Visit our Popular Forums

donradcliffe · 21-11-2016, 14:09

Ccruising catamaran capsizes are rare events, but they do happen. After the survivors have been rescued, what do you do with an upside down cat in the open ocean, which shows no inclination to sink.

I've given the matter some preliminary thinking, but would love to hear from anyone who has successfully salvaged one.

My plan would be to use a power boat and a diver.

First, the diver would get rid of any sails that are deployed. Second, dive down to the tip of the mast and attached a lift bag(s) with 1000 lb capacity. The bag would be inflated to about 25%, to allow for fourfold expansion from 60 ft to the surface. Finally the diver attaches a long line where the shrouds attach to the mast, and to the rescue boat.

The next phase is for the rescue boat to pull sideways to the hulls until the boat heels about 20%. After that, the bag should take over and you should end up with a stable boat with the mast tip near the surface and about 105 degrees of heel.

The rescue boat is then attached with a long line to the upper hull, and pulls until the boat is about 80-85% of heel. At that point, nature should take over and the boat should go fully upright.

Looking at the loads involved, a 35,000 lb Lagoon 450 cat with a 25 ft beam has a righting moment of 35,000 x 25/2 = 440,000 ft lbs, roughly the same whether it is right side up or upside down. The pull you will need on the mast (say 44 ft from the pivot point) is 440,000/40 = 10,000 lbs. To get that pull, the rescue boat will need 500+ hp, and you will need a line and attachments with a breaking strength of 50,000 lbs to get a 5:1 safety margin. You would need at least 5/8 inch spectra or 1.5 inch dacron/nylon to avoid line partings.

Once you are pulling on the upper hull, the righting arm is down to 25 ft, but the righting moment you have to overcome is much lower. I would expect that you will need less than half the earlier maximum pull in this phase.

I doubt that you will break the mast or rigging, as they are sized to fly a hull (440,000 ft lbs righting moment) with some safety margin.

Comments and suggestions are always welcome.

**Lepke** · 21-11-2016, 14:19

The sea conditions would dictate even trying to right a cat. The CG usually shoots holes in the bottoms to let the air out.

Stumble · 21-11-2016, 14:53

Generally the mast is already gone. Masts simply are not built to handle a roll over.

After that the normal recovery method for a large cat is to tow it to a crane.

On smaller boats you can try to flip them but it's a risky operation. The preferred option is to try to flip the boat end over end (normally bow over stern) but it depends on which end is deeper in the water. Typically the sterns will be deeper thanks to the engines and gear while the bows are relatively light.

Controlled flooding, or adding additional temporary ballast to the low end can help, but it has a lot to do with the size of the boat. It would take a lot of additional ballast to sink a 40' cat appreciably.

**Cotemar** · 21-11-2016, 15:17

donradcliffe would you be planning for the eventual asteroid hitting earth also?

You do know that cruising catamarans are not designed to fly a hull, right?

You do know that cruising catamarans mast are designed to break away before a catamaran would flip, right?

barnakiel · 21-11-2016, 15:43

Yes, a crane, in shallows.

In deep water you load one end and float the other then start pulling with a rib by the floated end. The low end tips and you pull slowly while the water flows out from the high side.

Make sure there is positive buoyancy before doing this in open water. It can sink once the right side up.

b.

tp12 · 21-11-2016, 16:01

Quote:

Originally Posted by Cotemar

[B]
You do know that cruising catamarans mast are designed to break away before a catamaran would flip, right?

Please don't take this as an antagonistic post, as I'm genuinely curious. I've heard people say this before, also more generally regarding the rigging, and looked for information to support this without finding any. I asked reps from Outremer, Seawind and FP about this at the recent Sydney boat show and they all said it's not true. Do you have any information to support this? Is it a specific manufacturer that does this?

**Cotemar** · 21-11-2016, 16:20

tp12,

CRUISING CATAMARANS are are designed to be safer than RACING / PERFORMANCE CATAMARANS.

Flipping a CRUISING CATAMARANS is like earth getting hit by a very large asteroid.

Both of these things will not happen to you, so do you want to waste your day talking about something that will not happen to you?

No boat manufacturer will answer you, because there is no answer.

barnakiel · 21-11-2016, 16:21

Masts are not designed for the kind of loads (mostly - the direction the loads are applied) when the mast meets the ocean. I do not think it is a cat specific thing.

These are fine alloy extrusions designed for compression (mostly) I think.

It would take an immensely thick wall and outrageously oversized rigging elements to allow for the forces during capsizing.

Off course. you can design such a mast. Except it is not normally found on maybe 99% of sailing boats today.

I may be wrong but I think Hugo Boss mast snapped in recent capsize (?) And here we are talking an immensely strong carbon spar attached to an unusually light hull.

Normally, masts snap during capsizes.

b.

