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Old 05-02-2018, 04:33   #16
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Re: Making a diesel electric trawler for coastal/loop

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Everyone said you can't air condition an RV with solar, yet we probably spend over 150 days on our trip where we were running our 6000 BTU modified window unit in our RV straight from the sun (actually charging the house batteries a little bit at the same time). It was simple. Our A/C used about 650 watts and during the day we were getting up to 1200 watts from our panels.

If you're not aware, Greenline (I think) makes an all-electric and a hybrid, and Duffy makes electric boats. Might get some ideas looking at their details...

If you think the word "schedule" might ever force movement, you could consider two gensets, one for normal conditions and another one to bring on line if conditions require it. Alternate use, maybe.

A data point: we have two 16K BTU ACs and they do OK (just) on hot muggy 95F days...

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Old 05-02-2018, 06:48   #17
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Re: Making a diesel electric trawler for coastal/loop

First, you run the air on the RV by using a drastically smaller unit. The typical RV air/con unit is 15k btu or 2.5 times the size of your 6k btu unit...but hey it shows you understand some of this stuff, so we'll move on.

Big issue I see is your assumption that 10kw propulsion motor is sufficient. Ocean crossing where you can drift along and wait for the wind to pick up before making headway under sail...it's annoying but can be done.

On the Great Loop, you have significant stretches of river where there are limited place to tie up or anchor and big currents to fight. All this with barge traffic that has no option to avoid you if you can't get out of the way. I would get nervous in a boat that can't maintain 6kts. Example: Our Gemini Catamaran with 25hp had a top speed of about 7.5kts. South of St Louis, we docked at full throttle. If we maxed out at 4kts, we would have been swept by with no chance of recovery. There were a few places we really had to pour on the power to fight the current. Then when you hit the Ohio & Tenn Rivers, you have to go upstream fighting the current for miles. If you are trying to cruise at 3kts fighting a 2kt current, it takes a really long time to get anywhere and traveling at night is not recommended.

Seriously consider setting the boat up so it can do 6-7kts continuously. You can go slow and run on solar where it makes sense but this is a trip where it really makes sense to have more power available.

As far as the "donner" boat, if you are still insistent on it, I would look for a 30-35' sail cat. We took the mast with us, took a couple hour to pull and secure on deck (you have to take it down twice). Alternatively, you could leave the mast at home and reinstall it later. The downside to a mono is they get really rolly without the mast (this is why a sailboat hull can be more efficient than a trawler hull as the mast resists rolling not the hull form). A cat doesn't have this issue. Also, cats are usually shallow draft (huge plus along the route) and are very efficient under power. The cat also has a ton of room for solar panels.
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Old 05-02-2018, 09:57   #18
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Re: Making a diesel electric trawler for coastal/loop

If it was ANYBODY else Id say youre crazy.

You though, sound like you could pull this off ;-)
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Old 05-02-2018, 10:14   #19
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Re: Making a diesel electric trawler for coastal/loop

I had originally thought about a catamaran but dang there are so few used ones available across the USA compared to trawlers and monohulls.

Anyway, we are going to look at sailboats this week for actually using as a sailing vessel but I will keep the trawler and catamaran in the back of my mind as we go to boat yards.
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Old 05-02-2018, 10:21   #20
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Re: Making a diesel electric trawler for coastal/loop

I think what you are talking about is dangerous on a boat.

I would thing a sizable diesel engine running a sizable electric motor with the solar backup would be more feasible. I think most modern cruise ships use electric motors run by diesels. There are times on the water when you need speed for safety not to mention peace of mind. When you are able, run on solar alone with batteries.

Sounds like you have the expertise to pull this off. The trawler mentioned above maybe along the right idea. If you have a system that would run the boat at hull speed efficiently, you could become a very rich couple with some patents.

I believe this is the way of the future for motor yachts, trawlers, etc, who are interested in the journey, not racing to get somewhere or sitting at the dock.

I wish you the best and hope you keep us informed of your progress.
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Old 05-02-2018, 10:24   #21
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Re: Making a diesel electric trawler for coastal/loop

If you look, most successful Solar designs are Cats, with very fine hulls.
With Solar, or any other very low power propulsion, you really need to have as easily driven a hull as is possible.

