Does a genset still make sense?

[mako]

Originally Posted by Kinkircating

We went without a generator and instead are installing dual Integrel chargers. Also 3.2kW of solar feeding a 29kWh lithium bank at 48V.

What vessel do you have to mount that much solar?

[Simi 60]

Originally Posted by s/v Jedi

But that isn’t a valid argument.

It's a perfectly valid argument
Small battery bank does not require as large a charging source as a large battery bank
And I did say the Honda is fine on a small battery bank running a smaller charger.

because the next boat will have a 18kW genset and claim your silly small 6kW isn’t up to the task

If they have an 18kw Genset I would assume they have an even larger battery bank and probably 3x 120 amp chargers.

So they to would have a valid argument, for their big battery bank
As would we that the 6kw genset and 1 X 130amp charger is ok for medium battery bank
As would the Honda with 40 amp charger be good for a smaller battery bank.

[Na Mara]

Like many here I think it comes very much down to what kind of boat you have and what kind of sailing you do.

With her raised aft cockpit and beautiful lines I just cant motivate putting an arch om my boat. Passages tend to be 60nm plus and we tend to do those twice a week. Consumption underway and at rest is about the same (electric cooking takes more at rest, instruments and auto more underway) and is about 2+kWh.

Without doing an arch the maximum permanently mounted solar I can fit is just shy of 600W. Where I sail that should deliver about 2.4kWh of energy per day on average (its being fitted for next season so we will see what the numbers truly pan out as). With 7kWh of battery storage we are good for about 3 days without any generation. We don't have AC (the boat is very well ventilated with opening hull ports that catch cooling breezes off the water) and we don't have water makers (we carry 600l) and we only heat water off the engine (which we run for a few hours every third day or so as we move into and out of anchorages and marinas) or off shore power, and we are often in marinas with shore power.

As solar production is a bit over consumption, as we get a few kWh every few days off the engine when motoring as well as hot water, and as we don't have any need for AC or water making, a genset would be a total waste of money and precious space aboard for us. If this changes its far cheaper and easier to add rail mounted temporary panels when in harbour and hydrogenators when in motion than it is to add a genset. So we would still not go the genset route.

That said, if you move less frequently than we do or do longer passages under sail, use more hot water than we do, use AC regularly, and have similar panel mounting restrictions as we do, then a gen set makes more environmental and financial sense than running the main engine.

[Dockhead]

Originally Posted by pwillems

I have always read that the purpose behind installing a standalone genset rather than just using the main engine to charge batteries is due to the inefficiencies of running a diesel engine with only the light load from the alternator. This makes sense, and I would agree. But, these days, it is quite easy to get hold of some very large alternators and very large inverters, so I am not sure it always makes all that much sense anymore.

Let's say a small catamaran owner has 2 * 20hp and a decent lithium bank that will happily accept high charge rates. A 400amp/12v alternator uses ~16hp (1 hp per 25 amps). At the full 400 amps output, that engine is at over 75% working load. Taking into account heat derating and other inefficiencies, the engine is still getting a pretty good workout for the entire duration of the charge.

Of course, you wouldn't want that alternator putting out its full charge when you actually need that engine to push the boat into some challenging seas, but that is easily managed with a clever regulator, or even a potentiometer if required.

I never thought it made any sense to have three diesel engines on a sailboat. Especially on one which is weight sensitive like a cat.



I think your idea makes sense, BUT -- you will have a somewhat tricky installation. Such a large alternator on such a small engine would need to be setup so that it doesn't run when the engine is being used for propulsion. And I don't think you'd want to load it 75% of max in any case.

[Dockhead]

Originally Posted by malbert73

Is this on a different thread? Definitely want to check it out. But, with only 40 feet LOA don’t think I’m willing to install the kind of solar farm and battery bank to run the AC for 8 hours straight. I’m not disagreeing that it’s possible to get rid of the genset, AC aside.
But, my point is if you do have a genset, using all of the power to do multiple things- like water making, bulk charging, and others- makes sense and is very economical on fuel burn

I had solar on my previous boat and no genset; on my present boat (last 14 years) I have a 6.5kW heavy duty genset and no solar. I also have a 110 amps (x24v) so 2.5kW second alternator on the main engine.



I don't have solar on this boat for one reason only -- windage and upwind sailing performance. Genset with lead-acid batteries (which I still have) is not an ideal combination, because you need longer generator runs, but when it's a heavy-duty, quiet, low speed genset it's OK. I use it just like you say -- bunch up different tasks and do them all at once. Genset with LiFePo is perfect.

[Na Mara]

I’m with dockhead on the windage. I’m always surprised at how little the extra windage of panels on an arch, not to mention their weight, bothers people.

I calculated once that the drag and turning forces of 3m2 of panels at 20 degrees of heel 45 degrees off the wind in a force 6 (I think) is about 300kg. That ignores all the windage from the arch. That is about the drag exerted on your stern from a hydrogenerator at hullspeed. That will take a good half knot off boat speed. Worse still is the turning force exerted on the boat and the effect it will have on the balance on the helm. Then add the 100kg right aft and its effect on the boat’s motion.

I recall a magazine article that I read of a guy who bought a boat with a stern arch and was very disappointed in its handling and motion upwind. He ripped the arch off and reported that it was like a different and far superior boat.

Maybe for some people the gain in utility of all the windage and weight is worth it but for me the idea of doing that to Na Mara is akin to vandalizing her. I just can’t bring myself to do it and if my power needs got to that level, I would fit a genset as the lesser of two evils.

[sailingharry]

Originally Posted by Na Mara

I’m with dockhead on the windage. I’m always surprised at how little the extra windage of panels on an arch, not to mention their weight, bothers people.

