Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors

Go Back   Boat Design Forums > Design > Boat Design
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read Most Recent Posts Gallery Images Search

Reply
 
Thread Tools Search this Thread Display Modes
  #16  
Old 06-23-2009, 10:04 AM
Jeremy Harris's Avatar
Jeremy Harris Jeremy Harris is offline
Senior Member
 
Join Date: Jun 2009
Rep: 707 Posts: 958
Location: Salisbury, UK
As you rightly say, I'm a bit far away, but it's mouthwatering to see the range of things available, at such reasonable prices, in other countries. I bought my motors and a controller from Hobby City, even though they are across the other side of the world from me, just because they were such good value when compared to our local vendors.

The wind generator is an excellent idea. You probably need to go for a motor with the lowest Kv you can find though, otherwise the voltage output will be very low. Virtually all of these outrunner motors can be easily reconnected from delta to star, which decreases Kv by a factor of 1.73 (or in your wind generator example, increases the output voltage by a factor of 1.73 for any given rpm). Here's how I did this on my Towerpro motor, others should be very similar.

The three phase wires that go into the motor are internally hooked up to the three windings such that the start of one winding is connected to the end of the next winding and one phase wire. The aim is to change this, so that the starts of each winding are connected to the three phase wires and the ends of each winding are connected together to a common point (the centre of the "star").

This is complicated by the way that the Chinese wind these motors. To make life easier, they use several strands of thin wire in parallel, rather than a single thick strand. In the case of the Towerpro, I found that each winding was actually 14 strands of about 30g wire.

First thing to do is take the motor rotor off (usually held on by a circlip or clamp ring, watch out for the strong magnet pull) and then carefully push the outer two phase wires back into the motor and out of one of the slots in the base. Next, carefully tease apart the winding wires where they join the phase wire, identifying the two groups (the start of one winding and the end of the next). You should now have something that looks a bit like this:



The phase wires can now be unsoldered from the joints and each winding start/end separated out. It doesn't matter which end of each winding is considered to be the start, as long as it's consistent. I chose to define the left-most wires of each pair to be the starts and reconnected these to the three phase wires, using heatshrink sleeving over the joints.

The centre phase wire was tricky to separate out on my motor, as the internal winding wires were short:

With a bit of careful unsoldering I managed to separate them out though, it just took patience and care to not damage the other windings.

The next stage is to connect the three remaining winding ends together. I found that I needed to extend one winding end with a short bit of wire, as it was easier to terminate the three wires in one of the base cut-outs. The joints were all insulated well with sleeving. Here's a picture of the new star joint:



Ignore the yellow wire at the bottom, that's the five core Hall sensor cable. The star connection is at the top on the picture.

That's all there is to it. The motor will now run just as before on an ordinary controller, but will be 1.73 times slower than it was before. There's no need to fit Hall sensors for this mod to work, I found that it worked well with an ordinary Turnigy 100 amp brushless controller.

For my modded Towerpro motor, with a Kv of 124, it's going to need to spin at about 1500 rpm as a wind generator to put out 12V AC, which is pretty fast. For your much higher Kv Turnigy motor then it's going to be spinning at a fair old lick to get any useful voltage, although I guess you could always gear the motor up a fair bit with a belt drive.

Jeremy
Reply With Quote


  #17  
Old 06-23-2009, 05:16 PM
Guest625101138 Guest625101138 is offline
Previous Member
 
Jeremy
My intention with the wind generator would be to use one of the small toothed belts with maybe 1:6 speed step up. My turbine has a design speed of 700rpm. Hence generator would spin over 4000rpm. I would need a larger motor than the current one in the final set up but it is a neater solution than I planned with the Mars motor. Considerably lighter over all. I want about 700W from the generator but with capacity to push higher in strong wind.

My design windspeed is 10m/s. I am designing for a very efficient turbine so I can operate it into a head wind for overall benefit. I am well below the Betz limit.

Rick W
Reply With Quote
  #18  
Old 06-23-2009, 05:41 PM
Jeremy Harris's Avatar
Jeremy Harris Jeremy Harris is offline
Senior Member
 
Join Date: Jun 2009
Rep: 707 Posts: 958
Location: Salisbury, UK
Sounds good, Rick, but you might still benefit from rewiring the motor to star, as it would reduce the step-up ratio a fair bit. This might reduce the losses,

I like the idea of being able to motor into a head-wind, using the power in the wind to drive the boat (if this is what you meant). I've followed endless arguments between people who are convinced that it's not possible for a wind powered boat (or vehicle) to go directly into wind, many people seem to miss the fundamental point that it's got little to do with wind speed and everything to do with the effective gearing between the two propulsion systems, plus drag..

