I set the Max Charge rate to 90%. The charger specifications say that it will only pump a maximum of 125 amps into the batteries, but when we pulled into port and plugged in yesterday, there were 132 amps going in. The max charge rate (C/5) of 600 amp hour batteries is about 120. Now, the amp meter function of the inverter/charger (without the BMK) is only accurate to within 20%. Plus the solar charger may have been pumping in some amps. But just in case I bumped it down and it dropped to a much more battery-life-friendly 114 amps.

[EDIT – back in May I set max charge back to 100%. Per the specs, the batteries can take up to 300 amps during bulk, so 132 should be fine]

Next, I need to reconfigure the solar charger to match the charge profile of the shore power charger, and get rid of the monthly “equalize” function, which I think might be death for AGMs…

This is a bit of a long one, and I am still not done figuring it out. But, it was one of those issues that lead me down a rabbit hole, and when I came out the other side I knew a ton more about how the boat works. 

  • Thing #1 – When we were at anchor and the house banks were at 53%, the solar panels didn’t seem to be putting out enough charge. 
  • Thing #2 – After plugging into shore power at 77% SOC, the Magnum shore power charger just went straight to float (instead of bulk, as expected). The next day, the house banks were still only at 80%, but the charger said “battery full”. 

This lead me down a winding path of poorly-translated charger manuals, battery theory, and system integration philosophy, which I will mostly leave out here. But, here’s what I learned in the nutshell. 

When the batteries were low and I saw this on the charger:

I’m like, “Why aren’t the panels putting out as much as possible? Shouldn’t they be in ‘Bulk’?” The answer was, of course, that they were. “Bulk” charging just means that the charger is putting as much as it can into the batteries. In this case, the panels are generating 88.56 watts, which the MPPT charger is converting into something that the DC system can use, in this case 7.7 amps at 12.5 volts (though, how it’s converting it up to 96.25 watts is a question for another day). The voltage is determined by the resistance of the battery, not by some setting on the charger. So the charger cranks as much current (amps) into the battery as possible and the voltage builds as the battery resists the charge. In this case, the sun was still relatively low in the sky.

Lesson Learned #1 – The solar MPPT charger will push as much current into the batteries as it can up until the voltage hits the absorb setting (14.4v in this case). If the sun is low or obscured, it will be less than if the sun is directly overhead. I thought that the voltage of the system was a set value, but that’s only true when the batteries are charged enough that they create some resistance to the charging sources. Once that resistance passes the absorb threshold, the charger will hold the voltage stable and continue to lower the charge to keep it there.

Lesson Learned #2 – The reported voltage of the DC system is a combination of all of the load, all of the charge, and passive resistance of the various components.

In practice this means that the voltage I see on different components will be different. So, in this case, the panels saw 12.5v. But, the battery monitor saw 12.31v. So we’re seeing a .3v difference between the charge output and all of the resistance in the system (the batteries and any devices using power).

Since the battery monitor (BMK) is a shunt that is the last link between all of the negative bus items and the battery, it is the most accurate measure of the voltage on the negative battery terminal.

Note that the solar charger is bridged directly to the charging input on the positive side of the batteries.

So any current from the solar panels is combined with current from the charger.

Lesson Learned #3 – the reported current in the system will be different depending on where it’s being measured. This one really confused me. I was trying to do simple math – if the DC + AC loads are X (a negative number) and the solar panels are outputting Y, the the reported load on the battery monitor should be X + Y. Nope. While that’s generally true, there are so many devices on the system (all fluctuating) the numbers will not add up exactly. Ultimately, the battery monitor will tell you what is going into or coming out of the house bank. But, trying to add up the loads across the system is imprecise. However, it is directionally true. So, at one point, the sun got bright enough and the batteries were charged enough (we ran the generator) that the resistance (voltage) increased and we saw a net surplus on the BMK. This means the sun was charging the batteries enough to produce a small surplus (over the house loads).

Also, the components all measure with different levels of precision. From the manual: “The DC Amps meter displays the amount of current going in or out of the battery. A negative number shows the amount of current being removed from the battery. A positive number shows the amount of current delivered to the batteries. This meter converts AC amps to display DC amps, so the accuracy below one amp AC (~10 amps DC @ 12 VDC) is not detected. When the current detected is greater than one amp AC, the accuracy of this meter is ±20%.” I’ll trust the BMK more than the regular DC volts.

Lesson Learned #4 – There are race conditions between the three phase solar panel charger and the three phase shore power charger. Each are using different voltage levels and thresholds for absorb and float settings. Also, since voltage is a trigger, the charging volts from one system can cause the other to go into an incorrect state. In most cases, this just means that the chargers take turns doing what they can to charge the batteries, (backing off when the other one is working harder). In some cases, it can prevent charging.  This has been a problem for a while.

