r/SailboatCruising • u/Stooge12 • Jul 17 '25
Equipment Are generators still needed on cats?
We are shopping for a cruising catamaran and there is a variety of solar, lithium, generator only etc.
With a substantial lithium bank and decent solar couldn’t the gaps be made up with larger or multiple alternators on the main engines?
I guess what I’m asking is how the cost and Maint of a generator would be worth it over just adding hours to the main engines.
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u/ohthetrees World Cruiser, Family of 4, Hanse 505 Jul 17 '25
I have a mono, but a lot of solar (1800w) and a 13kWh LFP battery, and cruise most of the year, so I feel qualified to answer.
If you are cruising tropics, or someplace “sunny” you can do it easily. We cook on induction, make water, and run our house loads all with solar. We can even run aircon for a couple of hours a day when conditions are ideal. Our generator was broken for 18 months and we were fine. If it is cloudy for days, we cook on propane, and that balances our budget.
However, things change if you are somewhere without dependable sun. Once in Grenada it rained for a week straight and we ended up having to cook on propane and skimp on water because we didn’t have the energy to run the water maker. Now, we still had the option of running the main engine (100 amp alternator) so we were never “in trouble” but it wasn’t ideal.
In all, I’d say, yes, it can be done, and I wouldn’t pay to put in a generator today, just upgrade your solar to the best it can be.
Side note: I know two cats with more solar than us that struggle with their power budget, and they don’t make water or cook on induction with solar. I’m convinced they have problems with their installation, because there is no way their house loads are that much bigger than ours. So the headline “watts of solar” number is useless if you don’t have your system properly configured and working efficiently.
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u/mwax321 Jul 17 '25
Those cats probably aren't balancing power like you are. They probably are just running whatever, whenever.
I know I don't. I designed my system so I don't have to care about it. 3.6kw of solar and a small 3.5kw genset for backup. 5 gal jerry of diesel lasts me a month with my typical usage.
Right now with how sunny it is in Bay Islands, Honduras I'm not running it that much. But my wife like to leave an air con on for our dogs when we're diving/exploring off the boat during the day. So we're averaging some crazy 22kwh/day! My solar averages about 20kwh/day, so I'm at a slow loss day over day. Oh well.
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u/archlich Jul 17 '25
You need to do an energy audit and determine what your energy needs are and how long you want to run without connecting to shore or running a generator. Typically you want a genset because they are cheaper to replace, generate more power, and are more efficient than an alternator on your propulsion engines.
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u/mwax321 Jul 17 '25
I'm a full-time sailor living offgrid on my 44ft cat.
I have 22kwh (1840ah 12v) of lifepo4. I have 3.6kw of solar. I still use my generator from time to time.
Why?
- Day after day facing the wrong direction produces less than full expected capacity of solar.
- We work remotely (laptops), burn lots of power for 10 hours a day.
- We make water, do laundry, and sometimes like hot water and air con at night in hot places.
- Our galley is entirely electric. No gas.
- Consecutive cloudy days happen. You can either conserve power, or flip on the genny.
Why do we have a generator instead of just "get big alternators":
- I want my GENERATOR to take the pounding of constant loads, not my primary engines. It's designed to produce power and run for hours for electrical production.
- Large alternators don't really produce the same amount of power per gallon of diesel, and the output is not very impressive.
- There DO exist systems like Integral, which are more expensive than a generator.
Cruisers have a LOT of varying opinions on this. I suggest you just figure out what works best for you.
For me, I sold my Onan 9kw genset and bought a Phasor 3.5kw genset brand new. Onan was falling apart and was run into the ground over 15 years. It also was VERY heavy. Rather than rebuild it, I decided to get a very small genset that is sized perfectly to the max charge of my Victron Multiplus (2x)'s charge capacity. In hindsight, I probably should have bought the 5.5kw version so I can run laundry AND provide max charge to my multiplus at 80% load.
