Is a Merlin Jib a Merlin Jib regardles of the age or mast it comes from? I appreciate there are differences on the mainsail due to loose footed, carbon spars etc but what about that jib?

I'm not aware of any significant differances in jibs these days, apart from sailmakers differing theories about how to make them work. I don't think the mast section/material has any great input, but will stand corrected if someone knows better!

In days gone by though the sheeting angles were wider, and the jibs were often slightly larger (Around 3.0m2 instead of 2.8m2) so this may have had an influence on shape.

That said i'm certain a 2 year old modern jib would perform better on an old boat than a 25 year old knackered one!!

The things that do vary are the luff and leech lengths. These are fine provided you account for the differanced when setting up the boat: A differant luff length will render your rake settings useless while a differant leech length will require you to move the jib car either forward if it's shorteror back if it's longer.

Your measurement certificate will have a sail configuration for your boat.  This gives the maximum sizes for the jib and main.  Should you change the configuation, technically you will need a new measurement certificate.  In other words, you cant have a number of different set ups!  It makes sense, otherwise the black bands on spars would have to be moved too!

Standard config for most boats today is a 2.8 m2 job matching a 2.503m jib 'foot' (ie the black band measurement)  These measurements are written on the sail by the measurer.

On the other hand, unless yo are competing at the top level, i dont suppose a different matched pair really matters.  But a big jib with a big main...

From my certificate Mainsail Luff 5820, Foot 2405 and Headsail area is 2.9m. With an 8year old crew a huge jib is not realy an advantage as when it blows they can't pull it as easily!! I have two mainsails in nice condition but my jib's have seen better days.

If I wanted to measure the luff would I include wire eyes or just the cloth?

Have a look at the class rules, it states in those how to measure the sails. Rules can be found on the RYA  site.

Perhaps Mags can put a link in?

requires PDF reader which you probably have

Measurement definitions are all as the Equipment Rules of Sailing (Downloadable free from the ISAF site, www.sailing.org) nowadays, and the merlin rules don't really tell you alot about how to measure the sails.  For a jib luff, you are just measuring the cloth, so your forestay wire will be longer.. If you are ordering a new jib, take a few moments to clarify the situation with your sailmaker.

Thanks for the advice, I was thinking of looking for a second hand sail but as mine is 2.9 and newer ones seem to be 2.8 that might be an issue.

Going with a smaller jib isn't necessarily an issue, however, most of the 2.8sqm jibs that still exist have been cut to go with the narrower sheeting angle that came with raking rigs.  From my memory (limited to the last 21yrs I grant you)it was the launch of Canterbury Tales (3413) with her deck stepped rig that set the now standard 5702/2503 mainsail with 2.8sqm jib, although I stand to be corrected on that..

Trying to set a jib cut for a narrow sheeting angle on a boat designed for a wider sheeting angle is much more of an issue..

New jibs are not huge money so it would be worth talking to Dick Batt or someone else whao was making Merlin sails in the era of your boat to talk about it..

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