Reserve buoyancy

[onenyala]

Have just been reading the thread on liferafts. I have considered using three or four car tyre inner tubes dispersed in captured positions about the boat and using a cylinder of compressed air to inflate then in the event of a catastrophic broaching of the hull.
As the general opinion seems to be that it is better to stay with the boat rather than using a life raft I feel that the inner tube option has some merit.
Any experience of this idea out there?

<hr width=100% size=1>

 

[sailbadthesinner]

what boat?
your profile is blank.
can't comment further withoutinfo. but in the event of catstrophic hit enough to sink boat you are going to get the compressor find the tubes that your wife has now moved as they were in the way and start that

mmmm
better than nothing tho.

<hr width=100% size=1><font color=red>Ok brain let's just do this and I can get back to killing you with beer</font color=red>

 

[tcm]

on a charter boat, in otherwise fine weather f3, caribean, 1 mile from land so bit far to swim but bit disastrous kit/money/passport wise, the engine exhaust blew and promptly started to fill the boat with nice warm water. All up top, so floor awash bnefore we noticed.

Now, I have to say it was very easy with us - it was a charter boat, so value of boat £0, value of deposit on dinghy towed behind $300, value of our gear more than $300. So, pack gear and make ready to abandon was taken by swmbo very early. But would not have been had it been our own boat.

My belief is that with many problem, unless super-disastrous such as massive non-fixable holing (in which case quick liferafts) the gradually developing prob is one where you make all attempts to resolve and fix the problem, rather prematurely put into action some long-stop backup plan. In other words - would you inflate the monster airbags early (which might stop the fixing taking place, so i think not) or continue with bilge pumps, buckets, spanners, etc etc and so on until a bit too late for airbags and eventually run up to liferafts?

Oh, and we did sort it. But "packing up" after 2 week cruise can be done in under 200 seconds.


<hr width=100% size=1>

 

[Twister_Ken]

Oh dear, the air bag in the forecabin has fired and ripped the hull/deck joint apart.

Seriously, someone asked this in one of the mags a month or two back. I seem to remember the answer went along the lines:

a) you need a lot of bouyancy
b) you need it in a place that reduces the amount of free water sloshing around the boat, otherwise the free water will punch the craft apart
c) you need the bouyancy in a stable-when-upright config, otherwise it might capsize and flloat bottoms-up.

<hr width=100% size=1>

 

[Jacket]

Three or four inner tubes would just about keep a small sailing dinghy and crew afloat.

The total volume of the inner tubes used would have to be the same as the volume of boat you have below the waterline if you're to keep the boat afloat. thats a lot of tubes!

<hr width=100% size=1>

 

[onenyala]

It appears that more often than not after having boarded the liferaft the stricken boat remains afloat for days and becomes a danger to navigation. The idea of the inner tubes was not for them to restore the boat to its original attitude but to make it a bit more bouyant than it otherwise might be. The idea of the smaller tubes was to spread the upward forces to avoid breaking the boat apart.

<hr width=100% size=1>

 

[alpha]

Interesting...

Helicopters use inflatable floats on the skids in the event of ditching, so the technology is there in principle. The 'right way up' problem could be solved with another airbag on the top of the mast (or part way up it in case of mast breakage) to ensure self-righting, but the effects of the positioning of the mass plus the need to protect it from knocks and scrapes when mooring etc makes this a puzzler.

Perhaps in 20 years everyone will have such a system, but it won't come soon.

I agree. Always step upwards into the life-raft.

<hr width=100% size=1>

 

[spark]

I have done a bit of research (including the buoyancy sums) into this and it seems feasible. There was a system on the market called 'Yachtsaver' that did more or less what you want. No longer in production and I have been unable to discover if it was a commercial or technical problem that put a stop to them. I did have an email from a blue water skipper who had fitted the system but he had not had to use it in anger so could not comment on effectiveness.

The buoyancy and stability sums are important. There's no point in putting 'a few' airbags in and hoping they will do the job. You must have enough bouyancy to keep the boat floating sufficiently high to remain stable. This means that the bouyancy needs to be fitted as low down as possible, ideally below the waterline, which may not be practical in a modern fibreglass boat.

You also have to take care that the inflating bags/tubes cannot trap a crew member and thay they are fixed to suitably strong parts of the hull. From what I've seen of fibreglass boat construction if you let the bouyancy bags float up against the deckhead you will probably break the hull/deck joint and find the hull disappearing under your feet.

I am building a boat at the moment and, having considered inflatable emergency buoyancy I am going to go for permanent bouyancy in the form of 3" dia flexible hose with end plugs fitted between the frames. It's a wooden boat so has the advantage of inherent bouyancy, thus reducing volume of emergency buoyancy required. I can fit enough hose to keep her floating high enough in the water to continue sailing (in theory).

The principle of keeping the boat afloat after holing or swamping seems infinitely more sensible than letting it sink and taking to the deathraft. There will be a way of doing it for your boat but it needs to be done carefully and thoroughly to be a safe solution.



