Many rivers in North America are a series of pools created by dams. When the dams also include locks, navigation is possible beyond the dam. Locks are watertight chambers with gates at each end. They raise and lower boats from one water level to the next. Many cruisers find locking through a pleasant experience and part of the adventure of boating.
- Conventional lift locks are single chambers that raise and lower boats.
- Flight locks are a series of conventional lift locks.
- Hydraulic lift locks have water-filled chambers supported by rams or pistons that move in opposite directions. The movement of one chamber forces the movement of the other via a connected valve. The chamber in the upper position adds sufficient water to cause it to drop, forcing the lower chamber to rise. The chambers have hinged gates fore and aft that contain the water and allow boats to enter or leave.
- Marine railways convey boats over obstacles, usually a landmass, by containing boats in a gantry crane that moves over the land and deposits the boat on the other side of the obstruction.
River locks are usually conventional lift locks. The dam deepens water around shoals and the lock allows vessels to bypass the dam. Conventional lift locks work by gravity alone. Water passively flows into or out of the lock. When the lock is filling, the valve at the upper end of the lock is opened and water flows in. The downstream lock gate is closed, preventing the escape of the water. This is the time of greatest turbulence in the locks and the time of greatest vigilance for boaters. When the upper water level is reached, the upper lock gate opens to allow boats to exit or enter.
When the lock empties, both lock doors are closed, a valve on the lower end of the lock is opened and water exits. This creates a surge of water outside the lock but inside the lock, the water recedes like water in a tub. When the water level in the lock is the same as the lower river level, the lower lock gate opens and vessels leave.
Call ahead on VHF Channel 13 (or sound three blasts) for permission to lock through. Indicate whether you are northbound (upbound) or southbound (downbound). Your presence and communication indicate to the locktender your desire to lock through. Wait a safe distance from the lock or find an anchorage nearby and within sight of the lock.
Prepare for locking by placing large fenders fore and aft and having lines ready. Fender boards are useful because they protect your fenders and provide a skid plate against the dirt and algae on the lock wall.
When approaching the lock, stay back to allow outbound vessels to clear the lock. Do not enter until signaled to do so. Signals vary. Look for a telephone/pull rope at the lock wall; listen for a whistle blast–one long and one short blast or three blasts; look for a "traffic" light–green, yellow or red. Follow directions given by the locktender. The order of priority is:
- U.S. Military
- Mail boats
- Commercial passenger boats
- Commercial tows
- Commercial fishermen
- Pleasure craft
When the locktender turns on the green light or calls for you to enter, enter in the order that boats arrived at the lock. The longest waiting boat goes first, unless directed by the locktender, who may call boats in according to size and the configuration of the lock. Do not jump the line, do not scoot in front of others and defer to faster boats so you do not have them behind you after you leave the lock.
When entering the lock, leave no wake, heed instruction and respect other boaters. If they are having trouble and appear unsettled, stand by until they are secure. Listen to the directives of the locktenders. Some lock systems require all line handlers to wear personal flotation devices (PFDs). Crew members on the bow should wear PFDs.
You will be directed by the locktender to a place along the lock wall. You will find an inset mooring pin (floating bollard), vertical cable or a rope.
- If there is a floating bollard, secure the boat to the pin via a center cleat by wrapping the line around the pin then back to the boat cleat.
- If there is a vertical cable, wrap the line around the cable and bring it back to the boat; the loop will ride up or down the cable.
- If there is a drop-down line, bring the line around a cleat and hold it. DO NOT TIE THE LINES!
If you are asked to provide a line, throw it to the locktender. After the locktender has secured it, take the bitter end and wrap–but do not tie–around a cleat. Attend the bow and the stern, and adjust the line(s) as the boat rises or falls in the lock chamber.
In crowded locks, move forward as far as you can to make room for others coming in behind you. Small boats may raft to bigger boats. Set adequate fenders for fending off another vessel.
Inside the lock chamber, turn off engines when secure. Exhaust fumes contained in the lock chamber are an irritant to people in small, open boats. Attend the lines at all times. Be prepared for turbulence when the lock fills. Never use hands or feet to fend a boat off a lock wall. Stay alert to other boats. Be prepared to quickly cut a line if needed.
When the lock reaches its determined depth/height, the locktender will loosen the line and drop it to you if you are using a line attached at the top of the lock. After receiving a whistle blast by the locktender, recover any lines used, and prepare to exit. Leave the lock in the same order as entering. Do not rush ahead of those in front of you.