Electric Hull Designs

[Matt76]

Would everyone agree that the canoe is the most efficient hull design?
Could we also say that the hull design is best for electric power?
If so, should i be looking for a multi-hull design if i want to carry more weight for the batteries?
I'm shooting for at least 12 knots, if not more, powered by a Perm132, 72volt electric motor. Small lake usage.
I've been reading all kinds of articles and web sites about this. Phil Bolger's hull designs are said to be good in having very little wake. He achieved this by making the curve of the bottom of the boat the same as the sides.
Isn't that what a canoe does?
The multi-hull designs i've seen, seem to be really flat on the sides, sharp angled. Shouldn't they be more like a canoe, round, soft curves?
Does anyone have any examples of multi-hulls that would work for me?

[Thorne]

Way too many questions at once, and many have been answered in your previous post on the contender hull.

You seem to be re-inventing the wheel here -- if you look at a number of electric hull designs and none are multi-hulls, why assume that a multi-hull would be good for the extra weight? In fact the opposite is true, as multi-hulls are often fast and stable, but not good for carrying lots of weight.

Rather than assume that all previous electric launch designers/builders were wrong, why not assume that they were intelligent, competent individuals who knew what they were doing? That way you can learn from their mistakes, benefit from their research, and save lots of time and money in the process.

What you will discover is that electric boats have a very high propulsion system/boat weight ratio, MUCH more than the paddle on a canoe, outboard motor on a skiff, or inboard motor and fueltanks on a runabout. So for an equal distance/time/speed result, an electric boat will be heavier than most other propulsion-system boats. This means that most larger electric designs trade distance for speed, and are often too heavy to trailer -- they live in the water.

If you join the Yahoo Electric Boats group, they will be able to answer many of your questions, or at least point you to existing electric launches that are close to your design specs. They can also recommend various electric motors and systems -- I think the eTec is the current favorite for relatively high-speed use. Subscribe: electricboats-subscribe@yahoogroups.com

But I seriously doubt that you can have a "lightweight lake cruiser" that will do 12 knots over any real distance or time!

To answer the last one, go to the undesired thread that you created, click the EDIT button and select DELETE in the next window.

[Matt76]

don't get upset Thorne,
I don't have any experience in hull design, that's why I'm here. I also never took physics in school.

I'm not assuming that all previous electric launch designers/builders are wrong. I'm just saying a majority of them build to accommodate a lot of passengers and top speeds of maybe 7knots, for eight hours. and a lot of them are 16 to 20 foot long. I just need two passengers and want to get the most out of the motor set up. I figured i could replace the passenger weight with batteries. I also thought i could get more buoyancy with larger bulk heads and foams.

I'm learning.

Thanks with the help on editing.

[P.I. Stazzer-Newt]

Would everyone agree that the canoe is the most efficient hull design?......

No, I would not agree with that statement.

Maximising hull efficiency, by which I assume you mean speed for a given power input, is a very specific task and produces hulls very carefully matched to the task.

Contrast the racing hydroplane with the olympic rowing regatta very very different, but each might be considered "the most efficient hull" - and I'd fancy neither as a cruiser.

[Matt76]

http://www.electricrecordteam.com/

if these guys can get to 70mph for even ten seconds, then there should be a way to achieve 10-12 mph for a half hour or so with the right hull and motor set up.

Take a look at this site, he was able to achieve a little over 10mph, in a 26 foot Sneakeasy.
http://www.psnw.com/~jmrudholm/etekoutboard4.html (http://www.psnw.com/%7Ejmrudholm/etekoutboard4.html)

If i could match this performance in a hull with a max length of 16 foot, i would be happy. Theres even more efficient motors out there too. Cost you an arm and a leg. I think it's worth it if i could find a hull that will work well.

I understand i'm not going to be able to get the hull to plane. But these motors can produce some good power. I don't need to be able to run for long, small lakes, 40-140 acres. And i wouldn't be running around full throttle, it would be nice to be able to throttle up, and pass a neighbor, maybe impress a lady.

I was also thinking one of these may work.
http://www.boatplans.dk/boat_plans.asp?id=41

any thoughts? thanks for all the replies.

