without getting into all the technicalities that make everything hard(er) to understand, the boats are scaled down but the forces(in this case the wind) are not. So the wind is equivalant to a much stronger breeze if you were figuring on the scale up/down factor. 1/12 scale boat, 1 knot equals 12 knots or whatever it is. Sorry to be so vague.
USA2; If it was only that simple! You cant really scale windspeed just like that because the viscosity and and density of the wind doesn’t scale (Insert large amount of confusing areofoil theory here), and also becase the boat is moving slower its apparent wind is natually slower than the fullsize (12m yacht going upwind in 12 knots will see about 20 knots apparent, 1m yacht at hullspeed will see around 13knots, no small difference, dead downwind this inverts as the 12m will have an apparent wind of say 3 knots while the 1m has 10, which might lead to explain why models are more easily overpowered downwind than their big brothers, ignoring the large flappy things the big ones deply downwind).
This might not be all totally correct but I dont think its too far off! I will see if i can find somone to ask…
Luff 'em & leave 'em.
Matthew-
Your right about the density and viscousity of the wind not scaling as easily as i tried to simplify it to. Since the force of the wind is sqared if the windspeed is multiplied, that may also have something to do with the scaling factors. Most of the model yachts i have seen have around scale rigs, with the underbody foils being much more larger than the full size counterparts. Also, the 2.4 meter boats are technically “Mini 12s” but if you look at them some things are different than full size 12s(other than size).
The amount of energy contained in a certain wind velocity per unit area is the same regardless of whether the force is exerted on a large object or smaller one. A 10 mph wind working on a 1/6 scale model is still a 10 mph wind, not a 60 mph wind. Yes, there are some vicosity effects, but the main reason models need deeper keels,etc, is simply scaling effects as I noted in an earlier post:
“Part of the reason “scale” boats may need a longer keel than the original design is the so called “scaling effect”. An object may be scaled down in terms of the lineal dimensions, but ratios of area and volume are no longer proportional. Area dimensions will change exponentially at a square (2nd power) rate and volume scales change at the 3rd power. Since righting moment is dependent on mass (volume of ballast)& distance from the center of buoyancy, the length of the moment arm (fin) must be lengthened to make up for the loss of mass due to the reduced scale. This is why most models need to have disproportionately deep keels (or reduced rigs) in order to sail properly in anything other than light wind.”
Getting back to the original subject, my recent trip to the lakebed yielded a GPS documented speed of 30.3 mph. Sorry, Muzza, just had to sqeeze that in[:D][:-cowboy][:-jump][:-jump2]
Love it! Both the scale explanations and the land yacht speed. I’ve got my hands full with projects at the moment. I’ve been a confirmed monohull sailor for 30 years, but I can see I’m gong to have to add a land yacht to the wish list (and a multi sooner or later).
Muzza