Airbags!?

gunnarsilins

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My friend, cruising around Scandinavia in his Fjord 34 has the following thoughts!
In the unlucky event of a knock-down in rough seas it´s quite possible the boat will remain lying on it´s side, and slowly go down.
He´s thinking of having two "airbags" mounted on port and starboard side, high up on the flybridge. In the case of a knock-down they should inflate and thus help the boat to right herself.

The boat is a 34 feet twin screw semi-displacing motorcruiser powered with two heavy diesels and carries her big water and fueltanks low. The open aftdeck/cockpit is made watertight and the wheelhouse is enclosed with watertight doors. So she should not take any big quantities of water when lying on her side.
I have seen this arrangement on some RIB rescue boats, but is there anyone who have seen or experienced something like this on a bigger motoryacht?
 

jfm

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Sounds like it should work if get details right. Pretty ugly though. Also the deadweight of the 2 airbags, when not deployed (hopefully that's all the time) will not be helpful
 

kimhollamby

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Two problems in a knock-down that may mean your friend should save his money:

a) get him to check the engineroom and note what might shift if the boat hits 90 degrees or worse. Could even be the engines, depending on how they are secured. Certainly might be the batteries, perhaps the tanks. Leisure boats are not built like lifeboats;

b) the minute the boat is on its side a lot of water is going to get in through the engine vents and potentially through windows and doors as well. The buoyancy bags, even if they are big enough, are not going to be in the right place to deal with the destabilising effect of all that water swooshing around inside and it's likely to be an abandon ship job anyway. There's also the little matter of whether he can find substantial enough structure high up to deal with the considerable forces involved.

If he's looking to be inventive it might be a whole heap better to consider an inflatable collar that sits at gunwale height. Not going to be any cheaper, might in fact be more expensive but it would do more for saving the boat at an earlier stage and it would be installed at a stronger point in the structure.
 
G

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Re: Good idea? NOT

umm. I thought I was the one with the daft ideas?

If the boat falls to its side, it will probably lie in the water with the flybridge below the horizontal, thereby needing a monstrous airbag, close to the volume of the boat. Attaching to the flybridge sounds ok, but I'm not at all sure how strongly the flybrisge is attached - usually it isn't very strongly. Also, once on it's side, some large things will move -very probably the fuel tanks , and praps engines too as Kim says. Even if they don't move, the movement of water/fuel will inhibit any "self-righting" properties. So the airbags would have to be independent of other propulsion system to enable inflation, and would have to be very quick to inflate to minimise flooding. They also have to be able to lift the (heavy) weight of airbag on the other side. So the the boat, with monstrous airbags costing perhaps 5 grand each might well be inflated, but without the airbags would possibly be somewhat quicker and able to reach port before the storm. He could considr sell the boat and buy a lifeboat which actualy is tested by dropping from a height, tho not all are self righting. Note that if you did want to trigger the airbags, you would have to be a very cool cucumber to sit in the pilot seat and press button a, instead ooh hell leap off, or indeed (more likely) already have been blown or thrown from the flybridge. This all assumes, of course, that the gathering storm hasn't already sunk the thing with weight of un-triggered airbags. More relaible flotation would be an internal single airbag, which would save the boat, but accidental inflation is likely to be a problem if it goes off while you are having tea. If they worked, the soaking wet nowwith quite alot of water would be something of a write-off -but without being a write-off cos still afloat, and a large portion of the valeu of the boat (the flotation devices) evidently working so inhibiting a write-off. Much better to drive the thing up the beach? Or get in the liferaft, let off a flare, get on the vhf and help others instead of twatting about with the magic airbag contraption? Or look at the weather forecast and not go out in a force 8 +?
 

zefender

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I think it would take a lot less than a sideways hit with a tidal wave to put a boat on its ears. I can't remember the figures but it takes a surprisingly small wave to do it. A bit of engine trouble is all it needs to stop being bows to the waves. An alternative to the airbags is of course a keel...but now I've just given the game away!
 
G

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Re: how about

hmm, I'm not sure the normal boaty would want to check how big a wave is needed.

A more useable (tho still a pleasing mad scandinavian-style) alternative would be large telescopic hydralic rams/stilts, to allow the boat to find shallow water (say, 10 metres) and then lift the entire boat above the waves, until the storm abates. When retracted and in planing mode, the large flat feet would rest extenally and snugly againt the hull. An additional non-marine generator would be needed to provide power once the boat is lifted, as raw water intake won't be possible. Also, the user might have to forget about a forwards berth and an aft cabin, as these will be full of the works. However, unlike the airbag scheme , the (massive) costs could be recouped against mooring and lift-out fees.
 

BarryD

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Re: how about - modified

Excellent idea, if I might add a varient however. For economy a real engineer would place flexible hoses in the aft legs and use them to draw water in thereby saving the cost of the secondary generator. The same collapsed pipework would serve the raw water cooling in the retracted mode.

With a bit of gear work it might even be feasible to have the whole contraption walk to shore in the event that the seas got too rough.

Now that's a soution.
 
G

Guest

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Re: more modifications

Not sure about sucking the water up the legs, as they're tescopic, so a raw watr slooshing around would cause problems, and remebr the feet are fully retracted. Raw water might be sucked through the base of the feet, with side vents for when the feet are on the sea bed, but there's a danger of sucking in lots of shellfish if drawing water from a depth, and (more importantly) too much load on impellor which elminates any possibiolty of using other than a separate normally-cooled genny - not too great a weight penalty considering tyhe fairly monstrous amount of kit.

