# Solar catamaran

Discussion in 'Multihulls' started by guzzis3, May 20, 2021.

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### Mr EfficiencySenior Member

Those boats look like they could be very useful recreational vessels Oscar, but probably pretty hefty and with a resistance factor that would make them rather slow with minimal solar power.

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### DejaySenior Newbie

Wait, Summer is wet and rainy and winter is dry and sunny? What kind of upside down weather do you have there haha.
The base number for "solar watt hours per square meter per day" should include cloud cover though, just on average. So might be most days are less and a few days are much more. Which would affect trip planning much more.

I'm sorry the spreadsheet is a bit convoluted. It's really just:
range = average-solar-energy-per-day * efficiency * area / energy-per-mile

It starts at the bottom with the monthly average for a location.
In the middle (B14) I average for the four summer months, the four sping/fall months and the four winter months.
Then calculate the overall energy gain per day (C14).
Then I calculate the hours you could drive with that daily energy (J14) with the required motor power.
This assumes you do have a buffer because the solar gain would be less in the morning and the evening. So in reality you need at least something like quarter to half a day of battery reserve at the start of day.
And the range is then just driving either 24h a day or a maximum of 10 hours.
I think that gives an idea of how well a solar boat could be used for a certain season and location.

So for australian winter this would be 51 miles at 5.8knots sailing 8.7 hours. Or 89 miles if you go 4.9 knots for 24h. At 3.9 knots you could go pretty much all day anywhere in any season except northern germany.

The resistance numbers come from prelimina so waves and wind might reduce those numbers a bit. On the other hand I assumed 50% efficiency, so with a 90% efficient motor and 80% efficient propeller you could get more range.

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### DejaySenior Newbie

Welcome to the forum!
Looking forward to your build. There are two other recent thread with a lifeboat projects 1, 2.

That boat looks very cool and much easier than to start from scratch. I'd love to see the resistance numbers. You mention 9-10t empty in your reddit post so I'd expect it to be less efficient than the SolarWave 46.
If you consider a slower speed of 4 knots and mostly as a river boat and smaller pure solar range you hopefully won't dump 200.000€ into the project. I think you mentioned using it mostly for day trips like once a week?
Maybe you could get used EV packs for less than 200€/kWh.
Two 5kW BLDC motors for EVs as an inboard drive should also be much cheaper than typical electric outboard motors in that range.

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### BlueBell. . . _ _ _ . . . _ _ _

Guzzis3,

Have you considered leaving the battery out of the equation?
It would be a fair weather sailor, for sure.
Think about it, before all the critics get to you.

BB

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### DejaySenior Newbie

Just put a Ford F-150 Lighting on the deck and use that as a 115kWh battery

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### SolGatoSenior Member

Here’s another example similar to what I plan to scale up to in the next few years when I’m tired, sore and beat up from fast Trimaran and BeachCat sailing.

Project Stiletto hulls are available from time to time, and there are similar big cats like Conser Warrior and McGreggor, etc.. that were produced in numbers that are getting older and have been neglected over the years and could be repurposed for Electric Propulsion conversion.

The only problem with a lot of these designs is since they are high performance sailing Cats, they lack volume in the stern so you have to be careful with weight distribution which means moving batteries up front, using lightweight material for a hard deck, flexible panels, etc..

I came close to starting this build a year ago when I was at a crossroads, but the lack of reliable motor options was a hang up for me, and the opportunity to purchase a one of a kind Trimaran kept me sailing.

However between Torqeedo, EPropuslion, Hasswing, etc.. there are more viable options now along with affordable safe LiFePo4 batteries, and competition is now driving innovation and flexibility of use for more than just dinghy and fishing boats.

Last edited: May 23, 2021
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### SolGatoSenior Member

How would this work? (Says the critic)

DC brushless motors controllers need steady voltages. You can’t run them directly off a Solar Charge Controller without damaging them if you want speed control.

So you would have to build a system capable of producing more power than the motors consume then using a DC to DC converter to regulate voltage which is inefficient.

Theoretically, one could use a non PWM DC brushed motor and shunt extra current in order to get multiple preset speeds, but again you are wasting a lot of energy this way unless you use it to make coffee and toast

A lot of people gripe about the cost of batteries. Yes, high performance batteries are expensive. But some of these LiFePo4 batteries have a 10 year lifespan and are good for thousands and thousands of charge cycles.

Cost/range wise, you can’t compare them to a tank of gas, but what if you had to buy all the gas you were going to need for the next 10 years up front? It would be a major investment as well.

Point is, if you want a boat that is going to get the job done and offer as similar an experience to a ICE powered boat, you really need to have all the major systems in place and matched together to work as a team, from motors, to controllers, batteries, to panels, solar charge controllers, to wiring, etc..

The best systems don’t just cover the typical usage loads, but are designed to be able to harvest and store as much energy as possible when the sun is shining while offsetting loads, then cover and offset all loads with that stored energy for as long as you might foresee under normal operating conditions, until the system can harvest again.

The more efficient you can make every part of the system the better, otherwise it will only be as efficient as its weakest link. And the faster a system can recover, the better.

