Jumping or sweating a line is a technique of using your body as a fulcrum to add tension to the line and take it up with a cleat or bollard. It’s an excellent skill you’ll use frequently, once mastered and one that takes some practice.
Jump a line by grabbing (ideally about a ten foot section) it before a cleat or winch and have someone else or once you learn this trick, yourself, tail or take up the slack. At all times while jumping, the line must be strenuously tailed. This prevents the line from just being plucked like a violin string without going anywhere. Tailing keeps the line from going back out and at the end of the jump, pulls in the line gained. At no point is the line slack in this process. Here’s how to jump a line:
(1) Wrap the line with an acute angle, around the far end of a cleat or with one full wrap around a winch. Grab the tail at a comfortable place that will allow you to pull strongly throughout this procedure.
(2) Reach up or out to 45° and grab the line there.
Tailing hand is close to cleat and pulling hand is farther out, at start of the jump.
(3) Lean back, until your arm is fairly close to perpendicular to the path of the line, before you started hauling it sideways.
Pull hard with both hands, simultaneously. Don't let the rope slip around the cleat in the wrong direction!
(4) Lean towards the cleat, hauling hard, while taking up the excess you’re pulling around the cleat. When you’re done with this move, the line should be back to its original position.
As you pull towards the cleat with your forward, pulling hand, take up the slack with your tailing hand. You can see I hauled nearly a foot of line with this one jump.
(5) Lower your grip on the tail of the line and repeat, until the line is as tight as you want or can manage.
The difficult part of learning to jump a line is to take up the line after the cleat, so you’re actually making progress. Watch the line at the cleat as you jump it, so you can see when you are not pulling enough with the tail and when it goes backwards - That’s what you want to prevent. As you haul the line sideways, the line at the cleat should be stationary and as you haul it towards the cleat, you should see the line pulling around it, making the tail longer.
If you don't have enough friction on the cleat, wrapping the line around the back of the cleat and under the other horn will greatly help.
The added friction of passing the line around the cleat is often needed when jumping lines, particularly with larger line, double braid and heavier loads.
You can jump a line to be much tighter than you could otherwise pull directly, except by a strong winch.
Jumping a line is the method used to tension a boat’s line at dock and it’s a skill you’ll enjoy using regularly. In square rigged sailing ships, this is how lines are tightened, as there are no winches. It’s also the fastest way to heave a heavy object, such as a large mainsail and this method is used on race boats on halyards, raising sails. In tall (square-rigged) ships, it’s called “sweating a line.” The large lines are the only ones sweated, as the small lines control delicate parts of the sailing gear that can be ripped by too much force. This is where the saying “Don’t sweat the small stuff” comes from.