Solar Catamarans

Rwc13

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Anybody here have any experience of one of these? Considering one for a combination of charter and private family use.
 

Rwc13

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With all the environmental concerns, nobody has looked at or has any opinion on these catamarans entirely powered by solar energy?
 

henryf

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There are a number of things to consider. The first is whether or not a manufacturer produces a good boat regardless of the technology. There have been a number of troubled purchases within the catamaran world probably based around low production volumes. Make sure you have a local representative able to support your new buy.

Then there is the solar technology. On a bright sunny day in a warm climate your hotel needs might exceed your propulsion needs so don’t forget to factor that in. Even worse a dull cold day when you need to keep warm.

With regards chartering speed can be an issue. We find the ability to relocate or to cover longer distances over a short period of time invaluable.
 

Rwc13

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This boat won the 2021 multi-hull of the year award based on its sailing performance, and I have also been given positive personal reviews by two transatlantic sailors that have purchased them here. The boat is built 5 kms from where I live and will use it in the Algarve.

I was concerned about the solar and engine performance, but have been assured by the manufacturer and independently it will do a full day easily at a speed of 7-8 knots with normal stops, even with hotel services and continuous use of the air conditioning. This translates into 4 hours at a top speed of 10-11 knots, and 24 hour use at 3-4 knots. With a back up diesel generator capable of powering the engines and hotel services in an emergency, I am now pretty relaxed about this.

For chartering, the boat will mostly be used around the Ria Formosa where speed and distance are not what really matters. And of course the environmental fit will be powerful. The top speed is a parameter of the hull, but distance can again be augmented by the generator if need be on occasions.

I am pretty excited about the boat and the opportunity, but still wondering if I am missing something.
 

dunedin

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Sounds an interesting boat. But I suspect “solar powered“ is extremely unlikely.

With these sorts of things, it is important to see and review the mathematical calculations / science underpinning the salesman’s promises before signing a contract.
  • Firstly, can you convert to kWh of demand the statement - “it will do a full day easily at a speed of 7-8 knots with normal stops, even with hotel services and continuous use of the air conditioning. This translates into 4 hours at a top speed of 10-11 knots, and 24 hour use at 3-4 knots.”
  • Secondly, do a sense check - even of the domestic demand (DD) of “continuous” running air conditioning, fridge and freezer for 24 hours in a warm climate. That will be quite a lot of power. Then add a lot more if have electric induction hob, microwave, water maker etc. I expect a biggish number of kWh.
  • Thirdly do a sense check of the propulsion power demand (PD) In kWh. It will likely be very efficient at 3-4 knots, a lot less at 10-11 knots (which is reflected in 6 times less hours, which is encouraging). But depending on weight, even if only using 4kW at 4 knots that might be nearly 100kWh for 24 hours (just a rough guess, need the correct maths). You don’t state the engine power ratings in kW.
  • Fourth add these daily demands DD + PD and advise us the total daily demand (TD).
  • Fifth advise the size of battery pack in kWh as supplied, and compare to the total daily demand. Note that even with best batteries, you don’t want to regularly use more than 80% of battery capacity.
  • Sixth compare to a typical electric car battery for a sense check - most better ones are in the 70-80 kWh range (slightly more for the €100k plus category of car).
  • Seventh calculate the typical daily solar charge output from solar panels in kWh per sq metre. Then tell us how many sq m of solar panels are needed to recharge the total daily demand (TD) in a day.
  • Finally, sense check, how many Tesla cars are recharged by solar panels (indeed hoe many even bother to fit solar panels to their roof, bonnet and boot panels, which would seem an obvious start)
Having done so, please report back, as genuinely interested and would be good information to understand.

Of course putting aside the solar aspect, electric propulsion does make sense for a new build catamaran intended for short distances, provided capital cost is not a huge priority. But it will need a BIG battery in kWh numbers.
And realistically, the charging will need to be done by shore power - and even then do the maths to identify what Voltage and Amps of shore power is needed. For a large battery, a typical marina 220V 16 Amp socket will not cut it, and even 32 Amp will be very slow. Will the cruise route allow access to suitable shore power.