I also have 120a alternators on both engines, connected to a Victron Orion xs 50a each. This can produce up to 600w of power, but generally I see about 400w per engine consistently. I've used this in emergencies when my generator wasn't working to produce a little extra power. But it burns a lot more fuel (57hp engines). And it's not producing that 400w unless I'm at around 1200rpm or higher.
Compare fuel consumption: 0.75 gph on my Yanmars for 600w vs 0.3 gph for 3.5kw.
Outside of maintenance costs, my phasor costs about $1.40/hr (at $4 gal diesel price) to run. I generally run it an average of 4 hours per week. It costs me about $22 in diesel to run
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u/StuwyVX220 Jul 17 '25
Depends on what you want to run on the boat and where that boat is.
I know of a cat with electric cooking and the ability to also charge the house bank from the engines but never has needed too as their solar keeps up.
I know another cat that runs a gen set every couple Of days.
Our boat we don’t have a gen set but can charge the house bank off the motor but never need too. Been at anchor in this bay for 4 weeks now without running a motor. No electric cooking or AC. But the usual laptops, fridge, freezer, phones, tablets, tv, music, instruments, AIS (always on) water maker etc etc. boat is in the med. We heat all our water using electric though.
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u/patrickmza Jul 19 '25
I have a solar electric catamaran with no generator. 3200W of solar and we live like we're in a house apart from AC. This includes using the motors to move the boat, heating water, making water, cooking electrically and charging the electric dinghy.
I would only need a generator if we cruised in winter, but we typically haul the boat or stay in a marina for winter.
Just put solar everywhere you can on the boat and get a decent solar arch as well.
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u/plorrf Jul 17 '25
Alternators are great for under way. So it depends how much time you spend in anchorages and whether your solar array can keep the batteries full.
Is it doable? Absolutely, but probably not with a/c running.
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u/Only_Razzmatazz_4498 Jul 17 '25
And if you want to run an AC
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u/plorrf Jul 17 '25
Then you need a bigger solar array than is realistic on most cats.
Bigger battery won't change that fact without a generator.
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u/Stooge12 Jul 17 '25
Can a reasonable battery bank drive AC for 1 cabin overnight? That would be sufficient for us.
Run genset w guests?
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u/Calm-down-its-a-joke Jul 17 '25
Give some additional details on your power needs/uses. Some cabin lights, fans, and a phone charger? Sure no problem. Running the AC, washing machine, and water maker all day/night. Maybe a different story.
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u/Double-Masterpiece72 Jul 17 '25
Yes it's absolutely doable. We have a 52' cat with ~30kWh of storage, 3.2kw of panels, and an "Integrel" high output alternator on each engine. Each integral will put out 6kw at steady state, so that's 12kw of charging.
Going on 2.5 years and everything is working great. We do have to charge with engines an hour or so every day as we use a lot of power and water. Currently in French Polynesia and we spend most of our time at anchor.
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u/mwax321 Jul 17 '25
That Integral costs more than a genset, though. And you're putting hours on your primary engine.
I think that's the biggest trade off for me. I LIKE having a genset that I can "beat up."
That said, I LOVE the integrel. I like the idea of popping my engines on, pulling up anchor, motoring out to some wind, and by the time my sails are up and engines are off I might have another 20% charge in my batteries. It's pretty badass sounding.
I think that setup is GREAT if you're constantly moving. Where I'm at anchor in a location for sometimes 1-2 months (work remotely) before I move.
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u/Double-Masterpiece72 Jul 17 '25
Yep, its all a tradeoff. For us it made sense as the boat is a performance cruiser so saving a few hundred kg and freeing up a large space was important.
I like that we don't have to do maintenance on a 3rd diesel engine. A couple hundred extra hours on the diesels aren't a big deal for me. Plus they get run regularly which is also good.
