What degree of buoyancy do you need?
The March 2007 issue of YM contains a reader’s question on the ability of lifejackets to support two people in the water. We asked Warsash Maritime Academy for their opinion and the next thing we heard was a splash as they jumped in the pool to find out.
Here’s the full text of the quesion and answer.
Q: Please could you advise me, based on your own or your readers experience,
rather than manufacturers brochures, what size lifejacket (in Newton’s)
should be worn to support two fully booted and oil-skinned, average sized
males, in a moderate sea, where one has gone over the side without wearing
a lifejacket and the other wearing a lifejacket has to go in and support
A: Before going further it is probably a good time to make a general statement about using and the use of lifejackets. Many different bodies, both in the commercial and leisure world, advocate the use of lifejackets at all times when afloat or around water. It makes sense, a lifejacket is designed to give someone support in the water and prevent them drowning. The school who consider lifejackets are only there for when one abandons a craft and have them stowed away in a locker are encouraged to rethink. Are they so much in control of events that they can say 100% “I will never enter the water unless I decide?” Following this recommendation then hopefully it should make the initial scenario unlikely.
However, in answering the original question, it must be stated that only lifejackets (those jackets that meet the standards and will turn and support an unconscious person on their back, keeping the airway 120mm clear of the water’s surface) are being considered here. Our pool experiment showed that a buoyancy aid could provide significant assistance, but only to a conscious swimmer.
Lifejackets can be broadly categorised into inherently buoyant and inflatable types. Another type offering both inherently buoyant and a separate orally inflated section are also available on the market. Of these, the most popular within the leisure marine sector is the inflatable jacket, being less restrictive and obstructive than the other types. It allows ease of movement when undertaking a variety of activities on board in the different clothing types you would need to wear.
Inflatable lifejackets can be either auto/ manual inflate or simply manual inflation only and come in 4 categories of buoyancy force (rated in Newtons). These are 50, 100, 150 and 275N. Of these four categories, the 150N and 275N are only really worth considering in the context of the original question as anything less than this would not support two people in a moderate sea with full clothing on. The 50N and 100N are designated for children and should not be worn by adults. Buoyancy aids nominally offer 50N support and only offer support, rather than the functions of a proper lifejacket which were mentioned previously.
We decided to conduct a test experiment in the relative calm of a pool environment with different types of lifejacket and clothing worn to ascertain the benefits of each jacket in varying scenarios. As the photographs show, the 275N clearly provides the extra buoyancy required to support the additional person in the water with the airway well clear of the water’s surface. However, it must be recognised with this jacket that for it to work effectively (and also the other smaller inflatable jackets), the crotch strap must be worn. If not, then the vastness of the air bladders in the case of the 275N jacket will cause them to rise up above the wearer, reduce their vision and potentially result in drowning. This has happened on more than one occasion in UK this year. For single person use, the 150N has ample buoyancy even when used with heavily saturated clothing. Despite this, the all important height of airway above the water’s surface was reduced when supporting two people and would be significantly less in moderate sea conditions.
Of the inherently buoyant types, the new jacket incorporating neoprene upper body and hood, was as effective in supporting two persons as the 275N inflatable jacket.
? The 275N inflatable jacket performed best during pool test conditions for one person rescuing another.
? Any lifejacket worn must fit correctly and the manufacturers donning instructions followed.
From this article you can now see that it might be best if the original scenario is avoided and that all crew on board craft wear a lifejacket. When choosing a lifejacket there are certain aspects to consider:
? There are many different standards applied to lifejacket design and their fittings (lights, etc.); National, European and international, therefore in making your choice ensure it meets the standard best suited to the anticipated use.
? Type of lifejacket again should be that suited for the anticipated use: inherently buoyant, although cumbersome and maybe uncomfortable for continuous wearing, will always work; inflatable jackets are compact, comfortable to wear for long periods and less restrictive, but they do not offer support unless the chambers are inflated. The hybrid jackets of inherently buoyant/inflatable type offer both support, are a more compact arrangement than the inherently buoyant type and offer some support without being inflated.
? Ensure the jacket, of whatever type, is the correct size for the intended wearer. Children should have children’s lifejackets not adult sizes, or the lifejacket will not function as intended and may result in serious consequences.
? Use the experience of the establishment you are buying from or recommendations through an association/club to get the correct type of lifejacket, hearsay on the pontoon/marina isn’t always the best source for guidance.
? Don’t forget to follow the manufacturer’s instructions for normal use, checking the condition of the lifejacket and any recommended service periods.
? For inflatable lifejackets it may be worth considering having on board close at hand a spare gas cartridge and arming kit if required in case the jacket is accidentally set off and inflated.
? One final point worth considering when choosing a lifejacket is the splashguard/spray hood (See photo). Not fitted as standard on many lifejackets, these provide good airway protection for a survivor in the water and can significantly reduce the chance of taking spray into the lungs and commencing the drowning process. These are a relatively inexpensive additional cost in the overall scheme of things and it cannot be stressed enough how good these items can be in making you a survivor, who lives to tell the tale, or just a statistic for someone without one who drowns.
J. Cunningham & K. Hopkins
Maritime and Offshore Safety Section
Warsash Maritime Academy