[Lewisboats]

The shorter the hull the wider it has to be to handle the weight. The wider it is the harder it is to drive through the water. Where he sees 10.4 mph you might only get 7...carrying the same load. You are up against physics and physical properties...throwing more power at it just won't work unless you have the proper hull shape to plane...then you need more power than you can carry batteries for and still get the speed to plane...you are up against the limitations of electrical storage...too much weight for the power available. The only way to overcome this is with length...and a carefully shaped hull that is slim and has as little resistance as possible. It only takes a few hp to push a long hull to it's top speed which goes up as the hull gets longer. It is a relationship between the length of the hull and the wave shape it generates going through the water. The shape of the wave is related to its speed and the boat reaches diminishing returns when the bow and the stern are level on the crest of the hull wave with the trough in between. Once you go faster the wave trough gets longer and the stern starts to go down into the trough, the bow tries to climb the bow wave and the power required goes up exponentially. You can tweak this with hull shape so that certain shapes will go faster with the same waterline length but there a point of diminishing returns with all displacement hulls. Pushing past this point requires relatively enormous power in a light weight package with a hull shape that provides lift to semi plane or get to full plane. Basically you are stuck...have a short hull that can carry all that weight and is limited to a slow speed or go long and lean (still able to carry the weight because of the length) and increase your speed to the maximum available. Obviously it is possible to go fast on battery power but the cost does the exponential thing along with the power. That record hull is probably carbon fiber or kevlar or both...costing in the 6 figures...the motors probably run 4 figures apiece and the batteries are probably a many hundreds each. The design has a FEW NAs working on it and plenty of costly tank testing to obtain maximum performance. Unless you want to shell out a chunk of bucks to have One NA work on it...one who has some experience with electric propulsion on top of that...then you will have to go with what is out there and that leaves the alternative of...long and slim.

[Matt76]

so when i look at a particular hull, i need to determine what the maximum hull speed is first? then calculate from there?

whats the easiest way to determine max hull speeds if their not listed in the boat specs?

[Lewisboats]

so when i look at a particular hull, i need to determine what the maximum hull speed is first? then calculate from there?

whats the easiest way to determine max hull speeds if their not listed in the boat specs?

A rule of thumb is 1.2 to 1.8 or so times the sq root of the length of the waterline. The multiplying factor depends heavily on the shape of the hull as the water sees it. This is for non planing hulls. A short wide hull with fuller ends and deeper draft will be on the low side and a long lean shallow hull will be on the high side. an example is the sneakeasy in your link. He ran at about 1.79 times the root of the waterline length. Go shorter, fatter and deeper (to carry the weight and maintain stability) and your multiplying factor goes down quickly. If you try to be as lean at the shorter length it will be highly unstable and won't be able to carry a fraction of the weight needed.

[Lewisboats]

I see that the folks on Boatdesign.net are telling you the same thing...just in different terms.

[Matt76]

thanks for the help steve, i'm getting the idea.
take a look at this one.
http://www.stillwaterdesign.com/pages/18Solo.html

this seems to be a good design for what i'm looking for. the only
thing i've found close to this in plans is the 15 ft row cat from boatplansdk.

any ideas where i could get plans like the stillwater 18?

[Woxbox]

If the waterline length to beam ratio is 1:12, and the bottom is nicely shaped and clean and shiny, you ought to be able to get as much as 2x root of waterline length out of your boat. But that's a monohull. If you make a catamaran, don't kid yourself, you've now got two hulls to push through the water.
So for 10 knots, you'd be looking at a single hull 25 feet long at the waterline. (Root of 25 is 5, times two = 10.) There's no escaping the math. (And this hull would only be 27" wide on the water -- a long canoe).
Thorne is right about the weight of an electric drive compared to gas, but go farther back in history and look at the old steam launches. Also very heavy engines for their output. The boats they drove were quite elegant.
Someone was selling old fantail-style hulls for electric propulsion a few years ago. I don't know if they're still out there.
But if you want maximum speed, you've got to start with the longest boat you can manage.
But why the preocupation with speed?

[George Roberts]

Length does not matter.

1/2hp will get a several hundred pound boat + crew up to 20mph. That determines the motor size.

So figure 700 watts for 12 hours for power - 9000wH. That determines your battery size. 150wH/kg of battery - 120 pounds of battery.

Motor and prop under 40 pounds. Hull under 50 pounds. Crew weight 150 pounds. 360 pounds total.

I can put one together in 6 months using off the shelf parts.


---

We don't use boxes around here.

[Woxbox]

OK, George, name that boat!
1/2 hp. is basically a trolling motor. And you're going to reach water skiing speed with it?

[George Roberts]

1/2hp is all a human powered aircraft needs.

