Parts Shop

Jack Plates

 

The jack plate accomplishes several significant functions: 

• It enables you to run in shallower water than allowed by a standard, fixed engine mount.

• It allows you to get up on plane in shallower water than allowed by a standard, fixed engine mount. 

• When trimming an engine for best performance, a jack plate affords you better fuel economy, thanks to channeling thrust in the most efficient direction – parallel to the water’s surface.

Without a Jack Plate

In shallow water, your outboard’s skeg and propeller represents the deepest parts of your boat. Whether you need to get up on a plane from a standstill or you’re already running, you must always remember that your prop and skeg both hang below your hull. 

When you’re ready to throttle up in shallow water, simply trimming up your drive actually hinders performance as it alters the direction of your propeller’s thrust to a less efficient angle. Additionally, tilting your engine degrades your performance as the water approaching the prop gets blocked by the cavitation plate as the angle of the engine changes outward. This is one reason why it takes longer to get on plane with your engine trimmed up rather than all the way down.

A better way to “shallow up” your prop and skeg is to lift them straight up rather than tilting them. Mounting your outboard to a hydraulic- or electric-powered jack plate affixed to the transom of the boat allows you to lift your engine vertically rather than change the angle of thrust. 

How Does a Jack Plate Work?

On standard engine mounts (with no jack plate), the outboard must be mounted low enough so as not to cause cavitation when running into chop or executing turns. In calm water on a straight course, it could be mounted higher, but when it’s bolted tightly to the transom, moving it up or down obviously can’t be accomplished. That’s where a hydraulic/electric jack plate comes in. 

Lifting the engine vertically keeps the plate above the propeller and aligned with the movement of the boat. Thrust channels directly parallel to the surface of the water – the most efficient direction.

A dramatically tilted engine throws a rooster tail of water up into the air, wasting energy. Plus, Newton’s Third Law of Motion says that thrust upward must equal thrust downward. If you’re in shallow water, you don’t want your boat to be pushed down, especially at the stern. An engine tilted up at a high angle to go across shallow water will raise the bow and lower the stern of a boat, making the draft of your boat deeper as the boat’s speed increases

A boat equipped with a jack plate can avoid all those negative consequences of tilting the engine. By simply raising the engine up with the jack plate until it is just on the verge of cavitation (drawing air from the surface into the propeller blades), you can start up and run in shallower depths than you ever imagined. If you want the ability to run with near impunity in shallow water, meaning without tearing up the bottom habitat or your equipment, one way or another you need to raise the skeg and propeller on your boat higher, and the jack plate represents the best possible means to accomplish that.