Powercats: You either love them or hate them.

You probably already know that twin hulls offer many advantages over monohulls, and that they offer some significant disadvantages as well. The cat-versus-mono debate has been driven into the ground through years of discourse.

But whichever hull design you favor, the basic argument can be boiled down to this: Powercats usually display superior efficiency and stability, a softer ride and more deck space than a monohull. But, they also look ugly (well, some people think so), feel strange when turning, may "snap roll" in escalating seas, and generally cost more than monohulls.

Which is better? Neither, either and both. It depends on which factors are important to you personally. Yet there's no denying that catamarans – both power and sail – have continued to grow in the marketplace, seducing interested boaters. If you are one of those flirting with the idea, read on.

SEA CAT BOATSPowercats like this Sea Cat are roomier than their monohull counterparts because they can carry the beam all the way forward.SMOOTH RIDE

For most boaters, the biggest attraction to powercats is their soft ride. But, is it really softer? Some would argue no, but they probably don't have much cat time under their belts. The fact that cats can run smoother than monohulls has been proven numerically, as well as anecdotally.

In one cat-versus-mono test I was involved in, we rigged a 26-foot Glacier Bay catamaran and a 26 Regulator, a monohull well known for its smooth-riding deep-V hull, with an accelerometer. This gadget measures the severity of impacts, and interfaces with a laptop computer, which then translates the impacts into a graphical format. We ran the two boats side by side in identical conditions: into, with and across the prevailing seas. Time and time again, the powercat posted drastically reduced impacts. The degree of reduction varied a bit, depending on which direction the boat was going, with the most impressive results in a head sea. In some cases, the cat experienced fully half the impact of the monohull.

How is this possible? Look at the tunnel on most powercats, and you'll notice a surprising feature: they grow smaller as you move aft. These are called compression tunnels, because they use the forward motion of the boat to compress air as the space between the hulls grows smaller. That compressed air then acts as a cushion, which absorbs a great deal of the impact when the boat hits waves. Combine this with the fact that cat hulls are much finer at the entry than monohulls, and thus have less impact when the fiberglass meets the waves – and a much smoother ride.

So it's true: We have numerically proved, at least in this case, that a cat is smoother than a monohull – when, that is, it was being operated properly. When driven improperly, the same tests prove that a cat significantly loses its ability to smooth out the ride. What do you do differently when driving a cat? More on that later. First, let's look at some other advantages and disadvantages.

SNAP ROLL

Stability is another big factor that's notably different between the two. Cats are far more stable, which seems like an advantage – and usually it is. But in certain conditions, when the seas overcome the inherent stability of twin hulls, the shift from stable to rocking is abrupt and severe.

In other words, the monohull rocks a little, then a little more, then a lot. But a cat will go from an essentially static position in little waves into a sudden roll when those waves really increase. That roll motion is commonly called a "snap roll." Still, on nine days out of 10, the super-stable platform will make you glad you're on a cat.

Modern powercats also win the space race. Since the two hulls run parallel to each other all the way from the transom to the stem, the boat enjoys its full beam for its entire length. Take a few deck measurements, and you'll discover that in most cases, this gives cats a 20- to 30-percent deck-space advantage when compared to monohulls of the same length. That also translates into more stowage space, higher passenger capacity, and larger cabins.

GLACIER BAY CATAMARANSA powercat's fine entry has less buoyancy then a monohull's, so weight distribution is a factor.The final advantage of running a cat is improved efficiency. Remember the comparison between the 26 Glacier Bay and the 26 Regulator? The cat needed just 300 total horsepower to cruise in the mid 30s and top out in the low 40s. The Regulator requires another 100 horsepower to post similar performance numbers. And fewer horses translate into a lower fuel burn.

What gives? There are several reasons, but to understand them, first we have to look at the major difference between cats: Some are planing, some are displacement, and some are semi-displacement. Just exactly which boat is which, however, is tough to identify.

As a rule of thumb, slow, trawler-style cats are commonly thought of as displacement. A Glacier Bay is often pointed to as a classic semi-displacement hull; a Twin Vee is known as a fully planing hull. There's just one problem: There is no mathematical formula that provides "hull speed," which is the hull's maximum displacement speed.

When it comes to monohulls, it's easy to do the math: 1.34 x square root of LWL (length at the waterline) = hull speed in knots. Take a boat with a 25-foot-long waterline as an example. The formula is 1.34 x 5 = 6.7. When that 25-foot-long boat hits 6.8 knots, it is, at least to some degree, planing. But there is no similar formula that works for powercats. Since no one can prove exactly when a cat hits planing speed, the determination between planing, displacement, and semi-displacement is usually left up to the marketing gurus.

The bottom line: How efficient a hull is depends on many factors. But when it comes to displacement hulls, cats gain an advantage over monos because they have less resistance going through the water. And when it comes to planing hulls, they have the edge because that cushion of compressed air helps raise the boat higher, minimizing the amount of hull in the water, thus reducing resistance. Either way, the cat's a winner when efficiency is in question.

CAT CONS

Oddly, the biggest complaint one hears about powercats is that thy're not as pretty as monohulls. Fair enough – if that's all it takes to turn you off to cats, so be it.

Another common complaint is that they lean outward in a turn. This feels strange and can make an experienced monohull boater feel uncomfortable. It takes quite a while to grow used to. Occasionally, it even causes some people to fall down. Then there's the snap roll, which we discussed earlier; this also can occasionally cause someone to lose his or her balance.

The final issue with powercats is cost. Two hulls require more raw materials than one, and it also takes more time and manpower to build them. On average, a powercat usually costs about 20 percent more than a monohull of similar length. In addition, cats more than 22 feet long also require twin engines, because turbulence from the tunnel makes it impossible for a center-mounted motor to get a solid bite in the water. Many monohulls this size perform just fine with one engine.

