Voltage drop from a boat start battery to the engine really does effect starting. Why? Because a cold engine takes less voltage to start than a hot engine. Now, imagine sailing along but NEEDING to start the engine...but you can't. Here's my story about how we've finally taken the time to fix this problem.

For Boat Dummies Like Me:

For the last three years, we’ve been challenged to get our engine to crank back over and start within two hours of turning it off…..ie: not enough voltage from the start battery to the starter to crank a hot engine.  But once the engine cooled back down (after about two hours), we would be able to start again with no problem.  This is a no-brainer to some of you….voltage drop between the start battery and the engine!  And we think that is the problem, so we finally took the time to fix it.  Here’s our story:

After borrowing a small compact emergency starting battery from the crack diesel mechanic on S/V Mango (Colt) and having it crank Tulum’s engine in a millisecond when power was put on, I was convinced that we probably had a voltage drop problem from start battery to starter on the engine.  See, Tulum’s start battery is more than 10 feet from the engine, not great if there’s a problem with voltage drop.  At one point in her life, Tulum’s start battery was used to start the engine on the boat and power equipment forward of the engine.  So her cable runs are really, really long.  We quickly changed the power setup on the boat so the bow thruster and new windlass had their own separate batteries in the forward locker with a charger up there that would keep those batteries up to speed.  But our start battery still had a cable run of more than 25 feet, even if it is 4-ought wire.  Check out this next picture and it will help explain:

The arrow points to where our start battery is located….not near the engine. The black line up the settee and across the table indicates the 4-ought cable run (under the settee and floor) that we took out.

So with some help from Ms. Gabriela at Banana Bay Marina in Golfito, Costa Rica we found a great electrician who was able to come help us fix the voltage drop problem.  After testing the battery then the starter, we knew we had a significant voltage drop problem.  We also found out (to our surprise) that our AGM start battery was basically dead, so we had to start the process by finding and buying a new starter battery.  Here in Golfito…this was surprisingly easy.  The electrician knew where to go and we had a big deep cycle starting battery secured within an hour.

Moving the entire battery to the engine room was discussed, but we really don’t have room for a big deep cycle battery in the engine room, so the next best solution was to shorten the 4-ought cable run…..significantly.  That night I traced where the battery cables went to all the way from battery to engine room.  The next day, we cut one length of cable so we could pull it through and start pulling cable.  This was a job.  Eventually the wire was through but the electrician had to spend a bit of time widening the hole under the salon with a drill and saw to get both 4-ought wires to go through.  This done, he did the final wire cuts and started to do the hand crimps to get ends put on the wire.  Not the way I expected it to get done but it was done well.


No big mechanical crimper here, just a very basic hammer and crimp set.

Finally the crimping was done and we put the cables on the battery.  Starting the engine was like night and day from ANYTHING we’ve experienced since owning the boat.  The engine started with no extra cranking or lag and sounded really, really happy.  The electrician and his apprentice and I worked our tails off on this project for a day and a half and I’m happy with the work done.

Here’s the aftermath:

Yup, that’s nearly 25 feet of 4-ought cable that we took out of the boat. No wonder we had a voltage drop?

If you read many of my other “Boat Dummy” stories, you’ll see a continuing thread about constantly trying to improve and update this wonderful lady that we live on (our boat).  This project was no different.  We are actively trying to improve Tulum as we go along, making her more modern, safer and up to date.  As a bonus while we had the electrician onboard, we also had him electrify our new galley lights and that night I installed them, meaning we could get rid of the old burned out LED’s.  What an improvement and the HelmsMistress approves.

What I didn’t mention in the story above (because I try not to be much of a wuss); is that while I was down in a lower compartment under our salon table pulling cable while the electrician pushed on it, my hand decided to jerk back into the extended section of a metal clamp.  These are very sharp and normally just left in place as you can tighten or loosen a clamp.  But because they are sharp, they cut very nicely and I cut my hand nearly to the bone as I pulled the cable through.  This put me out of action for a bit, but luckily I travel with a very competent ER Nurse onboard.  She said I needed a stitch or two… I said I didn’t and we ended up skin gluing/bandaging my hand.  I still went back to work on the project, but my hand was out of action.

Ok everyone, have a great Monday and a great week.


Wanna buy us a cold Imperial? Check out our Patreon Page! 


5 Responses

    1. The HelmsMistress put on a real bandage when she got back from the duty free zone and now I’m down to no bandage but still healing. It happens.

Wanna reach out to us with comments or discussion...use the comments button:

Keep Reading!

%d bloggers like this: