solar electric propulsion of a power kat, 6.3 m

Designs and general discussion of craft that are not reliant on the wind. Includes human-powered, internal or external combustion, electric, etc
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Heimfried
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solar electric propulsion of a power kat, 6.3 m

Post by Heimfried »

I'm currently building a 6 meter power kat, which will be driven by 2 electric motors, (hopefully) mostly powered by solar panels. State of the build: the semi hulls are fitted on the bridge deck and the cabin is erected and covered.

I would like to discuss some questions of electric boat drives with interested members. (I attended the zoom meeting yesterday (late after its start). Solar electric drive was a point, but because of technical issues and my slow comprehension of the english language, I understood near to nothing.)

My ideas of now are: each of the semi hulls is outfitted with a selfmade outboard motor, starting with a 3 kW water cooled Golden Motor (4,000 rpm without load). A toothed belt 2:1 gear ratio from (vertical) motor shaft to drive shaft (covered drive shaft = "outboard leg"). Submersed a bevel gear 2:1 driving a propeller shaft. A relatively slow turning prop with a relatively large diameter.

This is at odds with most of all drives common in boating and may be I'll not achieve what I'm wishing for, but I'll give it a try. (I own an "pair" of small trolling motors to step in if my project crashes.)

AlexQ23
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Re: solar electric propulsion of a power kat, 6.3 m

Post by AlexQ23 »

Few things about electric boating...
There are at least three different chapters in your tips: The motor that assume the propulsion, the batteries or how the electric power is stored and then the solar panels themselves or how to reload batteries.
1. The motor. I think that first of all it would be a good thing to know exactly what power you need to propel your boat. For that, it’s easy to calculate theoretically and what thrust you need to navigate at a certain speed for a period of time. Different formulae do exist for the type of hull you have. It could be suitable at this stage to decide at what voltage you are going to work with and to comply with the number and type of batteries. That will give you the weight you have to take in consideration for your project. So, in final, you will be able to say that for example you will need one or two motor that can deliver a thrust of 70 or 80 pounds to achieve a speed of 5 or 6 knots.
2. The batteries: there are for sure a lot of different batteries, all suitable to your project. Some are cheaper than other... I just want to mentioned that Caterpillar make a really good hybrid battery available worldwide and at an affordable price. It’s a regular 12V hybrid lead battery of 100 AH, group 31, maintenance free. The particularity of this battery comes from his grid made out lead calcium. That prevents the battery to discharge by them self even in winter time when the battery is not in use.
3. Solar panels: I thing that you have already a good idea what to use and the available space you have. And for sure that you will use a MPPT regulator of the last generation. But with a maximum of only 5 hours of sun a day you easily understand that the batteries are the main source of power readily available at all time and that the panels can only be there to reload them (occasionally).
4. A last point is the cost or the budget you want to put in. For sure you can build your own motor but that came to a price (parts to machined and so on..). And it’s also true that electric outboard motors we find on the market are most of the time really expensive.
But depending on the power you are looking for, you can maybe found your happiness with the N series of Caroute electric trolling motor. It’s a brushless electric motor coming from China than you can easily modify to make a pod for your boat. it can offer a thrust from 80 to 180 pounds depending on the voltage it operates. But I’m sure it could be a good and cheaper alternative to what you want to build. Good luck anyhow!

Heimfried
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Re: solar electric propulsion of a power kat, 6.3 m

Post by Heimfried »

Thank you Alex for your reply.
I like to do calculations and to use mathematical tools, sometimes I write small pieces of software to create my own mathematical tools. But resistance prediction will be not easy in my case. Mainly because the boat has a relatively huge cabin with standing headroom and therefore is object to a lot of windage. The design (ECO 62, Bernd Kohler) is about 5 years old and to my knowledge there is no boat of this design on the water but at least three under construction (in Germany).

