Reply to Derek Kelsall. Like Derek I have been designing catamarans for more than 40 years. For 26 of those years I have been designing power catamarans and all that experience means that I very much concur with his comments concerning the variables that are important when designing a power catamaran. Derek is talking about "straddle stability" conferred by the beam of the power catamaran being an important factor in the seaworthiness of catamarans. There is a very good discussion on this particular aspect in a paper presented to a US Coast Guard symposium in 1988 by John Shuttleworth. This was called "Multihull design considerations for seaworthiness" and can be read on www.john-shuttleworth.com This is primarily concerned with sailing multihulls [there really were no ocean going power multihulls at this time] but take off the rigs and the basic premises are still true. It is worth noting that the Crowther designed ferry tested at Southampton has a cabin that extended right out to the gunwales. This is very common in catamaran ferry design [most of our ferries are also of this configuration]and our stability calculations show that a power catamaran of this configuration still has a poitive righting moment when lying on its side.Hence the difficulty of actually capsizing such a vessel in the test tank.We have used this configuration in several of our pleasure power catamaran designs. Might be worth retaining for off shore power cats. Derek is correct. Most power catamaran designers are now using a displacement hull form. The one most of them [including Derek] are using is the one that was developed in this office in 1983 and that we have called the "CS" hull form. This wasn't always the case. When we started designing displacement power cats [in 1979] everyone "knew" that you could not go fast in a power boat unless it planed. So a high speed displacement power cat was a contradiction in terms. Even the high speed catamaran ferries of those early days were using low deadrise planing hull forms even though it was painfully obvious, to me anyway, that there was no way that they were planing and that they should have been using round bilge displacement forms.It took a few years but our displacement hull form is now the de facto standard. Given that, both Derek and myself are bemoaning the tendency to lump all power catamarans together,here might be the place to attach an article I wrote for PassageMaker magazine. [see attachment]This tries to differentiate between the different types as much as possible to hopefully allow you to make an informed decision about which type, if any, is the most suitable for you. Georges has asked that perhaps I could list the power cats of our design that have crossed the Pacific:- To the best of my knowledge here is a list. I supect there may be some more that I do not know about but here goes. Awesome 2000:- Sometime around 1996. From Long Beach, California to Hawaii. This was the boat belonging to Jack O'Neill of wet suit fame. I believe the average speed for the trip was around 20 knots. I do know if they made the return trip. I also believe that a number of this particular design may have made the same, or very similar, trips. Bluefin 60: This was "Superfun" that travelled from New Zealand to the Philippines. Not sure when exactly but around 1988. Has since travelled from the Philippines to Australia. 14m Ferry: this was one of the ferries [14 in all] built for use when building the Hong Kong airport.These are now scattered all over the world. At least one travelled from Vanuatu to New Zealand in 2000.Is now operating in the Marlborough Sounds. Ka Ipo Manutahi: One of our Barracuda design that went to Hawaii in 2002. Icebear: New Zealand to Hawaii in 2002. WildWind IV: Dennis Raedecke's now well travelled cruiser went from New Zealand to Seattle in 2002. Pacific Harmony: From New Zealand to Fort Lauderdale in 2004. I hope all this has added a little more to the discussion about power catamarans. Malcolm Tennant Multihull Design Ltd PO Box 60513 Titirangi, Auckland 1007 NEW ZEALAND ph +64 9 817 1988 fax +64 9 817 6080 e-mail malcolm@tennantdesign.co.nz www.tennantdesign.co.nz www.catdesigners.com