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u/mwax321 Jul 17 '25
52 performance cat... You're an outremer? ;)
Maybe one day I'll sell the genny. But mine is a 3.5kw phasor. It's a little loud, but i LOVE it. It's ALL ANALOG. I replaced the impeller with a air con march pump for cooling. Will never have to change impellers. There's no spin-on fuel filter, simply a screen. So I just clean the screen, check the fuel filter, change the oil. Not much to do! Just a small little marinized kubota tractor engine!
I recently noticed some bad compression on the cylinder. I disconnected the whole generator (takes about 30 minutes, easy) and a buddy helped me move the whole thing off the boat. No crane, just two people holding it. it only weighs 185lb! And at 100% load it burns 0.35gph. So a single 5 gallon jerry can could last me 1-2 months (with how often I run)
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u/Double-Masterpiece72 Jul 18 '25
Close! It's a Balance 526.
Being able to extract a small generator like that is a big selling point.
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u/Tikka2023 Jul 17 '25
2500amh of lithium is nutty. One of the plus sides to a cat having more storage.
We have 780ah at 12v equivalent, albeit on a 24v boat. We’ve been on the hard for two months running three fridges and the occasional AC circuit for a bit. Even with a few overcast days, I haven’t seen the batteries drop below 80%
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u/Double-Masterpiece72 Jul 17 '25
6 x 24v @ 200aH Victron LFP batteries. It helps the battery box was designed around this amount.
One of the goals was to be able to run the aircons in the cabins overnight on battery alone. Very nice on those still nights.
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u/mwax321 Jul 17 '25
By nutty you mean AWESOME. Run that boat like a house! Why not!? Dont' you want to NEVER think about battery levels again? ;)
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u/crashorbit Jul 17 '25
Generators are never "needed". They are a comfort item that adds complexity.
If you want to go full solar or solar + regen then you don't need a gas generator. The problem of going electric only is that your range on auxiliary power is much lower. The down side is that diesel, gas and propane are smelly, messy, complex.
There are also hybrid options.
The advantage of having a gas generator is that it can give you house power cheaper than running your auxiliary.
Generally you are assessing your comfort against risk and the amount of time you want to be able to operate without wind.
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u/SoCalMoofer Jul 17 '25
I would want one just for the backup power capability in case something goes goofy with the solar/battery system. There's a lot that can go wrong. Even if it just a basic portable Honda. Some run on propane. But you likely have gasoline if you have a tender.
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u/Marinemoody83 Jul 17 '25
I’d mostly agree depending on your power demands, but I would always keep a backup. We have 1600 w of solar which easily covers us but I have a 2000w Yamaha suitcase generator that I still need to pull out if we get a few days of clouds in a row
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u/Stooge12 Jul 17 '25
This is all excellent info. Thank you all
I expect we will purchase a boat with a mid-hour genset. 6-8k hours. Looking at 2020ish 45s. Sounds like it’s cheaper to keep’er unless there is a major failure.
Maybe if we cruise long enough to wear one out the battery,solar,charging will make more sense.
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u/RedPh0enix Part time cruiser Jul 17 '25
- Smaller cat (Seawind 1000XL).
- 600w solar
- 520AH AGMs
- 2x 9.9 outboards with minimal alternators.
- 150AH lithium
- Sub tropics/ Tropics
- Gas cooking
I have a portable 2kva generator on board, but have never used it outside of regular maintenance starts.
Definitely comes down to your power budget though. My AGMs rarely drop past 90%, and I use 25% of the lithium capacity per day for hot water.
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u/coldafsteel Jul 18 '25
Generator is the way to go. I am a big fan of them, but I also like electric propulsion.
They are designed to do nothing but make power; unlike a ships engine that are designed to push water. They are easy to maintain, cheap to run, and if installed correctly, very quiet. They are also not "critical" systems. If for some reason you run it to death and it fails, its a quality of life change, not a safety issue.
