boat fridge - do you keep them on when cruising?

[vandy]

Do you guys keep the fridge on the boat switched on (to keep things cool of course!) whilst cruising? I've heard from a few people who strongly believe it must be turned off (despite engine is charging the batteries when cruising) and only switched on when having shore power?

 

[PetiteFleur]

Yes, it stays on all the time - and I'm a sailing boat, never had a problem and it keeps the beer cold!

 

[Richard10002]

I never have shore power and it's on from the moment I get on board mid week, to the moment I leave on a Sunday.

Why would you turnit off? Apart from the batteries not being able to cope?

 

[Racingfrank7]

On the min get on board and sometimes for 3 days and nights with no cruising or shore power.

 

[landlockedpirate]

Its always on, whats the point of a fridge if the beers not cold ?

If im cruising in an area with no shore power I always turn it up to full as soon as the engine is started and then down when we stop to reduce power consumption.

 

[Alpha22]

We have a 3 way fridge. Usually running on gas but 240v when available. The gas goes off at sea and we use 12v. As a mobo we generally have the engines running whilst at sea!!

 

[ctva]

As others have said, first thing on when we arrive onboard is the fridge and it remains on till the morning we leave. Never had problems unless we stay put for more than two days at which point I charge the batteries with a generator.

I too have never understood those that leave it switched off most of the time, it is then pointless having it!

Remember that a well stocked fridge (beer of course) is an efficient fridge.

 

[jfm]

It depends on the maths. A large mobo will invariably have enough alternator power. But a small single engine mobo with say 100 amp alternator at 12 volts will provide only 5 amps at 230v through an inverter so will not run a big fridge in summer but will easily run a small fridge

So just compare the output of your alternator with the consumption of your fridge and allow for nav electrics etc, and check it is enough. It usually will be perfectly ok

The full=efficient thing is urban myth. In steady state the power consumption and efficiency of fridge are identical whether completely empty or with normal food and beer on the shelves

 

[jfm]

It depends on the maths. A large mobo will invariably have enough alternator power. But a small single engine mobo with say 100 amp alternator at 12 volts will provide only 5 amps at 230v through an inverter so will not run a big fridge in summer but will easily run a small fridge

So just compare the output of your alternator with the consumption of your fridge and allow for nav electrics etc, and check it is enough. It usually will be perfectly ok

The full=efficient thing is urban myth. In steady state the power consumption and efficiency of fridge are identical whether completely empty or with normal food and beer on the shelves

 

[prv]

We are a sailing boat, and keep ours on all the time we're on board (in fact, if I can get to the boat the night before going away, I'll turn it on then to cool down). We don't have mains power at our home berth and rarely plug in when away, so it's all down to the alternator which (being a sailing boat) we hope to run as little as possible!

I have been on sailing boats in the past where the regime was to turn the fridge off overnight to save power, but I would expect a motorboat to have plenty of juice and not even think about turning it off.

Pete

 

[adey]

The full=efficient thing is urban myth. In steady state the power consumption and efficiency of fridge are identical whether completely empty or with normal food and beer on the shelves

Until you open the door?... Less cold air will spill out of a full fridge than an empty one.
I make sure my fridge is full (of beer and limoncello) and the freezer compartment with cool blocks (or oven chips) and cool it on max with shore power before setting off.
I sometimes switch it off at night if there's no food in the freezer bit because it's noisy.

 

[[2068]]

The "downstairs" fridge is always on.
The fridge in the cockpit gets turned off at night because it's a bit noisy, and to save on amps, but contains only non-perishables such as drinks.

With good batteries, we can just about survive a weekend without shore power. With the current batteries, only overnight :ambivalence:

 

[boatone]

But a small single engine mobo with say 100 amp alternator at 12 volts will provide only 5 amps at 230v through an inverter so will not run a big fridge in summer but will easily run a small fridge

Suppose it depend on what you mean by small but don't see many small single engine mobos (sub 36feet) with 100 amp alternators jfm - more likely 60amp, Also most will be using 12volt fridges so don't understand comment re 230volts. Its all about watts anyway - most small 12v fridges rated around 50 watts so draw around 4 amps on surge. I reckon my Waeco draws around 50 amp hours per 24 hours if running 24/7.

