Boat Tuning

Introduction

Following the success of the course on interpretation of the Rules for Racing, the following has been produced by Bill Letten, These have been produced to help achieve better results by understanding tuning fundamentals. The concepts discussed, in most cases, are basic but should be helpful for all boat classes when tuning. To the experienced the notes may be fairly obvious but to the novice they may seem complex. It is well worth examining your boat against these notes to improve your understanding.
The following is the recommended sequence of working through the tuning of any boat although the notes are largely associated with the one-metre:

Checking Boat Balance

Start by sailing the boat on a whole-sail breeze day. Firstly visually check the rudder is centred prior to sailing. Then sail as close to the wind as possible and then take your hands off the transmitter sticks. Observe whether the boat tends to Luff (sails closer to the wind) or bears away from the wind. If the boat does the former then it is balanced, providing the alterations are minimal (gentle luffing). If it bears away from the wind then tuning becomes very necessary.
Figure_1.jpg
Figure 1
If the boat Luffs heavily then it has weather helm (Figure 1, item 2). This is NOT acceptable; normally a maximum of 3 to 5 degrees of weather helm is all that should be necessary (Figure 1, item 1).
A definition of weather helm is the amount of rudder needed to maintain a course and is achieved by pushing the tiller to the windward side of the boat.
Leeward helm is the opposite (dreaded in all respects) as it reduces windward sailing efficiency in hydrodynamic and aerodynamic terms and becomes very obvious problem when comparing performance against other boats in the vicinity.
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Spreaders

In Figure 3, for a one-metre:
Item 1 – The spreader width should be narrower than the deck base shroud attachment point. Each spreader is approximately 45/55 mm.
Item 2 – The shroud deck attachment points are approximately 40 mm aft of the mast.
Item 3 – The mast is bent forward from the spreader position approximately 30/40 mm for a one-metre.
Note: Bend the mast before drilling any holes.
Item 4 – Use backstay tension to straighten the bent mast.
Item 5 – Spreaders are fitted halfway between the deck and the Jib take-off point.
Figure_3.jpg
Figure 3
The most effective tip for the one-metre top-suit is to bend the mast forward from the spreaders to the tip by about 25/35 millimetres from upright; then neutralise this effect by use of back-stay tension to regain the masts vertical state. This achieves a very vital requirement by putting more tension on the jib-Luff thus allowing the boat to sail at a finer angle to the wind.
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The Slot

It is essential to have the correct slot between the jib-boom and mainsail as measured from the centre-line of the boat. This has to be done by trial and error – if too close the mainsail Luff will be back winded (will empty of flow); if too open the low pressure on the lee side of the mainsail will not be maintained. Small adjustments must be made in millimetres and can result in a much increased speed.

Figure_4.jpg
Figure 4

Flow & Sail Shape

Flow and sail shape are controlled by the clews of the Jib and the Mainsail (rear lower corner of each sail) plus kicking strap tension.
Sails should be adjusted as follows:
In light airs use Minimal flow plus a little kicking strap per figure 5 item 1.
In medium airs use Maximum flow and power (big sail aerofoil) and a much tighter kicking strap per figure 5 item 2.
In a blow use Minimal flow with a tight kicking strap per figure 5 item 3.

Figure_5.jpg
Figure 5
The kicking strap can be adjusted so that you can see the exact shape of the mainsail and its flow. When it is highly tensioned the leech of the sail (aft edge) will increase sail power by making it flatter and bringing it nearer the centre-line and lower to the deck. The best way to view this is looking forward from the stern with the boat heeled on its stand.
In light airs the clew (aft lower corner) should be moved slightly forward and the kicking strap eased; the object is to allow twist into the height of the sail. This will make the top of the sail operate at a wider angle than the lower half which is relatively sheeted closer to the centre line.
The reason for this is the wind in fluky areas (uneven wind speed) often is stronger at the top of the sail than nearer the water surface. Another reason for having little flow, or a flat sail, is the wind often does not have the strength to follow the curve of the sail and the mainsail will stall.
In a blow, on open water, the sail again must be kept flatter because as the wind increases the flow moves aft and makes the sail less efficient. In this case when sailing at Hove with more open water, a combination of a tight kicking strap and lots of Cunningham is needed. (Cunningham is used to tension the lower forward corner of the mainsail).
Tensioning with the kicking strap, clew outhaul and Cunningham all require sensible use, if you sail on a park lake you need a looser set-up than perhaps at Hove Lagoon where the winds are steadier by comparison.

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Racing Tips

Above all else use your observation powers.
When sailing to windward, respond to heading puffs and tack if you are confident that they will fill in.
Do not sail blindly into a calm patch if it can be avoided.
Watch for ripples on the water for a guide as to where the best wind is located.
Avoid the vicinity of banks, reeds and trees because in many cases the wind is lifting over them and the lower part of the rig will not be working. The exception to this is mainly in the summer when thermal action can take place, but it can be hard to observe.
When sailing downwind and the wind slackens, Luff a few degrees to bring the apparent wind further ahead. Equally when you receive a strong gust, bear away from the wind so the boat can absorb the extra wind pressure and stay on course.
Do not sail the boat over-heeled it will not go any faster and will not point. So ease the mainsheet.
Round the marks from the outside to the inside at a speed the boat can cope with to avoid stalling. Nearing a stall the rudder is overpowered and the boat may end up head to wind. Above all maintain steerage way because without boat speed you are a dead duck. The surrounding boats have you at their mercy due to possible rule infringements and lack of maneuverability.


Drum Winches

When re-rigging, check the drum winch sheeting will not come to the end of it's travel. If you have end point adjustment on your transmitter set these to 125% both ways. Run the Winch from full-in to full-out and count the number of turns. The sheeting then needs to be wound on at least these number of turns, including any partial turns. Return the end point adjustments to 100% and rig in the normal way. I found out the hard way when the force of the winch decided it had right of way and nothing was going to stop it.



Salt Water in Radio Gear

Wash off thoroughly in fresh water then soak in solution of bicarb of soda having first put a small amount of bicarb onto any spots of blue verdigris on the board/component. Soak in the bicarb solution for 24 hours, rinse well in fresh water dry off for 24 to 48 hours, then see if it works. this has worked very well for three 2.4 receivers that were submerged in Hove water.

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