Collission Bulkheads on Multihulls...

[Skip JayR]

Safety first... generally I like to think about - before skippering a boat - what security reserves I will have around. SOLAS is a clear instrument to get oriented as yacht sailor. So I was educated and that way I like to handle it.

As I love speedy boats, e.g. Trimarans it is a big issue for me to handle collissions on high seas safely, at higher speed. Luckily yet not experienced personally.

Actually I get the chance to proof a sales offer by an owner who has to give up his 40 Foot racing trimaran because of health issues. So it looks in a short video... :-) I just got the plans and equipment list. It has a maximum speed of 24 knots.

This 3-hull boat was used mainly for pleasure sailing (mostly coastal areas). Yet it is not equipped to go on high seas safely... but the original plans show optional three bulkheads:

1. Bow (anchor chain hutch) | foreship cabin (double bed)
2. foreship - saloon/galley + navi) / under cockpit 2x single berth
3. astern rudder segment + engine

The boat as you can see in the vid is built with a fully open segment of double bed cabin in the foreship + Saloon/galley/navigation + two single beds under the cockpit. Imagine this whole segment under water after a collission of the main hull. Not amusing...

Personally I'd prefer to install a bulkhead between foreship and saloon. Kind of collission door.

For now the whole boat (roughly 4-4.5 tons) is unsinkable by the amas/outriggers, as it was built with composite epoxy-foam and the cross beam section stiffed with cevlar. So after capsizing it still can work as a floating life raft.

But a smaller collission in the front part of the main hull shall keep maximum water outside; bulkheads target at to keep the boat safely manoeverable with all relevant functions.

Yesterday I discussed the given construction with the GL (Germanischer Lloyd) which is one of the leading certification and classification society worldwide. GLhas merged in 2013 with DNV (Det Norske Veritas) another big classicifcation society. GL still is operating worldwide 80 offices. https://en.wikipedia.org/wiki/Germanischer_Lloyd

Actually there are no safety rules for privately used yacht boats under the size of 23 metres, thats what I was told by GL. So its up to me to find a constructor and boat builder for making a bulkhead door.

A modern hydraulic watertight sliding door made of steel has a weight of up to 400 kilogrammes. Too heavy for a small leight weighted 40 Foot trimaran... :-).



Do exist bulkhead doors for yachts made of Carbon ?

Collission at night is the biggest nightmare I have. Not funny to imagine to crash into a drifting 40 foot ISO sea container (which mostly are unseen and swapping close under surface) at a speed of 22 knots, isnt ?

Or does it look harmless what experienced skipper Thomas Coville's Maxi-Trimaran Sodebo which lost its front of the starboard float and central hull nose after a collission during the night shortly after the start of the Route de Rhum 2014 ?







Similar happened with Loic Fequet’s trimaran Maitre Jacques (which belongs to Multi 50 class). The bow broke off her starboard float. Not clear if it was a collission or a material defect as it happened a year ago, already.



Dragonfly is building the small Dragonfly 25 with a collission bulkhead in the mainhull... I suppose it makes sense.


What are your experiences ? Any ideas how to handle this situation for a safe sailing on board of speedy multihulls ?

[44'cruisingcat]

On our cat, the hulls first 3 metres or so are closed off up to about waist height, and divided into sealed buoyancy compartments.


Also, we never plan to sail at 20 knots at night.


You don't need the massive watertight doors shown. A well fitting reasonably strong door that fits well enough to slow the water flow to quantities a bilge pump can handle would be enough.

[CarstenWL]

... on the 92ft sloop I currently work the watertight door to the forward section looks like this:

https://www.dropbox.com/s/3a5gobczl0...27.58.png?dl=0

I can look up the manufacturer for you in 2 weeks or so if needed (I know you will need a smaller one ;-)). Of course if you put in a collision bulkhead with a watertight door all wires, hoses, ... running through the new bulkhead should be as much as possible watertight sealed to the bulkhead ;-)

Regards,

Carsten

[Matt Johnson]

Originally Posted by 44'cruisingcat

On our cat, the hulls first 3 metres or so are closed off up to about waist height, and divided into sealed buoyancy compartments.


Also, we never plan to sail at 20 knots at night.


You don't need the massive watertight doors shown. A well fitting reasonably strong door that fits well enough to slow the water flow to quantities a bilge pump can handle would be enough.

Monohull here, but we have a similar set-up. First meter is a waterproof bulkhead (anchor locker/sail), followed by the next meter and a half around waist height (v-berth) that is sealed too. The top of the sealed v-berth area is just caulked/ bolted and epoxied 3/4" plywood. It may not be totally water tight, but the bilge pumps will keep up with it just fine and allow a emergency fix to be put in place. All in all, pretty easy to put in place.

Matt

[Skip JayR]

Originally Posted by 44'cruisingcat

On our cat, the hulls first 3 metres or so are closed off up to about waist height, and divided into sealed buoyancy compartments.

yeah... the security standards are 5% of boat length the first segment wall in front bow. So for a 40 Footer its 2 foot = 70 centimetres minimum for compensating a frontal crash.

Originally Posted by 44'cruisingcat

Also, we never plan to sail at 20 knots at night.

Yes, that makes sense... otherwise the crew has to wear survival suits (I think the correct name is "Immersion Suits") even while staying in bearth. On racing mashines they handle it like that as there is lack of time under deck when the water is flooding in. Just enough time to go on deck and jump into the life raft.

