Collapsible Flettner Rotor Project

Finally, back from the working week.

" Originally Posted by Sailor Alan View Post
None at all, you just need a suitable variable frequency drive for the rated power. Im surprised no one mentioned hydraulics?"

Hydraulics got covered before the project got moved to this thread
http://www.boatdesign.net/forums/bo...-rotor-ship-launched-24081-20.html#post690532




The contributions since then have been great. I am glad we are looking at space frame structures at last, thanks to Zilver.



The only thing I can think of mentioning, is that I don't think we need to worry about being able to reef the rig in the case of a big blow.

My opinion is that the only reason to have a rig you can disassemble is for ease of trailering.


Calculations -
In a hurricane of 30mph winds ( 13 metres per second) , the drag seems to be around 120 N/m per square metre. On a square surface of an area 10 ( 2 x 5 metres) square metres, this would be about 1 kilonewton. But, I figure you could multiply that by .6 on a cylinder,

"Cd , Drag coefficient, = 2.0 for flat plates. For a long cylinder (like most antenna tubes), Cd = 1.2.
Note the relationship between them is 1.2/2 = .6, not quite 2/3."
http://www.arraysolutions.com/Products/windloads.htm


so say .5 kilonewton, ( ~ 1100 pounds) of which half will be close to the deck. This is not a huge amount. The hull, side on to the wind, will be subject to about a Tonne itself.

In any event, you will most likely want to spin the rotor to get some drive from a gale of this magnitude.

I recall reports from the original rotor ships, that claimed that the drag on a stationary rotor was less than the ship would get under the bare poles of a traditionally rigged craft.



If this is true, then the expense and trouble of making the rig supper flexible for easy lowering at sea can be avoided. You just need to be able to dismount it for towing purposes.

 

I'm reasonably certain your 30mph hurricane was a typo?

Hurricanes and hurricane force winds are not the same thing.
In the Great Lakes region, straight line wind storms of hurricane force occur. basically, they are jet streams that drop down to the surface and create havoc. Very unpredictable.
Hurricanes being cyclonic storms, have faster more dangerous apparent winds on one side, because the speed of storms advance is added to the vortex speed.
In the northern hemisphere, cyclones spin counter-clockwise, so the eastern half is the dangerous semi-circle. Actually, dividing the storm by a line approximately NW to SE, the eastern half is the dangerous side, often with wind strengths 60 to 80 mph faster than the western half. West half called "the navigable" semi-circle. Hurricanes normally advance towards the northwest. The apparent wind on the southwestern half is REDUCED by speed of advance. If speed of advance is 40 mph, the difference between two halves will be 80mph.
Florida where my boats are, usually gets several hurricanes every year.

http://www.nhc.noaa.gov/aboutsshws.php

The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based on a hurricane's sustained wind speed. This scale estimates potential property damage. Hurricanes reaching Category 3 and higher are considered major hurricanes because of their potential for significant loss of life and damage. Category 1 and 2 storms are still dangerous, however, and require preventative measures. In the western North Pacific, the term "super typhoon" is used for tropical cyclones with sustained winds exceeding 150 mph.
Category Sustained Winds Types of Damage Due to Hurricane Winds
1 74-95 mph or 64-82 kt or 119-153 km/h
Very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.
2 96-110 mph or 83-95 kt or 154-177 km/h
Extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.
3
(major) 111-129 mph or 96-112 kt or 178-208 km/h
Devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.
4
(major) 130-156 mph or 113-136 kt or 209-251 km/h
Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.
5
(major) 157 mph or higher or 137 kt or higher or 252 km/h or higher
Catastrophic damage will occur: A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.

Storm winds les than 74 mph is a tropical storm, but potentially a hurricane if it worsens.
We get some of those too. Plus frequent electrical storms with 60 mph gusts, and occasional ordinary gales.

Florida is the 4th largest state in USA. Only Alaska, Texas, and California have more square miles. And only Alaska has more coast.

 

It was a bit tongue in cheek, just as an example of a calculation.

The point is, that in the majority of sailing, reefing is probably not going to be as big an issue as it is when you have to try sailing with a conventional rig. If you get caught in 80 mph winds - will it really be that much of a problem if you have to leave the rotor up ?

