Today's Topics: 9. Fin stabilizers on cats (Georgs Kolesnikovs) 10. Re: Fin stabilizers on cats (Robert Deering) ---------------------------------------------------------------------- Hello Tim, We're currently exploring static "T" foils for our TCM 49' GT (Green Technology) power catamaran and we've designed the foils to have a large surface area, chord length and angle of attack that we believe will start to provide effective lift at 9 knots and maximum lift at 15 knots at which point they should support 30% of the boats weight. The "T" foils are optional and will be mounted on heavily re-enforced areas on the under wing deck three feet above the water and extending 3' below the water so that if they were to hit something catastrophic and break off no water can enter the hulls. This is unlike other foil designs that are attached to the bottom and sides of the hulls. Using aeronautical theory, computer math and experience we have a design we believe will provide lift at 9 or 10 knots or when the boat gets over the 'hump'. At this point it will commence supporting and lifting the 29,000 lb of displacement and lift will continue to increase with increased speed until the foils reach equilibrium with the weight they can support from the density of the water. Bernoulli's principle applies equally as well in water as it does in air and water being over 800 times denser than air we know that lift can be achieved at slower speeds in this denser body. I used the same principle to design a wave energy generator capable of supplying power to a power grid and the same principle has been well proven in the UK with tide generators. The 'T' foils also act as vertical motion dampers and as the hulls commence to be raised up by a wave the top surface of the foils exert a pressure that resists the upwards motion. Conversely when the hulls are forced down the bottom surface of the foils exert a pressure that resists the downwards motion. The combined effect will be a much smoother ride which will improve the boats performance and the level of comfort onboard. We are well aware of the increased drag the foils will induce, but we feel confident that the improvements will be well worth the trade off. We are also considering having them tilt up for slower speeds when they are not effective, or if they should strike a solid object, but this is another complication so the jury is still out on that one. Unfortunately this is proprietary information for now so I cannot share it further. Cheers, Graham Captain Graham Pfister President & Principle Designer TrawlerCat Marine Designs ------------------------------ Message: 9 Date: Sun, 15 Nov 2009 20:46:55 -0500 From: Georgs Kolesnikovs <gxk@earthlink.net> To: Power Catamaran List <power-catamaran@lists.samurai.com> Cc: Tim Chrisp <tchrisp@cedenco.co.nz> Subject: [PCW] Fin stabilizers on cats Message-ID: <79EB2508-503B-4B73-8A14-9A7BA56A5000@earthlink.net> Content-Type: text/plain; charset="us-ascii" From: "Tim Chrisp" <tchrisp@cedenco.co.nz> Date: November 14, 2009 5:38:11 PM GMT-05:00 To: <power-catamaran@lists.samurai.com> Subject: fin stabilisation Dear Sirs, I am not sure if your forum is still operating bit I am keen to hear if anyone has experience with passive fins set between the hulls of a displacement catamaran for slow or modest speed stabilisation. Look forward to hearing from you Tim Chrisp New Zealand