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These things are seriously addictive and you could do worse than contact Mike, above, for loads of info. Also Dave Potter at Potter Solutions.  The Model Multihull web site has sadly lapsed, so it comes down to a handful of enthusiasts. Ian Holt "Perthmini40man"  also has loads of development info. The holy grail of these boats is speed; particularly spectacular foiling. The three main considerations are weight, lightness and even less weight. I have built a couple now, the first being a modified "Ghost Train design" built from pre preg C/F and moulded in an autoclave. This design was one of the first to foil. As mentioned, really depends on what you are after. Let us know how you get on. Richard  

Gents, These discussions provide some great reading and there is a lot of information that other skippers can take from this post. However, can we start to steer away from the idea of using carbon rigs for an IOM. The initial basic concept of developing the IOM class was to provide skippers, with a cheaper option to continue racing. At the time the Marblehead Class was the most popular and prices were escalating out of control. The IOM became the cheaper and perhaps fairer option for others to keep racing, because carbon was not allowed within the rigs or hull construction. Therefore, grass route or skippers sailing to a budget remained competitive. The idea of carbon masts etc, on these types of boats has already been established in the form of the US1m Class. A brief description from my experiences with this class can be read here (Click)   Although I like everyone's input, lets just keep to the basics of my original post. Refurbish Rigs vs A new IOM? JT

Michael, lets start with your prebend question. Could you get away with no prebend? possibly in a Zephyr, anything above that would simply not work. There would be insufficient tension on both the forestay and jib boom topping lift allowing the jib boom to rise uncontrollably, causing excessive weather helm, that won't be quick! I notice you are not a million miles from Catsails so i'd suggest that possibly the best course of action might be to contact Nigel and ask nicely if he could add prebend to a tube, when Covid restrictions allow. With regards Richards post, if you are using a genuine french PG mast and it is prebent correctly the prebend will not flatten off over time. Prebend will flatten out on the sails etc and similar tubes which are softer however they are easier to bend in the first instance! As mentioned it is tricky to add pre bend to PG tubes, they are not soft, therefore don't flatten out with age. If you venture to the top of a IOM fleet anywhere in the world, PG masts are used for a reason, if bent and built correctly they last a long time, they recover quickly from any side bend offering good gust response. With regards to Carbon spars, you can buy cheap carbon tubes however we all know that if the class were to move to Carbon we'd all end up using expensive high modulus sections. Many would argue that IOM's are expensive enough without adding high modulus carbon tubes to the list. Secondly, it wouldn't end at Carbon masts, all experienced IOM designers will design a boat around a set of parameters, mast stiffness will reflect hull design, foil design and placement and rig placement, IMHO to change to Carbon would completely open the floodgates to a generation of completely different hull designs, more cost. Finally, sails have to compliment the mast, a carbon mast will have very different bend characteristics, therefore the distribution of both luff curve and camber for the mainsail would change, the cut of the jib would also change as rig tension would be different. Unfortunately its never as easy as changing the material of the spars! There are some great tips and webinar videos updated most days at present on the BG sails and design website that i'm sure would be very useful for anyone looking to update rigs or update an older design.  http://www.bgsailsanddesign.com/toptips.html  

Thanks Richard for your comments especially on carbon rigs.  I also sail a Marblehead with both carbon swing rigs and an A2 conventional carbon rig with shrouds and spreader. It would appear to me a simple rule change to allow carbon rigs to be used on the IOM either unstayed or with shrouds. I wonder what the purists would make of a suggestion to a rule change to permit? Seems an obvious update in line with current thinking. I recall some time ago that a rule change permitted pigmented grp hulls. 

Diamond 10 Rater, built by Graham Bantock in 2018. Comes with 3 Sailsetc rigs, No 1, 2 and 3. Craig Smith fin. RMG winch, servo. In almost new condition. £3200 No 2 Rig No 3 Rig