UNCIVILIZED · 21-11-2016, 17:01

Much of these incidences of masts snapping when the boats flip, is due to their being carbon, & thus brittle. Along with the fact that "normally" they're striking the water when the boats are moving at quite high speeds. Thus the major forces on them are dynamically created ones. Usually from speeds well in the double digits, unlike those that a (metal) cruising boat mast would face.

Plus which, on a number of such breakages, the masts are a completely different breed of animal than found on cruisers. Being either rotating, or having deck spreaders, etc. And tend to be designed to much finer tolerances, both in terms of spar section (Ixx, & Iyy) vs. righting moment, & their staying setups, than are cruising boat masts. Since few, if any, have permanent backstays, or permanent stays in place to hold them up against just standard loads. Let alone if/when they strike the water.
IE; They're fully runner dependent. When the runners, or runner trimmer fail, so does the spar. Ditto if caught aback unawares, or accidentally gybed (most likely).

Also, when righting a big multi, you'll need to first assess the integrity of her connectives. And if they're intact, then figure out how to keep them that way when putting her right side up.

tp12 · 21-11-2016, 17:04

Quote:

Originally Posted by Cotemar

tp12,

CRUISING CATAMARANS are are designed to be safer than RACING CATAMARANS.

Flipping a CRUISING CATAMARANS is like earth getting hit by a very large asteroid.

Both of these things will not happen to you, so do you want to waste your day talking about something that will not happen to you?

No boat manufacturer will answer you, because there is no answer.

No need to get shirty; I agree with a lot of what you say. Except your last sentence.

My question was genuine and didn't require your response, so please play nice. None of these things relate to the question I asked you which leaves me doubting that any mast is designed break under wind loading.

Just Another Sa · 21-11-2016, 17:10

"The next phase is for the rescue boat to pull sideways to the hulls until the boat heels about 20%. After that, the bag should take over and you should end up with a stable boat with the mast tip near the surface and about 105 degrees of heel."

When you wrote 20%, did you meant 20 degrees?
If not please explain what that means.

If yes, how many lift bags you intend to use?
Your calc was 440 000 ft lbs and 1000 lbs each bag not only if full and not just 25% full.
I don't think you have leverage of 440 ft at 16 degrees of heel (20 degrees change from fully inverted)

Second much bigger problem is that when intending to lift one of the hulls off the water, you have to lift also all the water inside that hull that does not come out. You can as well have 10 times more weight on that hull than you think. And then you also stated you tie that bag to the top of the mast, not near the part of the mast supported by shrouds and stays. If the mast was intact it won't be after your rescue effort, and the cat remains capsized.

It takes substantially less effort to right a cat end over end, as you don't lift water due to flooding, and part of empty weight is supported by buoyancy, not just the force you apply. That is far more significant than the beam being less than length.
The leverage of the cat weight and buoyancy produce therefore substantially less righting moment longitudinally than than a cat with no water inside. could easily be 90% less.

UNCIVILIZED · 21-11-2016, 17:11

Quote:

Originally Posted by tp12

which leaves me doubting that any mast is designed break under wind loading.

This one has me wondering as well. It just doesn't ring true somehow.

And no doubt I'll figure out why come 0300

Edit: Wouldn't designing a rig in such a manner be a liablity for the manufacturer? Since if you designed it to break under a load less than that required to say, fly a hull, then it's margin of safety the rest of the time would be razor thin at best. And you'd have them breaking with some regularity in quite tame conditions, simply due to fatigue stresses causing them to reach their yield point.
So I can't see this as being correct, nor true, most likely.

On the having water in her hulls when righting her. I should think that unless she's righted very carefully, this trapped water could quite easily tear her apart. Both structurally, in terms of her connectives, & macro structure. As well as it ripping apart every internal structure within the boat, & each hull or major sub-component. Such as bulkheads, longitudinals, & connectives. Which then would also degrade the integrity of her macro-structure, while being righted. Resulting again, in tearing her into large chunks if one wasn't exceedingly careful. If, in fact, it's possible at all.

Though I know that it has been done. But in a cruising boat, would then she be worth repairing, after her guts have been fully ripped out? Both by the water, & later by shipwrights, for her rebuild. With the truly pricey bit being that all of her coring would then likely need replacing.
Which in a racing, maxi multihull, with virtually no interior is possible, & fiscally makes sense. Given the cost of her hulls. But in a cruising boat? Likely not. Thoughts?

donradcliffe · 21-11-2016, 17:44

Quote:

Originally Posted by Cotemar

donradcliffe would you be planning for the eventual asteroid hitting earth also?

You do know that cruising catamarans are not designed to fly a hull, right?

You do know that cruising catamarans mast are designed to break away before a catamaran would flip, right?

No, I don't know that cruising catamarans masts are designed to break away before they fly a hull. I believe that is a misconception that is restricted to some CF posters. I would love to know where you get your information.

Reality is more like this

https://catamaranconcepts.com/2013/08/27/mastload/

where the diagram states that the Antares 44 mast is designed for 3 times the load it takes to fly a hull/ flip.