If nothing else, alt least be sure to fit the dinghys motor to the boat, try to get a high thrust motor, which is not the best motor for a dinghy, but will push a heavy object much more successfully.
Think of it as a safety back up, and youll need a dinghy anyway, may as well not row.
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Old 05-02-2018, 10:35   #22
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Re: Making a diesel electric trawler for coastal/loop

I think you have an excellent idea. And as a mechanical engineer, I can also say it can be done.

Its all about efficiency.

So, I respecfully, and with a friendly tone, suggest you consider the efficiency of the hull you intend to buy. A hull that will move easily through the water with little hp applied will vastly increase your range. To that end, you might consider a shallow draft sailboat, and remove the mast and sailing gear. To be clear, (most) sailboats move easily through the water to speeds near hull speed.

Consider something like an older Pearson 35. Shallow draft (swing keel), lots of space for batteries and solar panels. And a long waterline for better speed. Plus these older boats can be picked up very cheap...especially if you are not concerned with the rig/sails or engine!!!!

I would be very interested to follow your adventure building a solar sailor for the great loop!
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Old 05-02-2018, 10:41   #23
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Re: Making a diesel electric trawler for coastal/loop

If I may add my 2 cents as an electrical engineer.

For a number of reasons I would love to convert my sailboat to electric but after analyzing all the pros and cons decided against it. Maybe in the future but that isn't going to be soon.

The problems I found.

- Not enough room on most boats to mount enough solar panels. Your RV has a large, flat unshaded roof. Boats don't generally come that way unless you go with a houseboat.

- Range. Unless you add a large diesel generator you will not be able to install enough battery power to motor a decent distance. 20-30 miles is a typical range. You say you won't motor against the current but sometimes you want to go somewhere and the current or wind is against you.

- Power. Most marine systems are woefully underpowered. Just fine when you're motoring with no wind or current. Add a tiny bit of current or a little bit of wind and you will be going backwards. Another issue with power that is often ignored or glossed over is maneuvering in marinas or other close quarters. More than a few times I've needed all the power I had to turn or stop my boat when docking. Most recently in an unfamiliar marina where I found a 3 kt current running when I was already committed. Strong winds can pin you to the dock if you don't have the power to pull away.

After a lot of research I've figured all the above can be overcome by either a lot of expense or a lot of time and custom work or a lot of both. Also the final result to overcome all the limitations will result in not only more expensive installation but also more complex.

Your milage may vary.
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Old 05-02-2018, 14:56   #24
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Re: Making a diesel electric trawler for coastal/loop

I fully support you taking on these challenges so I can learn from your experience as it really is a great off-the-grid idea. Your RV set up was a great example of thinking outside the box (truck)! Ha! Why not buy a sailboat that was dismasted by Irma so you can avoid the pain of doing so and, perhaps, save some green at the same time?
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Old 05-02-2018, 15:18   #25
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Re: Making a diesel electric trawler for coastal/loop

The prop doesn't care where it gets the torque and RPM from. It only cares that it gets enuff. If it wants, say, 250 HP to drive the ship, it wants 250HP, or the skipper won't be happy. You can supply it through a mechanical tranny or you can supply it through an electrical tranny. The tranny has to get the energy from somewhere. If it's an electrical tranny-cum-motor it can take the energy from batteries with a very low power density or if it's a mechanical tranny, it can take it from liquid fuel with an enormously high power density.

So what's to choose? If you go electric you get (questionable) bragging rights. If you go mechanical you get performance. Either way you need to have a bejasus big diesel to either drive the tranny or to drive the generator to recharge the batteries so they can drive the tranny-cum-motor. But, of course, you can just skip the batteries in that case.

Diesel-electric locomotives and diesel-electrically propelled ships run their diesel engines at the top of the power curve about 80% of the time and at less about 20% of the time. Electric cars run at very low draw more than 80% of the time and at full draw very, very little of the time. There is a lesson there, somewhere.

But somebody has to lead the way and as we all know, the bumble bee can't fly :-)!

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Old 05-02-2018, 21:06   #26
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Re: Making a diesel electric trawler for coastal/loop

A diesel engine is what, 40% efficient at best? So a gallon of diesel, with 40kwh of energy will only provide 16kwh to the prop through the engine (this is if the transmission is 100% efficient).