I'd not thought of doing this electrically, but in many ways this makes more sense than the purely mechanical transmission arrangements I've seen, like the old Redwing experiments here in the Solent when I was a youngster.

I'll stick with solar panels, as I think the wind generator will be a bit too intrusive on the design I'm working towards. I might take a look at a small, deployable wind generator later though, as it might be a way to charge the batteries up more effectively when moored up.

I managed to get up to speed with Freeship this afternoon, and am pleased with the outcome. I modified the stern of the basic ply model design and managed to optimise the waterline fairly well. Freeship is giving a resistance at 4kts of about 5lbsf, less than I'd predicted by empirical means. I've now finished re-shaping the model hull and have added a transom (that's clear of the LWL) to keep a better shape to the stern. As soon as the glue as hardened I will take some more photos, overall I'm pretty pleased with the way it's worked out.

Jeremy
Reply With Quote
  #19  
Old 06-23-2009, 05:58 PM
Guest625101138 Guest625101138 is offline
Previous Member
 
The electric turbine/battery/electric motor works out to be a good solution. You get very wide range of gearing and you can hold the boat at constant speed so charging goes up in strong winds. A mechanical system is very wasteful in these circumstances and needs variable pitch to avoid overloading the drive train.
http://www.youtube.com/watch?v=B7h6ZGOsa-Y

You can also store energy when anchored with the electrical system.

If you post the .fbm file when you have finished it I can do a drag check with Michlet. The 5lb sounds about right. The optimum hull was 3.6lbf at 2m/s.

Rick W
Reply With Quote
  #20  
Old 06-24-2009, 01:31 PM
Jeremy Harris's Avatar
Jeremy Harris Jeremy Harris is offline
Senior Member
 
Join Date: Jun 2009
Rep: 707 Posts: 958
Location: Salisbury, UK
Very interesting project, Rick. Thinking about it, the idea of a wind/electric series hybrid system like this makes a great deal of sense for a sustainable power source. What's more, the idea is scalable, and could be made to work on quite large vessels better than on small ones.

The downside for me is that a pretty big wind generator is needed for a small vessel like mine. A 1 metre diameter swept area can theoretically produce just under 4 watts for a 2m/S speed differential, which isn't much. Admittedly this rises in proportion to the cube of wind speed, but this system still looks best suited to large vessels working in open waters.

I've finished playing about with Freeship, although the hull form in the attached file is slightly different to the shape I can get by torturing thin ply. Having run several variations through the calculation process, I've not seen any major differences from small dimensional changes, so am reasonably confident that the ply design will work pretty much like this model.

Thanks very much for offering to run this through Michlet for me, it's much appreciated.
Attached Files
File Type: fbm Model 2.fbm (59.3 KB, 249 views)
Reply With Quote
  #21  
Old 06-24-2009, 01:59 PM
BeauVrolyk's Avatar
BeauVrolyk BeauVrolyk is offline
Sailor
 
Join Date: Apr 2009
Rep: 153 Posts: 160
Location: San Francisco, CA
Quote:
Originally Posted by Rick Willoughby View Post

...snip...

You may find a small wind turbine better value than solar panels. I intend to use both for energy collection. Something like this:
http://www.bettergeneration.com/turb....5lh-300w.html
Or even smaller. They have blades as well. The outrunners would enable very low weight generator.

Rick W
I have done a number of passages on boats in the 30 to 50 foot LWL range and windmills drive me nuts. It's the noise and vibration that seems to travel through the entire boat. For a small day boat, in which the windmill would be running when you're not around, it might be fine. But, I consider them unacceptable when I'm aboard.

I was bringing a boat up from S. Calif to San Francisco once and had a windmill whirring away. When we stopped in Half Moon bay for a bit of a rest, three people took the trouble to row over to the boat and ask us to stop the darned thing. It was making enough noise (wind speed was 25 to 30 knots) that it was bothering them and they were 100 yards away!

