EV powered boats?

[storx]

I was curious if there are any folks out there who have repowered to EV. Been doing research and reading lots of blogs of people who live aboard on boats with the intentions of buying in the future possibly to live aboard. During my process of reading some these blogs, i found a couple who have sailed from Florida to Greece and back down to the Dominican Republic by nothing more than sails and a small electric motor. They are on a 36ft monohaul they replaced the old locked up diesel motor with a 4.5kw electric motor they bought off Ebay ran off a 48v setup they put together for under $1000. After reading the blogs and sending a few emails, they said they can run the electric motor off a full battery for almost 2 hours at full power and hit about 5-6 knots. They said during the day with full sun out on their 2 solar panels they can run the electric motor at part throttle and hit a constant 1.5-2 knots on solar if there is 0 wind to sail on. On the days the sun is absent and no wind, they can run a Honda 2200i generator they said and maintain a steady 2+ knots while trickle charging the battery bank.


Anyways, Im a big fan of EV, currently own an electric car "Tesla Model 3" and an electric bicycle I built from scratch using a Catrike Expedition frame and power it with recycled 18650 cells from old laptop batteries i salvaged. My old house i installed a custom solar system and built a 40kw homemade powerwall from old salvaged laptop 18650 cells that ran beautifully for over 2 years while i owned the house without any hiccups.

I am no engineer, but I don't see a reason slightly larger electric motors in a pair couldn't power a nice trawler a decent pace. The reason i am asking under this section of the forum is due to looking into possible boats to turn into a liveaboard. I have come across a good handful of deep deeply discounted trawlers with missing motors or bad engines needing to be overhauled for a fraction of the same boat with a good set of motors.

Example: right now there is a Bayliner 4388 listed for sale on my local marketplace for $15,000 because the 2 diesel motors onboard are both non-functional. and a Carver 35 for $12,000 because the MerCruiser motors are smoking, needing to be overhauled.

[valhalla360]

Do a search on the forum...the subject has been beat to death.

If you are willing to accept significant limitations, you can do it now with a sailboat. That limitation is typically extremely slow speed under power with limited range, so mostly used to get in and out of a marina before switching to sail.

A big power boat...particularly a planing power boat...the limitations are an order of magnitude worse.

[tp12]

I'd suggest funding a forum that is focused on electric propulsion as you're more likely to talk actual numbers.

[valhalla360]

Originally Posted by tp12

I'd suggest funding a forum that is focused on electric propulsion as you're more likely to talk actual numbers.

Lots of folks on this forum love to talk actual numbers...but the pro-EV crowd typically doesn't like the answers.

[a64pilot]

A sailboat typically has a hull that is optimized to be moved under very, very low power, cause of course the amount of power that can be harnessed from wind is limited, and slow boats are not sought after.
They of course give up other niceties, no free lunch.

Power boats hull designs are usually driven by other considerations as it’s not difficult to use bigger motors if more speed is desired.


So if you desire electric propulsion, then maybe you should consider the most easily driven hull you can find, and at a good price if money is a consideration.
That will most likely drive you towards and older maybe mid 30’s Ft sailboat. Ones with bad motors ought to literally be pretty much free.

[billknny]

Originally Posted by valhalla360

Lots of folks on this forum love to talk actual numbers...but the pro-EV crowd typically doesn't like the answers.

It’s also amazing how many of the “pro-EV” posts include the phrase, “I’m not an engineer, but it seems to me...”

A case where everything AFTER the “but” is BS.

[Singularity]

Originally Posted by storx

Anyways, Im a big fan of EV, currently own an electric car "Tesla Model 3"...

As a point to ponder...when you bought the Tesla, you had the opportunity to instead convert an old VW or more modern small-mid sized truck for half the cost of the Tesla. Please forgive my presumptions, but it would seem as though you valued utility in the Tesla that an older car/truck conversion wouldn't provide...particularly range and/or modern safety features.

My daily driver is an old CNG-only work truck; when I need to look presentable I drive my Prius. My family otherwise still has >100 year old electric cars with the original Edison cells. I state these facts as evidence that I'm invested into alternative power for whatever reasons.

Back to the Tesla vs VW conversion-type deliberations. Hopefully this makes sense to you (and likely too tangential for others...) but I see the electric conversions of boats to be sort of like providing the utility of a VW conversion, except much much more limited, and with less "safety" capacity. Sure you can do it, but I think you really need to use a boat for a while that has an internal combustion engine as the primary power source and/or spend a lot more time considering the limitations that an electric conversion will place on you.

A64pilot gave the best advice there is to give on this subject. If you can get over the thought that a big boat gives more living space as a liveaboard and accept a smaller volume sailboat...you can get a sailboat for practically free (plus elbow grease, that you apparently have) that can take you around the world without the need for an engine in the first place. But push come to shove, most here rely on the fact that they have an ICE with sufficient fuel to push them to hull speed for many many hours when the external world dictates that that using power is safer than going under sail (or just sail alone).

