Guidance Request for Rule C.6.3
Posted: 14 Oct 2025, 13:52
IOM rule C.6.3 (b) states "The hull appendages shall not project outboard of the hull". My question relates to T-foil rudders, for which there are precedents in the class.
If the rule was taken literally, it could be interpreted that the span of the foil would not be allowed to project beyond the local beam of the boat, which restricts the span of the foil. It could also be interpreted that when the rudder is turned, the foil may project beyond the transom, further restricting the achievable span.
The intent of the rule is not provided. If the intent is to prevent appendages that could interfere with or damage other boats in close proximity, then a T-foil, being well below the waterline, is unlikely to cause a problem, and I would argue that the rule does not apply in its literal sense.
My interest in T-foils comes from using them on a local RC class, to reasonable effect. The benefits are a reduction of weather helm when sailing upwind and a reduction in nose diving when sailing downwind. These benefits have to be balanced against the added drag, and the overall effectiveness is not clear-cut. However it poses an interesting line of experimentation and it would be nice if the design parameters were not unduly restricted.
If the rule was taken literally, it could be interpreted that the span of the foil would not be allowed to project beyond the local beam of the boat, which restricts the span of the foil. It could also be interpreted that when the rudder is turned, the foil may project beyond the transom, further restricting the achievable span.
The intent of the rule is not provided. If the intent is to prevent appendages that could interfere with or damage other boats in close proximity, then a T-foil, being well below the waterline, is unlikely to cause a problem, and I would argue that the rule does not apply in its literal sense.
My interest in T-foils comes from using them on a local RC class, to reasonable effect. The benefits are a reduction of weather helm when sailing upwind and a reduction in nose diving when sailing downwind. These benefits have to be balanced against the added drag, and the overall effectiveness is not clear-cut. However it poses an interesting line of experimentation and it would be nice if the design parameters were not unduly restricted.