Jan 16, 2013, 11:20 AM Registered User Joined Apr 2010 61 Posts Question Scale Wind Speed What is the formula for scale wind speed? Thanks. Clay
Jan 16, 2013, 03:03 PM
Registered User
United States, MN, Brainerd
Joined Oct 2004
2,488 Posts
Uh, I never figured it out...

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 Jan 16, 2013, 04:17 PM Registered User Joined Feb 2009 25 Posts This is pretty interesting tho not totally simple. Pages 3 thru 6, Might be useful. Swede Johnson's HOW TO Vol 1 issuu.com/fcb2868/docs/img
 Jan 16, 2013, 06:18 PM Registered User Joined Apr 2010 61 Posts 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, 12:26 AM
Taking care of the pond.
United States, CA, Sanger
Joined Apr 2004
7,492 Posts
This is what I use.

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Jan 17, 2013, 08:23 AM
Registered User
United States, MN, Brainerd
Joined Oct 2004
2,488 Posts
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.

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Last edited by DanL; Jan 19, 2013 at 03:32 AM.
 Jan 17, 2013, 10:39 AM Registered User Joined Apr 2010 61 Posts 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? Clay
 Jan 17, 2013, 10:54 AM Registered User United States, MN, Brainerd Joined Oct 2004 2,488 Posts Clay, 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, 11:54 AM Registered User Joined Oct 2006 899 Posts one would need to go to and astrologer...a psychic....weather man....astronmer....a visonary...to plan a trip to the pond....not to mention ...the wife...... a murphy's delight millertime...
 Jan 17, 2013, 01:28 PM Registered User Joined Apr 2010 61 Posts 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, 08:58 PM Damp and Dizzy member Bozeman, Montana, United States Joined Aug 2003 3,496 Posts 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 09:04 PM.
 Jan 18, 2013, 01:16 PM Registered User Joined Apr 2010 61 Posts 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! Clay