420 Tuning Guide by Sailboats Speedsails

The aim of this tuning guide is to help you get the most out of your 420. Although the following measurements should enable you to set your boat up close to its ideal settings, it is worth bearing in mind that it is only a guide and minor alterations may be required for different boats and helmsmen.

Spreader Settings

The two measurements for spreader settings are length and deflection. Spreader length
controls the sideways stiffness of the mast and is taken by measuring the side wall of
the mast to the shroud. We recommend sailing with 470mm spreaders although very
heavy crews may wish to increase this to 480mm to keep the rig powered up in
breezier conditions. Spreader Deflection is measured by putting a straight edge from
shroud to shroud and then measuring from the mast to this edge. This measurement is
not critical as it is only a guide to getting the correct pre-bend which we check again
later..

Setting	Superspar	Proctor Kappa
Spreader Length (L)	470mm	470mm
Spreader Deflection (D)	160mm	155mm

Rig Tension

Wind	Rig Tension
Light	~400lbs (30 on Super Spars Gauge)
Heavy	~470lbs (32 on Super Spars Gauge)

Rig tension is measured on the shroud and varies with wind strength. Start off with
400lbs in all light winds (30 on the Superspar tension gauge) and increase up to
470lbs (32 on Super Spars gauge) in heavier winds to prevent excessive luff sag..

Mast Rake

Conditions	Mast Rake
< 15 knots	19’10 1/2” – 19’11 3/4” (400lbs)
> 15 knots	19’8 1/2” - 19’9” (470lbs)

Mast rake is measured from the top of the mast to the top of the transom. To do this hoist the jib with 400lbs and no chocks. Attach a long measuring tape to the main halyard and hoist to measure 16’1” to the top of the black band at the gooseneck. Cleat the halyard and swing the tape around to measure the distance to the top of the transom. This is the mast rake.

Chocks

The masts neutral position is where the mast sits with full rig tension on but no forces
acting upon the sails.

Conditions	Chocks
0-5 knots	0 Chocks when crew siting to leeward. This allows the bottom of the mast to bend, flattening the bottom of the mainsail and reducing the tension in the leech
5-10 knots	1 Chock to fill the gap when mast is in neutral position. Crew sitting to windward or high wiring
10-18 knots	When the crew is flat out trapezing, putting in a second chock will help to maintain the desired pre-bend.
18+ knots	1 Chock. When you are really overpowered, removing the 2nd chock again allows the mast to bend, opening the leech and de-powering the sail

Centreboard

In sub-trapezing the board should be angled forward. As you get to flat wiring (almost
planing upwind) the leading edge of the board should be vertical. As it gets windier
the board can be raked further back. In flat water you may raise it up to 3” on the
handle. In rough seas it can be lifted up to 6” to help you steer around the waves.

Mainsail

Top Batten: Push in gently in light air. As the wind builds you should push it in more
to remove the vertical creases from the batten pocket (it should be in quite firmly).
Outhaul: This should be pulled out tight almost all the time upwind and should only
be eased up to 1” in moderate breezes when it is very choppy. Downwind the outhaul
can be eased 11/2 – 2”.
Kicker: Until you are overpowered and have to ease the main upwind, the kicker
should only have the slack taken up as mainsheet tension will control the leech
profile. Above this wind strength you should ensure there is enough tension to keep
the top tell-tale flying approximately 80% of the time.
Cunningham: In 18+ knots you can gradually apply cunningham to de-power the sail
and remove some of the horizontal creases on the luff.

Jib

Sheet Tension: The jib sheet is used to control the jib leech and slot shape. Generally
the slot should be kept parallel all the way up which is achieved with a combination of
jib sheet tension and barber hauler. If it is light and choppy you may need to ease it
more to give more twist to keep you going through the waves.
Jib Cunningham: This should be tightened sufficiently to remove the creases from
the luff of the sail. More tension is required as it gets windier.

Barberhauler

Windspeed	Amount of Barberhauler
0-6 knots	None
6-18 knots	Pull in 2-3” when jib sheet is tight
18+ knots	Ease it off as you get more overpowered

Spinnaker

The head of the spinnaker is flown 2-3” from the mast. This is done by tying a stopper
knot on the spinnaker halyard.
Setting the pole height is very important as it controls the shape of the sail. It should
be set to keep both of the clews level. The only exception is on occasions when the
wind drops very light and the pole should be lowered to encourage the spinnaker to
set.

Windspeed	0-5 Knots	5-10 Knots	10-18 Knots	18+ Knots
Mast Rake	19’ 113/4”	19’ 11”	19’ 101/2”	19’ 9” / 19’ 8”
Chocks	0	1 Neutral Position	2 Straighter than neutral	1 Back to neutral
Centreboard	Angled Forward	Leading Edge Vertical	Lift as you start planing	Raised – not more than 6”
Kicker	Slack	Take up slack	Begin to Apply	Pull Hard
Cunningham	None	None	Begin to Apply	Pull Hard
Barberhauler	None	2-3”	2-3” Ease as overpowered	No Barbers
Rig Tension	30	30	31	32