Why did Asteria sink o quickly?

[BurnitBlue]

During the thread about the Contessa doppelganger i read about a boat in the GGR that had just sunk in about 5 minutes with water pouring unchecked into the saloon. The report caught my eye because the Contessa 32 has a counter stern. Somehow I knew that the boat that sank had a similar cointer. It generated a small amount of speculation.

There is a fascinating round table discussion on youtube between Tapio the owner Skipper, a Navel Achitect, and someone from GGR (I think). The Navel Achitect had made simulations of the forces on the counter.from backstay, two running backstays and the Hydrovane steering system.

The discussion on you tube is under the title GGR2022 Tapio and his team talk about Why Asteria saink. I can't do links on my PC. Sorry if this has already been posted elsewhere. How could a yacht in relative calm seas sink so quickly when the boat had 6 (SIX) watertight bulkheads installed.

The Navel designer actually discounted the counter causing the sinking. My thoughts are that the owner installed bulkheads, created a stress point which ripped the boat in half. Fascinating stuff. The drawings and simulations are presented for the discussion.

BTW, Apropo the thread about the Contesss 32. My old passport arrived at the passport office yesterday. I now wait for the new passport then I can travel to view the doppelganger suggestion made on that thread.

 

[lustyd]

 

[BurnitBlue]

I won't ask you how you managed to post that video because I won't understand the answer. But thank you.

 

[Sandy]

Good lord what a rambling conversation, I lost the will to live, and I've been in some tortuously detailed meetings in the past! Did they come up with any conclusions apart from my 10 second one I posted in the original thread? They had forgotten basic Year 10 mechanics; a triangle is stronger and they should have fitted the Hydrovane using one.

@BurnitBlue use the icon arrowed below to insert links to YouTube.

 

[doug748]

I could not stick the video out either.

However I hope someone did careful sums over the 1/2 inch (12mm) rigging wire ( )

.

 

[BurnitBlue]

Good lord what a rambling conversation, I lost the will to live, and I've been in some tortuously detailed meetings in the past! Did they come up with any conclusions apart from my 10 second one I posted in the original thread? They had forgotten basic Year 10 mechanics; a triangle is stronger and they should have fitted the Hydrovane using one.

@BurnitBlue use the icon arrowed below to insert links to YouTube.

View attachment 150651

I am quite used to listenibg to non English speaking people but even so, they seemed to struggle for every word. Very frustrating. There was only a vague conclusion and that ir was caused by a very big hole or crack in the saloon area. They concluded that the breach in the hull was NOT caused by a whale, a container, a bulkhead stress point, a collapse of the counter, or the rudder or prop shaft. The hole in the hull was calculated from buoyancy figures and time to sink to be equivalent to 10 through hull fittings all open at the same instant.

My take is that there were so many modifications with additional watertight bulkheads a hydrovane on a flimsy counter, two forestays with roller gear that all normal design parameters are invalid. I still suspect the counter causing stress at the extra bulkheads.

On the subject of liferafts, I have always followed the Pardey advise that the boat should be strong and bullet proof to become its own liferaft. I have changed my mind so I will be researching liferafts for 2023. Boy, have I got a lot to learn. A liferaft certainly saved the skipper of Asteria. However the liferaft alone would be useless for him without the epirbs, and sat phones and a team from GG22

 

[BurnitBlue]

I could not stick the video out either.

However I hope someone did careful sums over the 1/2 inch (12mm) rigging wire ( )

.

I agree. Some years ago I was involved with a boat that went banana shape while on the hard. The owner had just fitted twin forestays. He used stress guages to make each forestay equal to his measurement when the boat had only one. He did not want any sag in the genoas so he wound up the backstay to get the numbers he wanted. At one stroke he doubled the bending moment on the boat. I think the same thing would happen if the standing rigging was increased in diameter.

 

[Slowboat35]

Unsure what cosmetic surgeons have to do with structural issues in boats...

 

[eebygum]

I give a potential another scenario why Asteria sank; which is based upon the sinking of the 37ft Inis Mor off the Saltees Islands on the 3rd June 2017.

I was actually sailing westbound inside of Tuskar rock on the day this happened and responded to the RNLI call for assistance (the crew were quickly picked up by helicopter but the boat sank within minutes).

It wasn’t a particularly bad day and we had saw the yacht breeze past us earlier in the afternoon so why did a well founded racing yacht and previous winner of the Round Ireland race with competent crew sink and are there any lessons learnt in respect to Asteria ?

I’ve not been able to find a marine accident report but there was speculation at the time it was a damaged seacock:

Did Failed Seacock Sink Inis Mor?

