I hear the logic and understand the physiology, but that really has to be balanced against the extra time, and complexity of lifting someone horizontally--which is virtually impossible with the number of crew and equipment normally available on cruising sailboats. The number of victims who are in that narrow band where they will experience a dramatically better outcome ONLY because they were lifted horizontally, is really small.
If this is really the RYA's standard recommendation for routine MOB recovery, in my opinion, it is unrealistic and impractical--no matter how valid its theoretical benefits. I'd expect better, and more practical, advice from them.
Think about this. It is way more complex than just lifting someone with two lines... if you attach one at the chest, where to you attach the other? How many people does this take to rig and execute?
In any man-overboard situation, rapid recovery will trump perfect technique--every time.
Any halyard on an Amel is capable of lifting someone out of the water, and any of the winches, manual or electric, will give enough power to lift someone two or three meters.
I have had the valuable experience of participating in an organized evaluation of man-overboard recovery techniques as the "volunteer" in the water who had to be lifted into the boat by a variety of techniques. It is not easy with a short handed crew and a victim who might not be able to offer much assistance themselves.
If there is only one person left on board, I would not recommend using the mizzen boom as a lifting crane unless the victim is alert and fully functional. The danger is if the boat is rolling at all, a person hanging off the end of the boom will swing wildly from side to side, unless they can hold on to something, or someone is on deck can restrain the boom's swing. Maybe you could rig something up, but that would just take more time.The person at the winch in the cockpit is also out of visual and easy auditory contact with the victim.
It really is an easy ride up out of the water on any mast top halyard in a lifesling, or even just in a bowline. Just remember, have the victim face in toward the boat so the lifting halyard is between their head and the hull. This was an important lesson learned, if the victim is face out, the back of his head bangs against the hull as he is lifted. Unless someone is there at the rail to hold them, do not lift them all the way over the liferails with the halyard, even in calm conditions they will pendulum around wildly.
SOOO much depends on the conditions, the strength and number of remaining crew, and especially the condition of the victim. Are they conscious? Hypothermic? Wearing a lifejacket? A harness? Are they panicked?
We found a lifesling to be a valuable tool to lift someone. It was easy to get into, even for a victim with restricted mobility, and was simple for the crew onboard to reach and attach to.
If there are two crew left aboard, it might be best to use a mizzen halyard to lift/slide a marginally conscious person up the slope of the reverse transom, if the boat is not pitching too badly.
If there is one person left onboard, and the victim in the water is incapable of helping in any meaningful way, there are no sure-fire solutions in rough conditions. It is a situation I hope I never have to deal with.
Finally... most inflatable lifevests have a serious design flaw. When inflated it is impossible for the rescue crew or the victim to attach a line to the lifting harness because the attachment point is buried and inaccessible below the inflated bladders. With many of them, there is no provision AT ALL for snagging the person in the water with a boathook to hold them alongside.
Moraine Cay, Abacos, Bahamas