Electric Boating

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bobkart said:
I've settled on the following requirements:

- boat length in the 3-5-meter range
- reasonably seaworthy as I won't be confined to just rivers and lakes (Puget Sound is calling)
- minimum two persons capacity, four is more likely what we want
- around 20mph top speed would be the target
- I'd like to get at least one hour of battery runtime at that top speed

I've settled on the catamaran approach. These are typically termed 'semi displacement' hulls. With long/narrow ('fine') hulls you can overcome the so-called 'hull speed' limit much more easily, because the waves generated are small enough to not contribute to overall drag as much as those of a monohull boat.

This boat would be an example of what I'm talking about:


(But longer than I'm looking for.) This style of boat has advantages (beyond better hydrodynamic efficiency) of a larger deck area than a similar sized monohull boat, and less risk of sinking (and no need for a bilge pump), as they can't be swamped ('self bailing'). Good rough-water handling is also a common feature of this style of boat, due to the 'wave-piercing' style of the hulls.

I've also broadened the scope of my interest to include 'personal watercraft' of the style outlined. Advantages here include hand-launchability (no need for a trailer or boat ramp) and two people (in two boats) can split up during explorations, and just generally have more fun, chasing/following each other around. There's also more redundancy in the event of a failure. And, this approach gives me something of a testbed, to try out ideas that may carry over to the full-sized version. These boats would of course only be suitable for small rivers and lakes.

Pursuant to that one-person-boat interest, I just ordered the Build Your Own Boat version of a Hydrobike:


You get a pair of hulls and a pair of crossbars. I'll add a small deck, seat, and motor mount, and try the two electric motors I have so far, and take it from there.
A much more detailed discussion starts here:


I'll most likely limit my updates here to significant developments.

(Thanks to LeftieBiker for pointing out that forum.)

That's the Build-Your-Own-Boat kit from Hydrobikes (not counting the end table in the middle).

Near as I can make it with my bathroom scale, it weighs between 80 and 81 pounds. So I have ~445 pounds left to work with if I want to stay within the claimed capacity of the bike version (that weighs 125 pounds and can take another 400).

First up is to build a low-cost deck for prototyping purposes. I'll probably use Western Red Cedar fence slats for that, as they're light and cheap, and will allow me to easily experiment with different configurations and additions (transom, seat, battery box, ...).

Once prototyping is nearing completion, I'm going to want a lighter and more durable material to use for the deck. I have a number of options on my list so far, and other than aluminum diamond plate, composite material is looking the most promising. Coosa Composites makes some that's lighter/stronger than plywood, virtually impervious to the elements, and reasonably priced.

Besides opening up access to waters with no boat ramp access, this boat (and perhaps a second one like it) will serve as a test bed for trying out various propulsion and control approaches, with the hope that lessons learned there can carry over to the larger model I'll most likely be building later in the year.
Thanks for the encouragement, Brian.

The deck is shaping up, and looks like it will come to somewhere in the 30-something-pound range. So I'll have around 410 pounds left to play with for batteries, motor, seat, and pilot. This initial deck is just a prototype; I can probably cut the weight down by almost half with use of better material.

In another few days, when the last of the parts I've ordered arrive, I should have this ready to go in the water. I'll post some more pictures then.
Cool stuff. The only real project I have been kicking around is expanding the house bank on my O'Day 22 in order to provide more range to my Torqeedo Travel. But the big question is how to charge it. I don't want to pull a bunch of lead batteries every time, nor do I want to pay for a slip with electrical hookup. Solar could be a viable option.
I could see solar working for you, the biggest question would be how much panel space you have. And if you have a low duty cycle of using the batteries versus sitting in the sun, you could possibly get by with hardly any panel space needed.

At 20% efficiency (about as good as you'll easily get), 1kWp of panels needs five square meters. That's about three of the standard-size panels, which are about 1m x 1.5m. But you probably don't want panels made for the roof of a house (heavy), instead I see very light ('flexible') panels out there, that come in at around 40 pounds per kWp. Rigid panels are over three times that.

I find a good solar system topology to be one panel per 12V-nominal of battery pack. So a 48V-nominal pack would use four panels, then each panel feeds a small charge controller to charge their part of the pack. This can help solve balancing problems between the pack segments, but of course can actually cause those problems if your panels don't get similar amounts of sun. And, you can double/triple the panel count, with small, per-panel charge controllers in parallel to each 12V-nominal pack segment.

For the LiFePO4 packs I have, I find that these charge controllers work well:


But I usually refit the outputs with 50A Anderson connectors due to some of the 45A connectors failing/melting.
Yeah the adjustable shaft length is important for this setup, as my current transom is probably nowhere near a standard height. I'm actually going to start with the smaller motor I have (~550W), and have turned the tiller arm on that around 180 degrees, so I can mount it facing forward, and control it more easily (no reaching back). But I think this arrangement suffers on practicality, as beaching/etc. will be more challenging, and tipping up to clear obstacles is less effective. So motor at the rear will likely be the more final arrangement. These trial runs will allow me to determine what prop depth the boat needs, so when I build a more proper transom (at a standard height), I can know where to locate it height-wise.

