Your Guide to Outboards: Chapter 1

What Buyers Need to Know

Once you've identified your needs, it will be easier to narrow the field of outboards that will match your boat's specific hull style andpower requirements.

If you're mainly interested in leisurely cruising aboard a lightly- loaded runabout, you obviously won't need mega-horsepower, but if your plans include pulling waterskiers, wakeboarders or inflatable watertoys, a small outboard won't get the job done. Taking this example a step further, while a modest-size engine may be adequate for towing younger children, assuming you plan to keep the boat for several years, will it be adequate when the kids are teenagers?

Some boats lend themselves to certain styles of outboards. For example, a deep-V hull with 22° of transom deadrise is more difficult to plane than a flat-bottom hull, and thus requires a more powerful engine. And while you'll commonly see semi-V boats rigged with V4s or V6s for peppy performance, certain pontoon and houseboat hulls are more suited to high-thrust, mid-sized powerplants. In all applications, the goal is to choose an outboard that matches the hull and your particular requirements.

The number one rule in any application is to buy the maximum power you anticipate ever needing when you buy the boat. Upgrading to a more powerful engine later will be very costly.

Most boat manufacturers provide recommendations regarding appropriate power or minimum recommended power, and this is a good starting point. When considering power, remember to factor in the weight of fuel, water (if your boat has a freshwater system), batteries and gear, as well as passengers. Be wary of dealers who recommend a smaller outboard to keep the package price down. It's better to have too much engine than too little; an under-powered boat will be a continual disappointment. Also bear in mind that a small engine operating at maximum throttle most of the time is going to be noisy, far less fuel-efficient and have a shorter life expectancy than a larger engine operating at lower throttle settings. Another plus is that your investment will be returned when it comes time to trade or sell.

Don't go overboard, however. Pay heed to the boat's Australian compliance plate maximum capacity statement for horsepower rating. Exceeding it is not only dangerous, but may make the boat uninsurable. It could also drastically increase your liability in the event of mishap.

Where you plan to use the boat is another consideration. Elevation is a major factor in some areas. Engines lose power as elevation increases and it is more noticeable in boats than in automobiles. Outboards with electronic fuel injection (EFI), usually operate more efficiently at higher elevations than carbureted engines, as the electronic engine controls compensate for changes in air density. If performance at high elevations is a requirement, buy a larger outboard - preferably one equipped with electronic engine controls.

When it comes to shaft length, small engines designed for cartoppers, skiffs and some auxiliary-outboard installations will feature 15-inch shafts. Most boats require a 20-inch-shaft outboard, although larger craft (particularly those with significant freeboard or draft) require a 25-inch shaft length. On offshore boats, 30-inch-shaft outboards are increasingly common.

Choice of Technologies
Never before have boaters enjoyed such a wealth of choices in outboard power. These include conventional two-strokes featuring either carburetors or EFI, and the "new-technology" direct-fuel-injected (DFI) two-strokes and four-stroke outboards that offer increased fuel efficiency and reduced emissions.

From a price standpoint, carbureted two-stroke models are the least expensive, followed by EFI two-strokes. Next up the price scale are DFI two-strokes. These direct-injected outboards are heavier and more expensive than conventional two-strokes due to added components, but offer several advantages. They are much cleaner burning and comply not only with the USA's EPA emissions regulations, but also the California Air Resources Board's (CARB) tough Tier 2 standards, set to take effect in the USA in 2004. (Mercury's OptiMax 135 already complies with CARB's Tier 3 standard, which will go into effect in 2008.)

A DFI outboard will provide a 10 to 30 percent improvement in fuel efficiency, with the greatest savings occurring at trolling speeds and at (or near) wide-open throttle. Compared to conventional two-strokes, DFI outboards idle more smoothly and are less apt to foul spark plugs at prolonged idling speeds.

As a rule, four-strokes are the heaviest and most expensive members of the outboard family, and offer advantages similar to DFI two-strokes - including low emissions compliance. Four-stroke outboards are generally quieter than two-strokes of comparable power, and testing has shown that fuel economy is roughly equal to that of DFI two-strokes. In most applications, four-strokes are not quite as quick in popping a boat onto plane as two-strokes - although clever engineering (such as props, tuned intakes and exhausts) is changing that.

When repowering a boat, engine weight is a factor to consider. Today's two-strokes are heavier than engines of a few years ago due to more rugged construction and increased features. Four-stroke outboards are heavier still. Talk to your dealer to get an estimate of the actual rigged weight, which includes propeller, battery cables and a remote oil reservoir, if applicable. It may be quite different than the data published in the brochure. This is another situation where it's wise to refer to the boat's maximum capacity specification plate.

Back up engines
Also referred to as trolling motors, an auxiliary outboard is a backup to your main engine and can provide considerable peace of mind. If the boat loses primary power, you can still get home. Depending on the boat, auxiliary engines can either be transom mounted or bracket mounted. Many brackets allow you to raise or lower the auxiliary and tilt it forward, which gives you some leeway in choosing the outboard's shaft length (usually 15 or 20 inches). Freshwater fishing boats commonly use 8 to 9.9hp auxiliaries, while larger saltwater craft may require 15 to 25hp engines for sufficient thrust.

In fact, if an auxiliary outboard is intended chiefly for trolling or pushing a large boat, you may want to buy a high-thrust long-shaft model. These are generally designed with larger propellers, gearcase units and lower gearing to enhance slow-speed directional control.

One of the bonuses of owning an auxiliary outboard is that it can serve double duty on cartoppers, tenders and rental boats.

In this case, choose a standard model (not a high-thrust BigFoot version), as it will still give satisfactory performance on a larger boat.

Single vs Twins
When considering power for offshore use, many boaters must decide between single and twin engines. Although the added manoeuvrability and safety factor of twins are often cited as major selling points, there's another camp that feels you only need twins if a single outboard won't get the job done in a satisfactory manner. There are pros and cons to each side.

Contaminated fuel is a primary cause of engine failure, and with twins, when one outboard quits the other is usually close behind - particularly if both draw from the same fuel tank. Regarding the "limp-home" factor, when choosing twins it's helpful if each engine is capable of planing the boat by itself. If not, you may be better off with a single large outboard and an auxiliary. Not only will this setup be less expensive to purchase and maintain, a husky auxiliary outboard will bring you home nearly as fast as a larger engine that won't plane the boat.

Twin outboards are more expensive to buy, service and operate. Although our testing has shown this isn't always the case, often times twins of equal horsepower are slower than a single-engine rig due to the increased drag of two lower units. The extra blade area of two propellers, however, provides better slow-speed maneuverability, as well as stronger acceleration when putting a heavy load on plane. Finally, there is the panache factor. Twin throttles feel good in your hand, the engines sound good when running in sync, and they look good.

Counter-rotation is an additional consideration. Counter-rotating propellers provide a slight increase in performance and manoeuvrability, but the major advantage is they cancel steering torque. Unfortunately, having both right-hand- and left-hand-rotating props means you'll have to carry two spares. This is a wise idea, incidentally, because a V-bottom hull tends to funnel debris to the side and into the props. A potential upside is that twins offer reduced draft due to the outboards being offset on either side of the keel - an advantage for boaters who commonly run in shallow areas.

As you can see, there's much to consider when selecting an outboard. Ultimately, your choice depends on the type of boat you have and how you plan to use it. The key to satisfaction is buying the maximum power you anticipate needing - now, and in the future.

Your Guide to Outboards