Unsinkable Monohull - Why Not ?

[Marqus]

Originally Posted by TeddyDiver

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)

I have a question about the failure of a thru-hull when you are aboard. Just for the sake of insight.

Obviously, if unattended, a failure can sink the boat, and that could rightly be the main concern. But if you are sailing or are actually on board, is it true to say that you can readily resolve most types of thru-hull failure?

Obviously, the matter would be very difficult if you already have 3ft of water before you start to act (even locating the leak), but say you have bilge alarms or whatever that alert you fairly early on that there is a leak, is it unwise to assume you can readily attack and resolve ingress via a thru-hull?

A few types of thru-hull failure I can image, can be addressed by pushing in one of those soft, synthetic rubber cones that don't need a smooth, round rim to work. For example, if the ball valve got stuck in the open position, the handle/lever broke off, or even if the entire seacock broke off at the hull with sharp bits sticking out. Same with a vertical crack in the threads or hosetail. What types of failure would be real tough to handle?

(BTW nice post from Jedi).

[delmarrey]

Originally Posted by Marqus

What types of failure would be real tough to handle?

To get holed below the waterline is pretty serious but I think a broken stern tube or a broken off rudder rupturing the hull is about as bad as it gets w/o an actual massive hull failure, which I've only heard of on performance racing hulls.

Getting holed can be slowed fairly well by putting a tarp or sail over the side and tying it in place around the hull, then stuffing it from the inside to try slow as much as one can. Navy damage control.
Loosing a keel can be bad too but the boat usually remains upside down floating.

[muskoka]

Etap. I've been on tha Etap 39, which won Boat of the Year about 5 years back. The volume of foam they use is unobtrusive, and I couldn't see any negative aspects. The general finish was good and I personally really liked the boat. I believe the 39 has been discontinued, and the top of the range is now 48 feet.

http://www.etapyachting.com/index.html

I wish they built cats!

[TeddyDiver]

Originally Posted by Marqus

I have a question about the failure of a thru-hull when you are aboard. Just for the sake of insight.

Obviously, if unattended, a failure can sink the boat, and that could rightly be the main concern. But if you are sailing or are actually on board, is it true to say that you can readily resolve most types of thru-hull failure?

Obviously, the matter would be very difficult if you already have 3ft of water before you start to act (even locating the leak), but say you have bilge alarms or whatever that alert you fairly early on that there is a leak, is it unwise to assume you can readily attack and resolve ingress via a thru-hull?.

Right so if it's conventional thru-hull, but the point with a seachest as I described it means it leaks air in the chest, not water in to the boat..

[s/v Jedi]

Originally Posted by TeddyDiver

Right so if it's conventional thru-hull, but the point with a seachest as I described it means it leaks air in the chest, not water in to the boat..

The sea chests I see on motorboats still have the thru hull fittings below waterline.....

cheers,
Nick.

[TeddyDiver]

That's not right way to make one. The idea of sea chest is you can open it anytime to clean or maintenance. So if the top is over waterline there's no good reason to put cocks down of it..

[s/v Jedi]

Originally Posted by TeddyDiver

That's not right way to make one. The idea of sea chest is you can open it anytime to clean or maintenance. So if the top is over waterline there's no good reason to put cocks down of it..

Yes, the top is above waterline for cleaning from inside, but the fittings are always low under waterline... the ones I have seen like on a Grand Banks etc. May be because engine would start drawing air otherwise?

cheers,
nick.

[TeddyDiver]

Originally Posted by s/v Jedi

May be because engine would start drawing air otherwise?

No it wouldn't. If, like after cleaning, there's air in the upper part of the chest and the engine cooling intake dry Jabsco sucks it in no time and to be sure I got the varning light I previously mentioned incase of it doesn't.
Remember the only other case (besides opening the chest purposely) when this could happen is when there's a leak in the some place, and in all other setup's it would cause a flood in the compartment now only air in the intake..
BR Teddy

[minaret]

Not sure why you would need to have the top above the waterline. On most sailboats you need the intake thru hull down low on the hull so it's always under water at any angle of heel. If you have the sea chest attached directly to the thru hull (as I do), it would need to be about 8' tall on my boat to have the top above the waterline. That would be crazy. On mine I just close the thru hull ball valve to open the chest for cleaning or changing the zinc. Easy and simple. Not having a ball valve on the intake is nuts, what if your chest fails? Or anything downstream of it. I have a ball valve between the thru hull and the chest, and individual ball valves on each fitting coming from the chest as well. This allows me to turn off various systems without shutting down the whole chest, either because of an emergency/failure, or for maintenance.

[s/v Jedi]

@Minaret,

what you have is a big thru-hull with seacock that connects to a small tank into which the other thru-hull fittings are connected.
That is different from the setup where the sea-chest is part of the hull.
Also, is your thru-hull fitting 8' below waterline?!

@TeddyDiver,

I understand what you mean, but didn't see one like you describe yet. I have never seen one on a sailboat and don't look much at motorboats so I didn't see many sea chests at all.

ciao!
Nick.

[TeddyDiver]

To Minaret
You are not talking about sea chest.. what you have is a strainer totally, and another mather and good to have in sea chest intallations too.
To make it clear to those not familiar with the consept. It's a box or tube attached directly to the bottom of the boat and it opens directly to the sea. It has a rigid or removable grill to prevent algae and garbage ending up in the chest or further. The upper part is above the waterline and sealed with inspection hatch to make it accessible for cleaning. All raw water intakes (sea cocks) are attached to this sea chest. Ships have two sea chest so other one can be opened while making way for maintenance if needed.
BR Teddy

[TeddyDiver]

Originally Posted by s/v Jedi

I understand what you mean, but didn't see one like you describe yet. I have never seen one on a sailboat and don't look much at motorboats so I didn't see many sea chests at all.

It's not in any production sailboat I know. Where I came familiar with it is fishing vessels up here by Barents sea. Placing the intakes up in the chest is not a common practice but have seen it couple of times but dunno who and where has made it first but it's quite clever IMHO
BR Teddy

[BirdoPassage]

Hi,

I have built a monohull designed to be unsinkable. See: S/Y Bird of Passage

1. Low weight hull/deck in strip plank/glass/epoxy
2. Watertight bulkheads in both ends
3. Fixed expanded styrene flotation
4. Hard dinghy (polyethylene) securley fixed on deck.

Theoretically she will float on a level where it is still possible to stay inside (in the deckhouse) protected to bad weather. Batteries, electric system and radio communication is placed high.

Don't know if it works and don't want to know either but it feels fine.

Johan

[minaret]

Originally Posted by TeddyDiver

To Minaret
You are not talking about sea chest.. what you have is a strainer totally, and another mather and good to have in sea chest intallations too.
To make it clear to those not familiar with the consept. It's a box or tube attached directly to the bottom of the boat and it opens directly to the sea. It has a rigid or removable grill to prevent algae and garbage ending up in the chest or further. The upper part is above the waterline and sealed with inspection hatch to make it accessible for cleaning. All raw water intakes (sea cocks) are attached to this sea chest. Ships have two sea chest so other one can be opened while making way for maintenance if needed.
BR Teddy

Definitely a sea chest, not a strainer.

[TeddyDiver]

Sorry but no.. sea chest doesn't have tube to sea