Efficient electric boat

Hi Jeremy,
Thanks for the reply, i have taken note of your comments about the "at low speed" hovercraft power requirements.
During my traveling, i saw leg row boats in vietnam, they were very relaxed on them and it was an advantage to see forward while paddling.
Okoume plywood being likely the material i will use (Meranti being too expensive) with epoxy (i have not yet chosen among the epoxies systems) Noah's boat building supplies has a wide list of epoxies available. I just saw a Kurt Hughes Cat DIY built near Lake champlain on the Canuck side. The owner is happy and he would consider the Eric Lerouge designs next time around. With the KH design, he used Cylinder Mould construction technique, makes sence with PLY.
On interesting note is that i saw a design for a monohull that resembles my first approach 10 years ago being a monohull with a huge concave arch bottom all but the Bow, all the way to stern. This shape could probably be fit for a small (look like other monos) craft and could be done in either strip planking (probably heavier) or a kind of c.m. system with small "shopvac" vaccum bagging system. I purchased KH videos on the web and it is very informative.
Many years ago, my grand facther built small "not so small" row boats.
Contrary to the common designs at the time being "canoes" , he built them in wood plys (he made) with "bouchains" (i dont know the english word for it and its not in my dictionnary), with almost perfectly flat bottoms being for very low tide capabilities in shallow waters and we had almost vertical bows for high tide wave piercing. Although the wood was heavy, these were pretty fast and tracked very well. Perhaps with a concave bottom, these would have being faster when we tried sails (laser 1 gear) and later 20 hps outboards.
They were faster than the first fiberglass fishing boats. They rotted overtime after being used for hideouts for duck and goose hunting.
Catamaran inflated dinghies are fast and furious, this could be interesting and the photov. cells could be under a transparent bottom (saw that in Pompano FL) and on part of the top of the tubes. In architecture, usually, if it looks like "form follows function" it looks good and it performs good.
To reduce solar charge time, you can also consider a roll up floating system that would charge while in lunch break ... and even a solar dodger/bimini to protect against uvs.
So many possibilties R&D and so little time.
There has been headlines and warnings issued on the effect of magnetism and health. I am really keeping an open ear on the subject.
There has been discussions on the effect of high tension lines related to children leukemia, one of the reply was that the closer they lived from them, the poorer they were hence the less healthy they were ... i guess the difference between 100 m and 600 m makes all the difference in wealth ...
By the way, if you plan to be on rivers with currents, it could be an idea to combine wind/water turbines, i will with the tidal currents (5 - 6 knts) and they come every every day /night, with predictable time charts. You can probably gismo a regen motor and use the same prop ...
There is a new product on the market (havent seen it yet) that is apparently derived from the paddle windsurf , it is beleived to be fast. West Marine sells something ...
I used my fins on my Cat when no wind last wkend, it was faster than my "mandatory" useless row. Unfortunately i had to sit on the stern crossbar and it was "whellying" too much, should have been two on board for balance.
It was good exercise ... and fast and furious.
The Hybrid Watercycle is about to be born ?
Mike (Yellow Cat is my nick name ...still sticks)

 

Jeremy, first let me say that it's a pleasure reading about what you're up to. There aren't many folks who do as professional a job, even fewer who are as careful with their testing.

Second, I wanted to provide a piece of information you might find helpful. We humans tend to be linear thinkers, by that I mean that most things in our personal experience are linear in nature and don't resemble an exponential change of any kind. In my work in the computer business I'm constantly running into places where people can't really internalize a non-linear change.

The reason I bring this up is your comment (above) about initial stability vs ultimate stability. If the stability of a boat is quite low initially, most people will assume that it will remain low, they assume linearity in stability. As many of us know there are extreme non-linearities in stability of boats, particularly ones with bits of the hull that aren't in the water and then are submerged as something happens in either pitching or rolling. I think you'll find that a boat with little stability, initially, and a great deal of it later on will still have its sailors a bit panicked. For exactly the same reason, a multi-hull with massive initial stability and almost none later on has the opposite effect, providing a false sense of security based on that initial stability and the sailors tendency to assume that stability is a linear function.

