Propeller

Controllable Pitch Propeller  (I wish)

The benefits of controllable pitch propellers (CPP) specifically for a sailing/cursing/workboat.

* The props speed vs. power can be adjusted according to varying cargo loads.
* Drag can be reduced or increased to meet the sailing conditions.
* The pitch can be adjusted match meet the required rpm of a generator that is being powered from the drive shaft.
* No reversing gear is required.
* Prop walk can be reduced by reducing the pitch.
* With a reversing gear and prop you can prop walk the boat in either direction.
* Individual blades can be replaced.

Typically, the drop in propeller efficiency owing to the larger boss (prop hub) size of a controllable pitch propeller is about 2 percent. However, if a controllable-pitch propeller is well designed and correctly operated, it can result in fuel savings of up to 15 percent compared with a fixed-pitch propeller operating in a nozzle. --www.fao.org

The big down side to a controllable pitch prop is the cost. Hundested; www.hundestedpropeller.dk, is renown for some of the best controllable pitch props so got a quote from McGowan Marine Inc. 1-508 990-1114  stevegow@aol.com, on a new system for a 70ft motor sailor is $66,913 plus shipping. Needless to say I am no longer looking a new Hundested drive systems.
 

Our Used Hundested CPP

Paul Liebenberg sold us one of two Hundested controllable pitch propeller drives he had collected for possible use on his 65 footer.  The price was great, but the problem is that we have to figure out how to make the blades that are missing.  They are no longer in stock in Denmark and to have them made there will cost us close to $10,000.  But the more we look at it the more it looks like casting and milling our own blades will be the thing to do.  So the Hundested is getting it's own web page: Controllable Pitch

Folding or Feathering Props (Still too pricy)

Max-Prop self feathering prop

If you can control the pitch at the push of a button then the next best thing for a sailboat is to fold or feather the props blades so the don't slow the boat down when it's under sail power. Max-Prop; www.max-prop.com manufactures and sells a self feathering props in a range of blade configurations. I'd love to have one, but our boat would require a 35", 3 blade propeller and the cost is $15,500.   And being a workboat I doubt it would be very long before I was needing to replace a blade or two due to damage caused by operator error.

Affordable Fixed Pitch Props  (Better)

Buying a Prop

If you live on the coast this will be a piece of cake, but if you live in Tulsa, Oklahoma you will likely have to shop by email.

Brent Swain's advise "Get a prop within 4 inches of the pitch you want, preferably closer. Any more and if you try to re-pitch a prop more than 4 inches the blade breaks off."

To test a used prop is to rest it on the hub and then tap the end of each blade.  It should produce a clear ringing.  If it is dull and short lived then pass it up.

CraigsList turned up more than a few props down toward New Orleans, so they are out there. Check: www.propellerplace.com

A new 36" bronze prop from deepblueyachtsupply.com is $3,610. 

Another option is a new stainless steel prop from Kahlenberg propeller that is intended for use on work boats.  We plan to frequently work in shallow waters and close to obstacles so a stronger prop might be worth the extra money. The price for
a 3 blade 304 stainless steel propeller 32" in diameter with a 27" pitch, left hand, bored for a 2.5" shaft is $3,995; F.O.B. Two Rivers, Wi. Contact: Steve Kahlenberg, Kahlenberg Bros. Co., Ph: 920-793-4507, www.kahlenberg.com. 

Kevin Morin builds boats up in Alaska and he highly recommended stainless steel wheels; "My examples were fishing commercially, justification for these wheels was their ability to run in gravel bars of Bristol Bay and keep running without damage."

Rotation

Most engines are left hand rotation.  Meaning that if you look at the engine's  fly wheel from the back it will rotate counter clockwise, or the top of the flywheel will be moving toward the left. Also most inboard props are left hand meaning they push the boat forward when they spin counter clockwise as seen from the back end.

Prop Sizing

A good place to start is with some of the manufacturers sites like Michigan Wheel: www.miwheel.com/propellers/prop-it-right/

Max allowable propeller diameter 34" - 36"  Need 10% clearance between the blade tip and bottom to reduce noise.
Vessel Max & cruising boat speeds 12 knts max 10 knts cruise in 15 knt wind
Displacement, length & LWL of the vessel 40 ton, 20 ton cargo, 74ft, 28ft
Shaft length:  20 ft ??

