Norwegian Escape. How to handle gusts?

[rmlarson1098]

Originally Posted by donradcliffe

I would be a really bad day if you were on a catamaran. Fortunately its not very common.

Yes, very tough on a multi-hull. I read with interest recently that Heavenly Twins catamarans (UK) were built with a rig that would come down before she capsized, or even before a hull came out of the water! Of course, losing the rig presents other problems, but it's an interesting concept.

[Otia]

Sinking of SV Concordia
Here is a simulation of what happened:

https://www.youtube.com/watch?v=OQgCv-ruu1I

(by the The Transportation Safety Board of Canada)

[a64pilot]

I am no multi hull guy, but assume that capsize is about as likely as winning the lottery.
I assume this because even I with my limited brain power could come up with a system that would release the boom in a controlled manner similar to a boom brake, and seeing as how that apparently isn’t done, must mean that a capsize isn’t really much of a possibility.

[Otia]

Originally Posted by a64pilot

I assume this because even I with my limited brain power could come up with a system that would release the boom in a controlled manner similar to a boom brake, and seeing as how that apparently isn’t done, must mean that a capsize isn’t really much of a possibility.

There exists a boom fuse to put on the main sheet.
However, cats have a tendency to get lifted and flipped over when strong winds funnel in-between their hulls.

[Fiveslide]

Originally Posted by Otia

However, cats have a tendency to get lifted and flipped over when strong winds funnel in-between their hulls.

Uh oh! Now you've done it! 44cruisingcat, flip your boat back over and join this discussion![emoji1]

[roverhi]

Florida and the Gulf have isolated thunder clouds that can pack winds 50k plus. Fortunately they are usually visible during the day and largely dissipate at night. Saw one coming that I couldn't avoid, lowered the sails and gasketed them but still nearly got the spreader in the water when it hit. Lasted a few minutes and was gone.

Coastlines with deep canyons often have wild wind gusts.

It's exciting in a mono if you get hit with too much or any sail for a micro burst condition but not a problem unless you tear a sail or lose the stick. The latter shouldn't happen. If you do lose the stick, it's from a fault in the system that was just waiting for such an opportune time to let go. Not so benign on a multihull unless you want to clean the bottom without diving.

[bongo]

As the watch engineer on a container ship, in coordination with the mate in the wheelhouse, I was ballasting like crazy to take the list off of the vessel. Before the heel was corrected the wheelhouse had me reverse the ballasting to put more of a list on the vessel. I was informed that we were about to go through a squall line, (near the center of the low pressure, as I recall), and that the high wind would be from the opposite side. A few minutes later the vessel was heeled over the opposite direction. If you've got a 50 knot wind, and you are on a vessel doing 20 knots, you have ~70 knots of apparent wind. When that shifts suddenly from one side of the vessel to another, you have a difference of 140 knots. We've been talking about sudden winds seemingly out of nowhere, well, just as potentially catastrophic, (for a top-heavy ship), can be instantaneous wind direction change.

[PaulSommers]

Robson Strait in British Columbia, a narrow pass between Vancouver Island and the mainland, is infamous for katabatic bursts. But not 100 kt bursts. There must be many places around the globe with passes between islands or fjord-like settings where these phenomena can occur.

More tales of how you coped with this sort of situation would be useful. I have a junk-rigged vessel - just release the mainsheet, and hope for the best, maybe the halyard as well if you are a few seconds ahead of the burst. It doesn't take long to get the sail down normally, but if you are already at 90 degrees with the sail in the water, do what you can to get pressure off of the sail. And, if I turned downwind in these conditions as one poster did, the sail would not come down - I have to turn into it and then it will come down quickly unless so much wind is hitting the sail horizontally that it sort of stalls in place - then I imagineI would be dismasted. If the burst is coming down from a mountain it could help the sail come down. All tactics are specific to the particular situation and the rig you have.

