September 2, 2000 Aviation Life Rafts, Part Two: A Life Raft Primer

Email this article |Print this article

by	Doug Ritter

About the Author ... Doug Ritter is former News Editor of AVweb and now contributes on special projects. An experienced and respected aviation journalist, Doug is a contributing editor to The Aviation Consumer and Aviation Safety and a former contributing editor to Flight Training. He also writes for CODE ONE and AOPA Pilot, as well as other aviation publications. Doug is best known for his insightful product evaluation and comparison articles, his interpretation and explanation of complex technical and engineering concerns related to aircraft systems and products, and his in-depth investigation of aviation products, flight safety, and human factors issues. He is a leading expert in the area of aviation survival and a working member of the SAE Aerospace Council S-9 Cabin Safety Provisions Committee and S9-GA General Aviation Sub-Committee. Doug is also the publisher and editor of Equipped to Survive, a web site devoted to survival equipment and techniques. Articles in This Series Part One: Requirements and Expectations Part Two: A Life Raft Primer Part Three: Single-Tube Life Rafts Part Four: Double-Tube Life Rafts Supplement: Manufacturer Contact Information

In this four-part series, AVweb provides an in-depth look at aviation life rafts. We examine the regulatory requirements, the common-sense requirements and what you should look for when selecting a life raft. We also examine both the approved and unapproved rafts for the GA market and let you know which ones will more likely save your life if you ever need to use them.

The rafts we tested ranged widely in price, features, and capability. When all was said and done, our overriding concern focused on capability — would it save our lives? There is no other reason for a life raft's existence. As we spent hours, days and weeks with these rafts, a related concern came to the fore. The raft must be designed and equipped to take care of the survivor; it should demand little or nothing of the survivor, who may be unable to do much on his or her own behalf. Everything should be obvious and intuitive to survivors who most likely have no survival training.

A life raft is an integrated system where the performance of individual features, or lack thereof, can significantly affect overall performance, both for better or worse. The devil is often in the details.

Choosing a raft can be difficult: the selection is confusing and the terminology often doesn't help. Moreover, despite the existence of an FAA standard to which some rafts are manufactured, not all FAA-approved rafts actually meet the standard in all regards, in our opinion. For rafts not FAA-approved, not even these laxly-enforced standards apply.

In this second of this four-part series, we will examine some general considerations and issues regarding basic raft design and specific features that affect the raft's capabilities — what you might call a life-raft primer.

Criteria For Evaluations

In evaluating the rafts we were concerned with a number of attributes: ease of deployment and operation; ease of entry, both from the aircraft and the water; protection from the sea and elements; functionality; livability; comfort; survival equipment selection and quality; and of course, price. Some of these are more critical than others, but all have a bearing when making a choice.

Some might question the inclusion of livability and comfort in our criteria. After all, they will contend, the issue is survival. It's not supposed to be a pleasure cruise. Survival experts and actual survivors counter that these factors are of far greater importance than most people recognize.

Your most important survival tool is your brain. The ability to make clear, rational decisions is of the utmost importance. The capability of the raft and its equipment to mitigate the deleterious effects of shock, injury, hypothermia, seasickness, dehydration, hunger and cramped, wet, and often cold living conditions will have a significant impact upon your state of mind. This, in turn, affects your ability to make sound survival decisions. One shouldn't underestimate the importance of these factors.

Size Does Matter...

Life-raft capacity is rated based upon a variety of possible factors including floor area, seating space and buoyancy. Rated capacity is the number of survivors the raft is supposed to hold with a minimal amount of space for each survivor and a certain degree of buoyancy. TSO C70a provides for a whopping minimum of 3.6 square feet per person, or using a seating-demonstration method, a minimum of no less than 3 square feet, along with certain other limiting dimensions.

Only one raft we evaluated, from Air Cruisers, didn't meet the 3.6 sq. ft. per person standard. Their 13-person raft provided only 3.36 sq. ft. per person. While they assured us that it did, indeed, meet that standard (guess our tape measure shrunk), Air Cruisers also said that it meets the requirements of the TSO via the alternative compliance methods provided (para. 4.1.1). It may, but it's too small in our opinion.

Some of the rafts provide a bit more room and the configuration and shape can make a difference, but any way you slice it up there isn't much room. "Close" takes on a whole new meaning in a life raft. It is so tight that we recommend that those for whom a few extra pounds and a few inches one way or another in payload will not make a big difference, ought to seriously consider going up one or two sizes if they purchase a well-ballasted raft. For example, if you need a four-person raft, you might want to consider one designed for five or six persons. In a raft without effective ballast, it is better to stick with the rated capacity, maximizing the ballast effect of the survivors.

