"Sneezing" is primarily caused by the bridgedeck being too close to the water. However, as always, it is not quite that simple. If it was, simply raisng the wingdeck at the design stage would remove the problem. As the boat pitchs and heaves air pressure is increased in the tunnel. If it cannot exit cleanly astern then it exits at the bow and in the process takes water with it- "sneezing". This phenomenon can be exacerbated by the shape of the bridgedeck . On most designs the bridgedeck sweeps up at the bow which creates a "ram effect" thereby causing even higher pressures in the tunnel. But of course if something like this is not done then the leading edge of the bridgedeck will slam sooner and harder. So what to do? Firstly just make the bridgedeck clearance greater. The bridgedeck can also be swept up further aft and have a flat deck up at gunwale level. This latter approach will not stop the "sneezing" but will allow for an "expansion" chamber up forward which will stop it blowing back over the boat. "Sniffling" or water blowing back from the bow of a displacement catamaran can be caused by a number of things, either alone or in concert with each other. The blunt bow we see on so many cruising sailing cats is perfect for creating a fine mist and the same applies to their use on power catamarans. The simple answer to this is to use fine bows, very fine bows, which stops the water climbing up the stem. However this is not easily moulded in glass fibre. We have occassionally fitted stainless steel "cutwaters" to a boat if sniffling is a problem. These need to be sharp so don't do it on Dolphin and Whale watching boats! This climbing of the water up the bow is compounded if the blunt stem is also vertical. Even on our racing sail boats we put at least 50 to 60mm of rake in the stem. You can also fit a "knuckle" but this must be exactly the right height, shape and size. If it is too high it will either do nothing or break up the bow wave into fine droplets which are then blown back over the boat. If it is too low it will slap when you are at anchor which is not conducive to a good nights sleep. If it is too wide and the wrong shape it will slam and may actually cause the boat to lurch in a beam sea. Just to make life difficult for the designer, the height of the knuckle and the wing deck will change. On a long range cruising boat which is carrying a lot of fuel the height may vary up to 500mm [18"] between lightship and full load displacement. Regards, Malcolm Tennant. 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