What statistical method should I be using?

I have 47,000 sound data files from a hydrophone recorded over a period of months, some of which contain boat noises. I have an algorithm in matlab that gives me a list of files which might be boat noises. I listen to these files and record which ones really are. Then I have listened to 2% of the total number of files and recorded how many them are boats. I would like to know how I can use the results of listening to the random files to calculate how many boats I have missed in the rest of the files that I haven't listened to.