Whether we like it or not, we are committed to some 160 g. of electronics. If that was the ONLY weight involved, on a 12” waterline we would have a displacement/length ratio of 157. This is potentially a surfing hull and occasionally capable of a sustained plane when given a little assistance by a wave. For comparison an IOM has a displacement/length ratio of around 111. However, a 500 g Footy has a displacement length ratio of 491 !
Brett’s scow Moths (I’m guessing the figures – Brett correct me if I’m wrong) had a waterline length of about 10 feet and a displacement of around 250 lb (allowing 140 lb for a youthful Brett). This gives a displacement/length ratio of 111 – coincidentally (honest) identical to that of the IOM. Given that the scow Moth is much wider and shallower than the IOM in proportion, it is not surprising that it planes well.
Where does this get us?
I think that it leaves us in the position that a ballasted planing Footy is impossible. Merely adding 50 g. for hull, deck servo tray, rudder to the weight of the electronics gives a displacement length ratio of 206 (probably optimistic) which will give an occasional wild surf. When my father’s half tonner Skulmartin (displacement length ratio about 255) climbed onto a wave one dark and stormy night and took off like a rocket (speedo off the clock at 12 knots) it was such a surprise that I vividly remember it almost 40 years later.
That’s the boring naval architecture numbers. Now somebody come up with some imaginative solutions.
Just another thought - a vane-steered Footy could be about 150 g. lighter - so say Disp = 350 g. This gives a displacement/length ratio of 343 which is in line with successful full size racing boats of the early to mid 1970s. It’s still not fgoing to plane, but it should be faster.
maybe try
4 x lithium Energiser AA batteries 58g
lightweight RX…around 10g maybe less
micro rudder servo 9g
micro digital ball raced 4.1kg torque sail servo 17g
Total weight of radio 94grams
Still don’t think you will plane though,displ/length ratio is one thing,you need power to carry sail to generate the force required.
btw modern moths don’t plane(not talking about the foiler moths)
the narrow (350mm wl) skiffs slice through the water like a catarmaran hull.
Since the mid 80s this way has been found to be faster than planing(scow style)
The overwhelming ratio in force here is the righting momment…you need to generate as much power as possible whilst staying upright.
Bethwaites book “High performance sailing” has the the low down on all this.
Without doing the sum. you’rte still talking about a displacement length ratio in the high 300s - S&S leadmine 1-tonner. ‘Only level withe you at the leward mark, up to weather a minute a mile faster’.
Some time ago we wrote here of a Footy design called “Ode To Roger”
It was drawn by Bob or Charles and was based on the Roger Stollary “Crazy Tube” type designs.
Well I have been thinking about it for the last six months and had drawn my version about five months ago.
Today I finally got the urge to move on with it and had a little play (as you do, right)
Here is what I did…:graduate:
Cardboard cutouts… sounds like therepy…ha…it is.
Anyway it taught be a few things which should make the build go easier.