Hi All. Came upon this 'Mottle 33' thread by chance, really interesting! Some have mentioned the Mottle 33 'Cryptic', that's me. Have owned her now for over 30 years and, as Wavesong said, I've no reason to change. At times I've thought 'bigger is better' but the bi-annual slip corrects my thinking!
Cryptic was built by Naut Yachts and launched new in 1980 as a Whitsunday charter yacht. My understanding is that when Naut Yachts acquired the moulds from George Mottle they had the charter market in mind and so took the fit-out up a notch: headliner, transom liner, chain plate covers, etc. Those built to survey for the charter fleets were well built. For example I had seen Naut 33's with a transom liner. Mine had none. While back-tracking proof of ownership for Australian Registration purposes I asked John Simpson, the former Director of Naut Yachts, 'why?', and he replied 'because the transom layup was too thick!' This explains why there is no simple answer to Frank101's original question: 'What are they like on the open ocean' (i.e. as a bluewater boat)? The boat was available from hull and deck kits through to survey standard so it all depends on who put it together. I have no hesitation heading offshore. Based in Brisbane we have sailed as far north as Lizard Island, South to Coffs Harbour and offshore to New Caledonia and to Lord Howe (hove-to in 30+knots and huge seas) confidently and with no issues. 10 years ago I gave her a decent refurb - hull, deck and mast professionally sprayed, new hatches, toe-rail, windows etc. Overall she's looks pretty sharp for her age. I kid you not, shortly after the refurb a yachtbroker walking past stopped to look, thinking it was a new boat. When I said it was over 30 yrs old, he took a bunch of photos to send to his boss!
Wavesong mentioned that the Mottle 33 Timana completed a circumnavigation. I met the owners back in the 80's while they were lounging on their Mottle at the marina in the Whitsundays. As Mottle owners, we bonded for life. Before setting off they extended the chain plate knees (elbows?) down past the second stringer, the way the Naut-built boats were done. This was to reduce flex. Same hull and deck, different builder. As an aside, after their circumnavigation I asked Geoff 'if you were to do it again, would you choose the same sized boat?' He said 'Smaller'. His wife said 'Bigger'. Since then they bought and sailed a Jeanneau 37 from California to Brisbane and a few months ago bought a Beneteau Oceanis 42. You can tell who wears the pants in the family.
The 'Mottle 33' 'Catherine Anne' (as mentioned above by julesmoto) featured in Bill Hatfield's attempt to be the first person to sail westabout in an under 40ft boat. A couple years ago I asked Bill if it was a Mottle and he said it was like a Mottle hull but with a different deck. The hull looks to have less sheer than the standard Mottle so perhaps it was cut down to match the deck. Just speculating.
Bill is an amazing, no-frills, concentrated-saltwater-in-the-veins kind of guy. 'Catherine Anne' was named after his daughter who was born while sailing the South Pacific on their earlier small (28ft?) yacht. Unfortunately Catherine Anne (the boat) was knocked down while rounding Cape Horn and suffered too much damage to continue.
Julesmoto: He limped back to the Falklands where he sold the boat (its still there) and flew back to Brisbane. His understated blogs are riveting. Twice he's been washed overboard only to get a foot tangled in ropes by which he pulled himself backup. You can read his blog of the event and all his blogs at: L'Eau Commotion Westabout (sailblogs.com). His current Northshore 38 hasn't left the dock since breaking the Westabout under 40ft record 2 years ago (at 81yrs!).

Mottle 33 'Cryptic'