505 Tuning Guide

  • Last Updated: agosto 23, 2017
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This tuning guide has been put together by Ethan Bixby from North Sails in North America, who is the designer of our newest 505 sails.

The calibration scheme below does not reuse existing numbering schemes. We have tried to develop a calibration scheme that supports the following:


Uses reference points common to all builder’s 505s, forward tack and aft tack 505s, etc.
Uses zero as the neutral, or basis datum setting.
Uses negative numbers for LESS of a control and uses positive numbers for MORE of a control. If that is not clear, the light air settings are on the negative side of the datum and the positive numbers are heavier air settings, finally forward is negative, aft is positive.

Mast Step

Measure from the back of the mast along the top of the CB cap, aft, over transom, to the aft most point of the hull (it may be slightly aft of the transom). Ignore the rudder fittings. The mast should be stepped as close to 10′ 0″ as you can get it and still get the right low bend at max. rake and not hit the partners. Don’t worry if the step extrusion in the boat keeps you about 1/2″ or an inch forward of this point.
Note: The aft end of the hull is where the class rule measurements are taken, not the actual face of the transom. This value is more reproducable across different hulls.


With no jib hoisted, connect a tape measure to the end of the jib halyard. Hoist and cleat the halyard to the point where the «O» on the tape measure starts at the top of the the «gooseneck band» on the mast, with reasonable tension applied. On a boat with an integral wire in the luff of the jib, you can use the topping lift as long as it is very close to the jib halyard/headstay intersection with the mast.

Take the jib halyard (or topping lift) forward and measure from the end of the halyard (at the same tension) to the top of the rail at the bow. This is the top forward part of the boat, regardless of where the headstay is.

Adjust the forestay/jib halyard and shrouds until a measurement of 3 ‘4″ is obtained. The shrouds should not be excessively tight, but snug. Mark that setting on the forestay tackle in the boat, where you can see it. This is the datum rake number, mark it in the boat as «0». Measuring aft this should be 25’8″.

For future reference record the distance from the eye to the fork pin to some reproduceable point on the boat. On a Waterat I use the bearing point of the jib tack fitting to the headstay fork/eye junction, and on my boat the distance is 5.5″ as an example. Mark that setting as «0».

All of your rake settings can be simply marked on the luff of the jib adjacent to the fork/eye junction. This is the best repeater and easy to see! Mark one inch increments at additonal inches, i.e. 1,2,3,4,5,6,7.

Note: that the forward rake measurement is much less sensitive to mast bend, shroud tension, hull rocker, and height of transom.

Mast Ram (Bend)

Set rake to 0 (3 ‘4″ forward) or 25’8″ (aft) with mast dead straight and the rig just snug.

Jib Leads (Fore & Aft)

In light or no wind, with the mast rake set to «0» as above, and the ram set to «0» as above, sheet jib in hard. Sight down lead lines on the jib clew. Move jib cars fore or aft until the jib sheet is lined up with the more vertical line. That is the standard power setting. Mark that hole on the jib track as «0». Number holes with negative numbers forward from there, and positive numbers aft of that hole. The angled aft (slightly closer to the horizontal line) is for heavy air depowering when raked. In practice, you may not need to actually move the jib car for heavy air, as rake changes the lead angle for you. You may need to move the jib lead aft for light air, flat water.

Jib Lead Tension

With the jib still sheeted as above. Mark a spot on the jib sheet that is clear of the cleat and turning blocks. You will be calibrating the jib lead tension based on that mark, so mark the corresponding point on the seat tank as well.

Note: that we use the «normal» trim line on the jib as this allows us to reproduce fore-aft or up-down jib lead measurements across any jib sheeting system, long and short luff jibs, and forward tack and aft tack boats.


Roll the boat over on it’s side. Pull board out and put it in the down position. Set the leading edge of the CB perpendicular to the bottom of boat at the centreboard trunk. Mark the head of the board (perhaps aft end of the head) level with the top of the CB cap. Mark this as «0». Mark increasing numbers in 1″intervals up the back end of the head. Mark «1,2,3,4,5,6,7,8». Also mark a position with the board as far down (raked forward) as possible.
Also measure from the top of the centreboard to the aft end of the hull on the centreline. With an HA board this number should be roughly (depends on rake and board depth) 122″.

Note: we’re open to suggestions on this. This measurement will result in different effects with different CB planforms. I think what we are really trying to measure is where the centre of area or pressure is fore and aft and below the hull.


Set the spreaders to 16.5″ length (measured from the side of the mast to the shroud), and for 6.5″ poke. For lighter teams, and in very light or very heavy air, increase sweep to 7″. Lighter teams can also shorten spreaders to 16″.

Note: that this measurement is from the shrould to the closest part of the mast, along the spreader. This measurement assumes that your spreaders are 124 inches above deck level (old US specs) AND assumes your shroud chainplates and mast step locations are the same as other boats. If any of spreader bracket height, mast step position and shroud chainplate location are different on your boat, these measurements will not result in the same effects we get.

We have a comprehensive measurement system to relate spreader height, hounds height, spreader details, and triangulation of the chainplates. Please contact us for this as it is a much better tool to obtain the actual deflections and angles.

Class Experts

Charlie Cumbley

Gosport, United Kingdom
Manufacturing – Gosport, UK

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