---

Water skiing requires a greater power output.

[Ron Paro]

1/2hp is all a human powered aircraft needs.

---

Water skiing requires a greater power output.

:confused: What? :confused:

[paladin]

That's basically true about the aircraft....but water is 800 times more dense......:D and the speed of the aircraft was not great, just a lot of lift for the weight.....

[P.I. Stazzer-Newt]

OK, George, name that boat!
1/2 hp. is basically a trolling motor. And you're going to reach water skiing speed with it?

Decavitator (http://lancet.mit.edu/decavitator/)

N.B. it dont weigh all that much.

[Lewisboats]

OK...lets get real here...he wants to be able to carry a passenger and tool around a lake...I doubt he wants to spend a ****load of money for an experimental boat using exotic materials that is damn near useless

[P.I. Stazzer-Newt]

OK...lets get real here...he wants to be able to carry a passenger and tool around a lake...I doubt he wants to spend a ****load of money for an experimental boat using exotic materials that is damn near useless

Bang on. all the talk of "most efficient hull design" is very misleading - as are the speeds mentioned "at least 12 knots".

At 12 knots, on the "small lakes, 40-140 acres" - you run out of lake in less than six minutes.

It might be worth setting down a list of what is wanted and why - and then prioritising the list - this is entirely personal - when you talk of "making good time" is it the speed that matters or the quality of the individual minutes?

[Lewisboats]

What is the shaft hp of your motor? And you do realize that you are looking at about 250-300 +/- lbs of batteries to supply it, plus up to 2 people (americans @ 180 each)(360 lbs) and the motor weight (?) and the hull wt to support all the other weight (at least 150 lbs)...so...about 850-900 lbs. Thats roughly 14.25 cu ft of displacement in a 16 ft boat. You wouldn't want it very deep...say 4" so that leaves a beam of around 4 ft in a hull that looks like the first picture. You aint gonna get no 12 kts/13.8 mph out of this I don't care how much hp you push it with. Anything you do this hull other than lengthen it and narrow it (at the same time) will increase the resistance and therefore the speed. Max hull speed for this would be about 5.5 kts...strictly displacement. Narrowing the beam amidship and widening the beam aft to a planning skiff shape of say 39 inch beam bumps up the displacement at 4" draft just a smidge to 925 lbs but you have just increased your drag and resistance significantly at sub planning speeds. This hull would plane if sufficient power were applied...but I don't think you would have it with your motor and it would take more power to get it to the same hull speed as the first hull. However...I think you might have the excess power to push this to a faster (sub planning or semi planning) speed but I still don't think you would even reach 10 kts (considered planning with this length hull)...perhaps 7.5-8 kts or so. I would expect this to boogie pretty good with a 10 hp though. If we went the other way you might be able to hit your target speed with a small (8 ft) very wide hydroplane...but then you would have severe issues with where to store the batteries and the weights involved. Light weight Li ion batteries would probably do the trick...provided Bill Gates is your very most favorite uncle. Play with these hull shapes all you want...you are going to run up against Plysics or Money.


http://angelfire.com/ego/lewisboatworks/Stuff/Step1.JPG


http://angelfire.com/ego/lewisboatworks/Stuff/Step2.JPG

[Matt76]

I'm still here, i'm reading everything everyone has to say and researching the advice.

My over all length can't be over 16 feet (because of the size of my shop)
Up to 500lbs of batteries if needed (at least 300lbs)
Two passengers (no more)
Maybe 50 lbs for the motor 72 V Performance
Peak efficiency: 88.6%
Peak power: 34.3 hp
Cont. power: 8hp
No-load speed: 3590 rpm
Stall current: 1440A
Stall torque: 200 ft-lb
Cedar Strip and fiberglass construction (i don't like plywood, i'm a stripper, i know the cost)
Small lake usage only
I want to be able to go as fast as the hull and motor combination will allow
I want to be able to have her completely decked except the cockpit, batteries and motor will be under a hatch with cooling fan Thank you for all the advice, I'm learning more and more. I'm aware i'll need to spend maybe $5000.00 in motor, batteries, controllers, chargers, prop, ect. And probably another $2000.00 in wood, glass, and hardware.

[P.I. Stazzer-Newt]

You could do worse than contact Paul Fisher
http://www.selway-fisher.com/Mcanoe.htm

He has in the past taken his designs from Stripper to Stich-n-glue or vice versa - to suit an individual client - similarly longer or shorther to suit....