Clearly the diesel generator is a good fallback. But again what is the kW output of the generator, and precisely how many hours will the generator need to run to meet the daily demand of off shore power. If end up running a generator 12 hours a day to keep the air conditioning and freezer running, it might be better to have runna bigger engine form4 hours and have silence at anchor.

look forward to seeing your calculations
 

Rwc13

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This is really helpful dunedi. Thank you. I have received some independent confirmation of what I have been told by the manufacturer, but it makes sense to get some numbers and do the maths as well.

I know that the battery capacity is 160 kWh, and the boat has 2 x 25kw motors. I have asked from some other data so that I can do the calculations you suggest.
 

ShaneAtSea

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This is really helpful dunedi. Thank you. I have received some independent confirmation of what I have been told by the manufacturer, but it makes sense to get some numbers and do the maths as well.

I know that the battery capacity is 160 kWh, and the boat has 2 x 25kw motors. I have asked from some other data so that I can do the calculations you suggest.

Here's a more recent tour of the Silent 60

 

dunedin

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This is really helpful dunedi. Thank you. I have received some independent confirmation of what I have been told by the manufacturer, but it makes sense to get some numbers and do the maths as well.

I know that the battery capacity is 160 kWh, and the boat has 2 x 25kw motors. I have asked from some other data so that I can do the calculations you suggest.
Great, look forward to hearing more.

At 160 kWh that does qualify as the “BIG battery” which I suspected it pull need. Thats like a couple of decent electric car packs, so a sizeable (and expensive) set of batteries. And for a 12m cat (assuming the link earlier), that would equate with the 3-4 knots for 24 hours though perhaps not the 4 hours at full speed (if that means wide open throttle) => 160 kWh / (25kW x 2) = 3.2 hours, or better 2.6 hours allowing for 80% battery depletion (both before any domestic or ship navigation demand).

But as well as a deep wallet, that will take a heck of a lot of charging - even from a hefty shore power link. Look forward to your calc of the solar area needed to recharge 160 kWh in a day :cool:
Sounds a fun prospect though
 

henryf

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I was just working out the batteries as well.

24 volt DC you would need 6700 amps of battery capacity to provide 160.8 kw. Assuming you use 100amp 12 volt batteries in series to make 24 volts thats 134 batteries I think. As has been said already the charging demand would be pretty huge. One assumes that using a 13 amp supply to charge 6700 amps of battery takes 515 hours or 21 days.

Forgive me if I’ve got the maths wrong ?
 

Rwc13

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Just to correct something I said earlier, they are 2 x 20kw motors (not 25kw), which possibly makes the 4 hours at full speed seem possible.

The diesel generator is a 10kVA unit which seems likely to provide sufficient output to drive the motors and other electrical functions as both a back up and range extender.
 

vas

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I counted 5X8=40 solar panels on the roof and they state 150W each for a total of 6kW (as reported at their site).
Being flat on the roof and extrapolating from my also flat on the hardtop 600W solar, I'd guess on a summer day you'll "produce" 40-50kWh (compared to my measly 4-5kWh)

If you use the thing for a 5-6h slow cruise wherever you are (and assuming day and assuming decent summer sunshine) you'll "burn" say 2X5kW X 6h == 60kWh!

So assuming my calcs are right, a 6h stroll at 4kn will burn whatever is produced by all the panels. and that is WITHOUT ANY SERVICES consumption (not even the a/p and plotter, and forget about fridges and aircon!)

A system like that would work on my usage where fe this summer spent around 50days on anchor and only burnt 600lt of diesel as I spent 5+ days on every destination. But if you're planning to move about a lot, expect the geny to work a lot :)
Just put it down in the equation.

