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Old 24-06-2012, 00:21   #196
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Re: Capsize Ratio's

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Originally Posted by cwyckham View Post
A cored hull with a well designed lay-up and vacuum bag construction (or infused would be even better) is going to be much lighter and possibly somewhat stronger than earlier builds were. This will make it safer in breaking seas.
Exactly. Sundeers have all that: very light and very strong. But there are only a few production builders who do the dry layup / infusion process correctly to achieve the goal. TPI Rhode Island is one of them, using the SCRIMP process.

ps, I was reading back a bit... wind can't capsize, waves do. This is true for monohulls but not multihulls, which can theoretically capsize from wind force alone.

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Old 24-06-2012, 00:28   #197
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Re: Capsize Ratio's

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Originally Posted by cwyckham View Post
A cored hull with a well designed lay-up and vacuum bag construction (or infused would be even better) is going to be much lighter and possibly somewhat stronger than earlier builds were. This will make it safer in breaking seas.
Lighter yes, stronger no. Old rules for plank on frame construction had enermous safety factors compared what's used today. That's mostly becouse the advances happened in the engineering practices as well as the homogenous materials so we know now the strength of materials exactly. With wood it's allways a bit quess work as it was with the earliest glassfiber designs so the designs had more safety factor, and the overall strength was more than today.
But..
What comes breaking seas I'm not worried about the hull integrity what ever the material. I would be worrying more about the hatches, lights, vent's, thruhulls etc, mast and other gear staying intact and in their place..
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Old 24-06-2012, 01:11   #198
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Originally Posted by TeddyDiver
Lighter yes, stronger no. Old rules for plank on frame construction had enermous safety factors compared what's used today. That's mostly becouse the advances happened in the engineering practices as well as the homogenous materials so we know now the strength of materials exactly. With wood it's allways a bit quess work as it was with the earliest glassfiber designs so the designs had more safety factor, and the overall strength was more than today.
But..
What comes breaking seas I'm not worried about the hull integrity what ever the material. I would be worrying more about the hatches, lights, vent's, thruhulls etc, mast and other gear staying intact and in their place..
BR Teddy
Interesting. But either strength or weight isn't the question, but the ratio. I'd be surprised if traditional wooden designs can match modern plastic boats.

The waves aren't really breaking onto the boat (making hatches and fittings a weak point). The issue is the boat being on the lee side of a large breaking wave, beam on. The top third of the wave just breaks of and falls into the trough. The boat will be rolled on is side and then fall through the air for 20'or so and land in the trough.

That's why light is good (less momentum when you hit) and strong is good (you just feel 20' on your side. Jordan, the series drogue guy published some great reports on this. They're googlable.

In fact, Jordan started by trying to find a hull design that would have prevented the Fastnet disaster and realized he was barking up the wrong tree. That's when he went after tactics and drogue design instead.
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Old 24-06-2012, 02:26   #199
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Re: Capsize Ratio's

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The waves aren't really breaking onto the boat (making hatches and fittings a weak point). The issue is the boat being on the lee side of a large breaking wave, beam on. The top third of the wave just breaks of and falls into the trough. The boat will be rolled on is side and then fall through the air for 20'or so and land in the trough..
Sorry being so negative all the time , the weight of the boat doesn't change anything. It's still the gravity that drops the boat and it's allways 10m/s­² and the end velocity down in the trough is the same and so is the impact.. I have no doupt that any sound sailboat A class hull wouldn't stand that impact but as I said not all the addons including keels, masts and hatches..
Agree about JSD
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Old 24-06-2012, 03:03   #200
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Re: Capsize Ratio's

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ps, I was reading back a bit... wind can't capsize, waves do. This is true for monohulls but not multihulls, which can theoretically capsize from wind force alone. .
Not just theorettically there was a catamaran that was capsized recently near here while at anchor in an enclosed bay. One woman was trapped inside and was very lucky to survive after a very brave individual dived down and rescued her.
The cat did not even have any sail up.
Yes it was windy!
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Old 24-06-2012, 04:20   #201
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In April I sailed my factory made boat from Valencia in Spain to The east coast of England some 1700 nm. Took all precautions for a serious journey planning to stop just once at Vilamoura in Portugal. We left with a good weather prospect and obviously kept a good eye on the weather forecast. Not the most experienced crew but with a good background especially in the safety aspect which as skipper and having my son on board was utmost in my preparations and mind.
We left heading south in a 4/5 NE wind, it was good and we made progress. Eight hours later we turned to the south west and as we did so the weather changed to an un forecast 7/8 from the WSW and the sea grew quickly. With gusts of 45-50 knots we decided to haul the sails and use the engine to keep us off the coast and under control. Things deteriorated rapidly, the radar came down off the mast and we managed to have our gps/plotter and radio go out of service. Anyway we carried on and kept control albeit a very slow bumpy and loud experience. Using iPad we managed to overcome the technical problems and although my crew member became badly sea sick I managed the situation efficiently..
Reading this thread I would concur that staying with the boat as long as possible is the best idea. We did loose a hatch catch on the focsale but hauled the dingy over it and that stopped too much water ingress (why do they stick hatch clips on with double sided tape? ) the out come was good although when we got home inspection of the hull and interior found we had sustained serious structural damage around the front of the hull especially around the bow thruster, the inside strengthening pieces were broken away from the hull.

