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Old 03-12-2010, 08:12   #46
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Now perhaps those with mulithulls can continue on the discussion of this incident, what led to it and how it can be avoided in the future.

Brad
It would be interesting to know how many production cats actually do have water tight bulkheads and if they are penetrated, how high above the water line. And is that level above the waterline enough to keep the boat from flooding if one compartment is compromised.
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Old 03-12-2010, 09:15   #47
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It would be interesting to know how many production cats actually do have water tight bulkheads and if they are penetrated, how high above the water line. And is that level above the waterline enough to keep the boat from flooding if one compartment is compromised.
Urban legend (in conjunction with verbal marketing at boat shows) has it (yes I know I'm feeding the anti-multihull trolls), that my boat (FP Belize) will float with ~1.5 foot of water above the cabin sole if holed in the main cabin of one hull. I've never witnessed it, but have talked to people who have.

Fact (not urban legend), my boat has solid bulkheads fore and aft of the engine. The bulkhead fore of the engine has a hole in it leading to the aft stateroom with an easy-to-push plug for the purpose of dosing the engine room with a fire extinguisher from the cabin if needed. This hole is ~20-24" above the waterline. If a passive leak developed in the engine room, the water level would never make up to this fire-extinguisher-hole as there's simply not enough space there for the volume of water required to push the hull down far enough for the water to make it to that hole. Results of multiple simultaneous hull failures are undeterminable. Aft of the engine room (aft) bulkhead is foam filling the space under the sugar scoop steps.

In the forepeak(s) is a crashbox that extends ~1' back with a solid bulkhead. Aft of this solid bulkhead and ~30" high by ~6+' long is solid foam (under the single 'crew' berth) with another solid bulkhead between it and the main cabin. Per the urban legend, it is the foam fore and aft that provides the floatation needed to keep the vessel from going all the way down.

Although this provides one with peace of mind that the boat won't go out from underneath you in 30 seconds like a boat full of lead, I recommend to all and personally carry a 6 person offshore liferaft.
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Old 03-12-2010, 10:33   #48
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Originally Posted by DotDun View Post
Urban legend (in conjunction with verbal marketing at boat shows) has it (yes I know I'm feeding the anti-multihull trolls), that my boat (FP Belize) will float with ~1.5 foot of water above the cabin sole if holed in the main cabin of one hull. I've never witnessed it, but have talked to people who have.

Fact (not urban legend), my boat has solid bulkheads fore and aft of the engine. The bulkhead fore of the engine has a hole in it leading to the aft stateroom with an easy-to-push plug for the purpose of dosing the engine room with a fire extinguisher from the cabin if needed. This hole is ~20-24" above the waterline. If a passive leak developed in the engine room, the water level would never make up to this fire-extinguisher-hole as there's simply not enough space there for the volume of water required to push the hull down far enough for the water to make it to that hole. Results of multiple simultaneous hull failures are undeterminable. Aft of the engine room (aft) bulkhead is foam filling the space under the sugar scoop steps.

In the forepeak(s) is a crashbox that extends ~1' back with a solid bulkhead. Aft of this solid bulkhead and ~30" high by ~6+' long is solid foam (under the single 'crew' berth) with another solid bulkhead between it and the main cabin. Per the urban legend, it is the foam fore and aft that provides the floatation needed to keep the vessel from going all the way down.

Although this provides one with peace of mind that the boat won't go out from underneath you in 30 seconds like a boat full of lead, I recommend to all and personally carry a 6 person offshore liferaft.
Good points. I have a PDQ 32 and can make statments for her:

Fact. There are sealed crash tanks in both bows.

Fact. About 4 feet in front of the mast in each hull there is another full-height bulkhead. I have flooded on one side (due to failed through hull) and nothing important came of it; finished the cruise with 15 inches of water in front of the bulkhead.

Fact. The rudder posts are in sealed crash tanks. They hold water, since I have had them fill with rain water. The baffles go to the deck.

