Get some rules setup as F17 along the lines of the F16's rules and you would be surprised just how quickly the F18 dominance will be over.
Who wants to push another 50 kilos of outdated boat up and down the slipways when you could have the latest up to date toys to play with.
I've already stepped down from a 20 foot boat to an 18 footer. I'm not going to a 17 foot boat. Not only due to the size of the boat, but it's light and small making it even more sensitive to proper sailing crew weight. I'm pretty happy with my F18 and while it's heavy by F16 standards, it evens out the playing feild a little...and when two of us can no longer manage moving the boat around on shore, I need to quit anyway.
