Some of the big keelboat events in the Solent solve this problem by having a final short leg that is deliberately processional. They similarly might have 30-40 boats finishing within a couple of minutes.

So you might do start-beat-run-beat-run. From the last leeward mark, the line is 400m away on a close fetch. The last leeward mark pretty much arranges the boats into a single file and since it is practically impossible to overtake on a close fetch, they stay that way to the finish.

I've used a dicta-phone or small recording device so I can just say the numbers in quick succession and sort out the order later; I'd also consider a Video camera on the finish line for this reason too. 

Had many a conversation about putting a small tracking device in boats so that you did not have to worry about this....  

Yes we've tried the dictaphone and video camera techniques.  The dictaphone is not a good idea in that you think you've recorded the times and numbers but if there's any mistake its too late to do anything about it when transcribing it ashore.  The video is slightly better in as mych as you can play it slow or pause as many times as you like, but again if you've missed something its too late to look up the fleet and fill in the gaps.

However the idea of a short close reach to get the boats into single file is worth consideration.  So thanks for the thoughts.

And thanks James for your suggestion.  We have a race timer with the ability to do just what you suggest but marrying up the boat numbers with the times is a problem.

I'll give you the benifit of my experience.  Don't do anything fancy, for instance don't try and separate out Juniors from Seniors and record their times on separate sheets (as was attempted on Saturday), that just takes extra time and can cause errors.  Just simply record sail number and time as each boat passes.  Don't try and keep separate lists for separate laps, just keep recording number and time and the number of laps of each competitor will emerge from the records you keep.  Don't write down the whole long number - Lasers prompt you by making the higher digits red - for you to ignore, try the same technique for Toppers, Mirrors and other high numbered classes.  Do use lined paper and if loads of boats cross at almost at once just get the number of each and the time of the first and the last and interpolate.

I said "close fetch" which isn't quite right, but what I was trying to express was something just off close-hauled - so perhaps a bit closer than "close reach" would imply. The point is that it's a "no overtaking" point of sailing.

Having suffered on numerous occasions with trying to accurately record boats coming over the line (especially large G Handicaps) I now adopt the following (where the class permits)

Set a course with a short fetch to the line. There are samples  for single class events on http://www.sailor.org.uk/raceman - www.sailor.org.uk/raceman . For large GH events, I use a trapezoid where the committee boat is about 30 yards up from mark 4 & the pin end is to stb of the CB & 45 degrees off the wind, quite a distance from the CB (to cover any wind shifts). As boats round 4, their natural line up the beat takes them through the gate/finish line & much closer to the CB than the pin end . This results in boats going round mark 4 & through the finsh line in virtual single file.   No kites to block out the main number, or create confusion when the number on the kite is different to the main  A copy of this course is on the Rutland web site in the SIs for the Symmetric Grand Prix

My recording equipment is a video camera which identifies boats in the general finish area and also has excellent voice recording facilities. So when I call the line, I have a voice record with the piccies attached, in case I miss a boat. I tend  to pan the camera right & left & zoom in & out, to cover the area between mark 4 & the finish line. I have now been able to dump my dictaphone. Also if necessary, I sometimes have duplicate recorders taking positions as the boats round mark 4 (just as an extra backup)

Finally, use scoring software which does not require you to record fleets/starting goups. Sailwave has an excellent facility where you can set up starts & classes in each start so that all you have to do is input the sail number & SW works out which fleet/start the boat was in & corrects times and/or allocates the correct finishing place.

Does this work??? Certainly does! I used it for the SGP (85 mixed class General Handicap) & apart from the odd user input error, all results were spot on each time.

Before any SGP people identify that it took a long time for the results, that was another problem which I have now resolved

For those limited to paper recording  -

Take a good supply of decent pencils (pens stop working just when you least want).

Invest in a supply of waterproof paper. A standard lined A4 pad will disintegrate into a soggy mess as soon as its wet - especially if you have to use more than one sheet. Its hard to decipher the times from a pile of pulp (and again it will always rain at the least convenient time). Surveyors books are excellent for this purpose.

Plan ahead - if there is a bunch of boats approaching, prewrite the time onto the sheet at say 15 second intervals. Then as boats finish just record numbers within the relevant time range (have someone shout out the 15 sec intervals) - interpolate actual times. And yes, that is similar to redbacks suggestion.