Cavitatation Plate or Whale Tail?

What is the difference between a cavitation plate and a whale tail and when do you know if you need one or the other?

Outboard engines are equipped with an anti-ventilation fin, an integral part of the mid-section casting, located directly above the propeller.

The cavitation plate, or more correctly anti-cavitation plate, is a full-wrap device that is secured completely around the anti-ventilation fin, extending both forward and trailing behind the outboard's midsection.

The whale tail is not a full-wrap, designed to be installed on the anti-ventilation plate, extending only behind the midsection.

There are many manufacturers that build these great products and each one has a variance that caters to specific desirable results.

The cavitation plate is very desirable on most tunnel hull designs. We prefer to use this on the boats that have a full tunnel.

There are three types of tunnel hull boats.

Full tunnel - The area starting from approximately under the boat's center console, center of the keel, designed into the hull going all the way to the transom. (Used to feed water to the prop while on plane and to achieve maximum shallow water ability while using a jack plate).

Half tunnel - Same as above but the tunnel starts further astern between the center console and transom, approximately mid-way. (Function is similar but not as aggressive as the full tunnel).

Pocket tunnel or no tunnel - This would be described as more of an indentation or pan-shaped depression at the keel going toward the bow approximately 8 to 15 inches. (This is usually very moderate and is intended to provide greater stability for the hull while increasing shallow planing performance.)

The cavitation plate would be used on full tunnel hull applications where the desire to get up shallow would be enhanced by forcing the bow down and creating lift on the furthest most point rearward on the boat. (The theory of hydraulics - you can't compress a fluid).

This also keeps water around the propeller while getting up on plane, maintaining plane in shallow water, and allowing less cavitation while turning. (Anti-Cavitation in this case - would be described as improving the propellers ability to maintain a solid bite - minimizing slippage due to air being introduced into the stream of water feeding the prop while running.)

The whale tail also helps reduce cavitation on boats with partial or no tunnels and really enhances the same abilities but in a less aggressive way. These also are great tools for boats that have stabilization issues or have to compensate for bow porpoising while on plane.

Think of the cavitation plate or whale tail as a water suppressor and great performance enhancer.

Have a great boating season,

Chris Mapp

Coastal Bend Marine
Port O'Connor, Texas
361 983 4841