Is a power cat good in a head sea? Someone asked me that question lately, and my eyebrows hit the ceiling—how could one even ask? Running in a head sea is the situation in which a cat shines, and anyone who’s been aboard one for any extended period of time knows it.
Just look at a cat’s bow, and your eyes will show you the first reason why: plenty of boat brochures talk about a boat’s “knife like” entry, but few monos have an entry that’s anywhere nearly as sharp as the average cat’s. As common sense tells you, a thinner entry means the boat can cut open waves instead of slamming against them. Meanwhile, the tunnel between the two hulls helps cushion the blows of a head sea by compressing air. Remember your basic hydraulics; water can’t be compressed, but air can be. As a cat moves forward it crams air in-between the boat’s hulls, the tunnel, and the water, creating an air-water slurry that acts as a cushion. The whooshing noises you often hear when running a cat are that compressed air escaping. And this is also why some cats “sneeze,” or shoot a fine puff of mist out, as the air gets pushed forward. Yes, sneezing is one of the potential down-sides to owning a cat (most newer designs have eliminated or greatly reduced the problem, but some still do it to one degree or another.) For those of us who have bad backs due to decades of pounding through the seas in relatively small monohulls, however, a puff of mist is a small price to pay for greatly reduce pounding.
So how could someone even raise this question? Maybe monohull salesmen taking verbal potshots is the problem, or maybe someone charged full-tilt into an eight foot head sea and expected the boat to remain perfectly level. It could also be that people have mistaken tunnel slap for a “bad” ride. So let’s clear the air on tunnel slap: this pounding sensation occurs when a wave strikes the underside of the tunnel, and it feels a lot like a monohull slamming into a wave. In short, the sensation stinks. Most of the time this is the result of an overload situation. You have to remember that cats are more weight-sensitive then monos, and if one’s loaded down in the bow, tunnel slap can be the result. If you’re feeling it, the boat simply isn’t loaded properly. Get rid of the heavy stuff, point the bow at the waves, and let her ride—into a head sea, that is!