Stupid idea No.2

[NUTMEG]

Nothing on telly so been thinking about repairs and
improvements to be carried out (inflicted) on Sophie this winter. Sophie (19' Sadler Seawych) has a displacement of just under 850kgms. Less than a tonne. A cubic meter of water weighs (I have been told) a tonne. So if I fit a cubic meter of polystyrene foam under the cockpit and in two forward lockers she will become unsinkable, right? These spaces are unused, just a few unidentified bits and bobs chucked in them.

I now withdraw and brace myself to be corrected and shown to be the idiot I rather suspect I am!!

 

[trapezeartist]

Seems reasonable to me. Our old 470 had blocks of foam inside the buoyancy tanks (required by class rules). They were wrapped in plastic to minimise the possibility of becoming waterlogged.

I'm trying to think of what might be wrong with the idea in your context. Are you sure you really have room for it? One cubic metre is huge when you see it sitting there in front of you. Effectively you would be asking the blocks of polystyrene to float and hold up the boat, so the load would have to be evenly spread in order to prevent the foam being crushed or distorted.

 

[sarabande]

you would have to be very certain that the upthrust generated by the flotation blocks could be contained by the deck fastenings - which are almost certainly not designed to resist that level of force. Poly blocks are also pretty fragile and would need wrapping or otherwise 'containing' to prevent them abrading and disintegrating.

 

[donm]

Good advice from Sarabande. I remember fitting nice cheap polystyrene blocks beneath the floorboards of our National 18. When we flooded the boat to check it all worked, the blocks burst through the floorboards and floated away leaving the boat awash and without bottom boards!

 

[ianabc]

Flotation

There is a story, probably true, of a new aluminium sailboat, just a metal hull, no interior, that was bottom paintred on the tidal grid in Comox BC.

Owners left through hulls open, boat floated while they had retreated to nearby pub after anti fouling the hull.

Foam floated said boat.

Trouble with foam is in the placement.

The height of the placed foam alters the balance of the craft.

 

[Blueboatman]

Not so stupid idea.

I am sure the hull/deck joint will support the upthrust.

Dont forget that the foam itself weighs something ( but not much).

With around 1 1/4 cu metres of foam all you have achieved is little more than neutral bouyancy, it will float but with decks awash..

However if you could then part inflate the dinghy,dinghy seat,fenders etc and jam these inside the cabin the freeboard of your new liferaft improves.

Another alternative is to save those 1 litre plastic milk cartons..Yup, 1000 will give you nigh on a ton of upthrust, 2000 and you're laughing..-Might be neater than using foam? I always liked this idea for temporary unsinkability when ocean sailing, cos the boat will be full of extra juice and water cartons anyway..

 

[BrendanS]

There was a long thread on this sort of idea some years ago on here (on scuttlebutt I think) where the idea was dissected in detail. The outcome was along the lines of (from memory) that inflated bag etc inside cabin was a non starter, once the maths was done. If I get time, I'll see if I can find the thread

 

[Wansworth]

Have a really good think about it,as said a cubic metre is a lot of material.In the event of it actually being put to the test there will be a lot of water sloshing about so foam has to be protected and fastened strongly down in the bottom of the boat to give lift.It probably is possible but you wont have much storage space left in a 19 footer.

 

[Blueboatman]

Hi Brendan,

Yup, somewhere on t'internet will be the pics of a Sadler32 sailing with decks awash.

 

[Wansworth]

Have I commited "partiale Lakesailoring "in my reply above .Or being aware that its could be "lakesailored" not countas said "lakesailoring" as given in the rules.I stand corrected if this is the case.

 

[Bajansailor]

An alternative to installing permanent buoyancy in the form of foam (or plastic bottles) is to consider some compartment sub-division, ie water tight bulkheads.
However this would probably be a bit impractical on a Sea Wych!

Here is an interesting article by James Baldwin about how he effectively made his 28' Pearson Triton theoretically unsinkable (discounting fire) by building water tight compartments - http://atomvoyages.com/projects/UnsinkableBoat.htm

In fact the whole website is fascinating, with so many useful cruising ideas and tips - I like his design for his home made beaching legs.

 

[cliff]

Hi Brendan,

Yup, somewhere on t'internet will be the pics of a Sadler32 sailing with decks awash.

 

[Pye_End]

That is an interesting picture. Makes you realise what you might end up with if you have barely enough buoyancy to float a boat. Just wonder how useful standing on a yacht that is awash compared to say carrying a dinghy/liferaft - he looks very exposed to the weather (even if fully clad). Not too bad in a flat sea as he has got. Much of a swell and he is in danger of being washed off. Anything inside to aid his survival will be hard to get at.

 

[bilbobaggins]

Anything inside to aid his survival will be hard to get at.

I seem to recall the RAF survival instructor's advice that "One should step up into one's liferaft...."

And that several RTW solo yachtsmen have been rescued from decks-awash boats - for example, Raphael Dinelli. Nor should we forget the lessons to be learned from the indestructible Tony Bullimore....

 

[Refueler]

Not so stupid idea.

I am sure the hull/deck joint will support the upthrust.

Dont forget that the foam itself weighs something ( but not much).

