Cat Capsize Lake Macquarie

[chrisr]

Originally Posted by catsketcher

If you count the area under the stability curve, then this is not always the case. Even performance cats have tremendous stability as measured by the torque required to rotate them.

As to being light, all boats require weight to make them stable. That is because weight is part of the stability equation. A designer has to make the judgment as to when to stop adding weight. Even the heaviest boat could be more stable if someone added more weight to it. So no designer would like to make their boats lighter ad infinitum. To do so would reduce the boat's stability to zero. They design the hulls to cope with a certain weight, usually boats, like people, find it hard to keep the weight off. Hence the striving to keep the weight down. If you build a boat, there is always the pre-occupation with weight saving, so that the structure is light and you can carry more stuff.

that's a very interesting graph...can you tell me where you got it ?

as a totally theoretical point : i suspect a boat with zero weight would still have stability if fitted with foils. such rely on dynamic lift - not a righting couple.

cheers,

[44'cruisingcat]

Originally Posted by arsenelupiga

there is no doubt keeled monohul is more stable than cat.

https://m.facebook.com/story.php?sto...&id=1044520998

[catsketcher]

The graph is from John Shuttleworth's website. He is a very clever designer who has a maths and engineering background.

The only boat I know of that does not require weight is the world speed record holder Sailrocket. It uses a downward acting foil (called a Bruce foil) to counter the rig loading at its windward side. Leeward side foils lift, then you need either weight or some other downward acting force to windward to resist the torque created by the rig.

Monos, multis, heavy or light, all boats (apart from Sailrocket and other Bruce foil boats) have to have a CG to windward of the CB when sailing. The locations may be higher or lower but there is nothing that special about the idea. It is just torque - Torque = Force x distance. The rig produces a torque that the boat needs to equal - or it falls over. Multis reduce the size of the weight force but increase the lever arm to get a large torque. Heavy monos increase the weight force because the lever arm is reduced and get similar torque. Its all pretty basic physics and each way produces a torque. There are no magic numbers - just ones that fit the purpose of the boat.

[chrisr]

Originally Posted by catsketcher

The graph is from John Shuttleworth's website. He is a very clever designer who has a maths and engineering background.

The only boat I know of that does not require weight is the world speed record holder Sailrocket. It uses a downward acting foil (called a Bruce foil) to counter the rig loading at its windward side. Leeward side foils lift, then you need either weight or some other downward acting force to windward to resist the torque created by the rig.

Monos, multis, heavy or light, all boats (apart from Sailrocket and other Bruce foil boats) have to have a CG to windward of the CB when sailing. The locations may be higher or lower but there is nothing that special about the idea. It is just torque - Torque = Force x distance. The rig produces a torque that the boat needs to equal - or it falls over. Multis reduce the size of the weight force but increase the lever arm to get a large torque. Heavy monos increase the weight force because the lever arm is reduced and get similar torque. Its all pretty basic physics and each way produces a torque. There are no magic numbers - just ones that fit the purpose of the boat.

thanks

i know (of) john. will have a look at his website. always looking to learn more

incidentally, all my stability training was to do with ships. in such, the COG is above the COB (unlike eg yachts). ships rely on transverse shift of COB when they heel, to create the righting moment. iow a ship, sitting upright, is inherently unstable and wanting to turn over.

cheers,

[conchaway]

Someone (note, moderators-- not me) said that you are all missing the point: It's not whether a monohull or a catamaran is easier to get knocked down; it's that if a catamaran goes far enough over, it stays upside down-- a well designed and sealed mono rights itself (At least that's what someone said).

[arsenelupiga]

Originally Posted by 44'cruisingcat

https://m.facebook.com/story.php?sto...&id=1044520998

[valhalla360]

Originally Posted by conchaway

Someone (note, moderators-- not me) said that you are all missing the point: It's not whether a monohull or a catamaran is easier to get knocked down; it's that if a catamaran goes far enough over, it stays upside down-- a well designed and sealed mono rights itself (At least that's what someone said).

