Making a diesel electric trawler for coastal/loop

[KTP]

My wife and I have plans to do some full time cruising (retired software/electrical engineers). We built our own RV from the ground up using welded steel/aluminum and did everything on it including the solar system (1600 watts into a Midnite Classic charge controller). We did not even fill up the roof space with panels (we carry a canoe, portabote and kayak up there) and yet are able to run our air conditioner completely off of the sun.

Anyway, we sail (pull a 17 foot Montgomery behind our RV) but would like to do a bit more cruising full time and need a larger space. We want to do the great loop, which is probably done best on some form of non sailing boat. I totally enjoy the silent nature of sailing though.

Enter the idea to buy a used trawler with under 4 foot draft and replace the engine with something like a 10kW brushless electric motor driven off of a rewired salvage electric vehicle battery bank of 20kWh or better with a 10kW or so diesel generator and as much solar as possible (perhaps as much as 3 to 4kW depending on space).

On flat water a trawler such as this would probably move at 3 to 4 knots with about 2kW going to the motor meaning a sunny day quiet cruise range of 20 miles or so off the sun plus another 20 miles on battery. When moored the battery bank could be charged up via 30 or 50 amp shore power overnight. For long distances or cloudy days, the diesel generator could provide the needed power, although in our RV in Florida we were getting about 400 watts out of our 1600 watt system in total overcast conditions, meaning a 3kW bank might actually produce enough juice for several hours of cruising even on cloudy days.

Because I could do almost everything myself, including sourcing the batteries and building a solid BMS and safety systems, I think I could keep the cost down to about what a new repower would cost on a typical trawler. The panels nowadays are just dirt cheap, $0.30 a watt at some sizes. We use 275 watt panels on our RV which are about 60 inch by 39 inch.

I recognize that solar won't do everything, hence a decent diesel gen and a modest fuel tank as backup power source.


Thoughts? Ideas?

[KTP]

Some pics of our RV build (which many said could not be done and we would not finish). The pods (living pod and garage/workshop pod) come on and off of a 2006 Isuzu NRR 20 foot flatbed truck. We took her on a 12,000 mile trip around the USA pulling our 17 foot Montgomery sailboat and we launched the boat with the RV at least 25 times on the trip.

[a64pilot]

Why didn’t you use electricity as propulsive power for the truck?
I’d go so far as to say that a boat is not different, not really. The same reasons that make it illogical for the truck, make it so for the Boat.
Yes you can have a Solar powered Boat, and sometimes there is wind and current, often in your favor, often times not.
It can be done of course, has been done, just there are some very real shortcomings with one, that you have to live with.
If you can accept the shortcomings then it’s fine.
However the question is, it can be done, but why?

[misfits]

KTP,

You should check out the electricseas.org & the yahoo electric boat forum. There are alot of knowledgeable folks there who's passion are electric boats. You'd get some pretty sound advice to help you decide if this is feasible for you.

Got to go, time for football, Go Pats!

[KTP]

Originally Posted by a64pilot

Why didn’t you use electricity as propulsive power for the truck?
I’d go so far as to say that a boat is not different, not really. The same reasons that make it illogical for the truck, make it so for the Boat.
Yes you can have a Solar powered Boat, and sometimes there is wind and current, often in your favor, often times not.
It can be done of course, has been done, just there are some very real shortcomings with one, that you have to live with.
If you can accept the shortcomings then it’s fine.
However the question is, it can be done, but why?

Electric big trucks are probably coming at some point in the future, likely when battery technology takes another leap.

Boats can go 4kts and be fine but if you get on the interstate and go 5mph you are going to have a bad time. Boats also move a large amount of mass efficiently at slow speeds, which is why a horse was able to pull such a large load down a canal.

Not really fair to compare an electric boat to an electric vehicle.

[a64pilot]

Originally Posted by KTP

Not really fair to compare an electric boat to an electric vehicle.

That’s just it, in a nutshell, I’d say a motor yacht, is a vehicle.
It’s just simple physics, really. It takes X amount of energy to move said vessel at X number of kts.
Most of us can’t get enough Solar to run our systems and often have to resort to burning fossil fuels to keep our beer from getting warm.
Now add the amount of energy to move a boat any significant distance and your talking orders of magnitude more energy required.
But, but there is this multi million dollar ultra light multihull that shows Solar electric propulsion is feasible. Just don’t forget that multimillion dollar part, and how feasible is it really?
Well, then we will have a generator to make electricity to drive the electric motor for when there isn’t enough Solar, or to augment the panels.
Yes, at an efficiency that is lower than direct drive from the Diesel, so you will burn more fuel with your hybrid drive than pure mechanical Diesel propulsion.

Didn’t Lagoon build a hybrid? How successful was it?
I may be wrong, maybe it was someone else.

The only successful Solar powered boat design that exist, is a sailboat. You want to be Solar powered? Buy a sailboat. It is really that simple.