The full=efficient thing is urban myth. In steady state the power consumption and efficiency of fridge are identical whether completely empty or with normal food and beer on the shelves

As others have said, a full fridge is easier to keep cold as the contents tend to act as an accumulator?

I certainly don't see any problem keeping fridges running when under power and charge reaching the batteries and 12v circuit. For most of us on the non tidal Thames the real issue is keeping them running when moored for longer periods without significant battery capacity and no access to shore power as we tend not to overnight in marinas when cruising the river.

 

[Elessar]

Do you guys keep the fridge on the boat switched on (to keep things cool of course!) whilst cruising? I've heard from a few people who strongly believe it must be turned off (despite engine is charging the batteries when cruising) and only switched on when having shore power?

I keep both mine on 365 days a year. Even at anchor/away form shorepower. Off for an hour to defrost every couple of months and thats it. Unless it is a very inefficient fridge and a very small alternator I can't see any problem.

 

[boatone]

I keep both mine on 365 days a year. Even at anchor/away form shorepower. Off for an hour to defrost every couple of months and thats it. Unless it is a very inefficient fridge and a very small alternator I can't see any problem.

Which begs some questions - what is your electrical installation, battery capacity, charging system and availability of shore power? Suspect your spec is well above average ?

 

[CX54WEK]

We leave ours on all the time.

Who wants warm beer?

We have shore power on our home mooring so it stays on even during the week when we are at work. Have never seen the point of turning it off.

Our battery bank is more than capable of powering it whilst we are out cruising, so again why switch it off?

 

[boatmike]

I recognise that this is a MoBo thread but as a recent convert to power I think that your battery bank should be well able to cope when not motoring and when you are there should be no problem as alternators are charging. When I was sailing for long periods without an engine or generator running my solution was a couple of solar panels. Ideal because when its hot and you need the fridge most the panels are giving maximum charge while at night when its cooler they don't. With a Mobo however I am basking in the luxury of two 90 amp alternators so have no need to suppliment them.

 

[Scubadoo]

We leave ours on all the time.

Who wants warm beer?

We have shore power on our home mooring so it stays on even during the week when we are at work. Have never seen the point of turning it off.

Our battery bank is more than capable of powering it whilst we are out cruising, so again why switch it off?

Just curious on your set-up, if the shore power fails, does the fridge run off the batteries or is it dual voltage fridge (240/12v), just thinking I would want maximum battery capacity for emergencies like bilge pump when away from the boat.

 

[jfm]

Until you open the door?... Less cold air will spill out of a full fridge than an empty one.

Yes, that's true of course but the energy quantities are tiny, due to the tiny heat capacity of air. Let's say a "full" fridge has half its volume used up by stored food/drink. So you open the door on a 4 cuFt fridge (OP was probably referring to something even smaller) and 2 cu feet of 4 deg C air falls out, replaced by 19deg C ambient air. The fridge compressor therefore has to cool 2 cu ft of air (=70grammes) by 15 deg as a result of the door opening. Air's heat capacity is 1 joule per gramme per degC so that's 1000 joules of energy to take out of the air. Assume a conservative CoP for the fridge compressor of 3ish, so the energy consumed is 300 joules. That is 300 watt seconds, or .3 Kw seconds. That's 0.0001 KwH per door opening

Now, home electricity is say 20p per KwH, but let's assume a big shorepower mark up or a badly tuned generator running on taxed diesel, resulting in a cost to the boater of £1 per KwH.

Therefore if a boater opens and closes the fridge door one thousand times per season the cash saving by having the fridge full as opposed to empty is £0.10p per year. Even if you drastically alter my assumptions and assume much larger fridges, much higher ambient temp, much less efficient fridge compressor, etc, you are never in your wildest dreams going to get anywhere near £5 per year

 

[jfm]

a full fridge is easier to keep cold as the contents tend to act as an accumulator

That is urban myth not supported by science/engineering/physics. Sure, the fridge contents act as an accumulator but that doesn't save you any running costs and is a solution to a problem you don't have. I mean, filling the fridge even with a perfectly-fitting cube shaped bucket of water (water having the highest heat capacity of any readily available substance) isn't going to change its running cost once in the steady state, but the energy burn of getting that water down to 4 degrees will be very high indeed