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  #11  
Old 07-08-2005
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Sailmc is on a distinguished road
the concept of unsinkable yachts

Watertight bulkheads and compartments are probably the best way to guard against catastrophic collision damage. Amels and a few others have them. It would not be very difficult for even production boat builders to design them in.
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  #12  
Old 07-08-2005
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JeffC_ is on a distinguished road
the concept of unsinkable yachts

Whoosh posted:<blockquote>''Unsinkable'' boats are not UNcatastrophic Event boats, and so a fire may still require the crew to abandon the boat...but that´s a small portion of the issues faced by an owner today. Beyond this, <em>I´m not sure what motivated this post.</em> (empahsis added)</blockquote>
What motivated it, indeed? That seems to be the central question.
As they say in Britian, "He''s certainly on about <em>something…</em>
+++ +++

While I''m here:
Isn''t it just scandalous that Etap is so concerned about safety? That they''ve left the mold (er, fold) to pursue it? That they take it upon themselves to <em>innovate</em>? Why don''t they just follow accepted practice, and quit fiddling with things like buoyancy & steering systems? Things are just fine the way they are. It pumps up the price of boats, and we all know that''s just bad for sailing.

What do they think they are, visionaries, or something?
+++ +++

Good point, Jack, about the skin-foam-skin arrangement protecting against a holing in the first place.
<blockquote>Ha-ha, you nasty sumberged rock. So you reached out and bit me, and thought you would tear a gaping hole along the underside of my yacht, and laugh to see me founder in your little graveyard, bailing, bailing, but sinking to my death exhausted and defeated? But wait: you think you have punctured my hull, but you have only broken the outer shell. Did you not feel the cushion of my foam against your granite teeth? You have not killed me; you have only scratched me, like an insect. See, I stand in my saloon, and my feet are not wet. My bilge pumps remain asleep. My cans of beans remain dry. My EPIRB remains in its prayerful case. And I sail on.

You have claimed many ships, you treacherous, slime-covered stone. But things are changing. Go, tell your sinister friends, the logs, and the sleeping metal whales of the world''s seas, the shipping containers. Tell them! We shall no longer be so easily pulled down to the watery death you desire for us. Ha! I no longer worry through the night watch. I no longer eye my liferaft with such loathing love. You do not strike the fear in my heart that you once did, for now I know I will arrive safely in my port despite you!</blockquote>
Distance-voyaging singlehanders get a bit, um, detached.
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  #13  
Old 07-12-2005
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splitmind is on a distinguished road
the concept of unsinkable yachts

One benefit of the foam often not mentioned is the insulating effect. The hull is quieter, dryer, and more temperate than an uninsulated hull.

For cold climate sailors this is a definate plus that could negate the lost space issue when making a decision.
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  #14  
Old 07-13-2005
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GordMay is on a distinguished road
the concept of unsinkable yachts

I did NOT write this article, but (unfortunately) I cannot recall where I originally got it. FWIW:

Making a Boat Unsinkable ~ by "Unknown"

Fibreglass does not float, an early objection - but the same was said of the first iron ships. If flooded, few wooden yachts with ballast and an engine will float either. So making a boat unsinkable is a problem to be tackled at the design stage. The structural requirements would make it very difficult to achieve later. There are two fundamental principles:
1) Even the lightest buoyancy material, air, requires space: for one ton of buoyancy you need one cubic metre (roughly 35 cubic feet) of air - the equivalent volume of five big oil drums. For the average 35- to 40-foot ocean cruiser weighing ten tons, there would have to be room for the equivalent of 50 oil drums! Moreover the paper displacement figure is just for the bare boat. To this must be added the two or three tons of stores, equipment and possessions - and for any ocean cruiser we really are talking about tons, and probably underestimating. The more stores and equipment, all absolutely essential, the less room for buoyancy, and conversely the more buoyancy the less room for essentials. There has to be room to work the boat and live in reasonable comfort when in harbour where the boat will spend a lot more time than at sea. Therefore the sheer space required for using trapped air as a buoyancy material rules out anything except emergency air bags, and once those are operated, on purpose or accidentally, the boat becomes unliveable and "unsailable".

2) It is not sufficient just to keep the boat afloat, decks awash. Sheer survival requires a degree of shelter, habitability and perhaps "sailability". The widow maker is exposure and hypothermia. This means the boat must float high enough for the crew to remain reasonably dry, sheltered from wind and water, able to cook, and have electrical power to operate a radio and lights. Perhaps also to run an engine, especially if a power boat, and ideally to sail after a fashion. Morale too is very important. It is far better to stick with the boat, if possible, than take to a "liferaft". However in practical terms this amount of buoyancy is almost impossible to achieve with a ballasted, well-equipped cruising monohull, although feasible with a catamaran.

Sadlers'', for example, have built unsinkable boats by use of double skinned, foam-injected hulls, but even so still have to steal essential storage space. Both skins are fairly light construction and do not allow for the tons of extra weight essential for ocean cruising. Double skinned hulls like this and foam-filled spaces can only be done while the boat is being moulded, and are therefore design features. It is claimed that damage is limited with this type of construction. This may be so with minor damage. But the foam filling must be weak, or it becomes too heavy, and would not prevent a serious impact from damaging the inner skin too. Foamed compartments can become waterlogged and are then almost impossible to dry. Even closed-cell foam will disintegrate when wet, and then flotation is lost.

Aiming at unsinkability, ships have watertight doors and bulkheads. This is not practicable on a yacht. The interference with habitability would be unacceptable on anything but the most dedicated, large, ocean-going racer. The average yacht bulkhead is not strong enough; the sheer pressure of, say, a forecabin full of water would be formidable, even without surging. Most bulkheads, being designed for inward compression only, are secured by weak angles, sometimes none at all, and would be torn adrift. Possibly the hull or deck would burst too. The weight would also affect the stability.