I calculated once that the drag and turning forces of 3m2 of panels at 20 degrees of heel 45 degrees off the wind in a force 6 (I think) is about 300kg.

I really think your assessment is way off.

I'm astounded at the windage calculations. My arch is about 2 tubes 15 feet/5m long and 3"/8cm diameter. I'm not sure, but I suspect one guy could hold it still in a force 6. Nothing near 300kg! The panels themselves are even less -- presenting a surface area of 2 inches by 6 feet (5 cm x 2m). 300kg just doesn't pass a reality check!

Weight is an issue, always. My arch, in stainless, weighs under 200lb. My 600W of solar, about 3m2, is under 100lb. All in, 300lb/150kg. Sure, it's weight in the cockpit. But less than two guests along for the day.

But with weight, it's important to consider the "marginal weight” -- how much extra does it add. In my case, it's just the panels themselves. The arch predates any solar. But, when the PO went to the arch, he removed a radar post, and a wind generator post. The arch also adds davits and a place to mount the iridium, 3gps antennas, and an ais antenna. Any weight savings of removing an arc would be offset by adding all this back in.

But it is about trade offs. In the 5 years we've owned the boat we've gone 8000 miles, rarely pierside. We need to make 100% of our electric. Even with 270A of alternators, before solar we ran the engine far too much. I'm hoping the near double in solar this winter (the panels mentioned above are the new one) will greatly reduce that. The davits (with motor mounted!) are mandatory -- we sail with a dog which means twice a day trips ashore, many times over 1/2 mile each way, so storing on deck is a non-starter.

But then again, we care so little about weight that as we pushed off last year, we had nearly 80 liters of wine stored in the lazarette directly under the arch mounts -- that's half of the arch weight in wine!!!! And right next to that is our JSD, easily another 60lb/30kg. And probably 200lb/100kg in canned goods in the bow of the boat over the chain locker, an even more horrible place for weight. And let's not forget 120lb/60kg of anchor backed up by 350lb/180kg of chain (seriously, imagine the performance gain if I got rid of the spare anchor and went to an all nylon rode).

I just looked up the Regina 43. An absolutely stunning yacht, and one that could easily have made our short list. Truly beautiful! She's very similar to our Saga 43, same length/beam. She does weigh 30% more. And the one on yachtworld has davits that probably weigh as much as my arch, teak decks that weigh vastly more than our arch, and an in mast furler that certainly hurts performance. All compromises that are considered "reasonable" -- but imagine how much better she would perform if they cut 30% out of the displacement, ditched the davits and teak decks, and put in a conventional mast.

[team karst]

Originally Posted by Dockhead

I never thought it made any sense to have three diesel engines on a sailboat. Especially on one which is weight sensitive like a cat.

One of Our OEM 300 l water tanks i removed. Replaced it with a 100 l diesel tank, a 37 gph watermaker, and a 5.5kW genset, which in totality, weigh lighter than 300 l of water.

Yes, forgive me for the mixed USA units of measure. [emoji848]

[Na Mara]

When your boat heels the underside of your panels is exposed to the wind doing the heeling. A 3m2 panel heeled 20 degrees has the same windage as a 1m2 panel. Try holding a 1m2 panel face on into a Force 6.

[rslifkin]

Originally Posted by Na Mara

When your boat heels the undersida of your panels is exposé to the wind doing the heeling. A 3m2 panel heles 20 degrees has the same windage as a 1m2 panel. Try holding a 1m2 panel face on into a Forex 6.

Very true. But if you're going to have a bimini to keep from roasting in the sun, then there's no loss if you make it out of solar panels rather than canvas as you'll have the windage either way.

[Kinkircating]

Originally Posted by mako

What vessel do you have to mount that much solar?

Balance 526, five 400W glass panels on the coachroof and three over the davits.

[dhenline]

I hope a generator is still needed. I am buying a new Cat and opted for the Generator and did NOT opt for Lithium batteries.
in all my previous chartering in the Caribbean, I use AC most evenings and since we are headed to the Pacific Ocean, I know I will use AC. the amount of Lithium needed to run AC is mind boggling. So a generator for me. I will find out later if I made the correct decision

[Kinkircating]

Originally Posted by dhenline

I hope a generator is still needed. I am buying a new Cat and opted for the Generator and did NOT opt for Lithium batteries.
in all my previous chartering in the Caribbean, I use AC most evenings and since we are headed to the Pacific Ocean, I know I will use AC. the amount of Lithium needed to run AC is mind boggling. So a generator for me. I will find out later if I made the correct decision

You'll be fine, just less freedom from the fuel docks. It's all a series of compromises and lots of people have done exactly what you are doing and survived to tell the tale...and had a hell of a good time along the way (while repairing their boat in gorgeous locations : )

[noelex 77]

Originally Posted by Na Mara

When your boat heels the underside of your panels is exposed to the wind doing the heeling. A 3m2 panel heeled 20 degrees has the same windage as a 1m2 panel. Try holding a 1m2 panel face on into a Force 6.

You are assuming the same drag coefficient, which is not accurate. The drag coefficient of a 20° inclined plane is around 20% of a flat surface.

[Na Mara]

Originally Posted by rslifkin

Very true. But if you're going to have a bimini to keep from roasting in the sun, then there's no loss if you make it out of solar panels rather than canvas as you'll have the windage either way.

For this very reason I also refuse to have a bimini on Na Mara. I’m a tilly hat and full length clothing kind of guy when on deck, else I’m below in the pilothouse. But in very hot climes and on boats without a pilothouse I can except your logic.