Using a Cummins C8.3 210 hp, 2400 max rpm,  446 lbft @ 1300 rpm 
The following calculations are from Boat Mechanical Systems Handbook
DAR=0.5 for 3 bladed standard prop, 0.7 for 4 blades.
Min Prop Diameter Inches as a function of blade area or DAR = sqrt( ( 125 * hp)  / (DAR * max kts * sqrt( max kts) ) )
sqrt( ( 125 * 210) / ( 0.5 * 11 * sqrt(11) ) ) = 37.9 inches for 3 blade
sqrt( ( 125 * 210) / ( 0.7 * 11 * sqrt(11) ) ) = 32 inches for 4 blade
Ballpark shaft diameter is 1/14 of the prop diameter; or 37.9 / 14 = 2.7 in for 3 blade and  32 / 14 = 2.3 in for 4 blade.
Shaft Dia In = cube root ( (321000 * ( .96 * hp ) * SF ) / ( 316 Stainless Steel Yield * ( rpm / reduction ) ) )
SF= Safety Factor
Shaft Dia In = cube root ( (321000 * ( .96 * 210 ) * 4 ) / ( 40000 * (2400 / 3 ) ) ) = 2 inches
Using an Allison 545 automatic transmission in 1st gear with reduction of 3.45:1
Engine 2,500 RPM = 725 Shaft RPM
Engine 1,600 RPM = 464 Shaft RPM

From Dave Gerr's book "Boat Mechanical Systems Handbook"

Minimum Blade Area & Diameter for Displacement Hulls
= sqrt((125 * hp) / (Disk Area Ratio .5 for a 3 blade std prop * kts * sqrt(kts)))
= sqrt( (125 * 200) / (.5 * 11 * sqrt(11) ) = 37.0 inches

Prop Tip to Bottom of  Hull = .2 * prop diameter 37.0 =  7.5 inches
Between Prop and Rudder = .15 * prop diameter 37.0 =  5.75 inches
Between Prop and Skeg = .3  * prop diameter 37.0 = 11.25 inches

Rough Shaft Diameter = 1/15 * prop diameter 37.0 = 2.5 inches

Shaft Dia = cubrt( (321,000 * 200 hp * .96 [shaft hp] * 4 Safety Factor) / ( 20,000 psi yield strength 304 stainless * 725 rpm))
= cube root ( (321000 * (200 * .96) * 4) / (20000 * 725) ) = 2.57 inches

An 36" bronze prop from deepblueyachtsupply.com is $3,610 (2011) and it requires a 2.75" shaft.
A 2.75" x 10ft shaft in Aqualoy 17 from deepblueyachtsupply.com is $1,700.  (2011)

Shaft Bearing Spacing if feet = 4.6 * sqrt( Shaft Dia )
= 4.6 * sqrt( 2.5 ) = 7.27 feet
= 4.6 * sqrt( 2.75 ) = 7.62 feet

Thrust Pounds = ( 326 * shaft hp [200 * .96] * displacement hull propeller efficiency .55 ) / ( .9 * knots 10 )
= ( 326 * 200 * .96 * .55 ) / ( .9 * 10 ) = 3,825 pounds
1,275 pounds per 16 inch blade

From Dave Gerr's "Propeller Handbook"

Torque = (5,252 * hp) / rpm
(5,252 * 200 * .96) / 2,500 = 404 pounds feet

Hull Speed = 1.34 * sqrt ( water line length )
1.34 * sqrt ( 68 ) = 11 knts

SL Ratio - Speed / Length or theoretical hull speed when the wave length is equal to the waterline length.

Kts =11 Desired Speed in knots
WL=68  Water Line
LB=80,000  Displacement in Pounds
SHP= 200 * .85 Shaft Horsepower  = 170 Hp
SL RATIO = Kts / sqrt(WL)   = 11 / sqrt(68)  =1.33
From the SL RATIO chart, an SL RATIO of 1.33 gives LB/HP (Pounds/Horsepower) of 525
80,000 / 525 = 152.3 Hp

Pitch and angle of the blade are not the same.  Consider that the root of the blade closest to the boss cuts through much less water in one revolution than does the tip of the blade.  So the tip of the blade has a much smaller angle to the shaft that the root.  If both the tip and the root are pitched the same then both would travel the same distance through the water when given one rotation.

