PS Advisor 3/01/98
Outboard vs. Inboard Power
Those who build in the 28 to 40-foot range choose to install inboard engines rather than an outboard. What advantages does an inboard have over an outboard that justifies putting inboards into all of those new boats?
• Pivoting an outboard makes the yacht more maneuverable, especially at low speeds and in close quarters.
• An outboard makes the yacht a lot more maneuverable backing down. Inboards are terrible turning to port in reverse.
• When not motoring, the skipper can pull the prop out of the water, reducing drag.
• Without a stuffing box, the boat has one less source of water in the bilge.
• At the end of the season, the owner can take the engine home and do the off-season overhaul at any time, rather than rush with it in the fall or spring.
• With gas four-stroke outboards, the owner can drain the fuel tank and put the fuel in his car’s tank. The owner will not need fuel stabilizers, can get fresh fuel in the spring, and does not store flammable, explosive fuel in his yacht all winter long.
• An outboard can do double-duty on the yacht and on the dinghy.
• Some on-the-water repairs, such as replacing a raw water impeller, will more likely be successful on an outboard.
• If the engine is a total loss from breakdown, collision, misuse, or whatever, getting a new outboard is a lot simpler.
• An outboard leaves more space inside the boat where the engine compartment would have been.
• An outboard will be quieter inside the boat when it runs.
I can anticipate some of your responses:
• Inboards keep their weight near the center of the boat.
• An inboard is less likely to separate from its mounting.
• Diesel engines have some advantages over gas engines. (Inboards tend to be diesel and outboards tend to be gas engines.)
• Buyers associate an inboard with an expensive, premium yacht and associate an outboard with a low-end boat.
Most of the reasons you cite are certainly true of outboards, and explain why they are common on many performance multihulls and trailerable monohulls.
Your anticipated response items also are true, though diesel outboards now are available and quite attractive, if a little heavier than gas models of the same horsepower.
We do take exception to several items on your list, however. For one, a displacement boat in the size range you mention will require a fairly large outboard, too large for the dinghy. And, repairs will not necessarily be easier leaning over the transom. Dropped tools and parts are a risk. It will be much easier to work in the cabin, assuming there is reasonable access.
On the flip side, we certainly agree that eliminating the inboard opens up all kinds of space inside the boat. Some “purist” cruisers such as Lin and Larry Pardey, as well as our friend, Danny Greene, have never wanted an inboard to sully their interiors. Danny calls the vast space under his 34-foot steel ketch’s cockpit his “garage.” No oil, grease, water leaks or diesel smell either.
We guess the main reason builders/consumers favor inboards is that for many boats, a large, powerful engine is needed to push the boat through head seas when the crew wants to get home. Second, on too many outboard-powered sailboats, the prop is never low enough, and being located on the transom it rises too easily out of the water when the boat pitches. Lastly, you can’t run a very big alternator on an outboard for the recharging of batteries. On most larger boats, the inboard engine not only provides propulsion, but does other duty as well—charging batteries, running refrigeration compressors, etc.