[Paddlewise] An old topic revisited

During the heated exchanges on sponsons Tim Ingram often said that life
rafts had high form stability and that should prove conclusively that beam
(and consequently form stability) was best for safety at sea. At the time I
suspected an error in this but
did not have the resources at hand to find the truth. I have obtained the
information (much embarrassed to find out it had been on the net all along
and I had been searching incorrectly) and it is a good example of how one
can be easily led astray by selective reading. The following comes from the
Canadian specs that are virtual copies of the IMO (International Marine
organisation SOLAS (Safety Of Life at Sea) regulations

15. (1) Every inflatable life raft that has the complement set out in
column I of an item of the table to this subsection shall be fitted on the
underside with the number of water pockets set out in column II of that
item.
>What followed was a table showing the required size of ballast pockets
that you need not be bothered with<

(2) Water pockets shall be of a highly visible colour and distributed
evenly around the circumference of the life raft at each side of the gas
bottles, with sufficient separation between them to allow air to escape
readily.
(3) The cross-sectional area of a water pocket shall form the shape of an
isosceles triangle, the base of the triangle being the part that is
attached to the life raft.
16. (1) The aggregate capacity of the water pockets of a life raft shall be
(a) where the complement of the life raft is fewer than nine persons, not
less than 225 L; and
(b) where the complement of the life raft is nine or more persons, not less
than the greater of
(I) 225 L, and
(ii) (18 x N) L, where N equals the number of persons in the complement.
(2) Water pockets shall be designed in such a way that the pockets fill to
at least 60 per cent of their capacity within 25 seconds after the
deployment of the life raft.

Clearly the IMO believes that only ballasted life rafts are acceptable.
This is supported by US Coast Guard studies.


Doug Ritter in a review of rafts for Aviation Consumer says, "The less
expensive unapproved rafts, commonly purchased for Part 91 light plane use,
were potential death traps, though assuredly much better than nothing."
Note the "potential death traps".

Now let us hear what one life raft manufacturer says about unballasted life
rafts.

Winslow also offers a single tube, double cell "Rescueraft" in 4, 6 and 8
person size, starting at 16 lbs. and $1,069. It represents the very bottom
of Winslow's line. It is simply a GA-ST with no ballast or most of the
other accouterments, except entry aids. President Fred Shoaff commented, "I
hate selling that Rescueraft, but some people simply will not pay any more
and for sheltered waters in fair weather it is probably adequate and far
better than nothing." Winslow pointedly refuse to even call it a "life
raft" in their literature or when discussing it, since it has no ballast.

Notice the reference to ballast and the reference to sheltered waters.

Givens, a maker of life rafts boasts that their life raft is self righting
due to water ballast the equivalent of 4700 lb. of lead ballast!!!!

Another aspect of life raft design is particularly appropriate where boats
are concerned. This quote from a study of aviation life rafts.

>From the Aviation Consumer article comes this gem. "Rectangular and square
rafts are more likely to settle in a wave trough, dig into the water and
capsize while a round raft will tend to carrousel rather than capsize. A
number of studies have shown that rectangular rafts are particularly prone
to being capsized in conditions where they end up broadside to a wave.

Keep in mind that boats are much closer to the rectangular model than the
round model.

The point in all this is that people will look at rafts and assume that,
because they are wide and stable that it is the beam that makes them
seaworthy when in fact they are only safe when equipped with large amounts
of ballast - something sea kayaks rarely have. without the ballast they are
potentially dangerous just a I was trying to point out in my discussion of
sponsons.

Tim made assumptions about rafts that weren't valid. Worst of all he
assumed that, because some people survived in them that proved how good
they were. Listen to what Doug Ritter says again, " Even those rafts rated
"unacceptable" have "saves" they can claim. Of course, those not saved
rarely get the opportunity to complain. "

This is important. Just because some people are saved by a device that does
not mean all people will be saved by it a Tim claimed.

I wish I had taken time to look this up back when we  were discussing this
topic and extravagant claims were being bandied about.

Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/


***************************************************************************
PaddleWise Paddling Mailing List
Submissions:     paddlewise_at_lists.intelenet.net
Subscriptions:   paddlewise-request_at_lists.intelenet.net
Website:         http://www.gasp-seakayak.net/paddlewise/
***************************************************************************