Mast Control on IOM

Hi all,

I’m a new boy on this site and relatively new to RC sailing, though not to sailing as a sport.
I have an IOM (GBR 2612) and race it successfully at Emsworth (UK). The design is a Triple Crown that was originally built for Martin Roberts.
The mast wa sprebent (even bend over whole length) when I bought it and the only alteration I have made to date is to fit a bar across in front of the spreaders to force them forwards , thereby stiffening the mast below the hounds and enabling me to adjust that stiffness with the shroud tension.
Measuring from the top of the mast:
Forestay 230 mm
Hounds 483 mm
Spreaders 1084 mm
I am contemplating lowering the hounds to 700 mm
My theory is based on my experience racing Folkboats, when we discovered - after breaking the backstay control - that by letting off the jumpers and thereby allowing the mast ftop top bend to leward we were much faster than boats relying on tightening the backstay.
Has anyone tried doing this with IOM’s; does anyone have any thoughts for or aginst on the subject.

Look forwrd to hearing from you,


Happy sailing

I have my Victoria set up like that, with good results. Check some of the photos and their comments at Anders Wallin’s site. He comments on some of the Aussie boats having their shrouds attached well below the forestay.

What a grreat site Hew. Many thanks for the response and the pointer.


Well… I’ve now tried the set up I proposed above and whilst it worked well when the wind picked up it allowed the top of the mast to bend off too much in the lighter stuff. Result - the boat was dead.
I have now adjusted the hounds height to 640mm (from the upper measurement point) and in initial trials - 3 to 8 knts - proved very successful. It will be interesting to compare later this week as on Sunday the bulk of our fleet were away at Gosport.
Whilst I am experimenting I have fitted a strangulation loop round the mast, over the shrouds, tied to a bowie loped under the spreader roots. I don’t know wether this could be kept as an adjustment method - all be it tidied up - in the long term or wether it would be considered out of calss. Any comments here would be of interest.


Take a look at the rigging guide for the TS2 or TS3. The TS3 especially, is known as a stiff boat and uses a low shroud position to allow the mast to twist off. See page 8. I used these measurements on one of my stiff IOM’s and it worked fine.

The IOM rule is a closed rule. You can only do what is specified. So the strangulation loop is almost certainly not legal (in my opinion).


Many thanks for the link John - very interesting.

Regarding the rules - that was rather what I suspected, but I wondered if it would be allowable under:
(a) Terminations.
(b) Length and tension adjustments

I guess the full answer would have to come from the Class Assoc. or ISAF


Hi James,
John is absolutely correct. Definitely a no-no with your strangulation loop. Might I suggest you check out Lester Gilberts excellent site. You will find an interesting page on rig set up. To get a tight forestay its al about mast pre-bend, backstay and mast jack. Getting the correct combination is what it’s all about.

Hi Tony,

I took my own advice and refered the matter on the IOMICA forum Link:
The descision from Robert Grubisa was:
“IOM CR F.5.3 is explicit in allowing both length AND tension adjustments. Choke ring or similar method of adjusting tension is perfectly fine and doesn’t preclude you from having turnbuckles at deck level as an independent means of adjusting LENGTH as well.”

For full details please use the link.

Thanks all for your input.