WestlawnMasthead27_Sept2013H.pub - page 12

The Masthead
Sept. 2013 Page 12
1. BACKGROUND
During the late 18th century, small boats specifically
designed for saving life from shipwreck started to appear at
dangerous harbor and river entrances around the UK. These
early lifeboats were manned by large crews, the majority of
whom were oarsmen providing motive power. The boats
rarely operated far from shore, often within the surf line, so
featured a self-draining cockpit plus permanent buoyancy to
ensure they remained afloat if swamped (originally termed
“the unimergible boat”).
Despite the strong likelihood of capsize, very few boats were
actually designed to self-right, crews preferring high initial
stability and a buoyant hull-form that would ride the seas. In
reality, lack of righting ability was no great disadvantage;
crew members were not attached to the boat and capsize
invariably resulted in them being thrown into the sea. Re-
boarding any boat in breaking seas is difficult enough, but
for a lifeboat crew, already tired by having to row against
wind and waves and wearing heavy waterlogged clothing,
the relatively high freeboard of an upright self-righter would
have presented an almost insurmountable obstacle. An up-
right vessel also experiences greater hull windage, which
could result in the boat being blown away from the crew. By
contrast, an inverted vessel tends to float lower, making it
less influenced by wind and sea and easier to climb onto.
Most lifeboat-men at this time were seafarers, often fisher-
men, who recognized the risks associated with their profes-
sion and accepted that accidents frequently resulted in loss
of life.
1824 saw formation of the National Institution for the Pres-
ervation of Life From Shipwreck, now the Royal National
Lifeboat Institution (RNLI), which led the way in lifeboat de-
velopment throughout much of the 19th century. By 1880
self-righting and un-sinkability had been successfully
merged, but with the need to accommodate a large crew
plus survivors, any mechanism to facilitate self-righting was
pushed to the extreme ends of the hull. This limited its effec-
tiveness and meant that late 19th and early 20th century
self-righting lifeboats were generally narrower and had less
upright stability than their non-self-righting counterparts.
Lifeboat crews nick-named these boats “Roly-Polys,” often
refusing to accept them on the grounds that they were
unsafe. Analysis of RNLI statistics for the late 19th century
indicates these concerns to be understandable, showing
crew losses from self-righting boats to be slightly higher
than those from non-self-righters.
The introduction of mechanical propulsion in 1904 saw little
change. The then RNLI Consulting Naval Architect, J R Bar-
nett, of G L Watson & Co, did not believe self-righting to be
suitable for large offshore lifeboats, so very few new designs
were produced. All changed in 1958 when the RNLI intro-
duced the Oakley 37, the first self-righting lifeboat to com-
bine high initial stability with a reliable self-righting system.
Although still essentially an open boat, the Oakley 37
became an instant hit and served the Institution well for
over thirty years.
The next significant development, surprisingly, did not come
from the RNLI or even Europe. In 1966 the United States
Coast Guard (USCG) exhibited a 44ft surf lifeboat at the In-
ternational Lifeboat Federation Conference in Edinburgh.
With a speed of fourteen knots, the USCG 44 was almost
twice as fast as most lifeboats then in service, but more im-
portantly, was self- righting by virtue of a buoyant super-
structure. The design was subsequently adopted by other
rescue organizations, including the RNLI, and paved the way
for the highly sophisticated vessels we see today.
Basic Principles and Design Requirements
By K C Thatcher CEng MRINA
Principal Naval Architect (Retired), RNLI, UK
SUMMARY
Records show that the naval architecture of self-righting has been known and understood for at least two hundred years.
For much of this time, its application was limited to small, shore-based, rescue boats, but the past few decades have seen
the provision of self-righting capability widen into a diverse range of craft from offshore standby vessels to trans-ocean
rowing boats. Whatever the size and use, the aim is always the same – to provide safe refuge for the crew by incorporating
a mechanism whereby the vessel will return upright following a knockdown or capsize.
Despite this growing popularity, self-righting vessel design is still viewed by some naval architects with suspicion. The pur-
pose of this paper is to provide a background for self-righting methods and basic guidance on design, testing and outfit
requirements. Although much of the content has been based on the author’s experience with rescue craft, it should be
noted that the principles and techniques described are applicable to all types of vessel.
1...,2,3,4,5,6,7,8,9,10,11 13,14,15,16,17,18,19,20,21,22,...36
Powered by FlippingBook