Building a Steel Propeller from Scratch ( Yeah Baby - Field Repairable )

I came across a bit below in the Wylo-II group from Lex Hodgkinson.

"Hi Passepatu has had a mild steel propeller welded to a mild steel shaft for over 14 years now, I welded up the prop from 5mm (.1967" 3/16=0.1875)  plate scraps and welded this directly on to the shaft. This system has been pretty much trouble free
with only two cases of mild pitting on the blades when I allowed the small anode on the prop boss to get eaten away. This was remedied with an electric weld build up of the pitted areas followed by grinding, all done in Situ. (on the hard!) The system has a small anode on the prop boss, a small one on the rudder and a similar one on the hull close to the prop shaft area. I cast these myself, they are roughly 1" dia by one inch long and last around a year.

The propeller is painted with chlorinated rubber paint (as is the whole boat) and antifouled with the same paint as the hull (ablating, not the best but I found "hard" antifouling to last even less) The shaft bearing is "Thordon" or similar, some sort of fibre, and has never been replaced, the inboard seal is a "dripless" fibre ring that bears on a bronze plate, which I replaced with stainless steel. Works ok but the grease filled shaft leaks grease inboard, just a nuisance. No water leakage at all, just cobwebs in our bilge! We have no inboard bearing, all thrust being taken by the Hurth gearbox.

We have a dry exhaust and therefore no cooling water to exit at this seal and cool it, (I think that was the cause of the bronze plate wearing too fast) The whole thing works very very well, cost begger all and seems to incur no problems, I would be far more nervous with a thousand dollars or more tied up in a machined stainless shaft with bronze prop. I have a grease gun piped into the prop shaft tube and give it a squirt now an then.

Incidentally it is easy to alter the pitch if you feel so inclined, by either belting it with a hammer or twisting the blades with a large wrench The prop is two blade 17x11 approx and the motor a 35hp Nannidiesel. It will max out at around 2500 rpm (max design rpm 3000) Hope this helps, DONT let the "experts" say you cant do this in mild steel, it works and can be repaired or replaced easily and cheaply, Incidentall we have been careful not to have anything but mild steel underwater. Lex"

Lex is using a 1.8 to 1 Hurth gearbox, so the 3000 engine RPM is 1666 at the prop.

"The prop was built using a simple steel jig to compare the blade shapes to ensure they were the same and at right angles to each other, pitch was checked at two or three locations with more attention paid to the outer 1/4 and the tips. Balance was checked simply by mounting on centers and grinding to achieve no bias. The blades with some reinforcement at the roots were mounted into slots cut into a 2"dia hub which was drilled to 1 1/4" to accept the shaft. The hub is welded to the shaft only at the aft end."  --Lex.

Our prop is 36", not 17" so we got a bit more force involved in order to pitch the blades.  They make special anvil called a "pitch block" for hammering a prop into shape, but that's for smaller speed boat props.  However a pattern would be really helpful when bending the blades.

Vibrators

The frequency in Hz transmitted by the propeller to the hull is given by
where: n = number of blades N = number of rpm of the propeller shaft.
Source: www.nautica.it/superyacht/527/tecnica/vibrations.htm

So our 3 blade prop turning at 500 cruising to 719 RPM running at wide open throttle gives us an frequency from 25 to 36Hz. If we dropped to 2 blades, that would be 17 to 24Hz.

A prop also have a natural frequency which is mainly derived by the length and thickness of the blades. If you whack the blade with a hammer, it will resonate at it's "natural frequency", like a tuning fork. If the generated frequency from the RPM is close to the props natural frequency then the amplitude or strength of the vibrations will greatly increase. Like two kids on either end of a jump rope. If one shakes the rope up and down fast and the other does it slow then the rope never bounces that high. But if they get in sync with each other then the wave in the rope is magnified. Soon the rope breaks and hits both kids in the head and their parents subsequently sue the school for not training their kids on how to properly use a jump rope; but I digress.

