IOM Discussion

[Steve]

HOW TO IMPROVE OUR IOM PERFORMANCE

Summary of a series of discussions between: David Balsdon, Glen Barrett, Doug Christmas, Michael Steele, Victor Wong, John Ball (CRYA), Julian Kenney

RIG & SAIL SET-UP

<https://radiosailingtechnology.com/index.php/9-uncategorised/161-prebend-and-sail-shape&gt;

Ian Vicker’s video. <https://www.youtube.com/watch?v=VnxF3rNDxj4&gt;

On-line rig set-up guides: https://planb.peterburford.com.au/set-up-and-tuning

<http://www.bgsailsanddesign.com/uploads/7/0/6/9/70698521/bg_sails_rig_tuning_iom.pdf&gt;

Peter Sutton’s simple guide to setting up an IOM boat: <https://mya-uk.org.uk/wpcontent/uploads/2015/10/20_IOMTuning_2013_2.pdf&gt;

Other resources forwarded by John Ball

John Ball’s simple IOM rig set up guide: <https://crya.ca/wp-content/uploads/2020/05/Quick-guide-tosail-trim-for-normal-wind-and-flat-water.pdf&gt;

As a supplement to the Brad Gibson IOM tubing guide, here is a video of top sailors at the 2011 IOM Worlds. Look for the foot round, twist and sheeting angles <https://www.youtube.com/watch?v=VPmPkq5kRY4&gt;

39 britpop is the ultimate winner – Peter Stollery; 95 is Graham Bantock with one of his own designs; 22 I think is Graham Elliott’s 3rd place Britpop; 42 is 2nd place Brad Gibson an dhis britpop

• John Taylor IOM tuning guide • K2 assembly & trim (Sailboat RC) • Zvonko sails tuning set-up • Making a tensionometer

Comments on rig set-up (various)

Comments by John Ball: Mast ram closes the main sail twist and is the last item to adjust. It is used to increase or decrease sail twist. Pre-bend is used to increase forestay tension. In lighter winds less tension is needed.

Comments by Sailboat RC: [Note: the Jelacic brand no longer exists. Jelacic guidelines are switched to new Sailboat RC guidelines]. Some orders are without and some orders are with pre-bend. Less pre-bend is usually better for speeding up (good in shifty conditions) and not so good in keeping the good angle and VMG on upwind. And vice e versa, of course. It is the recommended default option and the Kantun 2 [K2] should usually have pre-bend.

Comments by Glen Barrett: My observation is that in general, most of us set up with too much twist. Look at all the YouTube videos of top level IOM races and pay close attention to the sails. You can learn a lot from that.

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Comments by Frank Russell: This will give you starting mast rake. I usually don’t bother with measurements as all IOM’s are pretty much the same, foot curves and twist etc. I just learn how to set up a rig by sight. Foot curves A rig 25mm main jib 30mm 35 in chop. Standard stuff. Sheet the main 10mm off the centerline and point the jib boom just inside the sidestays, then sail the boat and make the jib break the same as the main when you luff. Make it a bit more open in light wind. B rig likes a bit of twist. C rig the jib is too big so you need to use less twist in the main to balance the boat. If the main backwinds, you are not using enough twist in the jib, which should be open more at the top at all times. Match the main to that. What really matters is sail shape and no one ever worries about that or gives any curve percentages or placement or how shape needs to change in different wind speed or sea conditions. Funny about that.

Comments by Jess Atkinson (V8): Rake at 1505 (Ian calls for 1508)

. this means mast-ram all the way off and it seems to just about right.

Spreader angle is important -too much angle the mast bends too much in the mid section.. Ian was always correcting my mast bend to make the mast straight.

Jib 65 – 68mm from center of the mast to the inside of the jib boom. Ian calls for a jib angle of 70 deg. I do click out my trim as the wind goes up and tend to play that feature a little during a weather leg .. guessing that my average is close to his 70 deg but I think the range of travel is important to have just as you would ease a sheet in a big puff on a full size boat I do the same and then come back in He does have the tighter angle in the guide for light air.. I use that one most all the time and just trim out as the puffs hit.. and then back in.. Important to ease out not to hold it down with rudder.. I make the sails work for me rather than the rudder.

The main 10 – 12mm I have out more than the guide which calls for about 8 mm. I have it at 10-12mm from the main sheet post and as with the jib trimmed out in puffs.

In this position you may find you need just a small amount of additional vang 1/2-3/4 turn is all .. so tighter leach? Measure to backstay?

