The World’s First Outboard Powered PROA Catamaran is Developed


The World’s First Outboard Powered PROA Catamaran is Developed

By Ron Parker

Aspen Power Catamarans feature a unique patented PROA catamaran design that creates stability, and efficient performance while also providing a platform ideal for maximizing accommodations. They have been building and selling diesel-powered catamarans for a decade and are now are introducing a new series of Outboard powered boats. Larry Graf, the founder of Aspen, developed a revolutionary Power PROA design and drive system where the hulls look identical from the side but upon careful observation fore and aft, one hull is 35% smaller than the other. Each hull is shaped differently since the larger hull is the only driving hull. The inboard models use a single diesel engine, shaft, prop, and rudder in the larger hull to reduce drag. The hulls have unique hydrodynamic properties that work together to maintain tracking. Propulsion and thrust only come from the single larger hull, yet the vessel moves straight ahead. This design has proved to be extremely efficient giving the vessels longer range and modest fuel burn. The catamaran design also provides a wide platform with a lot of accommodation space. Owners get a large roomy interior, ample cockpits, and decks, in a boat with the range of a typical trawler but can run at much higher speeds.

Outboard engines have come a long way, and a lot of boaters are turning to modern outboards for the convenience, economy, and speed they provide. Hearing from some prospects a desire for outboards, Larry set to work to see how his patented PROA catamaran design could best be configured with outboards. Larry founded Glacier Bay Catamarans in 1987 and built many outboard driven cats before selling the company and moving on to Aspen, so he was very familiar with the design of outboard powered boats. He modified the popular C100 hull, first removing the keel and rudder assembly and streamlining the area where the inboard engine is housed. He then added mounting hardware aft for the 200 HP Yamaha outboard, and since a trolling motor had been a common request, he mounted a 25HP Yamaha on the smaller hull. Initial testing of the prototype showed tremendous promise as the PROA hull form seemed comfortable with the new gasoline outboard power. Larry and his team were immediately impressed with the results. The outboard-powered boat handled and tracked well, and reached speeds of 25mph, similar to the inboard. Waterflow aft needed adjustment as evidenced by water bubbling around the engines. The thin yet deep hulls force the water up rapidly after it exits the transom just where the outboards lie.



Having a trailerable boat made this testing easy. The boat was hauled out and brought back to the shop for modification. Foam and fiberglass wedges were created protruding from the transom to extend the hull slightly beneath the swim platform and engine mounts and provide cleaner water flow. Retesting showed improvement, and the additional buoyancy aft also helped the boat’s balance. Speeds improved a few knots, and while the second smaller engine was originally supposed to only be used when trawling, they experimented with running both engines. What they found was that having both engines lowered seemed to improve performance slightly. Removing the keel had affected the balance between the two hulls and having the second outboard in the water helped compensate for this. Since the smaller engine was already in the water, they tried running both engines and found this improved top end speed.


Back in the shop Larry continued to dial in the aft water flow and modified the smaller of the PROA hulls to help compensate for the fact that this hull would now be powered. They also decided to try out a bigger outboard on the small hull. A Yamaha 70 eliminates an expensive jack plate, weighs only 85lbs more, has fuel injection, a larger alternator to keep electronics running even at slow speeds, and has a trolling option. Further testing with this engine combo demonstrated that it was the right combination, but further hull modifications were required. These real-world tests were conducted in salt water, and with weights and water, jugs moved around the vessel to simulate actual loading and conditions.


This valuable testing and modification process yielded excellent results. The 200HP/70HP combination was adjusted to correct the water flow and stop ventilation even while turning at speed. High-end performance yielded a top speed of 32mph with a fuel burn of 23.3 GPH. More importantly, a cruising speed of 20mph with fuel burn of 7.7gph/2.6mpg gives her a range of over 250 miles. The boat accelerates smoothly since the narrow hulls remain in the water, it does not have to push up onto a plane, but gently rises and gains speed. Her handling is concise, turns are sharp and accurate even at speed because of the catamaran hulls’ inherent stability and the fact that they remain in the water eliminating chine walk and skipping during turns.

Larry and his team are satisfied. They have the right combination of boat and power to produce a top-notch outboard driven PROA catamaran. Interested in finding our more about Aspen and the design and testing of the Outboard powered models? Go to;




Original Source: Sportsmans


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