Hydration packs: PFD vs on-boat

As a sufferer of "too much kit" syndrom I am trying to declutter things.
For hydration I usually use a backpack style pack that I keep on the rear deck. This adds to carrying and the on-shore steps. I am thinking that if my PFD had a pocket at the back It'd help.
No water bottle space in soon-to-be-mine Evo, so that's not an option, besides I'd prefer a pack anyways.
Any serious drawbacks to carrying a bladder on the back of the PFD? I typically use less than a litter at a time. Added fatique, imbalance, etc? 

Coming from a sea kayak background, I always had my Camelback strapped to the deck in front of my cockpit. When switching to the surfski, hydration is a little different. You might want to keep the center of gravity lower. I usually put just the Camelback bladder in front of the foot pedals and run the tube under the pedal to the cockpit. Its a little short, and I'll need a tube extension at some point. If you put the bladder or hydration pack on the back deck it might slosh around or roll off in big waves. For flatware racing it would probably be OK. Having it in your PFD might throw off your balance or it could come out if you get dumped. Give it a try and see what works best for you.

Mocke PFD's (and probably some others - Vaikobi maybe?)  have a pocket in the back specifically for a cambebak bladder, so the Mocke's endorse carrying it on your back

I'd say its probably personal preference whether its carried in the foot well, on your back, or on the back deck.

It works ok-ish with a pack on the rear deck of a V7 and an extra-long tube. It's a whole backpack that secures well. At times I have difficulty with water flow when it gets low. I have the tube attached with a clip to my pfd and it is a little annoying during remount work, I need to pull it off while in water (comes off easy) and when back in I need to remember to attach it. Often I forget and and up dragging the tube behind me. Not to mention that it's a whole extra piece of luggage which is the main irritant at this point.
The whole thing has served the purpose so far but feels cumbersome and I want to improve on it.
I want to try a Mocke or Vaikobi pfd with a pocket. On the Vaikobi it seems to go low enough so maybe it will be good enough with a moderately small bladder. Mocke is similar, I just prefer pfds with the front zipper and side-access pockets.

I use a Mocke PFD regularly, it's the best. The main reason: hydration bladder in the back. Can't go wrong with this.

On the back in PFD pocket for me.
Less to get tangled in in case of swim/remount!

Having hydration in your PFD does not affect your balance as much as having it on the deck of your boat, because it becomes part of your body weight and does not move with the boat.

That's what I was thinking too. It's a vertical weight centered on your back, in theory does not seem like a significant factor...But what do I know.

If the mass of the liquid is 1-3kg and is mounted at the torso (therefore raising the centre of gravity), that you'll get a sloshing effect as the bladder empties and considering that the main axis of roll of the boat is through the centreline of the boat, it is less stable if you mount this to the PFD then the deck or footwell of the ski.

Well, if you are sitting completely stiff in your ski, or leaning back and resting on it like some people do in a sea kayak, then your body and your boat will move together, and the effect on stability depends only of the height above the center of rotation.
However, most paddlers are sitting upright in the seat at all time (as long as possible, at least), and it's only the boat that rotates. We all know how much stability depends on the height of the seat. This is not because your center of gravity is raised by a few centimeters,  it is because the weight of the upper body is transfered to surface of the seat, so if the seat is at the water level, a hydration pack in your PFD will not affect your balance at all.
On the other hand, hydration placed in your boat will move with the rotation of the boat, and because it is fluent, it will even move to the lowest end of the hydration pack when possible, which is why water in the boat is bad for your balance no matter at what height it is "stored". It will always flow to the side where it contributes to decrease stability.

Henning DK wrote: On the other hand, hydration placed in your boat will move with the rotation of the boat, and because it is fluent, it will even move to the lowest end of the hydration pack when possible, which is why water in the boat is bad for your balance no matter at what height it is "stored". It will always flow to the side where it contributes to decrease stability.

....except that if tis the boat that moves and not the paddler, adding the mass at boat level will change the inertia of the boat (for the better) thereby slowing the rate of roll ? 

Yes, I couldn't agree more with this statement.  I have placed weight in the middle of my ski (Swordfish S) in the form of a small sandbag under my knees in the early days in rough open water.  It definitely helps to improve balance in that it provides the paddler with more time to react to 'roll' forces acting on the boat.  I must admit that I haven't experimented with a hydration bladder in the same respect, but I suspect that the movement of the water in the bladder would not contribute to instability.

I know it's not the same thing, but I've worn a 3liter Camelbak on my back while mountain biking for the past 20 years. Never thrown off my balance even a little. I've worn it paddling my SUP without issue either. I guess I've gotten lazy with my ski and just tossed it under the bungee in front of the pedals. I haven't had any balance issues, but I don't like the position of the drinking tube when used that way. 

More than balance I find the extra weight of the water pack on my back a bother. I have the Mocke PFD with a small VHF and cell in the front pocket and then the bladder in the back. If I'm in 2mm neoprene then it doesn't make much of a difference but when I take that off in the spring it feels like freedom. More freedom again by removing the bladder and VHF (on calm days with other folks around). Somehow the whole rotation and paddling becomes easier. I'm sure I still need to apply the same amount of force to the paddle, it just feels better. Result: hydration pack is now in front of the footrest. I use a weak clip to attach the tube to the front of the PFD, it slides off when I fall in, it's easy to reclip with one hand without looking. I want to experiment with using a stainless water bottle with an internal straw and attached tube to replace the plastic bag (not a fan of mixing food and plastic). I hope I can make that work and that for sure won't go on my back...

Well, there are different opinions on the effect on balance, I see. That's fine, try it yourself. I've had it in front of my feet as well, and that was nice. I just don't think that balance is an issue when having it in your PFD, either. Having it on the deck is worse, I'm sure.
Re. the weight on your shoulders, I agree that the Mocke PFD is not so comfortable with hydration loaded, but with other PFD's it is less of a problem, e.g. the Vaikobi.
And when it comes to rotation, I actually think a tight fitting PFD like my Vaikobi enforces good rotation, because you are helped to use the lower part of your body, below the PFD

My preference, for what it is worth, is PFD rear pouch for water bladder. Otherwise, too much clutter to deal with in serious more extreme downwind conditions. I put VHF and bladder in rear pouch. Other soft stuff in front pouch. remounting much easier.
As for "Too much kit syndrome" those were the days. Warm summertime paddles in speedos and visor hat. Oh to be young again! Good way to keep people at a distance now though.

Yeah, I am growing to hate the clutter. Alas, my gear budget is running out and it's now between a new paddle and a pfd with a back pocket. So far the paddle is winning.

Back in a day we used to paddle out into the open on inflatable mattresses with nothing more than speedos and sunburn  

So as far as a PFD with front/rear pockets go, the only one I know of is the Mocke(r) PFD. Nice jacket if it fits you properly. My problem was I am too short for the XL version. Rubbed me on chin. L version doesn't fit around my chest. I bought a neoprene wake board vest. Cut up some old wetsuits and had the local shoe repair dude sew the pouches onto the vest. Works great in cooler climes. The one in the center of pic.

I have similar reservations about Mocke. It looks pretty large area-wise. I am usually L in the chest circumference but short. For pfds and suits store stuff usually pegs me as M just to find out I can't fit it around my chest.
Been thinking about modding my pfd as well. It's a cheapie but works pretty well.

I moved from a Stohlquist to a Mocke PFD however I do not hydrate on the move so paddle with a 500ml bottle in the boat instead. This is adequate for me for a 2 hour paddle.

I find the Mocke PFD allows freedom movement to the extent that I don't even know that I'm wearing it. The mesh design also makes it much cooler than other vests in warm weather.