What uses all the electricity on superyachts?

Electric pod drives maybe?

Many 500 & 1000 GT plus size yachts will have very large 3 phase electric bow thruster requirements / loads. This is one large factor in determining generator sizing, redundancies, and power management system design. Also in many cases, in addition to large kW bow thruster you will also find 3 phase electric azimuthing stern thruster arrangements that can sometimes propel the yacht forward at 2 - 4 knots. While the yacht is maneuvering it requires 100% availability of the thruster(s) electric motor(s) combined kW.

I have been on several 70M + size yachts with these type of systems. Say you have a 380kW bow thruster and 260kW stern thruster, very common on board 1000Gt and larger yachts. Whilst maneuvering the vessel requiring 640kW of available power. This is without consideration to the house load(inlcduing multiple jacuzzi arrangements and heat plants). The captain may not need to use all of the available thruster power but it needs to be available on the switchboard regardless should he require it.

Another large house consumer is the laundry center you will find on these size yachts. These areas can have up to 10 machines or more. During peak hours these will be running often to keep up with the 20 + crew and 12 or more guests.

Zero speed stabilization is also typically 3 phase driven HPU's on larger yachts, in many cases have (4) external fins which can require more then one HPU to operate. These hydraulic pumps can be 20kW or more.

At the end of the day these boats really do not plug into shore power often(200A services are required and sometimes not enough). They are designed with redundancy to rely on their power generation plant no matter how great the load and with loss of a generator or two in emergency cases. Power management on these boats is a whole sperate topic and is something you are constantly monitoring.

3 phase power production is a more efficient means of providing high load capacity. It's also a more simple manner of balancing very large loads. Multiple generators (as mentioned) provide duplicitous backup to limit the hours on any one device, long term wear and tear.

The larger the boat, the more bells and whistles, from HVAC to water making/conditioning/heating, larger crew quarters and subsequent support, refrigeration, and toy or house management. You aren't getting all of these assets of luxury and function into a house and a 200 amp breaker panel. You're also set up afloat so that every system aboard can be on and in use at the same time without concern.

My experience has been 3 phase electric heating for laundry and jacuzzi systems. Some of these systems are more clever then others.

I'm not terribly familiar with land based estate infrastructure and layout. Also, doesn't natural gas and solar play a large role nowadays ashore?

Operating the generators is preference of the C/E. The PMS(power management system) system monitors hundreds of parameters real time with all sorts of thresholds, time delays etc. for each. Depending what mode the main switch board is in, the PMS it is capable of switching to another / between generator(s) automatically should the generator(s) online have a pre alarm condition(PMS systems are a whole separate in depth topic). When maneuvering in port, close quarters, or anchorage we would have all three generators in parallel. This allowed full availability of power to the bow / stern thrusters and three phase anchor windlesses. When not maneuvering you could manage between one and two generators running at a time. This of course depending on guest load, ambient air and water temps, zero speed stabilizers etc.

Generators (and mains) often have PTO’s on them to network hydraulic systems used for stabilization and maneuvering as well as anchoring and windlasses. Requires the hydraulic pump to be operating, but doesn’t require much electricity. The best setups have redundancy in the pumping to allow for variations in operating conditions.

Note, a boat has no ability to “spike” line voltage while off the dock. Only perhaps 80-85% of the available max should be relied upon. A 100% load is rarely a good idea beyond momentary use.

HVAC, just the chiller system alone (and related air handlers) will consume 30 amps per 5 ton.

Cooking, the galley with the refrigeration all in motion will consume another 100 amps, perhaps more if larger.

Housekeeping and maintenance can consume another 100 amps at peak.

All of these systems have to be able to run simultaneously at any hour. It all adds up. In a hurry.

Aluminum conducts water temp quite well on a vessel, as you’ve stated. R value in comparison to a home is an absurd comparison when considered. The temp of the sea is a huge impact on a boat. Same with sun on that pretty Flag Blue hull.

Carrying this one step further, put that boat into cooler waters, and place a charter aboard. The boat needs to meet the whims and wants of every passenger. Water temp is 70. Wife wants a little heat in her bedroom. Husband heads to an area of the boat where he can deal with too much Sun by dropping the temp to 60. Meanwhile both are hungry and the chef is cooking. Laundry from the day is being handled. Beds and linens have been turned and the store is washing and prepping the spares for the next change. The kids are enjoying the hot tub under the stars. The various toys are being cleaned and reset for the next day. Not one of these features can hear the concept of “no”, and loads can’t be trimmed to bolster any of the peaks demands of the various functions.

If you’re aboard your own private vessel, you don’t think twice about shutting down a chiller to clear the way for dinner prep. It’s second nature, and you’re working with what you have.

Yacht's need A LOT more BTUs of air conditioning, then you have items like water makers, stabilizers running while anchored, stewardesses running 3 washing machines and 3 dryers at the same time. A lot more refrigerators, freezers, ice makers spread throughout the boat, all electric appliances in the galley and a chef that's cooking almost non stop, because the crew eats at different times than the guests etc. etc. etc...... it all adds up.

Backup when at sea .

All the usual suspects, A/C, cooking and refro.

On one boat we had a dry-cleaning machine in the Laundry Room. Have a guess which idiot was put in charge?

Utterly useless hunk of junk, used maybe 3 or 4 times for waterproofing in 5 years. It sucked so much power to do one simple act. The Drycleaners were on speedial.

Just for another point of reference- the 113 I ran had two 70KW generators. When we used the bow thrusters both generators powered up. Most of the time in the Summer we used almost the entire capacity of one generator to power the boat. As usual- YMMV.