I've heard of people asking for a 16 footer in two halves for ease of build...

[Lewisboats]

I'm still here, i'm reading everything everyone has to say and researching the advice.

My over all length can't be over 16 feet (because of the size of my shop)
Up to 500lbs of batteries if needed (at least 300lbs)
Two passengers (no more)
Maybe 50 lbs for the motor 72 V Performance
Peak efficiency: 88.6%
Peak power: 34.3 hp
Cont. power: 8hp
No-load speed: 3590 rpm
Stall current: 1440A
Stall torque: 200 ft-lb
Cedar Strip and fiberglass construction (i don't like plywood, i'm a stripper, i know the cost)
Small lake usage only
I want to be able to go as fast as the hull and motor combination will allow
I want to be able to have her completely decked except the cockpit, batteries and motor will be under a hatch with cooling fanThank you for all the advice, I'm learning more and more. I'm aware i'll need to spend maybe $5000.00 in motor, batteries, controllers, chargers, prop, ect. And probably another $2000.00 in wood, glass, and hardware.

proposal...just a sketch now but it might...just MIGHT mind you...run to what you want. The LOA is 16.2 ft...and Max Beam is 4.087 ft (4ft 1 in), the beam at WL 44.75 in, with a disp of 1100 lbs (if need be but less is better). The decks would be of 1/8" ply, the sides of 1/4" and a whopping 3/8" for the bottom if possible...(it might not be due to the bow forefoot). Some minimal framing of spruce would be in order... the lighter the better. This design should let you run two people to about 10 mph in ( if I do say so myself...) SOME style (enough to catch the eye of a lady or few I would bet... for a pass or two at least) and still provide a few amps to limp home on.... Provided the available HP is enough to put the hull shape on plane...once on plane the hp reduces to about .666 to keep it on plane. Semi Plane is a grey area and subject to more experience than I have in this area.



http://angelfire.com/ego/lewisboatworks/Stuff/Step3.JPG

today it is beer!

[George Roberts]

P.I. Stazzer-Newt ---

Just put a bit of electric power to it. Make the passenger more comfortable. All off the shelf parts.

[Lewisboats]

P.I. Stazzer-Newt ---

Just put a bit of electric power to it. Make the passenger more comfortable. All off the shelf parts.

It would need a tad more than 1/2 hp to push THIS through the water at speed....

[Lewisboats]

I betcha it would just rip with a 15 hp motor...or better yet a 25. Still...thirty somethin' to get it on plane and 10 or so to keep it there...nice cruisin' on less amps!

[Matt76]

read this page about hull designs
http://www.electricboats.co.uk/hullform.html

the whole site is great

[P.I. Stazzer-Newt]

read this page about hull designs
http://www.electricboats.co.uk/hullform.html

the whole site is great


You're right - its a nice site - two of the designs on it are from the Selway-Fisher stuff linked above.... and all of the designs are for UK inland waterway use - either the Norfolk Broads, of the Thames.
So these are 6 knot cruisers NOT 12 knot - these are hull forms which are efficient within these parameters - try to drive them at 12 knots and you'd want a very different shape indeed either short wider planing forms, or the pencil thin form of an olympic scull, or most radically something foil-borne.

What do you want?

[Matt76]

i wanted lewisboats to read that page to help with the drawing. it has a lot of good points about hull shapes.

[Lewisboats]

yeah...but you tell me your motor is peak 34 hp and continuous 8hp...so I give you a shape that can use that overpower to get to around 10 mph in a semi-planning mode....that's what you wanted isn't it. the shapes in the short boats on that site are DISPLACEMENT...THEY AIN'T GONNA GO FASTER THAN HULL SPEED.

[Matt76]

I think i could make that work, and i know i could make her look nice.
I'm wanting to cedar strip and fiberglass her. i understand the savings in time and money when using ply. but i can do a lot of detail work with the strips and still make her lite and strong.

If i decide on an inboard set up, where should the prop shaft exit the hull? Is it even possible with that design? some of these guys props their using can are 10 to 12 inches in diameter.

again i don't know anything about hull design. she's so flat, straight sides or freeboard, hard corners. Are you limiting the curvature of the design with the thought of plywood construction? i have no idea, my 16 foot john boat is shaped like a brick and she moves just fine. i just don't want you to choose a hull thinking she'll be constructed out of plywood.

[Matt76]

lewisboats, would you mind posting your drawings on the boatdesign.net to see what others think?
thanks