Rick, "The Crouch formula is nonsense applied to a displacement hull. I can get it to give 16.8MPH with a 9900lb hull using 40HP -absolute nonsense. It is meaningless. It can produce any figure you want depending on the Hull Factor chosen but then does not produce a cube relationship for a given Hull Factor that is a fundamental where viscous drag dominates."
I don't think you understand what the Proa Hull is or what the limiting factor for a displacement boat is. For a displacement boat it is the square root of the boats wavelength that dominates, 1.34 times the square root to be more precise, NOT viscous drag. What is happening is that the curved hull starts generating infinite lift (downward) at hull speed. Unless the boats bottom is fouled, viscous drag is relatively minor. Skegs, rudders, props, shafts, hull shape, cavitation, ventilation, etc can all produce more drag than clean laminar flow viscous drag.
A fast displacement hull on the other hand does not produce the 'lift' a curved bottom minimal wetted surface hull does with the bow climbing a wave and the stern in a hole.
If you will look at any of the HP videos you will see that the bow is down piercing the waves and the stern is up with minimal waves being created, clearly the hull is planning. The Hull design and shape is almost perfect, it would be perfect if the hull was perfectly flat.
But don't take my word for it, look at the videos, the video that you posted shows it clearly.
__._,_.___
Posted by: taladorwood@yahoo.com.au
| Reply via web post | • | Reply to sender | • | Reply to group | • | Start a new topic | • | Messages in this topic (27) |
.