Want to design only a top part of catamaran, looking of plans for hulls 14m, aluminum

[Daniel Mazurkiewicz]

The problems are in coastal waters, when you want to go somewhere against the wind and waves, where you don't have searoom to simply drift around, etc. This ca all be avoided by good planing and waiting for suitable weather.

But, all of the above might collide with your expectations, that's why the SOR is important. You have to have a good ideea about what the boat should be capable to do, how it is going to be used, in order to be able to design it. The sun21, while a proven transatlantic and coastal sailor is not a comfortable cruiser, and it will not be able to go around Cape Horn east to west.

but a situation where wind is pushing you towards lee shore and you _have to_ keep powering. or Crazy weather that needs constant active powering and steering. Maybe the generator will provide this ability in a dire need)

So what power for electric motors you'd consider relatively "safe" or able to go around Cape Horn?

 

[SolGato]

The Leaf motors can be run at lower voltages which is why I said you could grow into them. There are people running them at lower voltages. They are less efficient at lower voltages, but still better than a lot of other options.

You might want to check out Heart of Gold Lifeboat on YouTube to get a better understanding of what’s involved in adapting the motors.

I agree with what others have stated, that 10kW motors might be fine for slow cruising, but will be inadequate in challenging conditions like wind, swell, and current with a boat as large as you intend to build with respect to windage and displacement. You need reserve power for those situations.

Another thing to consider is battery management. To build a LifePo4 bank large enough for capacity you’ll need, you would have to use a large number of batteries wired in series and parallel to achieve the capacity and voltage needed. The problem is it is very difficult to make sure the batteries all stay in sync. Management is key to protecting your investment and being able to use full capacity. You can buy balancers, and battery protect devices, and eternal BMS’s and shunts, but when it comes down to it, you really need to be able to monitor each individual cell, and have full over/under/temp protection.

For this reason, a specialized battery system or battery modules from an E/V would be the best choice since they are designed for cellular reporting to a BMS to be monitored properly. There are a few manufactures making deep cycle 12V/24V batteries with a BMS that will daisy chain to others which then use a Master BMS to control and monitor the full bank.

Something to think more about if you had planned on just buying a bunch of batteries and wiring them together.

Maybe a diesel electric hybrid drive might be a better way to go for your build and ocean crossing goals?

That way you have the reserve power and onboard charging to supplement the solar if need be. You can cruise around on electric only most of the time, but still have ability to achieve planing speeds and handle rough conditions, or recharge batteries when weather is not ideal.

There are some compact hybrid diesel electric outdrive products starting to hit the market. Expensive I’m sure, especially since you need two, but they might be a better fit for your goals.

I’m going to be building a 30’ solar electric catamaran soon, a scaled up version of my 17’. However my needs are very different from yours, requiring much smaller motors (48V DC 2X3kW) less battery capacity and solar, minimal superstructure, etc.. I’ll be using high performance lightweight sailing catamaran hulls and will only use it for coastal cruising. In the future as more motor offering and better battery systems become available at more affordable prices, I may refit for interisland crossing.

 

[Daniel Mazurkiewicz]

The Leaf motors can be run at lower voltages which is why I said you could grow into them. There are people running them at lower voltages. They are less efficient at lower voltages, but still better than a lot of other options.

Max safe DC voltage in potentially wet conditions is 60V, so getting from 400 down to 60 gives you like 15% of nominal power. Unless you're willing to risk with higher voltages it doesn't seem best option.

Maybe a diesel electric hybrid drive might be a better way to go for your build and ocean crossing goals?

And that is actually an interesting idea! Will dig it!

I’m going to be building a 30’ solar electric catamaran soon, a scaled up version of my 17’. However my needs are very different from yours, requiring much smaller motors (48V DC 2X3kW) less battery capacity and solar. I’ll be using high performance lightweight sailing catamaran hulls and will only use it for coastal cruising. In the future as more motor offering and better battery systems become available at more affordable prices, I intend to refit for interisland crossing.

Nice! 30 isn't that small already. Where did you get plans for yours?

 

[SolGato]

Technically anything over 30V is considered “dangerous”, but then there are a number of electric propulsion manufacturers designing around V’s 48V and higher.

Also consider that in order to properly feed an MPPT you want to wire solar panels in Series, which means you have high voltage on deck just from your array.

I think minimally a few of the aftermarket control interfaces for the Leaf motor require around 150V.

I think one major advantage to the Leaf setup versus piecing a system together comprising of a motor, controller, etc.., is that the Leaf motor and other EV motors like it are already well protected from the environment.

I will be recycling/modifying a pair of performance sailing production molded catamaran hulls as I don’t have the time or energy to build from scratch, and would prefer to spend my time refining and splurging on the other systems and components.

That’s why I posted the link to the 40’ aluminum Cat in Texas. If it’s well built and modifiable, you’d be money ahead, but I understand the logistics involved are challenging as I live on a little island in the middle of the Pacific and have to deal with getting everything over here. Last 30’ boat on trailer cost $7500 from CA to me, and that was before Covid. Now closer to $10K.

