D4 Tuning

IOM radio control yacht sail tuning

We are constantly working and thinking how we can improve IOM radio control yacht sail tuning as big speed gains can me made from a efficient rig.

Some basic principles that we work with.

  1. Fore stay tension  It is very important that the fore stay does not sag as this results in the jib becoming too full and this happens when the breeze is up and right at the time when you don’t need it ! Pre bend in the mast will fix this. A mast with no pre bend will need  the side stay chainplate base  about 20 mm aft of mast step with a lot of tension on the rigging to keep fore stay tight without bending the top of the mast too much.
  2. Mast bend for and aft  With a perfect sail and the right wind conditions the mast will be best straight once the pre bend is pulled out with the back stay. However, not all sails are perfect and the wind is always changing in wind strength ! When rigging the boat I always first set up the mast so it is straight. Then I will set up the sail with the right amount of twist for the given conditions .  I then will look at the fullness and shape of the sail and put more back stay on or less, alter the spreader angle and change the mast ram to get the desired shape in the sail . After doing that often the mast will not be straight at all and sometimes it may have a S bend  however I see the result of a good sail shape is most  important. We use a lot of side stay tension and adjustable spreaders to enable us to easily adjust the sail shape. I have also found by letting the mast gate off and letting the mast bend a lot fore and aft down low in a breeze can be very fast. This may cause wrinkles across the bottom of the main .I call this a speed pump and dont get distracted by it as I know it is fast in a strong breeze
  3. Mast bend sideways Usually when the mast bends a lot sideways the boat does not point as well. That is one reason we use the mast gate in our boats so we know it does not have side bend down low . The spreaders also control sideways bend. If the spreaders are too long it can cause the mast to bend to leeward in the middle and this can result in the jib slot being closed that is not efficient. Some people have windward side bend down low to open the jib slot but I dont think this helps the main sail setting. If excessive pre bend is used the mast is very difficult to control sideways with it always trying to flick off one way or the other. If you can make the mast flick off sideways at the very top  this can be a good thing as it can free the main leach in the puffs
  4. Mast rake This is all about balance . We aim for a neutral helm  when the boat is sailing on the wind with the controls are  let go and almost lea helm when the boat is flat in light conditions.(when the boat leans it naturally wants to round up from the hull shape) The further forward the mast is raked results in more lea helm and the further aft the mast is raked results in more windward helm. Twist in the sails has the same affect. The more twist in the main the more lea helm and the tighter leach in the main the more windward helm.Opposite with the jib. More twist in the jib results in windward helm  and the less twist in the jib results in lea helm. We set our boats up with a lot of rake as we like to have a lot of twist in the main
  5. Jib sheeting  We have found best results when the mainsail is central the distance between the center of the jib boom and the center of the mast is between 65mm and 70mm. Downwind when the main boom hits the stay the jib should never goes past 90 deg to the interline and back to 75 deg when it is nose diving conditions
  6. Main sheeting We have a high button on our radio so if we want to point f0r whatever reason we press this and it brings the main sail into the center line . Normal sailing with all rigs the main is off the post between 8-10mm
  7. Vang  This will totally control your twist upwind and down. The  variable geometry vang  is very good to enable the right amount of twist down wind . We have found the less twist down wind is fast unless the boom hits the water too much
  8. Jib up-haul The amount of tension on this depends on how far forward the pivot point is and how much tension is on your back stay . The more pre bend on a mast results in more tension on the up haul. Ideally the jib will twist off when a gust hits and this will not happen if too much tension is on the up haul
  9. Main boom height This needs to be low as possible without hitting the water. This is all about less sideways force in the breeze
  10. Jib boom height  Again this needs to be low as possible without hitting the water  A boat will nosedive twice as quickly when the goose winged jib hits the water
  11. Counter weight   15 gram is best for A rig and 20 gram for B rig .Usually best if when the boat is held tipped on its side that the end of the boom stays level. Also if the weight is higher it seems to be more responsive and helps with getting the jib boom out sooner
  12. Rigs quick to change If sailing in regattas it is very important to be able to change rigs quickly. Many regattas have been lost because a fellow competitor saw the breeze and swapped rigs while the rest were napping. This means having rig boxes that are set up carefully so rigs can be stored in tune and only requires attaching the rigging screws and sheets to quickly get under way. Always check mast bend and sail shape before sending boat out.