Whether you have a multihull or a small monohull, do you know whether your boat will float if it is completely full of water? How can you find this out before you are in a life-threatening situation? We beachcat sailors all seem to complacently accept that our boats will capsize but at least they will not sink. But is that definitely true? Nobody seems to know. I have recently heard that some of the newer, lighter, more high-tech cats, partly because of their hull construction, can definitely sink. So how can you be sure, aside from taking your boat out into relatively shallow water and deliberately trying to sink it? But nobody wants to do that, because if it really does sink, how do you get it floating again so you can get it back on shore? So if you have any doubt about whether your boat would float, do you stuff it full of styrofoam -- how do you know how much is enough?
My 1976 Hobie 16 had blocks of styrofoam built into it from the factory, plus it was made with fiberglass / foam sandwich construction. My Prindle 18 hulls contain no foam and I think it is solid fiberglass construction. The only hope for flotation with the Prindle would be if the bow or stern is pointed up to trap some air.
Jack (now you got me worried, Mary)
Hi Mary:
A simple and inexpensive solution are camping or mountain climbing cubitainers. They are collapsable water bottles that can be inflated once in your hull and provide dsiplacement that should help the boat limp to shore in the event of a hull failure.
MM
My first boat, a P18, yellow asym. hulls, #333.
While ~5mi offshore of West Beach, Galveston this boat began to take on water. I had a recent bottom job done, that had ruptured and leaked. To make a long stroy short, it floated after righting with the tops of the decks at the waterline, most everything underwater, but it floated my brother and I as a friend on a P16 towed the boat and us back to shore. It seemed that it had the floatation inherent in it not to sink, that was salt water however, may have made a difference.
I think someone should try it, take out the plugs, and inspection port lids, fully rigged, and see what it does, salt and fresh water. We could post it here in sort of a table format. I"m sure someone with a 6.0 could tell me their results 8'), it's be in the interest of safety research, let me know how your 6.0 does, I'll make a note.
Todd Bouton
N6.0na+
#111
the problem would then be getting the water out of the boat. Maybe the boat could be in shallow water and then you could replace the inspection ports and use an airpump (hopefully electric) to fill them mostly with air again. On my 6.0, the only holes in the hulls are the rear plugs and a rear inspection ports. The bulkheads would likely prevent air from escaping the bow of the boat if you just took the plugs and port covers off. That being said, it seems that it will be necessary to drill a hole in the bow of the boat ... I can't seem to find my drill at the moment but I'm pretty sure Todd has one. Let's use Todd's boat! 
Mary,
If the risk of sinking is something that should be considered, what about using the flotation bags that are common in canoes and kayaks. Insert through the inspection ports and inflate.
you would have to have both hulls fail for the boat to completely sink. that being said, the best recommendation is to keep a radio, phone, and/or flares on the boat.
My TheMightyHobie18 has big foam blocks, one in each hull so that theoretically it would be pretty tough to sink it unless you broke both hulls so badly that these huge blocks would escape. Even then the boat would probably float.
David Ho
TheMightyHobie18 1067
Mary-
My first Sol Cat 18 sank on the first sail. There was flotation but the water overwhelmed it. They had apparently not sealed the sandwich hull/deck properly and the hulls filled with water. We ended up turtled about four feet below the water. So the mast was released when it snagged. The boat raised about a foot. Finally we were close enough to shore to swim for it. The boat got dragged to shore after a few hours of looking for it. They replaced the boat and sails. They also accused me of hiting something that caused the soft deck to rupture outward. When I said the water filled hulls may have caused unusual stress they shut up. I sold the replacement boat after one season and bought a Tornado. I really don't know how that boat stood up overtime.
That was myy first negative experience in catsailing the next came when i saw a family of five on a Sol Cat 18. All three children were under five years old. That same dealer told them the boat would not capsize or sink...according to the new owner. I never saw them after that.
thom
Some times it’s better if the boat sinks….
Our Solcat was sailed long and hard. It finally experienced major and catastrophic delaminating of its foam-sandwich hull construction.
After giving its all and sailing every mile it could possibly be sailed, a hull finally broke in two, at the front beam intersection. At that point the problem was: it WOULDN'T sink. NOT sinking meant we had to drag its broken and battered remnants back to shore. There we had to cut it up prior to burial in the local landfill, via the garbage can.
Thinking about it being cut up and waiting for the garbage collector still brings a tear to my eye and a quiver to my voice….. (Don’t worry, I’ll be OK. after my next whaaa-hooo sailing opportunity.)
Don’t you think, sinking with dignity, would have been a better suited and classier burial...???!!
Tom H.
I can remember hearing of a well known sailor who would pour acetone through the hull on his Hobies to get rid of the extra weight of the styro blocks. The a-tone would melt the foam and it would pour out the drain holes.
Anything to save a pound or two.
Tom-
Thats exactly where my SOl Cat 18 gave way as well. WHat year was yours?