[a64pilot]

I think the average boat if hit hard will round up on their own won’t they?
I know when you are laid well over you rudder authority isn’t what it is when your upright.

[a64pilot]

Originally Posted by bongo

As the watch engineer on a container ship, in coordination with the mate in the wheelhouse, I was ballasting like crazy to take the list off of the vessel. Before the heel was corrected the wheelhouse had me reverse the ballasting to put more of a list on the vessel. I was informed that we were about to go through a squall line, (near the center of the low pressure, as I recall), and that the high wind would be from the opposite side. A few minutes later the vessel was heeled over the opposite direction. If you've got a 50 knot wind, and you are on a vessel doing 20 knots, you have ~70 knots of apparent wind. When that shifts suddenly from one side of the vessel to another, you have a difference of 140 knots. We've been talking about sudden winds seemingly out of nowhere, well, just as potentially catastrophic, (for a top-heavy ship), can be instantaneous wind direction change.

It’s my understanding that cruise ships are intentionally top heavy, being top heavy means they correct for roll very slowly and this is more comfortable to the passengers?

It’s sort of like a mono hull without the mast, they are extremely stable, so stable that the motion to right itself is very quick and uncomfortable I’ve been told.

[Jim Cate]

I suspect that 45 degrees is well past the angle of vanishing stability for that cruise ship, and if she had really heeled that much, she would not have recovered.

Any NAs out there who could comment?

Jim

[Uricanejack]

No not top heavy.

Passenger ships have to conform to SOLAS stability requirements including damaged stability requirements. Which among other things require two compartment damaged stability and a Max righting leaver at greater than 53 deg. Vanishing stability would be nearer 90 with a minimum area under the curve of something I forgot long ago.

The angle of deck edge immersion and the angle of down flooding are probably more significant and would occur well before vanishing stability.

There is a tendency for some passenger ships to be designed to be "tender" for comfort. A Tender ship typically rolls slowly or gently. This doesn't mean top Heavy. Minimum GM would probably be 0.15 m probably quite a bit more than this.
At the other end of the scale would be a "Stiff" ship. Ferries are quite often built stiff with a large GM of several meters. Allows them to load vehicles without taking a big list.

A stiff ship will roll quickly and uncomfortably.

As for this cruise ship I don't know where it was or what happened. 100 knot winds are extremely rare. Wind induced angle of heel is a potential issue with high sided vessels. They are designed to be able to withstand a wind induced angle of heel. In addition to angle of heel induced by excess rudder. Usually they limit rate of turn and exposure to high winds.
Bottom line its very unlikely the ship was in any real danger. Which doesn't mean people wouldn't have been worried.

One kind of ship which may be loaded "Top Heavy" is a vessel carrying a timber deck cargo. If the deck cargo is loaded in a block and secured so it can be released. The additional reserve buoyancy of the deck cargo is permitted to be taken into account.
and the ship may load to a slightly negative GM. So She is initially Top heavy. When the ship heels the center of buoyancy moves to the lower side and the metacentric Hight or M drops back bellow the center of gravity G and the ship has a positive GM at a small angle of heel usually 2 or 3 degrees either side of upright referred to as an angle of Loll.
Timber ships tend to be very "tender" rolling very slowly.
Ore ships tend to be very stiff and roll very quickly.

Passenger ships somewhere in between. possibly a bit on the tender side for comfort but by comparison to cargo ships quite stable.

One of the Solas requirements. If damaged and any two compartments flooded and open to the sea. If all the passengers and crew were to stand on one side the upper deck. The ship has to retain positive stability or not be top heavy.

The Costa Concordia flooded more than 2 compartments. So all bets were off. She lost stability fortunately by sheer dumb luck she tipped over and sank in shallow water adjacent to the island.

[Jim Cate]

thanks, Hurricane! I'm very surprised at those numbers, but am in a sense relieved. Don't intend to travel on one of those monstrosities, but i'll feel safer now if it should happen!

Jim