A group of 505 sailors including Ethan Bixby and I have been discussing a calibration scheme. We believe that some of the measurements used earlier, such as measuring rake from the mast tip to where the hull and transom meet, are not very reproducible across different 505s. We decided to alter the way some of the measurements were taken so they would be more consistent across different 505s.
We have tried to develop a calibration scheme that supports the following:
North Sails has a Tuning Matrix that tells you what numbers to set each control to, for a given wind range.
The back of the mast (back of the extrusion) measured at the height of the mast step/centreboard cap should be just over 10 feet zero inches from the aft end of the boat.
Measure from back of mast (extend the sail track down if it is cut away) along top of CB cap, aft, over transom, to aft most point of hull (may be slightly aft of transom).
Ignore rudder fittings.
The mast should be stepped as close to 10' 0" as you can get without being too close to transom.
10' 0.375" is close enough.
Note 1. 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 reproducible across different 505 hulls.
Note 2. Many 505s have a mast gate positioned such that you cannot step the mast at 10' 0" and still ram it straight
at the standard rake.
If this is the case, move the mast butt forward in the step until you can rake to 3'4" with a straight mast.
You may wish to consider rebuilding the back of the mast gate area so that you can rake to 3'4" with a straight mast.
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1. Ensure your spinnaker pole topping lift enters the mast just below your jib halyard turning block.
Remove the topping lift from the pole, and tie a small loop in the spinnaker pole end of the spinnaker pole topping lift.
Insert the end of a tape measure in the loop. If you happen to have a shackle on the topping lift, use that to fasten the tape measure to the topping lift.
If you have a stuff luff boat, you can use the jib halyard instead of the topping lift.
Cleat the topping lift or jib halyard such that the tape measure inserted in to the loop or shackled to the line starts a
t the top of the "gooseneck band" on the mast, with reasonable tension applied. Don't have a gooseneck band?
It helps if you have a low stretch spinnaker pole topping lift, as the measurement will vary less with the tension you put on the tape measure. Try to pull a similar tension |
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2. Take the tape measure forward and measure from the end of the halyard/topping lift (at the same tension) to the top of the rail at the bow.
3. Adjust forestay/jib halyard and shroud tensions until a measurement of 3'4" is obtained. |
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The shrouds should be just tight; I use 180 pounds, which is number 18 on the Loos gauge. At this low tension the mast should be straight without having to play with the mast ram, but check anyway and use some ram down if necessary to get it straight.
4. Mark that setting on the forestay tackle in the boat, where you can see it. This is the standard rake number; mark it in the boat as "4". By the way, this is the same as the old 25'8" aft rake measurement. If you have a stuff luff jib system, you can also mark the luff of the jib at the height of the cotter pin connecting the forestay to the forestay extension. 5. Ease forestay/jib halyard and tighten shrouds until the measurement is 3'5" (tighten the shrouds to keep them at 18 on the Loos gauge). Mark that setting as "5". Mark 3'6", 3'7", 3'8", 3'9" (if you can rake that far) as 6,7,8 and 9, respectively. If your boat can rake further forward than 3'4", mark that as well. We are currently using rake positions as far forward as 3'2". |
Using the marks that you put on in the Mast Rake step above, set the mast back to the 3'4" rake,
with the Loos gauge at 18 (180 pounds of tension).
Check that the mast is straight fore and aft (it should also be straight sideways!), and adjust the ram if necessary to get it straight fore and aft. You can check the mast by sighting up the mast track after taking the boom off the gooseneck. A more thorough way of checking is to run the main halyard down the back of the mast with enough tension for it to be straight. Then check for any gap between it and the back of the mast part way up the mast.
With the mast straight, put the deck scale on the deck, with "0" lined up with the back edge of the chafe plate, with
3/16" increments, positive going forward and negative going aft.
You will find it hard or impossible to read these numbers while sailing the boat, so you now have to create
a "repeater" set of numbers that you can easily read.
A good way to do this is to mark lines on each side of the mast,
such that you can line up the line and the top of the ram car, while sitting in the normal skipper's position on the seat
tank.
Some of the European 505 sailors make a pointer to reduce any parallax error.