So the idea is to separate the frequencies as much as possible. The natural frequency of the prop is a function measurement of how stiff the blade is built. A really thick, stiff blade will have a higher frequency that an thinner, floppier blade. Since a floppy blade is easier to destroy it makes since to make the blade with a higher frequency. The problem is that the bigger the blades the lower the natural frequency. We could make the frequency created by spinning the prop higher by increase the rpm, but that adversely impacts power. However a 3 blade prop is better that 2 so that is an easy choice. And since adding thickness to a blade only slightly affects it's performance. Doubling the plate at the root of the blade would likely go a long way increasing it's frequency. It won't do any harm when it smacks into a log either.

Is that it? I don't guess there is an easy way to predict the natural frequency of a blade is there?

Stuffing Box / Shaft Seal

PSS Seal Volvo, Rubber Stuffing Box

PSS Dripless Shaft Seals are a popular choice but they do leak when shifting directions if the shaft has any slip in a thrust bearing, and they are also $440 for a 2" shaft.  For me the down side is that the PSS is not designed for contact with oil or grease and I may want to use a mild steel driveshaft and protect it by sealing the outboard end of the shaft log and flooding the log with oil.

Volvo Penta makes a Rubber Stuffing Box for 2" shafts with 2 3/4” sleeves which sell for $165 (2010).  They say to grease it every 200 hours so it should be fine to flood the shaft log with oil. The requirement for a 2 3/4" sleeve is a bit of a problem too as a 2 1/2" pipe has an OD of  2.88". Water resistant grease is applied to the inside of the seal by squeezing the sleeve to vent it and then applying the grease to the inside.

A Traditional Stuffing Box, drips, and we don't want the drip, especially if we flood the shaft log with oil to protect the log and steel shaft.

Seeker's Prop & Drive Under Consideration

Shaft 2" Mild Steel with 1:10 Taper
Shaft Log: 3 1/2"  Sch80 steel pipe, 4.00" OD , 3.36"ID
Cutlass:  Corn 2.5" ID, 3 3/8" (3.375") OD

Prop Resources

www.boatdiesel.com
www.usedprop.com
www.a1discountprop.com
www.tacomapropeller.com
 

Hundested Controllable Pitch Prop

So we have all of the working bits except for the blades.  We could go with stainless steel plate bent to shape and welded onto lathed stainless bar.  Or we can go for a closer proximity to the original and cast our own from scrap props.

Why Controllable Pitch?

Used Hundested VP-3 FR-H Teardown

The weather is getting colder so we moved the Hundested inside and starting taking it apart and cleaning it up.

Unfortunately we discovered that their is a collar for the hydraulic system missing from the controller. The real name from this is the distributor ring.

For support for Hundested you can actually call Mogens Christensen in Denmark who now owns the Hundested company.  Or you can call Joel with Pacific Marine Equipment Sales in Seattle at 1-206 281 9841 .  I've spoken to both, and both are very helpful, but Joel  understands my Oki accent better. :)

How Ship Propeller Blades are Cast

These illustrations from Marine Propellers and Propulsion show how propellers were traditionally molded and cast.

I contacted Brain at Boat City Prop Shop in Oklahoma City. And he'll sell us the Nibral out of his pile of scrap props for scrap metal prices.

So the next step is to start on a CAD design that approximates the original blades, but with the diameter and surface area appropriate for our boat.

Propeller Blade Design

Background

Examples for Variable Pitch Props

Resources: http://charlesroring.blogspot.com/2010_02_01_archive.html
Measuring Propeller Pitch: http://propellerhub.com/simple-pitch-measuring.html

Manually Measuring Prop Pitch

http://www.propellerpages.com/?c=articles&f=2006-03-27_manual_pitch_measurement

Find the difference between the leading and trailing edges of the blade at a point 2/3 to 3/4 radius from the center of the hub.

Height for leading edge.   Less the height for trailing edge.   And the angle formed between the center of the hub and each of the two measured points

Formula
Pitch = Difference between the leading and trailing edges of the blade at a point 2/3 to 3/4 radius from the center of the hub * 360 degrees / the angle formed between the center of the hub and each of the two measured points.