The crew allegedly all been on deck for a couple of hours and had not been down below to notice the water ingress; no high Water bilge alarms went off and by the time the crew realised it was too late and the yacht sank within minutes.

Scottish Yacht 'Inis Mor' Sinks On Way to ICRA Championships at Royal Cork, All Crew Safe

Could exactly the same sort of ‘slow water’ ingress from a failed thru-hull fitting potentially leading to a catastrophic failure be the cause ?

I guess we will never know unless a robot goes down and has a look !

 

[oldharry]

How do you locate even a bad leak once the point of ingress is well submerged? You may if you are lucky see daylight,through it, but that's about your only chance of finding it.

 

[oldbloke]

I agree. Some years ago I was involved with a boat that went banana shape while on the hard. The owner had just fitted twin forestays. He used stress guages to make each forestay equal to his measurement when the boat had only one. He did not want any sag in the genoas so he wound up the backstay to get the numbers he wanted. At one stroke he doubled the bending moment on the boat. I think the same thing would happen if the standing rigging was increased in diameter.

As someone who mainly sails dinghies and small keelboats I am used to thinking about and measuring rig tensions in kilograms. The tendency on here to measure tension by stretch might be a reasonable and convenient proxy in terms of the AWB with usual rigging but has worried me that it is a step too remote from what you are actually trying to achieve.
So , increasing your shrouds from 6 to 12mm would have minimal effect on your rig tension (sl less elastic and sl heavier rig) unless instead of maintaining a preexisting rig tension of ,say, 100kg, you tried to maintain a stretch of 5mm which might well bend your boat in half.
I can't quite work out whether 2 forestays of the same tension double the force ,or have no effect.

 

[BurnitBlue]

As someone who mainly sails dinghies and small keelboats I am used to thinking about and measuring rig tensions in kilograms. The tendency on here to measure tension by stretch might be a reasonable and convenient proxy in terms of the AWB with usual rigging but has worried me that it is a step too remote from what you are actually trying to achieve.
So , increasing your shrouds from 6 to 12mm would have minimal effect on your rig tension (sl less elastic and sl heavier rig) unless instead of maintaining a preexisting rig tension of ,say, 100kg, you tried to maintain a stretch of 5mm which might well bend your boat in half.
I can't quite work out whether 2 forestays of the same tension double the force ,or have no effect.

The way I saw it was a tug of war. If you have one man at one end A of the rope pulling at (say) 500 pounds and another man on the other end B also pulling at 500 pounds you have balance. Then if another man joins at end B also pulling at 500 pounds then 500 pounds at A is opposed by 1000 pounds at B. To get back in balance the man at end (A) must increase his effort by another 500 pounds. If he does that 1000 pounds at one end will balance out the 1000 pounds at the other end. BUT, the rope may snap. Substituting A and B to forestay and backstay on a boat the doubling of the force may bend the boat. Am I right or wrong?

 

[oldbloke]

I think you are probably right.

 

[lustyd]

force may bend the boat

Or it could pull the mast through the deck/hull. It all just depends where the weak points are. I'm pretty sure on my old vivacity it would have crushed the deck before bending the boat

 

[BurnitBlue]

Or it could pull the mast through the deck/hull. It all just depends where the weak points are. I'm pretty sure on my old vivacity it would have crushed the deck before bending the boat

Whatever the effect of adding a second forestay it must be done knowing the danger. The problem arises because many sailors do not like a sagging leading edge on a genoa, so they crank up the forestay and/or backstay. Actually Doug748 implied that Asteria raised the diameter of his standing rigging. I am not mathematically smart enough to know how much the diameter must be increased to get the same effect as adding a second wire.

 

[mjcoon]

... I am not mathematically smart enough to know how much the diameter must be increased to get the same effect as adding a second wire.

By root-two? (Square law.)

 

[BurnitBlue]

By root-two? (Square law.)

Not that easy because rigging wire is in itself a twisted bunch of 19 seperate wires. Google does not know either.

 

[mjcoon]

Not that easy because rigging wire is in itself a twisted bunch of 19 separate wires. Google does not know either.

But with the same number of component wires the ratio of wire cross-section to overall area should be consistent. Thus just a scale change.

 

[BurnitBlue]

But with the same number of component wires the ratio of wire cross-section to overall area should be consistent. Thus just a scale change.

You may be right. It must be a well studied subject. Think of all those other applications of wire diameter. Suspension bridges, cranes, airplane wings, elevator cables, etc. There could be a simple app on Google store to calculate the strains and stresses. I bet every yacht designer has a table of wire dimensions pinned to his wall.

 

[lustyd]

But with the same number of component wires the ratio of wire cross-section to overall area should be consistent. Thus just a scale change.

But did you account for the extra weight of steel in the wire?