Here is a great reference to wind forces on a cylinder
http://www.vishaypg.com/docs/11874/vpg-07.pdf

I have also attached an Excel spreadsheet, that does the calculations from that site. In a Hurricane, the maximum amount of force on a cylinder is about 7 Tonnes. In a Storm, about 3 Tonnes. When you apply that to the righting moment of a ballasted sailboat, how does dangerous does that become.

Better get Mr D to advise here.

 

If a rigid rotor could be built for $1000 and a collapsible rotor cost $10,000, then I'd agree probably not worth the additional money.
I'm hoping the cost will be roughly equal, one style or the other.
If that is indeed the case, tophamper (windage) of rig with rotor collapsed is logically less than tophamper with rotor deployed. Rig plus rotor vs rig minus rotor.
At any rate, I hear of approach of hurricane, I'm one of the first leaving town with at least one boat trailered up behind my truck. Destination? an elevation as high above sea level and distance as far inland as I can get in time allotted.

Oh! when I click on the excel spread sheet calculators you generously post? They are automatically saved to my software download file. I have all of them. But for some reason, that doesn't increment the "viewed" times. yes, I am viewing them, and saving them for future reference, inspite of what the thread reports. I don't want you to think they or you are unappreciated.
I'm reposting them from MY computer, so you know I'm not BS.

 

Oops; two kinds of PWM, AC and DC. The one i described was 3 phase AC, and uses a standard squirrel cage three phase motor. The one you are describing is the DC kind, and works with a permanent magnet motor like an RC airplane, or the motorized hub i sent the webpage for. As far as i know, 220V 3 phase standard squirrel cage motors are readily available in marine certified housings, complete with gearboxes of various reductions. Heavy, cheap, but supremely reliable. Permanent magnet DC motors, are also available with gearboxes, but may not be available with marine seals and casings etc. I suspect they will be a lot more expensive as well.

Actually the PWM is always switching voltage, and the current, amps, is the result of the difference between the phase angle and the back EMF.

 

No i don't mind, i was debating whether to post it both places anyway.

Your summation is correct, and masterly. It’s amps that kill, but you need voltage to force the current through the body. DC is a bit more dangerous because its harder to ‘interrupt’ at high voltages, i.e. one can get an arc.

The bus is DC and therefore a transformer is of little use directly. Using another inverter to ‘make’ AC then feed that through a transformer down to low voltage, then rectifying that, is an option, but very complicated, and probably not a standard component. 26 motor bike batteries might work?

Standard ships practice on your small boat will be safe, but probably heavy. Be careful with flexible wiring, though a case could be made for doing the whole installation using marine grade flexible rubber coated cables.

 

I thought 3 phase induction motors as designed by Tesla used permanent magnets or A single permanent magnet in the rotor or armature and are brushless. No?

 

a favorite anecdote:
Professor was introducing topic of electricity and asked if anyone could tell the class what electricity IS. Student Brown, accustomed to responding amid competition, automatically raised his hand, but quickly jerked it back down. Not quickly enough. Professor invited Mr Brown's explanation. Mr Brown apologized that he knew the answer moments before, but the information had just fled his consciousness. Professor lamented witnessing the tragedy of the century. Since only God and Mr Brown knew what electricity is, and God not telling, what a misfortune was Mr Brown's memory lapse.

 

Thanks for the invitation Yobarnacle!

Unfortunately I know very little about Magnus forces, only that they are responsible for the strange curves in the trajectory of a tennis ball or in fact any ball that spins. But I don't play ball games, so I never gave it much thought.

So I can't say anything about the feasibility of using the Magnus effect for the propulsion of a vessel, but you seem to be pretty sure it works so maybe I can contribute with some basic knowledge about electric motors and generators.

Industrial 3 phase motors are cheap but inefficient, because they are meant to be used where abundant electricity from the power grid is present. They run at a fixed rpm except special ones with a lot of coils and a complicated switch to obtain 2 or even 3 speeds.
Because there is no magnetic field present when they are not powered, they cannot generate electricity unless they are connected to the grid and are made to spin faster than their nominal rpm like in a wind turbine.

It is possible to obtain different speeds by varying the frequency, but that is not easy because at lower speeds the voltage must also be reduced to avoid saturation.

For the purpose of rotating a cylinder on a vessel, a permanent magnet DC motor is the way to go. Varying the rpm between 20 and 100% is easy by using pulse width modulation without feedback, with an rpm sensor the speed can be controlled from almost zero.
I would start with the cheapest type that has carbon brushes. A bit old fashioned but very simple so set up. There are large diameter low revving types on the market, intended for DC voltages starting at 48V. To drive the rotor I would use a timing belt and two sprocket wheels, the ratio such that at 100% power the cylinder spins at the desired maximum rpm.

