building a mirror

Take your time,don't cut corners on the quality of materials and the most important,measure twice,cut once. Even measure a dozen times,cut once.
As for the fast boat,a few of the racing fraternity will be along shortly to help you out.
Have you bought a kit or are you building from your own sourced materials?

Wholeheartedly agree with "haventaclue" about cutting.
You might find this article worth studying carefully before you pick up that first tool!
http://semlab5.sbs.sunysb.edu/~rlarson/ConstructingAMirror/

I haven't built a Mirror and don't know if there are any special ways of making a faster hull, but I've raced a very ordinary one that was overweight against top hulls without being able to detect any difference in raw speed. Drag is probably the main thing to think about, so I'd make sure all the external taped parts are smooth, then maybe paint the hull with Durepox rather than ordinary paint - they claim a 15% reduction in drag and I assume it's race legal as it's often been used on boats in the America's Cup, but you'd want to check to make sure. I've seen hulls with the gunwales rounded off to reduce weight right down to the 100lb limit (to the point that a cross section would be near to circular rather than square), and visually it's more attractive, though hiking over it may be a bit less comforable - I would round them off substantially for aesthetics reasons, but maybe not quite as much on the top side in places where they'll be pressing into legs. I've also seen a beautifully built boat where only one floor batten had been used on each side instead of two - its owner reported that it was noticeably weak as a result and he advised people not to copy it. Weight savings add very little speed because they hardly remove any drag at all (just think about the lack of any measurable distance to how high it will float in the water), so it's always better to focus on building a strong hull.

Hello Ali

Races tend to be won or lost on the upwind leg. Whether you are racing or not a boat which is fast on the wind is usually fast overall.

Apart from a light slippery hull you want a good match of gear properly set up. This means buying the spars, knowing your crew weight and then going to your sailmaker to order the sails. He will take spar type and crew weight into account when he cuts the luff of the sail.

Set the mast rake and rig tension according to a tuning guide. Your sailmaker can advise. Position the jib fairleads for upwind work. Note there are two cuts of jib, the original high clew type, sheeted to the gunwale or side bench and the newer "mini genoa" style most of the race boats use which normally sheet to the thwart. Use lightweight low stretch sheets and halyards - find out what the current race boats are using.

Put a lot of effort into getting the best centreboard you can. Make sure it is to maximum length for the class. If you are not racing you can go a little longer. Mine is 5 inches longer than standard and the boat goes upwind better than it did with a standard plywood board.

I can't advise on spinnakers. Sorry, it's not my style.

Guy Wilkin's book "Mirror racing" is a bit out of date but goes into the details of building a fast boat. New and second hand copies should be available from Amazon.

Cliff

The owner/builder of 70362 is in the racing fraternity and has published an account of his building the boat, which has competed on the international and national class association circuit:
http://www.mirrorsailing.org/images/mirrorsailing/docs/buildingmirror_gb... .
You can probably contact him via the UK MIrror Association site.
There is also a Mirror building slide show on Youtube : https://www.youtube.com/watch?v=bEe8n4ML-P0 .
This shows a totally different approach.
I hope this helps you!
Cheers,
Gernot H.