Building the Bargain Boat Horn

With the snow starting to recede in my part of the planet, the mind starts having visions of warmer weather activities. In my particular case, I love to spend a weekend afternoon out in my boat with a pole in my hand, trying to determine if there was anything hungry for worms in the water beneath me. 

When out in the boat, it is vitally important (in fact it's the law in my country) to have certain safety equipment on your boat at all times. Besides the usual life jackets, flashlights, and tow ropes, you are supposed to have some sort of sound signaling device. In the little safety kit that I bought for my boat, that came in the form of a small whistle that you are supposed to blow into to signal for help. 

Personally, I found the whistle a bit lacking in the sound volume department, but to be quite frank, installing an air horn on a small 14-foot boat with an outboard motor seems a bit ridiculous. 

The other day I was prowling through some of the back issues of Popular Mechanics when I came across a small article in the March 1968 issue of the magazine that outlines a project to create a "Bargain Boat Horn" 

 In the article, the horn was very simple to make, comprising of a speaker that was hooked up to a siren module that was, in turn, hooked up to batteries and a switch. 

The whole horn was housed in a tin can that was attached to a piece of wood which served as a handle for the horn. 

Intrigued by the idea, I decided to give the project a go, but with some modern twists, taking advantage of some tools that I have at my disposal that would have seemed to be complete science fiction back in 1968.

Looking at the project, I knew that I could fairly easily condense the speaker and siren module into a single unit by using a small 12-volt security system siren that I had picked up on my last trip to the surplus store (to be honest, I couldn't get the siren module listed in the article even if I wanted to, since the company that made it has virtually disappeared from the face of the earth some time in the past 50 years). 

Playing around with the siren, I noticed that I could still get quite a large amount of sound from the siren by just using a 9-volt battery, which was great news since that meant that I could keep the horn at a reasonable size, without the need to have a huge wad of batteries to make up 12 volts. 

With those details, I could create a very simple circuit to make my horn work which would basically just be the siren hooked up to a push-button switch that is used to activate the siren, and the battery with an appropriate connector, 

Of course, after hooking everything up, the arrangement worked quite well. 

The other main component of the horn is the housing that will contain the electronic part. 

The plans called for using a small tin can, which can increase the volume of the horn as well as providing some ability to aim the direction that you want to alert someone, and a pistol grip on the end of the can allow the user to hold onto the horn.   

While I know I could quite easily recreate this housing today for that cool retro feel, I did want to update the project to the 21st century and take advantage of all the nice tools that we have at our disposal today. 

In keeping with that idea, I set about to design a housing for the horn in Tinkercad that I could then create on my 3D printer. 

The design was pretty easy to create. I started by creating a tube in Tinkercad that was about 4 inches long and had an outer diameter of 3 inches. I made the inner diameter hole in the tube to be the same diameter as the siren. 

Next, I found a design for a pistol grip in Tinkercad and grafted it to one end of the tube. When the grip was attached I also created an opening in the grip that extended up into the inside opening of the tube to allow mounting and wiring of the switch. 

For mounting the 9-volt battery I decided that for the sake of convenience, I wanted the battery to be located on the side of the tube, allowing for easy replacement or disconnecting of the battery. Within Tinkercad, I found a design for a 9-volt battery clip, which I grafted to the side of the tube, near the pistol grip. 

With the design figured out, I then let the 3D printer do its thing. 

Once the housing was printed, I started the install of the electronics by first fishing 2 small hook-up wires through the hole in the pistol grip, feeding them through the hole going into the inside of the tube. 

Next, I soldered the 2 wires that were coming out of the pistol grip to the terminals of the push button switch and I seated the switch into the opening of the grip, sealing the base of the switch with some silicon sealant to provide some waterproofing. 

Once the switch was installed I started to assemble the rest of the horn. Taking the siren I first shortened the leads on it until they were about a couple of inches long and stripped the insulation off the ends of the leads. 

Next, I took a 9-volt snap battery clip connector and soldered the negative (black) wire of the connector to the negative lead of the siren (which was marked with a black stripe)   

After that, I took one of the wires that were connected to the switch in the pistol grip and soldered it to the positive (red) wire of the battery connector.  The other wire that is connected to the switch is soldered to the positive lead of the siren. 

With the completion of the electrical connections, it was now time to button things up. 

I tucked the wires in around the siren's housing, leaving a few inches of the wire for the 9-volt connector sticking out and I carefully slid the siren into the back end of the horn housing. 

The siren had a mounting tab on the back of it, which made it a simple matter of securing the siren to the housing with a couple of small machine screws. If I didn't have that tab, I could have also simply glued the siren into the housing with some plastic cement. 

After neatening up the wiring a bit more with some electrical tape, I installed the battery in the side battery holder and the horn was ready for testing. 

It is definitely louder than the wimpy whistle I had before and with its fairly compact size and fairly rugged construction, it should take the bumps that it would get out in the boat.

It's going immediately in my boat's equipment box - I'll report back at the end of the boating season on how it faired roaming the seas (well, small lakes).