That said if I have clear air and feel I just want the boat to foot for speed, i go to a trimmed out position additional 5-8 mm and just put the bow down for speed .. The fin seems to kick in nicely and the boat lifts right up I do not find I lose anything… Hard to do when you are in close with others as it feels like everyone is out pointing you.. I do find the boat really likes to foot and be held down just a touch. Jib draft currently at about 25 normal 27mm light from the boom the sails

Main draft is at 20-22 The main I keep just under the jib so in short if my jib is at 25mm then main is 20. If the jib is 30 my main is 25-27

Jib twist 35mm from leach to topping lift. Ian goes to 45 at top of range and waves. So I hope this helps a little, Everything I have chatted about is for the A rig.. I do about the same for the B but I have an angle on the jib closer to 70mm and main at 12-14 I gauge that based on my helm and how puffy it is C rig the same but I use the fine trim to click in out just a touch so I may be just a few mm out from 7- & 12 .. when is C conditions.

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Comments by Vickers from 2017 Worlds: Biggest changes is in the jib set up, we are setting the A rig jib at 63 to 65 and the twist at 35, Why, we were sailing to low off the line and not getting the bite sheeting tighter gives you, some here are around 60 by the look of it, admittingly the water here is flat with little chop. Main sail wise we are at 8 out and the twist between 55 and 60. Rig tensions look quite tight but the sail setups are all tighter (than we use in NZ) as you would expect at a world champs, where at club sailing you get the freedom to sail free and wider angles, sailing tight and higher takes way more concentration, but itís what we need to practise at (says I who reaches around like a sick dog)

As for B rig, much the same at 65 and 35 twist with the main out to 15 but twist still at 60, donít think C rig will come out of the bag?

Observations: JibsÖÖ we are sheeting (Ian not me) at 55 and twist of 35, with the main flatter on the foot (a little) and out at 8 with twist of about 55 to 60. this is way tighter than the manual and the norm in NZ, but if youíre not tight you miss the bite in the gusts and canít hold a lane (not grant lane). From what I can see this tighter mode is the normal in big regattas where competitors are evenly balanced, we can learn a lot from this, as club sailing (while being great) allows us to be in a more cruiser mode. Our sails are defiantly on the fuller side and to be honest I havenít seen any I would rather have, as for the hulls same !! the new Italian Cedici is very sweet but looks soft in the stern and dated (to me) apart from quite a sexy keel. One interesting thing our spreaders on NO1 are about 40 to 43, the others seem to range between 50 and 65, like cow horns!!

I have observed our masts are dropping off the leeward (about 20+ mils) while the others seem more in column (longer spreaders), not sure if this is good or not, I am thinking it is as Ian is very fast at the top of the ranges for A and B, which suggest the rig is being allowed to breath in the gusts, as for mast rake, not a lot of difference most are quite upright, when questioned those who play with this are not sure, I for one think we need to play around with rake as it can load the rudder supporting hyronamic lift, ( no questions please)

HULL, KEEL, BULB & RUDDER

Canoe hull form should be long and thin. WL beam 162-169 mm, WSA 0.145-0.147 m^2 (See BritPop, K2 and V8 as examples)

Fin should be long, thin and strong. Carbon fibre is the only realistic option. About 320 mm x 90 mm and less than 10% of chord thick. (ie less than 9 mm). Need to identify the best NACA section

Bulb should be long and thin. L/D greater than 10. Need to identify the best cross sectional shape. See for example the bulb in Ian Vicker’s video and discussion at <https://radiosailingtechnology.com/index.php/9-uncategorised/161-prebend-and-sail-shape&gt;

SAILS

BG Sails is the most respected and has the longest track record

RC Sailing (was Jalinck)

Vickers Sails. It is understood that Trevor Bamforth makes sails under Ian’s name

Housemartin (UK). Makes sails for masts that do not have pre-bend

Others: Vector Sails, Carr Sails, Sails Etc, Power Sails, Black Magic, Hot RC Sails
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Note that some sail makers provide wire luff, but not all. Some have jack line.

GETTING ONTO THE WATER

Two boat tuning is difficult. Do racing but treat as a ladder

Adopt clinics. Use 3 boats to practice starts etc. Practice starts, rounding the first mark and lay lines. Plus rounding downwind marks.

John Ball’s web site on rules and tactics: <https://sites.google.com/site/johnsrcsailingrulesandtactics/&gt;

National organisations, hull and sails makers etc: https://crya.ca/sailing-related-sites/

And finally, read Ray Davidson’s book!

Julian Kenney 25 June 2020

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