[miahmouse]

a little bit of corrosion doesn''t mean the end for the rudder (I''m not there to judge but if it''s just on the surface, sand it off polish it up and keep on rolling). If it has definitely had it, then it''s time to start searching for a reputable machine shop. Then there''s choosing the metal. 302/304 Stainless will be slightly more flexible/less prone to cracking but more prone to rusting. 316 Stainless will be less prone to rusting but is more rigid and therefore prone to breaking/cracking. 316 will also be more expensive. Next up will be the design/copy of the old rudder. Being that you haven''t sailed the boat I''d try and contact another owner of a Mariner 39 and see what they have to say. Figure out what materials you want to use for the core, skin and most importantly, resin. If you have access to a vacuum pump, you might consider vacuum bagging to increase rigidity. I''ve never build a rudder for a boat over 20ft so I can''t give much advice on design matters dealing with the loads of a larger boat. But I will say this, do it once and do it right.