Single Engine Catamarans are becoming more popular due to their larger interior space (compared with their mono-hull counterparts) and the quality, stable ride they provide despite the smaller size of the rig. However, they still have a few “quirks” that will be remedied with a Permatrim. Single engine cats tend to have ventilation issues because of the style of the hull and engine location. With a single outboard engine mounted in the center of the tunnel section, aerated water that moves through the tunnel travels past the propeller. Engine transom height is very important in outboard engine installation. If installed too low, the outboard will be too low in the water and push water forward, towards the transom and create drag while underway. Engines that are mounted at the correct height allow the propeller to be placed directly in the heavier current of water, but without a Permatrim there is still increased chance of propeller ventilation. Turning at planing speeds with a single engine Cat may also send aerated water from the inboard side of the sponson to the tunnel section. For example, on a hard port turn the sponson on the port side will shoot aerated water from lifting strakes into the tunnel section and then send it towards the engine/propeller, again increasing the chance of propeller ventilation. With a Permatrim installed, the engine transom installation height will be at a higher level and still keep the aerated water away from the propeller.
We own a 16 ft. Livingston Cat with a Yamaha F75 outboard, so I am personally familiar with this type of boat. With a Permatrim installed, I can have the engine at its correct height and the engine performs as intended and even similarly to an equally sized mono-hull. Propeller ventilation is diminished, with rare cases when the boat is overloaded with added weight. Other benefits of installing a Permatrim include lower planing speeds, reduced bow rise while accelerating, and better turning with the ability to lower the bow more easily in choppy waters.
Along with the Permatrim we are also running a Powertech 4-bladed SS propeller, which improved the performance as well. If you are running a single engine Cat, in addition to installing a Permatrim on your boat, I would highly suggest installing a 4-bladed Powertech propeller.