WORLD CAT BOATSA powercat like this World Cat offers top-notch performance -- if you know how to operate it.HANDLING TIPS

If you run a cat like a traditional monohull, you'll almost certainly be disappointed by the results because you won't be enjoying the advantages twin hulls can offer. Often, a test drive with a salesman who doesn't understand how to properly run a twin-hulled boat turns a potential cat-lover away from the fold. Here's what you need to know about captaining a cat.

Trim at a Whim. On a cat, trimming is nothing like a monohull. Most cats run most efficiently with a neutral trim, though tucking the bow in just a hair in rough seas can help smooth out the ride. If the boat is "sneezing" – sending puffs of mist out of the tunnel, and soaking the passengers – you likely have the motor trimmed in too much.

Of course, just as every monohull is different, every cat is different. Some run best with the bow trimmed up in a following sea, and trimmed down (again, just slightly in most cases) with a head sea. Others continue to perform best at neutral trim. And with some powercats, changing the trim setting has little to no affect on ride. If this is the case, simply set it for the most efficient fuel burn.

How do you know which setting to try for the particular boat you're interested in? You'll have to experiment, but bear in mind that cats displacing less and planning more tend to act more like monohulls. Those that displace more and plane less tend to act differently.

Turn and Burn. While monohulls bank into a turn, cats often remain flat, and some even bank outwards. While this doesn't present any real problem, it does catch people off guard simply because it feels strange, especially to experienced boaters who have always run monohulls.

Take heart in the fact that after a season or two, it will feel every bit as natural as turning a monohull ever did. However, if you feel the need to, you can mitigate the phenomenon by trimming up the outboard engine as you go into the turn. This will help bring that side of the boat up, pushing the inboard side down, and will replicate the inward bank of a monohull.

How Fast? In a monohull, when the going gets tough and the trim has been properly set, there's only one way to smooth out the ride: slow down. Oddly, in a cat, this may have the opposite effect. Chopping the throttle can cause the boat to pound and slap, and ending the pounding is probably why you were interested in twin hulls in the first place.

What gives? Remember that a powercat gets its smooth ride from the cushion of air compressed between the two hulls. In certain sea conditions, going faster will help build that cushion and reduce impacts. Naturally you have to use caution when speeding up in rough seas, but it's an option that should be explored when the going gets tough. You'd be surprised at how often boosting your speed boosts your comfort level.

LENNY RUDOWNotice how the tunnel grows smaller as you look aft; this compresses air between the hulls, cushioning the blow when the boat strikes a wave.Slim Down. One of the most important, often-overlooked factors in how a cat rides is load. The thin hulls found beneath the deck are driven deeper into the water by adding weight, which often produces "tunnel slap," when the top of the tunnel slams down onto the waves. While the softness of the ride on many monohulls improves with additional weight, when it comes to cats, it can deteriorate quickly as weight grows.

Beware of the Beam Sea. The snap-roll phenomenon is one of the worst of the powercat attributes. These boats are exceptionally stable, but in some ways, too stable. What makes the snap roll motion even worse is the fact that people often become accustomed to riding on an incredibly stable platform, relax their handholds, and are startled by the sudden shift.

The captain can, however, mitigate this problem by simply paying attention to the seas. Snap rolls are most often caused by boat wakes, thanks to their even spacing and height. When at the helm of a powercat, always be on the lookout for boat wakes approaching the beam. Slightly changing course to take the waves from a different angle is usually all it takes to eliminate a snap roll.

Get buoyant. The vast majority of modern powercat designs feature fine entries. As a result, cats tend to have relatively low buoyancy forward. At low speeds in heavy head seas, many cats throw spray, tunnel slap and sometimes take water over the bow, because the bow doesn't have enough buoyancy to rise up and over the waves. (When they're at faster speeds, the air being shoved into the tunnel makes up for the lack of buoyancy.) Usually this occurs between 1500 and 2000 rpm, but the exact point at which it happens varies from boat to boat. The solution is to simply avoid running the boat into a head sea in this rpm range. When slowing down to investigate a fishing spot, or when approaching a waypoint, either come all the way back to idle or maintain enough throttle to keep the bow slightly raised. Weight distribution can also contribute to this problem. When loading a powercat, always try to keep the weight aft.

One other oddball cat trait to look out for: Some of those with the slimmest of bows can actually cut the tops off waves, instead of rising over them. There isn't any real danger here. Even with waves voluminous enough to swamp the boat, the bow generally rises up and won't allow this to happen. But when running quickly into a standing head sea, where the waves are tall but relatively thin and tight, shaving the tops can soak the boat's occupants. If this happens, trim the bow up a hair more or back off a little on the speed.

Open Minded. When running a cat, you need to remain open-minded and be willing to experiment. Every boat is different. Even boats of the exact same model can run different, thanks to load, engine mounting and a plethora of other factors. You should therefore run an unfamiliar boat many, many different ways until you discover how it runs best. One cat I captained for several seasons seemed to like a slightly different trim setting every time I took it off the dock, depending on sea conditions and how many passengers and how much gear I had on board. But if I made the effort to experiment, I could usually dial in the best running attitude and speed in a matter of one or two minutes. The boat then provided a softer ride than any monohull of comparable length.

So now you know powercat pros, cons and handling tricks. But you still wonder, is this the right kind of boat for you? There's only one way to be sure: Try one out. Actually, try two or six or eight of them, because just as no two monohulls are the same, no two cats are the same. In any case, now you'll look like a pro when you decide to go driving Miss Kitty.

Lenny Rudow was senior technical editor for Boating Magazine for more than 10 years, and is currently the electronics editor for Marlin and GoBoating magazines.