Worth noting is that marine life rafts use a 4 sq. ft. per person standard and a few aviation rafts actually meet that standard, Winslow's Ultra-Lights for example. They are still crowded.

...Packed Like Sardines...

Besides their rated capacity, aviation rafts also have an overload capacity. Generally this amounts to half again more than the rated capacity; six people, for example, in a typical four-man-rated raft, or nine in a six-person raft. As you might expect, if it is tight at rated capacity, then you will be packed like sardines at overload capacity, as can be seen in the image to the right. It makes for extreme discomfort and short tempers.

Raft manufacturers usually take pains to clearly delineate the difference between the two, i.e.: "4 person capacity, 6 person overload." One exception is Survival Products, which for example list their non-TSO'd rafts in some of their literature and, in fact, printed on the raft and valise itself, as "4 to 6 Person" and "9 to 13 Person." Another exception is RFD's Navigator raft which is rated at "4/6 Persons." These are very misleading, in our opinion. Based on calls made to companies who offer these rafts for sale or rent, we found that most make no distinction about the raft's capacity in the case of the SPI rafts, probably based upon the manufacturer's own misleading presentations. Buyer — or renter — beware.

EAM also sells a line of lower-priced, non-TSO'd rafts, its "EAM" series. Some of these rafts are rated at higher capacities, even though they are sized exactly the same as the TSO'd rafts. For example, the EAM-5 (five-person) is the exact same size as the company's TSO'd four-person raft. EAM explained they do this to compete against "the others," using SPI's rating as an example. Due to overcrowding, we would caution against relying on EAM's inflated capacity ratings for these non-TSO'd rafts, just as with SPI's misleading capacity ratings.

We tested all the rafts at both their rated capacity and all but some of the largest at their overload capacity. Even at the rated capacity they were all uncomfortably crowded. At the overload capacity they were simply unmanageable and other potential problems were also distressingly evident. Freeboard (the distance the raft rides out of the water; in other words, the distance from the surface of the water to the top of the raft's buoyancy tube) is reduced significantly when overloaded. With most single-tube rafts, which have minimal freeboard to begin with, this simply exacerbates the problem. In any but the calmest water, the raft will be underwater, though it may still be providing some degree of buoyancy for survivors.

When you select the capacity raft you want, rely only on its listed rated capacity, never on its overload capacity. If carrying six people, get no less than a six-person raft, not a four-person raft with six-person overload capacity. For SPI's non-TSO'd rafts, the first number they list is the rated capacity.

...Pick A Shape...

When examining the differences between rafts, some are immediately obvious. Aviation rafts come in three basic shapes: round or nearly so (6-, 8-, 10- and 12-sided), square and "boat-shaped" (rectangular with rounded ends).

All other things being equal (they rarely were in any of our raft evaluations), a square or elongated raft may provide more comfortable seating with survivors side-by-side, alternating one way and another, though things can get messy at the ends in some boat-shaped rafts. With a single exception, in all but the most spacious round rafts, everyone's feet generally tangle in the middle when stretched out. This can get uncomfortable and requires some added organization and management to accommodate. (In an RFD raft model that we have not tested, the occupants sit on an inflatable "donut" in the center facing out, with no possibility of stretching out your legs.)

A boat-shaped raft, running with wind and waves, is probably somewhat less like to overturn, end-over-end in this case, than a comparably-sized and -ballasted round raft, all other things being equal (again, they usually are not). Unfortunately, experience tells us that drogues (commonly referred to as a "sea anchor" in many aviation references) are often lost in heavy weather. Lose the drogue on a boat-shaped raft and it is likely to quickly turn broadside and settle in a wave trough, as would a boat without its steering. Unless the ballast compensates, it is then more likely to capsize in conditions that might otherwise not cause a problem. If a round raft loses its drogue, it may carousel and lose some resistance against capsizing, but it generally has no inherently less-stable configuration.

Multi-sided equilateral rafts can have a structural advantage over round or elongated rafts. The short-coupled, reinforced mitered joints can provide significant added rigidity, which was evident when reviewing video of our tests.

...One Tube Or Two?

Another obvious distinction between rafts is whether they have a single tube for floatation or if they use two stacked tubes. The difference in freeboard is significant. In any real weather, the more freeboard you have, the better. With double-tube rafts, larger tubes provide greater freeboard and more reserve buoyancy than smaller ones. Twin tubes also offer a much more supportive backrest, whereas the single-tube rafts were deemed to be much more uncomfortable. Higher sides become much more important in rough seas when it's necessary to brace oneself against the violent motion of the raft.

