Wetdream solar 100% electric Catamaran

[yabert]

Hi
Based on some tests I did during the last weeks with our 38' Beneteau sailboat, I remarked two main things:
-Cruiser sailboat are slow.
-Cruising at low speed require really low power (I've tested 1 kW at 3 knot).

Clearly, instead of beating to windward at an average of 4-5 knot, why not simply go in strait line with a solar Catamaran?
That our conclusion and here is a potential plan:
40-45 ft Catamaran without sails and mast, add 10-12 kW of solar, add 120-170 kWh of battery and there you go.
Everything in 48V to access typical component's.
Here two good examples:

Indigo Lady

I am a retired educator married to a retired chemist/engineer/educator. We will be living aboard our solar electric catamaran for as long as possible.

lisamarchi.com

L

Thread '100% Solar Electric Catamaran'

Jun 4, 2024

I've built a solar catamaran out of a 2000 Gemini 105M sailing cat. Some basic specs:

- 2x ePropulsion Navy 6.0 motors, 6000w each max.
- 16x BlueSun Bifacial 575w solar panels, max output 9200w.
- 2x EG4 100amp MPPT solar charge controllers
- 4x 48v 160ah LiFePO4 batteries
- 2x EG4 5000w shore chargers 120v/240v
- 5000w Inverter
- Starlink Internet
- Openplotter navigation with AIS

I've got two independent setups, motor, battery, chargers and panels. No fossil fuels of any kind on the boat.

Sweet spot is 5.3 knots @ 3200w, max speed is around 7.3 knots @12,000w. You pay dearly for that...

• lborkey
• Replies: 43
• Forum: Marine

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Questions about design:

1-Solar panel qty: I can start with 400W to 600W solar panels and there is place for 16-30 panel on a frame. I think it's a good plan to have a space in the center to let exit the wind and also to have access to clean the panel (see pictures).

2-MPPT qty: From 2 MPPT up to 12 MPPT (or more) what can be the sweet spot? It highly depend of the panels and I thought about a configuration of 3 panels with around 45V Voc for each Victron 150/35 MPPT... or 12 Victron 100/20 for 24 panels or 2 EG4 MPPT for 20 panels or even one Boost MPPT for each panel... There is many choice. What is a the best one?

3-Lightning: What to do about lightning with this kind of giant aluminum antenna over the boat?

4-Power requirement: Based on searches and tests, this kind of 15 000 - 20 000 lbs boat will cruise at 4 to 7 knot with as low than 3-4 kW and up to 10-20 kW. So the power requirement is low. I will still be able to output 40-50 kW, but this is not cruising speed power requirement.

5-Range expect: 100 to 200 nautical miles, not more. Still 100 miles can take 24 hours

6-Expect production: Based on 10kW installed and no shade, I think this will produce between 25 kWh to 60 kWh per day. Right? Let say in Caribbean. Flat orientation is not awesome in winter, but is this realistic?

Below is a rough 3D of a 40' boat with 20 panels of 500W.
Please share your inputs!

 

[aliarifat794]

Using 400W to 600W solar panels sounds fine. The idea of leaving space in the centre for ventilation and maintenance access is practical.

 

[IGBT]

Way small on the battery. I have more LiFePO4 on my 17 foot electric sailboat (200AH at 48V). A 38 foot Cat you should go for at least 30kWh, which is only about $6,000 and 550 pounds.

Edit: Oh, mistake, I misread your list. I think you were saying Four 160AH 48V batteries. That is actually quite reasonable.

 

[yabert]

Way small on the battery...
Edit: Oh, mistake...

Hahaha! I also think that 120-170 kWh of battery is not bad at all.
So, 2500-3500Ah at 48V

 

[Kaz]

Going slow is definitely the way to efficiency on the water.
I troll around on my 3,100 isg pound Center console boat for hours and hours at 2mph. With a 80 pound thrust 24v trolling motor with a 2 amg 12v 100ah batteries and never break 50%. I bought them before the bottom feel out of lithium. I believe the max draw is 1300 watts.
When I fire up the twin jet engines and go 35mph .. whopping 2.3 mpg.
I'd like to get a small pilot house boat and spend some time slow solar sailing.

 

[Solar Guppy]

I believe this will end badly, for starters, with such small propulsion, you will be at the mercy of wind and currents and the solar could actually be cause the boat to capsize, think about a large wave or swell in winds get under the array in a storm.

