Some insight to balance the double entendre's...
There is a relatively high coastal ridge south of Wannanup that the southerely breeze needs to get over hence creating gusty conditions with any west in the wind.
I heard somewhere the Mandurah estuary has 3 times the water capacity as the Sydney harbour (not definite about this but you get the picture, it's a bloody big water body of water) with a relatively thin coastal land strip (and that ridge).
As the colder ocean wind 'fills in' the rising thermals from the land, it then hits this large body of relatively less warm water (or the air above it at least).
hence you will notice the mandurah wind lifts (as normal with the south west change) but then drops back. It can then lift again, but tends to oscillate at times between south west, South south west, South and at times even back to west south west. That ridge then comes into play a fair bit.
This doesn't happen all the time, but most times if you know what I mean.
..and yes the water can be shallow, crabs, cobblers, weed, bla bla bla but those become irrelevant if the wind is smoking.
But this poorer wind quality is countered by the general lack of crowds as well.
Nothing better than to feel the consistent power of the mid west breeze over your shoulder when you are dealing with these type of conditions most of the time in summer here.
But honestly just come down knowing what you could be in for and mow the lawn with the rest of them, have fun and grab a crab or two for dinner when you get back home...
ps sounds like that local lad had one hell of a night. it was actually a bit nippy down here last night and blew all bloody night. He must have been freezing! Glad he's all okay.