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.
Guidance Request for Rule C.6.3
Moderators: Pedro Egea, jeffbyerley
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Malcolm Smith
- Posts: 1
- Joined: 14 Oct 2025, 00:52
- Sail number: AUS
- Design: own design
- Location: Bowral, NSW, Australia
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Andrew Crocker
- Posts: 22
- Joined: 19 Dec 2025, 21:45
- Sail number: AUS 36
- Club: Albert Park Model Yacht Club
- Design: Blitz 6
- Location: Melbourne, Australia
Re: Guidance Request for Rule C.6.3
Hi Malcolm,
Thanks for your query. It is being reviewed and we will get back to you with a perspective shortly.
Regards,
Andrew Crocker
Vice Chair Technical
Thanks for your query. It is being reviewed and we will get back to you with a perspective shortly.
Regards,
Andrew Crocker
Vice Chair Technical
-
Andrew Crocker
- Posts: 22
- Joined: 19 Dec 2025, 21:45
- Sail number: AUS 36
- Club: Albert Park Model Yacht Club
- Design: Blitz 6
- Location: Melbourne, Australia
Re: Guidance Request for Rule C.6.3
Hi Malcom, thanks again for your query and apologies for the delay in responding.
The question of foils on rudders is addressed in the Q&A section of this website (https://www.iomclass.org/iom-questions-and-answers/) and, while the text is being revised to incorporate changes to the ERS, the answer remains the same: foils on rudders are not permitted under the IOM class rules. As a result, your central question is moot.
However, I would observe that the IOM class rules are very much meant to be taken literally. The requirement of C.6.3(b) that hull appendages not project outboard of the hull should therefore be understood to mean exactly that.
Regards
Andrew Crocker
Vice Chair Technical
The question of foils on rudders is addressed in the Q&A section of this website (https://www.iomclass.org/iom-questions-and-answers/) and, while the text is being revised to incorporate changes to the ERS, the answer remains the same: foils on rudders are not permitted under the IOM class rules. As a result, your central question is moot.
However, I would observe that the IOM class rules are very much meant to be taken literally. The requirement of C.6.3(b) that hull appendages not project outboard of the hull should therefore be understood to mean exactly that.
Regards
Andrew Crocker
Vice Chair Technical