Catching a
crab is one of the worst, and most embarrassing, things that can happen while rowing. The term "catching crabs" refers to sticking an
oar in the water and not being able to release it. When the oar fails to come out of the water, all of the forward momentum of the boat is focused on the offending oar,
rigger, and
oarsman behind it. If someone catches a crab, it looks as if the oar had hit a crab swimming in the water, stopping the oar
dead in the water. Crabs are almost always devastating to the boat's speed and may even cause a small boat to flip.
Crabs are usually the result of bad technical rowing. There's very little chance of catching crabs if the boat is balanced properly and all oars are being feathered and squared in time. It's only when clean entry and exit from the water are hindered that crabs are caught. Two balance issues are the greatest causes of catching crabs. If the boat crashes to one side at the catch, or if the boat is unstable at the finish, crabs become much more likely. In addition to this, improper feathering leads to crabs. If someone squares their blade too much, or not enough, it will enter at an angle. Instead of backing in softly and squarely, it will be caught up by the water and you're in crab city.
Bad rigging can also result in crabs, and this is generally the reason that experienced rowers catch crabs. Riggers are connected to the hull in a variety of ways, depending on the type and quality of the boat, but somewhere in the connection there have to be nuts and bolts. If these are not tight enough, the rigger can wiggle around a little and interfere with blade movement. Other equipment failures can occur. The top nut connecting the rigger and oarlock can become loose, which is also a problem. If you've ever seen the movie The Skulls, you already know what happens if someone doesn't tighten their oarlock enough. (However, in the event that the oarlock bursts open, the proper response is definitely NOT to jump out of the boat.)
Crabs can be really bad news. Most crabs are a result of small errors or a random gust of wind, and they tend to be smaller. Those minor crabs barely interrupt the stroke cycle, but having an oar in the water that's not moving the boat forward is counterproductive and slows the crew down appreciably. Bigger crabs come from bigger errors, but are often more unpredictable. Exactly how bad can crabs get? Pretty damn bad. If you've ever seen a crew stop and turn, you've noticed that they slowly square their blades in the water to slow their boat down (known as checking it down or dragging), then rowers on alternative sides take turns backing and rowing. Imagine having one oar suddenly start dragging or backing while having the rest rowing full pressure forward. It's not a ponderous mental exercise to picture what happens next. It's as if one person were trying to stop the boat single-handedly while all the others push forward. The oarsman can completely lose control of his oar as it gives in to the forward momentum. People can get hit in the face or chest with their oar if it has enough force behind it. If the oar leaves the oarsman's hands with enough force, it can end up behind him.
The smaller the boat, the worse the crab's effect. Crabs are seldom seen and quickly recovered in eights, where the balance is better and losing only one oar does not mean as much. Rowers in pairs and singles often go for a dip after catching any sort of crab. Oars cannot support you and help you balance if they are not in your control or behind you.
Often more is hurt by catching crabs than just an oarsman's pride. Crabs put a ton of pressure on the oar, rigger, and shell. A bad crab that is not recovered in time can leave riggers permanently bent. In rare cases, crabs can even cause damage to the fragile shell.