Not sure you're concerned about resale but resale of a cheaper old boat should suffer the same problem that the old VW conversions suffer from...you'll never get back your out of pocket expenses. If you bought a sailboat with a sour ICE and repaired it yourself, you'd fair longer in the long run financially, I think...if financials are of any interest.

[jeff gedgaud]

I'm a noob here and know nothing about boats or electric propulsion but have a question that I could not find but was wondering from the proponents of electric propulsion. Could you hang a generator off the back end of the boat and generate power regardless of type of propulsion at that time, i.e. wind or electric motors and gain back at least some power? I understand drag on the generator blades etc but it should not amount to much compared to being able to gain some power back even while motoring with the other motors/generators. Of course there will be a point where hanging bigger or more generators will add more drag than you get back but a small one that would at least add some back or at the very least not draw as much while motoring from battery banks does not seem to be discussed anywhere I could find.

[tp12]

Originally Posted by valhalla360

Lots of folks on this forum love to talk actual numbers...but the pro-EV crowd typically doesn't like the answers.

We'll have to agree to disagree on that.

[Singularity]

Originally Posted by jeff gedgaud

...have a question that I could not find but was wondering from the proponents of electric propulsion. Could you hang a generator off the back end of the boat....

You are onto something, but the power generated with such devices is very tiny. Enough to power the boat's refrigerator and maybe autopilot underway, certainly not enough to be relied upon to propel the boat later (do the math on the energy captured vs required for an electric propulsion motor).

This link reviews the most common external drag devices:
https://www.practical-sailor.com/blo...t-11090-1.html

Otherwise google 'propshaft drag generator sailboat' to see how to connect a generator to the boat's propeller that, depending on the boat's transmission, can use a freewheeling main propeller to turn a little generator. If you don't know what TANSTAAFL means in physics/engineering...google that too.

[cj88]

I have been thinking about what would make a good candidate for electric propulsion for a sailboat for one or two people and I'm leaning towards a 28-32' racer-cruiser from the 80's or later. Lighter displacement so sails well even in lighter airs so less likely to need to motor, sails quicker for a given wind speed so more opportunity for reasonable recharging via hydrogeneration, generally wider beam for a given length so more area for mounting solar. Also, you'll want lithium batteries for better charge/discharge characteristics.

You'll want to enjoy sailing more than motoring, you don't want to be locked into having to sail to a schedule over any distance and you need to think with a more minimalist outlook about what you really need vs. what you want with regards to comfort and convenience items as you'll be restricted with space, weight and power.

[valhalla360]

Originally Posted by jeff gedgaud

I'm a noob here and know nothing about boats or electric propulsion but have a question that I could not find but was wondering from the proponents of electric propulsion. Could you hang a generator off the back end of the boat and generate power regardless of type of propulsion at that time, i.e. wind or electric motors and gain back at least some power? I understand drag on the generator blades etc but it should not amount to much compared to being able to gain some power back even while motoring with the other motors/generators. Of course there will be a point where hanging bigger or more generators will add more drag than you get back but a small one that would at least add some back or at the very least not draw as much while motoring from battery banks does not seem to be discussed anywhere I could find.

You just described a perpetual motion machine. If you make it work you will be a rich man.

In real life, the drag pulling a generator prop thru the water will always be greater than the power generated, so it's a losing proposition when you are powering the boat via a propeller (regardless of how the propeller is powered)

You can do this while sailing at the expense of slower sailing speeds but unless you sail a lot and in high winds, getting enough to generate a meaningful amount of power isn't going to happen.

[Simi 60]

Originally Posted by storx

I am no engineer, but I don't see a reason slightly larger electric motors in a pair couldn't power a nice trawler a decent pace. .

Example of electric motor, battery bank and how you will get the power back in.


Use us as an example if you like, 60 ft, 65 tonne, economy cruise speed 7.5 knots.
Range at that speed is approx 3500 nm and I wouldn't want to have less.

Example: right now there is a Bayliner 4388

Not a trawler

. and a Carver 35

And neither is this.

[jeff gedgaud]

I understand no free lunch, Wish more people did, My point being that a small generator other than the motors, solar panels, maybe even a wind turbine or two as well on deck and you've got a few ways to capture at least some energy. I'm not saying you could even come close to powering everything but you can at least slow the drain and make what you have last. That plus it seems to me, from watching videos that cruising is not for people in a rush to get somewhere but to enjoy the passage while getting to someplace interesting.

[44'cruisingcat]

The towed generator will consume more power than it produces. It's just physics.

Even if the towed generator was 100% efficient, (which it won't be) you'd still gain nothing.

Ie, if it was putting 500 Watts back into the battery, the loss in speed would cost you at least 500 Watts.

It is possible to power a propulsion system entirely off solar panels. You need to build a boat specifically for this purpose though. It needs to be very light and efficient, with a huge deck area covered in solar panels.

It's been done, it ended up being an extremely expensive way to travel slowly. (Even worse than sailing) And it's worth pointing out that this boat, completely covered in solar panels, used propane for cooking. Apparently there weren't many excess Watts available for non propulsive use.