However it can be done, I’m not saying it can’t, I’m saying it’s not practical and likely less efficient than a sailboat with its mast removed, motoring down the ICW. I’m sure of that actually. I have been amazed at how efficient a motor Boat, a sail boat is.
I came from Brunswick Ga Down to Port Canaveral in the ICW on 33 gls of Diesel, and ran the generator for 20 hours also.

[KTP]

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. There were even times where I used a small rice maker which took about 200 watts for 25 minutes at the same time I was running the air conditioner and still brought our battery bank from 84% to 97% during that day.

A sailboat probably would be the easiest thing to move through the water at low speeds but I don't know if I can bring myself to dismast one. That would be painful.

We still may just go sailboat and sail. It is only if we go trawler that I was seriously considering the electric hybrid drive.

[a64pilot]

You air conditioned an RV by using a baby air conditioner.
My 5th wheel by comparison, had I think two 18,000 BTU AC’s as do most RV’s, or six times the power required from what you had.
I assume you were both smaller and better insulated, and maybe not in the direct S Fl sun.

The hull design of a sailboat has evolved into a hull design that requires the absolute minimum power to drive it.
Almost any powerboat the hull design is primarily driven by other concerns, how much room, how good a ride etc, if it doesn’t meet performance requirements, fit a bigger motor.
Only a very few powerboats have gone to the extreme of being as easily driven through the water as a sailboat.
Quite a few do the great loop in sailboats, many skip portions so they don’t have to step the mast, many step it.
A trawler is thought of as the boat to do the great loop as in truth fuel cost isn’t that big a driver in overall Boat ownership costs, and your not going to sail much on the ICW, and most sailboats draw more water than a trawler, and have less room inside etc.

However if your seriously considering a Solar powered Boat, a sailboat hull requires much less power to drive it, and if you remove all that sail stuff, you could fit a huge Solar roof if you will over the entire boat, cause your going to need huge amounts of panel space.

Go watch a sailboat either sail or motor by, unless it’s going close to hull speed there is essentially no wake at all behind one, it takes a huge amount of energy to generate a wake.
Now watch a powerboat, even moving slow, there is usually some wake.

[john61ct]

I think there could be many critical situations where you'd wish you had diesel propulsion available.

Some even life-threatening?

Certainly would be **hugely** expensive, and with regular usage patterns solar will contribute a small fraction of the energy used.

Aircon off solar is a walk in the park comparatively.

[uncle stinkybob]

Originally Posted by KTP

Electric big trucks are probably coming at some point in the future, likely when battery technology takes another leap.

Boats can go 4kts and be fine but if you get on the interstate and go 5mph you are going to have a bad time. Boats also move a large amount of mass efficiently at slow speeds, which is why a horse was able to pull such a large load down a canal.

Not really fair to compare an electric boat to an electric vehicle.

around here we get 6 knt tides, sometimes more depending on area and tide change. your electric 4 knt trawler would only survive going with the tide. maybe a horse or something will help you out when the wind comes up to help push you up on a leeward shore but I doubt it.

[Simi 60]

Solar powered ferry in India


https://en.m.wikipedia.org/wiki/Aditya_(boat)

[Simi 60]

China's all electric cargo ship used for hauling..........coal.

http://www.chinadaily.com.cn/busines...t_34511312.htm

https://cleantechnica.com/2017/12/02...use-haul-coal/

[KTP]

Originally Posted by uncle stinkybob

around here we get 6 knt tides, sometimes more depending on area and tide change. your electric 4 knt trawler would only survive going with the tide. maybe a horse or something will help you out when the wind comes up to help push you up on a leeward shore but I doubt it.

I sail in the PNW. We use these things called tide charts and don't try to motor against a 6 knot tide.

[Kokanee]

Power boats cover a wide spectrum of hull designs. Full displacement hull trawler style boats that are nearly as efficient as many sail boats in the water.

I don't know what size boat you are considering but something like a Pilgrim 40 would give you plenty of real estate for solar panels, and would slide through the water fairly easily.

This one doesn't seem to be throwing much of a wake.

https://www.youtube.com/watch?v=EYatkdyYwnY

[Dockhead]

Just one word of advice from me, and I'll shut up --

Don't go out into the sea in a powerboat which is grossly underpowered.

It's not just tides -- it's the huge windage that those things have.

If you buy a trawler with a broken 200 hp engine, you are not going to be either safe or happy with 20hp. You might not need 200 hp if you are willing to live with a lower top speed, but you need to have enough power to get out of tough situation (for example, get off a lee shore), which will sooner or later arise.

This is different from the situation of an electric powered sailboat, where you at least have sails to fall back on.


Do the numbers, and make a budget. Then you'll see what realistic % of your propulsion can be supplied by solar, and how much all this will cost vs. a normal direct drive diesel. Then you can answer for yourself the question: Is it worth it?

Doing the Great Loop in a power boat means motoring day in and day out and covering a few thousand miles in total. 4 knots as a cruising speed is not going to be very satisfactory; and as a top speed will not be safe. Avoiding adverse tides using tide charts will help somewhat; but that tactic doesn't work in rivers.