Lessons learnt were that my plan worked, we survived three days of terrible conditions, the boat structure and sea keeping was above my expectations, constant pounding does damage the structure and if this happens again I will try and head a bit more off the swell to avoid the slamming you get.

Preparation and plans for eventualities are best mad BEFORE it happens and reading, talking and taking advice will prepare you more than you can imagine.

As an addendum the 'beast' of the Bay of Biscay was like a lamb - 3kn wind and like a mill pond, the metal sail helped us across the 350 nm.

Think this journey at 60 was my Everest !!!
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Old 24-06-2012, 04:54   #202
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Re: Capsize Ratio's

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Think this journey at 60 was my Everest !!!
sounds like you handled problems in some terrible conditions very well.
What kind of boat is it?
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Old 24-06-2012, 06:48   #203
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Re: Capsize Ratio's

Benateau 40 Oceanus 2008. I should have added that although capsize ratio figures may be nice to have, it comes down to skill in keeping your boat out of the situation that will overturn it. Trying to keep heading into the swell is uncomfortable but negates to a certain degree the problem of sliding down the side of a wave and overturning or being dismasted or worse. From my conversations with those that know the damage I sustained can be expected from the stresses of water smashing into the hull like a lump of concrete.
To be honest most sailors avoid bad weather in the first place and when presented with it manage to overcome. Obviously luck also comes into it and I wish all good luck if the do come across such conditions.
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Old 24-06-2012, 07:06   #204
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Quote:
Originally Posted by TeddyDiver
Sorry being so negative all the time , the weight of the boat doesn't change anything. It's still the gravity that drops the boat and it's allways 10m/s*² and the end velocity down in the trough is the same and so is the impact.. I have no doupt that any sound sailboat A class hull wouldn't stand that impact but as I said not all the addons including keels, masts and hatches..
Agree about JSD
How can you quote the right math for acceleration by gravity and then make the collossal mistake by keaving out mass in the impact math?! It is speed multipled by mass that gives the power of impact. That is why big bullets hurt more...

No wooden planked on frame boats will do better than modern fiberglass designs on hull strength in big seas. And that is even before considering keel and rudder.

cheers,
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Old 24-06-2012, 09:32   #205
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Re: Capsize Ratio's

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How can you quote the right math for acceleration by gravity and then make the collossal mistake by keaving out mass in the impact math?! It is speed multipled by mass that gives the power of impact. That is why big bullets hurt more....
It's not a comparison like feather vs stone . Think about it more like crashing head on on a wall, water can be hard sometimes and it has nothing to do with thge weight of our heads. Where the mass comes in the equation is all the other things attached to boat wanting to continue their way and something gives up like alba mentioned and they didn't even capsize

"Things deteriorated rapidly, the radar came down off the mast..
..We did loose a hatch catch on the focsale ..
.. inspection of the hull and interior found we had sustained serious structural damage around the front of the hull especially around the bow thruster, the inside strengthening pieces were broken away from the hull."
BR Teddy
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Old 24-06-2012, 09:51   #206
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Quote:
Originally Posted by TeddyDiver
It's not a comparison like feather vs stone . Think about it more like crashing head on on a wall, water can be hard sometimes and it has nothing to do with thge weight of our heads. Where the mass comes in the equation is all the other things attached to boat wanting to continue their way and something gives up like alba mentioned and they didn't even capsize

"Things deteriorated rapidly, the radar came down off the mast..
..We did loose a hatch catch on the focsale ..
.. inspection of the hull and interior found we had sustained serious structural damage around the front of the hull especially around the bow thruster, the inside strengthening pieces were broken away from the hull."
BR Teddy
You have the image right. It is exactly like crashing into a wall. And that is why momentum and not speed is what is important to determine the damage done.

which identical truck will sustain more damage when it his the wall, the one carrying feathers or lead?

You're right about the hatches, etc. wanting to keep going after the impact. But you need to think of the hull itself. When the leeward side hits, the windward side wants to keep going. If the hull is very weak, the hull will completely pancake on impact as the windward side won't stop until it his the water too.

