Foiling - the Future or a Folly

If you work hard on the design to get best lift to drag for the desired speed you could expect L/D of 30.

So lets say you can build it to weigh 200kg. The drag will be 70N near enough.

To do 15m/s (say 30kts) the power will be just over 1kW for water drag. Windage would be significant at this speed even with a nicely faired hull and sitting low. So more like 1.5kW allowing for wind. With a good prop you need 2kW at the motor. So 3HP should keep you there.

Getting to that speed is a different matter because the foils need to be optimised for the design speed. You would need to be able to get the hull through the displacement mode at something like 20kts and that is going to take more than 3HP. 5HP might just be enough if the hull is long enough.

Other ideas used for this conundrum is two sets of foils; one for the low speed mode and the other for high speed. Ladder foils also do this. Either option adds weight and complexity.

A feature of the electric motors is that they have tremendous overload capability. This one weighs 1.5kg and peaks at 8.5HP:
http://www.hobbycity.com/hobbycity/...80-100-B_130Kv_Brushless_Outrunner_(eq:_70-55)
These are ideal for a foiler because they have the peak rating for take-off and their continuous rating will be good enough for continuous operation. Their low weight is handy as well.

Rick W

 

Well, surely some of use a "handle" because that was (and still is) the accepted etiquette on the net and, as Bistros pointed out, it has been for a long while. When in Rome etc.

And in many situations, it seems to be more tasteful to be semi-anonymous if you have to refer to the factors underlying a poster's knowledge and opinions. If you're discussing Peanut 24 class boats, for example, saying "I know how a Peanut 24 handles in strong winds because I'm the intergalactic champ" seems a lot less like bragging if it's done anonymously, but it still shows that the poster has good reason to claim expertise in the area.

And why use a name in this context? Why is it important? Sometimes it smacks of "look at me, look at me". And it's hard to see that the ****** count is any lower among those who use their full names.

 

If I was greeted by someone in the street who said "Hi you can call me CT249" I could not help but think what a ******. Same thing happens on this forum. I have no hesitation in calling some anonymous handle a ******. It would certainly be different if I was referring to an individual. If you want the respect an individual is accorded how about using given names.

There may have been some justification for 8 letter "handles" 20 years ago but these days it is just nonsense on a technical forum.

I do not value opinions of handles. If you have an opinion you should be prepared to put your name to it. Anything less is just being rude and self indulgent.

Rick W

 

seems like in an era were identity theft and ciber crime are so rampant it is prudent to maintain some level of anonymity

to each his own
B

 

Rick: you’re dead on about the remarkable efficiency of small boats. Somewhat less ambitiously I found that I can comfortably match a brisk walking speed for hours even at my age and condition when I took up paddling, and I find that my range is comparable in either mode.

Boston: I would imagine 5 horses would be adequate for flying. I think Rick’s numbers are correct but I followed a different route. The Flyak site http://www.foilkayak.com/faq/theory/ doesn’t give a take-off speed but there’s a chart that shows a power level cross over between the Flyak and a “regular” kayak at 4 m/s or about 8 k for 225 W power, or 1/3 HP. From the chart 3/4 HP should get you a respectable 20 k, with a total weight of 90 kg. So about 3 HP should fly 4x that all-up weight which should accommodate 2 crew and a reasonably durable hull and motor, perhaps some beer. 5 HP should allow a margin so that time and distance to get up on the foils is acceptable. I assumed horses of the fuel-burning persuasion. I was initially less sanguine about electric power but Rick has found interesting motor data, and elsewhere in the forum there’s a thread on super capacitors.

Perhaps there’s a viable market here, although hull design is a challenge and but we must not forget Chris’s warnings about deadhead logs and other debris, though.

RE: the name debate: I think use of a proper name is appropriate for a professional, optional for others. Whatever one’s opinion on this subject, surely we can all agree to disagree and let it go.

 

Hmmmm. Personally, I'm happy to let people call themselves whatever they want, and reserve the term "******" for those who decide that they alone have the god-like power to determine proper etiquette.

 

Good enough, Terry. I'll join you in that effort. I've been known to be a ****** every once in awhile... happens like that when one has opinions.

;-)

 

Taken from the link mentioned previously in this thread:

Is this DC motor as I assume ?
If that motor is connected to 48V voltage and no load is there, it draws 2 amps, so Resistance is R=48V / 2A = 24 ohm
If it's loaded up to have 48V & 130 Amps consume 6240Watts of electic power it gives out less since it's not 100% efficient. At that operation point R=48V / 130A = 0.369 ohm
In some load between those 2 examples amps are between 2 and 130 and as a result R is between 24 ohm & 0.369 ohm. With less voltage resistance is even smaller for same amps.