Originally Posted by 44'cruisingcat

You don't need the massive watertight doors shown. A well fitting reasonably strong door that fits well enough to slow the water flow to quantities a bilge pump can handle would be enough.

Yes, I have thought about this... probably this will be the "low cost" alternative to get some time in reserves. The boat already has two bilge pumps on board.

[Skip JayR]

Originally Posted by CarstenWL

... on the 92ft sloop I currently work the watertight door to the forward section looks like this...

Lucky man working on such a beauty... :-)

Tks for the photo. Yes, something like this we know from "traditional tall ships" and cargo ships, too...




I have found a company for commercial ships which is building such doors... they call it "QUICK ACTION Watertight Door" or "Quick Action Pressure Holding Door" (mainly made of steel). The name of this corporation is HISE MARINE in China. They produce certified steel and aluminium doors.





Such doors are built in Asia more cheaply at a prize between 400-800 US dollars... here such one, called "Marine Quick Action Watertight Door".
It seems a supplier company in Shanghai (Nanjing Jingyun Ship Fittings Co., Ltd). Mostly such companies only service bigger orders (e.g. minimum 100 doors) :-) I suppose I wont buy 100 Trimarans to need such a package.

Originally Posted by CarstenWL

I can look up the manufacturer for you in 2 weeks or so if needed (I know you will need a smaller one ;-)).

Would be fine... tks in advance.

Originally Posted by CarstenWL

Of course if you put in a collision bulkhead with a watertight door all wires, hoses, ... running through the new bulkhead should be as much as possible watertight sealed to the bulkhead ;-)

Yes, I am aware of that... all electric cable, pipelines etc. ... must be sealed, too. :-)

Preferible I like to get a door made of leight weighted carbon-epoxy... as "heavy weight steel" is the killer effect for every speedy trimaran. Probably such a Carbon-Door has not the stiffness like one made of steel to stand huge water pressure. But as 44'cruisingcat mentined it will slow down the flow of the water so the bilge pumps can do the work.

The trimaran is unsinkable because of the foam (Divinicell). So there is some "security zone" built into the structure. But even a hull with full of water can get lots of damages (e.g. all electronics are destroyed) so better keeping out the water as much (and as quick) as possible.

[Skip JayR]

Originally Posted by CarstenWL

I know you will need a smaller one ;-)

This is the situation.... just put together a photo and extract from the plan in the segment of stringer 6 to 7. You can see that it is 'open space' from saloon to foreship, on port side the transition to the double berth, and starbord the toilet.

Naturally on a Trimaran between both we have the vertical tunnel for centre daggerboard which can be uplifted to a minimum draft of only 0.46 cm.

[Timethief]

Just a random thought while reading these posts......

If you are worried about just being holed below the water line - not talking about having the bow ripped off like the racing tris- say hitting said semi-submerged con box, and you have an air compressor aboard (again, if we are not talking racing), then you might want to consider putting a quick disconnect into the space (a female disconnect in the bulkhead will not violate watertight integrity). Figure with a draft of 2 feet all you need is 1 psi of overpressure to push the water back out to the hole depth if the hole is in the bottom of the hull. It would keep the space from filling entirely and lowering the hull, and give you time to gather repair supplies, etc. - unless you have a bilge pump in the space, once you close the door, you can't do anything to better your situation.

Sorry - the idea is still rattling around my head.

[mikereed100]

Originally Posted by Timethief

Sorry - the idea is still rattling around my head.

I like the way you think, but it would probably be simpler and more effective to just put urethane pour foam in the area of the crash box that is below the waterline .

[barnakiel]

In a tri you can achieve what you want by simply building the fore bunks (if you envision any) as a dam. There is no ballast and your watertight compartments do not have to be full height.

You do not want to rip off the bow of the main hull like pictured. If you do, build an extended false bow in foam and epoxy. It will be a huge sacrificial crash box of sorts. Vide images of IDEC.

Cheers,
b.

[Skip JayR]

Originally Posted by Timethief

...just being holed below the water line - not talking about having the bow ripped off like the racing tris...

If that happens, then probably the Tri capsized... :-)

As I wont sail this boat under "racing conditions" I rarely have the chance to experience nose diving and pitch pole.... which even can happen to monohulls as we can see :-)


Actually this is nearby impossible as we see even with the extreme Trimarans nowadays, that there are enough reserves the boat falls back onto its 3 legs...

https://www.youtube.com/watch?v=QP-67_sPgGc

Similar happens nowadays on smaller Trimarans... as the uplift volume in the main hull is big enough to resist against a 180° turn.

https://www.youtube.com/watch?v=Ylm_MYu74Wk

So long you get loose the traveller sheet the boat won't capsize. If it happens, I think more relevant is to get a floor hatch to escape... as we can see in this video - as it happened last year in January of capsized 80 Foot Maxi Trimaran Prince de Bretagne - in a close up at 02:32 . Luckily this extra ordinary boat was rescued.

https://www.youtube.com/watch?v=NvmDoQirLzg

Its great for French skipper Lionel Lemonchois, that the sponsor didn't leave him in 2014... and the boat is ready with new rig to go for the Transat Jacques Vabre. What a beauty ! :-)


You can see the escape hatch window on starbord side within the silver painting. Hopefully never needed anymore by Lionel Lemonchois.