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Tachometer troubles and lazy jack mounting questions

2023 November 1

Dear Boat Doctor,

I have two issues on my boat that I hope you can help with. 

I need to install lazy jacks by mounting eye straps on the boom and mast but I don’t know what the best way to attach them is without negatively affecting my mast or boom. What should I use in this case to get the job done without affecting the integrity of the rig?

My tachometer is baffling to me. Most of the time it works great, but often fails when I run the engine for a long time. Everything will go fine, and then the tachometer will drop to zero. It always comes back to life, but usually not until the next day.

Steve Kampf

Columbia, South Carolina

Dear Steve,

Thanks for the questions. I think I can help with both.

You can drill and pop rivet the hardware for the lazy jack straps or drill and tap for a machine screw. I prefer to drill and tap for the simple reason that I can remove the hardware. Pop rivets work just fine but are tough to remove.

Whichever option you choose, isolate the fastener from the aluminum spar. Use a stainless steel machine screw (or stainless or monel rivets), but the fastener will corrode the aluminum if left unchecked. Isolation is as simple as coating the fastener in TefGel, or an alternative isolation compound, before you install it.

I have an idea of what is going on with your tachometer. A tachometer indicates engine speed by interpreting a pulse train from the engine. The faster the engine turns, the faster the pulse train alternates. I am assuming that your engine uses a pulse train generated by the alternator and perhaps you have an external regulator.

What I think might be happening is that your alternator is doing a good job charging your batteries; on a long passage your batteries are fully charging and signalling the regulator to stop charging. When the regulator stops charging, the pulse train from the alternator stops, causing the alternator to stop. A good way to diagnose this is to force the regulator to restart by connecting a large load. For example, start your inverter and run an AC load for a little while. I think you’ll see that the tachometer will restart when the regulator starts up.

If this is the problem, you’ll likely be able to fix it. Many regulators have a constant alternator-out output, you’ll need to move your tach connection from the alternator output to this dedicated terminal. The dedicated output will stay active, even when the regulator shuts down.

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