Liferaft or foam?

[ntica]

having simular thoughts in this subject. How can I CALCULATE HOW MUCH FOAM, AND WHERE TO PLACE IT IN MY TYPE OF BOAT??? Is it possible at all? or go with the liferaft option instead? someone?

[Bill NH]

having simular thoughts in this subject. How can I CALCULATE HOW MUCH FOAM?

Take the loaded displacement of your boat in pounds and divide it by 64 (the density of seawater in lbs/ft3).  This will give you the number of cubic feet of foam required to float your holed boat with the deck right at the water.  Any more flotation will float the boat higher in the water...

[Bill NH]

There's a photo out there (which I'll try to find) of a SeaRunner trimaran like we used to live on that sailed across a reef and ripped the bottoms out of all 3 hulls.  It was swamped but still sailing with the deck just above the water. 

Getting rid of the lead makes alot of sense in my book!

[SeaHusky]

SeaHusky, how has this decision process been coming along?

Sorry for the late reply. It's really not a decision but more just thinking around the KISS principle - what is the simplest solution to a problem liable to give the desired result, much like the inboard/outboard discussion??
As said, you pack your fears and the probability you will have to abandon ship is very small but the amount of debris from the tsunami floating around has changed the odds in an unknown way and hitting a shippingcontainer while singlehanding is not really up to good skippering is it?
Anyway, I still feel that a floating boat with all the tools, provisions etc. is much more survivable than a minimal liferaft which may or may not function when you need it. Roger Taylor has showed that you can fit enough stores in half a 21-footer for at least two months sailing. What he can not do is live comfortably for two months at his destination aboard the same boat (i.e. cruising) so it is also a question of what is your intention with sailing. The easiest solution (not the simplest) is  to pack a good liferaft, or better yet a survivable dinghy, which is what most people do and is sometimes required by regulations. If I wanted to use foam I think that in a boat like an Albin Vega, which has a large volume for its displacement, I could fill enough foam for positive buoyancy and still have the same living/storagespace as in a 25-footer. As Bill, and also Sven Yrvind points out, the best solution is to not use lead ballast. That way you minimise the necessary buoyancy needed.
In the end though I believe I will just get a good liferaft, take a course in using it, and be happy with the probability that I will never have to use it. Sometimes the easiest is also the simplest way.

[CharlieJ]

Jim has that picture in his book-  "Case For the Cruising Trimaran"

Washed across a jetty.

I found it fascinating, looking up through the hulls from below. The boat was Do-Raka, a SeaRunner 31, and was totally repaired. (I just looked in the book) ;)

[Captain Smollett]

Take the loaded displacement of your boat in pounds and divide it by 64 (the density of seawater in lbs/ft3).  This will give you the number of cubic feet of foam required to float your holed boat with the deck right at the water.  Any more flotation will float the boat higher in the water...

Hi Bill,

Doesn't this assume a truly empty hull and that nothing in the boat is buoyant?

Using the displacement to get the volume of foam needed will give an overestimate.  Some of the boat's volume is already displaced.  It may not seem like much, but it adds up.  That's the reason (I think) most estimates of needed flotation seem on the small side compared to the displacement of the hull.

The other thought is that in practical terms, we don't necessarily have to completely float a fully flooded hull.  This assumes no damage control (stuffing the hole, pumping, etc).  It also assumes that in a true emergency we are not doing anything to lighten the boat - dumping unnecessary (in an acute survival sense) stores and goodies.  Pumping water out of tanks, for example, is a cheap way to buy some extra flotation via the empty tanks. 

I've always viewed the idea behind flotation as being "buying time," rather than true floating of the hull.  Maybe that's just me.

By the time we fit in true hull-in-cruising-trim-displacement-floating flotation, there will be little room left for stores, or anything else allowing practical use of the boat. 

Everything is a trade-off....how much space do we sacrifice for how much flotation?  Sometimes, you roll your dice and take your chances.

[David_Old_Jersey]

I would not personally bother to retrofit any foam - instead adopt the same principle by using watertight compartments. Not simply barriers between forecabin to saloon to Engine Compartment - but equally importantly as many lockers as possible.

If Water can't get into a locker or get out of! then that is one part of the boat that is ok. A couple of my lockers won't be totally watertight - but Plan B is to empty them ASAP and refill with fenders or anything else that doesn't soak up water (Maybe even some builders foam from a can - into a black binliner?) to simply displace 80? / 90?% of the water from the locker.

On my boat I have four compartments to seal off from each other (I have an aft cabin).

Forepeak to Saloon already has a door - first step is to close it! and then use predrilled bracing to secure it shut - whilst I drill and screw it closed. Won't be a 100% watertight door, but won't be anymore than the bilgepump can cope with. Under the door frame is the bilge - that has been amended to allow a bung to be inserted to close that water flow. Access to the forepeak (to sort out the leak / hole! will be via the foredeck hatch.....with 80% of the boat not flooded the water level in there should not be above waist height.

Saloon to Engine Compartment  - that's another simple bung in the bilge.

Engine Compatment to Aft Cabin - I have not quite got this one nailed down yet!, will involve sealing a couple of the lockers above and around the prop shaft, rudder head and steering arm and the exhaust. Probably not permanently sealed, just capable of being so in a hurry!


Will let you all know how it goes  ;D

[Captain Smollett]

David, that's my "plan," also.

Water tight (or snuggish?) compartments seems the best route for us given the boat size and locker locations, etc.

Having the chain locker at the bow seal-off-able is a big space, as are the lockers in the cockpit and under the settees.  Be pretty easy to use the v-berth/fore cabin door as a water-snug door, but the aft door (between main cabin and head) is problematic.

To reiterate, I don't think that this stuff has to be 'bombproof,' as in my mind at least, it's more about buying time to jury a repair.  I recall that Neal Peterson was holed in the Atlantic and between stuffing life jackets and the like in the hole (cushions, sails, whatever), he was able to make port - several days away - with 20 minutes of hand pumping per hour.

Also, Dave Martin discovered a crack in the steel hull en route from Bermuda to Iceland, and repaired at sea by making a kind of coffer dam out of some spare wood and underwater epoxy.  It got them to port where he could make a proper welded repair on the outside of the hull.

[David_Old_Jersey]

Yeah, am all for the coffer dam approach - working on the inside far more likely to be succesful (and possible!) than working on the outside, even if not neat! - and probably have to "recycle" some of the interior to section off the affected area.

Hope I never have to find out!, but have always been happier having a Plan B, C and D - even if not all fully specced out.

[sharkbait]

The 12' sit-on-top kayak that I use for my dinghy doubles as my liferaft
and fits just fine between cabintop and standing rigging during a cruise.
When out for a daysail I leave it in the slip.

[Travelnik]

Our float bags are of the enclosed sort (http://www.subsalve.com/flotation.htm)...

That's a pretty good idea. I would be able to use just use one to keep my 3100lb. boat from going completely under, and then stay with the boat, or even be able to keep it from sinking while I made repairs and pumped it out.