretched to make room for an extra battery.
>>
You two!!! :0)
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New Fri 31 Jan 14 22:19 
 Cut and Shut - Nautical style - Ted

I seem to remember in the last few years a big lump of ship's middle was built in a shipyard...possibly Cammell or Harland. The order was cancelled even though it had been completed.

What happened to that ? Did someone just make a bow/stern section...weld it together...and create a dinky little liner ?

HO
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New Sat 1 Feb 14 14:16 
 Cut and Shut - Nautical style - Auntie Lockbrakes
One of the Inter-Island ferries in New Zealand was sent off to dry dock in Asia somewhere a couple of years ago to be sliced in two and lengthened. It had all kinds of anecdotal problems upon its return to service, with torsional rigidity compromised, flexing under load, loading doors jamming as a result, etc. Lots of delayed sailings IIRC.

The re-fitters also changed the prop and fitted bigger propellers... One of them fell off and sank to the bottom of the Cook Straight a few months ago. Ship now out of service whilst investigations and repairs are made. Not a success story.
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