Catamarans International Model Testing Program
Model Testing; 1:10 scale models of 15metre (50ft) Powercat
Catamarans International has invested tens of thousands of dollars on extensive models testing. 1 to 10 scale models have been made and tested of a typical full displacement catamaran and a typical semi displacement style catamaran. These were then tested against the new generation hull form that has been developed by Catamarans International. Testing over 5 different test sessions were carried out and refinements made on each occasion to the new generation models. These refinements to the New Generation hull were not just related to resistance but were also aimed at ride angle, wave action, spray generation and spray down turn. Once the New Generation hull had been clearly defined as offering significant improvements over the full displacement and semi displacement models we then developed a second identical New Generation model. We used this to new model to make small adjustments to the hull design and tested these refinements against the existing New Generation hull. A further 5 test sessions were carried out to test these refinements and in December 2006 we finally settled on the hull shape and the manufacture of the full sized hull then commenced.
This photo is of one of our first model testing sessions with the New Generation hull developed by Catamarans International. We used computer drafting combined with extensive research and years of experience with power catamarans to come up with the design for the first 1 to 10 scale model.
This first model showed excellent promise from the outset. We built an almost identical model so we could run accurate 2 boat testing sessions to further maximise gains we had made and to refine the hull shape, bow profile, spray rails and foil design. These tests resulted in a hull design that provided minimal wave making and very little spray, a sign of a highly efficient hull.
This photo shows a typical semi displacement hull form which we tested initially against the new generation hull. Typically the bow ride angle of the typical semi displacement hull form is higher and increases at speed and the wave and spray generated was greater than the New Generation hull form. This testing was very helpful in enabling us to establish trend lines in hull form and hull characteristics and to also confirm the advances we had made on the New Generation hulls.
The owners of Catamarans International currently own a 15 metre (50ft) semi displacement catamaran, (pictured above). The wave making of this full size Catamaran and the typical 15m semi displacement 1 to 10 scale models are very similar, as can be seen in the photos. In the tests we conducted we found the characteristics of the model and full size vessel were very similar.
This included tests loading the full size vessel with 3,000 kg’s of additional weight and then doing the same in scale form with the model to compare the accuracy of the date we were collecting. The full size vessel had foils fitted after it had been in the water for 3 years. We did tests with the model with and without foils and compared that to the performance of full size craft before and after it had foils fitted. The results achieved between the model with and without foils were very consistent with the actual figures achieved on the full size vessel.
Model Testing
This photo is of a 1 to 10 scale model of a 15 metre (50ft) typical semi displacement hull form fitted with foils and at a scale speed of 26 knots. Note the bow is lifting and the stern is sucking down. The wave creation aft and the spray making along the topsides of the model were to prove very similar to the full size semi displacement powercats. Our testing results showed the New Generation hull offered significant advantages over the typical semi displacement hull form in both efficiency and in ride and motion.
This photo is a 15 metre (50ft) semi displacement powercat fitted with foils and doing 26 knots. The angle of attack, the spray generated along the topsides and the wave pattern created were all very similar to that produced on the semi displacement styled models we tested as shown in the photo immediately above.
The wave making and spray was significantly less on the New Generation models we tested compared with the typical semi displacement models tested.
Other tests included studies on rate of immersion and pitch and roll speed. In this photo a full displacement hull form is been compared to the New Generation hull form Catamarans International have developed. Both models had the equivalent of 2,500 kg’s (5,500lb’s) placed on one side.
The narrow water plane area of the full displacement styled cat gave a massive increase in rate of immersion and was also subject to significantly quicker and more severe rolling motion. A similar experiment weighting the bows of each model had similar results with the full displacement hull having a significantly greater sensitivity to fore and aft trim. The New Generation hull provided a level of stability that would generate a far superior ride and give improved sea keeping characteristics.
Model Testing: One Tenth Scale Models
Models tested were of the same size and tested at the same speeds, over similar conditions and with the same displacement. The photos on this page were all at model speed equivalent of 20 knots.
Scale model of 15 metre New Generation Hull Form.
Note the very low wave and spray making.
Scale model of 15 metre Typical Semi Displacement Hull Form.
Note the wave and spray making.
Scale model of 15 metre New Generation Hull Form.
Note the minimal spray and very clean tunnel.
Scale model of 15 metre Typical Semi Displacement Hull Form.
Note the choked tunnel and spray.
Scale model of 15 metre Typical Full Displacement Hull Form. Model was efficient up to 16 knots but was very subject to pitching and to load variations. In full size it has major limitations when fitting accommodation and engine installation due to the very narrow hulls. The very deep forefoot also showed a greater tendency to bow steer than the other models tested.