Hi I have some heavily oxidised - splotchy, rusty and chalky corner castings on my Hobie 14.

Does anyone have any suggestions on how to clean these up?

Well... I found this explanation on the web and it is pretty thorough:

OK, Hobie Cat rudder history lesson:

1967-1975
Rudders were made from ABS plastic. Gets yellow and brittle from UV exposure. Has a bad tendency to snap off right below the casting when loaded up. Spawns a whole cottage industry of aftermarket fiberglass rudders.

1975-1984
Rudders made from Lexan polycarbonate. Will not break, but very flexible. Thin cross section and prone to stalling and ventillation. Not very good for racing.

1984-1989
EPO rudder era - super light, stiff black rudders (epoxy/fiberglass/foam core). Thicker and much more forgiving. Only drawback was the trailing edge needed a lot of work to stop the humming. Still very much sought after as the ultimate racing rudder.

This was an upgrade - stock rudders were still Lexan.

1990-2005
Racer Rudder era - polyester/fiberglass/foam core. Not as light as EPO's, but still a good rudder. Gel coat finish was much softer than the EPO.

Starting in 2004, you could get epoxy/carbon fiber/foam core rudders from Europe. The section was not as thick as the EPO, but they are lighter than the Racer Rudders.

Racer Rudders were also an upgrade. Stock rudders were nylon.

2005 - present
EPO2 Rudder era - based on the original foil shape of the EPO, you have a choice of polyester/fiberglass/foam core or epoxy/carbon/foam core or epoxy/carbon/kevlar/foam core. These are the ultimate Hobie rudder, and at $250 each, they better be. It's nice that they require no prep whatsoever and are well-behaved right out of the box.

The polyester ones are now stock on the 16. For $60, you can upgrade to the carbon one

Sail Series Promotions (SSP) has achieved their goal of helping bring back the Worrell 1000. With that goal achieved, they decided to close out the corporation and disperse funds to other 501c3 charities for youth sailing programs.

The Endurance Series combined some of Florida’s premiere distance races to help promote the sport. The series ran from 2004 to 2015. The Endurance Series participants and winners have been some of the top distance sailors in the country and include Worrell 1000, Tybee 500 and Olympic sailors.

Now that the SSP is no longer organizing the Florida 300, Steeplechase and Hiram's Haul, there is a big hole in distance racing. Local sailors stepped up and will be running Hiram's Haul on November 16-17. The Endurance Series organizer, Craig Van Eaton, is considering bringing back the Endurance Series to help fill the hole.

With the Worrell 1000 being brought back, it is more important now than ever to provide proving grounds for sailors to hone their skills on their “Road to 1000.” The goal of the Endurance Series is not to bring back the Florida 300 but to ensure current races are supported and possibly expand to more unique and challenging races to the Bahamas and Cuba.

The Endurance Series is looking for partners to help promote and rebuild distance racing. In order to move forward with new projects, someone with “Race Official" training will be necessary.

The Worrell 1000 is boosting interest in distance catamaran racing and now is a great time to rebuild this very unique sport.

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