Hi from Victoria, BC, Canada

My name is David Cook. I’m an amateur IOM designer, builder and sailor. Over the 4 years I’ve designed 7 boats with moderate success on all but 1. I’m also building a Goth RG 65. I’ve sailed for over 35 years, enjoy the challenge and competition. I’m good friends with Don from Campbell River who told me about this forum.

Welcome David… Hope you stay around and add to the threads here… there are no BAD ideas… some ideas may not pass with others… but still offer them up… YOU are a designer so i am sure there are a few people here… that will welcome new ideas… I for one have designed 10 IOMs and a couple of 3r and 1 Marblehead that i absolutely love… and If you want to exchange idea. and pass ideas… welcome…
BTW… I am in Waterloo Ontario…

Thanks Cougar

My current dilemma is trying to get a grip on IOM mast fore and aft location. In other boats I look at, the trend seems to be to get the mast as close to the fin leading edge.
I’ve notched my last boat’s fin leading edge to do this and have made a longer keel fin box to adjust aft if necessary. It’s probably better to error with the mast too far forward as you can always put more make in to induce more weatherhelm and move the fin aft to do the opposite.

An IOM design and Kiwi sailing legend Geoff Smale taught me to locate your fin over the hulls CLR by taking 25% of the fin chord length measured aft of the average leading edge.

Does anyone have any suggestions where to locate the mast fore and aft as a starting point?


I Know what you mean by “guessing” where to put everything. But what I have found and this is by no means the correct way. Just my way… ok…
I take what i design and put the same numbers in as always mast in at 47 %. or 470 mm from the bow. the keel/fin leading edge would follow 25-50 mm behind that… then with my new desing I would look at the C/B and the CLR and compare that to the NEW design and if the numbers are close I keep it there… but the one thing that you should also include in your calc… is the COE… For me… i would like to keep the COE and the CLR in a straight line… IF one moves back. then the other moves back…IF that makes any sense…IF your COE is too far forward. is is going to make no difference as to where the CLR is… MY new IOM that i am building right now. i am trying the mast at 470 but fin at 525… thinking less bow to turn