Throwing Methods
There are three basic ways to toss a throw rope. It is a good idea to practice all three since different conditions call for different techniques. For full size ropes - 75' and 3/8" diameter ropes, the underhand toss often gives you the most distance. Make certain your footing is very sturdy and you can drop into a strong bracing position quickly. Establish a belay stance when tossing a throw rope so you can quickly release the rope at the first sign of trouble. Here is a nice video demonstration by Tom Westwater: Throw Rope Demonstration.
The overhand throw is quite useful when tossing small throw ropes. The technique is just like throwing a baseball. This method is often very accurate at shorter distances but is pretty unweildy with large bags. The sidearm pitch is another variation. A sidearm toss is often used to avoid branches hanging overhead.
Now it is time for targeting. In moving water, aim a couple of feet in front of the swimmer's head (just like skeet shooting). Yell or blow a single whistle blast to get their attention. Bulls-eye is anywhere they can reach the rope, about an arm's length in front, behind, or right on top of them. Once they grab the rope, be prepared for the sudden tug. This is where you need to be carefully braced for impact. Now you can carefully swing them into shore or let go quickly if they are tangled in the line (shouldn't happen if they follow they correct technique).
Metering the Throw
Another factor is how much rope to throw out. Avoid the mega-shot - one that passes over the swimmer by a long distance. That dangling line can easily get snagged in rocks below and mess up a perfectly good rescue toss. Too short is bad news as well since many swimmers will try to grab the end of the line - the throw bag. Overshooting their chest by roughly 5' is just about perfect.
If you miss quickly gather the rope at your feet, don't bother re-stuffing. Consider dipping the bag in water to give it some weight or coil 3 - 4 loops to give it some weight. Step on the end of the rope and quickly toss again. The rope should fly freely over the swimmer and you will need to quickly set your bracing position once again.
Like a chess master, think a few moves ahead. If you have properly reached the swimmer, where am I going to swing them? Ideally, you want to swing them into a nice safe eddy. Check out the planned arc of the swing. Are there any holes, sticks, or jagged rocks that will interfere? Do your best to avoid these hazards. Is the boater hanging on to their boat? If so, expect a really strong and sudden tug. It doesn't hurt to have an extra person press down on your shoulders to keep you from falling in.