The biggest downsides of double tubes are generally weight and volume, often an important concern for the light GA operator.

...Redundancy...

Redundancy is another critical concern. We are discussing inflatables that, while pretty darn tough, are still subject to puncture by any number of means. Even in closely-supervised training, rafts are often punctured.

We feel strongly that there must be means to ensure that if there is a puncture, some buoyancy will remain. Whether by having multiple tubes or by dividing up a single-tube raft internally, puncturing one buoyancy chamber should not sink the whole raft.

However, buoyancy doesn't necessarily mean you'll stay dry. In single-tube rafts the tube is divided in half by vertical bulkheads. If one chamber deflates, survivors in that half are going into the water and everyone is going to get wet. You are left with a half circle of tube open to the water across the diameter, like a donut broken in half. Even a partial deflation swamped the raft and presented problems for our volunteers.

The practical advantages of single-tube rafts are weight and space savings. They also generally cost a good deal less, though not just because they are single-tube designs.

...New Fabric Introduced

Late 1995 marked the introduction of polyurethane-coated fabric (PCF) into the U.S. general aviation life-raft market by RFD (it had been available on the marine market for some time before then). BFGoodrich, RFD and Air Cruisers have also opted for this type of fabric for their new rafts. This material offers some potential advantages over traditional neoprene rubber-based fabrics. Most aviators will be familiar with this type of fabric from its use in aviation life vests, where it is the standard these days.

The manufacturers claim extended service life for the newer material, which has the potential of saving consumers money. Other advantages claimed, such as increased abrasion and puncture resistance, would provide an extra margin of protection that is nothing to sneeze at. On the down side, the PCF used in these aviation life rafts is all single-coated, meaning that the poly coating is applied to only one side of the nylon fabric substrate. Marine life rafts using this material use double-coated fabric. The single coating can compromise the raft's integrity under some conditions, in our opinion.

For the year 2000 test, we had developed an apparatus to test puncture and abrasion resistance to see how well the claims held up. We requested fabric samples of those participating. Winslow supplied samples of their neoprene fabric (the same as used by Hoover and non-participants Survival Products and EAM), but both Air Cruisers and BFGoodrich, using lightweight PCF, declined, as did Hoover. Both Air Cruiser's Al Wigert and Leibert Danielson, Director of Engineering at BFGoodrich, expressed similar concerns — namely that consumers would not be able to make value judgments regarding the relative importance of the materials' performance in our tests versus the light weight of their products. Since our tests were to be comparative in nature, not absolute values, we have no meaningful results to report.

Deploying The Raft

As soon as we started unloading and moving the rafts around, the issue of weight was raised by the volunteers. The weight and volume of the raft is affected by its capacity, its design, its accoutrements, and the materials from which it is made. The selection of raft and survival equipment can also make a huge difference in overall weight.

Packaging...

The rafts are tightly packed in valises which are designed to open as the raft inflates. While hard-sided plastic containers are used in some corporate and commercial installations, the soft-sided (something of a misnomer as they are packed nearly as hard as rocks) valise is the most common in general aviation and this packaging formed the majority of what we tested. Hard packs should be designed to drop clear from their mooring/inflation line after the raft inflates so that they don't pose a hazard to either raft or survivors. The ones we tested from BFGoodrich and Winslow did so.

In the valise configuration, the raft is secured inside the tough fabric valise with metal snaps, Velcro or with lacings. During our tests and on many other occasions, users often began by peeling open the valise instead of uncovering the inflation release handle or line. In most instances this is the result of either poor inflation instructions or basic design deficiencies that don't make it easy to find the mooring/inflation line. Being unfamiliar with exactly how each raft would be deployed, our "life raft virgins" often had some difficulties. These were caused either by misunderstood directions printed on the raft or by difficulties in performing the inflation procedure itself. If you own or rent a raft, review the deployment instructions ahead of time, when you can concentrate on them without distraction.

...Mooring Lines And Inflation Handles...

The mooring/inflation lines varied in length from a much-too-short six feet (RFD Navigator) to a reasonable 32 feet (BFGoodrich and Winslow). The FAA's technical standard order (TSO) calls for "at least 20 feet" and we think 30 to 40 feet is a practical length. The idea behind the mooring/inflation line is to prevent the raft from being blown away, out of reach. Yet, it also has to be allowed to extend far enough away to not be imperiled by the aircraft as it goes under. The mooring/inflation line should lead directly to the primary boarding station (BFGoodrich and Winslow), but manufacturers doesn't always do it that way (Air Cruisers).