<hr width=100% size=1><A target="_blank" HREF=http://www.qei.co.uk/spark>http://www.qei.co.uk/spark</A>

 

[Jacket]

I think 'Yachtsaver' died because the pressure from inflating the bags had the habit of popping out the bulkheads and removing the deck from the hull. As a result of this, insurance companies were unwilling to insure boats fitted with it.

Still, if it keeps boats afloat to the extent that you don't drown, the system seems worth it.

<hr width=100% size=1>

 

[Twister_Ken]

DIY rib

Maybe what's needed is an inflatable tube around the outside of the boat, a foot or so below the deck edge (it could be disguised as a rubbing strake). When the time comes, light the blue touch paper, and the collar inflates, turning the whole kit and caboodle into a giant RIB. Good party trick, too.

<hr width=100% size=1>

 

[Strathglass]

When I raced an E-boat I fitted inside the bunks and under the fore/aft decks with enough polystyrene foam to make it self buoyant. This was only possible because of the low weight of the keel. It was also mainly used for racing so storage space was not important.
It is very important thet there is a lot of high up buoyancy fore and aft otherwise it will turn turtle when swamped. Some classes of dinghies suffer from too much underfloor buoyancy and tend to bury their masts too easily after a capsise.

And yes, it did work someone did deliberately swamp an E-boat after fitting polystyrene block buoyancy and it remained floating and upright.

It can be done but perhaps would be more sucessful on a cat ad they do not carry a lump of lead around with them.

Iain

<hr width=100% size=1>

 

[onenyala]

The buoyancy needs to be high in the hull to try and maintain the upright position. I think Donald Crowhurst first thought up the idea of an inflatable bag at the top of the mast to bring a catamaran from the completely inverted position through 90 degrees till the mast was level with the surface so exposing one float and increasing the chance of ultimately getting it right way up.

<hr width=100% size=1>

 

[chriscallender]

Re: DIY rib

Just don't press the button when youre rafted up in the middle of a ten deep raft in some busy marina!

Chris

<hr width=100% size=1>

 

[alpha]

Crucial to the inflatable system will be keeping the requisite pressure low enough and the rate of inflation under control, to minimise the risk of damage. Also, a boat designed for this system would feature additional strengthening features to cope. Perhaps this was the problem with the now-defunct device?

<hr width=100% size=1>

 

[kindredspirit]

The best system might be "external inflatable sponsons". Possibly like "No Limit" Boats from Holland but in a protected external casing that could then be inflated rapidly by a cylinder.

Just a thought.

<hr width=100% size=1>

 

[Magic_Sailor]

Spark

You're actually building a boat - so my comment comes with the "greatest respect" tag.

You mention that any bouyancy device should be as far below waterline as possible. Is that correct? Surely, if it is as you say - say in the bilge, then if the boat turns turtle, she will float but extremely low in the water - mostly submerged. Surely, you want it the other way round so that you could shelter inside the hull (a la Tony Bullimore) if necessary - plus the boat will be more likely to right itself if it's point of rotation is lower (when upside down).





<hr width=100% size=1><A target="_blank" HREF=http://hometown.aol.co.uk/geoffwestgarth/myhomepage/travelwriting.html>Click for website!</A>

 

[spark]

You are all, of course, absolutely correct when you say that buoyancy in a swamped boat should be high up to discourage it from turning turtle.

I, on the other hand, have been looking at it from the perspective of fitting sufficient buoyancy below the waterline so that the boat cannot become swamped to the extent of losing stability. Ideally this means filling the displaced volume with reserve buoyancy. In practice, even in my traditional hull form, only a percentage of the displaced volume can be filled with buoyant material but that percentage, along with the added bouyancy of the wooden hull as it sits lower in the water, may be enough to do the job.

This is, as yet, just theory. If anyone thinks I'm missing something important please don't be shy.



<hr width=100% size=1><A target="_blank" HREF=http://www.qei.co.uk/spark>http://www.qei.co.uk/spark</A>

 

[andy_wilson]

Form stability depends on having no water inside the hull.

Once you take on water you need a very different pattern of buoyancy to stay upright - with the empasis on it being towards the top of the swamped hull, with the weight hanging from it to keep things upright.

Look what happened to The Herald of Free Enterprise - normally as buoyant as a cork - once a small amount of water was taken in.

<hr width=100% size=1>

 

[Guest]

Could not let this one go, been waiting all weekend for a password!

Reading this thread is like hearing the plans to reinvent the wheel.

How to keep a boat afloat when flooded was resolved years ago by ETAP! Always criticised for lack of locker space, Etap's solution looks a lot neater than stuffing the cabin and lockers full of old inner tubes.
The ETAP solution has been tested too, how will you know if you have enough inner tubes?

<hr width=100% size=1>

 

[Twister_Ken]

Nice boats, Etaps. Just a shame you've got to hack all of that foam out of the lockers to get any stowage space.

<hr width=100% size=1>