Pitch Angle for a Desired Pitch

In order to design a prop of Seeker in CAD we need to find the pitch angle that will create a desired pitch. Pitch Angle is the angle of the pressure face along the line from the leading edge to the trailing edge at a given radius with respect to the plane of rotation measured in degrees. Pitch angle decreases from the blade root to the tip in order to maintain constant pitch.

Finding Pitch Angle: http://www.halepropeller.com/PropellerTerminology.html

If Seeker's prop was fixed pitch, then it should have a pitch around 25 to 27 inches.  So we can optimize the blade for 26" pitch and then the Hundested can adjust it from there.  This will make for a prop that has a twist and therefore it will have more drag when feathered for sailing, but it will be more efficient when we are burning diesel, which unlike wind, is not free.

Need a great calculator?  Use: http://www.wolframalpha.com

Determining the Pitch Angle (not Pitch) for each of the blade crosssections. Checking by using the Manually Measuring Prop Pitch method.

The formula for the pitch angle at a specific radius for a desired pitch.

Pitch angle = tan^-1( Pitch / (2Pi r) )  where: r = radius

So the root of our blade is 3.45" from the center of the hub or r = 3.45, and desired pitch is 26, so:

a = tan^-1(26 / (2 * Pi * 3.45))  = 50.18
...and so on for each cross-section:
a = tan^-1(26 / (2 * Pi * 6.36)) = 33.05
a = tan^-1(26 / (2 * Pi * 13.55)) = 16.98
a = tan^-1(26 / (2 * Pi * 18.22)) = 12.8
a = tan^-1(26 / (2 * Pi * 18.75)) = 12.45

 

We can then check it using the Manually Measuring Prop Pitch formula above:

Pitch = (Difference between the leading and trailing edges of the blade * 360 degrees) / angle formed between the center of the hub and each of the two measured points.

Pitch = (3.06 * 360) / 40.88  = 26.94 ( close enough for me)

I had to test adding a skin many times before I was satisfied with the results, but in the end there were only 7 cross-sections.  Each of these cross-sections were the aligned to the desired 26" pitch using the process outlined above.

Next the skin is applied.  The nipple on the top was added to remove distortion in the skin due to the quick change in shape.  It will be cut away later.

The normal load on each blade is just under 1,300 pounds and the cross section of the root without any fillet is 3.74 sq in.

CNC Cut Pattern

Hundested Blade Patterns

After four test or or failed attempts we got a pattern cut from MDF, or fiberboard.

There is some unwanted high spots on the blade due to the BobCAD software. It did fine where the changes are gradual but it make the tip thinker than planned. However the MDF sands down easily and a slightly thinker tip may be a good improvement when doing battle with sand and gravel.

Propeller Materials

NiBrAl Cast Material  =  0.2745674 lbs/cu inch * 193 cu inches * .5 in avg blade thickness = approximately 27 pounds in the blade + 8 pounds for the gating system or about 35 pounds.

Stainless Steel Bolts: Mertensitic, Hardened and Tempered (HT), 410 or 416 HT.  These aren't as corrosion resistant.
http://www.americanboltcorp.com/astm/grade_markings.htm

Read more: Stainless Steel Bolt Loads & Strengths | eHow.co.uk http://www.ehow.co.uk/list_6547611_stainless-steel-bolt-loads-strengths.html#ixzz1a9k4plhF

Needed:
Pyro Meter  http://www.budgetcastingsupply.com/Pyrometer.php  BCS #7410 Digital Meter, $49
or use a Volt Meter and the Type K Probe Millivolt to Fahrenheit chart.
Tool & Probe release agent, http://www.budgetcastingsupply.com/Marcote-7.php #1050 Marcote 7 Refractory Coating, $22.50
Probe: McMaster-Carr http://www.mcmaster.com Extended-Life Thermocouple Probes, 24",  Number: 3859K46 $10.87 each
  or: http://mifco.com/MS/catalog.php?op=detailed&id=175
  or: http://www.omega.ca/shop/pptsc.asp?ref=TJ36-XCiB_chb&flag=1
 

The thermocouple must be connected to the volt meter correctly.

