High power alternators vs Genny on a Cat

[Thalas]

To my understanding the advantages of upgrading to high power alternators are:

Much less weight (no generator is at least a 500lb savings)
Much less maintenance (one less engine on board)
No loss in redundancy (on a Cat with 2 engines)
Lower cost than a generator installation
Both engines running can charge LiPo setups VERY fast

Yet, most modern cats from the big 3 almost always include a generator. What are the advantages of having a generator on a Cat in place of installing high power alternators?

[Barra]

Aircon.

If you dont want that you dont need a genny these days.

Cats have plenty of space for solar which these days is so efficient it can pretty much do everything else. Add enough lifepo and you are covered for a few back to back cloudy days too so even the high output alternators are less and less necessary

[robert sailor]

Originally Posted by Barra

Aircon.

If you dont want that you dont need a genny these days.

Cats have plenty of space for solar which these days is so efficient it can pretty much do everything else. Add enough lifepo and you are covered for a few back to back cloudy days too so even the high output alternators are less and less necessary

You can't be sailing in the Western Caribbean its been raining here for close to a month and this is dry season. We are supposed to get some sun very soon, panels not cutting it these days, high output alternator is needed daily.
My view on your question is that if you are not using an AC watermaker, nor air conditioning then I'd have two large alternators for your amp hungry lithium batteries.

[catsketcher]

Like Barra, I can't get the fact that anyone needs a genset. Even on multiple overcast days our 400 watts of solar keeps us all fine electrically. I could easily add another 600 watts of solar on our 38 footer. This would cost about $700 for the panels and then installation. That would get me through any months of overcast days silently. As it is we use about about double what the fridge uses - about 60AH for the fridge so 100Ah per day. The panels can sometimes start tripping at 10am in nice weather. Then again I still think having electric light is great and a fridge is totally amazing. Start with little and you are happy with less.

I don't even use a genset for power tools. I just turn on my inverter and work away. The panels might put in 25 amps for a few minutes but they settle down soon after. When my little genset died I didn't bother replacing it.

I am no expert but running diesels to charge batteries may be bad news for the diesels. I can't see how any alternator is going to load up a diesel enough to get it loaded up where it likes. It used to be that running diesels with light loads was very bad for the bore and the rest of the donk. So you may save a little at first but be up for engine rebuilds earlier if you use the main donk to charge the batteries for a few hours every day. Read Nigel Calders book on the subject or ask in the engine forum about light loading.

Or you could reduce the load and stay solar.

[44'cruisingcat]

Originally Posted by Barra

Aircon.

If you dont want that you dont need a genny these days.

Cats have plenty of space for solar which these days is so efficient it can pretty much do everything else. Add enough lifepo and you are covered for a few back to back cloudy days too so even the high output alternators are less and less necessary

This.

[valhalla360]

Another vote for it's about running the air/con (or other high power demand items).

Another complication is maintenance. Drawing 5-10hp off a belt driven alternator and you better have the belts perfectly aligned or it can start eating them.

On a cat, if you don't run the air/con, it's very much viable to handle almost all your power needs with solar.

[belizesailor]

Yep, AirCon is the usual reason to have a genset. That and or a big AC driven WM...washer, dryer, etc...

A better way to answer the question is what are your anticipated loads?

[travellerw]

Funny.. Just yesterday I completely disconnected my alternators from my house bank. Between our solar (900W) and our backup Honda 2000 we just found that the complexity of alternators charging a house bank wasn't worth it. To be honest, we haven't completely disconnected them. We left one alternator wired through a large relay (default off). This will allow us to connect the house bank in an emergency by simply engaging the relay.

For us, we decided that installing a second 120V battery charger was smarter. 2 60A battery chargers would provide all the high speed charging we require and the Honda can handle them. 1 hour of running would put back all the Ah we use in a day.

