[PSUBS-MAILIST] Velocity and Acceleration

["Marsee Skidmore" <heyred@email.msn.com>]

My two cents on the speed and power of personal submersibles:

 

A submerged body has the inertia of its displaced volume of water. Wet, dry or anywhere in between, the mass of a submerged boat is equal to the mass of the water it displaces. This mass has a large effect on the acceleration (how quickly it starts or stops), but has no effect on the velocity. The velocity is determined by thrust and drag. Velocity is hard to calculate with certainty because of the many and mysterious elements of drag (profile, skin, wave, parasitic), and the complex interactions of hull, prop and water. Authors of cookbooks tend to present their formula without showing their homework, which is unsettling for those of us without the gift of faith. If I have enough cookbooks to compare, I'll eventually develop some confidence in a common thread. But we have the additional disadvantage of dealing in an obscure cuisine (small, low powered displacement hulls.) I'm always on the lookout for applicable formulae, but I haven't found anything short and sweet. - Joe