How to Increase the Performance of an Outboard Motor

Ten tips to make your outboards faster and last longer.

Improve the Performance of Your Outboards
The fastest boats in the world don’t leave a roostertail.Ken Miller

Improving Outboard Performance Comes Downs to Setup

The day before offshore racing's national championships in Clearwater, Florida, Dan Lawrence, throttle man for The Hulk, made what sounded like a simple statement.

“It’s all going to come down to setup,” said the 11-year veteran.

Lawrence, from Sarasota, Florida, and driver Rob Nunziato, from Dania Beach across the state, race a 32-foot Doug Wright catamaran in the Superboat Stock class. They were the 2014 national champions under the sanctioning body Super Boat International. The Stock class is one of the most competitive in the sport because all the teams run stock Mercury Racing offshore outboards.

The owner of a performance boat powered by twin Mercury high-performance outboards myself, I went to Clearwater hoping to learn how to get the most out of my engines by talking to the guys in the Stock class, many of whom I’ve known for decades. Here are 10 tips I learned.

Improve the Performance of Your Outboards
Don’t tinker with modifications to your engine, as they can do more harm than good.Mercury

1. Modifying Your Outboard Engine Can Lessen Reliability

Recreational boaters may have an image of these high-level racers tinkering with their engines, but that’s not true. Lawrence recommends: “Do not modify your engines. Run them the way Mercury makes them. Every time you modify it for 2 or 3 mph, you’ll lose reliability.” And note that any modifications will void the warranty. All in all, you may not want to make outboard motor performance upgrades.

2. Trimming Your Engine Loses Efficiency

Lawrence sets up his boat to use less positive trim. "The boat is much more efficient if you don't need to trim it out," he says. Lawrence wants the noses of his outboards' lower units pointed as straight forward as possible. When the lower units are pointed straight, the thrust from the propellers goes straight aft. When the outboards or lower units are trimmed out/up, the noses point down and the thrust is directed up, not aft. This increases fuel consumption and reduces efficiency.

Lawrence’s competitor, Chris Schoenbohm, who owns Smart Marine Group and Smart Marine Service in Orlando, echoes Lawrence’s point about trim and says, “More than 3 degrees nose up is detrimental at 55 mph.”

Improve the Performance of Your Outboards
Try different props to see which works best for your engine.Mercury

3. Try Different Props to Maximize Performance

In addition to racing The Hulk, Lawrence owns a flats boat and a 28-foot Spectre center console powered by twin 250 horsepower Mercury outboards. After some trial and error, he found that the best propellers for the Spectre were five-blade Mercury 15-by-30-inch Maximus stainless-steel props. These help him achieve a top speed of 78 mph (when not carrying the weight of a full fuel tank) and a best cruise of 56 mph at 3,500 rpm, which gets him to the fishing grounds quickly without using much fuel. He wants to try 14.375-inch-diameter wheels. So, like the pros, try different props until the performance you desire is met. The right prop is a definite way to make your outboard faster.

Improve the Performance of Your Outboards
The Super Boat class features some of the fastest racing boats in the world.Eric Colby

4. Get Rid of the Roostertail Behind the Boat

Regardless of the class of boat, during a race you can tell which team is running at its most efficient because the roostertail lowers as the boat accelerates. When a high-speed catamaran or stepped V-bottom runs at high speed, it has virtually no roostertail at all. If your boat’s roostertail gets smaller as you make improvements, you are probably doing things right.

Improve the Performance of Your Outboards
A jack plate can help maximize boat speed.CMC Marine

5. Get a Jack Plate for Your Outboard Engine

To get the most out of your outboards, Schoenbohm recommends mounting them on a jack plate such as those made by CMC Marine (cmcmarineproducts.com), Bob's Machine Shop (bobsmachine.com) or T-H Marine (thmarine.com). Expect to pay about $1,000 for a hydraulic unit. Manual models cost about $400 to $500 and are intended for less-frequent adjustments.

