Power requirement for 10m canoe

Thanks for the tips! This is a capstone project for our school. It was a bit bait and switchy. Initial problem statement was to retrofit an electric engine onto a boat. Easy. Well, the scope has....shifted and now we find ourselves in the current predicament.

This isn't so much a fleet as of yet, but they do want to be able to replicate the design in the future.

Using an existing design is fine, I guess, but outright paying a designer probably wouldn't do. We're on a shoestring budget to simply design the thing.

 

It is a pretty simple business. The hull can be displacement, in wich case speed is governed by lenght, planing, where you need ample power, or very narrow (over 8:1 L:B ratio). Narrow hulls can pose stability problems wich are usually cured by going multihull.

You need a certain amount of power to reach 11kn regardless of hull type. To operate for 2h you need to double the necessary kW's to arrive at the battery capacity. If for example the boat requires 10kW you need a 20kWh battery. Then you need some way to recharge it in the available time. This means either enough solar for direct charging, or an additional battery as intermediate storage.

Can the problem be solved, yes it can, but something has to give. If you keep lenght and speed, it either planes or is a multihull. You are not going to achieve 11kn with 1-2kW of outboard, regardless of hull type.

Just to be clear, 11kn are 20km/h, wich means the 2km run takes 6min, and a 2h runtime means 20 runs. Do they actually need this speed?

 

20 kmh is what they are asking for. As an option for improvement they are even asking for 25 kmh. I guess the community has actually been gifted boats in the past by donors, but when the boats failed to reach speed, they were rejected. This seems like an astonishing denial. Up until the 70s this had been an unc0ntacted tribe, so it would seem the conveniences we desire are very different from their priorities.

This is, for the time being, a boat being made for the eco-lodge and not the community, so when we lay bare all of the intricacies of what they're asking, there will hopefully be some re-alignment of the constraints.

Multi-hull isn't out of the question, but the width of the river becomes a limiting factor, and perhaps maneuverability as well.

They are very explicit that they don't want a roof. Their would obviously make guided boat tours far more difficult. This, however, negates the ability of roofed solar panels. The option, when we thought we'd be dealing with much smaller engines, was to simply store multiple batteries onboard. Given the size of the engine, the battery space demands may be too much to be able to hold multiple on board.

 

The first boat in fiberglass is really building three, so it is not economic. In general it takes maybe 5-6 boats to break even when compared to a plywood/fiberglass boat. Capstone projects do get out of hand. Mine started as a test for a shipping box for GE Medical and turned into a machine to crush-test packaging to comply with international regulations. You can get a flat bottom boat to do 11 knots with relatively low power. However, it will probably rattle the fillings off your teeth. It would be uncomfortable and dangerous for the passengers. Designing a successful boat is not easy. Can you go back to retrofitting an electric motor? That in itself is a fairly complicated design. You need to match a motor to the application, specify batteries, design a power management system, design or specify a charging system, speed control for the motor, match a propeller to the torque/power curve of the motor, specify the physical installation of the batteries with cooling, cabling and connections. I would narrow it back to what you started with. As an engineer, sometimes you need to stop the customer from adding unreasonable extras. The design of a boat is not something that can be done in a semester. From what I gather, they did not give you the operating parameters of the boat. It is like if someone asks you to design a truck, but doesn't say if it will operate on the highway, muddy construction sites or a pit mine. For example, is the boat going to be in a shallow river, a lake or the ocean? I am not trying to give you guys a hard time. It is that people have put me, or I allowed them to put me, in similar situations.

I just read what you posted while I was typing. They seem totally unreasonable.

 

We do have some parameters that I haven't really explicitly stated yet. This will be for use on the Amazon river in Ecuador. There is little current that we need to account for and the river path is very wide and over 30' deep. There are some debris considerations. I guess they've ruined one of their electric engines already by going over a tree branch. Dugout canoes have been the historical method used by the indigenous communities, but even they are opting for more conventional methods (by our standards).

As for the project itself, I think that maybe the constraints weren't properly relayed to our school sponsor/liason to begin with. This was originally going to affix motors to those dugout canoes as it was described to us by our school's sponsor. That is absolutely not the case once we got in contact with our client. At no point during this process since working with this Eco-lodge have they directly intended for this boat to even be used by the locals. The locals have virtually no direct benefit from it. So, in short, there's no way to backpedal, because there's no back to go to.

