Most, if not all, full size racing yacht skippers will use telltales to assist them in sail setting and steering. On full size yachts and dinghies there are likely to be telltales at various places on both the main and jib sails, in addition to leech telltales, such as those fitted to the RC Laser.
In a radio controlled boats like the RC Laser, because the skipper is not on board, there is little point in having streamers that help with sail settings that cannot be adjusted from the shore. Also, telltales that assist steering are of little value as they are too difficult to ‘read’ from any distance.
To get maximum benefit from leech telltales you will, on the RC Laser, need to add one more telltale to the leech, in the area of the ‘Laser’ logo (but do not cover it). This additional telltale should be permissible within the rules as the added telltale can be considered as ‘decoration’. You will have to find some material similar to that used for the original ‘as supplied’ telltales – possibly in the form of ‘gift/Christmas decoration’ or similar. It does not have to be the same length as the ‘supplied’ telltales, in fact slightly shorter may prove more effective for this particular position.
The main value of these telltales is in setting the amount of sail twist you have.
The second telltale down from the top (the one you just added) is the most important and should be streaming nicely with the other/s lower down (ignore the streamer at the very top for this purpose). If it is not then it is likely you have either too much or too little twist in the sail.
To correct the amount of twist (see diagram below) in the sail you will have to tighten or slacken the sail leech tension by moving the inner slider of the outhaul towards or away from the mast, depending on whether you wish to increase or decrease the amount of twist. When this telltale disappears behind the sail (as seen by a skipper if he were in the boat) you have too little twist and when it flutters in front of the sail you have too much twist.
Try experimenting with the settings until you have the feel that the boat is sailing as fast as you can make it go.
When the sail is set correctly you will be able to get some feedback from the telltales while racing. Try to keep them streaming nicely as this means the wind is leaving the sail leech in ‘laminar’ flow rather than ‘turbulent’ flow. Laminar flow is to be preferred.
The very top telltale is useful as a wind direction indicator. If you are out on the water and are not sure from which direction the wind is coming look to the top telltale for help. It is amazing how wrong you can be about wind direction out on the water when you are seeing the boat from from the shore.
Unfortunately, there is a bit more to sail trim than this. There will be occasions when you will want ‘excessive’ sail twist and that is when you are being overpowered and it is not possible to change down into a smaller sail. If your boat is continually winding up into the wind you have too much of what we call weather helm. To reduce weather helm let off the outhaul a little so the amount of twist in the sail increases. This will ‘spill’ some of the wind power and help you keep the boat under control. In addition, because the mast will straighten as you do this, the centre of area of the sail moves forward. This forward movement of the centre of area also has the effect of reducing weather helm.
Some skippers like to set their sail so the boat sails in a straight line with hands off the control sticks (rudder centred). Some prefer a set up which gives the boat a little ‘weather’ helm with ‘hands off’. See what suits you best.
For a rough guide to setting the correct sail foot curve Jon Elmaleh suggests “A good indicator is that the boat should be able to sail itself going to windward (neutral helm). Too much weather helm (the boat rotating into the wind) indicates that you need to flatten the foot curve. A leeward helm (the boat falling off the wind) shows the need for an increased foot curve.”