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Old 06-02-2008, 13:14   #16
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Gideon - I hereby say you're full of chit. You have no direct knowledge of what took place with that overturned Voyage cat because NOBODY does. You have no idea whether the rig was lost immediately or was lost when it drug the bottom upon coming ashore. You have no idea that other production boats will sink if capsized. You're postering for your own benefit and it shows no class on your part. You should know better and I think you need a huge slice of humble pie.

dave
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Old 06-02-2008, 14:17   #17
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I haven't been following this thread, but I will soon go back and study it.

I enjoy a spirited debate, but this one appears to be occasionally bordering on personal disrespect; which the CruisersForum does NOT TOLERATE.

Please, let us take some care in choosing our words. As Southern Star said, "Heat does not make light."

BTW: Nice phrase Brad, I'm going to steal it.
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Old 06-02-2008, 14:33   #18
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Originally Posted by GordMay View Post
I haven't been following this thread, but I will soon go back and study it.

I enjoy a spirited debate, but this one appears to be occasionally bordering on personal disrespect; which the CruisersForum does NOT TOLERATE.

Please, let us take some care in choosing our words. As Southern Star said, "Heat does not make light."

BTW: Nice phrase Brad, I'm going to steal it.
Hey Gordo - while you're reviewing this for "personal disrespect" also be looking for "lack of professional integrity" or "misrepresentations" by commercial vendors. I would presume the forum does not tolerate those attributes either.

Dave
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Old 06-02-2008, 16:14   #19
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Hallo Dave


Gideon stated:
11200 lbs of floatable foam at a weight of ,8 kilo per liter gives you 9000 lbs of lifting force.

Gideon
How do you work that out?

First the figures don't add up, secondly, do you have the specific layup information on this boat? Do you know what all the internal furniture will give in the way of bouyancy?

Let's just work with your figures:

11200 lbs/2.2 = 5090 kg. Foam is 80 kg/m3 not 800 kg/m3! 5090/80 = 63.6 m3
This gives a buoyancy of 63,6 x 1025 (salt water density) = 65190 kgs.
From this we subtract the weight of the foam wich is 63,6 x 80 = 5090 kg
Difference is: 65190 - 5090 = 60100 kgs

Your result was "9000 lbs of lifting force" or around 4090 kgs. So 60100/4090=14.7 times off the mark!

Diesel is lighter than salt water, so will also give buoyancy.

I would suggest a more cautious approach to knocking other peoples designs would be more beneficial for all involved.

Alan
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Old 06-02-2008, 16:39   #20
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What does it matter if when a catamaran capsizes that it sinks or floats? You are STILL in the water and the way to survive is to get OUT of the water and OUT of the weather. Isn't this why it is a good idea to have a life raft or at least an unsinkable small boat that you can get up into and OUT of the water?

Also it is very ignorant and arrogant to think that one design is inherently better or superior to another. That depends on the needs of the individual. There are as many design needs as there are people who go out on the water. This means that there is no such thing as the ideal boat, or the ideal rig or the ideal hull material...etc etc etc. Anybody who thinks there is does not understand people.
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Old 06-02-2008, 17:21   #21
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What does it matter if when a catamaran capsizes that it sinks or floats? You are STILL in the water and the way to survive is to get OUT of the water and OUT of the weather. Isn't this why it is a good idea to have a life raft or at least an unsinkable small boat that you can get up into and OUT of the water?
It can make a huge difference. It's been years since I read it, and I forget the details of it, but there is a book about a catamaran which capsized somewhere in the pacific, and remained afloat and habitable for months (3 or 4 months? I cant remember) . The crew (of 3 I think) lived in and on the upturned boat until it drifted ashore.

When they were found they were in such good health that the story was at first thought to be a hoax!

Compared to Steven Callahan who survived in a liferaft for a long time, but who's condition left no doubt that he had done it very tough!

