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BOAT SPEED

Speed of a sailboat something many potential owners overlook in favor of other presumed qualities of the vessel such as 'seaworthiness', etc. It is, however, one of the primary considerations the shopper should be looking for as it affects safety in a manner far more effective than the before-mentioned idea of 'seaworthiness'. Speed is safety. The less time you are in harms way, the safer you will be. It a function of boat design and can, to a large extent, be predicted and even calculated. There are four main areas to consider. 

The hull displacement is the first thing to look at. The term 'seaworthy' has been defined as the ability of sailing safely at sea. Unfortunately, this simple definition has been misapplied to overly heavy hulls, and some have even gone so far as to note the presence of certain equipment or materials, and deduce the boat is 'seaworthy' (i.e. wood construction, brass port-lights, etc). Unfortunately, the 'seaworthy' considerations should be directed at the hull integrity, and hull integrity is difficult to estimate, and unrelated to weight or materials. A proven design with quality construction with whichever chosen materials (and simple, as less detail means less potential failures) can be very strong without being overly heavy. Weight, or displacement, is the first factor in speed performance, as for every pound of displacement a pound of water must be moved in the boats passage.

The next factor in speed is the waterline length (LWL). In a non-planeing vessel (one which cannot leave the water as many small powerboats do) the maximum speed is a mathematical function of waterline length (1.34 times the square root of LWL). Note that waterline length is not the same as overall length. A vessel with protruding bowsprits or extending transoms (i.e. canoe transoms, overhanging transoms) will only cause the owner to pay more in moorage fees! In fact, the best way to increase waterline length is to do the opposite, and fast hull designs have a very blunt or 'destroyer' bow, and a reverse transom (looking like the transom 'overhangs upside down' as it is swept back towards the surface of the water).

A full keel, as opposed to fin keel, has been the normal feature of offshore boats for many decades. It provides tracking ability, extra impact protection (torque only), and 'dry-out' ability using tides. It does, however, add to the next factor in speed which, is wetted surface. Friction caused by the hull surface. The more hull (which includes keel) the more wetted surface and the more drag from this friction. In addition to increased wetted surface when compared to fin keels, full keels are not as hydro-dynamically efficient as a well designed fin keels. The higher aspect (deeper and shorter) fin keel is faster, and one should go for the maximum aspect ratio that can still provide (with construction method) a reasonable amount of strength against impact, and remember that any keel types will be destroyed in impact with large logs or shipping containers.  

The last item in a quick and simple evaluation of speed is sail area and is applied to the rig (mast, boom, etc.). The more the merrier in this feature. You can always reduce sail area on a large rig, but you will never grow a bigger one when you need it. The higher aspect rig wins out here too, as did the high aspect fin keel, so the operative phrase is 'tall mast'. Bowsprits and long booms provide more sail area, but they are  lower aspect sail plans and are not as efficient as a taller sail plan.

There are computer programs available to work with these and other variables and calculate and compare sailboat speed performance, however PHRF Ratings (performance handicap racing fleet) can be found in database form and easily printed and referenced before a yacht purchase. There are slightly different databases for different areas, as these ratings have also time-tested in those areas with their particular wind, but for the most part the numbers are consistent. The lower the number, the faster the boat has performed in historic racing. 

With a very fast boat, your passage times will be as much as a third or half. This relates to less stores to carry, less time in storms (and easier staying inside forecasted weather windows), less time on watch looking for flotsam, and more reserve speed to counter very strong ocean currents. All this increases your safety and this is what 'seaworthiness' is all about. Plus you will be better rested with more time to spend enjoying your recreation on arrival.