You are going to end up with a nice scale at deck level that you cannot read, and a bunch of magic marker marks on the side of the mast, but the point is that when comparing two 505s, the marks on the side of the mast are in different places, with different increments unless the boats happen to have very similar ram geometry (fittings in same location, same length tube, etc.). So we cannot make a pre-fab scale for the side of the mast that works on all 505s.
We have ready made scales for deck level mast bend and jib lead you can print off, cut out, and tape to the boat or mast with clear packing tape. We also have scales for centreboard angle.
While a new or a well built older 505 can handle high rig tension, many older boats do not have the structure or fittings to handle very high rig loads.
With the rake at 3 and the mast ram at 4, set shroud tension to 300 lbs. Mark the shroud tackle here as 3,3.
With the rake at 4 and the mast ram at 3, set shroud tension to 500 lbs. Mark the shroud tackle here as 4,6.
With the rake at 5 and the mast ram at 3, set shroud tension to 500 lbs. Mark the shroud tackle here as 5,5.
With the rake at 6 and the mast ram at 3, set shroud tension to 600 lbs. Mark the shroud tackle here as 6,6.
With the rake at 7 and the mast ram at 3, set shroud tension to 700 lbs. Mark the shroud tackle here as 7,7.
With the rake at 8 and the mast ram at 3, set shroud tension to 800 lbs. Mark the shroud tackle here as 8,8
If you've gotten this far without breaking the boat, congratulations!
In light or no wind (or in the lee of something), with the mast rake set to "4" as above, and the ram set to "0" as above,
sheet the jib in tight. Snug up the jib cunningham to a normal sailing tension and so there are no wrinkles in the luff.
A loose jib cunningham leaves the jib slightly higher or lower (depending on how the cunningham is rigged) and could
affect your jib sheet calibration.
Sight down the trim lines drawn on the jib clew (The North jib has two trim lines, use the upper one).
Move the jib cars fore or aft (or move the lead block up and down if that is how your boat is rigged) until the jib sheet
is lined up with the more vertical trim line.
I sight the trim line by standing on the leeward side of the boat in the dinghy park and pushing my head against the jib
until I can line up the trim line with the jib sheet. Mark that hole on the jib track as "0".
Number holes with positive numbers forward from there, and negative numbers aft of that hole.
The angled aft (slightly closer to 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 up to 3 holes for light air, flat water conditions, and forward 1 or 2 holes for
light or medium air and lumpy conditions.
I normally sail forward one hole, so at the +1 setting.
Note the Ronstan track used on many 505s has holes spaced at 3/4" intervals, so our scale does too.
A capability to move the lead inboard may be an advantage, particularly on a forward tack boat.
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 center of area or pressure is fore and aft and below the hull
Note that this measurement is from the shroud to the closest part of the mast, along the spreader. This measurement assumes that your spreaders are 124 inches above deck level (both UK and US specs call for this) 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.
Rake:
Note that the forward rake measurement is much less sensitive to mast bend, shroud tension, hull rocker, and height of transom than the old way of measuring aft using the main halyard. Most 505s have straight rails, whereas transom height and rocker are different. This measurement is sensitive to the height of the deck and gooseneck band above the rail,
but I believe most 505s have maximum round in the deck, to raise the deck and gooseneck bands as high as possible.
For comparison purposes the following table compares mast rake measured aft and measured forward.
| Measured Aft | Measured Forward |
|---|---|
| 25' 0" | 3' 8" |
| 25' 2" | 3' 7" |
| 25' 3" | 3' 6" |
| 25' 5.5" | 3' 5" |
| 25' 8" | 3' 4" |
| 25' 9.5" | 3' 3" |
| 25' 10.5" | 3' 2" |
You will note that these marks on the side of the mast have different spacing between them than those on the deck, which were all 3/16". On the side of the mast the increments will be smaller at the bottom of the range than at the top, and they will be larger than 3/16".
For reference to Ullman numbers.. The Ullman/West Coast system had "7" as the straight mast setting, while the North system has "0". The Ullman system uses fixed 1/4" increments on the side of the mast. With typical Waterat mast ram height on mast and tube length, these 1/4" increments are very roughly 3/16" inches at deck level, though as you go lower on the mast 1/4" translates to less and less measured at deck level. You might try the approximation of the Ullman bend number as 7-North number, as they use "7" as the straight mast number and increase the numbers going down the mast. The Ullman mast bend number that corresponds to our mast bend of "3" is "4" (7-3=4).