Looking back, it was inevitable. For the last, oh, forever, the most popular boats on the water were runabouts. Then, about four or five years ago, deck boats became all the rage, with their wide-open layouts and all-around versatility. So like the kids who crashed on their bikes and got chocolate in their peanut butter (or peanut butter on their chocolate), Maxum's design team got together and came up with the SD 2100 Sport Deck, a deck boat that's really a runabout, or maybe a runabout that's really a deck boat.

On first impression, the SD 2100 looks for all the world like a traditional runabout. The body lines are those of a runabout. The cockpit/bow seating arrangement is that of a runabout. The rakish windshield is that of a runabout. Get inside, though, and the deck boat side of the 2100's personality starts to show, just like those cartoons in the Sunday paper that suddenly become 3D if you stare at them long enough.

Up front, the bow seating area features a walk-through bow that incorporates a small, but completely adequate, swim platform and boarding ladder. That's pure deck boat. So is the actual seat layout in the bow, with bench seats on either side and a walkway between. There's storage beneath the seats, of course, and room for a cocktail table. But like the bow area of a runabout, the SD 2100's bow seating gives you a relatively 'enclosed' feel. As with any 21-foot boat, runabout or deck, there's not a lot of excess room in the SD 2100's bow area, although there is an integrated cooler. Add the optional filler cushions and walk-through door with backrest, though, and the bow area becomes a pretty good-sized playpen, big enough for the kids to catch a quick nap. Maybe even big enough for Dad, provided he goes a little easy on the burgers at lunch.

The walk-through, a pure runabout touch, is nice and wide, with a generous in-floor ski locker. The ski locker will easily accommodate a wakeboard or kneeboard as well as skis.

In the cockpit, the driver and passenger each get an adjustable bucket seat with flip-up bolster that swivels a full 360 degrees so you can both join in the conversation when you're not on the move. In front of the passenger is the enclosed head, an unexpected touch. It's no surprise that the head will prove to be a bit cramped for anyone bigger than about 5 feet 8 inches tall, or carrying more than about 150 pounds, but it's not there for the big guys, it's there for the kids, and they'll fit with no problem. And you'll all be happier for it. Above the head is a small wet bar and a freshwater sink with a small prep area.

Across the walkthrough, beneath the helm, is a large storage area that houses the standard ice chest. The rear bench seat, a sort of semi-L lounge, features some of the deepest seats you'll ever see on a boat this size. That's something that might not mean much to the small fry, but taller folks know how important depth is on a seat, so you can actually enjoy some leg support beyond your hip bones when you sit down. Actually, the rear bench is nearly deep enough for two people to lie side by side. The depth of the seats is one of the secrets of the SD 2100 design. The center section of the rear bench is the engine cover, so it more or less replaces what would be the sunpad on a traditional runabout. As a result, the SD 2100 gives you a precious couple of extra inches of cockpit room.

The starboard corner of the rear bench backrest flips up to act as a transom door. It's a nice touch, but on the test boat, flipping the seat back open or just leaving it open while underway (not recommended in real life) caused some gel coat scratching. All that's needed to fix this little problem is a small rubber bumper either on the door or on the seat back, and Maxum is working on just such a solution.

Past the transom door is a small step (which is used as a ski trunk on larger Maxums and would be well-used that way on this boat) that leads to the standard extended swim platform. Another welcome change would be to hide the rear boarding ladder, since it's almost exactly where you step when you walk through the transom door.

One knock on deck boats has always been that they're great for entertaining but not so great when it comes to getting from one part of the lake to another in a smooth and timely manner. If that's your attitude, then the fact that the SD 2100 drives and handles like a pure runabout will be good news. Even better news is that the SD 2100 comes with two of the best features Maxum's come up with lately ' a sweet inte-grated electronics switch that includes keyless ignition, and the cutting-edge Control Max docking system.

The electronics are something that most manufacturers are already starting to use; within a couple of years it'll seem odd to see an old-fashioned rocker switch on a helm. The Control Max, or something very similar, is a feature that will probably be on every new boat even sooner. In case you haven't heard, the Control Max system is a thruster setup that's operated by a simple knob-style joystick at the helm. You can push the knob the direction you want to go and the boat will head, very gently, in that direction, even directly sideways. Rotate the knob and the boat will literally pivot on its axis. With the Control Max system, anyone can dock a boat, even if it's windy, even if there's a current, even if he or she has never tried to dock before. It's one of the best innovations in quite some time.

The Control Max doesn't have much to do with how the SD 2100 performs in open water, though. That's the job of the Max Trac hull and the (in this test boat) MerCruiser 5.7L EFI Bravo III. On a warm-but-blustery afternoon, in semi-rough water, the SD 2100 delivers outstanding handling, even at speeds greater than 40 mph, and a perfectly dry ride. Acceleration is strong enough, going from 0 to 30 mph in a little more than 8 seconds, on the way to a 44.5-mph top speed. At 30 mph, the Max Trac hull delivers an acceptable recreational ski wake, and at 20 mph it gives up a first-rate wakeboard wake, even with only two people on board. Load it up with some gear and the SD 2100 may be one of the better recreational wakeboard boats of its size.

So that means the SD 2100 is a deck boat that's a runabout that may wind up being a wakeboard boat. Should've seen it coming.