It is fun for a thought experiment, hope its never built as I would hate to read one day the above happens with a loss of life. Being a mariner is serious business, threat it as so.

 

[mikefitz]

Please share your inputs!

Agree with the last post. In very sheltered waters with gentle weather its a possible idea. Is real conditions its a possible killer.
With due respect to the original poster, you have no idea about safety at sea, In the Caribbean, between Islands, the wind strength and sea state would destroy such a vessel.
The concept of using solar and battery to power totally replace wind power in a sailing boat is a bizarre idea.

 

[wpns]

Depends on the location, a small lake in Quebec with no current and only mild breezes should be no problem. Great Lakes or open ocean might get you a Darwin Award.

 

[yabert]

I believe this will end badly, for starters, with such small propulsion

Is real conditions its a possible killer.

Great Lakes or open ocean might get you a Darwin Award

Oh! absolutely not related to solar, but you have all my attention. Please explain me how this will be worse than a regular 35-45' sailboat.
I mean, most cruising sailboat can't reach over 7-8 knot of top speed on sail or even with a 40-60 kW diesel.
So, what wrong if I design this boat to reach similar top speed?

Many new Catamaran have some insane double deck and boom 20 ft above waterline who clearly catch the wind during storm.
Below is simply few examples.
Or even compare with real company building solar Cat: solar catamaran Aquanima Azura Marine or Silent-yachts
So how much worst can be this solar catamaran with all panel 10 ft above waterline?

 

[Solar Guppy]

Without propulsion or one that is underpowered to the environment it transverses a vessel can be pushed into things like rocks or out of range of rescue, with a sail, one can tack into any wind. If the winds exceed the design of the vessel, sails can be lowered. A solar wing would be fixed and with high winds and a swell could be flipped without any means to stop it.

You seem to lack basic knowledge in this domain

 

[wpns]

Oh! absolutely not related to solar, but you have all my attention. Please explain me how this will be worse than a regular 35-45' sailboat.
I mean, most cruising sailboat can't reach over 7-8 knot of top speed on sail or even with a 40-60 kW diesel.
So, what wrong if I design this boat to reach similar top speed?

It _should_ work, but there are two issues:

1) Sailboats work with the wind, even when tacking upwind they are using wind power. A solar catamaran will have to push against the wind. I have no idea how you estimate the power requirements to push your catamaran-with-horizontal-sail upwind in choppy seas, but you might want to prototype it with a small outboard?

2) You are comparing a 40-60KW diesel to a pair of 6KW electric motors.

Sure, most of the time you can get away with 3 knots, but how do you fight a 5-knot current? I mean, all power to you, (if you see what I did there), but at least do a proper design review (if you can survive this crowd you are doing pretty well!), and know your operating conditions and limitations.

 

[yabert]

You are comparing a 40-60KW diesel to a pair of 6KW electric motors.

Ok ,it was not clear, so I clarify my first post:

this kind of 15 000 - 20 000 lbs boat will cruise at 4 to 7 knot with as low than 3-4 kW and up to 10-20 kW. So the power requirement is low. I will still be able to output 40-50 kW, but this is not cruising speed power requirement.

 

[yabert]

A solar wing would be fixed and with high winds and a swell could be flipped without any means to stop it.

From what I know and I've seen, a Cat will be flip in high wind. Especially in big wave when boat is already at angle, but even at anchorage.
So, yeah it a good point.
It will be impossible to remove all panels if we face a storm, but I bet it's a really good idea to reduce the surface.
In case of 2 rows of 10 panels like what appear on the 3D of my first post, it's seem fairly easy to have a mechanism to flip the outer panels over the panels in the center.
I imagine something efficient where all outer panels can be flip in 10-15 minutes with two peoples before the storm came in.

 

[Kaz]

Off topic kinda, but I seen somewhere that a electric motors can run props that would stall a ice motor and keep it from starting. The prop of a ice motor has to be small enough to spin on start up. Whereas ev boat motors have instant leverage.

 

[yabert]

The prop of a ice motor has to be small enough to spin on start up. Whereas ev boat motors have instant leverage.

