One comment I read about one of our top radio sailors which surprised me was how little he varied the back stay, plus or minus 2 mm. I put four marks 5mm apart, 15mm in total, on the back stay adjuster and now vary the backstay tension within that. I always watch the mast bend from the bottom of the mast to check I am not overbending the A rig. 5mm too much can destroy a good set up.
How can you set your boat up for consistent results?
Boat Tuning and Setup
What you need to know
Rig fittings, Mast rake etc. See the designer's plan as starting point
Set kicker to hold mainsail leach twist on run
Fine tune mainsail leach twist for windward sailing using backstay and mast ram
Set jib twist parallel to main when viewing boat from behind
Use boat manufacturers advice as starting point for sail depth at the boom set up and sheeting angles
My settings are on the checklist.
Shroud tension - enough to just stop leeward shroud flapping. I find softer rigs work better in gusty/variable conditions
The Details
There are several things you can do on dry land, to ensure your boat is set up in an optimal manner. First you can view a lot of setup up techniques on the Internet. Look at the “Useful websites” menu and go to "Tuning your IOM". There are a mixture of articles and videos to puruse and you can pick tips from the best of those. I think I have found most of them.
You can practice setting up in you home for very light weather and observe what happens when you make changes. If there is wind outside, you can run through the same procedure, but you can use wind rather than gravity to set the rig up. Here is a sequence of actions that I believe is best practice, for you to try to set your boat up.
Setting up the mast and mainsail
You have seven variables to play with setting up the mainsail. Backstay, spreader angle, shroud tension, mast ram, mainsail foot depth, kicker and cunningham. I tend to fix the spreader angle, foot depth, shroud tension and ignore the cunningham in light weather leaving only four variables to work on.
With your boat fully rigged with the A rig, make sure the mast rake, measured from the upper band (forestay entry) is either vertical or set at the angle in your boat specification. Set the shroud tension so its just tight enough so that when sailing the leeward shroud won’t hang loose. If the shrouds are too tight the mast will not be able to work in the puffs and lulls during racing. The backstay should be tensioned so the mast is straight. The foot of the main should have a depth of approx 15-20mm from the centreline of the boom or a depth provided by your sailmaker. The mast ram should be set so that there is a slight amount of reverse bend at the deck level.
Stand the hull up vertically so the bow is directly under the stern. let the mainsheet out so the boom is just touching the shrouds and tighten the kicker so the mainsail leech twists by half an inch or so. Check both gybes to make sure the twist is the same to check that the mast is straight, upright and the spreaders are equal length.
Put the boat on it side with the mast lying horizontal. Tension or ease the backstay until the top batten is parallel to the centreline of the boat giving the mainsail the right twist. The boom centreline should be a few mm away from the central post.
Looking down the mast from the top, check the mast is evenly bent in a slight S curve (slight reverse curve at the mast ram). See if there are any hard points in the luff of your mainsail, ie creases. If there are, it maybe you need to pull your spreaders forward to straighten the mast, or you need more mast ram or less backstay. If there is too much fullness at the front the first try tightening the back stay and if that creates uneven fullness, experiment with moving the spreader back a mm or two and easing the mast ram.
The aim of this exercise is to play with the settings until you get the mast to match the luff curve on your mainsail. Then see how you can power up or de-power the sail. For light weather the cunningham should remain loose and the kicker unchanged from run to beat.
Setting up the jib
Once you have set up the main look at the jib. Your boat specification should tell you how far in or out to sheet the jib. The goal in this exercise is to look from behind the boat at the twist in the jib leach which you vary with the topping lift to set the twist so it matches the mainsail and that will give you a nice even slot between the jib and the main.
What to do when conditions change.
Power up - slightly less backstay, more mast ram, maybe a tad more rig tension.
De-power - a tad more backstay and less mast ram.
As a rule the main should be slightly flatter with less twist on flat water and fuller with more twist to provide more drive in wavy conditions.
A final comment on fluky conditions
The challenge in light fluky weather when on the water, is to set your boat up for the average condition. As a result, when sailing to windward, if you hit a patch of breeze, your leech may be too soft and the boat might not accelerate enough. In this condition I will make sure I can slightly over sheet the mainsail, to firm the leech in the puffs but ensure softness in the leach in the lulls when I ease it off again. Bear in mind I sail on a pond where the wind is often blowing over trees.
By experimenting with the variables, you should be a lot more confident that you have the right set up when you next go sailing. If you have identified a good set up then write down the variables, mast rake, spreader angle, back stay etc.
My Goto Document BG Sails and Design
Tips from the guru himself Central Park Model Yacht Club zoom meeting with Brad Gibson