Can someone explain why it claims R to be 32ohm ????
Under what conditions could that possibly be correct ?
What voltage & what current ?
Even with minimum idle current of 2Amps R=32ohms means 64Volts, which is well above allovable operating range.

If it's AC motor, then impedance is larger than resistance, not smaller.

 

It depends what kind of motor it is, at a guess I would say it is a shunt-wound electronically-commutated motor closely related to a servo motor. If that is the case the 32 ohms applies only to the field winding and the rest of the current passes through the armature. The armature winding will be very low resistance. If the armature is rotating within the magnetic field generated by the field winding it acts like a generator and produces back EMF (EMF = volts) opposing the applied EMF. The armature current flowing is produced by whatever EMF remains divided by the armature resistance. When the armature is free running the armature current is reduced to almost zero, hence only 2A all-up current. Apply drag to the motor so it has to produce torque, and the armature speed slows fractionally, reducing back EMF, allowing armature current to increase. Stall it and it will probably melt!

 

And it takes less than 5 minutes, if you know anything about CT's interests, to identify him on the net. Some folks user names go back some considerable time to when it was, as another poster noted, impossible to have usemames with spaces or more than 8 characters. And its a lot easier to identify CT249 from Google than it might be to identify which of the hundreds of C**** T***** in the world he is...

In my case I choose to stay anonymous on this forum and this one only because, to be frank, the fruitcake index. I have had concerns about some of the particpants in a way that I don't on, for instance, Sailing Anarchy.

 

It is a 3-phase AC motor. You need an ESC to run it. One like this:
http://www.hobbycity.com/hobbycity/...Name=TURNIGY_Sentilon100A_HV_5-12S_BESC_(Ver4)

The winding resistance is a misprint. It should be 32mohm.

Rick W

 

Thanks, makes a lot more sense now.
Is ESC (electronic speed controller ?) then just same as variable frequency DC/AC converter or is there more into it. Suppose there must be as the motor was speced like the revs being proportional to voltage, so frequency must also be. Or am I completely off here ?
I'm certainly not upto date about these things anymore, just what they used to be something like 12 years ago. Can similar ESC be used on any other 3-phase AC motor as well and with what voltage range ? Are there something for normal household voltage (230/380V in europe) range with similar cost that allows for using higher frequencys than with direct connection (50hz) ? Would be very useful with my vacuum pump for lamination work.

 

These are variable frequency. They are referred to as sensorless type. The motors are actually synchronous because they use magnets for excitation. Hence speed is locked to frequency although they also use voltage chopping to get the variable voltage. The speed control is not very precise but it is fine for a boat or plane type application. You also pay a bit more for reversing controller if you want that.

I have not tried an ESC on a normal induction motor but I expect it would work if you could get suitable voltage. These sort of controllers are being used in industry but they cost a lot more. I am not up with the electronics these days but I have a feeling that the power MOSFETS used on the LV stuff get expensive for higher voltage.

I have a couple of Mars motor with controllers. These motors are quite large by comparison with the HXT. The ones I have is continuous rated at 4.5kW on 48V and peak at 9kW. I made a test outboard using one. I just ran off two little 12V batterues that llimited power to around 270W but I was pleased with the result:
http://www.boatdesign.net/forums/at...288392-electric-boat-data-drive_leg_test1.wmv
The Kelly controller I have gives very accurate speed control because the Mars motors have flux sensors but it is really complications that are not needed for a boat motor. One nice feature is that it is switch reversible and, in fact, the controller is full 4-quadrant so I can use for generating as well. This means the same type of motor and controller can be used for a wind generator.

Rick W

 

Hey Rick,

Can you link me to a site where I can price/compare those motors & controllers for my wind-power app. plz? I've been having a hard time finding a suitable motor/generator for my 5KW (7.5KW Max) turbine.

 

Rob
This is the place I got mine from:
http://www.kellycontroller.com/

Using the Mars motor as a generator is potentially a compromise because the motor/generator has magnetic cogging. It means it will have trouble self-starting in light wind.

I intended to make a generator with about a 3m blade with the motor/generator connected through a 1:1 right angle drive. It would mean I would not use the unit in its best operating range but I got a good deal on buying both together and it means my generator would be a back up to motor if I wanted.

At this stage I have not even tested the Mars motor in regenerative mode but they are widely used on bikes with this function.

Rick W