Last edited: May 23, 2021
8. Joined: Nov 2009
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### guzzis3Senior Member

Funny.

There is a picture somewhere which overlays Australia on Europe. It stretches from Russia to Britain and down to north Africa. I was born 1000 kms from where I now live, as the crow flies. Both are in the same state and my home town is about half way to the northern tip of queensland. Qld is 2000 kms top to bottom and 1500kms east to west. And we are only the second biggest state

The point is the solar conditions across Australia vary considerably. People in Melbourne get excited (and confused) if they ever see the sun, while we up here pray for winter to come. We have been having rain in winter the last few years but this is atypical. There are plenty of years when we get almost no rain and little cloud in winter. A climate perhaps more like India.

Anyway..

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### Oliver LichtensteinNew Member

Working on resistance numbers, but I need to take lots of measurements and the boat is still on the factory premises where I cannot access it whenever I want. This will change on the 5th, when I'm picking it up to take it down the Elbe river to its new home. 200k€ is a hopefully fairly conservative estimate of what it takes to make it ocean-ready, have adequate electric range and some comfort on the inside. For motors and batteries, I'm indeed looking at EV stuff, but I'm not sure about the effects of salt on automotive grade components.

Also, thanks for the links to the lifeboat threads, interesting stuff!

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### DolfimanSenior Member

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11. Joined: Mar 2018
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### DejaySenior Newbie

Thanks, that looks like a well made solar boat. My list hasn't been updated for a while (partially because I hate that card format - there probably is a better way).

So I only added cruisers that are or could have liveaboard space and cruise. There are a ton of smaller solar boats, probably too much to keep track.

Also that size class allow you to solve the problems of e.g. low energy density by spending enough on batteries. I feel there is a qualitative difference between the smaller ~20' solar boats and anything upwards of 32'. Suddenly they get much heavier and solutions like throwing enough batteries at the problem become expensive. To cruise you need more solar panels than for a day trip or camping trip. And where previously a few flexible solar panels were enough you need a huge area and want them to last longer. Accommodations add windage and complications like a side deck.

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### guzzis3Senior Member

Some people suggested earlier a solar trimaran. I wasn't keen but in further reflection the wider beam and limited space/carrying capacity probably help the numbers make more sense.

Take a Horstman style tri, extend that massive roof forward and back and cover it all in panels. Probably worth looking into.

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### SolGatoSenior Member

Yes, a Horstman would be an ideal platform, but with their big flat wing decks, I would invest in flexible walk-on panels and cover the hole deck with them.

They often come up for sale at a bargain price for their size, and they are laid out well for living aboard.

Plus they are not a performance sailing boat by any means, but are a proven design that would be ideal for a solar electric cruiser.

I also considered taking a Farrier folding type Trimaran design and installing panels that can fold/accordion together and expand out to cover the wing net area. When you want to use the wing nets, you just fold them up like a closet door sliding each section along tracks mounted on the insides of the beams stacking each section toward the main hull to expose the nets. Then when trailering the panels can be folded up completely so as to not add any width or extra windage to the vessel.

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### BlueBell. . . _ _ _ . . . _ _ _

You sound pretty committed there SolGato.
I wouldn't recommend my concept for you.
But I was addressing the OP not you.
The OP however, doesn't seem interested in responding.
Regards, BB

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### DejaySenior Newbie

Some more monstrous sketches and ideas from me:

I've considered this design as a "minimal" trimaran. 15m x 3m wide roof so would still be relatively easy to transport on a semi trailer in Europe. You have to imagine the amas. Basically just a T shaped box hull and a 1m wide and 2.2m tall corridor with plenty of 1m wide horizontal shelf space left and right for bunk and gallery or seating. This should have relatively low windage.

This should be easier to build structurally sound than a big container on top of a main hull with solar awnings / overhangs. And you could build a simple intelligent infusion mold for such sections. In the back you have standing or near standing headroom / cockpit with view all around.

This wider variation would be 5m wide roof and 7m wide beam overall and back solar roof. I don't know if this would still be stable and it's a bit excessive but would have insane 85m² solar panel surface (19kW solar + 1t glass weight).

This might be the sweet spot with 4m wide roof and 5m beam overall. Still massive 65m² (14.3kW) solar. The shelves would be ~1.4m for a wider bunk. This could still go through the french canals to go from the north sea to the mediterranian (only interesting for me). But no longer a backyard build. And compared to something like the pennywise these designs are so ugly haha.

I'm not sure how long the amas should to be or where they should be positioned. Maybe some kind of telescoping mechanism for the amas could make sense. And with this design you don't really have an easy way to go to the bow.

The front could be longer too like 20m / 65'. The Ilan Voyager is 21.3m long. But I think below 4t weight 15m is long enough, adding more doesn't reduce resistance at 6-8 knots. Still might be worth it if you can build this T shaped hull cheap enough (like cargo ferry)

I believe a catamaran would always be less efficient per length but somewhat easier and more traditional in design. I'm also wondering about modifying a harry proa with equal length hulls and an oversized cabin solar roof.

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