Thin and unsubstantial mooring/inflation lines, such as BFGoodrich's parachute cord, may be difficult to hold onto or follow to the raft in some circumstances and we prefer thicker lines such as used by Air Cruisers and Winslow. A snap clip at the end of the line makes it far easier to attach to the aircraft.

While the TSO doesn't specifically call for an immediate inflation handle allowing you to inflate the raft with one quick pull, we think it's an excellent idea and most raft manufacturers have interpreted the TSO in this manner (Air Cruisers being a notable exception). The TSO requires a "parachute ripcord grip" for inflation. Apparently there is wide interpretation of this section of the TSO by all concerned. Our interpretation of the spirit of this specification is that such a grip should be large enough to be easily grasped with the entire hand, facilitating a rapid inflation. Air Cruisers is the only one with such a grip; the rest vary from just acceptable (Winslow) to poor (BFGoodrich) to non-existent (Survival Products).

...Righting Wrongs

While only two rafts inflated upside down, it's always a possibility. With no wind or heavy seas to deal with, righting (turning the inverted raft right-side up) was relatively easy for most, but it was obvious that under real-world conditions some would be much more difficult than others due to inadequate righting aids. The larger BFGoodrich was a handful even in our tame circumstances. More critically perhaps, righting instructions were often woefully deficient; volunteers ignorant of the proper technique weren't helped much. At night, for most of the rafts, forget it. The Winslows, with excellent righting aids and their exclusive "righting locator light," were roundly applauded.

All Aboard!

If the raft is going to help you survive, you have to get into it. While you may be able to jump into the raft from the wing, most likely you'll have to board it from the water. There, the effectiveness of the boarding aids is absolutely critical. Some rafts with minimal aids and little more than a few loops of line for assist — EAM, Hoover and Survival Products for example — were extremely difficult for some volunteers to board without assistance, which may not be available. Some rafts, such as Hoover's FR6, Survival Products double-tube TSO'd raft, and Air Cruisers 13-person model were impossible for some volunteers to board unassisted.

Without considerable upper-body strength, you're in trouble with many rafts. Short volunteers and bottom-heavy women especially had difficulties. A few rafts made it relatively easy, including Winslow with its ample outside and inside ladders, stirrups, and grab handles and BFGoodrich with its inflatable "porch."

Staying Sunnyside Up...

The raft's stability is critical. Survival accounts are filled with tales of rafts capsizing again and again, usually losing precious supplies and equipment in the process. Lives which should have been saved have been lost due to capsizing.

Stability is a function of the raft's center of gravity, ballast, shape and its sea anchor. All contribute to keeping the raft upright in heavy weather.

The sea anchor and ballast are the two principle devices to help prevent the raft from capsizing. Ballast can also make initial boarding easier, the Hoover's lack thereof being a case in point as it often tipped over on top of testers trying to board. Finally, ballast is even more critical when the raft is not filled to capacity, if there are fewer persons aboard than the rated capacity or if only one or two survive in a four- or six-person raft. Ballast is also critical in windy conditions: A raft bottom even slightly raised off the water can be easily caught by wind that can capsize the raft in an instant. From a practical standpoint, ballast in a raft is limited to the people and equipment in and on the raft plus some means of retaining water below the raft to counteract the tendency to capsize as it lifts out of the water.

Ballast effectiveness is determined by the capacity of the water-retention devices, their configuration, and their placement. These range from none (Survival Products, Winslow's basic rafts, and EAM) to inadequate (Hoover) to modest (BFGoodrich) to excellent (Winslow).

...What A Drag...

The drogue is an integral part of the life raft's stability and seaworthiness equation. Ultimately, it may be even more critical to raft stability than ballast, though that controversy continues. In any case, a drogue is a drag-inducing device which is trailed behind the raft. When properly designed and deployed, it "anchors" the trailing side of the raft to the water, helping to prevent it from overturning. Good design requires that it be able to create sufficient resistance to the water (drag) and that the anchor line is long enough to give it the lever arm needed to be effective. To function properly as a stabilizer, slow drift and to help counter capsizing action, it must be strong enough to not be torn off in heavy seas, provide sufficient drag to be effective, offer adequate line length and at least a single swivel to cope with heavy seas. Also, it must not tangle and must not collapse when subjected to repeating wave action. Two styles are common, the conical and the "parachute" or "hemispherical" style. Both have their pros and cons, but if properly designed, both can do the job in our opinion.

In our tests, Winslow's hemispherical drogue was tops in drag, followed closely by Air Cruiser's conical. The remainder, where they existed, were much less effective. Only Winslow uses swivels on the sea anchor. These are essential to eliminate twisting of the rode, which is believed to be the primary cause of failures in actual use. Given the importance of the drogue in providing stability, we consider a swivel critical.