On seating, good question. Lots of options for sure. The answer will tie in to how I want to control the motor. One nice setup I've envisioned is to use a seat that swivels, and tie the swivel action to steering the motor. I.e. swivel yourself to look left and the boat turns left. (The linkage has to cross for that to work, for a front-mounted motor, the linkage could be parallel.) Then you just need a remote throttle mounted alongside the seat (that swivels with you). Turns out you can separate those trolling motor tiller arms from the shaft and use them separately, with added cabling between the parts. You can also ditch the tiller arm completely and use a PWM controller and have any kind of knob/lever control you can adapt to one of those. I see kayakers (for example) going with this approach.

My even-more-comfortable seating option would be to use one of those outdoor Zero-Gravity folding chairs (we have a couple in the back yard). Extremely comfortable, and still pretty light. Even comes with a side table for drinks/etc. The throttle could still be (right) side mounted, but swiveling to steer is no longer an option. Boats like the Craig-Cat use 'stick' steering, so something like that on the left side of the Zero-Gravity chair seems like it could work well. Pull back to turn left, push forward to turn right. The stick-steering approach could also be applied to a normal upright seating arrangement (swiveling or not), where the lever sticks straight up just ahead of your knees, and you move the lever to the left for left turns, right for right turns. So more intuitive than the side-mounted stick arrangement.

But for the first few outings, the simplest seating arrangement I can come up with will be used. I just need to tie it to the deck somehow. My goal is to be able to assemble the boat at the launch point with no tools, mostly for portability reasons. I suppose if the seat is small enough it could be pre-assembled onto the deck, but generally it would want to be attached via some tool-less mechanism (wing nuts perhaps).
The steer-by-seat idea is interesting. I'd make sure it can be disabled by moving a lever or switch, though, with an auxiliary tiller control. I think that a steering wheel or yoke would be ideal for me - I never liked having to reach back either, and now I have two 'frozen' shoulders.
Yeah I'm just trying to get on the water with as little fuss as possible. That 'seat' is nowhere near good enough, but it's better than kneeling. I just want to make sure this all works well enough to warrant additional improvements.

I've used that battery before with this motor, on the 10-foot inflatable that made those videos. You may also recognize it from the EV Gas Can video I posted here a while back. But the batteries I make myself (out of four prismatic cells) have 1/3 more capacity (200Ah versus 150Ah), and are only marginally heavier (37 versus 35 pounds). I'm not sure exactly how I'll integrate the battery into the more final versions of this, but there's a nice SKB case that nearly perfectly fits the 48V-nominal pack of the prismatic cells, and could easily serve as the base of a real seat. Maybe not a Zero-Gravity chair, but it might fit under it. I just have this one at the very rear because I feel like it could be bow-heavy otherwise.
Today went pretty close to how I expected it would. There were a couple surprises:

- the boat sat lower in the water that I was hoping (basically to the black tape line)
- the front-steer approach worked poorly

Less surprising: the bow was heavy (as I was concerned it might have been). Control in the forward direction was difficult. Facing the other way and using the motor in reverse worked well control-wise, but I don't believe all power is available in reverse, and of course the prop isn't as efficient in that direction. I managed to touch 9km/h now and then (by sitting practically on the battery), so close to 6mph, about what the much larger motor was able to push the 10-foot inflatable to (but with two people aboard).

I added up weights and I think I was right at 400 pounds total. The Hydrobike (complete) weighs 125 pounds and is supposed to have a 400-pound capacity on top of that. I have trouble seeing how I could have added another 125 pounds and been 'safe' . . . I feel like the hulls would have been nearly completely submerged. So trying the larger motor with the 150-pound battery pack looks to be out of the question, unless/until more hulls are involved. I'm thinking that a four-hull model could work out for that and another passenger, as I put the total weight of that setup at 800 pounds. But I have many more things to try before heading in that direction. One thing on that list is a 50Ah 48V-nominal battery pack. I got a line on one of those a few weeks back, and will likely touch base there again. Such a pack would come to somewhere in the low 40.x-pound range. That and the heavier 2.2kW motor (low 30.x-pound range) would come to just 10-15 pounds more than I was at today.


Changes since the previous run include:

- motor back to original rear-facing thrust
- aluminum crossbars and knobs
- quick-release deck pins
- better seat

I also tried some 40Ah LTO cells (5S). Seemed like less voltage than 4S LFP, so may try 6S next.

Speed was once again just at 9km/h peak (approaching 6mph). This is probably related to the propeller RPM/pitch limits typical of trolling motors. And it looks like I could stand to have a bit more weight towards the bow.

I have a real seat on the way, and I have a swivel to put between that and the base you see here. Also, a composite deck is coming. And I'm working towards trying the 2.2kW motor, but have to put together a much smaller 48V-nominal pack.