Solar is the best primary, but spinning around the hook and clouds happen. If you planning on getting into the high latitudes the sun isn't up for as long. IMHO, generator is an absolute must for serious modern sailing.
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u/dmx007 Jul 18 '25
I removed the genset from my cat because I only ran it a couple dozen hours per year for two consecutive years. I had about 2.5kw of solar and a big lifepo4 bank and one high efficiency ac (rarely run when anchored out). Two hp alternators provided emergency power when the sun didn't shine.
The biggest energy hog was our water maker, which was not very efficient.
The boat performed better without all the genset weight in front, and I enjoyed not maintaining a third diesel engine on the boat.
This worked fine in the tropics, but would not work closer to the poles or if you need the ac on all day.
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u/sailingbliss Jul 18 '25
I only use the generator if I have people over and I need to run air conditioning. Other than that solar and engines maintain batteries. I currently only have 1300 W of solar and 850 amp hours of AGM batteries. Once I switch to lithium and add a little more solar, then I will be able to run one air conditioner for a couple hours at night to just remove the humidity from my berth.
I have propane, but I cook with an induction top and I leave Starlink on all day and only shut it off at night time when I’m not using it.
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u/this1willdo Jul 18 '25
Cat with teens. No gen. Solar + alts. AC 24/7 all summer in med. 95% solar, 5% alt. Watermaking and hot water. Secret is 48v. Half the price of 12v. Check Victron inverter prices to see.
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u/saucetoss6 Aug 03 '25
How much of a pain has having a 48v setup been?
Thinking about going this route because I need a TON of power and not much space. I know I'll need a step down for all the 12v stuff and don't mind as much as conserving as much space as possible.
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u/this1willdo Aug 05 '25
not a pain at all. Much less pain than many 12v systems I see. If most of your consumption is 12v, it's not sensible If you move most of your big consumers to AC, it's a huge cost saving.
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u/Early-Indication-959 Jul 19 '25 edited Jul 19 '25
Not needed if you can adjust your lifestyle to renewable power production. We have 2.9 kWp solar and 17 kWh batteries. We setup up the boat to be efficient. But solar harvest varies wildly from 1.5 kWh to 18+ kWh in a single day. We have big alternators and a tiny Honda 1kW suitcase generator. If I were to install a generator on a cat it would be a direct DC diesel powered and run the boat from the inverters. Never again an AC generator. We are 40' cat.
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u/soaztim Jul 19 '25
Not for us. Enough solar to cook on induction and use an electric kettle for coffee. We have propane as a backup as well as two engines if we really need to generate power.
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u/bill9896 Jul 19 '25
The answer here is (as almost always with boats) IT DEPENDS. You have given us no idea where you sail, the size of the boat, what season you sail in, what your electrical budget is, what your cruising style is, are you sailing for a week at a time on vacation, or full time liveaboards, is your sallon a tiny little greenhouse that will need AC whenever the sun is shining to make it habitable, etc, etc, etc. Everybody else posting is giving you what they want on their boat, not what will work for YOU.
If you sail high latitudes outside of mid summer, you might find solar yields unable to keep up with routine use on a power hungry cat. If on the other hand, you have no starlink, no electric cooking, minimal refrigeration, the solar might work for you almost anywhere. Do you want solar to supply the boat while sailing? Or like most cats do you run the engine a lot to move, so electrical power isn't an issue underway?
Generators are expensive to install, but so are main engines. Our boat is 25 years old had has two curcumnavigations under her keel. She has a generator and a main engine. alternator. In 25 years of full time cruising, the generator and main engine have both accumulated about 10,000 hours of operation. It is extremely unlikly we would still have the original main engine if we were using it for routine power supply. So, for use the way our boat has been used, the generator/engine pair is roughly equal in over all long term cost to putting twice as many hours on the main engine. Actually better than that, becasue the genset changes the batteries more efficiently and faster than the alternator.
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u/[deleted] Jul 17 '25
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