Custom salt water electric cargo trike

I have a customer asking for a custom trike project and would love to crowd source some ideas about how to proceed.

This trike will be used for maintaining and harvesting oysters in a salt water environment. It will be ridden on sand flats that are exposed when the tide goes out, so not literally submerged in salt water, but definitely exposed to it. They will hose down the equipment with fresh water every day, but corrosion will still be a major issue. It will be an upright delta trike with a roughly 30" wide by 40" long cargo area over the rear wheels.

They want it to be as durable and environmentally friendly as possible, so minimal steel parts, and minimal oil/grease runoff. I'm considering using 5086 aluminum for the frame since that's often used in boat building, and I can source plate, tube, and other extruded shapes from a local supplier.

It doesn't need to go very far or very fast. A few miles at 5mph is plenty. Singlespeed would work, but some gearing, even a simple 3 speed planetary, would be better since they have to go up a boat ramp. I think a belt drive will be the way to go. I would like to drive both rear wheels (but not on a fixed axle), so that's going to mean using a differential, or doing that thing where you run an intermediate hub that drives two chains back to two freewheels on separate shafts.

For the electric assist, I'm currently considering three options.
1: Stock mid drive kit, could even be OEM style integrated into the frame since I'm making the frame. I'm concerned that this will have poor corrosion resistance in this environment.
2: Make that intermediate hub a hub motor with a healthy dose of Sprayon coating.
3: Some other outrunner with its own belt drive back to the intermediate hub or diff. Could be an e-bike motor, e-boat motor, or anything really.

Does anyone have any input on these ideas?

300 series stainless, particularly chloride resistant ones like 316 or 321, are what you want for components that will be exposed to salty crap. They're also pretty abrasion resistant, which is good in the application. 321 is the better of the two with regard to corrosion resistance.

Corrosion resistant aluminum is fine for boats, but boats often don't have as many interfaces between different metals as a bike would have. Add salt water and that's a battery; add the battery's voltage and things will corrode quickly. I'd look at reinforced plastics to the maximum degree possible. Wherever you can break the circuit between different metals, that is likely to help.

Fewer components is better in this situation. I'm familiar with Peerless differentials, but in this case I'm thinking they would fail early and ugly.

If it were my project, I'd try to house the motor, battery, and most of the reduction gear in a box that has bottom opening slots for toothed drive belts, and for draining any moisture that enters. Anything with gears, pawls, normal steel, ball bearings, goes inside the box. Two drive belts, because I'd use separate freewheels for separate half-axles, so whichever wheel gets better traction gets all the torque. (I assume tide flats don't generally require very tight turns.)

It leaves the question of what to use for the exposed axle bearings. Maybe plain pillow blocks made from low friction resin? Like these? whatever works for that, would work for the bottom bracket too. I'd want to fabricate my own 2-piece crank with a cotter or polygonal pinch clamp on the removable side, to minimize parts that can rust solid or seize up from sand. I'd consider making a plain plastic bearing headset with flat angle conical races.

Cheap interchangeable parts are awesome, but only if they work.

There aren't any motors I know of that aren't going to ingest water, thru bearings, cabling, etc.

I know of no easy way to completely seal one.

But...you could first do a complete coating / dip / soak of the motor's internals (magnets, winding, stator, etc) in one of the protective liquids, like the red paint commonly used for this, or the high-voltage protection lacquers, etc., that are thin enough before they dry to go everywhere water would, to seal up the metal stuff and keep the water out.

Then use a fluid (denser than saltwater?) to fill the motor with, so there's no "space" for the saltwater to get into. Should probably get checked inside periodically.

Or, vent the motor so it can be drained and cleaned with the rest of the trike.


The sealing problems may be true of a common IGH.

The Nuvinci IGH hubs *are* sealed pretty thoroughly (they have a liquid already in them that has to stay there) so they might be a better starting point than most of the other IGHs? Chalo could probably say better about that sort of thing.

I would have to agree about sealing motors. Using a hub motor to pull a chain drive, allowing it to be mounted high on the vehicle will help some. Cable actuate the throttle, which then goes in a box that can seal it up some. Controller in a box too, but with some metal attached to heat sink it. No plugs or connectors outside the boxes. Motor wires soldered to eliminate plug connectors. Inside the motor, high temp paint everything to reduce corrosion inside.

But there will be problems also, with batteries, particularly salting up a bms. So lead might be the best bet, and do your best to seal it into a plastic box. The short range will allow lead to work, where longer distance would require lithium.

dogman dan said:

But there will be problems also, with batteries, particularly salting up a bms. So lead might be the best bet, and do your best to seal it into a plastic box. The short range will allow lead to work, where longer distance would require lithium.