I'm in my seventies, have near to no experience as a boater and are building now my first boat (probably simultanously my last one) and I'm hoping to finish her (this year or next year), launch her and sail her before I'm no longer capable to do it for old age reasons. I hope to launch her as an incomplete boat (just able to float) and to do some trials regarding different aspects of operating. A friend of mine will tow her with his boat (large distance) and I will measure the towing force at different speeds and circumstances (wind). So I hope to gain some reliable numbers of boat resistance. Her first drives will not be the above projected outboards but two 24 V Haswing 3.0 elctric outboards or trolling motors 1.4 kW each (as far I can see, the Caroute motors you mentioned present the submerged part of these motors).
(To be continued.)

John Perry
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Re: solar electric propulsion of a power kat, 6.3 m

Post by John Perry »

Curiosity lead me to look up the specification for the Haswing 3.0 electric outboard motor that you mention. (https://www.boxmarine.co.uk/products/ha ... controller). One thing I noticed is that this is advertised as a 5hp motor, and the specification actually says that the shaft power is 5hp, but when you read the details it says that the maximum current is 105 amps at a nominal 24v so this cannot produce a shaft power of 5hp. Even if the electrical energy were entirely converted to shaft power the shaft power would only be 3.38 hp and allowing for losses in the motor, controller, cables, actual output would be something like 3hp. Maybe they mean that the motor itself is capable of producing 5hp but in this product it is limited to less than that, perhaps by the settings of a pwm controller, but in that case it is misleading to advertise it as 5hp.

Having said all that, I would have thought that a total motor shaft power of around 6hp from two of these motors should move your boat along on inland water ways, I guess fast enough for leasurely cruising. Since it has narrow beam hulls you should be able to use the Michlet software to get an idea of the water drag. The air drag is easy, at least for a rough estimate - its close to a bluff body so Cd will be around about 1.0. Taking the frontal area to be 2.5m x 2m = 5m^2, it would need a thrust of about 120kgf to just stand still heading into a 20m/s gale (F8), but in that sort of weather surely you just tie up to the bank and wait.

It looks a good boat for solar power, having a big flat roof and no sails or rigging to shade it. Should be space up there for about 10m^2 of solar panels giving an output based on panel rated power of a bit over 2kw, but of course actual output will be much less than that, and as Alex says, only for perhaps 5hours a day - on a sunny day. But then again, it does not take much power to move a boat like this on a calm day on a river or canal - much depends on what kind of boating you want to do.

Heimfried
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Re: solar electric propulsion of a power kat, 6.3 m

Post by Heimfried »

Thank you John,

"... much depends on what kind of boating you want to do"
I'll go slow and driving silently, That's the point for us to go electric and (partly) solar. 2014 and 2015 we were sailing a few days with roughly comparable electric boats we hired (but monohulls, 2 kW torqeedo outboard and the other one about unknown power inboard). No solar panels, only relying on batteries. We cruised the same bodies of water around Berlin we intend to do with our boat and there was only need to reload the batteries every second night. So we are somewhat confident that our planned drives will meet our needs.

Regarding the "5 hp" - my fresh Haswing booklet says (for the Protruar 3.0) "comparable gasoline outboards (thrust) = 4 HP". The comparison of electric motors and ICE's is a controversal issue, I'm not very much commited in. But if you read about the different norms with the exact test criteria to measure the shaft power of an ICE, you will find, that an ICE working in the real world will never have its rated "shaft power" on its shaft. At the test stand e.g. there is no air filter, no sound absorber, no alternator, no fuel pump, no water pump or fan belt.

My Haswings are said to have 1,44 kW power input, I don't know what output there will be.

AlexQ23
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Re: solar electric propulsion of a power kat, 6.3 m

Post by AlexQ23 »

Other few remarks...
-I thing that knowing the real thrust out an electric motor is most important than anything else. This value has to be comparing to the residuary resistance of yours hull(s). Keep in mind, that the last link of the kinematic chain is the propeller. And let’s say that the maximum propeller efficiency you can obtain is about 60%. In your case, if you design your own motor, 50% will be a real optimistic, good starting point. This mean that half the power of your motor is already lost here!!
-When installing solar panels on top of your cabin, I will recommend leaving a space between the rear face of the panels and the cabin top. This space will contribute to cool down the panels, increasing their efficiency and also prevent the heat to enter into the cabin roof (tropical roof).
-Wish you all the best with your boat.