Then there is Tony Bullimore, who would have been far less likely to have survived in the Southern ocean for as long as he did, if he had been forced into a liferaft. The ability to remain afloat upside down could be an asset in a monohull too.
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Old 06-02-2008, 17:36   #22
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Nordic Cat, you don't understand my procedure for calculating floatation. I put all of the displaced volume on one side of the equation, and all of the weight on the other. Your method is to calculate the net volume of each part of the boat. I am too lazy to do it your way, as your way has many more (unnecessary) steps. As to knowing the volume of the furnishings and bulkheads, I am the boat's designer. Of course I know the volume and weights of the furnishings--and they are amazingly high. I am less informed about the volume of the furnishings of your typical catamaran, but I can make a reasonable guess. ************************************************** * FastCat is a boat builder, and I suspect very involved in design, as well. Re-read his posts on the subject, which show a clear understanding of the question. Thanks for the kind thoughts, FastCat. Good luck with your new 52--it should sail like a rocket ship. How would you like to tell us what its price is? I figure my BigCat can be built by the home builder for less than $250,000 USD, ccsts as of 6 months ago. ************************************************** * As to looks, sorry, I am trying to make a really easy to build boat that doesn't cost much, and looks aren't high on my priorities list. I did put unnecessary curves in the sails to suit my tastes, just for looks-though some claim that an ellipse is the best shape for sails. Draw a cabin to suit your preferences, if you like--the design doesn't depend on its cabin to hold the hulls together, so you have no structural considerations to worry about. I didn't design the boat to sell or to sell plans--I am a jumped up home boat builder at heart. I started studying naval architecture 30 years ago, with Skene's Elements of Yacht Design, after I found my Ericson 35 to have serious deficiencies as a voyaging boat.
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Old 06-02-2008, 18:42   #23
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Fastcat did quote the density of flotation foam at 0.8 kg/litre. 80% of that of fresh water. Using that figure, it's not surprising he believes that most production cats will sink.

His figures for floatation force were correspondingly wrong. ie. 9000 lbs of floatation force would in reality be closer to 90,000 lbs.
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Old 06-02-2008, 19:10   #24
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Buoyancy -sink or swim?

Quote:
Originally Posted by 44'cruisingcat View Post
Fastcat did quote the density of flotation foam at 0.8 kg/litre. 80% of that of fresh water. Using that figure, it's not surprising he believes that most production cats will sink.

His figures for floatation force were correspondingly wrong. ie. 9000 lbs of floatation force would in reality be closer to 90,000 lbs.
I'll let Gideon check his own math. There is nothing wrong with mine, however, and I didn't bother to check the density of anything-just its volume on one side of the equation, and its weight on the other. Each is totaled separately, and they are brought together only at the end. I repeat, most average displacement stock catamarans hover right around neutral buoyancy, when loaded for voyaging, which is the subject of my thread. Very low weight-high cost catamarans which use the kind of materials Africancats use would come out better, because their volumes would be the same on one side of the equation, and their weights would come out lower on the other. How high they will float is another issue, and I would say that even these boats need extra buoyancy in order to float high enough to make them good liferafts. The buoyancy needs to be about halfway up in the structure if it is to be useful with the boat right side up or upside down. If you don't think Fastcat has a good grasp of the details, you should check out his website at African Cats: comfortable lightweight performance leisure catamarans -his attention to detail regarding weight is an obsession verging on fanatacism.
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Old 06-02-2008, 19:50   #25
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Originally Posted by 44'cruisingcat View Post
It can make a huge difference. It's been years since I read it, and I forget the details of it, but there is a book about a catamaran which capsized somewhere in the pacific, and remained afloat and habitable for months (3 or 4 months? I cant remember) . The crew (of 3 I think) lived in and on the upturned boat until it drifted ashore.

When they were found they were in such good health that the story was at first thought to be a hoax!

Compared to Steven Callahan who survived in a liferaft for a long time, but who's condition left no doubt that he had done it very tough!

Then there is Tony Bullimore, who would have been far less likely to have survived in the Southern ocean for as long as he did, if he had been forced into a liferaft. The ability to remain afloat upside down could be an asset in a monohull too.
How does one upright a capsized catamaran without some external means other than a freak wave? ...and then proceed to live on it? My impression has always been that cats are more stable capsized than shiny side up. My point is that it does not matter at all if you are in the water or grasping on to a capsized catamaran...you are still in the water, exposed to the elements and probably with no means of collecting fresh water.

