Maximum angle of positive stability

[westernman]

Any idea what it is for a clipper ship?

Look at around 50 seconds into the video.

 

[dom]

I'd guess that the ship rolled to about 50 degrees, which will not be a million miles from its point of maximum positive stability; on those types of boat its usually about 55-60 degrees I think. Tall ships are a bit weird in that the centre of bouyancy is usually below the centre of gravity like a regular ship. Nevertheless, assuming all hatches are shut to remove the risk of downflooding and everything is lashed down below, the AVS should be at least 90 degrees and possibly a little more. From what I understand by 110 degrees even the best of them are toast.

The centre of windage is quite high on tallships even when fully reefed, and the wind force than heels the boat around the boat's metacentric height. The metacentric height is in turn not constant as the boat heels; the calculations are a bit messy but at the end of the day certain boats are predisposed to roll like crazy. I think all that's going on here is a hefty roll - exciting for the peeps aloft though

 

[AngusMcDoon]

As long as we get our tea in a timely manner it's worth the risk.

 

[sarabande]

there must be quite an upward component from the windforces on those topsails, tending to provide some dynamic lift. But , goodness , is she shifting !

 

[prv]

I was on Stavros once when we managed to dunk the starboard RIB (orange, amidships) in the sea:

We don't know exactly how far she was heeling, as the clinometer on the bridge went off the end of the scale and jammed.

It's the only time I've ever known Clive the cook give up his planned menu of soup and main-course for lunch, main-course and pudding for tea. After a full vat of soup went down the galley scuppers we had 24 hours of bacon sandwiches only

Pete

 

[KellysEye]

She didn't get any water on her decks when rolling so she was nowhere near losing positive stability. Great video, thank you.

 

[Cruiser2B]

I'd guess that the ship rolled to about 50 degrees,

I don't think it's more than about 40º

 

[burgundyben]

we had 24 hours of bacon sandwiches only
Pete

Died and gone to heaven.

 

[elenya]

Every ship will be different. I have severed as master of four squate rig vessels. Best had 90 degrees and worst 60 degrees.

 

[snowleopard]

When STS Tenacious was first launched she rolled to 50°. They whacked in a bit more ballast PDQ. STS Lord Nelson on one trip I did rolled 30° one way and 40° the other. Trying, not always successfully, to stop wheelchairs capsizing was challenging.

 

[Porthandbuoy]

Jib, staysail, fore and mizzen topsails ??? And doing what; 12 kts? What sort of wind speed are we talking about here?

 

[westernman]

Jib, staysail, fore and mizzen topsails ??? And doing what; 12 kts? What sort of wind speed are we talking about here?

I think it is a fair bit more than 12 knots. It is a very big ship - I would guess more than 16 knots. Wikipedia says that 15 knots is a very normal speed for this particular ship.

I don't see any spray coming off the tops of waves - so it can't be very windy.

 

[rgarside]

As she's got the waves on the quarter, and overtaking her, the encounter frequency is closer to the roll period - hence the big amplitude. It'll be interesting to hear whether anything similar was relevant in the Pentland Firth recently.

 

[Sybarite]

I don't think it's more than about 40º

+1 I froze the image on the screen to get a better idea.

 

[Malo37]

Tall ships are a bit weird in that the centre of bouyancy is usually below the centre of gravity like a regular ship.

I'm curious - how can the centre of buoyancy be below the centre of gravity ? Surely this would result in a permanent list until metacentric height became positive ?

 

[TimBennet]

The centre of buoyancy is below the centre of gravity in most yachts as well.

 

[Cruiser2B]

Tall ships are a bit weird in that the centre of bouyancy is usually below the centre of gravity like a regular ship.

I'm curious - how can the centre of buoyancy be below the centre of gravity ? Surely this would result in a permanent list until metacentric height became positive ?

Seems counterintuitive, but centre of buoyancy(B) moves around as the under water shape changes with heel and pitch - it acts upwards to an invisible point called the metacentre(M). As long as M is above the centre of gravity(G), then stability is positive. The distance between G and M, known as GM determines how stable the boat is - a boat with a large GM is said to be 'stiff' and tends to snap back to the upright, whereas a short GM indicates a 'tender' vessel that slowly returns to the upright.

 

[dom]

Tall ships are a bit weird in that the centre of bouyancy is usually below the centre of gravity like a regular ship.

I'm curious - how can the centre of buoyancy be below the centre of gravity ? Surely this would result in a permanent list until metacentric height became positive ?

I know where you're coming from as metacentric heights are a bit weird and proper calculations can be horrendous double integral stuff! I'm useless at drawing, but Wiki has a good schematic explanation: http://en.wikipedia.org/wiki/Metacentric_height

 

[onesea]

I'm curious - how can the centre of buoyancy be below the centre of gravity ? Surely this would result in a permanent list until metacentric height became positive ?

You can even find ships with the centre of gravity above the main deck...