I'm surprised one of the canadian mil pilots hasn't come forward with this topic, they are the waterborne experts during their training.
Anyway, I'm sure I mentioned it somewhere yonks ago, it may even be in this thread, but can't be bothered to read thru it, so here goes:
I was a waterbird instructor for my sins during my exchange with the RCAF. It was our job to throw S61's at the water from all angles and even try to fly away after!
Bearing in mid that the S61 has a 'boat hull', if anything is going to remain stable on the water, this is the a/c to be in. I would suggest that anything else is less stable and will suffer the following consequences, more readily:
It is assumed that there is going to be no attempt to take off again!
1. Integrity of airframe affected depending on design. This means that water will flood the a/c faster or slower, depending on how well the a/c has been put together! Large quantities of water sloshing around the insides of the a/c will exacerbate uncontrolled instability, eventually leading to a top heavy a/c 'tipping' over.
2. If the rotors are still turning (quickly), they will strike the swell in anything >SS3. This could result in tipping the cab over or serious structural damage (not a problem if you intend to scrap the airframe after).
3. Water ingress will very very quickly affect the electrics. The most obvious problem being unable to communicate with the passengers/crew. This is by far the most serious issue especially when/if the cab turns over!
4. If the flot bags don't deploy evenly, the cab will sit skewed off to the swell / sit at an awkward angle and further exacerbate the eventual overturn.
5. If the drogue shute isnt deployed, the a/c will sit side onto the swell and within minutes, she will turn over in anything >SS4/5.
6. The worst I've heard of is SS6 and the a/c remained upright and pointing in the right direction for long enough to be recovered. The swell though was a long one and not too choppy.
The worst thing is thinking about all those people down the back while you are doing everything in your power to keep the ***er from tipping over! If she goes....God help the pax! At least you've got jettisonable doors and STASS and HUET training and correct gear and radio and ELT and and and.....
Don't go there.