How Hulls Displace Water

July 25, 2017

Vessels move through water by displacing water.    The vessel's bow cuts a path and moves water out of its way.  Water moves in the form of a bow wave or wake.  The more efficiently a vessel's bow displaces water, the faster and further the vessel can move.    The shape of the bow influences the speed and efficiency of water displacement.  Note spray from a bow wave under Mason's board, in the photo below.


 When water does not move out of the way fast enough, it blocks the vessel.  Boats and can add power, surfers cannot.  Moving at high speed, surfers cannot stay on their feet with abrupt changes in speed.














 Flat bows push water forward in the boats path, before directing it around the vessel.  This restricts speed in rough water.  Flat hulls are only efficient in flat water.  




Most ship and boat hulls use a Vee bow because it cuts through water effectively.   Round hulls absorb impact while moving water aside, like sail boats or canoes.  Many ships and boats use a combination of round and Vee. The following video demonstrate how a boat planes.





Surfboards plane like speed boats, on their tails.  The bow is out of water when planning. The bow contacts water when there is an irregularity in the water surface like a chop or trough.  At high speeds, when the bow is flat, a surfboard can stop on impact with water.  To efficiently maintain speed, a surfboard must be able to push water aside.  Vee or round bows will produce these results in large steep waves.



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