by Luke Shingledecker, Naval Architect
The trim tabs on the Farr Yacht Design Open 60’s PAPREC-VIRBAC 2 and GITANA 80 were inspired by the trim tabs that are quite common on powerboats. On powerboats, the tabs are generally hung off the back of the transom, while on our Open 60’s, they are underneath the aft end of the boat and do not extend past the transom. Motor boats only operate upright and are not as concerned with drag as a sail boat so they can get by with relatively narrow tabs, but since sailboats operate at a wide range of heel angles, the trim tabs on our Open 60’s extend almost the entire width of the boat.
The tabs allow the sailor to vary the fore and aft trim of the boat (bow up/down, stern up/down). Since these boats are very light for their size, they respond to the movement of weight forward and aft, exactly like a dinghy. In fact, the boats sometimes carry as much as a few tons of water ballast, and one of the primary reasons for this is to adjust the trim. By lowering the tabs, the flow of water over the tabs is deflected downwards, pushing up the stern, and marginally lowering the bow. The tabs can also be raised to decrease the lifting pressure on the stern, allowing the stern to sink and lift the bow. By adjusting the tabs for the conditions, drag can be reduced and handling can be improved. In moderate conditions, the tabs are adjusted to optimize trim, while in heavier conditions, the tabs can be raised to pick up the bow and improve handling. When combined with the effect of moveable weight (sails, gear, etc) and water ballast, the tabs significantly increase the amount that trim can be varied across the wide variety of conditions these boats see when sailing around the world.-Luke Shingledecker, Naval Architect
