Here's some answers to your questions.
I've pasted them in and will address them individually:
1-If the luff measurement on a sail is say 457 can I rig this on a regular 460 mast or is it best to go for a 430 with the exact amount of mast extension. Are you really trying to get the exact mast height is what I am really trying to ask?
You need to check the mast specifications on the sail (sail bag perhaps..?).
All windsurfing sails are "designed" on a specific mast.
The bend characteristics are different, for different length masts.
Most 430 cm masts have a 12% bend ratio and this translates to IMCS 21-23 (in the Indexed Mast Check System). If you want to know more about "IMCS" you can ccheck some sail/mast manufacturer's websites, or I can point you to some that give very detailed information on what the "Mast Check System" and "Indexed Mast Check System" are, and how mast bend characteristics are measured and specified using these "measurement systems".
Most 460 cm masts are MCS/IMCS 24-26, so they are a little stiffer.
If you want your sail to rig the way the sail designer intended it to rig, try to get a mast as close to the specifications printed on the bottom of the sail (or the sailbag).
When you purchase your sails (either new or used) ask who ever you buy them from to rig them up once so you can see how much extension they need and how much boom length, to get the correct downhaul tension to give the sail it's designed shape and tension.
On the "exact mast height" it depends on the sail and to some degree the sail designer.
Many sails rig right to the spec, but many others do not.
There are a couple of different ways that sail designeers use to develop the "correct luff length". Some rig the sail and when they have the tack pulley pulled right down into the sheaves at the bottom of the mast base, they use this length as the "spec.". But mast bases are sometimes a little longer and or the pulleys are placed a little higher or lower (or are a different diameter than what the sail designer used) so there can be as much as 5 cm (normally more like 2 cm) "tolerance" above and below the specified length, to get the sail tuned to perfection.
So, best way to "get it right" is to purchase the "recommended best mast" with each sail if you can afford it.
This way you do not have to "compromise" when rigging your sail for any mast incompatability.
If your new sail suggests a luff length of 457 cm, and recommends a 430 cm IMCS 21-23 mast, then get the 430 and put about 27-30 cm of mast bast extension under it to achieve the suggested 457 cm.
If the recommended luff length is 457 cm and the recommended best mast is a 46o cm IMCS 24-26, then you can rig the sail better on a 460 cm mast with zero extension and maybe a cm or 2 or extension on the adjustable top strap.
This can go either way, it all depends on what the sailmaker used when designing the sail.
2-When a sail gives a max boom size what does this mean? As long as the max size is in the range of the boom's parameters is it compatible? Is the figure a maximum because the sail can be "tuned down" and therefore needs less out haul? Does the boom need to be adjusted to the exact length before rigging?
Once again, not a question with a straight forward yes/no answer.
Here's the basic specs for a 6.0 m2 Sailworks Retro with a luff length very close to your example (457 cm).
Luff length (Median): 458 cm
Boom length (Median): 185 cm
Boom length (Max.): 190 cm
Recommended "Ideal" mast is a 430 cm 12% MCS Curve IMCS 21 - 25.
See this link for the entire range of '06 Sailworks Retro's:http://www.sailworks.com/06/document...etro/specs.cfm
So, the first time I go to rig my new 6.0 m2 Retro I would approach the rigging process as follows:
1/ Roll the sail out on a flat smooth grassy surface (or on a "rigging carpet" if you must rig on pavement).
Get out a 430 cm IMCS 21-23 mast and assemble the two halves, using a wrap of vinyl electrical tape over the joint to seal out any water or sand.
Get out a mast extension that will adjust up to at least 32 cm.
Set the mast extension to 28 cm (or the nearest hole above 28 cm).
Insert the mast and mast base up the luff sleeve of the sail and ensure that it goes all the way to the top and seats correctly in the mast cap (or many sails have a pin in the top webbing that needs to seat in a socket in the top of the mast).
Then thread the downhaul line from the base up to the first sheave on the tack pulley, back down to the 1st base sheave, back up through the 2nd sheave on the tack pulley, back down through the 2nd base sheave, then through the 3rd sheave on the tack pulley and back down through the cleat assembly on the mast base.
Pull the line tight with your hands, then get out your downhaul crank and wind the tension into the sail.
Watch as the battens "pull back" along the mast as the tension applied by the bending of the mast begins to spread throughout your new sail.
For the Retro (and other RAF or No cam sails) the minimum downhaul is normally the point at which the batten just above the boom cutout in the luff sleeve draws back to the fore and aft centerline of the mast.
This makes the front of that batten pretty much "tangent" to the mast.
At the same time, if your sail has "tuning indicators" (up in the 2nd or 3rd panel down from the top of the sail) you would want to watch the "scallop" (due to leech looseness which turns into "twist" in the top of the ail when you are sailing) that develops in the panel with the tuning indicator and stop downhauling when the tip of the scallop (closest to the mast) extends in across the panel to the tuning indicator.
Here's a link that demonstrates this:http://www.sailworks.com/06/document...ro/rigging.cfm
OK, now the downhaul is all set to spec, the batten above the boom has pulled back the appropriate amount, and the looseness in the upper panel of the sail extends in to the tuning indicator.
Now you are ready to set the outhaul.
If you want the max. power the sail can deliver (for a particular downhaul tension) grab the outhaul line between your thumb and forefinger and pull the line out directly away from the end of the boom (this assumes the normal 2 part tackle between the clew fitting in the sail and pulleys in the end of the boom. (Line runs from the boom end, to the clew grommet, through the clew grommet, back around a pulley in the end of the boom, back forward to the clew grommet, and then back through the cleat in the boom end.).
When pulling the line between your thumb and forefinger, when the line begins to slip is "neutral" or "zero" outhaul.
Any tension you pull onto the clew of the sail beyond "neutral outhaul" is considered "positive outhaul". Anything less than neutral is considered "negative outhaul". (Some sails work best with a bit of negative outhaul, but most require some degree of positive outhaul.)
Try to purchase a boom that's only about 75% extended with your largest sail. Using a boom that's fully extended tends to make the boom significantly less "stiff".
So, for the example above (the 6.0 m2 Retro with 185-190 cm "boom length") you would want a boom that extends out to at least 210-220 cm.
The boom length can be adjusted to the recommended length before rigging, as a "starting point", but normally you can just open the boom up to a length that clears the clew of the sail as you will probably be "adjusting" the length after you get the sail fully downhauled and get the boom clamped to the mast.
Actually, when "tuning down" or decreasing the available power in a sail, you generally"add" more downhaul, and add more outhaul to reduce the depth of the foil.
Downhaul affects the draft (foil) of the entire sail when tuning.
Outhaul affects the draft in the lower portions (batten above the boom and below) of your sail.
So, to depower your sail you add downhaul and outhaul, to "Power Up"
your sail you reduce both downhaul and outhaul.
3-Is there an on line guide to rigging that you know of? AS you can tell I have very little idea!
Yes, most sailmakers have some sort of "rigging guide" for each type of sail they design.
Sailworks actually has a DVD you can buy that applies pretty much to all windsurfing sails. It's titled "Rigging 101".
Here's the link:
Merry Christmas to you and all those you love,