I have an 01 Polaris 800 XC SP with a 1 1/2 track, no studs, and can start right from the water's edge. The water gives you lots of traction and it's easy to lift the skis. Turning is tricky. You can either leave the machine sit flat and turn the skis like you would in the snow and it will slowly respond, or you turn the bars the wrong way so your inside ski tip won't dig in the water, and lean. You turn much quicker but it's tricky balancing and you loose momentum and traction as the track comes out of the water. The main cause of sinking is the belt getting wet. When it does, you're done, it completely looses grip and you slow to a stop. Do whatever you can to keep the belt dry. I used some silicone and old inner tubes to seal up as many holes as I could. I also installed a small bilge pump under my driven clutch to pump out any water that may get in. Once it's sealed up, any water that gets in stays in.
Be prepared to sink. Wear a PFD. I run over water that is 40 feet deep, so I have a small bouy tied to my sled with 50 feet of rope in a bag. If it sinks I don't have to dive to the bottom to find it. Carry a knife. Last summer a fella got tangled in his rope and got dragged down with the sled. He was running across 2 up and his passenger managed to free him and get him back to shore but he was in bad shape. If you're sinking, shut off the engine before you go under. A lot of guys pin the throttle in a desperate last attempt, it doesn't work and you could suck in water and hydralic lock your engine. Sinking happens nice and slow. Take your time, shut off the engine and gracefully bail off the sled and start doing the dog paddle.
Here's a link to a short vid clip from last summer. Beware of Davy Jone's locker.
Wet Sled Learning Curve
On a bike you need a bit more speed.
Wow, I guess you can't post pics here. You can copy and paste the links (even in a word document) if you want to check them out.