Unsinkable

[Cotemar]

As a captain you never leave a vessel that is floating.
Set the EPIRB for a rescue.
Keep your crew safe and hydrated.
Use the life raft as a last resort or if the vessel catches fire.

[44'cruisingcat]

Originally Posted by svquintana

I told myself not to jump into this one. So I'll let a photo tell my side.
This was an attempted "insurance" job. She's as full as she'll get. The front of the cockpit has water to my waist, and the back of the cockpit is up to my armpits. Bridgedeck "lounge" area is awash. My wife and I towed it a few miles to shore with our monohull. Note, the forward hatches are open, no air pocket in there.






This was a light, custom build cat. Similar, but shorter, to mine or 44C. It has a foam core and two diesel engines. 44C would float higher in the stern since he's using outboards. Mine has diesels, so I would expect a similar attitude in the water whilst "full" of water.

When trying to sink this boat, did they puncture the buoyancy compartments?

I know my boat would float MUCH higher, unless the buoyancy compartments were flooded. School's out had 6 metres of it's port hull torn out, and one of the bow buoyancy chambers holed, but when it was being salvaged the port hull floated only about 18 inches below it's lines. The bridgedeck was still well clear of the water.

[pbmaise]

Okay class lets run some numbers.

In photo one you are looking at 1006 lbs of engine. That doesn't include the weight of the transmission, shaft, and propeller. So lets add another 500 lbs for that. Okay round to 1500 lbs of steel.

Now that is a good start. Hidden below deck level there are 3 anchors one really nice long chain, and a short length of chain. Combined weight of this is about 750 lbs of steel. Subtotal = 2250 lbs

Above deck we have 8 winches with an average weight of about 30 lbs. Okay round up to 250 lbs. Subtotal = 2500 lbs

Forgot to add the watermaker, pumps, fridge, power tools, hand tools, and electrical equipment, and electric wire. Would you accept 1500 lbs? Subtotal 4000 lbs.

All this stuff will have a density of about 500 lbs/ft3. Therefore, we have about 8 ft3 of steel. Saltwater has a density of 62 lbs/ft3. Therefore, we need to positive buoyancy of 3500 lbs to offset all this heavy stuff.

Next lets go top side and look at that mast. It is about 700 lbs, of aluminum and about 160 lbs/ft3. To off set this mast we need only 425 lbs of positive buoyancy.

Subtotal rounded up is 4000 lbs of net positive buoyancy keeps my sailboat floating.

Almost everything else either floats or as a density not to far different from seawater.

However since life is on the line...lets double the number 4000 lbs, and demand that we identify at least 8000 lbs of net positive buoyancy. This will account also for other items like glass, fiberglass, cans, and those shells picked up along the way.

To put this in prospective, 8,000 lbs is the weight 4 Volkswagen Beetles. So think of a platform sitting in the water and all 4 cars have dry wheels.

While we are at it, lets start assuming some really bad news.
There isn't a single compartment that still holds air. Wow, lets assume that both of the ama are gone and the 6 different aka that connect to the ama are also gone. This is really bad news since there is almost nothing in the ama or aka that sinks. All that net positive buoyancy is lost because we are looking at worst worst case.

Will the mainhull alone still float?

Lets begin with the walls. 65 feet by an average of 25 feet from top side around the bottom and back up the top side, and 1 inch thick means there is about 135 ft3 of balsa wood. At only about 10 lbs/ft3 this balsa wood will provide a net buoyancy of 7000 lbs.

Up on deck we are looking at combination foam core with plywood. Total cubic feet of decking on mainhull alone is 65ft *10ft *1.25 inches = 68 ft3. That has some plywood in it so lets call that density 22 lbs/ft3 and weight of 1500 lbs. The net buoyancy of the deck is 2700 lbs. Subtotal 9700 lbs.

Now lets go inside and start adding up the flooring that floats, the 8 inches of foam insulation around the refrigerator and we have at least another 2700 lbs of net buoyancy. Subtotal 12,400 lbs.

Summary
Worst case assumption of stuff that sinks = 8,000 lbs negative buoyancy
Worst case minimum of stuff that floats = 12,400 lbs positive buoyancy

In my case, my trimaran minus both ama and aka will still remain afloat with a net positive buoyancy of at least 4,400 lbs. Heck bring on the super-sized land lubbers and lets have a party! At least 10 of them should still be high and dry.
Philip Maise
HOT BuOYS Trimaran

[GRIT]

44C, I don't know whether the cat had buoyancy chambers, or if they were punctured. I wasn't privy to the forensics.

We were just there to ruin the guy's day.

We're also installing buoyancy chambers, where the plan shows storage in the bilges. Otherwise, our bilges are designed as tankage. Which will help increase buoyancy whilst upside up, and hinder buoyancy if inverted (while the tanks are full).

Cheers.
Paul.

[downunder]

You should not have any sinking issues with a foam core KH 49.
Have you kept track of the volume of foam you have used?

Nice vessel.

[GRIT]

Thanks Downunder. I have not kept track, but do have all my invoices if necessary.

I'm not worried much about sinking as we're building with the intent to keep the boat as light as possible (except the diesel engines).

Cheers.
Paul.

[mikereed100]

Originally Posted by minaret

Great example. In anything but the flat calm pictured, this boat would be untenable.

Untenable? Debatable. Uncomfortable? Undoubtedly. Unsinkable? Unequivocally.

[K_V_B]

The French Authorities have an official definition of "Unsinkable". In order to be classed as unsinkable a vessel must, when completely flooded:
- keep enough freeboard.
- be able to sail, and be maneuverable..
- be able to right itself from a 90 degree knockdown with the whole crew sitting on the lee rail.

Yachts that meet this definition don't need to carry a life raft.

Etap build yachts that met this definition. It's a pity they're gone...