1.34 times square root LWL and model yachts?

[grumpy_o_g]

...It's deceptive, I think we tend to look at them and judge their speed as fast in proportion to their size, not the sqrt of it.
Then there's the telephoto lens effect.
But even so they still look quick to me.
They race on a pond near me, but it's at a time when I'm normally racing my boat.

I agree, I think it is mostly perception. Model cars look like they're going incredibly fast but aren't really and model aircraft can be really dangerous to a pilot - they look incredibly fast until you are in an aircraft yourself in the same piece of air and realise you're about to hit the thing up the chuff at a considerable speed differential.

 

[johnalison]

The visual illusion is just due to the scaling. If a 1 metre model yacht is doing the 2 knots or so mentioned, then visually, it would look like a 10 metre yacht doing 20 knots. A similar thing occurs between yachts of very different size doing their maximum speed. With super-size yachts, it is sometimes only when you look at what is happening to the water in their bow-wave that you realise how fast they are going.

 

[lw395]

A 1 metre yacht at 2 knots is travelling more than one boatlength per second.
A 10 metre yacht at 8 knots is doing less than half a length per second.

The 10 metre yacht will be making huge waves, the 1 metre doesn't seem to....