So much of it depends on what type of PFD you use. The old Mae West design would not ever let you get onto your stomach. The jacket type all have different centers of flotation, and inflatables are a whole other animal.
The only way to know for sure is to wear one in the water. It is also the only way you can be sure of the fit. It needs to be tight enough that you can’t wiggle out of it, but loose enough not to be a hindrance.
I tested this a bit this summer. These are my swim speeds wearing a fairly standard Stohlquist PFD, measured over a 188 foot distance (it was from a buoy to shore).
on stomach 1.42 mph
on back 0.71 mph
on stomach using paddle for propulsion 1.42
on back using a paddle stroke 0.94
I was surprised the paddle didn’t improve my speed (only nominally for paddling on back) but still very useful be able to do this if you are swimming to your boat and want to get there with your paddle. Of course, your mileage may vary as they say. I seem to recall having an easier time maintaining a straight course on my stomach (where I could see what I was swimming to). Needless to say, you can exert yourself to a greater or lesser degree with any stroke by adjusting your effort (and consequently speed).
When you were on your back, was it feet or head first? When I tried it on my back using a paddle, I found it worked best to go feet first since it’s a more natural paddle stroke.
Head first, like I was doing a back stroke. I was actually doing sort of a reverse kayak stroke. I’ll have to try the feet first method. Hadn’t occurred to me at all since it’s not a natural swim stroke but I can see how it might work with a paddle.
In white water, with obstacles to negotiate, as is the usual case, you must head downstream feet first on your back. This is the safest way to go and is called the defensive way to negotiate fast current. You can either do an underwater elementary backstroke, or do the same stroke with your hands recovering above the surface. It is very effective in controlling your direction so that you avoid obstacles and move toward your desired target direction, toward rescue subject or to safety. I don’t know how you would do that while trying to hold a paddle. That is what I learned during the swiftwater rescue technician training course I took last summer.
Finally…the best way to swim with a pfd is in water.
It sounds like in whitewater, swimming is about slowing yourself down and steering, as opposed to calm water, where swimming is intended to get you somewhere. These are fundamentally different activities, obviously, so effective swimming will no doubt be different in those two regimes.
With SeaDart and a couple of others above, if you actually need to get somewhere and see what is going on I do a sidestroke. W or w/o PFD. It was my earliest stroke when I learned to swim because I could never stand having my eyes open under water, at least w/o goggles, so using the side stroke avoided bonking my head on the side of the pool. Found it also worked in waves to get me into a setup for minor body surfing on the Jersey shore.
If I need to swim in a PFD in calmer water I drop onto my back as I can to save energy, like if I have to fuss with something on the deck or a paddle while getting ready to execute a self-rescue of some kind.
Updated - I just read what pblanc said and I had forgotten about stuff like strainers in moving water. Aspect of my WW stuff being mostly class 2 simple stuff. So I just updated this part.
It is quite possible to keep your feet up swimming side stroke in current. And if you are approaching a strainer in current, never, ever stay on your back. You must turn onto your stomach, and as you reach the strainer, use your arms to vault onto the top of it. If you contact a strainer feet first, your feet will almost certainly go under it, along with the rest of you, and it will be curtains.
Vaulting over strainers is something that is practiced in swift water rescue training.
You are correct and I was thinking too much in the frame of the uncomplicated WW I have done. Just fixed what I said above.
We did practice vaulting over strainers during my recent swift water rescue training. After drifting down in backstroking defensive mode, we had to flip over to approach the strainer head first. Avoid if possible, but if not, use arms to vault over the top before legs wrap underneath in the current.
When approaching an eddy to cross over and exit a fast current, swim hard with the heads up aggressive crawl, ferrying your body across the current, then at the eddy edge it was very effective to flip to the side and roll into quieter water with sidestroke.
Yes, eddying out when swimming usually requires driving your body across the eddy line at an angle with some momentum, just like it does when paddling a canoe or a kayak. Sometimes as you reach the eddy line it is easier to enter it with a series of 360 degree barrel rolls towards the eddy. And if you find yourself going over a sizable drop because you missed that eddy, “ball up” (pull your legs up and wrap your arms around them) as you go over. A few years ago a skilled white water paddler drowned as a result of an arm entrapment swimming over a drop of approximately 5 feet.
Point being, there is no one correct way to swim in white water. The defensive “float on your back with nose and toes up” and maybe maneuver laterally a little by executing in effect back ferries, by back stroking with your hands, is OK for limited rapids with no real life-threatening hazards downstream. It is also easily taught to newbies on a raft trip where the goal is to simply keep them from sustaining a foot entrapment while waiting for someone to haul them back in the raft.
But if you are in sustained white water where you must locate an eddy well downstream and pierce an eddy line to enter it, or when the current is taking you directly towards a potentially lethal entrapment, a much more aggressive style is required.
A good variety of swimming skills is important to have in your swim rescue toolbox. Before I could attend the state sponsored swift water/flood rescue technician course, I had to demonstrate four designated strokes (side, back, breast, crawl) over a 250 meter course. Not all prospective students made it, and they were eliminated from the program before even starting. You have to know, almost automatically when to use what, as the situation arises. I liken it to canoe paddling, where you don’t think about what stroke you need next, you just do what is required by feel and muscle memory. It all takes practice, but unfortunately that kind of effective practice is hard to do easily or safely in WW conditions.