BV
__________________
-----
"Anything worth doing is worth doing to excess"
Reply With Quote
  #22  
Old 06-24-2009, 05:09 PM
mrnrami mrnrami is offline
 
Join Date: Jun 2009
Rep: 10 Posts: 4
Location: Barcelona
Hello. Im Marc
I have a little idea for a ecologic boat, this idea is a Monohull, but I think than the catamaran is better than monohull for you.
Attached Thumbnails
Efficient electric boat-mini-solar-boat-ver.0.jpg  

Last edited by mrnrami : 06-27-2009 at 07:41 PM.
Reply With Quote
  #23  
Old 06-24-2009, 05:45 PM
Guest625101138 Guest625101138 is offline
Previous Member
 
Quote:
Originally Posted by Jeremy Harris View Post
Very interesting project, Rick. Thinking about it, the idea of a wind/electr...
I've finished playing about with Freeship, although the hull form in the attached file is slightly different to the shape I can get by torturing thin ply. Having run several variations through the calculation process, I've not seen any major differences from small dimensional changes, so am reasonably confident that the ply design will work pretty much like this model.

Thanks very much for offering to run this through Michlet for me, it's much appreciated.
Jeremy
The attached is the power curve for the hull you have drawn. Requires 50W to do 4kts. So by the time you get at battery drain it will be very close to your target of 100W. With a curved shaft and high aspect prop you should be able to get down to 80W but that will be for later.

The boat will be very tender. The KMT is only 1.6ft. This means you have to position the centre of gravity, mainly you and crew body weight, lower than this to get the boat to stay upright. It is possible but boarding will be extremely delicate. The boat will need to be stabilised while it is boarded. This is cruising kayak type of stability.

I got my new LiPo battery and charger yesterday. The Turnigy SK sings with it. They are wonderful compact engineering.

I am travelling from today for all of next week so will not get a chance to test it for a while.


Rick W
Attached Files
File Type: pdf Drag_Curve.pdf (24.2 KB, 281 views)
Reply With Quote
  #24  
Old 06-25-2009, 02:47 AM
Jeremy Harris's Avatar
Jeremy Harris Jeremy Harris is offline
Senior Member
 
Join Date: Jun 2009
Rep: 707 Posts: 958
Location: Salisbury, UK
Marc,

Interesting design, but I'm constrained by my desire to make something light enough to be easily transported by car. I had thought of a multihull, primarily as it gives plenty of space for solar panels and would be very stable, but as I also want a boat that looks traditional I ruled it out.

To make up for the lack of big flat areas for panels, I'm planning to tile the decks with small, fibreglass/resin encapsulated solar panels, like this 167mm x 120mm module:



This will allow me to make best use of the available deck space, although I'll lose out on the ability to position the panels in the best direction. As the solar charging system is only a range extender, rather than a source of real-time motive power, I'm hopeful that this will be OK.

Rick,

Many thanks for taking the time to run the hull form through Michlet. The power requirement is OK, particularly as the notional inland waterway speed limit here is 4mph, rather than 4kts, which brings the power back to about 40 watts. Even at 100 watts average power from the battery, the small, house brick size, LiFePO4 battery pack I already would give me over 3.5 hours cruising time, with no solar charging assistance, pretty impressive really.

I may try and improve the secondary stability a bit by increasing the beam above the DWL, if I can. Now I have the model almost completed I can do a small inclining experiment and get an idea as to how the tortured ply shape really behaves and just how "tippy" it feels in practice. I believe that there is no need for any special correction when doing static stability tests on a model, scale factors only come into play when correcting for things like the differing Reynolds number and other viscosity related effects (happy to be corrected if I've got this wrong!).

LiPo cells really are suberb, aren't they? The only problem is the potential safety risk if they aren't charged/discharged carefully. I'm using LiFePO4 cells, which are significantly safer than LiPo, in that they don't burst into flames if something goes wrong. The downside to LiFePO4 is the higher volume/weight for any given capacity, plus the fact that they are still quite expensive.

Having said that, I may switch to LiPo for this boat project, most probably with a battery management system similar to the one I'm using on the LiFePO4 cells, adjusted to work at the slightly higher cell voltage.

Hope the trip away goes well.

Jeremy
Reply With Quote
  #25  
Old 06-26-2009, 12:33 PM
Jeremy Harris's Avatar
Jeremy Harris Jeremy Harris is offline
Senior Member
 
Join Date: Jun 2009
Rep: 707 Posts: 958
Location: Salisbury, UK
An update on progress.