Thom
One of the hulls of our first Hobie 16 split open along its keel (due to an accident on the trailer). We didn't notice the hull taking on water until it was too late and we capsized. With one hull full of water we could not right the boat because as it would begin to right all the water would ruch to the bow or stern and the bows or sterns would just sink. We eventaully were towed in by some friendly people in a motor boat. There was NO way the two of us could have righted the boat with the one hull full of water. The boat did not sink though...
Steve H.
Thom:
Our Solcat 18 was a 1978 or 9 (I think).
It really was a fun boat....with lots of forward floatation, due to those very long bows in front of the front beam.
It's low freeboard made for some exciting, wet and wild whaaa-hooo sailing....and there were lots of rigging adjustments to play with.
What did you do with yours after its unfortunate demise...???
Regards and Happy Thanksgiving to all.....
Tom H.
OK Jake,
Let's try it! C'mon down to Galveston Bay. We'll swamp'r and see!
Todd Bouton
N6.0na
#111
Tom-
After they drug the mast and sails out of the mud and decided it was a new boat and sails or litigation they gave me the boat in the pic. That was 1973 I think. I bought a couple of Sailcraft of Canada Tornados and sold the Sol Cat 18 to a guy I met on the beach. I don't know what happened after that for certain but I think I saw it under a tree all faded out. That boat did singlehand very well and you could fly the hull so high the jib lost air. The new boat didn't leak but the decks were soft on that one as well.
thom
I heard gasoline not acetone.
* Hobie 16's will float with both bows broken off at the crossbeams. It's like towing a wind chime though
* The pieces of old soft Gougeon Tornado's float after the boat breaks up. One nice thing about wood.
* Hobie 18's will sail with the first foot of both bows broken off. They do not point very well though.
* Reg White Tornado's will sail with one hull full of water and half the skin missing and only the sub deck holding the other togather. They go faster than a Hobie 18 with both bows broken off too.
* Marstrom Tornado's float with both hulls full of water. They reverse pitch pole if you are not careful though.
* H20's, P18-2 & N5.8 float with no bottoms. Hitting rocks or oyster reefs is a bad idea.
I seem to remember a couple of requirement that boats not sink. One was a US safety requirement and the other a general racing requirement from IYRU.
Mary... that was a great post....and I just smiled and smiled as I read it....
As I read it I thought you:
1. Have had lots of bad luck with boats....
2. Spent enough time on lots of boats to have had lots of "on the edge" experience...
3. Hang around some pretty wild and crazy boat driverds.... or
4. All of the above.
However, the question remainds...If you want to scuttle one that's given its all....how do you get it to sink... 
Maybe fill it with sand and/or dirt and/or rocks? This is all experimental because most people do not deliberately try to sink their beach cats. There's probably a law against it -- like littering, or damaging the sea grass. In these parts, getting rid of a boat usually involves a chainsaw.
Yes, we had a boat that sank, but it was a big monohull sailboat that we were traveling and living on at the time. It was raised by inflating bags inside the boat and gradually lifting it with two tow-truck hoists.
I know, now you want to know why it sank. We were tied up to a new dock in the Hudson River. It had replaced an old dock, and somebody had neglected to remove some steel pilings from the old dock. They were below the surface of the water and were invisible because the water was opaque. While we were gone for the day, the old pilings dug a hole in our hull.
The reason I asked the question about beach cats is because somebody mentioned to me recently that some of the new, high-tech hull construction materials do not use foam core and may not have any inherent buoyancy -- and also do not have auxiliary flotation materials in the hulls. I don't know whether this is true or not, but it started me thinking about it because, as I said, nobody wants to try to sink their boat on purpose just to see whether it floats. So we just take it on faith that it will float. And the assurance or guarantee of a dealer or manufacturer is not going to be much comfort to me if my boat is sinking out from under me in the Gulf Stream.
Anyway, my original question, Do you know for sure you boat won't sink, was actually sort of rhetorical, because how CAN you know for sure? Do manufacturers cut a boat in half crosswise and put it in the water to see if the front and aft halves will float independently of each other? Seems like that would be a really good test.
If you are not sure whether your boat will float and you are worried about it, you should put some kind of flotation into your hulls -- maybe the inflatable bags that someone else suggested. Or you could fill it with that styrofoam packing "popcorn" or lots of lobster pot floats or whatever will fit through your inspection hatches. (If you are going to use little, loose things like that, probably better to put big plastic bags into the hulls, put the flotation stuff into the bags and then seal the bags.)
Mary
I have looked at most of the new boats. The only boat, that I think might sink if both hulls are holed, is a monoque carbon A-class. The hulls are ~ 2mm stressed skin carbon and nothing else in the hulls. For a race I would probably risk it. For everything else, I would probably want 10-20 liters of airbags in each hull.
Recently a lot of my packages have been padded with little half liter airbags. They are permanently sealed plastic bags. They are pretty tough. I would probably use them for floatation
Attached is a photograph of an Auscat MkV A-class under construction. This photo came from the Australian High Performance Catamarans Website:
You will notice in the picture that the cross members (if that's what they are called) are made largely from polystyrene. It is partly this use of polystyrene that enables these boats to be built so light. The polystyrene of course acts as positive floatation.