A jack plate helps you get the most out of a boat because the best engine position might be between two sets of mounting holes on the transom. Brad Holbrook, a naval architect at CDI Marine Company in Glen Burnie, Maryland, and the crew chief for the Talbot Excavating team, explains why. “Most everybody’s motors are mounted too low,” he says. Higher mounting reduces drag but requires low-placed water intakes like those found on Mercury Racing outboards.

Jack plates can also be used to adjust the setback, or how far back the motors are from the transom. For example, you can get an Atlas jack plate from T-H Marine in 4-, 6-, 8- and 10-inch setbacks. Setback helps ensure the prop is not in aerated water.

Gary Ballough is a 14-time world champion and 13-time national champion in offshore racing, and the throttle man from Boca Raton, Florida, won all those titles in outboard-powered boats.

“Propeller, motor height and setback are everything,” he says. “You can make your boat pretty much do what you want if those three things are right.” A jack plate is one way to increase horsepower on an outboard motor.

Improve the Performance of Your Outboards
Gary Ballough is a 14-time world champion and 13-time national champion in offshore racing.Eric Colby

6. Get Advice from Other Boaters with Your Same Engine

All the racers advise to find a knowledgeable resource to turn to with questions about your engines. Most of the Superboat Stock competitors turn to Diamond Marine in Fort Lauderdale (diamondmarine.com) with questions ­because the high-performance outboard shop deals primarily in Mercury Racing outboards.

“Talk to your boat’s manufacturer, and find another customer who has the same power and ask what he did for setup,” Ballough says. “If a guy has done Bravos [Bravo One sterndrives], and gone through the hub and over the hub [routing exhaust], he’s done a lot of the work for you.” In other words, don’t be afraid to reap some benefits from others’ experiences.

Improve the Performance of Your Outboards
Check your boat hull for rocker and hook.Eric Colby

7. Check Your Hull for Spots that Need Fiberglass Work

Using tape and a straightedge are the most effective ways to find an efficiency-scrubbing flaw such as hook or rocker in the hull bottom. When there’s hook, the running surface is scalloped or shows a hollow just forward of the transom. This creates the same effect as having large trim tabs in the down position, which forces down the bow and scrubs speed. To check for hook, place a straightedge on the running surface at the transom running forward — a 3- to 4-foot level works well. If you see daylight between the straightedge and the bottom, there’s hook that needs to be repaired by filling and applying fiberglass.

Rocker is the opposite of hook and is usually designed into the bottom to help the boat rock back onto the aft section of the running surface to help carry the bow at cruising and high speeds. Be sure to check for rocker and hook.

Improve the Performance of Your Outboards
Leave all the extra gear and baggage at home.Bill Doster

8. Leave the Extra Boat and Fishing Gear at Home

To make your boat more efficient, take a hard look at how much gear you carry when you head out. Lawrence estimates that every 100 pounds is worth 4 mph in his race boat, so it can make a difference. Boating's own test of the effect of weight on speed and efficiency concluded that, for the test boat, a 1 percent efficiency gain was achieved for every 100 pounds we removed from the test boat (visit boatingmag.com/expert-tips-saving-fuel).

Improve the Performance of Your Outboards
Running your outboard engines at full throttle has major benefits.Eric Colby

9. Don't be Afraid to Run Your Engine Wide Open

Finally, as crazy as it sounds, make sure you spend enough time on the water. “So many problems are because people don’t use their boats,” Holbrook says. “Don’t be afraid to run it at wide open and let it clean out every now and then.” Just pretend you’re racing.

No matter what boat you own, “go boating more” may be the best advice ever offered.

Improve the Performance of Your Outboards
Become a DIY boater and do regular maintenance on your engine.Eric Colby

10. Maintain Your Outboard Engine

On the maintenance side, boat owners should make sure they run the correct octane fuel and use a quality two-stroke oil such as the Mercury synthetic blend. Change the lower unit’s oil frequently, and when you do, inspect the drain plug, which is magnetic, for metal shavings that could indicate wear. Also, change lower-unit impellers and propeller nuts annually.

Pull the cowlings and inspect your outboards’ powerheads to make sure nothing looks out of the ordinary. Keep the propeller shaft greased and, if you boat in salt water, take the cowling off and wipe down the motor with CRC or another lubricant. In short, become a DIY boater.