Let's calculate energy needed for two man boating and propelling yacht.
Case study:
Boat around 11m long, two people on board, 5C temperature outside and 6C water temperature.
our goal to obtain estimate how much energy, fuel and material we need to survive.
In this study I assume only sourses energies we can carry onboard. This case study based on few assumptions s. a. No shore power available and boat is in autonomous operation. b. Wood or coаl is not practical.
With electricity life is easy. Most appliances we could buy are electrical. It would be nice to utilize them. But life is not always about convenience.
Let's make a choice for fuel to heat. Energy density; diesel 42-46 MJ/kg, lpg 46-51 MJ/kg, coal >23.9 MJ/kg, firewood 16 MJ/kg.
From all of them diesel would be the best because it is also used for engine as well most ports has fueling stations.
Then comes a question about needed power to heat around 54m3 space. In reality it is much less space because most of it is for storage or utility spaces. But we will go under that assumption.
I run a few simulations for energy and here is the result:
First I simulated just 1000 watt heater. I programmed water at 6C, air 5C, boat presented as a shell with 15cm insulation similar to foamy rubber.
first hour:
second hour: 
Then it occur to me to add man inside as it will change energy balance. Normally one human inside inclosed space it is extra 100-150 Watt heat equivalent.
first hour: 
second hour:
as I can see the man is adding extra 1-2C in to environment.
More so, I can see my emulation showing 1000W is more then enough for this small space.
If it would be my choice, I would use 500W heater or 1706Btu.
Normally you may find those types of diesel/oil heaters on smaller yachts.
they are around 1000-3000 watt and in my opinion overkill for small spaces. Although they are built to last forever.
Downfall: they are wasting lots of space. The one I've seen has long exhaust pipe and mounted on bulkhead. Also the cheapest I've seen is around $1000.
In my opinion this type of heater is better and more portable:
It is cheaper -about $100, easy to find on Chinese sites and easy to install. Exhaust pipes way smaller then regular heaters.
Second picture showing it's internal design. It is very compact and dense. Also at 1000 watts it is using around 0.1L of diesel per hour.
Let's assume we have stuck at some place,where we don't have electricity and it is cold for about 3 months. That is around 200L fuel for 3 months .
If we have two people on board, this number will be less. I don't have exact estimate, but let's say it is 120L for 3 months.
In this study I don't talk about other sources of energy. I assumed:
a. No shore power available and boat is in autonomous operation. b. Wood or coal is not readily available or it is so hard to harvest and bring on board to make it impractical.
2. On board we will need energy to cook food. People used kerosene fueled cookers for very long time, even before electrical stoves. But they are very inconvenient and smelly, especially if you will use diesel instead of kerosene. There are some types of stoves, which has auto start and burning without fumes or smoke. They are based on pre-heating with electricity powered glow plugs (similar to heater mentioned above). They are very nice! But cost is extreme! $1500! Search internet for Wallace diesel stove and you shall see it for yourself. I'm not even considering them due to crazy cost.
What else is viable? just a simple kerosene burners or possibly modified kerosene burners .I used similar to this stove myself
Those are terrible to start up and shut down. It takes about 3-4 minutes to start (preheat). For boats it is almost useless because they emit lots of black smoke and it is very unreliable. Also they know to cause fires.
Most of boaters use alcohol burners. Those are very simple and reliable, but requires to carry 90% and up alcohol as an extra supply. If you don't cook much, this is the most commonly used for cooking. If you stay in ports all the time,the best is to carry inductive cooker. For $20 inductive stoves, you could always carry it on board as extra stove. We won't calculate energy consumption electric cookers because we have already discussed those here. Also, if boat is moored in civilized place, connection to electricity is easy and there is no discussion about energy starved environment.
All liquid fuels has approximately the same amount of energy density (+/- 15%) so in assumption of 45MJ/kg we could derive to needed amount of fuel to store for 1 month of cooking. I estimated at around 5KW per day but this was including all electric needs. For cooking alone it will be about 1200Watt per day total. if we convert this to Joule, it will be 4.3Mj or about 100gr of fuel or about 0.1L per hour of diesel. This is wonderful estimate as it completely proven by my practical living in autonomous mode. I used 8L LPG per 3 months in the kitchen by cooking every day 3 meals and making tea. That is 8L for 90 days and 0.09L per day. Wow, we derive by mathematical model the approximate amount of 0.1L fuel per day and it came in complete agreement to practical observation over period of 3 months!
Therefore you need extra 3L of fuel per month to cover your cooking needs.
3. Storing food. Fridge. In cold environment it is possible to store outside. Above10C it is recommended to use fridge. Fridge-freezer takes around 320Kw-hr per year or about 1KW per day or about 40W per hour. Per month it is 30000W or 30KW. This usage of energy more valid during warm season, but let's keep it in mind for calculation on installed equipment.
4. Above, we discussed basic energy needs to continue stay alive in moderately cold environment (as an example Black sea). Unfortunately in modern world we use to be connected to outside world and actively discuss or channel our own information. With a little exaggeration, it became as important as food supply. Also in the modern world boat must have electronic equipment.
