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Old 25-11-2011, 21:41   #31
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Re: Unsinkable Monohull - Why Not ?

explosive keel bolts and an anti-gravity device should do the trick!
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Old 25-11-2011, 22:09   #32
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Watertight bulkhead hatch - anyone seen one?

We have all seen photos of the watertight bulkheads in "Open 60" type ocean racers. They are designed at the drawing board stage, and often use an oval shaped hatch (probably Aluminum) with submarine style clamps to create a good pressure seal.

However, most of us would have to retrofit something less fancy.
Many monohulls have a one inch thick bulkhead around the mast area, with a simple 'doorway' to the forward quarters.

How practical is it to convert that doorway to a watertight, vertical hatch big enough for human passage?
I think it could be fairly straightforward to make all the electrical and plumbing conduits passing through the bulkhead, watertight. The problem is building a perimeter seal big enough for human entry/exit, while able to hold up a fair amount of water pressure.

It would not need to be perfectly watertight - to the extent that the leaking of a couple of pints of water per minute would be manageable.

Has anyone on this forum built such a hatch, or seen one that has been retrofitted to a typical cruising monohull?
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Old 26-11-2011, 00:33   #33
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Re: Unsinkable Monohull - Why Not ?

Didn't we just have this conversation?

Making a Boat Unsinkable with Expanding Foam
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Old 26-11-2011, 02:42   #34
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Re: Unsinkable Monohull - Why Not ?

Hmmm. When it's a monohull:

Quote:
Originally Posted by s/v Jedi View Post
Calculations are wrong... You only need that foam volume calculated minus the volume of the materials of the boat (they displace water just like the foam)

cheers,
Nick.
But for multihulls:

Quote:
Originally Posted by s/v Jedi View Post
erhmm.. you can only count volume of materials that are lighter than water and also have to distract that volume's own weight from the calculated displacement figure.

ciao!
Nick.
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Old 26-11-2011, 03:08   #35
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Re: Unsinkable Monohull - Why Not ?

I made my bristol 27 unsinkable with foam.
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Old 26-11-2011, 03:24   #36
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Re: Watertight bulkhead hatch - anyone seen one?

Quote:
Originally Posted by Marqus View Post
We have all seen photos of the watertight bulkheads in "Open 60" type ocean racers. They are designed at the drawing board stage, and often use an oval shaped hatch (probably Aluminum) with submarine style clamps to create a good pressure seal.

However, most of us would have to retrofit something less fancy.
Many monohulls have a one inch thick bulkhead around the mast area, with a simple 'doorway' to the forward quarters.

How practical is it to convert that doorway to a watertight, vertical hatch big enough for human passage?
I think it could be fairly straightforward to make all the electrical and plumbing conduits passing through the bulkhead, watertight. The problem is building a perimeter seal big enough for human entry/exit, while able to hold up a fair amount of water pressure.

It would not need to be perfectly watertight - to the extent that the leaking of a couple of pints of water per minute would be manageable.

Has anyone on this forum built such a hatch, or seen one that has been retrofitted to a typical cruising monohull?

A Freeman hatch will do this. Had one on my last boat. They dog down completely watertight and come in a variety of shapes and sizes. They are also very expensive.

Deck Hatches, Freeman Marine Equipment, Inc. provides the finest marine and specialty closures available. Custom fabricated doors, hatches, portlights and windows.
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Old 26-11-2011, 03:26   #37
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Re: Unsinkable Monohull - Why Not ?

Quote:
Originally Posted by geckosenator View Post
I made my bristol 27 unsinkable with foam.
How do you know?

FWIW folk also have to remember that boats are not designed to have a couple of tons of water sloshing around inside so even if initially doesn't sink, only a matter of time before she disintegrates.
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Old 26-11-2011, 03:33   #38
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Re: Unsinkable Monohull - Why Not ?

Quote:
Originally Posted by Ziggy View Post
And I do recall someone marketing inflatable bag system a while back just for this purpose. I don't think that ever caught on, though, due to practical issues.
I remember seeing a product demo somewhere online that was basically a plastic celled "tarp" with a small CO2 canister that you wrapped around a troubled hull and hit a button to activate. The video made the deployment seem easy. However after reading accounts of collisions with floating containers taking only a "few minutes" to go under, the product seemed a bit too poppycock of an idea. I can't even imagine how frantic that scenario would be, especially at night.

Speaking of watertight bulkheads as someone else mentioned, anyone have the picture of the individual that put a submarine door a few feet in front of the chain locker? I thought that was quite ingenious. It might have been a tug, I cant remember, but it was quite neat.
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Old 26-11-2011, 06:28   #39
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Re: Watertight bulkhead hatch - anyone seen one?

Quote:
Originally Posted by Marqus View Post
We have all seen photos of the watertight bulkheads in "Open 60" type ocean racers. They are designed at the drawing board stage, and often use an oval shaped hatch (probably Aluminum) with submarine style clamps to create a good pressure seal.

However, most of us would have to retrofit something less fancy.
Many monohulls have a one inch thick bulkhead around the mast area, with a simple 'doorway' to the forward quarters.

How practical is it to convert that doorway to a watertight, vertical hatch big enough for human passage?
I think it could be fairly straightforward to make all the electrical and plumbing conduits passing through the bulkhead, watertight. The problem is building a perimeter seal big enough for human entry/exit, while able to hold up a fair amount of water pressure.

It would not need to be perfectly watertight - to the extent that the leaking of a couple of pints of water per minute would be manageable.

