Your Guide to Outboards: Chapter 5

Gear That Provides the Finishing Touch

If you are in the first group, you probably have a fast boat. Trouble is, no matter how fast it is, it's still not fast enough. (Bass and bream competition fishermen fall into this category.) If you belong to the second group, you failed to follow our advice in Chapter 1. Instead you settled for an engine that's barely adequate.

Fortunately, there are solutions that can help optimise any boat's performance.

If your rig was not lavished with special attention during setup, the most promising place to start is the propeller. The right prop is the key to maximum performance. Let's say you are running an aluminum prop and V6 outboard on a hull that's capable of 100kmh-plus speed. Adding the right stainless prop can boost your top end by 5-10kmh. Unfortunately, propping is as much art as science, and as strange as it sounds, the best propeller at the start of a setup program may not be the best model at the end of the process. Before investing in an expensive propeller, ask your dealer or prop shop about demos and return policies.

In most cases, you'll want to prop for the upper end of your outboard's recommended wide-open-throttle (WOT) rpm range. Do this with the boat carrying a light to moderate load so that the engine won't bog down (or under-rev) when hauling a heavy load.

A different prop can markedly improve holeshot. Check out a four-blade model and aim for the very top of the rpm range for your engine. If your stock three-blade prop is providing a satisfactory WOT range, you'll probably want to drop an inch in pitch when going to a four-blade. You will lose some top end, but holeshot and ski-towing ability should improve.

Lose the weight
If you are towing a skier and the boat doesn't have the "grunt" to pop him out of the water, your first step should be to rid the boat of excess weight. Unload unneeded passengers. Take out the Igloo cooler/esky and remove all other non-essential gear (don't remove safety equipment or your ski observer, of course). Weight is a performance killer.

Keep it trimmed
A boat's optimum trim angle depends on hull design and water conditions, but it is usually around 3¡ of positive trim. Many boaters believe that maximum trim means maximum speed, but overtrimming a boat actually increases drag. If the prop is throwing a tall rooster tail, it's losing forward thrust.

Outboard set-up
Outboard jackplates, a device commonly used in America to actually raise and lower the outboard with a hydraulic ram, are fairly rare in Australia except in racing circles. However, you can still raise the outboard on the transom to minimise how much of the lower unit is introduced into the water. Although you won't have the precise range of adjustment of a jackplate and its "setback" advantages, the reduced drag should still let the boat go faster.

Be aware, however, that if you raise the engine, you reduce the leverage that the power trim system has to lift the bow. If it can't generate sufficient lift, the hull's wetted surface area increases and speed suffers.

A good stainless steel propeller is much less likely to ventilate at high speeds than an aluminium propeller.

Nose job
For high-performance rigs capable of extreme speeds, special high-performance lower units and nose cones are available. These components are specially designed to prevent blowout (the unwanted induction of air or exhaust fumes into the prop stream). Their hydrodynamic shape also improves water-flow efficiency across the lower unit.

While a stock outboard's lower unit generally is good for speeds well into the 120kmh region, in some cases, adding a race-style nosecone to boats that run to 100-120kmh may boost performance, especially on boats that like a high trim angle.

As the foregoing clearly demonstrates, there are many strategies for wringing every last pony from an outboard.

Your Guide to Outboards