Well meaning bureaucrats specify collision bulkheads. Sadly they know little about boats and their thinking is based on fast, wide-fronted cars on narrow roads where head-on collisions are the rule. With boats, free to move in any direction, head-on collisions between two pointed end shapes are very unusual, rather like two spears meeting in mid-air. Most impacts are glancing blows and if between two boats, the victim is usually hit on the forward topsides or amidships where it is weak. The victim sinks and the attacker, with its strong stem taking the impact, escapes relatively unscathed. Even a hard-sailed dinghy can sink a much larger boat. Because it interferes with the accommodation, a collision bulkhead is usually placed well forward. With the usual overhang this is above the waterline and is therefore just a token, the collision bulkhead commonly being the aft end of the chain locker. Most boats have an overhang forward and fast power boats in particular sail with a pronounced bows-high trim so that any impact with rocks or debris will be well aft of any collision bulkhead. In all my years as a surveyor I remember only one case of a dangerous leak due to impact on the waterline. This was when a Moody hit a heavy mooring buoy, and it was well aft of the mandatory collision bulkhead. I have seen a few crumpled bows from hitting dock walls or lock gates, most often just resulting in bent pulpits. But I have seen plenty of underwater damage from rocks. Because any dangerous impact will be at or below the waterline, it makes more sense to have a double bottom.

The Watertight Lockers Option
One idea seldom mentioned, and more in the way of damage control than unsinkability, is to have numerous small watertight compartments. This is copying ship practice, where each watertight section is small enough that flooding it does not affect the integrity of the ship. However, on a yacht it is not practicable to divide the boat with watertight bulkheads, and even if it was, the spaces would much too large. But almost every cruising boat has dozens of lockers which could be made watertight fairly easily. This is not the same as filling them with buoyancy, as is done with "unsinkable" boats. By making the lockers watertight and fitting watertight lids, such as large dinghy hatches, they would provide some limited buoyancy yet still remain useable, just as a ship cannot afford to lose the payload of a hold.

As well as providing buoyancy, making lockers watertight would have the even more important function of containing a serious leak. With good planning the boat could virtually have a double skin over the entire underwater area. (If a pan moulding was used it would need to be stronger and better attached than usual because, being considered just accommodation, most are lightly moulded and weakly bonded. They generally break away and split if the hull is damaged.) One or more such watertight lockers could flood without unduly affecting stability and, most important, would prevent the rest of the boat filling and sinking. Essential systems like batteries and engines could be in their own watertight compartments so that the boat remains operational.

Another important factor is that having many small, watertight compartments would prevent surging, which alone can cause damage and seriously upset the stability of a flooded boat, even if nominally unsinkable. Moreover, a lot of this work could be retrospective and done in preparation for an ocean cruise.
Buoyancy and unsinkability sound like nice safety features. But do your sums. Work out the weight of the boat - plus everything you have or intend to stuff inside it. To be on the safe side double this at least; it is invariably underestimated. On the first haul-out after an Atlantic crossing every crew finds they have to raise the waterline several inches! On my 31-foot-waterline boat the rate of waterline change is roughly two inches per ton, a fairly typical figure.
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  #15  
Old 07-13-2005
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owenmccall is on a distinguished road
the concept of unsinkable yachts

Your article is "Fibreglass Boats and Damage Control" by Hugo de Plessis, found in the November 2004 issue of "Caribbean Compass".

Owen
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  #16  
Old 07-14-2005
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Johnrb is on a distinguished road
the concept of unsinkable yachts

Gord:

I think the article you are referring to was written by James Baldwin and is called "In Search of the Unsinkable Boat" and was published here in Sailnet a few of years ago. Mr. Baldwin has circumnavigated (twice I believe) and wrote the article on making his Pearson Triton unsinkable. The link is below:

http://www.sailnet.com/collections/articles/index.cfm?articleid=baldwi0014
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  #17  
Old 07-14-2005
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JeffC_ is on a distinguished road
the concept of unsinkable yachts

John, if you''d read the article you linked, you could tell it''s not the same text.

The (allegedly) de Plessis article considers the idea of watertight compartments; Baldwin''s article is a practical "How I Did It" explanation detailing the conversion of his Pearson Triton.<hr><a href="http://www.atomvoyages.com">Baldwin is fun to read</a>, if only to be amazed at the ingenuity and resoursefulness of someone who has gone his own way: engineless, radical modifications to his boat, etc. Although I don''t think I''ll be following his model, I admire his determination, and without an engine, I''ll bet his seamanship is top notch.
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  #18  
Old 07-15-2005
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Johnrb is on a distinguished road
the concept of unsinkable yachts

Jeff, I had read the Baldwin article when it was first published a few years ago. I thought it a useful and practical demonstration of how someone, through ingenuity and with a limited budget, thought a problem out and solved it. Beyond that, I have no additional comment about the topic or the de Plessis article.
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  #19  
Old 07-15-2005
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h20ski is on a distinguished road
the concept of unsinkable yachts

is ETAP the only manufacturer of large "unsinkable" (theoretically), foam filled sailboats?
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  #20  
Old 07-15-2005
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JeffC_ is on a distinguished road
the concept of unsinkable yachts

Sorry, John: my post comes off reading kind of harsh, doesn''t it? That wasn''t my intention.

And I certainly wasn''t trying to school you about James Baldwin. I was just talking to the wind. (I''m like a lot of men; I sometimes like to hear my own voice).

Fair Winds,
Jeff
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