I was wondering if anyone could help me understand masts and the black band rule?
 
I'm on the lookout for a carbon mast for Once Bitten, and want to make sure it will fit! She was built as a tank-stepped, but converted to deck-stepped many years ago, so I don't know if the deck will be at the same height as 'standard' (if there even is such a thing), and if it matters if it's higher or lower.
 
So basically -  Are most/all deck-stepped masts the same length?
What height above the hog/keel is a 'standard' deck stepped mast foot?
What constraints do the rules put on mast height?
Can I buy just about any mast and stick it on?
Just what is the black band rule all about? :)
 
What I'm after is something reasonably good - but that gets me access to the greatest range of second hand sails. (In other words, if a super-spars is good enough, that's great, but if all the second hand sails in the next 5 years are for bendier masts - then I'd rather pay a few hundred extra for something better - even if it's overkill for me and the boat).
 
Cheers all, and hopefully see you on the water in a couple of months,
 
Andrew (Flowerchild) Maddison

The lower black band height is measured from the shearline (intersection of topsurface of deck and a intersecting line of the outer hull). You can always move the lower band within the limits mentioned within the class rules. You would of course have to adjust the gooseneck and top band.
 
If you measure the height of the mast step above the shearline,you then have a measurement to use for checking against any prospective mast. Add this measurement to the distance between the mast foot and lower band: if within limits of the rules you are ok.  If you have a high deck you can always chop a bit off the bottom of the mast. 

Different builders construct their decks differently, resulting in rather wide variances!
 
The good news is that generally wood decks tend to be higher, so therefore the mast is usually too long.
 
Mast manufacturers are generally interested in bulk production and this has resulted in a "one size fits all" approach. Most Superspar masts are well under the maximum tolerance, which ideally should be pushed as far as you dare to maximise headroom and hoop clearance.
 
If you buy a new mast for a wooden boat - or an older mast from a wooden boat to put on a plastic boat - it's worth checking this - isn't it Ian Mackenzie? ;) 

Glad this thread was brought up as I am starting to worry about it myself...

Cheers all

The tricky bit is measuring the vertical distance between the sheerline and the lower black band (or the mast step as you can work out the rest from this distance).  The point you are trying to measure from is the intersection of the outer surface of the hull skin and the upper surface of the deck - this is conveniently covered by the gunwale and the only way of working out where it is uses a template that goes round the gunwale.  You then measure across from this point to the corresponding one on the other side vertically below the aft face of the mast.  Have fun!  The mast & sail bit is much easier to answer.  The bend characteristics of the SuperSpars & the whippier masts are not that different and at the level you and I sail at you can pretty much reckon a sail cut for a Chipstow or Selden will work on a Superspar.  There's a big difference between a carbon mast & an alloy one particularly in gust response; the Superspar is relatively stiff for a carbon mast but it is also pretty bombproof - I've done several things with my 1st generation white mast which a Chipstow wouldn't have survived, such as sticking it into the mud in Southpool creek just recently as well as forgetting to put the puller on down a windy reach!  Incidentally, Once Bitten probably is still quite high in the foredeck like most early Ian Holt designs so most masts will fit but need trimming down.  You will probably find your present mast was made to the initial dimension of the rules which is now the mid-point of the tolerance (680mm) and most people go for the upper limit (730mm)

Dave Bursey has a mast for sale that would fit the bill.

Hi All,
 
Thanks for the replies. I've measured my old mast, and it seems to be 640cm long, measured right to the very end, with the bottom of the goose-neck black band at about 60.5 cm. I have no idea what the height above the sheerline is (I might try and measure it tonight, but from the sound of it, will get it wrong!)
 
Nice Mr Dave Bursey has measured his one that's for sale, and it's 637cm not counting the top pulley, so does that sound like it's basically the same length and worth the risk?
 
Cheers - Andrew. 

There were some photos of how to measure to sheerline here:
 
http://www.merlinrocket.co.uk/gallery/view_photo.asp?folder=gallery/building_and_repairs&file=sheerline_measurement.jpg 
 
But link no longer works, it is from old site. Does anyone know how to access the photo?

 I must ask what is happenning with the new photo gallery.
 
 
Here's the pic you need (but without the original comments):
http://www.merlinrocket.co.uk/gallery/building_and_repairs/sheerline_measurement.jpg 

A picture is worth a thousand words, thanks everyone.

Ok, so the black band above the shearline I now vaguely understand, but how does that then relate the the top band, luff length or overall mast height?
Cheers, Andrew.

Once you have the lower band position, distance between top of lower band and bottom of top band is the mainsail luff length as per your certificate. 

Once you have the lower band position, distance between top of lower band and bottom of top band is the mainsail luff length as per your certificate. 

Don't think there is really a good way round this without measuring the sheerline to mast step distance, however if Mr Bursey's mast is at least the same if not a little longer from the mast step to the lower black band you will be OK, but it's feasible the new mast might be a bit longer and so put you over the 730mm dimension (& so breaking a measurement rule) - unlikely, but you want to be close to this.  The lower black band upper edge is the measurement datum point and the standard rig height of 5720mm is to the lower edge of the upper band.  The mainsail area is measured as a nominal triangle using the distance between the mast bands & the distance from aft edge of extended sail track to the boom band.  Your mainsail cannot extend beyond these bands within the rules.

Who is our nearest class measurer to Lymington Hampshire...?

Hi All,
 
Well I bought the mast (Thanks Dave) and the boat is now with Laurie for a few minor repairs.  The mast went too and he's offered to measure the shearline, and shorten the mast for me if it needs it. Or to put in another way, it's now safely in the hands of an expert.
 
Thanks all for your help - Andrew.