Well if we are limiting it to well designed and the owner is paying attention to conditions (ie: seals up the openings)...

The comparable would be a cat not prone to falling over in a light breeze and an owner who keeps it properly reefed.

If you are going to assume a cat sailor on a light weight racing boat who doesn't know when to reef, we must likewise assume the mono sailor doesn't know to close up the hatches...because if you go 70-80 degrees over and the main companionway is wide open a lot of monos are going to the bottom before they have a chance to self right.

But back to the original discussion, did we ever hear why the cat went over? I'm still betting they hit bottom at high speed and cartwheeled into that position as I can't see them flipping due to wind alone and then drifting into that position.

[catsketcher]

Originally Posted by conchaway

Someone (note, moderators-- not me) said that you are all missing the point: It's not whether a monohull or a catamaran is easier to get knocked down; it's that if a catamaran goes far enough over, it stays upside down-- a well designed and sealed mono rights itself (At least that's what someone said).

This is obvious. Cats don't self right. Everyone already knows that, that is why we don't have to say it all the time. Boats get wet, they cost lost of money, barnacles grow when my antifoul gets old, a race occurs when two boats head the same way. Cats don't self right, monos dont like holes in them - each to their own.

[chrisr]

Originally Posted by valhalla360

Well if we are limiting it to well designed and the owner is paying attention to conditions (ie: seals up the openings)...

The comparable would be a cat not prone to falling over in a light breeze and an owner who keeps it properly reefed.

If you are going to assume a cat sailor on a light weight racing boat who doesn't know when to reef, we must likewise assume the mono sailor doesn't know to close up the hatches...because if you go 70-80 degrees over and the main companionway is wide open a lot of monos are going to the bottom before they have a chance to self right.

But back to the original discussion, did we ever hear why the cat went over? I'm still betting they hit bottom at high speed and cartwheeled into that position as I can't see them flipping due to wind alone and then drifting into that position.

nope...not a squeek...which is really disappointing. in the case with a sister boat a year or so ago folk died so police / coroner etc are involved so its sorta understandable that we never hear why it happened...but in this case no deaths or even serious injury (as far as we know). maybe because of insurance ?? or maybe owner is just too damn ashamed ??

cheers,

[44'cruisingcat]

Originally Posted by catsketcher

This is obvious. Cats don't self right. Everyone already knows that, that is why we don't have to say it all the time. .

No, apparently some people really do need to say it, over and over, all the time.

They probably think they're being very original. But they also probably think someone puts any value on their comments too.

[Mr B]

Originally Posted by catsketcher

This is obvious. Cats don't self right. Everyone already knows that, that is why we don't have to say it all the time.

Can you list all the cats upside down in the last year, ?????????????

[Tusitala]

It takes all kinds. Some people just need to yell about what is perfectly obvious to them that others seem oblivious to. I was at a mostly sailors party where I had a guy berating me for being irresponsible and putting my family in danger by sailing offshore with them on our trimaran. The same sailor attempted to power out one of the nastier inlets around here wind over tide while towing his dinghy and motor with pretty predictable results. Yeah, never did find that dinghy....

[Ssas5342]

It’s back! Mast is slightly bent but the boat is being fully restored better than new.

[Factor]

Originally Posted by Ssas5342

It’s back! Mast is slightly bent but the boat is being fully restored better than new.
Attachment 250602

Surely not, all the experts here reckoned a cat capsize is the end of the world as we know it.

[Mr B]

Originally Posted by Factor

Surely not, all the experts here reckoned a cat capsize is the end of the world as we know it.

Factor, Have you heard any more about the Cat that overturned near Green Island a couple of weeks back,
I was 3 hours north of it, Heading south, when they sent out the Mayday,
It hit a big sunfish,and overturned,
All three on board were rescued, I seen a piccy of it upside down,
I heard from another sailor in Refuge Cove that they had salvaged it,
But nothing since.
The owner only had it 3 days when it went over,
He bought it in Port Stephens and was on his way home,

Cheers Brian,