I am worried at the walking-ashore idea, in the event tht the shore is rocky rather than a shallow and gentle beach, and the walking will be impaired if the beach is gravelly. So the walking won't work

A better solution would be additional rocket powered anchor-hurling howitzer with variable angle of trajectory and range about 400yards (with chain attached , to allow the boat to be dragged ashore. Four large 4metre-diameter wheels with fat tyres attached to spindles at the end of (two more) legs on each side would allow the boat to be dragged ashore without grounding, whilst of course retacting the aformentioned legs. Two powerful cranes would allow the boat to "climb" up the rockier shores (definitely need that non-marine genny now) , with the wheels protecting the hull and sterngear as the boat hauls itself up the rocks.

Simplest of course would be to replace the entire flybridge with a helicopter, but ensuring that the blades are the retractable/detachable type for river work, and for coming alongside, and that the sleds are attached firmly to the hull topsides. This also ensure a good berth (literally overtaking the queue for the lock) and abilty to simply clear off to the med if it turns nasty. Note that we still want the legs, otherwsie the racket of the helicopter may be seen as a disturbance at night, as otheriise the boat will need to hover a few feet over the marina, again with a massive financial saving.
 

BarryD

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Re: more modifications

Well you've certainly thought this through. My alternative suggestion would be to to set some switches so that if the hull rolls past 80 degrees then rocket motors blow the flybridge off like an ejection seat, it's own floation collar inflates and the flybridge becomes a life raft. The remains of the hull would then be made to sink like a submarine via ballest tanks in the hull space achieving neutral buoyancy about 20' under. When the storm has passed puffer jets of water would right the hull and then compressed air be introduced into the ballast compartments and refloat the hull. The flybridge could then be towed back to port to be re-attached later.

Whilst this lacks the fun idea of legs and wheels on the boat, or indeed helicopter blades to lift the boat clear it could proabbly be enigineered from existing scrap bits. A winter project for someone on PBO maybe?
 

chas

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Excellent idea. they could also be used if collision was unavoidable. Second thoughts they might look better side by side in front of the bridge.
 
G

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Re: even more modifications

I think we ought to avoid rocket motors, where the kickback on the hull will sink it, or flip the superstruicture kersmack if one of them goes off and the other doesn't, or indeed if the thing rolls, and the rockets go off later, the superstructure will be blown another 20metres underwater to ear-pressurizing death

But the PBO angle is good, as is the careful use of superstructure form.

I fancy a gently concave industry-standard superstructure form which allows one boat to be stacked on top of another, still with the legs, such that everyone can launch lightning protests at marina fees rates by all stacking on top of each other, two or three high or more. Your inflatable collar jobbies will probably be needed in case they fall over, and the bottom one will need the legs option, otheriwise it'll sink.
 

zefender

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Re: even more modifications

These ideas are based on very sound engineering principles and worthy of commercial pursuit. I would propose a simpler chemical solution however.

We know (don't we?) that boats float higher in salt water than fresh. And a boat floats higher still in very salty water due to increased density. We also know that a boat floats higher in warm water than cold. So it seems obvious that what is needed when faced with huge seas and a sinking boat is lots of hot salt.
Simply resting 2kg water soluble bags around the engine room, maintaining them at an optimum temperature and in full readiness, could, in theory save lives, much embarassment and insurance premia.

Faced with mounting seas, the wise skipper reaches down into the engine room and hurls the bags manfully into the sea. The bags dissolve, the water becomes denser and the boat immediately resumes are more orderly angle.

Footnote: It is important to remember to throw two bags simultaneously - one for port and one for starboard - or the situation could become unstable very rapidly. Repeat as required.
 
G

Guest

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Re: yes yes

but the bags of salt will sink! So perhaps filling the fenders with salt and trailing them will allow a more gradual dispersal of salt? Also, running off the hot water? In extreme cases, a handy thermal lance will heat the water, and maybe even evaporate the sea, so is caution needed and training, as always, a wise idea.

Back to Byron's cautionary note about tsunami's : it is of course ridulous advice to "keep out of the way of " these as they travel very fast indeed, and can spring up on you, perhaps as often as once in a lifetime. Nitro "top fuel" injectors will give the necessary burst of 300% power to reach the beach in record time, and although bend/blow up the engine in the meantime, you can't be too safe...
 

zefender

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Re: Eureka!

Having pondered the niggling sinking bag problem, I've decided that salt, despite its excellent buoyancy properties, created practical difficulties viz bulk and weight. Then, thinking about the original air bags idea, I combo'd this with my heat thought. Obviously, the ultimate extreme survival system comes, not from buoyancy in the water, but floatation above it. Emergency hot air balloons would lift the boat out of danger - either to a safe port or raised only slightly above the more threatening peaks of green water.

Dribbling with excitement, I headed off to the bath with a scaled-down prototype. Immersing myself in the bath, I found that I was able to simulate the boiling cauldron of water effect, just as one might encounter in such extreme conditions. Amazingly, the prototype did rise out above the water. Certainly some care is needed to avoid excessive altitude, though the propellors were able to provide a reasonable degree of steerage, despite the conditions. I was unable to fit my prototype with bow thrusters so I cannot guarantee similar results for those with this mod but I suspect even more encouraging results could be achieved. Certainly, the idea needs a more scientific control/parallel testing under laboratory conditions and I'd be happy to loan my bath for such an endeavour.
 

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