Fact. The engine compartments (just storage on my boat, as it has the twin outboard option) could easily be sealed and SHOULD be if the engines are installed. I will seal them anyway, before any real passages. The bulkhead in this case is about 30 inches.
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Old 03-12-2010, 11:00   #49
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Facts are good!!

Here are mine: There is a bulkhead 8' back from the bows that is completely sealed. There is NO foam forward of this bulkhead to provide floatation. There isn't a bilge pump in this area either. I plan on changing this somehow.

The main cabin in both hulls have two bilge pumps each.

The bulkhead between the engine compartment and the main cabin has multiple unsealed pvc tubes approximately 18" above the water line. The bulkhead between the sugar scoops and engine compartment allows water to transer between them through a 3/4" hole. I'm not sure if this is on purpose or not. There are bilge pumps in both of those compartments. The only foam I have is in a 3' x 6' box under the aft cabin beds. Clearly not enough to keep the boat afloat if completely flooded.

I had 14 through hulls when I purchased the boat and have eliminated 7 of them. The boat is shaft drive.

I also believe the starboard engine compartment had a thru-hull fail and flood. The motor is exceptionally rusty and there was a small peice of seaweed stuck to a wire. This side doesn't have the pvc tubes penetrating the bulkhead like the port side does but isn't sealed completely.

I would guess the main idea from the factory is that if a thru-hull failed, they would have enough bilge pumps in that area to contain the flooding. Whether thats true or not, I don't know.
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Old 03-12-2010, 11:49   #50
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rtbates, it did not sink but rather was taken to a beach and bottomed out. No, it was not floating. But then again, neither are cats that are beached for bottom cleaning, or twin bilge-keeled monohulls in the UK that are frequently left sitting on the bottom when the tide goes out.

Back on topic, I do think that a couple of important lessons can be learned here. Yes, towing a dinghy is foolhardy. Yes, poly painters are better than dacron. Yes, line cutters on the props are likely a good investment for any boat. And yes, we should all check our 'sealed' compartments to make sure that they are, in fact, sealed.

The ones in my bows certainly are (except at deck level where wires run through for the electric windlass); the ones in my transoms are and are separate from the engine compartments, which are under the aft berths. I am, however, debating whether it would be worthwhile filling those areas with foam in case the compartments were compromised by collision. Has anyone done that on their boats?
Is there any reason I could not simply drill a hole, spray in styrofoam and then seal them back up?

Brad
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Old 03-12-2010, 12:18   #51
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Is there any reason I could not simply drill a hole, spray in styrofoam and then seal them back up?
Not all foam is created equal... You can get pourable two part closed cell foam in various densities. It is reasonably waterproof and less prone to mildew than typical Styrofoam. But, even the least dense stuff is heavier than air... Also, a foamed in area can be a PIA if you want to add hardware or do repairs. A compromise is a small crush box of foam right up in the eyes of the boat. If you really don't care about access you might fill the area with ping pong balls bedded in low density closed cell foam to save weight

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Old 03-12-2010, 12:37   #52
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Not all foam is created equal... You can get pourable two part closed cell foam in various densities. It is reasonably waterproof and less prone to mildew than typical Styrofoam. But, even the least dense stuff is heavier than air... Also, a foamed in area can be a PIA if you want to add hardware or do repairs. A compromise is a small crush box of foam right up in the eyes of the boat. If you really don't care about access you might fill the area with ping pong balls bedded in low density closed cell foam to save weight

Tom
There are more than a few boat owners that can testify that foam gets INCREDIBLY heavy after it soaks in water for a few years. Soda bottles or ping pong balls are far more practical for cruising boats.
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Old 03-12-2010, 12:44   #53
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Well, it did sink... As in it went all the way to the bottom and that's what stopped it from going any further down, IE it wasn't floating...
If that's the definition of sunk, then a boat on the beach, in a drydock or on a tidal grid is also sunk. Hmmmm....

Seems to me that a boat isn't sunk until its hull is entirely under water.

