Scale Wind Speed - RC Groups
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Jan 16, 2013, 12:20 PM
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Scale Wind Speed

What is the formula for scale wind speed?


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Jan 16, 2013, 04:03 PM
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DanL's Avatar
Uh, I never figured it out...
Jan 16, 2013, 05:17 PM
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This is pretty interesting tho not totally simple. Pages 3 thru 6, Might be useful.

Swede Johnson's HOW TO Vol 1
Jan 16, 2013, 07:18 PM
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What I've been able to find after going back yet again to Google was that the scale wind effect on a model seems to be a factor based on the square root of the scale of the model. That is, the multiplier for a 1:16 scale model would be 4, the square root of 16, and any given current wind speed would be the equivalent would be quadrupled at model level! Seems as though you guys are often sailing in squalls at the very least!
Jan 17, 2013, 01:26 AM
Taking care of the pond.
This is what I use.
Jan 17, 2013, 09:23 AM
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DanL's Avatar
I have a pretty accurate handheld anemometer. The highest wind speed I remember measuring when sailig Syren (1/24 scale) was gusts of about 15-17 mph. That was enough to really heel her over.
By your formula, the sqr rt of 24 is about 5, so 15 mph would be 75mph - That would be "12, Hurricane" on the Beufort scale.
I think the windiest day I sailed in was with Paratrooper on Lake Minnewaska near St Cloud MN. Maybe Ray can give his estimate of the windspeed on that day. More than 15 I'm sure.
Side note - a handheld GPS unit onboard Syren measured a max speed of 12mph one day. That seems really fast to me, but that's what the GPS clocked.
Some strong wind sailing pics: Syren and Ray's Surprise.
Last edited by DanL; Jan 19, 2013 at 04:32 AM.
Jan 17, 2013, 11:39 AM
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Hi, DanL-
I've got a handheld also- and old Kestrel that I recently put a new wheel on. Got it years ago when I was building and sailing full-size (thought small!) sailboats. I just have trouble imagining a real ship carrying that much sail in most winds equivalent to what's found at most times on most ponds (if that makes sense). Did large square riggers ever sail on their ear except by accident? I don't think so. I don't I think I will mind slow control systems, slow tacks or gybs and slow speed on the water; doesn't that look more realistic?

Jan 17, 2013, 11:54 AM
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DanL's Avatar
Yep, we hold our breath when the gust hits and the model gets bowled over. Best sailing is on a calm, even-winded day. Trouble is, those are rare. So usually sail is set for the avg wind, but all the gusts and swirls keep things interesting.
Jan 17, 2013, 12:54 PM
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one would need to go to and astrologer...a man....astronmer....a plan a trip to the pond....not to mention ...the wife...... a murphy's delight
Jan 17, 2013, 02:28 PM
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Yancovitch and Miller...sounds like my childhood in Milwaukee. Now that I'm grown and moved away, it's Sierra Nevada Pale Ale in California. Thanks, guys, for all the tips about wind effect.
Jan 17, 2013, 09:58 PM
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Brooks's Avatar
Clay, there is no such thing as "scale wind speed." This is because of the interplay of inertial forces and viscous forces (among others). The "Reynolds number" is one attempt to compare models to real sized using inertia and viscosity. As size goes down, viscous forces become "more important." But the Re is only a guideline, it is not exact (the Re number may be exact, but it's effect is always subject to the engineer's skill in interpreting what's happening.)

The same is true for "scale boat speed." For some circumstances, boat lengths/unit time for real and for model is appropriate ( eg. real boat moves 1 hull length/sec, so model should move 1 model hull length/sec). For other circumstances, Froude's method (using square roots, possibly the method you found via Google) is appropriate. You pays your money and takes your choice :-)

As far as what looks "realistic", that is entirely in the eye & mind of the observer. If you are satisfied with what you see at sea, then it makes no difference what I tell you (its too slow, its too fast). It matters not a whit what math either of us trots out to Prove Our Way is Right. It's like trying to prove Monet is better than van Gogh.
Last edited by Brooks; Jan 17, 2013 at 10:04 PM.
Jan 18, 2013, 02:16 PM
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Thanks, Brooks. That makes it all more understandable. To my eye, fast square-riggers, markedly heeling square-riggers and rapidly responding square-riggers just do not look realistic. I guess sooner or later I'll get the chance to work it out for myself. Just painting my hull now, then comes rudder installation, deck furniture, spars and rigging...and only then working out the details of the control system. I guess I'll be lucky if I get her in the water this year!

