Starting the boat while hooked up to shore power

Kevin Kidd

Kevin Kidd

Member
Oct 16, 2017
41
California Delta
Boat Info
270 Sundancer 2000
Engines
7.4 Mercruiser w/ Bravo 3 outdrive
While on a FB boat owners page I saw that someone posted that you shouldn't start your boat while still hooked up to shore power. Of course this started the usual going back and forth on should you or not. So I'm going to ask it here, is it alright to start up your engines while still hooked up to shore power? I always do it to get the engine warmed up while I'm getting ready to leave the slip. And I also do it when I don't plan on taking the boat out, but want to start it up for a few minutes just to let her run.
 
In all my years of boating I've never seen a single case of starting engines while still connected to shore power has caused a problem. The only issue I could forsee is when connected to shore the charger is most likely on and could assist a weak battery to start an engine that may not have started if the shore had been disconnected before starting. This would give the Captain the impression that the batteries are in good condition and lead to a subsequent stranding.
 
My charger has a hidden fuse and every time I do start with charger on, it blows the fuse. The mfg says it should not, but it does.

MM
 
Starting the engines is the first thing I do when I get to the boat. While they're warming up, we stow our gear, undo dock lines, etc., and shore power is just about the last thing we unhook.
 
There is a lot of variability about chargers ( old versus current) and the issues associate with charging from shore power. Be careful about what is correct on one boat versus your boat.

Our process

When we start the departure process, first step is start the genset (we always run the genset while under way).

Let the Genset warm up, then switch power over to the genset.

At that point then we disconnect from shore power, and pull the cables in. Once that is complete, next step is start the mains. While the engines are warming up, I am typically off the boat on the dock. Note that we cruise a lot, so every morning we are in a different tie up. I may have already formed ideas about the lines order to come off, but this when I walk the dock, look at which lines are "working" versus those that are slack. Decide on the order which the lines will come off. Decide on any short ties that we might do. Goal is to try to reduce to two lines which are short tied to hold the boat. Execute any line movements and reties. This takes 10 minutes or so.

At this point we have lines ready for departure without any shore side assistance. Main engines are warmed up, I move to the helm and we go.

Investigate how your boat is setup and the nature of the chargers, then build a process that you repeat every time.

Mark
 
Gofirstclass said:
Starting the engines is the first thing I do when I get to the boat. While they're warming up, we stow our gear, undo dock lines, etc., and shore power is just about the last thing we unhook.
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Agreed. I disconnect the shore power as I make my way around the dock taking off the dock lines.
 
Never heard that before. My process is go to ER and check fluids etc., blowers go on, check the cabin and cockpit for things that need stowed, fire engines, roll up electric and water, unhook lines (order depends on wind) and head out on the lake. We pretty much always come back to our dock so my electric, water and dock lines stay at the dock unless we are going on a trip then electric and water go in trunk.
 
This comes up on car forums all the time. Intuitively it would make sense to disconnect a battery charger before a 100-200 amp drain is applied to the battery but in reality I have never seen a problem with leaving it on. In fact most charger manufacturers (marine and car) are indifferent about the issue.

Modern chargers won't deliver more amps than they can which means a 30 amp boat charger or a 3 amp car charger won't fry itself if the battery cannot deliver enough amps to turn the starter.
 
Everybody has their own routine and this is ours. Firstly, I start the blowers, then we shut off the power pedestal breakers + Shore-1 & Shore-2 main breakers in the boat before disconnecting the shore power cables from the boat. This eliminates any accidental load arcing to the cable ends and receptacles. We leave our permanent cables on the dock ready for our return. We have an extra set on the boat for transient docking. Once the cables have been disconected from the boat, I start the engines for warm up prior to departure. This gives us ample time to attend to our dock lines. We have permanent dock lines set up for quick arrival & departure.
 
hottoddie said:
The only issue I could forsee is when connected to shore the charger is most likely on and could assist a weak battery to start an engine that may not have started if the shore had been disconnected before starting. This would give the Captain the impression that the batteries are in good condition and lead to a subsequent stranding.
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This happened to me. The generator wouldn't start when I wanted to leave the fuel dock, which of course had no shore power available.

Ever since, my routine is: shut off power, start engines/genny, then disconnect the cables.
 
MonacoMike said:
My charger has a hidden fuse and every time I do start with charger on, it blows the fuse. The mfg says it should not, but it does.

MM
Click to expand...

FYI, my charger is a newer Pro-Mariner. It is one of those things you just learn to live with. I have pondered if an alternator spike fries it???

MM
 
I'm curious as to why some people run with the generator on. I understand the theory of exercising a generator. Unless you also have your A/C on, what's the advantage?
 
AC/heat, ice and exercising. Most of the hours on mine are probably due to the latter. When I plan to anchor, I like to start off with a full bin in the icemaker because it's otherwise almost impossible to for it to keep up.
 
searay495 said:
I'm curious as to why some people run with the generator on. I understand the theory of exercising a generator. Unless you also have your A/C on, what's the advantage?
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Some folks like to run their AC all the time and love their electronic's. I like piece and quiet when I'm on the hook except in the AM for coffee or when popcorn is needed I'll fire up the generator. Otherwise I use a small AC/DC converter to charge my laptop.
 
My guess is that the best reason to disconnect the power cords FIRST is to avoid the chance of pulling the boat of the dock with the cords still attached, a potentially deadly event.
 
I also frequently run with the genset on, but I also always turn off the battery charger (aka ac converter) when the genny is running at the same time as the engines. I don't know if this is necessary, but why charge the batteries with the charger and the alternators at the same time? Probably just superstition, but I feel like I could potentially fry my batteries this way. Manual says always leave the charger on so I digress. Don't see any harm turning off the charger. Anyone else follow this while running with the genset?
 
gerryb said:
My guess is that the best reason to disconnect the power cords FIRST is to avoid the chance of pulling the boat of the dock with the cords still attached, a potentially deadly event.
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I have seen this happen to others a few times over the years and that is one of the main reasons why I do not start the engines until the power cords are disconnected. Get in the habit and it will soon become routine.
 
So this is a little off topic, but Little Ducky shuts his genny of while on the hook, but what happens to the refrigerator and Ice maker? If you leave my boat moored for a half day, do you leave the genny off or does the fridge stay cool with no power to it for 4-5 hours?
 
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