Henry, these systems are not like our 24V, most like not even 48VDC, so cabling is OKish, they'll be LifePO4 cells, with custom BMS to take care of charging and discharging rates/levels.
Still charging on a marina will be a serious 32A@230V -> say 145A @48V (leaving aside some efficiency loss) which would replenish circa 70kW in 10h. Not that bad, double that for a 16A supply still means it's feasible to recharge overnight in a marina. Now assuming there are plenty of marinas where the OP is boating and they wont charge an arm and a leg in electricity :)

V.
 

vas

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Just to correct something I said earlier, they are 2 x 20kw motors (not 25kw), which possibly makes the 4 hours at full speed seem possible.

The diesel generator is a 10kVA unit which seems likely to provide sufficient output to drive the motors and other electrical functions as both a back up and range extender.
along the same lines, keeping charge level constant, with the geny running its balls off, you'll be able to run the engine at say 4kn, doubt more as you'll be sucking from the batteries as well.
doable, guess you'll get to the habit of running the generator whenever you use the propulsion, and you may be in silence the rest of the day (which I v.much doubt if you start using the aircon!)

V.
 

SandyP

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So if your batteries are flat:
Need 2-3 days of solar (summer)(x5 in winter)
Need 2 daytimes of genny
To recharge them
Assuming no other draws on the electrics

But life in a marina is quite sweet

Warships have electric propulsion, and several generators in the MW range to power them

I'm pro-electric btw
 

dunedin

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Just to correct something I said earlier, they are 2 x 20kw motors (not 25kw), which possibly makes the 4 hours at full speed seem possible.

The diesel generator is a 10kVA unit which seems likely to provide sufficient output to drive the motors and other electrical functions as both a back up and range extender.

Yes - 160 kWh / (20kW x 2) = 4 hours (though better 3.2 hours at 80% battery use) .
And the generator should allow pootling at slow speed (3-4 knots)

But we are a million miles away from your initial thread title - a "solar catamaran". It is a battery electric vessel, with the generator giving limited serial hybrid propulsion capability. The 160kWh batter is serious stuff - and will presumably need a lot of shore power charging.

Definitely worth looking seriously at the domestic power demands (per my original series of questions) - this was what caused Jimmy Cornell to abandon his circumnavigation in his advanced "carbon zero" catamaran Elcano - and I don't think he was using any air conditioning.

Having said all that, this sounds like an expensive piece of kit (and perhaps take decades to save enough to offset build energy). And if seriously want to go green, why not start with a catamaran with mast and sails, like Jimmy Cornell did (just retain the backup generator, which he was too purist to allow)?
 

henryf

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We did a charter job for Arksen this year who build amazing aluminium hull serious exploration motor yachts in East Cowes. One of the boats I saw was being powered by electric motors which in turn were fed by 3 diesel generators not unlike a modern cruise ship.

There was a huge built in redundancy, just one of the generators could propel the vessel and supply the hotel side. I suspect 2 generators would be needed if you wanted to achieve the max 14 knots leaving 1 spare.

Diesel electric is a very viable option in my humble opinion, just make sure you’ve got plenty of diesel generating capacity for a worst case scenario. That will leave you ample redundant margin.
 

Tranona

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Diesel electric makes sense when the domestic energy requirement exceeds the propulsion requirement which is why cruise ships (slow moving floating hotels that need to park unassisted in awkward places) use it together with steerable pods.

As already suggested this Cat is a diesel electric which because it has a large flat top can carry enough solar for maybe 70% of its propulsion requirements on a good sunny day a small generator to make up the balance and much of the domestic but a daily visit to the mains to top up its huge and expensive buffer battery bank.

Wonderful bit of virtue signalling! if you ignore all the ungreen manufacturing costs and inefficiencies of converting hydrocarbons to electricity to propulsion. Might make sense if it had two small diesels and solar to power the domestics - plus a mast and sails as suggested . If operating in areas with decent wind you might get away without diesels and just use electric for low speed propulsion in and out of harbour.
 
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