Powerboat Designs & Options

This page is a compendium of my opinions as to the characteristics and equipment that I consider important in a cruising powerboat for making your trips as enjoyable and as safe as possible. For complete information on these subjects check out my recommended book list.

The only engine that I would recommend for power cruisers is the diesel engine, thus the only decision to make is whether to have a single or a twin engine installation. There is no doubt that the use of one engine is more efficient in fuel consumption and range than using twin engines, and the modern diesel engine is a very reliable piece of equipment as can be proven by the countless single engine fishing boats that cover the oceans of the world. The main reason for a twin engine installation (putting aside the tranquility factor) is controllability and maneuverability in tight situations, such as docking in wind or current. This can be done with a single engine boat, however, with the addition of bow or a stern thrusters, which are becoming more common each day.
One way to increase safety with a single engine installation is to have some sort of get-home setup, such as a small engine off to one side, or a hydraulic link to a generator. If you have two engines you can run them one at a time, which becomes more efficient than running the two engines but not quite as good as the single engine installation due to the increased drag of the extra running gear and the drag effect of the rudder angle necessary to offset the asymmetrical thrust of the single operating engine and its distance from hull centerline.
The two main types of hulls for trawlers are the full displacement and the semi-displacement. An example of the semi-displacement hull is the Grand Banks line of trawlers and the Kadey Krogen 42 is an example of the full displacement hull. The difference between the two hulls can be simplified by stating that the semi-displacement hull is designed, that with enough horsepower it is able to go faster than hull speed, while the full displacement hull can't exceed hull speed.Theoretical hull speed is a mathematical function and can be expressed in the formula:
Hull Speed in Knots= Square Root of the Waterline Length * 1.34
Of course, this speed is not the most efficient cruise speed: to achieve that use between 1.1 to 1.2 as the multiplier factor.
An advantage of the full displacement hull is that the weight of all the equipment, food, beverages, fuel and other material carried on board on a long cruise won't greatly affect the performance of the boat since the design of the boat is to stay at or under hull speed and thus the extra weight won't be a great factor in performance. In a planing hull or even a semi-displacement hull, the opposite is true, as it takes a lot more horsepower and fuel to achieve planing speed if you increase the weight.
Basically, if you want longer range and more blue water performance go with the displacement hull boats, if you do more coastal cruising and need more speed then look at the semi-displacement boats.
The rounded bilges of full displacement boats tend to make them roll more easily than the harder chined semi-displacement boats and this rolling motion can become almost unbearable in a beam sea. For this reason, stabilizers are more than a luxury and can be considered a necessity for a long range trip.
Stabilizers are of two kinds: passive and active. Passive stabilizers are usually paravanes or flopper stoppers which consist of steel winged-shaped weights at the end of booms that hang on both sides of the vessel from a central mast. These are quite effective but have the disadvantage of hanging out outside the boat and thus the operator has to be in the weather if there is any adjustment to be made to them while underway. An advantage is that they work at very low speeds and even while at anchor. Active stabilizers are usually activated fins on the underside and on each side of the boat. These fins are activated by either hydraulic or pneumatic pressure and the control is achieved through the use of gyroscopes. These systems work very well at speeds higher than 6 knots but are almost ineffectual at any speed lower than this.
Prices range from US$20,000 and up and usually the paravanes will cost about 40-60% of the cost of the comparable active fin system.
Bow & Stern Thrusters:
This is a piece of equipment whose value is appreciated any time you try to dock in a heavy wind or in a strong current, especially with a single engine installation. This equipment can turn a harrowing experience into a piece of cake. Bow thrusters are more common, but where the bow installation is not possible a stern thruster is an option. Some owners opt for an installation of both units, making their boat capable of sideways motion, pretty awesome. There are several manufacturers of these units in both electric and hydraulic operation. A highly recommended option for single engine boats.
Interior Design Options:
As everything else in life, design has to do a lot with tradeoffs as you can't get anything for free. If you want a pilothouse (I would very much so), you have to have a boat that rides higher in the water and thus loses a little stability. For this, you get privacy while controlling the vessel and an uncluttered space to keep you navigation materials. If you don't have a pilothouse, then you have to share the space with the going-ons in the salon area.
The forward master stateroom is a disadvantage as the owner will be closer to the movement of the boat and the noise of the water on the hull. However, if you want the stateroom towards the rear you will pay the price in less room in the salon or less room topside.
Exterior Design Options:
For those who enjoy water sports such as fishing, diving, swimming or even getting on your dinghy, a cockpit area is important. A gate to the outside from the cockpit area is also a distinct advantage. To have a cockpit in a smaller boat, however, you lose the rear stateroom with all its comfort.
A flying bridge is another option that I really consider important. If and when you are cruising in bad weather or cold temperatures, then its not as important. However, on a long trip and in good weather, a flying bridge allows the operator and guests to be enjoying the outdoors and the fresh air while underway. It's also important when entering a gunk holing cove or an unfamiliar harbor, as it gives the operator an unencumbered view of the surroundings.