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A funny: http://militaryhumor.net/appearances/#

And, some very thorough and comprehensive insights from a retired USCG pilot:

"From 1970 to 1976 most of my life evolved around Sikorsky HH-52As in the USCG doing SAR in southeast Alaska and southern California....about 1500 hours crew and left seat, and lots of maintenance.

https://en.wikipedia.org/wiki/Sikorsky_HH-52_Seaguard

They stay upright on the water very well, especially when the head is powered because we have full control - a little collective can help. When the head is not powered they can stay upright provided the water is calm. Had experience with that. In the event of engine failure (or someone totally blowing an autorotation to the water), auxiliary flotation in the sponsons provide additional stability, however given enough sea state, they will turn turtle - typically about 16 degrees = tip over.

They float because the hull is fairly water tight. There's few penetrations on the wet side (bottom), and the penetrations on the dry side - such as cockpit controls - are "booted" to minimize foreign object intrusions. The cockpit/cabin deck (floor) sealed the dry side. The 52 hull usually had good water integrity,...and was known to float for days - usually upside down. It's bigger and younger sibling - the H-3, in all it variants - generally didn't float too long after unintentional water contact.

We usually put at least one of our helos the sea every day - so very aggressive and well practiced corrosion control practices are necessary. Generally included fresh water wash and engine wash after the last scheduled flight of the day. In our case (unscheduled SAR flights), that often meant full washes after every flight. Hulls were drained and flushed frequently, and scheduled inspections included lots of corrosion control practices. When ship board deployed, either on coastal ships or ice breakers at North or South poles, we had limited fresh water, so engine washes were done but the rest of the bird got only hand-brush washing.

Landings and takeoffs on water are similar, but not the same as on land. Landing on the water surface could be challenging, because we're not accustomed to the land "moving" under us, like water can. At night in glass-smooth very clear water, landing could also be tricky because our depth perception was challenged . Lift off from water took more power than land, all other things being equal, and there's no running take offs in water. Yes, tail rotor "ground" clearance is reduced on the water, so that was always on our minds on the surface (keep an eye on the waves). At the time, we believed 3 foot sea state to be max tolerable - but had to keep the bow to the sea..

The US Coast Guard used amphibs for many years because at the time it was the best way of rescuing people - directly from the water. When survivors were unable to climb into a rescue basket lowered from the helo, the helo could land and water taxi to the people to help them in the helo. As mentioned above, water landings were limited by the sea state, and consequently we lost people because we could not assist them. That lesson wasn't lost on the Coast Guard, which fully implement the "Swimmer Program", which we see today.

I don't know of any regular boat-hull operators today. Their advantage of water landing has been eclipsed by more powerful and capable machines which can easily accommodate the additional crew weight for a swimmer. In my time - except for night ops which required 2 sets of eyes on the front and one out back, many of our ops saw only 2 of us in the helo - the Aircraft Commander (PiC) in the right seat, and then the left seat crew. We'd fly to the scene, then the left seater would go out back to hoist or pick up people. "

So it would seem that while some helicopters were designed to be amphibious and it was intended to land them on water, those are older designs and not much used anymore. More powerful, modern helicopters have obviated the need for landing on water. But, in special circumstances (like the CH-47 video), they can still do it.

I hope this helps satisfy your curiosity a little bit, rlmorel! I like helicopters a lot, but the people who operate them, and design them, and figure out what to do with them -- that's what really interests me. I am always happy to learn more, and I am happy to share, so if you ever want to know anything else about helicopters, let me know and I will put the word out!