Trying to design the boat from scratch is pretty much a non-starter for all of the obvious reasons. It seems likely that a solution to our problem already exists, but it's just a matter of finding it. Essentially, there has just GOT to be a boat plan out there that satisfies our requirements. It's just a matter of discovering the resources.

Also, we have until next spring to finish this.

I totally agree on the unreasonable part. I find it hard to believe that the solution they have now, essentially handheld gas motors, are operating to these standards

 

It sounds like your clients are not really too sure themselves as to exactly what they want, especially re their conflicting requirements.

Could something like a very simple, large 'jon boat' work?
If you omit the cabin and accommodation on this design in the link below, it might have a reasonable cargo carrying capacity?
https://www.boatbuildercentral.com/product/gt-cruiser-27-boat-plans-gt27/

 

The laws of physics don't care what a customer demands.

 

They demand a canoe, which is not the best hull for planing. Also, it will need a lot more power than requested.

 

Consider a search of long tail boats in Thailand, which can deal with some of the debris issues, but they may not meet your low power requirement if you need a high speed? Not sure if they can be done in fiberglass, though.

Traditional Longtail Boats For Transport On Beach, Krabi Province, Thailand Stock Image - Image of beach, coastline: 71490801 https://www.dreamstime.com/stock-photo-traditional-longtail-boats-transport-beach-krabi-province-thailand-image71490801

 

In that case you build from free plans, which have no tech support and may not be good. It is a rather bad choice. You are at a point where the options are to fail or to renegotiate and tell the sponsor that you will limit the job to the original request.

 

I expect the sponsor understands about as much as the OP when it comes to electric boats. Unless he is willing to part with a minimum of 50k$ for the propulsion package alone, it's not going to happen.

Since this is some sort of school project for you, the simplest way to access the required knowledge for free is to partner with another school that offers courses in naval arhitecture. Hint, if your location is correct you have one in town.

To electrify a dugout all you have to do is design a sidemount for a chinese trolling motor. If you want to do more than this you design a sidemount longtail motor based on components commonly available in the area.

 

The OP has a problem. From the SOR we can pinpoint it to between the customers ears. This is the state of the world -"if dreams were boats we'd all be sailing". The OP states that he has the engineering talent and needs boat design specific. I think what he needs is some reference points to present.
Reference 1 -a 10M canoe with the cargo specified needs (X) volume and weight of batteries to go 11Kn for that many hours (heavy, expensive to the point of sinking the project)
Reference 2 -an optimized planing hull for the 20km/h (a little less expensive)
Reference 3 -A freighter canoe optimized for the load near displacement speed (lower speed, far more reasonable cost and upkeep)

I don't know anything beyond what is printed here, but this looks to me like some do-gooders dreamed this up and gave some forms to the local tribe who passed them around to get the dreams of many different tribesmen. It may well be that the reason it must be a canoe with no roof is so that when this fails and the tourists go away (like always) the tribe boat kahuna (who answered that question) will have a hull that the tribe can paddle around fishing. And the reason it must go 20km/hr is that's what the resort guy wants to say to prospective customers (that way it's the same as a drive through traffic to another resort).

I would also give this advise to the OP ;These wonderful plans always fail on "sustainability". The requirements are dreamed up by people who will not be paying for anything, just living with the result. Ultimately this is a customer experience at a cost. They don't think in terms of "if the boat costs too much there will be nothing left to pay the captain".
For this to make it to reality you will need to find someone responsible for that customer experience and cost.

 

It simply can't be done. However, it is a good lesson for engineers. Don't let the customer corner you into promising a project that it physically impossible.

 

I don't understand why that project is physically impossible. I already know that for that length, at 16 knots, the boat should plane, if she had the right shapes. If she doesn't have them, she won't plane, but that happens to a lot of boats that size. The speed of 20 knots will not be optimal from the point of view of energy efficiency, but that does not make the project unfeasible and, furthermore, the normal thing is, probably, that the cruising speed is about 15 knots, below the theoretical planing speed.
I think it's worth waiting for the boat's detailed SOR before discouraging the OP by telling him, I don't know why, that his project is unfeasible. Like any other project, his will be a mix of SOR requirements that can be met and others that cannot.

 

All that Gonzo is saying is that it is not feasible with the current 'Statement of Requirements' - which appears to have conflicting desires.
Maybe we can help @DBarg to develop a more 'realistic' SOR for what they want to do?