Steve at SetSail, I’ve experienced significant weather helm sailing my 50′ custom design cruising catamaran in winds 12-15+ knots. When entering an inlet in confused tidal currents, the helm is heavy and the vessel slow to respond under power. A growing concern among my designer, sailmaker, rigger and a couple of experienced sailors who’ve been aboard is that the rudders are undersized and/or unbalanced. Can you recommend any source(s) to help me understand more about rudder design and performance? Kind regards, Jim
Hi Jim: There is a section in our Offshore Cruising Encyclopedia about this. Steering problems, typically blamed on rudders, are usually the result of something else that is going on. If the designer is at a loss, then I would look for another multihull designer who knows his business.
Increasing size and/or getting counter balance right is not difficult. The bigger question will be your rudder shafts, and how much load they can take. This will limit what you can do, unless you put in bigger rudder shafts.
If they have enough meat on them, I’d just slap on some foam and fiberglass. You can probably do this for less cost than what a good designer would charge to evaluate the problem and design new rudders for you.
Re counterbalance, we usually use between 17 and 19%. Varies with the rudder shape, proximity of the props, and if the rudders are buried below the hulls or not. Good luck – Steve