i am trying to understand why the Mandurah swell chart is so much less than Rotto. I can understand that the Cott buoy is inside the reef/Gage Roads harbour, so the swell is accurately less, but why is Mandurah typically less (like, measuring as mid-way between Rotto and Cott). Perhaps more specifically, is the Mandurah buoy an accurate indicator of the swell at Gearies?
Mandurah swell is definitely affected by the 5 fathom bank
As for the readings:
Rottnest Buoy seems to be located west of the West End meaning nothing is between it and the southern ocean
Mandurah Buoy is right up against the Fathom Bank reefs but still fairly offshore so at a guess, the more south the swell direction the more influence Cape Bouvarde and the outer reefs will have on the reading.
What ever the case, i think the swell at Avalon or Gearies will be less than the reading at the buoy.