In our real-world example, we returned from a cruise at 77% SOC with tons of sun. When we plugged into shore power, the solar panels were producing enough current (20.9A) that the battery was resisting at 13.7v, so the shore power charger went right into float (13.3 volts at the shunt). This is by design! From the manual: “If the battery is >13.0 VDC… then the battery was already charged and the charger automatically goes to Float charging to keep from overcharging the batteries.”

The next day, the batteries were still at 80%, though the charger said “full” Once again, this was explained in the manual. “After four hours of float charging, the charger turns off and “Full Charge” displays (charger is now in Battery SaverTM mode). If the battery voltage drops to ≥12.6v… the charger automatically initiates another four hours of float charging.” But, what happened is, the solar panels + shore power float got the batteries to 80% (~12.7v), so the second float cycle was never triggered.

The best way to avoid this is to force a Bulk / Absorb / Float cycle when you first plug into shore power. There’s a function on the Magnum remote under CTRL to do just this. When I tried it, the charger jumped into bulk and very quickly hit absorb. Right now, the absorb cycle is set to run for two hours, which is about right to get from an 80% charge to float.

There will be other race conditions. This is exacerbated by the chargers having slightly different set points for their various modes and triggers.

Start Bulk IfStart AbsorbAbsorb timeFloatBattery fullSkip to float
Magnum<= 12.8v>= 14.5v2 hrs13.5v for 4 hoursafter 4 hours float*>=12.9v
Tracer<= 12.6 (?)>= 14.4v2 hrs13.8vNA – stays in float if possibleNA

*When in “battery full” mode. The Magnum will enter absorb if the voltage drops to 12.6 and bulk if it drops to 12.1. 

Lesson Learned #5 – System integration is hard. The Tracer MPPT Solar charger uses different defaults than the Magnum. The magnum was set to the “wrong” type of AGM (Lifeline) (though since these are OEM batteries, there are no specs immediately available). There are also a number of settings like maximum charge rate, Absorb cycle time, etc. that probably need to be optimized. Don’t rely on the default settings and don’t assume the builder/commissioner set it up right. Even solid boats with experienced owners get this wrong.

Also, for posterity, here’s the cheatsheet for charge level per voltage for AGMs.

  • 100% – 12.8v+
  • 75% – 12.6v
  • 50% – 12.3v
  • ‘25% – 12.00v

We just passed 100 hours on the main.

I’m not sure when the official one year anniversary is, since the way we did the financing we actually owned her before she landed. She splashed on 17-Jun-2020 and I first boarded her in Blaine on 20-Jun-2020. Commissioning was complete on 11-Aug-2020. Regardless, 100 hours in eight months ain’t bad for two people with kids who work full time.

Now that Turtle’s not a new boat any more, it’s time to turn my attention to the potatoes* of boat ownership – maintenance. I decided a long time ago to embrace boat maintenance (I still reserve the right to whine about home maintenance). I’ll quote myself from the manual I wrote for my old boat:

“The two happiest days of a boat owner’s life are the day they buy it and the day they sell it.” 

I hate that saying. Yes, boats need maintenance. The sea is relentlessly pulling her apart and it’s your job to make sure she stays together. How you address the need for this maintenance will determine whether you enjoy owning a boat or whether the old saw becomes true. You can either perform maintenance yourself, which requires time and patience, or hire someone to do it for you, which costs money…. But, ultimately, you’re the owner – and it’s not always easy to find someone to do the work. Someday you will be stuck somewhere with something broken (hopefully it’s something minor) and there will be no one around to fix it. Your goal should be to learn how do to as much as possible yourself.


This is part of why I fell in love with the NP: Everything is designed for maintenance. If it’s not stainless steel, it’s accessible and serviceable. Now, every NP is custom, which is really nice for BS-ing with other boat owners (“what’s she powered by?”). But, it also means they don’t really come with a manual. In fact, they come with several:

Note the stylish handbag…

Boat maintenance is a journey, not a destination. The more I learn, the more I realize I don’t know. I still make stupid mistakes all the time (last weekend I spent five minutes troubleshooting the outboard, only to realize I hadn’t put the clip on the auto-kill switch). This beginner mind is humbling, but it also leads to over-cautiousness and probably far more anxiety than it should. But, so far my approach of “do your best and ask for help” seems to be working.