Running 1hp for an hour is 746 watt-hr. Thus a gallon of diesel can provide at best about 21 hp for one hour.

A 250hp engine then, running flat out is going to consume about 12 gallons of diesel an hour!

A 8 hour day of running like this and you consume 96 gallons of diesel.

Kind of eye opening. Fortunately, most people I guess don't actually run their 250hp engine at 250hp for any long length of time. Or they have very large tanks. I guess I have seen a trawler with a 800 gallon tank...
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Old 05-02-2018, 21:15   #27
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Re: Making a diesel electric trawler for coastal/loop

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A diesel engine is what, 40% efficient at best? So a gallon of diesel, with 40kwh of energy will only provide 16kwh to the prop through the engine (this is if the transmission is 100% efficient).

Running 1hp for an hour is 746 watt-hr. Thus a gallon of diesel can provide at best about 21 hp for one hour.

A 250hp engine then, running flat out is going to consume about 12 gallons of diesel an hour!

A 8 hour day of running like this and you consume 96 gallons of diesel.

Kind of eye opening. Fortunately, most people I guess don't actually run their 250hp engine at 250hp for any long length of time. Or they have very large tanks. I guess I have seen a trawler with a 800 gallon tank...
Now do the math for how many batteries it would take to supply that much power. That to me is even more of an eye opener. Basically you would need to two a small barge full of batteries.
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Old 05-02-2018, 21:54   #28
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Re: Making a diesel electric trawler for coastal/loop

I have an Albin 25 trawler with a 27 hp Volvo diesel that can push up to 9-10 knots, although I cruise more around 6.5 knots most. Its a small lightweight boat with a very efficient displacement hull.
It has a large mostly flat roof over the center cockpit. I have one solar panel up there now, but there is easily room for 4-6 more. I guess about a 6hp electric motor would give about the same power as the Volvo. I have thought that removing the fuel tank plus the space where the motor is could be filled with batteries but Im still thinking the range would be limited. With the diesel I have a 400 mile range on my 20 gallon tank.
Ive thought of wind generators which might make power at 6-7 knots that would add to the solar and slow the drain on the batteries.
Anyways, Albins like mine from the 70s are pretty tiny, but would be fine for one or two people. They later made a 27 and newer boats, but the newer ones have increasingly larger engines and go faster. There is a version of my 25 that came with a mast and while it wasnt designed for sailing it could make 4 knots under sail alone.
I have checked out several electric catamaran projects, but those boats are out of my budget range.
If I do ever convert my boat to electric, I probably would still carry a kicker motor on the transom. On one of my old sailboats I had a 6hp outboard with a charging circuit in addition to a small solar panel to keep everything charged.
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Old 05-02-2018, 22:19   #29
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Re: Making a diesel electric trawler for coastal/loop

Quote: "Now do the math for how many batteries it would take to supply that much power. That to me is even more of an eye opener. Basically you would need to two a small barge full of batteries."

Exactly! The long and the short of it is that the power that goes out through the prop has to come in through some means or another. The ins'n'outs are NEVER synchronous for more than the briefest periods of time. Outside those brief periods you need a buffer, a means of storage, of the energy. There is no more efficient and effective way at this juncture than to make that energy buffer a tank full of dino-juice.

Debates about anything else eventually descend into a defense of perpetual motion machines.

Rube Goldberg loves those:-)

TP
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Old 05-02-2018, 23:32   #30
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Re: Making a diesel electric trawler for coastal/loop

I used to have 14 solar panels and I could motor at 3 knots in full sun. With 8 golf cart batteries I could also motor all night. This was with inefficient electric trolling motors.

Eventually I built a much more efficient setup with a brushless motor driving a 14:1 2 stage planetary gear box, and 200 rpm propeller. I could go 2 knots using 12 amps at 12 volts. With a bigger slower propeller the efficiency would have improved, as this propeller was < 12 inches in diameter.

Finally I realized that a sculling oar made of wood is far more efficient in many respects. I traded my solar panels, and batteries. I can maintain 1.5 knots for up to 3 miles. It keeps me warm when I need to break through ice.

there is nearly always some wind, despite what is claimed. I'm sure it's possible to make the great loop with sail alone.
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