Thanks again for a lot of great posts,

Beau

 

Jeremy,
On stability issue.
Beau's post is quite on the money. For example, i designed a bldg that had large archiving areas, so, we designed the building with large live loads that behave like dead loads. Consequently, the tenant has decided to add dead weight to the structure because thay have decided to put less archiving into this particluar bldg. The structure was so strong that it created a sence of instability because of its arching up. With the dead load added up everybody is happy feeling stable. The same applies to boat stability, center of gravity being of essence, the more weight added to the lowest and centerest point will likely bring more stabiity. This not new to the monohullers. This is relatively new physics to the multihullers "user end" and, multihull designs have to take that into account. By virtue of intuition, the reverse bows dont make sence, but, with a specific program, it does. In my books, the instability of any sailing vessel (motor as well for most) comes from its resistance to move in a direction, i call it the stall, and you capsise. Yesterday we had a good example of that ... wont elaborate ... one would normally fear more speed for instability, on the contrary, the more initial speed , the less capsising effort will be generated , up to the point of drag and pull down forces. This is where the foils come into place, on the large trimarans, they are exactly using the "variable goemetry" of efforts. Masts angles, foils, ballasts, sail config, etc.
Hydraplaners (like a sea plane ) have a "redan" shape and disperse the energy sideways so that the water "attraction" doesn't overcome the forward forces. see mediatis parlier's hydraplaner on web. I saw it dead on coming towards me at full speed and this thing was ready for take off. At slow speed it seems unstable generating turbulence.
Hence the large difficulty for a designer is to create a linear behavior stability by adding stabilizing elements. Thereby create a user instruction manual for different situations. Formulas and indycars have to deal with these forces at each race situations.
The new kiting sailors will have lots of fun dealing with surprising potential of variable situations created by the elements and by the sailor. The "crash and up" allows to go up almost facing the wind, the heavier the sailor, the better... the first time one experiments it or sees it happenning , he goes "aw" . With the no wind feel and see the kiter pass by at 20 knts ! they all want to try it. Stability and wind range is at the top advertizing list for kite sales. You can see some of it on youtube if you seach for silverarrow speed low end wind.
Back to the original idea, "unacceptably tippy for leisure cruising" ; if it feels wrong, it is probably wrong , or, wrongly used.
Isn't R&D rewarding when one gets it right ... rebel thinking is quite often the only way out.
Welcome to the head killing world of designing from scratch ... compromise, always compromise ...

 

Thanks for the useful input, guys. I'm fairly comfortable with the a boat that has low initial, but high secondary, stability, as my old yacht was a bit like that. It always felt a bit tender until it heeled over, where it firmed up and felt very solid indeed. I got used to it, and tended to drive her hard because of it; my crew didn't, and always felt nervous. My guess is that she just didn't have enough confidence in the boat firming up as she heeled, so always expected it to go beyond the point of no return.

My crew most probably had the "linear thinking" mind set you describe, probably because her background was light dinghy sailing, whereas I learned to sail on a big, heavy, gaff rigged oyster dredger and was used to sailing a boat that was massively over-powered, like this:


A colleague, who also designs aeroplanes, often describes R & D as "Rip-off & Duplicate". I'm inclined to share his view sometimes, as we often seem to end up re-inventing ideas from long ago.

Anyway, I've realised that I've not mentioned the electric controller side of this project much. The controller I'm now using is exceptionally good value. It comes from China (what bit of electronic kit doesn't nowadays) and is available on eBay (don't laugh......) for just $22 (US) plus postage. It's an amazing bit of kit, intended for use on electric bicycles (which are very popular in China, I believe). The great thing about it is that it's programmable, it has an on-board serial interface that allows key parameters to be changed easily. Interestingly, it includes a regeneration capability, so if this is activated with the boat moored in a tideway or stream the motor can be used as a generator to re-charge the battery pack. It's more versatile than the RC model motor controllers, as it has an easier throttle control interface and a simple reverse control.