But before I can start new solar electric cat build, I have to first finish the cabin interior remodel on my Trimaran.

 

[Rumars]

So what power for electric motors you'd consider relatively "safe" or able to go around Cape Horn?

It's not about installed power, it's about range. Motoring against strong wind and waves for days on end is impossible on solar and battery. That's why you don't see any proposals for solar cargo ships, solar does not scale well, the power requirements quickly overtake the available production.

You have three scenarios:
1. Moving and charghing, solar production goes half to the motors and houseload and half to charge the batteries so you keep moving at night. Speed is whatever you achieve with what the panels produce at that moment. This will be typical daylight cruising on a multi day passage.
2. Moving without charging. This happens when you leave port with full batteries, all solar production goes to the motors and houseloads. Happens on the first day of every cruise, and is often the case in coastal sailing. Also happens on twilight, on overcast days, or whenever the batteries are already full.
3. Battery operation, at night and when you need more power than the momentary solar production.

Asuming 20kWp of solar, the motors must be at least as powerfull to be able to take it all. Depending on weight and windage you may need to go up from there to have power for certain situations (upwind, against tide/current, etc.) If you size the motors to be to large you run into problems of efficiency and range and need to go to a 4 motor installation (like Tûranor PlanetSolar).

 

[bajansailor]

Daniel, have you got an aversion to sailing?

I think that for what you want your cat to do (ie crossing oceans) it would be useful to at least have a motor sailer type of rig where the sails can give you a bit of extra power?

 

[Flotation]

Ocean crossing is simple as long as you don't go against the prevailing wind and have time. People regularly cross the Atlantic on rowboats, and a fit human can't make more then 250W if he has to do it for hours, plus a human can't row 24h a day, therefore such crossings usually take two months.

The first solar catamaran to cross the Atlantic (29 days from Canary Islands to Martinique) was the sun21 in 2007. Their data might be surprising to some, 14x6,6m, displacement 12t, 2x8kW motors, 10kWp solar panels and 24,9kWh of lead acid battery. transatlantic21: The world's first crossing of the Atlantic on a solar boat http://www.transatlantic21.org/
So yes, your proposed vessel will cross without problems, even on your initial design parameters.
In really bad weather you simply stop motoring, put out drouges or sea anchors to keep you from loosing to much ground in an unwanted direction, or get broached, and enjoy the ride. It's safe, there is nothing you can hit out there, close the hatches and go to sleep. The storm usually goes into the direction you want, it's free travel.
If your battery is low after several cloudy days, in the first day of sunshine you simply drift and wait to charge. The wind and sea push you to the destination anyway, just slower then you want to go. Or you motor just fast enough to keep the bows pointed in the right direction, it's not a race.

The problems are in coastal waters, when you want to go somewhere against the wind and waves, where you don't have searoom to simply drift around, etc. This ca all be avoided by good planing and waiting for suitable weather.

But, all of the above might collide with your expectations, that's why the SOR is important. You have to have a good ideea about what the boat should be capable to do, how it is going to be used, in order to be able to design it. The sun21, while a proven transatlantic and coastal sailor is not a comfortable cruiser, and it will not be able to go around Cape Horn east to west.

This is so very much on point. You have to approach ocean "sailing" with a low budget solar powered boat the same way as wind powered cargo vessel captains did ~100 years ago. Plan ahead and wait for favorable conditions to approach land.

 

[gonzo]

Data from boats that cross the ocean following the equatorial current are grossly misleading. After all Alain Bombard crossed the Atlantic with zero power. The claim could then be made that inflatable boats can cruise with zero power.

 

[Daniel Mazurkiewicz]

@bajansailor Got these study plans from Bruce Roberts, studied them a bit and ... looks like I'm gonna be at least 50k USD short, biggest discrepancy in my estimation was how much Al it requires. It is nearly twice as much as I assumed. Now trying to squeeze my requirements to 10-11m cat. Classic - expectations vs reality ;-)

 

[Rumars]

Contact forum member @Alik he has done Al cats and solar powered ones. Albatross Marine Design Thailand - Boat and Catamaran Design by Albert Nazarov http://www.amdesign.co.th/

 

[Daniel Mazurkiewicz]

@ad-hoc
@gonzo
@bajansailor
@kerosene
@Rumars
@SolGato

Guys, wanted to thank you for helping me this or another way. More than a week of intensive digging in my all spare time leads me to one conclusion - Al is expensive and not affordable for me in terms of size of boat I would like to have. For now I'm willing to consider plywood or wood or combination of both. Will do some more digging before coming back with questions in some new topic
Once again thanks!

 

[kerosene]

I want to remind that the rule of thumb is that hull is 1/3 of cost of a boat. or something along those lines.
for ocean crossing boat with water makers etc. the ratio might be even larger.