[Fuss]

Originally Posted by travellerw

Funny.. Just yesterday I completely disconnected my alternators from my house bank. Between our solar (900W) and our backup Honda 2000 we just found that the complexity of alternators charging a house bank wasn't worth it. To be honest, we haven't completely disconnected them. We left one alternator wired through a large relay (default off). This will allow us to connect the house bank in an emergency by simply engaging the relay.

For us, we decided that installing a second 120V battery charger was smarter. 2 60A battery chargers would provide all the high speed charging we require and the Honda can handle them. 1 hour of running would put back all the Ah we use in a day.

Really, you disconnected two working alternators and will instead use a honda 2000 to contribute to the topping up of the batteries using two 60a battery chargers.
So now when you motor anywhere only the solar contributes and the motors contribute nothing.
When you get to your destination, if the batteries need topping up, you start up the honda.

[travellerw]

Originally Posted by Fuss

Really, you disconnected two working alternators and will instead use a honda 2000 to contribute to the topping up of the batteries using two 60a battery chargers.
So now when you motor anywhere only the solar contributes and the motors contribute nothing.
When you get to your destination, if the batteries need topping up, you start up the honda.

Yes, the alternators are now disconnected from the house bank. They only charge the starting batteries now. The battery combiner died yesterday and even though I had a spare onboard, I decided it wasn't worth replacing (I disconnected the other alternator over a year ago). Yay.. No more belt dust.

Down here, we rarely motor these days and the amount the alternators were contributing was microscopic. With 900W of solar, we almost never "top up" the batteries. Even under sail with the autopilot working, we produce more than we use even when overcast. The Honda and 2 chargers will be employed during rainy periods. That has really been the only time we have required "topping up". A couple of weeks last year it rained soo hard that our whole 900W solar array was producing like 15W (for the whole 2 weeks).

[Bean Counter]

Originally Posted by Thalas

To my understanding the advantages of upgrading to high power alternators are:

Much less weight (no generator is at least a 500lb savings)
Much less maintenance (one less engine on board)
No loss in redundancy (on a Cat with 2 engines)
Lower cost than a generator installation
Both engines running can charge LiPo setups VERY fast

Yet, most modern cats from the big 3 almost always include a generator. What are the advantages of having a generator on a Cat in place of installing high power alternators?

To try to answer the question, to define " most modern cats from the big 3" - the majority of modern catamaran production is for charter fleets. A lot of charter fleets operate in tropical climes or mid summer. A lot of charter patrons who put up to 10 people aboard for a week like to run air conditioning. So in order to make your charter cat attractive to a larger market audience and so maximize your charter income - you put in air conditioning - and hence a generator. If you search yacht world you will see a lot of >42ft 4 cabin cats with Aircon.

For "owner version" cats you will see a mixture of both, some now days purely solar/lithium but no Aircon, and those that want as comfortable existence as possible with aircon, washer dryer, AC water heater, and other AC loads, who will put in a genny, and then hybrids of these two.

For those who buy a 5 year old charter cat, or a fully loaded private cat, it comes with the genny which probably has years of life left in it.

At diesel consumption rate of .5gph for 2 hrs per day = $3 per day.
Compared to a solar lithium replacement installation that delivers the same energy requirement would cost say $10,000 / 3 = 3,333 days or 9 years of diesel.

So that is probably why you see many cats with generators.

If you are starting from scratch - sure the solar lithium solution may be able to deliver most things (except Aircon unless a really big system) and will need topping up when there are weeks of low sunlight. Some people buy a cheap noisy gasoline genny to do this, (and I dislike being anchored next to them in a quiet harbor), and they will need to carry gasoline aboard to keep it fed. An alternative is to run a main propulsion engine, which when at anchor is an inefficient way to charge batteries even with high amp alternators. The main engines are not designed to run at 1500 rpm for hours in neutral - it wastes diesel and will probably prematurely wear out the engine, detracting from its prime purpose. The hi amp alternator comes in to its own when under way using motor(s) which in a cruising scenario is quite a low time percentage to warrant the upgrade cost.

