I was going through my literature archives the other day and came across a copy of the original Kiekhaefer Aeromarine, Inc., K-Plane Trim Tabs sales brochure. I’ve always respected the quality and functionality of Kiekhaefer’s literature. I thought a blog post regarding the history of K-Plane trim tabs would be of interest. More importantly, it will serve as a refresher regarding the fit, form and function of the world’s most durable trim tabs.
Kiekhaefer Aeromarine Motors first introduced K-Plane Trim Tabs in 1970. They were designed to keep the fastest, hardest running racing boats on an even keel in just about any water condition. US (APBA) and World Offshore (UIM) champions, Doc Magoon and Carlo Bonomi ran nothing else. In the mid 70s, Fred Kiekhaefer upgraded the product for recreational use.
If you have read our Prop School blog series, you know the name of the game is efficiency. You want to select the most efficient prop, with minimal slip combined with optimal outboard/sterndrive trim for maximum hull efficiency. That is all well and good. But larger vee-bottom hulls need assistance in a variety of modes of operation. This is where the trust worthy K-Planes go to work.
Getting on Plane
Trim tabs work in-concert with outdrives when powering a boat on plane. Tucking the drives under and the tabs down forces the bow of the boat down. This brings the boat on plane quicker, without a loss of visibility. Once on plane, the operator first trims the tabs up and then trims the drives out until the most efficient running attitude is achieved.
Heavy seas can create an uncomfortable ride. I’ve experience this more than once. One of my most memorable rides was with Vic Spellberg in the 2006 Chicago Poker Run. Lake Michigan was especially rough that day. The 380S K-Plane trim tabs earned their spot on the transom that day for sure.
Tabs, when put in a level position with the bottom of the hull, act as hull extensions or after planes. As a wave throws the bow up, the tabs dampen the boats reaction, leveling and smoothing the ride.
Tabs and drives should be trimmed up when operating in a follow sea. The raised bow will compensate for the waves lifting the stern. Tabs are also used to fine-tune the handling of a boat such as a catamaran that may have a gentle bounce or porpoise when accelerating to optimum running speed in mild water. In this case, the drives are set at their optimum trim. Dropping the tabs, a touch at a time, will dissipate the porpoising while maintaining hull efficiency.
At idle, trimming tabs full down will slow boat speed, reduce the wake size and straighten the boat’s track.
Sea conditions or an unbalanced load may cause the boat to lean (or list) to one side or the other. List may occur in a quarter following sea: The waves lift the stern unevenly, causing the boat to pitch forward and roll opposite the lift. Dropping the tab opposite of the side being lifted will correct the listing for a dryer ride. Similar adjustments can be made for boats listing due to an uneven load. Bumping the tab on the heavy load side down will cause the stern on that side to lift, leveling the load.
Seeing is Believing.
Boats equipped with K-Plane trim tabs require a trim indicator that provides the operator an accurate, real-time reference of both drive and tab positions. Mercury Racing continues to offer a full array of mechanical trim indicators first developed by Kiekhaefer Aeromarine for use with sterndrives, outboards and K-Plane Trim Tabs.
Recent updates include the addition of a SmartCraft electronic trim sender on 150S, 280S, and 380S K-Planes. The electronic sender provides the option of having drive and tab trim positions displayed digitally on a variety of large, easy-to-read electronic displays available from Mercury’s SmartCraft Vessel View to Garmin and other suppliers.
I hope this helps explain what those black metal plates extending off the transom do and how you can use them to make your next boating excursion more enjoyable.