Heimfried
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Re: solar electric propulsion of a power kat, 6.3 m

Post by Heimfried »

Thank you Alex,
I know about the comparatively large losses of the props. For this reason I try to go in the long term with a large and slow turning prop. I developed a software tool to calculate the shape of props - along the parameters given in the Dictionary of the International Towing Tank Conference - and have in mind to 3D print prop series in reinforced plastic to evaluate the optimal one. I don't know if it will fly and probably it will need years to start.

I also know about the negative thermal coefficient of solar panels. As my cabin top is thermally insulated (4 mm ply, 20 mm XPS, 4 mm ply), this problem is even greater for the panels. Therefore I would prefer to cool them with water. There is a guy in the Netherlands who will do likewise. But it may be because of complexity, weight, VCG, clogging and so on, I will reduce my plans to air cooling.

The thrust is given in the manual as 50 kgf / 110 lbs peak per motor, so I should have 100 kgf / 220 lbs thrust at WOT at disposal, so 90 kgf continuous, if the given values can be trusted.

Heimfried
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Re: solar electric propulsion of a power kat, 6.3 m

Post by Heimfried »

AlexQ23 wrote:
Sat Apr 17, 2021 10:59 pm
[...]
2. The batteries: there are for sure a lot of different batteries, all suitable to your project. Some are cheaper than other... I just want to mentioned that Caterpillar make a really good hybrid battery available worldwide and at an affordable price. It’s a regular 12V hybrid lead battery of 100 AH, group 31, maintenance free. The particularity of this battery comes from his grid made out lead calcium. That prevents the battery to discharge by them self even in winter time when the battery is not in use.
[...]
From my previous trials with two electric trolling motors (Haswing Protruar 2.0 and 3.0) I've got 4 AGM Batteries 12 V, 55 Ah each. Lable "Vision", made in Vietnam and of reasonable quality, as it seems. Until now I didn't test them hard. So I'll start with them. Later on I'll change to LiFePO4, 48 Volt.

AlexQ23 wrote:
Sat Apr 17, 2021 10:59 pm
[...]
3. Solar panels: I thing that you have already a good idea what to use and the available space you have. And for sure that you will use a MPPT regulator of the last generation. But with a maximum of only 5 hours of sun a day you easily understand that the batteries are the main source of power readily available at all time and that the panels can only be there to reload them (occasionally).
I'll use about 4 MPPT regulators (Victron), splitting the panels in groups. This is to achieve a better efficiency, as the cabin top is slightly curved, there is a different irradiation at starbord and port most of the time. As the MPPT is based on the average states of the panels, it is better to split.

AlexQ23 wrote:
Sat Apr 17, 2021 10:59 pm
[...]
4. A last point is the cost or the budget you want to put in. For sure you can build your own motor but that came to a price (parts to machined and so on..). And it’s also true that electric outboard motors we find on the market are most of the time really expensive.
But depending on the power you are looking for, you can maybe found your happiness with the N series of Caroute electric trolling motor. It’s a brushless electric motor coming from China than you can easily modify to make a pod for your boat. it can offer a thrust from 80 to 180 pounds depending on the voltage it operates. But I’m sure it could be a good and cheaper alternative to what you want to build. Good luck anyhow!
I already ordered some toothed belt discs with additional machining to fit on the shafts of the trolling motors. Clearly I'm not able to operate the two outboards with their tillers, as the helm is at cabin front and the motors 4 to 5 meters behind. So I have to do it with other means. For normal course it will be done with servo motors which turn the motor shafts, as a backup there will be a cable steering.

Otherwise I don't aim to give the prospective DIY motors the perfect outfit of an industrial one. So in this regard I will skimp a little with money.

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