...runs north/south from just north of Garden Island down to about halfway between Mandurah and the Dawesville Cut, averaging between 4 and 6 nautical miles offshore.

Typically the depth will drop out to around 20 metres as you approach the bank, before rapidly rising up as you pass over it. Can be as shallow as three or four metres in some places...Coventry's Reef, straight out from Warnbro Sound, is actually part of the FFB and is exposed, with waves breaking over it in virtually any size swell.

You'll know you've gone past it when the depth goes back down to 18-20 metres again...the bank varies in width, from a couple hundred metres to over a kilometre in some places.

So to finally answer your question , you should have no problems finding it with just a fish finder. If you haven't been out that far before, I do recommend taking a reciprocal heading off your compass on the way out, so that you can be reasonably accurate coming back in without having to rely on visual landmarks which may be obscured by fog/smoke haze.

One more tip...I personally find it more productive to fish the back edge, looking for small bits of broken up ground, as opposed to the main reef itself, which is full of pickers and snags.

Thank you so much for the info, much appreciated. looking foward to going out, previously owned a 350 traveller and could not really go anywhere. Now owning a bigger boat can't wait.. 

great bit of info there Auslobster. Ol YELLA, firstly <welcome to fishwrecked and take in the info. when fishing the back of FFB anchor on the lumps and burley up as the fish in the area will come to you, you will get the pickers but there are always bigger fish out there such as pinkies and bb;s and the odd dhuie.when you can afford it i would get yourself a gps so when you get a nice patch of fish you can mark it, just make sure you get one that will take a map cardas it will help find spots to try. you could get a hand held but they arent as good,good luck with your trip out

the bottom its so shallow just dont anchor on very shallow parts as a larger than normal waves is all it takes to break

i used to have agarmin e-trex hand held done the job you can get them for about 139-00 dollars now

ol yella...welcome.......have your wits about you on the five fathom.......keep an eye out for the odd breaking wave...gets pretty rough out there sometimes..

Thanks  for all info, i need to install seats in my boat. has a fiberglass deck,  i was hoping to do it myself. has anyone done it themselves?

any advice would be great...

if you need seat stands/seats go to bcf every where else is a ripoff

Use a lot of screws if you're going to get Andy Mac anywhere near it, just ask Tim.