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I don't have a salt water issue, but I happen to have my lithium batteries in a sealed Pelican style equipment case. I'd think that such a thing would provide good protection from salt water for the batteries, BMS and perhaps other electronics.

They make electric paddleboards and surfboards these days, so it is possible to seal the electronics enough if done properly.

One thing to consider is the tires. On beach sand, you will need some fat tires or it will sink in.

Chalo said:

300 series stainless, particularly chloride resistant ones like 316 or 321, are what you want for components that will be exposed to salty crap. They're also pretty abrasion resistant, which is good in the application. 321 is the better of the two with regard to corrosion resistance.

Corrosion resistant aluminum is fine for boats, but boats often don't have as many interfaces between different metals as a bike would have. Add salt water and that's a battery; add the battery's voltage and things will corrode quickly. I'd look at reinforced plastics to the maximum degree possible. Wherever you can break the circuit between different metals, that is likely to help.

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This is making me think maybe I should consider making the frame and everything from stainless. I don't relish the idea of doing all my cutting and welding in stainless, but I can get tube and shapes in 316 from the same supplier. I can get stainless bearings with stainless housings, stainless freewheel from White Industries, etc... But some bicycle components are going to be aluminum or steel. There's no way around that unless I want to make my own headset cups, bb cups, seatpost, stem, etc. (I don't)

So I guess the question is, is it better to use as much stainless as possible and deal with a few aluminum components, or use as much aluminum as possible and deal with a few steel components?

Fewer components is better in this situation. I'm familiar with Peerless differentials, but in this case I'm thinking they would fail early and ugly.

If it were my project, I'd try to house the motor, battery, and most of the reduction gear in a box that has bottom opening slots for toothed drive belts, and for draining any moisture that enters. Anything with gears, pawls, normal steel, ball bearings, goes inside the box. Two drive belts, because I'd use separate freewheels for separate half-axles, so whichever wheel gets better traction gets all the torque. (I assume tide flats don't generally require very tight turns.)

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I like this idea, too. Keep it simple, and keep the most sensitive stuff in a box.

This bike is not a salt water ready one but might be helpful for overall design ideas.



With the mid drive so far up in the air is might not be very effected by salt spray? For 5mph you could get away without any gears I would think and even just use a fixed cog front wheel drive like this.

I am curious as to what wheels you will spec? I would think they would have to be pretty fat to be able to float on the tidal plain?

Normally, oysters are harvested with a boat.

Your harvester machine must be engineered (and adjustable) to adapt the terrain, or to pull a drag harvester. This is more like wild clam harvesting than oyster farming.

Anyway, I see it pretty high on its wheels (or caterpillars), and that is not making salt water proofing mandatory for motor, transmission and battery at least. All that could be enclosed well above the water.

Reading this a few times now, why not go with an affordable IGH for your "transmission", I am talking about them $20 Sturmey Archer units, if the gearing is right for your needs. Get the fattest tires you can, a cheaper way, and a more durable way, but adding more weight is to use motorcycle rims and tires. Just an idea.

markz said:

Reading this a few times now, why not go with an affordable IGH for your "transmission", I am talking about them $20 Sturmey Archer units, if the gearing is right for your needs. Get the fattest tires you can, a cheaper way, and a more durable way, but adding more weight is to use motorcycle rims and tires. Just an idea.

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Yeah, I think that's probably what I'll do. 3 speed Sturmey Archer, and fat tires.

I should have just said pelican case everything. Could be cheaper, plastic ammo box, etc.

Re sealing up holes for wires, the specialty caulk made for rain gutters is the absolute best, regular silicone the worst.

I got my friend who used to work as an engineer at an aluminum boat manufacturer to give me some advice. According to him, galvanic corrosion will not be that big of an issue since my vehicle won't actually be submerged, but general corrosion due to salty air will definitely be an issue. 6xxx aluminum is often mixed with 5xxx aluminum in boat building and has good enough corrosion resistance, which is nice for me since there is a much wider variety of 6061 tube available. However, as Chalo says, 316 stainless is the way to go for fasteners and other hardware. 304 stainless will corrode in the sea air.

In addition, to minimize the potential for galvanic corrosion it is wise to isolate dissimilar metals with plastic washers where possible, and use anti-seize, loctite, or aqua-lube on threads, especially where stainless fasteners thread directly into aluminum parts. I'm hesitant to use petroleum-based lubricants that can wash off into the water due to my customer's deep concern of environmental impacts, but I found something called Forespar Lanocote which is a marine lubricant made from lanolin (from sheep!).