And to match power/torque and cruising speed.
Electric motor can output high torque from 0 rpm.
So I plan to have low speed/high diameter prop in order to increase prop efficiency.
This is generally how 20kW electric motor can compete with 50 kW engine. Higher torque and lower speed = higher prop efficiency = same performance with lower power.

 

[yabert]

Going slow is definitely the way to efficiency on the water.

Another data from 40' Soel Yachts.
2.4 kW at 5.0 knot
9.1 kW at 6.8 knot

From Silent Yachts 55 (32 tons Cat)
5 kW at 4.4 knot

6.8 knot sound ''crazy fast'' for me as most cruising sailboat average lower than that... and rarely in straight line.

 

[OffGridForGood]

Interesting topic.
Why not use solar panels AS a sail...see vertical mount PV thread...

 

[yabert]

Why not use solar panels AS a sail

No, simply no.
Sail have to be lightweight and able to be drop/roll in few seconds.
And have a variable wing shape in order to propels the boat.
No sail at all is way simpler.

 

[OffGridForGood]

36 PV panels - 600W each, collecting at 70% +/- for five hours per day = 75Wh per sunny day...
5kW motor plus some efficiency losses, say 6kW, 75/6 =12 hours of crusing per day of solar on average?
175kWh battery - needs 2.33 days of solar (with motor off) to fully charge battery ESS.

Looking at it another way, 75kWh per day/24hours = 3kW max steady output - for all loads, not just the motor.

How much efficiency lost to pull a "Cat-raft" behind the main Cat, with 36 more PV panels on it? (to increase power available to 6kW continuous?

 

[yabert]

I think

for all loads, not just the motor

Yeah, I should consider 2-3 kWh per day for fridge, water maker, inverter lost and other small load.

How much efficiency lost to pull a "Cat-raft" behind the main Cat, with 36 more PV panels on it?

Towing a lightweight solar panels Cat with the Cat should be awesome to increase production, but I bet is really not practical.

 

[yabert]

I think I found a good combination MPPT/panels with 24 panels 425W (10.2kW).
3 panels in series will give Vmp of 99V and 12.8A. I can put in parallel 3 other panels to input a Victron 150/45.
That 99V 25.6A or 2.53kW. 98% efficiency will give 2.48kW. MPPT will charge a 16S NMC battery at 58V nominal, so at 2.48/58=43Amps.
I do this 4 times with 3 other MPPT and all look good!
Victron consumption is given at 10 milliamps, so 0.6W each and 2.4W for the four MPPT.
I miss something?

 

[wpns]

Off topic kinda, but I seen somewhere that a electric motors can run props that would stall a ice motor and keep it from starting. The prop of a ice motor has to be small enough to spin on start up. Whereas ev boat motors have instant leverage.

Umm, not really. Too large a prop will prevent a gasoline motor from getting your boat up on plane, but it won't stall it or keep it from running. Electric motors produce maximum torque at zero RPM, so it's just a different power curve to take into account in your design.

 

[wpns]

How much efficiency lost to pull a "Cat-raft" behind the main Cat, with 36 more PV panels on it? (to increase power available to 6kW continuous?

As above, we don't even know how to estimate the drag on the 'cat with horizontal sail made of panels', much less the additional drag of the second one you are towing.

 

[AnarchyJet]

The Gemini 105 linked above is a much smaller boat than a 40-45' cat. It is only like 14' beam and 35' length. Even then I think twin 6kw motors are undersized. For example, a 42' Lagoon has a 25' beam.
I don't think 48v is going to cut it for a project of this scale. I would look at twin 20-25kw motors running 96-120vdc.
You can still go low and slow for max range, but at some point you will need to go into the wind and current. Then your 3 knots will take 20kw instead of 4

 

[yabert]

The Gemini 105 linked above is a much smaller boat than a 40-45' cat...

Yeap, but Indigo Lady is 44' and 23' wide. The owner is surprised by the power of his two 15 kW motor. Some details here:

Imagine, even the 55' and 70 000 lbs Silent Yachts cruise at over 4 knot with only 5 kW.

I don't think 48v is going to cut it for a project of this scale

I've also some doubt in the past, but not now for two reasons:
1-I push my 38' and 12 000 lbs boat at 3.7 knot with a ''trolling'' 24V motor (around 1.5 kW).
2-I plan 58V battery pack, so more power than 48V, and this battery will feed 2 motors able to output 20-25 kW each.