What they do
Hydrofoils are inexpensive, nearly indestructible plastic wings that bolt onto the cavitation plates of outboard or sterndrive engines. They help a boat run at a more level fore and aft trim and correct bad habits that can make life miserable aboard small powerboats such as runabouts, inflatables, center consoles, bow riders and pontoon boats. If your boat suffers from any of the following ills, hydrofoils may help give it an attitude adjustment:

Hydrofoils, Trim Tabs and Power Trim
Hydrofoils are not the only products that can overcome these defects. Trim tabs, adjustable flaps attached to a boat’s transom, are available in either hydraulic or automatic (non-powered) styles, and provide the same trim correction. Trim tabs also can correct a list (side-to-side weight imbalance). Costing several times more than hydrofoils, hydraulic trim tabs can be owner-installed with common tools. Rocker switch controls at the helm let you precisely control your tabs.

Automatic, non-hydraulic trim tabs work like shock absorbers using nitrogen gas cylinders, and require no adjustment while under way. Priced in between hydrofoils and hydraulic tabs, automatic tabs require no through-transom plumbing and are simple to install and to adjust when the boat is on the trailer.

Power trim and tilt controls allow you to change the vertical angle of your outboard or sterndrive, pivoting it forward or backward, and this accomplishes many of the same results as trim tabs and hydrofoils. Adjusting trim and tilt can also help hydrofoils work better at high speeds, where they would otherwise tend to press the boat’s bow down. We have seen boats using combinations of all three devices, hydrofoils, trim tabs and power trim and tilt.

Product Selection and Installation
Hydrofoils come in two size ranges. Installation is a quick bolt-on process, and requires drilling four holes in the cavitation plate.

Conclusion
We have used hydrofoils on small boats, especially tiller-steered outboard powered inflatables, and find them to be a simple addition that improves performance, but have done no scientific testing. Davis Instruments claims that their Doel Fin provides a fuel savings of up to 30%.

For a different point of view, we turn to the competition; John Diagro, who manufactures the Nauticus SmartTabs automatic trim tab systems. He says that hydrofoils are too small to work at low speeds and cause a bow-down attitude at speeds over 30mph (easy to correct if you have power trim and tilt control). He also believes that trim tabs offer more stability in turns, because they lift the outer corners of the stern, instead of the center of the hull below the waterline. Trim tabs may produce flatter cornering, and models with “Batwing” drop fins on the outer edges (like the Bennett Super Sport Tabs) will also help prevent skidding during fast cornering.

In fairness, we like the simplicity of hydrofoils, with no possibility of damage (as is possible with trim tabs if we accidentally back our boat into a dock or piling). With the price of gas and diesel at record levels, we believe that all of these boat-leveling devices will quickly pay for themselves in fuel savings, in addition to enhancing the way our boats perform.