With around 1 1/4 cu metres of foam all you have achieved is little more than neutral bouyancy, it will float but with decks awash..

However if you could then part inflate the dinghy,dinghy seat,fenders etc and jam these inside the cabin the freeboard of your new liferaft improves.

Another alternative is to save those 1 litre plastic milk cartons..Yup, 1000 will give you nigh on a ton of upthrust, 2000 and you're laughing..-Might be neater than using foam? I always liked this idea for temporary unsinkability when ocean sailing, cos the boat will be full of extra juice and water cartons anyway..

Out here for years in Latvia - it was common for people to satisfy local inspections req'ts for RESERVE buoyancy - by tying together strings of lemonade bottles. My 5.5m weekender had them in transom, under fwd bunk, in lockers ... literally any space they could cram them into.

Note the word RESERVE buoyancy. That is what you are talking about. Blocks, bottles etc. have no effect on a boat till boat sinks and then the RESERVE comes into play.
It's same as ships having raised bow and stern sections - they are watertight compartments designed to give RESERVE buoyancy.
A lifejacket works on same principle. It does nothing till you roll over and it then starts to submerge, it then wants to remain on surface ...

OK - what foam ? Cheap and cheerful, able to work ... Exterior Foam Wall cladding in 1m square panels .. cut to fit ... They do not, contrary to some peoples comments, absorb any water - they are easily shaped, cut etc. Can be glued to each other with standard PVA but not with Polyester or Contact Glue with solvents.
It's sensible to multiply the amount of buoyancy 'weight' required by 1.5 to maintain a safe margin. Also remember that Seawater around UK is generally about 1.020 - 1.028 kgs / cu.m .... depending on river feeds, outfalls and tides / currents etc. So your 1 cu.m = 1 tonne is actually not strictly correct. It's more like 1.025 tonne per 1 cu.m.

( Before anyone starts to argue - I do this rubbish as part of my work ! )

 

[David_Jersey]

An alternative to installing permanent buoyancy in the form of foam (or plastic bottles) is to consider some compartment sub-division, ie water tight bulkheads.
However this would probably be a bit impractical on a Sea Wych!

Here is an interesting article by James Baldwin about how he effectively made his 28' Pearson Triton theoretically unsinkable (discounting fire) by building water tight compartments - http://atomvoyages.com/projects/UnsinkableBoat.htm

In fact the whole website is fascinating, with so many useful cruising ideas and tips - I like his design for his home made beaching legs.

Cheers for that link, although I have read before - well worth another looksee .

BTW I am (slowly!) aiming for the collision bulkhead / watertight locker approach. My thinking is not so much about adding bouyancy, but displacing the water / preventing it moving to areas that are undamaged - probably will also be going for some inflatable emergency back up, more to fill / half fill a sealed locker that has been externally breached than to fill the whole boat..........but if push comes to shove I figure a strapped down 9 foot Avon in a cabin would displace a bit of water (hopefully some of it back outside )

 

[Blueboatman]

Has anyone been bored enough to do the maths on the volume of air trapped in a fully inflated Avon I wonder?

I suspect that it is more than one might think?

Secondary question: Hows about inflating an Avon UNDER a flat pontoon to verify whether or not the seams would withstand immersion in water at a depth of say O.5 m ? ( One for a PBO production team on a quiet issue month ?) As an aside, would the relative strength of Hypalon vs PVC and their adhesives come to light ?

 

[KenMcCulloch]

I think the idea of 'upthrust' in this context is a bit misguided. Really all you are doing is reducing the floodable volume inside the boat to the extent that the whole boat plus contents and all spare volume filled with water displaces less than its total mass. There will be some force exerted on the structures containing the buoyancy but if the structure is not strong enough to withstand that it would probably fail in normal use.

 

[Pye_End]

I seem to recall the RAF survival instructor's advice that "One should step up into one's liferaft...."

And that several RTW solo yachtsmen have been rescued from decks-awash boats - for example, Raphael Dinelli. Nor should we forget the lessons to be learned from the indestructible Tony Bullimore....

Very true. More often than not up-side-down as well, aiding the trapping of water so can float a bit higher (losing that weight under the boat helps as well!). Maybe a quick release keel might keep the craft afloat?

There are benefits of deliberately getting the bows to be the more buoyant part - eg you could be higher from the sea; there is a greater chance of trapped air so more buoyancy; more visible to passing craft. On the other hand it may be harder to hold on, and any chance of getting items from cockpit locker/cabin is rather reduced.

If it comes to a 'do I fill this space with foam or a life raft' there is still the issue of sinking due to fire to overcome.

 

[VicS]

Some thoughts.

The structure of the boat will be strong enough to withstand the effects of buoyancy under the cockpit sole I am sure but the forward bunk moulding and in particular its joint with the hull may not be, Remember that the majority of these boats were assembled by novices with little or no previous boat building experience.

I dont think the spaces you identify will hold the required 1m³ of polystyrene foam. I suggest you make some careful measurements and calculate the volume of those spaces.
To put the required volume into perspective it will be slightly more than the whole of the hull volume below the waterline, including the volume of the keels.

Have you posted the idea on the Owners Association message board or put it directly to any of the OA's panel of "Technical Advisors" for comment?