-Two way radio or transceiver or "walkie-talkie" or "communication radio". Most of time it is used in receive or listening mode. Per hour it takes 0.1W or about 24W per day or about 700W per month. In transmit mode radio use way more energy. So let's say you only use 15W transmit mode for only a few hours per month. That will be about 800W per month total.
-Cell tower communication in a form of modem or a cell phone. It is convenient if you near by cell phone tower and can have signal. A simple (small screen old Nokia) phone will take about 50-70mW per day or about 4W per month. But most people like to use digital phones or modems or both-old phone and modem at the same time. Modem takes about 4W per day if you use it 5 hours per day. Per month it is about 120-200W for modem and 400W per month on 5in screen cell phone. Total 600W
-If you need to have satellite connection, receivers are very power hungry. They are about 30W per hour to receive and 200W per hour to transmit.
Let's take 150 Watt as an estimate. Then per day in 8hr usage it is 1200W or 36KW per month! You'd better have diesel generator for that power hungry equipment.
-Laptop or Tablet. Assume it is smaller size, 10in screen. Modern tablets use from 30W per hour on smaller Android, 10in screens to 200Watt per hour on faster models and 17in screens.
Let's say it is 50W per hour, non video editing tablet for reading and typing purposes. 8hour usage will bring 400W per day for entertainment purposes. Or 12000W per month.
-Lights. Very important to use signal lights for safety to avoid collisions. Two bright 3W led is 6W per hour or about 10W per day on winter night and extra 6W during day time for fogs. That is around 70W per day. Plus lights inside. I would estimate this around 2watt per hour in 10hours of period or 20 more watts per day. Total lights would take about 90-100W per day or 3000W per month. If we just use very dim 0.5W parking light and other onboard lights, this number can beredused to 750watt per month.
-In humid environment fans are important. Small 2W fan and two of them on boat would take about 80-100W per day or 2400W per month. 2W is really small propeller.
-On-board computer or equipment to keep board alive. 2W per hour or 50W per day or 1500W per month.
-If boat is stationary it is only a few equipment are used. Presume it is used only 50% for moving. GPS is about 4W on small screens or normally 10W/hr or240W per day. 50% usage per month it is 3600W per month. navigation screen is another 10W per hour or the same 3600W per month.
-Autopilot is very power hungry regiment. it takes on 35-40ft yacht about from 2 to 6A on 12V. Or 24-72W. Let's assume medium 50W per hour or about 1200W per day or 36KW per month! You'd better have diesel generator for that. Even assuming you are using it 10hrs per day, it is 15KW per month.
-Pumps. Bilge pump for taking out seeping water is around 30W and it is used very seldom. But 30min per day it is 15W per day or 300W per month. Water pumps for kitchen:20W or with 45min total usage it is about 15W per day or 450W per month. Sewer pump:100W or for 10min usage per day it is 15W per day or 500W per month. Total for all pumps 1300W per month in round figure. Please note: we are talking about absolutely small pumps. In real life 5 times larger pumps are used.
-Anchor motor. 500W for 10 minutes per month. That is 83W or let's say 100W for month.
-Heater. Diesel heater uses around 25W per hour to run or about 400W per day if you run it 16hr per day. This is 12000W per month. If you use diesel cooker it will be about 1.2KW per month. total for al diesel equipment is 2400W
All added above energy consumption is around 130KW per month for one person if you moving! If you just stay stationary, it is 21850W or around 22KW. This number 22KW excluded satellite usage, fridge, with very dim lights and total energy economy. For each extra person you MUST add about 14400W for extra computer usage and cell phone. Staying moored for two people on board will take about 36.5KW per month. As you can see it is higher then in a regular house during winter. This energy consumption will be much more in summer as extra 30KW comes with fridge. So summer consumption staying stationary is about 66.5KW for two people.
5. I did not write about propelling boats with electric engines. Power to run small 10KW electric engines are huge. We are talking about very different concept about running yachts. If you need to just moor yacht on electric engine and you are very good with navigating in tight spaces, it might take 20minutes to get your boat moored. Let's say 30min. This is 5KW power or energy from battery. If I have 24V batteries, it is 416A current for 20min-which is 1/3 of hour. Using this calculator https://visbis.com/newsinfo/about-batteries/all-about-lead-acid/calculator3.html would give me 450Ah, 24V battery bank. I just used different numbers of battery capacity to come up with 0.3hour in the calculator. I will let you think about that on what it means in terms of weight and cost.
Just a few words about supplying with energy those things (excluding satellite and autopilot). 49KW per month that is 1.6KW or 1600W per day. Small yacht doesn't have much space for solar batteries. The biggest solar panels I've seen around 120W- real power per hour. Please do not think in terms of an ideal, theory. Use this calculator to estimate.
It comes to 3m2 or 412W of solar panels. Adding 400W suggested wind generator would give 100W realistic power. Per day that might bring another 300W of power per day.
I'm going to talk about realistic methods to bring this power in another article.
I may forgot some common energy eaters. Please let me know and I will edit this article.
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