The primary design and certification goal of installing an Emergency Floatation system is to allow the safe egress of the occupants.
Salvaging the aircraft is a bonus (or maybe not, depending on your point of view!), if it occurs. The majority of aircraft that survive the initial ditching and remain afloat, always seemed to be generally sunk or severely damaged in the salvage attempt.
I do recall a few succesful float-jobs off the top of my head. Quite a few 212's over the years (Worldwide), an S61 that was towed back to Aberdeen undamaged, (another one that spent a few days in the water and was rebuilt by Sikorsky, yet another that sank and was at the bottom of the Amazon for a couple of weeks, and was rebuilt). A B214ST off Peterhead that was relatively undamaged, BV234 that ditched and then sank(?), and I know there are more. Check out Bill Kellogg's experience at;
http://www.justhelicopters.com/picture_gallery.htm
Federal Aviation Regulations.
Part 29. Airworthiness Standards:
Transport Category Rotorcraft
Sec. 29.801 Ditching.
(a) If certification with ditching provisions is requested, the rotorcraft must meet the requirements of this section and Secs.29.807(d), 29.1411 and 29.1415.
(b) Each practicable design measure, compatible with the general characteristics of the rotorcraft, must be taken to minimize the probability that in an emergency landing on water, the behavior of the rotorcraft would cause immediate injury to the occupants or would make it impossible for them to escape.
(c) The probable behavior of the rotorcraft in a water landing must be investigated by model tests or by comparison with rotorcraft of similar configuration for which the ditching characteristics are known. Scoops, flaps, projections, and any other factors likely to affect the hydrodynamic characteristics of the rotorcraft must be considered.
(d) It must be shown that, under reasonably probable water conditions, the flotation time and trim of the rotorcraft will allow the occupants to leave the rotorcraft and enter the liferafts required by Sec. 29.1415. If compliance with this provision is shown by buoyancy and trim computations, appropriate allowances must be made for probable structural damage and leakage. If the rotorcraft has fuel tanks (with fuel jettisoning provisions) that can reasonably be expected to withstand a ditching without leakage, the jettisonable volume of fuel may be considered as buoyancy volume.
(e) Unless the effects of the collapse of external doors and windows are accounted for in the investigation of the probable behavior of the rotorcraft in a water landing (as prescribed in paragraphs (c) and (d) of this section), the external doors and
windows must be designed to withstand the probable maximum local pressures.
[ 09 November 2001: Message edited by: Cyclic Hotline ]