Q: What is “crabbing”?
Q: What is “crabbing”?
A: Crabbing is the way many experienced skippers keep their boats from being pushed to the side of a channel by a current that is running across the channel. The term comes from the way a crab scuttles across the bottom.
There are many channels, cuts and inlets that have creeks or smaller cuts or inlets entering the main channel from the side. These allow tidal or wind-driven currents to rush across the channel. The various intracoastal waterways are notorious for this. There also are many marinas that are in basins or up creeks off main thoroughfares or large bodies of water. As you follow the entrance channel to the marina, the flow of the larger body of water runs across the entrance channel, pushing you out of it.
There also are many other areas where you may need to crab, such as in the Bahamas and the Caribbean. Big Rock Cut in the Exumas is a good example. The inlet has rock and reef on both sides. Once you get in, you must turn hard to port if you’re heading for Staniel Cay. But on a strong tide, after you turn to port, there is a very strong current pushing you to the side. If you let this prevail you’ll find yourself on rocky ledge that will quickly hole your boat, particularly if there is any sea running.
When you encounter conditions such as this, the best way to remain on course may be to angle your bow toward the direction of the lateral push. This is easier said than done, because you have to correctly estimate the speed of the flow, its effect on your particular boat (and this can vary greatly with hull form, draft and power), and the angle and boat speed needed to correctly compensate to keep you on a straight course. Wind strength and direction also must be considered. For example, if the wind is blowing across the channel with the current, the need to compensate may be even greater. If it’s blowing against the side current and if your boat has a shallow draft with a lot of windage, the need to compensate may be less.
Boat speed can be more of a problem than you might think. If you’re going into a marina, too much speed may cause too much wake to follow you in. If you’re negotiating a tricky cut through the reef, too much speed may not give you time to make the precise turns required. But if you get all of this right, the boat will travel the correct course while appearing to the uninformed to be heading off to the side.
Getting it right requires not only an understanding of the principles involved but also a lot of experience. The use of ranges is helpful to the experienced as well as to those learning. If you just look ahead as you are trying to stay in a channel with side current, you won’t realize how far you’re being pushed aside. It can look OK until you’re really far out. Try to find two landmarks — one behind the other and the rear one taller than the front — on the shore ahead. They must be lined up when you are in the right place in the channel. Many guidebooks direct you to such landmark ranges. In fact, many marinas construct range marks. Aids to navigation in difficult areas often include ranges constructed by the government or sometimes by members of the local maritime community. They may be ahead of or behind you. It takes practice to steer and keep them lined up.
If there are no landmarks or other structures suitable for ranges, look both astern and ahead of you. Draw a mental line that follows your intended course and is between a point on the shore astern and a point ahead. Follow this line until you’re in easier water. It often helps to have someone else on the boat looking fore and aft and telling you whether you’re to one side or the other of the line, leaving you to concentrate on helming. Following a line on a chart plotter or computer monitor may be helpful to some, but don’t be distracted from the job at hand, which is being in the right place in the channel, not on a screen.