So, what to do for maintenance? I have some experience with this on my old boat, but it’s hard to know when to follow the recommended intervals and when to disregard them. Cummins, for example, recommends checking the gear oil daily. The engine oil change interval is 250 hours or 6 months, whichever is sooner. So, these guidelines are clearly for a motor that is being used every day. But, the intervals can and should be different for one that sits for weeks at a time. This is one place where I feel like North Pacific could be a little more structured in what they prepare for owners. Even if every boat is unique, having some kind of guidelines – something like the book people prepare for putting a boat into charter – would be incredibly helpful.

Since that doesn’t exist, I’ll have to write it.

As with most big hard problems that I don’t know how to solve, the best place to start is probably with a simple list. For each system, I’ll crack the included manuals and leverage the community to figure out what the real interval should be (though asking for advice on trawler forum can be like asking a bunch of pre-schoolers who the best Avenger is…). I don’t expect I’ll ever be “done” with this. But, I expect in a few years it will stabilize.

  • Main Engine
    • Oil and Filters
    • Primary and secondary fuel filters
    • Inspect / replace pencil anodes
    • Re-torque engine mounts (there are no factory specs for this – any suggestions?)
    • Re-torque shaft couplings
    • Change gear oil
    • Flush coolant
    • Inspect belts
    • Flush aftercooler
    • heat exchanger (?)
    • Raw water pump (impeller)
    • fresh water pump (?)
  • Generator
    • Oil and filter
    • primary and secondary fuel filters
    • zincs
    • flush coolant
    • belts
    • heat exchanger (?)
  • Water Maker
    • clean /change media filters
    • change high pressure oil
    • change membranes (~10 years)
  • Dinghy
    • Change oil and filter
    • inspect prop (need spare pin)
    • charge / change battery
    • change plugs
    • anodes (there must be some in there)
  • Hydronic system
    • Fuel filter
    • Clean inside unit
  • Bottom
    • Inspect and replace zincs (2-3 x year)
    • Bottom cleaning (2-3 x year)
    • Bottom paint (~2 years)
  • Misc
    • Change fresh water filters
    • Inspect through hulls (open and close, look for rust)
    • Test bilge pumps
    • Test / Replace batteries
    • Thrusters (?)
    • Propane (fill and inspect)
    • Grease steering coupling
    • heads (?)
    • Grease windlass
    • Wax hull

*as in “meat and…”

I met some new North Pacific customers the other day and they reminded me that I have one of the most popular North Pacific Enthusiast Sites on the Internet. All four of my readers demand content! (Just kidding, it was lovely meeting you – hope your build goes smoothly!).

Turtle has float gauges in her fuel tanks. Also, the engine data is not currently bridged to the NMEA 2000 network. This means that my fuel levels are ballpark and the burn rate that I get from the engine only shows up on one gauge, and can’t be used for calculations on the chart plotter. So, if I want MPG or average burn at different speeds, it’s a manual calculation. Not a big deal, but kind of a pain, given there’s more than enough compute on board to record this. [Apparently, I can bridge the engine data to the NMEA 2000 network via the Mercury vessel view, but I just don’t care enough right now].

Anyway, there are also site gauges on the tanks. We did a fuel up trip to Des Moines.

  • 320 gallons total @ $2.659/gal
  • Starboard – 182 gallons going from 8.5 to 41 on the site gauge. Float gauge went from 1/5 tank to 3/5 tank.
  • Port – 138 gallons going from 12.5 to 38.5 on the site gauge. Float gauge went from 1/4 tank to 3/5 tank (I put more in the starboard to counteract the list caused by the dinghy motor – that’s a subject for another post).

While there, I noticed that the top of the site gauge was nowhere near the top of the tank. I gave Trevor a call and he sent me the following diagram:

Note that the actual size of the tank is 347 gal.

Regardless this means that:

  • When the fuel is at the top of the site gauge, I have ~87 more gallons to fill in the tank
  • When it is at the bottom, I have ~43 more gallons

With 694 gallons total, 25% of the total fuel capacity is above the site gauges and 12.4% is below. Said another way, at my typical 3 gph / 7 kt burn rate, 406 miles are above the gauges and 200 are below (with a total range of ~1619 nm). Currents, conditions, variable speed, generator, hydronic all notwithstanding…

I also know the general shape of the tank from early drawings.

Sizes are in mm. After some very back-of-the-napkin math to convert 347 gallons to cubic mm – in a tank with an upside-down parallelogram-trapezoid-ish shape, each tick on the site gauge is ~5.5 gallons – more towards the top and less toward the bottom. So, basically, the level will drop faster as the fuel is drained from the tank.

Ultimately, I should get some better fuel sensors in the tanks and bridge them to the chartplotter so I don’t need to futz with this. But, now that I figured it out, it hardly seems worth it.