While some manufacturers require the survivor to deploy the drogue, being concerned about it becoming tangled in the aircraft, we prefer self-deploying drogues, one less thing for the survivor to worry about. As we have not heard of any instances where the drogue became hung-up on an aircraft, we don't feel this is a significant issue. The drogue line should be flaked so that it deploys without tangling itself.

...Shelter...

A weather-tight canopy is essential in adverse weather conditions. A canopy that leaks is not nearly as comfortable nor effective as one that really keeps the weather out. It must also support itself under adverse weather conditions; a collapsing canopy isn't much fun either.

The most basic rafts don't include a canopy and are thus unsuitable for colder climates or poor weather. Next up the food chain are manually-erected canopies. For the most part (EAM and Hoover), these entail installing multiple rods around the raft and then fitting the fabric canopy onto the rods and around the tube. This is difficult and time-consuming in the best of circumstances and, in our experience, invariably done incorrectly without training.

Survival Products requires oral inflation of a central support tube and then attachment of the canopy to the edges of the raft. Easier, though the result is less comfortable and not very effective, particularly when it collapses under heavy weather conditions. Other variants exist, but these, too, we find unacceptable for any but the most moderate circumstances.

Self-erecting canopies are at the top of the ladder and should be considered mandatory for rafts used in any but moderate conditions. These canopies use inflatable arches to erect the canopy when the raft deploys, thus shelter is immediately available to the survivors without much effort other than closing up the canopy.

However, multiple-arch canopies (Winlow TSO'd and BFGoodrich) are far better than single-arch styles. In addition, materials vary and we prefer heavier-weight, opaque-canopy material with substantial zippers. Both lighter-weight material and lightweight zippers failed in our tests. Entries with Velcro, hand-tied or snap closures proved ineffective at keeping our simulated rain out of the raft. All the closure systems are a compromise, but overall we prefer ease of use that doesn't require much manual manipulation. Driving our point of view is the realization that digital dexterity is one of the first things lost as a result of exposure.

Winslow offers their unique clear plastic "viewports" as standard equipment in some canopies; it's optional on others. These were widely lauded, both for contributing to a psychologically more comforting environment and as a potential antidote to seasickness, a serious concern for survivors.

...Insulated Floors...

An insulated floor can be a vital asset, and is a critical design feature for rafts that might be used in colder waters. It does a fair job of insulating the occupants from the colder water temperatures and combats deadly hypothermia. Even in warmer waters it can make a difference. Our volunteers noticed the difference in comfort, even with the warm water in which they were floating. Inflatable floors (Winslow and BFGoodrich), all of which must be inflated manually with a hand pump, also provide an additional floatation chamber, adding another measure of redundancy. When inflated, the floor serves to isolate the survivors from the bumping of the underside of the raft by fish and other "things" in the sea, something most survivors have reported as being very uncomfortable. Foam-insulated floors are also used (Air Cruisers), though in our experience they don't perform as well as the best inflatable floors. Their biggest advantage is that they don't have to be inflated; the survivor need not do anything to receive the insulating benefits.

...Equipment

The selection of raft and its included survival equipment ranged from virtually nothing, utterly deficient, to reasonably well-equipped. Often the quality of the equipment included was also questionable. It's important to go beyond the list of equipment provided and determine exactly what equipment is used. Some equipment is much more effective than others.

At a minimum, we recommend that your raft equipment include an effective bailer, sponge, manually-operated air pump and at least two raft repair clamps. The ineffective plugs used by RFD are not an acceptable substitute for clamps. Basic signaling equipment such as a good signal mirror, sea dye and flares can mean the difference between being found and not. A good flashlight will be extremely useful at night. Water is essential, despite its weight. An excellent alternative for those flying over the ocean, though we don't consider it a complete substitute for packaged water, is a PUR Survivor 06 manually-operated reverse osmosis pump (watermaker) that can produce fresh water from salt water. Chemical desalter packs are far less appealing and have limited capacity.

Generally speaking, you'd best plan on supplementing the raft's equipment with your own. The less expensive the raft, the more equipment you'll need to provide yourself.

Conclusion

This second installment of AVweb's four-part series on life rafts took a close look at the various features and equipment available from each manufacturer. Part One laid the regulatory and features-related groundwork involving aviation life rafts.

In Part Three of this series, we'll review single-tube life rafts and then dive in for some in-depth examinations of single- and double-tube rafts. We'll wind up Part Four with some specific product- and manufacturer-related conclusions. By then, you'll know exactly what to look for in an aviation life raft and, hopefully, won't get that sinking feeling if you ever have to use one.