Day 59
Days remaining: 175

Build it strong... - 4g is a lot!....

This G Meter goes down to -ve 4g

Just about enough for a Moth.

I'm building a lot of my boat stronger than I would build a 14. I'm on my weight budget to have a boat around 9.5kg, but some bits might look a bit rugged for a moth... I care not.

My worst case load test in my head for a 14 is a nose planting down the bottom of a wave, from max chat to almost stopped.  It is rare, and the fastest I've ever sailed a 14 is about 22 or 23 knots.. and we were so chicken we had the rudder wing on max bow up and never crashed it. If it ever got really sketchy, you just came off the wire, slowed it down and had a bout of tourettes...

A Moth will see 30knots or thereabouts max. High twenties are common when racing.  I predict that in 5 years boats will be reaching speeds higher than Crossbow II's 1980 top speed (and at that time World Speed Record) of 36 knots....

....and the classic main foils popping out at speed and the inevitable 30 degree nose down 'stick thrown into the pond' stop is commonplace.....

Well staggeringly that sort of a crash is a Negative 4g acceleration (or a 4g deceleration if you prefer)

Here's my maths to support that by the way..

Quick conversion first... 1 knot = 0.514 m/s so 30knots = 15.42m/s... So we'll use that speed as our start point.

A moth is 3.355 m long.   30 knots = 4.7 boatlengths per second  (Yeah, pause at that point- Crikey!!)

Crash stop from 30 knots to a dead stop = 2 boat lengths = 0.425 seconds... Which when watching video of pop-out / spear in crashes, and experiencing a few of them as everyone has, that seems about right....

Deceleration from 15.42 m/s to 0 in 0.425 seconds is around 36.28m/s/s (my mac doesn't do little uppy arrows to do a 'squared' it seems!)

1g = 9.82 m/s/s

36.28m/s/s = 3.69 x g

So all this time, the moth really has been pulling 4g negative dives, just like in the film!!


D