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Determine the True Draft of Your Hull for Shallow-Water Running

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On: Wed, Nov 25, 2015 at 10:33AM | By: Captain Ron Kowalyk

Every boat manufacturer in Florida will give you an estimated figure on your skiff without motor, fuel, add-on equipment and true passenger max load. Now there’s no subterfuge really implied, but the draft specified is for the bare hull. Additional outfitting must be considered when determining true draft capabilities. Other factors will help trim and adjust the true draft of your when not underway, not making way.

Simple formulas initially start with the basic hull boot top or waterline. If your hull is bottom-painted or has a decaled boot top you’re in business to start a formula for determining the true draft while dead in the water. Customarily with the engine down the engines cavitation plate must be under water below the boot top. Cavitation, props, and skeggs will add 7–12 inches to the draft of a hull. In other words, a hull designed to float bare in 10 inches of water may require 24 inches of water to get on plane. Boats designed with tunnel hulls will require less water to get on plane.

Trim and tilt features, fairly standard on modern outboards, will assist in standing starts and shallow water maneuvering. Low-water pickups can be installed that also help reduce initial draft. These add-ons also reduce the risk of engine overheating, very good for extra-shallow water running. Trim and tilt features provide more comfortable running on step and help with fuel efficiencies and reduce motor lugging.

The addition of a jack plate, which moves the mill up and down on a verticals axis, can further reduce initial draft requirements. This feature allows shallow-water startups without causing prop dredging, possible prop damage, and overheating due to clogged cooling water intakes. Generally a jack plate is a necessary add-on for running the flats. Just an opinion!

If you carefully balance your supplementary equipment—trolling motors and trolling motor batteries, livewell positioning, tackle and cooler storage—you’ll have a good start at determining your true draft dead in the water. Perhaps the most significant weight consideration will be the fuel capacity and tank location; this factor will help design the most efficient dispersion of the aforementioned items.

Power-to-weight ratio is a prime factor in getting your hull safely and efficiently outa the hole and on plane. Don’t skimp on powering up your hull; under-powered hulls waste more fuel than slightly overpowered hulls. Under-power hulls lug the engine, take longer to get on plane, and waste fuel. Most hulls come with suggested horsepower consideration from least to most horsepower. The middle options are generally very efficient, unless you’re hauling extra weight. If you max out the add-ons, fuel, and passenger weights, go for an upgrade in horsepower.

Don’t be penny wise and pound foolish when outfitting your hull. A simple formula is,a pound of weight on the stern equal three pounds of weight on the bow; in other words, weight on the ass end increases the draft, lugs the get-on-step time and distance needed to run efficiently.

Capt. Ron Kowalyk : 239-267-9312


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