Jeremy

 

Hello
Is there a simple formula that I can use to calculate the range of an electric boat?
I know there is a formula used for airplanes and ships, but that is not useful for electric vehicles 'cos the weight stays the same. I am also a bit confused about the specific fuel consumption that is needed in some formulas. What is the equivalent for electric systems?

I think that I will also need some sort of propulsive coefficient to use in the equation.

Are these sort of factors available for a few different electric motors, batteries and propellers so I can compare them?

Sorry to ask so many questions in my first post.

 

Calculating range is straightforward, the snag is knowing enough about the variables to be able to get a meaningful answer. Here's an example, using my design point (which is for a very light, low speed, low power, inland waterways day boat, so an extreme example):

Power needed to drive the hull at design speed of 4mph = 40 watts (derived from a worst case estimate based on hull resistance predictions, with about 20% added for good measure).

Motor and controller efficiency = 85% (derived from motor and controller specification)

Propeller efficiency = 70% (derived from prediction using Javaprop).

Electrical power required for cruise speed = 40 watts x (1/0.85) x (1/0.7) = 67 watts (rounded up to 70 watts)

Battery pack rated voltage = 36 volts

Battery pack rated capacity = 10 amp hours

Theoretical battery power capacity = 36 x 10 = 360 watt hours

Battery pack Peurkert factor = unity (this is a measure of the deliverable power for a battery and depends on battery chemistry and discharge rate. The LiFePO4 battery I'm using delivers its full rated power, a lead acid battery may only deliver 80% of it's rated power)

Available battery discharge capacity = 360 watt hours

Endurance = 360/70 = 5.14 hours

Range at 4mph = 4 x 5.14 = 20.56 miles

The same basic approach will work for any battery powered craft, irrespective of size, as long as you know the key variables, such as propulsive power, battery capacity etc and can estimate the efficiency figures. In general 80% is usually about right for the motor/controller and 70% should be reasonably close for a decent prop.

Hope this helps.

Jeremy

 

Thanks for a very clear explanation!

I need to consider two speeds in my design. A low speed for putt-putt-putting around, and a higher speed for dashing back to shore. I will have a look at Javaprop to see if it can give me offdesign performance coefficients.

 

You'll find that the low speed power requirement will be much lower than the high speed requirement, due to the approximate cube law power vs speed relationship that prevails for displacement speeds, so, the prop/motor combination will need to be optimised for either high speed or low speed, depending on the battery capacity used for each condition (the combination of power and time for each). Even if you only spend a short time at high speed, with a much longer time at low speed, you may find it better to optimise efficiency for the high speed case and accept the efficiency reduction at low speed.

As well as the hull resistance and prop efficiency changing with speed, you'll also find that the motor efficiency will change, too, particularly if you have a big difference between the two operating conditions (say a 4 or 5 to 1 speed ratio between "loiter" and "dash" modes). Most motor manufacturers publish curves showing this, but a good general rule is that electric motor are most efficient over the mid to upper speed rpm and lose efficiency at very low speeds. The same is true of the transmission and bearing losses; these are often fairly constant, so can be a bigger proportion of the total power at low rpm than they are at high rpm.

Depending on the size and type of vessel, plus the time spent in the low speed "loiter" mode, you may find that this is an ideal application for solar or wind power assistance. You may be able to gain enough extra battery charge during the low power operation period to provide much of the capacity needed to undertake the high speed dash. This might then reduce the size of the battery pack required, so reducing weight.

Jeremy

 

There are some seasonal factors I am trying to build in. I know how much sunshine is available at different locations and I know how much time is spent at low speeds and at high speed during those seasons.