Has anyone on this forum built such a hatch, or seen one that has been retrofitted to a typical cruising monohull?
Years ago when I was working at Tacoma Boat as an aluminum welder, I built many water tight doors & hatches for the gun boats we built for the Korean navy.
These were prefabed on the bench and cut to fit - some welded in, others bolted.
Later on down the line, I built and installed one on a freinds fishing boat.
It was very similar to what it would be like on a yacht. The boat was a 60' schooner with a cargo mast & boom which was keel stepped. I built the door and bolted it in place at the companion way that led forward to crews quarters. The area around the mast at the bulkhead was narrow and the hight was low because of the break timber in the deck forward of the mast. The dimesions were approx 18" wide x 60" tall. It was tight but it worked fine - all built of 5086 marine grade aluminum, 1/4" thick. All the hardware was
S.S. I even bolted in a porthole for light. I painted it all a satin blood red color that looked great against the mahogany wood work. I charged the guy $1500 for the job.
The door had double dog locks just like you will find on any navy boat. We were going to do the engine room next but he went fishing in Alaska and I never saw him again.
I should do this project on my own boat but I'm too lazy.
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Old 27-11-2011, 04:43   #40
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Re: Unsinkable Monohull - bulkhead door

Thanks Minaret and Geoduck for the useful info you posted re. bulkhead doors.
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Old 27-11-2011, 05:02   #41
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Re: Unsinkable Monohull - Why Not ?

For every ton of boat, you need 35 cubic feet of air in a sealed tank to make it unsinkable.

10 ton of boat = 350 cubic feet of air in a sealed container, the 10 ton will float.

Its the same calculus the pharoahs used to move 2000 ton rocks and the 500,000 ton super tankers that sail across the oceans today.

35 cubic feet will displace one ton of seawater. No if or buts,

The Titanic sank because the engineers and owners cheated on the steel in the hull.
Any hole in the bottom of the Titanic and it would have sunk. Guaranteed,
Its sister ship, The Eastern star, same design But with out cheating had a hole in its bottom 3 times the size of the Titanics hole and it steamed into New York harbour under full power. only the crew knew it had been holed, the passengers were blissfully unaware that it had also hit an iceberg,
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Old 27-11-2011, 05:17   #42
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Re: Unsinkable Monohull - Why Not ?

I have a bit different approach. Instead of a sealed compartments and foaming I build all tanks and compartments (with hatches) against the outer skin of the hull. All bulkhead openings are high enough to prevent flooding or with watertight doors (just DIY). So eventually to sink it got to be rammed throw...
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Old 27-11-2011, 05:40   #43
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Re: Unsinkable Monohull - Why Not ?

Hmmm, it would have to be fireproof, collision proof, childproof, waterproof, and idiot proof.
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Old 27-11-2011, 06:04   #44
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Re: Unsinkable Monohull - Why Not ?

Okay, let me write about the point of view of Dashew when he designs boats like our Sundeer:

The most likely points of water ingress are:

- prop shaft (like when you loose it, friends lost their boat that way)
- rudder lower seal/bearing (damage after hitting bottom)
- thru-hull fittings
- collision on or near the bow
- engine raw water plumbing problem.
- holed at the turn of the bilge (on reefs, rocks etc.)

He next took several counter measures to deal with these risks:

- make prop shaft so that it can't go overboard (can be as simple as a shaft-zinc on the inside; we have PSS seal and thrust bearing)
- design rudder with a weak spot so that the lower 1/3rd will break off in a grounding. This relieves pressure while keeping some steering
- minimize thru-hull fittings. Jedi had one (1). For discharge, there are standpipes, schedule 80 PVC pipes laminated into the hull and raised well above water line.
- a forward water tight bulkhead, separating the forward 14' of the hull. When I pull the depth transducer here and let water come in, it will stop at 1 foot high and only when you know the water is in there you can see the bow a bit down (an inch or so)
- an aft water tight bulkhead, separating the aft 16' of the hull. This is where thru-hull fitting, rudder, prop shaft, engine, genset etc. is. When this compartment get flooded it will lead to water damage on the engine and systems, but hull maintains maneuverability.
- an additional 3/8" fiberglass reinforcement in the turn of the keel. This was a customer option but every buyer opted for it at, I believe $5k extra cost.
- integral water tanks along 3/4 of the hull mid section between the water tight bulkheads. used as ballast tanks too.

While most of this needs to be addressed at design time, some can be done any time like the prop shaft issue. If you're designing/building your own boat, the above points are better than insurance!

There are some points to consider:

the standpipes mean that anything that gets discharged must be pumped out. The solution is to gravity feed all but toilets to a central, small gray water tank. Just like in a home. We have the tank in the keel sump and use float switch and Whale gulper 220 to pump it out the the closest standpipe. Toilets have no problem as they already have the pump needed.

One single thru-hull wasn't enough for us, spoiled as we are. We have 4 now; the three added are for genset, water maker and one shared between deck-wash and air conditioning unit. The original one is just for the engine now. We have eliminated feeds to toilets by switching to fresh water flush. That also eliminated two raw water circuits in the (vulnerable) mid section of the boat. We added a new raw water circuit to air conditioner which is now the only one. It could be eliminated with a more expensive split unit.
The trick to this is that there are still no thru-hull fittings in the mid section. All are in the end sections with the bulkheads providing safety.

When you build metal boats, you can (should) add 2-4" of foam insulation sprayed against the hull. This provides insulation for temperature and sound, solves condensation drips and provides (questionable, how much volume is this etc.) flotation support.

ciao!
Nick.
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Old 27-11-2011, 11:45   #45
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Re: Unsinkable Monohull - Why Not ?

Instead of thru hulls a single sea chest is far more better solution. The top over the waterline and each raw water intake from there. Warning light for air in the chest (any leak would drain the chest some)
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