Inches of Water, Miles of Possibility

For anglers operating high performance skiffs throughout the state’s various inshore venues, there’s no aftermarket addition quite as influential as a hydraulic jack plate. Combined with trim tabs and proper engine trim, a helmsman can precisely direct the motor’s thrust to get their craft in and out of some of the state’s shallowest waters without tearing off a lower unit and damaging the fragile ecosystem. However, you’ll only truly appreciate the benefits of accessing shallower water, running faster at lower RPM and jumping up on plane quicker when you know how to properly utilize these performance enhancing components individually and in unison.


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Photo: Mercury Marine

Navigating skinny water only inches deep requires a great deal of knowledge and experience. And although the latest accessories enable inshore anglers to target previously inaccessible waters, these advanced tools also give novice boaters a false sense of security, which is a serious cause for concern.

If you’re in calm water, lifting the jack plate to a point where the prop remains just below the surface will help reduce drag and increase fuel efficiency and overall top end speed.

Traditionally, when boaters idle through shallow water it’s common to trim the motor up so the prop doesn’t risk hitting bottom. Unfortunately, this negatively impacts the direction of thrust to a point where it is incredibly inefficient. Performance is further diminished because the odd angle of the cavitation plate on the lower unit blocks water from reaching the propeller, making it nearly impossible to get on plane without leaving a quarter-mile long prop scar in your wake.

With a hydraulic jack plate the engine can be raised or lowered vertically while keeping the direction of thrust parallel to the surface of the water, but there’s no perfect trim and you can’t set it and forget it. No two days or venues are alike, and you must be able to make slight adjustments on the fly depending on the surface conditions, load, depth of water and your specific vessel. To ensure the safety of your passengers and the environment you must be in full control of your craft at all times and have a firm understanding of how the correlation between engine trim, jack plate height and trim tab position influences your boat’s handling characteristics.

When attempting to jump on plane as quickly as possible on a flat you’ll want to start by putting the trim tabs all the way down. This will lift your hull as you accelerate and decrease the squat in the stern caused by the resulting force of your forward momentum. You’ll also want to trim your motor so it gets a good bite and the direction of thrust is parallel to the surface. Finally, raise the jack plate to the point where the prop is sitting just below the surface. Once you reach plane you can lower the jack plate slightly, trim up the tabs and trim the engine out to keep the same parallel thrust. In ultra shallow water only a few inches deep you may need to take it a step further and turn the wheel hard over to one side or the other to help get up on plane before straightening out.

Of course, it would be foolish not to mention tides and your vessel’s capabilities. Enter a shallow bay or a skinny grass flat on a flooding tide and work your way as shallow as you can, while planning your exit just as the tide starts to ebb. Otherwise, no matter what you do you may very well end up high and dry. It’s happened to the best of us and it can happen to you!

Once you’ve vacated the shallows you’ll want to make further adjustments to increase performance. If you’re in calm water, lifting the jack plate to a point where the prop remains just below the surface will help reduce drag and increase fuel efficiency and overall top end speed. Watch your gauges and you’ll notice that slightly raising the jack plate without increasing the throttle will increase RPM and overall speed. If you continue raising the jack plate to a point where the RPMs continue to increase but your speed stays the same, then you know you’ve gone past the sweet spot.

Trim tabs can also be adjusted to help avoid porpoising and to keep the bow down when plowing through a crisp chop. Conversely, positioning the tabs all the way up in following sea conditions will help achieve maximum speed as you’ll be reducing drag to a minimum.

While jack plates, trim tabs and outboard engine trim angle all offer numerous benefits to shallow water enthusiasts, perhaps their greatest benefit is providing increased access to and safe departure from shallow water venues with minimal impact. Remember that if you are running the flats and notice a trail of mud or grass in your prop wash, you are damaging the fragile ecosystem and ruining it for the rest of us!