Whilst waiting for the paint to harden on the new hull model, prior to doing some tests to confirm stability estimates, I have got on and finished the electric propulsion unit. This is a through-hull design, intended to be fitted to a hinged box section of hull that is enclosed in a large case, a little like a centreboard, so that the prop can be swung up to allow weed clearance and beaching. The underwater part is enclosed in a streamlined composite fairing, to reduce drag.

Here's a picture:




Jeremy
Reply With Quote
  #26  
Old 06-27-2009, 02:44 AM
Guest625101138 Guest625101138 is offline
Previous Member
 
Jeremy
It can be surprising how much power can be wasted without good fairing. What you have done looks superb. It should cost you no more than 3W in propulsive power at 2m/s. So something like 6W at the battery.

The main reason I use the curved shaft is because it has such low drag compared to other options. The flexibility also reduces the potential for getting bent as it just deflects.

Rick W
Reply With Quote
  #27  
Old 06-27-2009, 02:59 AM
Guest625101138 Guest625101138 is offline
Previous Member
 
Quote:
Originally Posted by Jeremy Harris View Post
An update on progress.

Whilst waiting for the paint to harden on the new hull model, prior to doing some tests to confirm stability estimates, ......
Jeremy

I will be interested to see the method you devise to test the stability with your model so you can relate to full size.

One method I devised is to suspend a drive frame with seat from the rafters with two ropes. The ropes connect to rigid supports on the frame located at a height that would correspond with the KMT on the hull. If you cannot mount the frame and sit in it without external support you will have the same problem in the boat. You could do the same thing with a seat mock up.

Not sure if you have seen my V12 design. It has a KMT 0.34m and is stable once I am seated but absolutely impossible to board unless the boat is held firm or I have external support until I am in the recumbent position. This is probably the lowest KMT you could safely pedal with in an unstabilised monohull.
http://www.youtube.com/watch?v=PYoW3XjHRbw

Rick W
Reply With Quote
  #28  
Old 06-27-2009, 06:50 AM
Jeremy Harris's Avatar
Jeremy Harris Jeremy Harris is offline
Senior Member
 
Join Date: Jun 2009
Rep: 707 Posts: 958
Location: Salisbury, UK
Thanks for the kind words about the fairing. Here's another photo that better shows the profile:



It's a bit fat, because the gearbox is around 30mm in diameter, but I'm hopeful that it should be reasonably efficient. I'm in two minds as to whether to just arrange for this to swivel for steering, outboard style, or use a separate rudder. The minimalist in me is encouraging the motor swivel option, although I think I may need to be cautious when turning hard, as the induced roll may be quite significant.

The plan at the moment is to just do a simple inclining experiment, with the model loaded to the DWL and an offset weight being used to induce roll. By plotting the roll angle vs applied roll torque I should be able to see how closely the model follows the predictions from Freeship. I'll probably have to wait until "She Who Must Be Obeyed" is out of the house, as the least windy place to do this will be the bath.............

V12 looks impressive, although your practical experience of the stability of such a hull form is a bit worrying. I plan on fitting the seats low in the hull, pretty much as you have done with this design, but I'm hoping that the slightly higher KMT of my broader beam design may make boarding acceptably wobble-free for my nervous crew member. I may need to increase the beam a little in order to stiffen the boat up, I think I could go to about 1m maximum beam, with a DWL maximum beam of perhaps 760mm using the construction method I'm currently thinking of.

I may need to re-think the hull design if it proves to be just too tippy, in the interests of marital harmony.

Jeremy
Reply With Quote
  #29  
Old 06-27-2009, 08:39 AM
Guest625101138 Guest625101138 is offline
Previous Member
 
Jeremy
The minimum drag fairing to surround a blunt object has a thickness to chord ratio around 4 so you will be close to minimum. There is another handy bit of software that you should find quite easy to use. It is called JavaFoil - google it and run the Java Applet. You will need to set the options page to suit water parameters of density 1025 and viscosity 0.0000013. If you have a play with it I can give you some idea how to estimate the drag for your drive leg.

If you use the drive leg for your rudder it will need to be toward the back of the boat. Any rudder is best placed toward the stern of the boat. A rudder would generate similar side forces to your drive leg. The lift of the foil will do more than the thrust at your 4mph. If the side force is low down and toward the stern it creates an overturning moment that sets the list into the turn. This is a good thing. Adding a rudder is more drag so it makes sense to use the leg.