The weight of the windward side of the hull will determine how much force the leeward side must produce to stop it pancaking, and the strength of the hull determines whether that force can be applied without breaking the hull. Therefore, it is strength to weight ratio that will determine damage level to the hull
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Old 24-06-2012, 10:37   #207
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Re: Capsize Ratio's

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You have the image right. It is exactly like crashing into a wall. And that is why momentum and not speed is what is important to determine the damage done.

which identical truck will sustain more damage when it his the wall, the one carrying feathers or lead?

You're right about the hatches, etc. wanting to keep going after the impact. But you need to think of the hull itself. When the leeward side hits, the windward side wants to keep going. If the hull is very weak, the hull will completely pancake on impact as the windward side won't stop until it his the water too.

The weight of the windward side of the hull will determine how much force the leeward side must produce to stop it pancaking, and the strength of the hull determines whether that force can be applied without breaking the hull. Therefore, it is strength to weight ratio that will determine damage level to the hull
How could I explain this.. err.. Most cruising boats equal size don't have so much difference in weight that it should matter, but if we take a simplified example of the extremes, two boat's other 4t and other 8t assuming other things so close to equal as possible (not likely but anyway). We drop them 20' and see what happens. Both have about as much leeside structure hitting the water so the inertia of the 8t boat takes twice as much energy to stop as the 4t boat. This means the acceleration (ie hit against the water) in the 8t boat takes twice the time of the 4t boat. The heavier weather side has therefore also longer time to stop and no pancakes this time.. However the gear on both boats has same weight and the ripping forces are double in the lighter one..
BR Teddy
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Old 24-06-2012, 10:50   #208
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Quote:
Originally Posted by TeddyDiver
How could I explain this.. err.. Most cruising boats equal size don't have so much difference in weight that it should matter, but if we take a simplified example of the extremes, two boat's other 4t and other 8t assuming other things so close to equal as possible (not likely but anyway). We drop them 20' and see what happens. Both have about as much leeside structure hitting the water so the inertia of the 8t boat takes twice as much energy to stop as the 4t boat. This means the acceleration (ie hit against the water) in the 8t boat takes twice the time of the 4t boat. The heavier weather side has therefore also longer time to stop and no pancakes this time.. However the gear on both boats has same weight and the ripping forces are double in the lighter one..
BR Teddy
Beautiful! You've hit on a great thought experiment.

Now earlier you said that hitting the trough was like hitting a wall. I've been using the same approximation. So let's add to your thought experiment that we are dropping onto concrete. If we can agree on the effect there, we can move onto dynamic hydrodynamic effects if need be.

If we drop onto concrete, the boats will decelerate in the same time and the heavier boat will have twice the stresses on it. Do you agree?
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Old 24-06-2012, 11:11   #209
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This is no longer about capsize ratio. My experience. 80 knots wind speed east of the golf stream confused seas. Generally we ran off bare pole and or a tad of jib. There was a primary wave direction but occasionally a wave would broadside us. Significant impact dead on broadside. Water would flood the cockpit and everything was wet. This sounded like a friggin canon hitting the hull. Sailing on and having forward motion worked best. I would not consider a sea anchor in this condition. For a while the frequency was getting short. Had it gotten shorter we would have been endanger of pitch pole. That is where a drogue would be best deployed. The keel was able to keep hold of most waves and we were able to dissipate energy by good steering as we came down the wave face. Mostly steering was done by sense of resistance. Many hours of dark nights. Why no sea anchor. We would have been restricted cuffed by the deployment. The boat would have been falling ass end off the waves. The Pardies have a solution using a bridle. I am not bold enough to stick that much line off the bow. I would choose to diminish the energy that I need to transfer to a device. Maintain control of the boat. Most reading of survived storms do not involve a full collapsed wave free fall. Most are of lost control coming down the side of a wave or a rogue direction wave collapsing the keels bite or adversely transferring the dig in a broad side affront. I ran a power boat through a canal entrance and I miss judged the tide and wind effect. We free fell off steep walls for a good hour. Sustained no damage. So maybe a light hull would suffer less on impact but I doubt it would survive these conditions long enough to allow the waves to develope to a breaking state. A proper boat with good keel and gear. Ability to maintain control
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Old 24-06-2012, 11:28   #210
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Re: Capsize Ratio's

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If we drop onto concrete, the boats will decelerate in the same time and the heavier boat will have twice the stresses on it. Do you agree?
and twice the structure to withstand it.. No seriously, both hulls would disintegrate without a doupt (there's no thumb down smilie). However this totally irrelevant subject or do you know such pancake occasions?

Sabray, this haven't been about capsize ratio for looong time
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