Here's why Downeast Semi-Displacement Hulls provide a safe, predictable ride at 12 knots or 18... in any sea condition!
The DUFFY downeast lobster boats trace their lineage of legendary performance down a long line of work boats in the Gulf of Maine, back to the days of working sail. For generations, Maine fishermen have relied on these rugged boats to take them to sea, function as stable, dependable work platforms, and then bring them safely home, burdened with the trip's catch, in weather that most of us wouldn't venture out in.
When Maine fishermen began switching from sail to power, the Downeast hull configuration evolved from a true displacement hull to a longer, wider, semi-displacement hull. In this long transition from sail to power, the builders shortened up the keep slightly, but kept the long and narrow hull. It was an easily driven shape with excellent sea-keeping characteristics. In fact, the early boats, with a ratio of three feet of length to one foot of beam, could be driven to hull speed with just 3-hp.
As engines became more readily available, and horsepower and displacement increased, the fishermen built their workboats with flatter aft sections to support the weight and bulk of the bigger engines, yet retained the boat's traditional fine entry. The keep of the traditional Downeast hull is similar to a sailboat's keel. Although it's not ballasted, the keel performs two important functions: First, it helps steady the boat in a seaway, especially a beam sea, limiting side-to-side motion. More importantly, the keel and skeg serve to protect the vessel's running gear in the case of accidental or deliberate groundings. The configuration allows lobsterman to come right up on a ledge at slow speed and ground - or "tunk" as it's known on the waterfront - without damage.
Today, with a single engine, our Atlantic boats can duplicate the performance of most deep-V boats with twin engines, but with single-engine efficiency and economy. The common hard chine or planing hull must utilize a great deal of power (with a corresponding leap in fuel consumption) to drive the boat up out of the water and onto a plane. Once on top of the water, the hull will pound and slap the waves, and has little lateral resistance to wave motion and, as a result, will pitch and roll, often lifting the props out of the water.
At slower speeds, these hulls point their bows high into the air reducing forward visibility to a dangerous level, and making for a very uncomfortable ride. In bad weather, then, the planing hull must either travel at a bone-jarring rate of speed to stay on plane (if the hull and crew can withstand the punishment) or reduce its speed to a crawl to maintain a relatively flat attitude.
The Downeast semi-displacement hull behaves in an entirely different manner. The fine entry of the forward section slices through the waves cleanly and without pounding. It's an exceptionally dry ride, with the flared bow effortlessly tossing aside the bow wave as the hull slips through the water without a fuss. The flat after section tends to squat slightly, keeping the propeller and rudder deep in the water for a solid bite and excellent steerage. At the same time, the full length skeg and keel resists side-to-side rocking, while helping the boat track effortlessly - even in a following sea. The Downeast hull, even in nasty chop and heavy swell conditions, can cruise comfortable all day long at 12 to 14 knots.
Today's true Downeast hulls use horsepower to get them up beyond displacement speeds, and yet these boats are still true to the central issue of providing predictable stability. They are simply about as stable a platform as you could ever want - and that means stable at 12 knots, stable at 18 knots.