For your stability test you need to set the CoG of the model at the same vertical height, in scale, as it will be in the full-size boat. I estimate that the CoG of your body in a seated position with the legs perpendicular to the trunk, as you have in a low seating position, will be around your belly button. I can get my CoG down to 280mm in the semi-recumbent postion so with V12 I had slightly better than a 40mm margin. The CoG of the hull alone is around 200mm high so this made it slightly better but I am around twice the weight of the hull.

I will be surprised if you do not find a KMT 0f 1.6ft intolerably low for practical relaxed use with inexperienced crew. If the crew has experience in a kayak then it is another matter. A kayak with a KMT of 1.5ft is sedate. Before you commit to the build it might pay you to find some hire places, or boat owning friends, to try little dinghies and kayaks. You can make quick models of these with Freeship to determine the KMT of each and what you find tolerable. Even asking others here for their opinions would be useful - maybe start a new thread like "Tolerable KMT for Powered Dinghy".

I would suggest a KMT around waist high for a dinghy based on what I have experience with. This means you can stabilise your bodyweight within the hull while standing and it will not capsize providing the dinghy is in calm water and you do not shift weight quickly. Light boats are skittish under foot.

Rick W
Reply With Quote


  #30  
Old 06-27-2009, 09:11 AM
Jeremy Harris's Avatar
Jeremy Harris Jeremy Harris is offline
Senior Member
 
Join Date: Jun 2009
Rep: 707 Posts: 958
Location: Salisbury, UK
Thanks for that, Rick. I've used Javafoil a fair bit in the past (I design light aircraft) and have been applying aerodynamic principles to this boat design. The main difference is that the much higher viscosity of water shifts the emphasis to reducing wetted area, something I've not ever worried to much about when optimising light aircraft designs.

You're right about the C of G position for a seated individual, with legs outstretched it's usually a short distance in front of, and perhaps slightly below, the belly button (at least it is for the "standard" 86kg male used in aircraft certification).

I've just done an ad hoc stability test, with the model ballasted to DWL. It's definitely very tender, with a fairly low initial stability. It stiffens up slightly by the point that the gunwales are just level with the water, but I think it may by unacceptably tippy for leisure cruising.

I've also done a quick test of the propulsion leg, in a dustbin filled with water. I'm really very impressed indeed with the available static thrust, even allowing for the high degree of recirculation I was getting in such a small container. Using a tiny 24 volt NiMH battery pack, the motor and controller was drawing 60mA at zero rpm and I found it impossible to hold the leg in place in the centre oif the bin with any current above about 1 amp. I could only increase the rpm up to the equivalent of 3 amps, because water was being thrown out everywhere. At that current the drive leg was pinned hard to the side of the dustbin. With my one spare hand I was unable to push it away from the side, so, allowing for the lever arm of around 300mm between the prop centre and my grip on the shaft, I'd say that it was probably producing between 2kgf and 3kgf of thrust at a bit over 70 watts power input. This is better than I expected, if it turns out to be correct. I need to make a test rig to hold the motor properly and take it down to the local boating lake to do some proper tests, with some form of load cell to measure thrust a bit more accurately.

Thanks for the tip about a suggested tolerable value for KMT. Waist height makes a lot of sense, so it looks like I need to just about double the current value of KMT if I want to get to dinghy-like stability. We've both been canoeing a couple of times, but in hired open canoes, rather than kayaks, which are probably fairly stiff. SWMBO was reasonably happy in an open canoe, even when paddling some tortuous routes in the mangrove swamp areas of the Florida Everglades (although she wasn't too keen on the 'gators).

I will do some research into some of the traditional hull forms used for easily driven rowing boats, like the Thames Skiffs or Cornish Pilot Gigs. These are reasonably stable (I rowed a Pilot Gig years ago, it's a remarkably seaworthy design for such a light, slim hull), and have a reputation for being slippery. I may even be able to buy a hull, rather than make one from scratch. Although this would be more costly, it would certainly be quicker.

Jeremy
Reply With Quote
Reply



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Electric Boat Design John Klimek Boat Design 42 09-05-2011 01:11 PM
Need fast, EFFICIENT, commuter boat MattM Boat Design 47 05-19-2009 09:39 AM
Solar Electric Boat Design DSGNA Boat Design 3 03-11-2009 08:44 PM
Electric Boat Data Guest625101138 Boat Design 12 10-02-2008 07:17 AM
Electric boat advice camglasgow Hybrid 3 04-07-2006 09:09 AM


All times are GMT -4. The time now is 06:07 PM.


Powered by: vBulletin Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2014 Boat Design Net