leave the dross on the melt, when you pout have then push it back
Borax for flux or Boric Acid with Sodium Carbonate 50 50 mix
flux tool to push the flux under the surface
clay-graphite crucible, Or coat a steel crucible with Marcote-7 or ITC-100
skimmer gate
ceramic filter www.ransom-randolph.com  www.tower-packing.com


Randupson Portland Cement -- Portland Cement can be and is used as a bonding agent. Known as the Randupson process, it concerns the use of 15 and 20 mesh, washed silica sand mixed with 10% cement and approximately 5% water. Moulds should be air dried for twenty-four hours and may then be dried out more rapidly.  Dry mix for 5 minutes then add the water.  The mould is formed around the pattern and allowed to air dry for 24 hours.  Once the pattern is removed the mould can be dried with hot air. The blade is cast flat with the boss end making the spure and a vent at the tip. Prior to pouring the mould is preheated the exhaust from the vent temperature is 245 degrees F.  The gate is located at the bottom of the boss so as to allow the molten metal to rise gently into the mould which reduces turbulence and so minimizes oxide formation. Casting temperature for NiBrAl is 2048F (1120C) to 2300F (1260C).  Rapid cooling of the casting will improved tensile properties. Contraction will be 2% in the heavy boss section and less than 1/5% in the blade tip.

Volume 0.2745674 lbs/cu inch

Nickel Aluminum Bronze; Ni-Al Bz, also called "Nibral" and frequently miss spelled as "Nibrill", has a melting point of 1913 to 1940F.  AA Num: 95800

Resources

http://www.copperinfo.co.uk/alloys/bronze/downloads/pub-81-designing-aluminium-bronze-castings.pdf

R & D Pattern & Foundry Co
711 South Wheeling Avenue, Tulsa, OK 74104-3215
(918) 587-2095 ‎

Ni Al Bz Ingot Suppliers

Atlas Bronze, Trenton, NJ  www.atlasbronze.com  800-478-0887
Federal Metal, Bedford, Ohio  www.federalmetal.com 800.736.6636

Hundested V-3 FR-H Documentation

Manufacture Number: 4574

Hydraulic pump maximum 19 inches above shaft.
Return line: 1.5"  Pressure Line: .5"
Flow rate: 4 to 6.5 gallons / minute
Normal pressure: 70 to 140 psi
Relief pressure: 20 bar, 290 psi
Use 350 psi hydraulic pressure gauge on console.
Maximum hydraulic oil temperature 122 to 149 F.
Replace after 2000 hours or 2 years.
Hub material is magnesium bronze.
Hub and internal shaft uses water soluble.
Fill bolt holes with hard tallow, or machinable wax.
Use long cutlass bearing.
Shaft diameter: 65 mm
Propeller shaft to controller shaft alignment: .03 to .05 over 9.75"  

Hydraulic oil degrees englar (E): 2 - 4
    Mobil DTE light or DTE 24
    Shell Turbo T32 or Tellus Plus 32
    Texaco Regal R&O 32 or Rando HD 32
    Conoco Hydroclear R&O 32 or Hydroclear AW 32

Hydraulic Supply

Cummins Power Steering Pump: Zahnradfabrik Friedrichshafen Type 76749?4150
 

Parker Cartridge Valves and Bodies from Aberdine Dynamics, Tulsa OK. 918 437 8000
Parker Cartridge Specifications

Parker: Pilot Operated Pressure Reducing Valve
Primary Bypass - Adjust to open at 290 psi and supply other equipment or dump back to Hundersted controller.
This simulates an autotive steering system that dumps excess when the wheels are not being turned.
PRH082S10 $52.00 Pilot Operated Pressure Reducing Valve: 100 - 1000 psi, 8 gpm, 80 psi drop. Max 200F, Cartridge 3-port B08-3-A6T $27.50 3 port aluminum body for cartridge B08-3-A6T 3/8"

Parker: Pilot Operated Relief Valve
Regulates pressure suppled to controller to 290 psi, when the controller is not using the supply the primary bypass will open
dump the excess pressure and flow.
RAH081S20 $48.50 Pilot Operated Relief Valve, 100 - 2000 psi
B08-2-A6T $19 Body 2-ports, 3/8" O-ring Port

Parts

Aft thrust bearing:  Koyo 6413
Forward thrust bearing: Koyo 6315