Jan 18, 2013, 04:41 PM
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Brooks's Avatar
Fast - Real ships of 1800-1900's moved at less than 20kts (about 34feet/sec). That means at top speed, a 100' hull would take 3 seconds to pass an observer. A more 'normal' speed would be half that, so you are looking at 6sec/hull length for a model. My computer keyboard, as a 100' hull, would be about 1:67 scale. Move your finger along the keyboard and time it to 6 seconds, if you want to get a feel for Slooowwww :-). Of course, a modeler can run his model at nearly any speed he wants. It just depends on your level of patience, if you want to mimic scale speeds for sailboats.

My 300' Pamir (3'hull, 1:100) will do a hull length in 4 seconds, 1.5 sec on a broad reach in a scale gale (with appropriate sails flying). At 4sec/hull, she's sailing at 44kts, while the real ship probably never broke 19kts. It would take a sea anchor to slow her to scale speed, but it could be done... if I had the patience. Aldebaran will hit 60kts (finer hull shape, more sail power).
Heel - This is easy to get right if you make your model has sails that can be reefed. The real ships only flew all sails in light winds. Most RC photos and videos I've seen don't show realistic sail sets, so naturally the models don't heel realistically.

You can't control for gusts, of course, but the excess heel that occurs is realistic - clipper ships got knocked down in willi-wa's off Patagonia (just like the school ship Concordia, 2 years ago; she sank but no loss of life). Pamir sank after a near knockdown in the Atlantic; unfortunately, incompetence of the officers led to great loss of life among cadets and professionals aboard).
Speed of maneuvers - Here, lack of inertia, compared to real vessels, hurts us modelers. If you tack your squareship model using real ship times (30-60sec), you will not make it. I have my doubts about a fore&after model taking real ship time too. The drag on the rigging will slow the ship, and she'll falter (convert to a tack with a lee board, or a boxhaul, legitimate real squaresail maneuvers covered in Harland). One reason I don't put a sea anchor on my ships is that momentum=mass X velocity. I can make up for some of the missing mass by using overscale speed.

Wears can be made to take realistic times. It requires a lot of sea-room, if you do it thusly. I don't drag them out, but try to wear with the least loss of sailing pond is small, and a big, sea-room-eating, wear may lose all the ground I had gained to windward. Hate it when that happens :-)
Motion - I found with Aldebaran that the deep fin keel reduced jerky, toy-like rolling, making a more realistic motion. So you can make your vessel roll in a more stately manner if you accept the inconvenience of launch and recovery with a deep keel (I've slopped water over the top of my hip boots by leaning to grab the model).

Putting the ballast at the end of the deep keel also makes it act like a pendulum, dampening both roll and pitch.... another argument against internal ballast.

We can't make waves to scale sizes (the biggest tip-off that a movie model is not real). Models will bob when a real ship would heave. CGI eliminates this hobby-horse motion, one reason studios have replaced neat models with computer screens.

I find it still lots of fun to sail historic models. I just have to tune my expectations a bit :-)
Last edited by Brooks; Jan 18, 2013 at 04:53 PM.
Jan 18, 2013, 07:02 PM
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Thank you!
Jan 19, 2013, 12:19 PM
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i just thought of something which is original to me but maybe to no one eltz ....if i were to remake the sails for my ship, i would make them out of some very flexible mesh material which would allow a certain amount of air to pass through it. a mesh which looks solid, so when the wind she blow blow blow on lac st. pierre, the ship would be able to sail without heeling too much...more scale appearance .....would increase the number of days one could go out.........hope this doesn' t sound silly....
Last edited by yancovitch; Jan 19, 2013 at 03:34 PM.

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