Do you have a door by the lower helm? If so, it is best mounted on the cowling above the door (and head height), probably in the area of your navigation light . If possible, mount it in a way that the nice bell lanyard that goes up under the side grab bar (assuming a GB 42 has them) such that when you pull down on the lanyard it pulls fore or aft on the bell clapper. In other words, the lanyard is threaded under the grab bar such that one of the stanchions makes it hangs down in front (preferable) or back of the door. If the length of lanyard above the hand rail is short, the weight of the clapper will keep it centered such that only really large waves on the beam will ring it. If your lanyard is too heavy, it will pull the clapper sideways and you won't get the full effect of the bell when you yank on it.
Now, all you have to do is open the door to ring the bell. Bell signals are the same as horn signals, but you can't find that info anymore. Bells were as good as horns back when all vessels were under sail. They don't have much of a chance against twin turbocharged diesels and a stereo. Still nice to hear them sometimes. We use ours when going astern in the marina (and using the horn would be obnoxious). But no way in a fog.