I'm not sure about the A-class rules but the Taipan 4.9 rules (which have a similar construction) suggest that each hull can support 50kg when swamped.
Rob Wilson
Taipan 4.9 AUS175
I lost my first cat about 2 months after I bought it. It was a '78 NACRA 5.2 with solid glass construction (no foam core). The previous owner had done a very poor job of installing ports just forward of the cross beams after doing repairs. We were about 2 miles of Va Beach when we flipped it for the first time (big lesson learned). It began to take on water and we could not right as every time we hiked out, water would run to the back and it would just roll over backwards. Finally a power boat spotted us and took us under tow. The towing only exacerbated the leakage rate and it began to sink. The Coast Guard finally showed up and took us on board. They also took on the task of towing the boat for about 15 minutes, but my crew began to show signs of hypothermia and the Coasties decided the best thing to do was to cut the boat loose and get my crew back to shore. Meanwhile, some of my friends who had been sailing out from the beach to check on our status witnessed the NACRA slip into the deep, never to return. The only thing to float was one daggerboard which they rescued and I still have as a reminder. We were very lucky that everything turned out OK. I was undeterred and within two weeks had purchased another 5.2, this time I spent twice the peanuts to get an ’83 (also solid glass) which I have put many miles on and still have today.
The Tornado and the Marstrom A-cats has a 10 mm thick nomex layer between the carbon skins. That volume gives a lift of about 50 kg / hull!
/hakan
i figured it out= i guess if you are really, really bored, on a wind less day with nothing else to do, and want to put your boat thru unnecessary stress and strain this is how to 'conrol sink' your boat= (this only works in tidal areas). at high tide anchor your boat in about 2' to 3' of water near shore. secure it so it want move around with 2 or more anchors. undo the drain plugs and watch her go down. you probably need to screw out the inspection holes to hasten process. you can even act like you are brave and 'go down with the ship'. oh, the beach goers will think your are wacko. as the tide goes out, she's on the hard again and should naturally drain! brilliant, huh?
Just thought I would bring this thread back to the top for possibly more debate, now that there seems to be some pictorial evidence that a Jav 2 hull will sink when holed. See attached photo that I borrowed from a post on the Old Forum. It is the Jav 2, sailed by Matt Struble and W.F. Oliver, that was T-boned at the Alter Cup.
Of course, it may be some sort of optical illusion. But there were verbal reports, as well, that the holed hull did indeed sink below the surface.
remember, it was believed the Titanic was unable to sink! Where is she now?
It's simple; I have a Hobie Cat with foam blocks. I'm glad the 1000 was cancelled now that we have all seen what one Jav218HT hull full of water looks like in flat water. Lord knows with heavy seas the outcome of the sailors!
BC 
I thought the USCG requirements for small boats require enough flotation to keep a swamped/holed boat afloat and stable to a certain level. It appears that if both hulls were breached, this boat could sink completely, or at least deep enough to persuade sailors to abandon. What are the USCG specs? Does the Jav 2 meet them somehow? This reminds of the situation that ended up in a major lawsuit for NACRA...
Mary and others,
>>>I have recently heard that some of the newer, lighter, more high-tech cats, partly because of their hull construction, can definitely sink.
Well it will be easy enought to establish which class designs will sink and which won't, just check the class rules.
Formula 18 rule B.1.2
Each hull shall carry at least 110 litres of flotation by solid closed cell foam, air bags, sealed air compartments in hulls and at least one inspection hatch.
source http:/
Formula 20 rule B.1.2.
drijflichamen Niet van toepassing.
Literallt translation from Dutch: Flotation devices not applicable.
Source : http://www.formula20.org/
Formula 16 rule 1.5.2
"Each hull shall carry at least 50 liters of flotation, either by solid closed cell foam, solid blocks of compacted foam granulate, air bags or sealed air compartments."
Source : http:/
Similar rule as the F16 rule in the Taipan 4.9 class rules.
The A-cats don't have floation rules and mostly don't have use garanteed floatation in teh shape of foam or sealed air compartments. For this reason they can not obtain an European CE quality mark. The F18 class has such a CE quality mark and the F16 class is working at getting it. Alot of paper work ! But we will get it. If we have to increase our floatation to get it then we will.
I know that the Hobie Fox as an F20 design has foam block in the hulls to get positive floatation. I assume that they still have that since the F20 no longer require each F20 design to have it. It has been the hobie way to do that and I assume that they will keep doing that.
>>So if you have any doubt about whether your boat would float, do you stuff it full of styrofoam -- how do you know how much is enough?
Styrofoam will work by I'm told it is an open cell foam that will absorp water over time and make your craft needless heavier. Closed cell foam is better. Or if you use styro foam or even foam granulated (can be molded) than pack it tightly in a sealed back. Perferable vacuumed to make it hold shape.
Best is to fix (!) low in the hull to make it work even when the hull is partly flooded. Also fix it always. There is no use when it just rests in the hull only to float the your stern on top of the water surface. You'll be riding high with your sterns out of the water and you bows pointing down. No good sailing that way.
Wouter