Category Archives: Outfitting The Boat

12v 101 For Dummies

Q:  How do I know how much power I’m generating and how much I’m using?  

A: Batteries hold juice and everything else uses that juice.

Look on your batteries and see if you can find a sticker that says something like 120 AH or amp hours.  Add them all together on your house batteries.  Amps are like measuring cups for electricity. Maybe a lightbulb draws 1 amp. That means that in one hour, it will use up 1 amp from the batteries. 10 hours = 10 amps etc.

Some things list the watts they use.  It’s just another measuring thing, but not much help cuz you have to convert them to amps.  Sigh.

Here’s how to convert: watts divided by 12 (12 volts – some folks have 24 volts and other weird things) equals amps.  So a 75 watt bulb draws 6.25 amps if it’s on for an hour. Yikes!!!

Now add up the amps for all the stuff you use.  Running lights might be on for 12 hours, but your fridge might cycle on and off and only use 7 amps in an hour.  You will have to pay attention to how long things are turned on.  Auto pilots use a lot and so do SSB radios when you are transmitting.

There should be a label on each light, pump, fridge, whatever – that states how much juice it uses.  Convert them all to amps and add them up. To be safe, round fractions up.

So lets say that your total is 80 amps in 24 hours, and your battery bank, all together holds 360 amps. You can only use half the amp hours in the batteries or it screws up the batteries, so you have 180 amps to work with. Woo Hoo! Your batteries can manage that!

Now, how do you put amps back in the batteries?  Run the engine, solar, battery charger (if you are plugged into a dock) etc.  What size alternator is on your engine? 50 amps, 80?  Look and see. Alternators charge fast when you first turn on the engine, but then taper off so you don’t fry the batteries.  Run the engine hard for about 20 minutes, then slow it down and charge them up!

Solar panels are rated in watts.  A 100 watt panel would crank out 8.3 amps every hour in perfect conditions, but not for more than maybe 4 or 5 hours every day, depending on where you are.  You still need to come up with 50 more amps…. does that make sense?  There is a doohickey called a Link Monitor, which you can install and it tells you how much you are using, how much you already used, how much you need back and how fast you are charging.  I put one in my boat and LOVE it.  No more worries.  Totally worth the time and money.

There’s a bunch of other technical stuff, but that’s the basics of what you need to know to figure this all out.  It’s kinda fun if you don’t get freaked out.

Smile and good luck!!!

Red Light at Night

As we all know, or ought to by now, using white cabin lights during a night watch is a bad thing.  Sure, you can see whatever you’re looking at really well at the time, but you and everybody near you, will be blinded for up to 20 minutes until your eyes adjust to the darkness again once the light is turned off.  Enter: red night lights.

Red light allows you to see well enough to read, navigate, cook, find your socks or what have you, but won’t overwhelm your night vision.  Once the light is turned off, you can still read the compass, search the horizon for MOBs, buoys, ships or other things to bump into. I have lots of them aboard Mahalo.

There are red lights in the galley, over the nav station, in the head and in the forward cabin.  I have a favorite dedicated flashlight with a red lens too.  I love my flashlight, it goes wherever I go on a boat, hangs around my neck and has thousands of miles under it’s tiny keel.  It was made by Pelican, the folks who make all those cool waterproof boxes, and several waterproof and shockproof flashlights.  Imagine my panic one night last summer when I couldn’t find it.

It was the first night of a nine day charter aboard Mahalo.  We had a boat load of ladies out for a learning adventure to the Channel Islands off the Southern California coast motorsailing from Long Beach to Santa Barbara.  We had finished dinner and cleaned up, and had given the crew a taste of night watches.  They were experiencing looking at other boats’ running lights, practicing using the radar, plotting our positions every hour, log keeping, eating cookies and pouring hot drinks.  As we started our watch schedule and the wind and waves built, slowly the number of bodies in the cockpit dwindled.  Guests aboard are not required to stand night watches so I soon found myself alone in the cockpit for another two hours.  No biggie, I decided to catch up on some reading. All I needed was my trusty flashlight and some fresh batteries.  It wasn’t in the drawer where it was supposed to be.  Maybe my duffle bag from the last delivery?  Nope.  A different drawer?  Under some junk?  My tool bag? Nope again.  This is so unlike me to misplace my stuff!  Try again.  Still nothing.

Ok, now it was time to get creative.  I remembered a cheapo flashlight that came with the boat, which of course I found on the first try, but it had a white lens.  I’d read about people using red nail polish to cover a light bulb, but I’m not really that kind of a girl, and certainly don’t have red nail polish onboard.  Red plastic sheets to repair tail lights on a car?  None of that stuff either.  Hmmm…  What about a red felt marker?

I put some batteries in the flashlight, grabbed a red marker and covered the lens with red ink.  I let it dry a minute and gave it another coat.  After a quick horizon check, I covered the lens with my hand and turned it on.  It looked like it might work, so I uncovered it and was quite happy with the result.  It wasn’t quite as red as the real flashlight, but when I turned it off, I could still see in the dark.  Wahoo!  Back to my reading..

Later in the charter, the florescent tube in the light over the galley broke when the light fixture took a direct hit from a pan lid.  I know the red tubes are next to impossible to replace.  Some company used to make red plastic sleeves to slide over florescent tubes, but I haven’t seen them in years and don’t have one on the boat anymore.  Would the felt marker work?  I had a spare white tube and gave it the treatment.  It worked like a charm after two coats were put on.  I wondered about the heat from the light burning the ink but after six months of use, they all seem to work just fine.

The rest of our trip was fantastic.  We made it to all the Channel Islands as well as Catalina Island, had some great passages, great food and lots of laughs.  I had tried for years to visit all the Islands in one trip, but had been turned back by nasty weather and time constraints.  I’m going on record as saying that bull Elephant Seals are really big when they swim up to you while you’re rowing ashore in your Avon Redcrest inflatable dinghy.  It’s amazing how fast you can row those things with three people in them when you are properly motivated.

So, toss a red marker in your fixit bag, it might just come in handy one of these days.

I found my favorite flashlight the next morning in the back of the drawer.  I guess we were heeling more than I remembered.


For more boating adventures with Captain Holly Scott and sidekick KC, find us at and