just wondering how you get both boats to sound an alarm with sensors only on the bow? They will all be pointing forward so will not detect each other. For it to work you would need sensor both on the bow and the stern and then you also need to find ir emitters with a greater range than a tv remote and also receivers that are not narrow beam. might it not be easier to use ultrasonic distance sensors or even good old fashioned torches and a photoresistor?