Given that, this whole debate about whether a catamaran floats or not is pretty irrelevant.
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Old 06-02-2008, 20:11   #26
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Diesel is lighter than salt water, so will also give buoyancy.
Fresh water is also less dense than salt water, so tankage will tend to float the boat, not sink it (whether they're empty or full).
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Old 06-02-2008, 21:00   #27
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Actually, I have a plan for "upside down" I haven't mentioned. It consists of pre-installing points to attach a "tennis net" at each end of the bridge deck. Why keep with the boat? Well, it is a very rich source of resources, for one thing. If your boat has multiple watertight compartments (an old, very old, junk idea, by the way,) most of your food and other stuff won't wash out. And even an upside down boat has got to be safer and more comfortable than a high-cost kiddie pool. Catamarans should either have entry hatches under the bridgedeck (not for me, thanks, no big holes near the waterline for me,) or carry a keyhole type saw to saw your way into upside down hulls. You'll find lots of advice for capsize situations in standard books like Chris White's book. **************************** And Lodesman, there is very little floatation value in fresh water and not much more in diesel. I repeat, however, that this method of analyzing floatation is doing things the hard way. My design is quite superior to the usual for the upside down scenario, because water won't be washing throughout the accommodation, and because of the location of its extra buoyancy. ***********************************To those that complain that I point out my experience, I can only say, life isn't fair. I made my first voyage 36 years ago, and I do know more of relevance than many, though certainly not all, posters. Further, I have dozens of books on boat building and yacht design, and I have studied them all at length. I learned fiberglass boatbuilding at Skookum's yard in the early 1970s, and finished out the boat I sailed across the Pacific. If you think that reading 5 books, doing a daysail and sailing vacation now and then, and reading a yachting magazine or two every month is going to put you in this league, guess again. Thirty five years ago I didn't bitch that others thought that knew more than I did-I learned from them. As far as I am concerned, Eric Hiscock is somewhere between Our Founder and Our Patron Saint. I don't whine that Chris White, Gregor Tarjan, and Derek Kelsall think they know more than I do about catamarans-I buy their books, study them as though I had to pass a test, and silently thank them for passing their knowledge on.
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Old 06-02-2008, 21:08   #28
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Perhaps this is a silly question but what if you do manage to cut your way into a capsized catamaran? ...what do you do when most all the air has been bled out and the boat is sitting even further down in the water...(provided it has positive flotation) and enough of an airspace and enough oxygen left to breathe...nevermind the probable layer of fuel and lube oil that would burn your eyes between the air and the water inside the hull. What would be the point of even attempting to access the inside of the hull?

I think I would prefer the glorified kiddie pool.
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Old 06-02-2008, 21:36   #29
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How does one upright a capsized catamaran without some external means other than a freak wave? ...and then proceed to live on it? My impression has always been that cats are more stable capsized than shiny side up. My point is that it does not matter at all if you are in the water or grasping on to a capsized catamaran...you are still in the water, exposed to the elements and probably with no means of collecting fresh water.

Given that, this whole debate about whether a catamaran floats or not is pretty irrelevant.
You don't right the boat, you live on and in it upside-down. What most people call "escape hatches" are actually more likely to be used as re-entry hatches.

No doubt, the interior of an upturned boat will be a mess - and possibly contaminated with diesel (although it shouldn't be if the diesel tank placement has been thought about) BUT, in any kind of sea, it would still be more comfortable and safer than a liferaft. It should also likely have plenty of fresh water still in the tanks, and will make a much more visible "target" for rescue. With some forward planning you can ensure that an upside-down cat would be a perfectly livable in a survival situation.
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Old 06-02-2008, 21:44   #30
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Quote:
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Gideon - I hereby say you're full of chit. You have no direct knowledge of what took place with that overturned Voyage cat because NOBODY does. You have no idea whether the rig was lost immediately or was lost when it drug the bottom upon coming ashore. You have no idea that other production boats will sink if capsized. You're postering for your own benefit and it shows no class on your part. You should know better and I think you need a huge slice of humble pie.

dave
You are rigth Dave I was not there when it happened ( very lucky )
In all calculations for safety trapped air is not counted for buoyancy. Even if the mast had been on and the bimini , rudder, etc there would not have been enough actual boyancy to keep the boat afloat.
It boils down to calculations, weigth of the boat versus in build buoyancy.
If the last is more than the first it will float, if not the fact that it stayed afloat is pure luck becasue of heaps of trapped air but in calculations you cannot count on trapped air. If you make your calculations on your boat surface area ( hull deck bulkheads floors and keep in mind that 20 mm foam of H 80 has been used and 50 squire meter of this foam makes one cubic meter and has a total lifting force of 800 kilo, now ad the space of your watertight chambers , 1 liter of space gives one kilo of upward force.
ad all this up , subtract all weight including rig , extra,s and even personal effects and you will see what i mean.

And I am not doing this for personal gain , we are sold out and I do this for a hobby, all I care about is that better and safer boats get build.

greetings.
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