All I really need now are curves of performance over a range of speeds for a variety of electric drives and propellers but I can get that from manufacturers specs.

Thanks again

 

Hi, first post, but have been following this thread for awhile. Thanks for your simple explanation of range calculation. I think I see what you mean about the difficulty of getting a meaningful answer. Like when there are factors of considerable wind, current, weedy water or low temperature,these calculations would be off, is what I think you say. Guess its best not to take these factors directly if possible... Like they say in water survival, conserve heat and do not exhaust yourself fighting current, but move diagonally with the force to reach your goal.

Porta

 

I've just been pointed to an interesting web site by one of the helpful posters on the "Song of the Paddle" forum:http://www.dippy.ca/index.htm

The neat thing about this idea is that it could be brought up to date and simplified a great deal if electric power plus the flexible shaft innovation that Rick has described were combined.

Imagine a lightweight composite internal housing, rather than the big casting in the original, with a low speed electric motor fitted above the waterline and directly coupled to a thin flexible shaft. The complex pivoting skeg/bearing could be replaced with an inclined sliding skeg, holding a PTFE bearing.

The advantages would be that the drive train losses would be low, due to the absence of seals, gears, etc and only one bearing (other than those in the motor), plus the prop could be swung up to allow grounding or weed clearance. The prop could also run parallel to the flow, which would reduce vibration and slightly improve efficiency, perhaps.

The only downside I can think of is the possible adverse effect of turbulence around the opening, but perhaps this could be alleviated by having a cover arranged to pivot up and down to close the hole off when the prop is fully down.

I may have some news on the hull front soon, as I'm off to see a helpful chap about in a week or so to discuss it.

Jeremy

 

I have a inboard Monterey with a Penta Volvo Engine in Faro Algarve Portgal.
I use may boat just in inside waters Ria Formosa to go to the beautifull beachs we have here.
I´m warried with the presarvation of nature, and I would like to transform the propusltion of may boat do a electric engine, solar or not.
Mário Fernandes

 

Transforming a gasoline inboard on a electric inboard

I have a inboard Monterey with a Penta Volvo Engine in Faro Algarve Portgal.
I use may boat just in inside waters Ria Formosa to go to the beautifull beachs we have here.
I´m warried with the presarvation of nature, and I would like to transform the propusltion of may boat do a electric engine, solar or not.
Mário Fernandes

 

Mario
What size/model Monterey?

What speed do you want travel at?

Rick W

 

Efficient boat design suggestion

Hello Jeremy,

We exchanged a couple of PMs on the WoodenBoat Forum a few months back. I just read, with great interest, your postings in the Hall sensor thread at Endless Sphere and the efficient boat design here.

Check out http://www.lunadadesign.com/strider.html Chris Ostlund has a sleek looking design that pretty much adresses your design brief. (Looks quite similar to Winsome from Swallowboats) The Strider described in the video is reported to weigh 90 lbs so it is close to your target weight. The builder says he can maintain a 3.9 kt speed for two hours pedalling so the power-speed relationship ought to be in your ballpark as well. You can buy plans at http://www.duckworksbbs.com/plans/ostlind/index.htm

Any actual sea trial data to report yet for your right angle drive? Your motor mods to get appropriate torque and speed for direct driving a prop is brilliant.

Assuming you are going to use 12v, a Kt of 124 would give 1488 rpm and 1190 rpm after the right angle box. That still might be too fast for an 8" pitch prop. Assuming 50% slip an 8" prop would be turning around 660 rpm at 5 mph. My Mars BLDC motor/Sevcon PMAC controller loses quite a bit of RPM with load; from 2320 RPM with the prop out of the water to 1480 rpm in the water and pulling 95 amps. Do you see a similar effect with your Tower 5330?

I see that the RC industry sells little planetary transmissions for some of the motors. Had you considered those?