Martin
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Old 03-12-2010, 13:01   #54
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There are more than a few boat owners that can testify that foam gets INCREDIBLY heavy after it soaks in water for a few years. Soda bottles or ping pong balls are far more practical for cruising boats.
You own an old Boston Whaler?

FWIW, some foams are better than others. There are lots of different kinds of foam out there. Generally "closed cell" foams take longer to get water-logged. Some reputable rudder manufactures use pourable two part closed cell foam. Lots of boats are made from closed cell sheet foam with FRP faces... For something like a crash box that should stay dry a good quality closed cell foam encased in FRP is probably not going to get waterlogged. But even dry foam will add weight compared to air.

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Old 03-12-2010, 13:05   #55
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Thanks Tom, good advice. While it is true that foam is heavier than air, at least it would still provide bouyoancy after a collision.

Brad
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Old 03-12-2010, 13:49   #56
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OK, regarding sinkability, it's simple math. Every cu ft of space that has air and is protected from flooding provide 63 lbs of flotation in seawater. To have a boat which could survive a breach of any compartment, you need the rest boat have enough protected bouyancy to provide enough floatation to compensate for the weight of the boat plus the loss of that compartment.

While some monohulls can have watertight bulkheads to protect certain areas, they weigh far more than cats due to their lead keels, their interior configuration has often one large living space, they have less interior space for their weight, and should that large interior space fill with water, it sinks. This really isn't a point of contention. Island Packet, Catalina, Hunter, Tartan, Hinkley, etc would sink like a stone should they get a breach below the waterline in their main living area. This really shouldn't surprise anyone. By contrast, multis have far less weight trying to pull them to the bottom, have their living spaces divided up into multiple sections and some like Prout 45s, FPs, Privileges have enough structural bouyancy forward and aft to keep that hull afloat in the event of a mid hull breach. Our catamaran has a great protected space up forward which would provide structural bouyancy should it get a mid hull breach, it would keep that section floating, but the aft part of that hull would be awash. Some cats have huge forward and aft compartments which provide lots of bouyancy so that in a worst case breach amidships, that hull would only flood a little bit. PDQ, FP, FastCat, are really good examples. Ours is less so. Some have relatively little structural bouyancy forward and aft and would probably sink, lagoon, moorings....these are choices the designers made. More weight, more accomodation space, less bouyancy for the unlikely event of a midhull breach.
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Old 03-12-2010, 14:23   #57
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BTW, for us, I'm thinking of the soda bottles in the bottom of our bow lockers in a crash compartment, with a large inspection port (watertight) and a pvc tube which goes to the lowest part so I can stick a bilge pump in it. The inspection port would be big enough to allow me to reach in and pull out bottles should I need to access something. Before putting in the bottles, I'd line the compartment with some spectra netting so in the event of a collision they don't go floating away.
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Old 03-12-2010, 16:55   #58
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...
[Most keel yachts]...sink like a stone should they get a breach below the waterline in their main living area.
Sorry about the slight misquote, and in general terms I agree with you, but just to provide an exception to the rule: ETAP - Unsinkable Sailing Pleasure. Obviously, solutions of that type are easier to pull off on boats that do no carry large amounts of ballast. On most boats there is an added complexity and cost and loss of space associated with unsinkable design and construction. A self-rescuing and unsinkable design is more expensive yet. These choices will be made by somebody during the design or construction so it's probably worth being aware of them.

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Old 03-12-2010, 19:19   #59
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Ill counter your sinking cat with humor. Ive been avoiding this thread as it is a misinformed title and a rehash of a rehash but I love this image and had a good laugh looking at the other shots from this article. The Fantastic Sinking Boat by Julien Berthier | Amusing Planet
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Old 03-12-2010, 19:35   #60
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Ill counter your sinking cat with humor. Ive been avoiding this thread as it is a misinformed title and a rehash of a rehash but I love this image and had a good laugh looking at the other shots from this article. The Fantastic Sinking Boat by Julien Berthier | Amusing Planet
LOL. Imagine if that thing came sailing by you with some bloke just calmly sitting there! Genius!
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