My guess is that motor, drive and controller can be had below 1000 US$.

 

That would be news to me. Never saw one with a permanent magnet

http://electrical-engineering-portal.com/three-phase-induction-motors-operating-principle


edit


"Advantages:
• Cheap
• Quiet
• Long lasting
• Creates no interference

Disadvantages:
• Wants to turn at constant speed (50Hz divided by half the number of poles)
• Cannot turn faster than 1500rpm (4-pole motor)
• Draws a massive starting current, or is inefficient, or both
• Kind of big and bulky for the power it develops"

good article here
http://www.phys.unsw.edu.au/hsc/hsc/electric_motors1.html

 

Okay. Thanks for straightening me out Mr R and welcome CDK. It is precisely for help with the electrical systems I invited you, but any other insights you may have are welcome too.
SailorAlan knows a great deal about electrical and many other aspects of physics, and I respect his input. He IS a physicist. And has a lifetime of work experience in the aeronautics industry.
I'm still learning and trying sort thru misinformation found on the web and shed my own misconceptions. Thanks to ALL of you.

I have small marine diesel engines in my two identical hull boats. I have dramatically modified the interior and cabin superstructure on one. I promise photos in September.

As a cheap experimental drive for this rotor, how about several of these?

http://www.allaboutcircuits.com/vol_6/chpt_4/8.html

"If you obtain two alternators, you may use one as a generator and the other as a motor. The steps needed to prepare an alternator as a three-phase generator and as a three-phase motor are the same."

I don't need big battery banks, not yet. I can drive the alternators with one of my diesels.
Can probably acquire half dozen alternators for a couple hundred bucks at junk yard.
Various estimates of HP when used as a motor are touted, from max of 8hp to as little as 2hp. Three at 2hp would provide the 5 hp needed for rotor?

 

In 1831, one of the first demonstrations of electromagnetism was to the Royal Society, and had a magnet being moved into and out of a wire coil. The force generated was so weak, that they had used a mirror suspended on a string reflecting a candle light onto the wall of the darkened room. When the reflected candle light moved, the room broke out in cheering.

Later the King, who had been present, was asked what happened, and he famously replied, i don't know, but it involved mirrors and pieces of string!

The movement of magnets by, or eventually in, wire coils led eventually to Edison's generation of DC current, and the electrification of houses, then cities in America. These early DC motors did use magnets, either permanent, or induced.

Slightly later, Tesla developed AC as a viable form of generation and transmission of electricity. His motor, the asynchronous induction motor, was brilliantly simple.

A rotating AC voltage in a motor winding induces (hence “Induction”) a current in the conducting rotor of a motor, and the eddy currents of which set up (virtual) ‘magnetic’ poles.

Now the 3 phase AC voltage set up across the stator winding of the same motor creates a kind of rotating ‘wave’ around the inside of the motor, just like a football crowd does in a stadium by standing and sitting in sequence around the stands. Now the rotor tries to follow this rotating ‘wave’ but can never quite catch it, hence ‘asynchronous’. The difference between the ‘wave’ and the ‘rotor’ being the ‘slip’ and the power generated by this form of motor.

This motor is virtually universal in industry today, BUT. The marine industry has always had their own requirements, not least of which is variable speed/torque for winches, cranes, etc. This means they have far fewer induction motors, and rather more ‘exotic’ motor types, wound rotor being one of the most common. The wound rotor had ‘extensions’ of the rotor windings brought out through slip rings to variable resistors. This, and other such specialist motor types must confuse the issue for marine installations.

When we get further down the track, and especially before you start buying motors and other gear, we should check they are compatible BEFORE you commit to ordering them.

 

"we should check they are compatible BEFORE you commit to ordering them"

This entire thread is about "checking" before I spend!

 

Remembering the trimaran project, are there any golf cart repairers in your area ?

"10 HP, 48 DC electric motor (golf cart motor) powered each rotor from a bank of batteries wired through a speed controller."

Why re-invent the rotor ?

 

Excellent idea. The only issue might be, golf cart motors are not at all water proof, so they will need shielding, without blocking the necessary cooling airflow.

Old car and truck alternators should give about 50-55V when unrestrained by a regulator, so could be used to charge 48V.