[smj]

Originally Posted by Bean Counter

To try to answer the question, to define " most modern cats from the big 3" - the majority of modern catamaran production is for charter fleets. A lot of charter fleets operate in tropical climes or mid summer. A lot of charter patrons who put up to 10 people aboard for a week like to run air conditioning. So in order to make your charter cat attractive to a larger market audience and so maximize your charter income - you put in air conditioning - and hence a generator. If you search yacht world you will see a lot of >42ft 4 cabin cats with Aircon.

For "owner version" cats you will see a mixture of both, some now days purely solar/lithium but no Aircon, and those that want as comfortable existence as possible with aircon, washer dryer, AC water heater, and other AC loads, who will put in a genny, and then hybrids of these two.

For those who buy a 5 year old charter cat, or a fully loaded private cat, it comes with the genny which probably has years of life left in it.

At diesel consumption rate of .5gph for 2 hrs per day = $3 per day.
Compared to a solar lithium replacement installation that delivers the same energy requirement would cost say $10,000 / 3 = 3,333 days or 9 years of diesel.

So that is probably why you see many cats with generators.

If you are starting from scratch - sure the solar lithium solution may be able to deliver most things (except Aircon unless a really big system) and will need topping up when there are weeks of low sunlight. Some people buy a cheap noisy gasoline genny to do this, (and I dislike being anchored next to them in a quiet harbor), and they will need to carry gasoline aboard to keep it fed. An alternative is to run a main propulsion engine, which when at anchor is an inefficient way to charge batteries even with high amp alternators. The main engines are not designed to run at 1500 rpm for hours in neutral - it wastes diesel and will probably prematurely wear out the engine, detracting from its prime purpose. The hi amp alternator comes in to its own when under way using motor(s) which in a cruising scenario is quite a low time percentage to warrant the upgrade cost.

You don’t mention the upkeep costs of the diesel generator just the fuel costs. Also after 9 years of generator use you will have over 6300 hours on the generator, maybe $10-$20k to replace at that point in time?

[oleman]

If you want to have a good life on the high seas most boaters will want good heating and air conditioning as a minimum. Most will want full size refers and freezers with an array of kitchen appliances, and washers and dryers. AND the ability to take a hot water shower daily using fresh water.
These needs will never be supported by a few hundred watts of solar panels and automotive generators on a 40 HP diesel.
When you have sailed many days near the equator, you can really appreciate amenities.
I guess the real question is which end of the boating use do you want to be on?

[smj]

Originally Posted by oleman

If you want to have a good life on the high seas most boaters will want good heating and air conditioning as a minimum. Most will want full size refers and freezers with an array of kitchen appliances, and washers and dryers. AND the ability to take a hot water shower daily using fresh water.
These needs will never be supported by a few hundred watts of solar panels and automotive generators on a 40 HP diesel.
When you have sailed many days near the equator, you can really appreciate amenities.
I guess the real question is which end of the boating use do you want to be on?

Your definition of good life is my definition of pure hell! I don't want all the shoreside amenities and their demanding upkeep on my boat. Been there done that and never again! However I also respect others that choose to have and use all the shoreside amenities as long as there running of their generator doesn't interfere with my peace and quiet.


Sent from my iPhone using Cruisers Sailing Forum

[Bean Counter]

Originally Posted by smj

You don’t mention the upkeep costs of the diesel generator just the fuel costs. Also after 9 years of generator use you will have over 6300 hours on the generator, maybe $10-$20k to replace at that point in time?

I built the upkeep in to the diesel price, diesel is less than $3 in the USA which is where we fill up (last fill in NC was $2.10) . Of course any alternate system also requires up keep.

At the end of the gennys life then you have the choice to either replace it or do the solar lithium thing, which in several years will be probably a lot less than today, or something better than lithium comes along and solar panels are twice as efficient for same surface area. Who knows, but to be on the bleeding edge of technology is capital intensive with higher risk and more computer circuitry to go wrong, which most of us can't fix out on the water.