Features March 1, 1998 Issue

Gimbaled Radar Mount Concern

Calypso is equipped with a Questus model 100 backstay-mounted gimbaling radar mount for her Furuno 1831 radar. We have always liked this system, since it allows the radar scanner to stay level at any angle of heel. At least one electronics dealer has warned us, however, that radar cables are not intended to undergo the constant flexing that is the inevitable result of a gimbaled scanner.

We now can report that he is correct.

Southbound from Bermuda to the Caribbean, we switched on the radar one night to check the range and bearing of a ship on a possible collision course with us. To our dismay, the ship could not be found on radar, although everything appeared to be operating normally.

In Antigua, John Ayres of Cay Electronics tentatively diagnosed a fractured conductor, one of 17 or so that make up the Furuno cable. His diagnosis was confirmed when flexing the cable resulted in an intermittent radar image. Sure enough, a post-mortem on the cable revealed one tiny broken conductor.

Fortunately, we had enough cable to spare to cut out the damaged section and install a terminal block inside the radome, making it unnecessary to replace the cable, which would have been costly, and required a full day of disassembly.

We are now designing a locking mechanism to disable the Questus gimbal when the radar is not in use. In the short run, a sail tie will do the trick. We would like to see the Questus folks come up with a lock or brake for this system, as we have firsthand knowledge of at least one other identical failure.

Self-leveling radar mounts may be ideal from a radar performance level, but replacing radar cables on a regular basis should not be part of the program.

We should point out that all the other freely gimbaling radar mounts we have examined have exactly the same potential to eat radar cables.

Fan Failure
A poorly ventilated boat in the tropics can be an oven. Big hatches, big cowl vents, lots of ports, and a lot of fans are required to keep the air moving. When Practical Sailor tested 12-volt cabin fans, the two-speed Hella Turbo Fan was the hands-down winner, moving more air and drawing less power than any other fan on the market.

After living with seven of these fans for more than a year in the heat of Florida and the Caribbean, we can report that they are still at the top of the list. We have had, however, one fan failure that scared the living daylights out of us.

We were about 500 miles offshore, headed south, with the engine running to charge batteries, when the cry of “electrical fire” came up from below.

We instantly shut down the engine and leaped below, welcomed by that unmistakable acrid smell of burning electrics.

The first thought was alternator failure, but opening the engine box showed everything seemingly fine. The smell seemed to be coming from the quarterberth area, which is chockablock with electrical gear: the batteries, inverter, and heavy wiring runs all lie beneath and behind the berth. I tore everything apart, sniffing like a terrier to find the source of the trouble. The smell was there, but it was too weak to be the primary culprit.

Eventually I looked up at the Hella fan over the berth. Sure enough, it smelled strongly of burned electrical components. My first thought was a wiring short, since the fan’s tiny-gauge wiring harness is particularly vulnerable. An autopsy showed undamaged wiring, but the Hella’s internal control circuits were totally fried.

The failure is still a mystery, but we suspect that a locked-rotor situation overheated the motor. It is possible that the wiring leads somehow fouled the blades, locking the fan and making it cook itself.

Since we carry spare fans, replacement was easy, but you can bet that we used extra care in securing the wiring to prevent any possibility of a recurrence. We also, of course, checked the wiring of the other fans at the same time. It is critical that the lead-in wiring be secured in such a way that it cannot possible get caught in the blades, which is difficult if these fans are mounted to the cabin overhead. We ended up drilling small holes through the fan support frame to hold the wires clear of the fan blades.

Some of our Hella fans now have thousands of hours on them as they run almost constantly in the tropics. We are starting to get nervous, since the advertising on the box says they are good for “at least 2,000 hours.” That’s only about four months of round-the-clock operation, which is precious little lifespan in hot weather.

These fans are a lifesaver, but you can bet we keep a wary eye on them.

Contacts- Hellamarine, 201 Kelly Dr., Peachtree City, GA 30269; 770/631-7500, fax 800-631-7575. Questus, Hood Yacht Systems (Pompanette), PO Box W, Charlestown, NH 03603; 603-826-4117.

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