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Installing a Fire Suppression System

Of all the things that scare boat owners the most, sinking is probably at the top of the list. But fire is no less of a threat. Indeed, a fire, even if you manage to put it out, can easily lead to a sinking.
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Of all the things that scare boat owners the most, sinking is probably at the top of the list. But fire is no less of a threat. Indeed, a fire, even if you manage to put it out, can easily lead to a sinking. The first line of defense when it comes to preventing a fire on board is to make sure that all systems are correctly installed and that there is nothing that can turn a small problem into a large one. Normally a single factor alone will not cause a fire; they are most often started by a combination of factors.

Should the worst happen you need to slant the odds in your favor of putting a fire out. The best fire extinguisher is probably a frightened sailor with a bucket, but after that it usually comes down to genuine fire extinguishers. Most boats have a few of these on board. There should be one in each cabin, visible and easily accessible so that it can be grabbed and used in a hurry; speed is of the essence here.

But what if the fire is in the engine space? You may not even realize you have a fire there until it is too late. Worse yet, opening the engine cover to see what’s going on is often a bad idea, as it feeds additional oxygen to the fire and may cause a flare-up. The ABYC recommends that engine fires be tackled without opening the engine cover or—in larger vessels—the door to the engine room. The cover or door maintains a physical barrier between you and the fire and restricts the amount of oxygen that can reach the flames. Often, sailboat builders thoughtfully install fire ports in the front of their engine boxes; a small plastic disc pops out, allowing you to deploy the nozzle of a fire extinguisher through the hole. This is very sensible, but is not necessarily the best solution.

Top of the tree is an automatic fire extinguisher system. In its simplest form, this senses the engine room temperature, and when it rises above a preset limit, deploys an inert gas to deprive the engine room of oxygen, thus putting out the fire. Halon used to be the gas of choice, but environmental concerns have resulted in it being outlawed. New systems use another gas called heptafluoropropane, although halon is still acceptable for existing systems. (If you do own a boat with a halon system, be aware that it cannot be refilled with halon when serviced; the same holds true for older refrigeration units that use halon as a refrigerant.)

Installing an automatic fire extinguisher in the engine room is well within the capabilities of a competent DIY owner, but it is necessary to do a little research first. I contacted Sea Fire, who supplied me with the necessary parts to complete the installation that you see here after sending me a worksheet that asked some questions about the boat, engine size, location and most important, the size of the space that the system would protect.

In theory it is possible to install an automatic extinguisher that employs a vial on a sprinkler head at the top of the extinguisher cylinder, which bursts at a certain temperature and smothers the fire. The advantage to this approach is that you don’t have to make any extraneous connections to your engine room. Most owners, though, will opt for a slightly more sophisticated system, which is what I did. Connected to the top of the cylinder in my system is a cable release controlled by a handle next to the helm that can be pulled to deploy the extinguishing agent manually. Because the boat in which I was making the installation had a large electronically controlled engine, I also installed an automatic shut-down system. With this, if the extinguisher is deployed either manually or automatically a relay trips and shuts down the engine. Shutting down the engine if it is running ensures that the extinguishing agent will not be sucked into the engine and ejected out of the exhaust before it has the chance to do its job and put the fire out. 

1. Decide where the extinguisher will go. In many cases the decision is made for you, as there is not much space in the average engine room. Bear in mind that you will have to make a connection to the top of the cylinder and that, depending on the type of system you have, the cylinder will either need to be mounted horizontally or vertically. This will be made clear in the installation instructions.

2. Measure carefully, then bolt the mounting bracket into position. I had a nice clear space on the aft bulkhead, which was just perfect. You may not be so lucky and may have to reroute wires or hoses if they are in the way.

3. Mount the extinguisher as outlined in the instructions. The Sea Fire I’m mounting has stainless steel worm-drive clips that pass through the bracket and around the cylinder. Make sure they are tight.


4. Install the manual release cable. Bear in mind that it is stiff, like a throttle or gear shift cable, and will not bend in a tight radius. Cables are supplied in almost any length, so measure the run of the cable before ordering. An old piece of 6mm 1x19 rigging wire is handy for this, as it has the same bend characteristics as the release cable.

4 A. After deciding where the cable will go, install the plate for the manual release, which should be near the helm. You will also need to drill a hole for the cable attachment; I was lucky to be able to use the plate to cover an unwanted hole where a gauge used to be mounted.

4 B. Install the brass nut and washer before passing the end of the cable through the hole.



4 C. Then install the other components on the other side: barrel nut, O ring, T handle, and safety clip. Connect the other end of the cable to the cylinder, which is retained by a spring clip. It is also worth noting that the cylinder has a safety pin in place that has to be removed, but leave that until you have completed the installation to avoid a possible accidental discharge.

5. Use a hole saw to drill a mounting hole for the monitor panel.


6. The panel is passed through the hole and secured by a straddle clip on the back.

7. Wiring is likely to be the most time-consuming part of the job, as it must be neat and well ordered. First mount the relay/control box. I put mine behind the breaker panel. Use cable of the correct gauge; Sea Fire recommends no smaller than 16 AWG. 

7 A. The wiring is fairly easy to follow, but requires connections from the top of the cylinder, a power feed and connections to the electrical engine shut-down solenoid. When connecting a shut-down solenoid, be aware that the contacts will either be normally open or normally closed. You may need to refer to the engine wiring diagram to identify your specific application and which wire you need to splice into.

7 B. Install the CAT 5 Ethernet cable between the monitor panel and control box.

7 C. Make the power connections to the fuse box, which must be protected with the correct amperage fuse. Don’t forget to mark up the fuse for identification later.

Finally, clip back the cables for a neat and orderly appearance.

With thanks to Brewer South Freeport and Matt Durkin.

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