My design points are now:
Frame: 6061 aluminum, heat treated after welding, leave bare for testing, possibly anodized if we do a production run.
Fork: Outsource an aftermarket aluminum fat tire fork.
Other components: All aluminum where possible. Replace steel or stainless 304 fasteners with stainless 316 fasteners.
Pedal drivetrain: Surly chainrings, KMC S10 chain, Sturmey Archer 3 Speed hub, custom stainless cogs bolted to flanges driving to White Industries freewheels on stainless half-axles.
Rear wheels: Precision Pedicab
Tires: 26" x 4"
Electric system: Battery, controller, and motor housed in Pelican case with downward facing holes for chain exit to Sturmey Archer hub.

I kind of like Dogman Dan's cable actuated throttle to the sealed box idea. If not that, I think I would want to use a Cycle Analyst 3 for its throttle overvoltage protection, but I'm concerned that it would not fare well in the sea air.

Still haven't settled on which battery, controller, or motor to use, but for the purposes of simplicity, low speed, and low range, I'm leaning toward 24V SLA and a small hub motor acting as a mid drive, also as suggested by Dogman. Would love some specific suggestions on this since I'm much more familiar with stuff like my personal QS205 setup.

Thanks for all the help so far!

Have you considered the use of a belt drive in this situation. Every time I hear about chains and saltwater/sand in the same paragraph, I cringe a bit.

Less metal = Less chance for corrosion.

I'm NOT heavily experienced with belt drives unless they are under my hood, but I do know that they can handle some nasty conditions.

Anyone else chime in on the pros/cons of a belt for this application?

https://en.wikipedia.org/wiki/Galvanic_anode#Design_considerations

A regular bike chain would get rusty pretty fast. I think you can get ones made from stainless steel which should work OK.
example: https://www.ebay.com/itm/KMC-S10-IN...er-Single-Speed-BMX-Track-Fixed-/371173197660
Belts are nice but might have issues with sand. The biggest problem with belts is just finding the sprockets for a reasonable price.

It will be important to get the gearing right so the motor won't be bogging down. You don't need high speed. Another thing to possibly consider is having the ability to reverse. If the motor and gear train don't have any freewheel clutches, you could reverse the motor and back up.

Another good reason to take a hub motor, which is more sealed than many other types of motors, and belt drive it down to a nice fat rear bike wheel. I start seeing something in a trike with two front fat bike wheels, a big tub mounted between the front wheels, and a fat rear wheel with a belt drive. Geared crazy low is the main reason to run a belt drive or chain.

But that does not mean something in a delta trike , with a nice fat front wheel, in 20" would not work. Schwinn trike, lengthened fork, electric wheelbarrow motor. If it bogs down on a soft spot, it will still push easy compared to taking a wheelbarrow down on that mud flat. just oil fill the hub motor, and refill as it leaks out.

dogman dan said:

Another good reason to take a hub motor, which is more sealed than many other types of motors,

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I'm happy to hear this advice, since I'm most familiar with and comfortable working on hub motors. I think a very small one will suffice for this since the additional gear reduction to the rear wheel will give us plenty of torque.

fechter said:

A regular bike chain would get rusty pretty fast. I think you can get ones made from stainless steel which should work OK.
example: https://www.ebay.com/itm/KMC-S10-IN...er-Single-Speed-BMX-Track-Fixed-/371173197660
Belts are nice but might have issues with sand. The biggest problem with belts is just finding the sprockets for a reasonable price.

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This is exactly what I'm thinking, too. Belts will be harder to source parts for, and chains will literally crush sand out of the way. That KMC S10 is very affordable. I don't know what alloy of stainless it is, but it's surely better than a standard steel chain.

haulincolin said:

This is exactly what I'm thinking, too. Belts will be harder to source parts for, and chains will literally crush sand out of the way. That KMC S10 is very affordable. I don't know what alloy of stainless it is, but it's surely better than a standard steel chain.

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Look into the KMC EPT chain. I'd also consider using paraffin wax instead of regular lube.

http://kmcchain.us/chain/z510-ept/
https://www.kmcchain.com/en/series/ept
[youtube]2uW3dxIHXK0[/youtube]

Do you want to throw money at the problem, or are you willing to put in time and effort to save money?

A custom frame out of stainless is going to be pricey. Is a trailer pulled by an ebike an option?

Do you especially want a delta trike with the box on the back, or do you want a bikefiets tadpole with the box in front (one wheel in back, two up front)?

spinningmagnets said:

Do you want to throw money at the problem, or are you willing to put in time and effort to save money?

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Colin runs a commercial machine shop. He's taking on this project for a commercial oyster operation.