60 is within reach, what’s next?
23 October 2011
I have been watching Sailrocket’s progress with great interest and there’s no question they have a winner. I fully expect to see them reach 60kt in the near future. Sailrocket has now demonstrated what I first learned with my models and again with my full-sized prototypes, that if you get the forces that act on a sailboat in proper alignment, the only limit to your speed is efficiency (for the techies, that’s L/D) and, of course, the conditions you’re sailing in (wind strength, sea state, etc.).
There have been some interesting comments on Paul’s blog including one asking what you call the craft when it’s only contacting the surface at two points (fore plane and aft foil). Paul’s reply was tops -- that’s it’s an aero-hydrofoil in acknowledgement to Bernard Smith. I titled my patent the same way, to show where my own craft derived from.
I’d like to expand on craft stability with reference to the number of points of contact to the surface. If we look at a child’s wagon we note four wheels that support it stably, whether it’s moving or not. Compare the wagon to a catamaran with the two bows and two sterns being the main points of stability, like the wagon wheels. A tricycle is a bit less stable than a wagon, but still quite stable while at rest or in motion. Compare the trike to a proa in which the bow and stern of the proa form two points and the ama, the third. A bicycle, with two points of contact is totally unstable unless in motion and even then balance has to be maintained by active control, however, if we put “trainer wheels” on the bike, it will be stable at rest or in motion as once again we have four points of contact. A mono-hull and a trimaran could both be compared to a bike with trainer wheels (although I risk the ire of mono or tri sailors for this – no belittlement intended). The monohull uses a weighted keel to add stability to a relatively narrow beam, while the tri spaces the amas fairly widely. There is one more possibility to consider, a unicycle (!) as we know this is unstable under all conditions and it takes great balance and skill to ride one successfully. There are a few sail-craft designs aimed at one point of contact. We can’t go below one point of contact, because as soon as we disconnect from the water, we loose all power (check my earlier posts explaining how a sailboat works using the “squeeze” between the wind and the water).
Here are two sites of craft aimed at one point of contact with the water; I believe there are others but I know of none that are active at this time.
There is really no reason one point of contact can’t be quite successful, however, it will take constant, active control (whether manual or automatic) to maintain stability.