Surfing & Windsurfing/Boom length
My mistral has a boom length of 2.4 written on it--what does that translate to in boom size since I have to but a new boom for the sail...
I'm getting the impression that you want to replace your old boom with a new boom.
I'm guessing that your boom is close to 8' in length and not adjustable. This was common for older style booms. The 2.4 is in meters. All newer booms are in cm and are adjustable. When you look at new booms you will see that they are all listed with a range of adjustability.
So to replace your old boom you would be looking at a boom that is 240cm minimum length. This size boom is going to be for larger sails and tend to be a bit more costly. Take a look at your sail to determine if it says what boom length it requires. There should be some information on the bottom of the sail that lists luff/mast, boom, MCS/stiffness.
Here is a link for a variety of booms at about the best prices you will find for new booms.
Other options would be to search ebay. If you decide to shop for used, get lots of information and pics of what you are potentially buying to verify condition.
Hope this helps.
Keep on sailing,