Proper propeller

[IwillIt]

any body know the right propeller of a westerbeke w70 on a 26 outer reef?

 

[Al]

IwillIt- Try filling in all the blanks as honest as you are able, into this site's format. It will give you a actuate wheel size required for the information given.
Al-Ketchikan (Bridge to Nowhere) Alaska

Vicprop - Propeller Calculator

 

[CPseudonym]

I'm as big a DIY'er as you'll ever meet and have a hard time understanding the fascination with prop calculators. Sitting down with a competent local "prop guy" is the route for me if and when I need the council. If it's because you're finding a good deal online, then the vendor supplying the wheel had better be able to calculate the size or they ain't getting my money.

My understanding of the subject is that online calculators can only get you in the ballpark. For the cost of a new wheel I want to deal with someone who can do better than get me in the ballpark and so far as I know that's the domain of a "prop guy".

If I'm wrong about this somebody please set me straight on the subject.

 

[FF]

My understanding of the subject is that online calculators can only get you in the ballpark.

Yes but the ballpark is quite large, there is no ONE PERFECT prop.

All props are a compromise , and the question then becomes what part of perfection should you desire.

A choice of say a 5 blade because the boat designer wanted minimum draft , and placed the prop so close to the hull bottom that a 3 or 4 blade would make noise ?

The choice of a cruising prop to cut down engine wear and noise by cruising at 1200 or 1500 rather than 2100?

These different props might offer near the same performance ,speed/fuel burn but be very different to live with, hence the prop guy ,
IF you cant work it out for yourself with Skeens.

 

[motion30]

I ran my vessel on the prop calculators several times. I talked to two local prop guys. I ended up buying what the calculator suggested . The props are perfect. the to prop shops I talked to were more interested in selling stock on hand then getting me exactly what I needed

 

[Al]

Forum,

Of the comments listed to date, I would think that Motion 30 is the more honest towards reality..
The calculator is a tool. It allows you to view options to discuss with your prop shop. Being somewhat knowledgeable would seem the smart way to go rather than a 'dumb blond ' approach.
Were you to use the aforementioned calculator you would receive recommendations for three and four bladed wheels, those results are worthy to the inexperienced. Very important aspects in making a selection.
Yes, you can vary with increased pitch and decreased diameter to obtain equal results. Knowing what the differences are with blade count is credical to ability of the power avaiable to perform, as you search the market place for wheels offered for sale.

Knowing as a general rule one inch in diameter equals two inches of pitch as a sidebar piece of information then gives you greater scope within the market as you calculate what the wheel d/p information shows.

FF is correct in his observation that all calculations are a compromise. that being said, finding a starting point with an online calculator seems reasonable.

In the case of our boat, the calculator hit the nail right on. It produced the data that matched our current wheel. That is why the comfort in offering it up as a response to somebody asking.
Given the results of a calculator, a site such as this will provide a wheel shopper the experence as to what is out there. Buy from it? Somebody is or the site would not be in business.

14 inch 3 Blade Aluminum Feathering Propellers,1 Bore 1.75 Opening items in donsmarine-2008 store on eBay!

The knowledge gained by having this starting point gives me comfort as I view the inventory.

Like many locations, we have a local propeller shop that has a wonderful reputation for wheel repair and wheel changes as required or selected. Yet even they have to use some sort of calculations to come to a result other than just listening to what a common regular boat owner profuse. That is the experience that I have had in discussions with them. The end result is putting the boat on the grid or hard, change out from their inventory, try the wheel and repeat or physically alter, till you are satisfied. There is an expense involved with that activity and it is not the propeller shop that pays. Just saying.
Al

 

[FF]

The end result is putting the boat on the grid or hard, change out from their inventory, try the wheel and repeat or physically alter, till you are satisfied.

Frequently , its 3rd time lucky!

 

[motion30]

The end result is putting the boat on the grid or hard, change out from their inventory, try the wheel and repeat or physically alter, till you are satisfied.

Frequently , its 3rd time lucky!

I changed mine underwater

 

[Nomad Willy]

I agree w Craig. Find a prop guy and a good one.

HOWEVER ...... one should gravitate toward a prop guy that works on props coming of boats similar to your own. A guy that works on yachts won't do a fish boat guy much good and those that work on commercial boats won't know much about what's good for your 26' Tolly or your IO.

ALSO ... some prop guys have serious obsessions like a fondness for excess rake. I personally believe cupped props have no business on a trawler but many prop guys will cup a prop. You can easily say the prop guy knows more than I do about props but there are times when that dos'nt hold water.

THE BEST information about re-powering comes from engineers and the best information about props comes from engineers too. Call Michigan. I have and I got what I think was real good information.

 

[Al]

Come to Union Machine Shop here in Ketchikan. The boys there are as equally up to commercial, pleasure, and now inboard/outboard and straight outboard props. rebuild, re-pitch, increase/decrease diameter and work with cupped wheels.

And when you have Michigan on the line, I'd bet a pretty penny that they will ask for similar information as does the submitted prop calculator. What do you suppose they do with that information? Hummmmmm. I'd bet another pretty penny that they put that information into some sort of Michigan calculator. Just saying.
Would it not be interesting to complete a independent calculator formula and then compare with Michigan given or desiring the comparison?

As to changing underwater, that works on the cheap if you are the diver and the wheel pulling is achievable. I'd bet yet a third pretty penny that many of us have had the damndest time pulling long stressed years on the shaft wheels. Some even requiring heat.

Good to hear all points of the discussion, It is thought that 'IwillIt' has received input with more perhaps to come.

Best of New Year to all above posters.

Al

 

[Nomad Willy]

Actually there are much better propellers than Michigan.

Yea Al I know about Union Propeller in Thomas Basin. Never had then do anything but I tried to buy a prop from them twice. Once he didn't have the prop I wanted and next time the price was almost as high as a new prop. Bought new from Tacoma Propeller in the city of that name and got exactly w hat I wanted. And I don't know anything about how good they are w pleasure boat props but I know they do some in the summer.

I miss Thomas Basin and "go'in to town". Do you ever come south Al? We are quite close to the ferry in Bellingham.

 

[jleonard]

When I repowered my Mainship 34 I used several calculators....boat diesel's ,Black Dogs,and Michigan's.
The Michigan one was right on the money. The others weren't, close. I ended up 30 rpm over rated at my heaviest loading, which is right about where I wanted to be on a Cummins 6bta.
All calculators are not the same

 

[Al]

Old computer adage: "Garbage in-Garbage out". At the very least you had comparable which in the end gave confidence to the purchase.

One subject that IwillIt may wish to consider is the factors with pitch and diameter changes. I believe the rough computations is: One inch of diameter equals approximately 400 RPM drop or 200 RPM drop per one inch of pitch increase. That based on one inch of diameter increase equals two inches of pitch. (cup blades differ, this is for straight blades computation . Using this one can bring other wheels with different pitch/diameter viewed into perspective of relationship to known pitch and diameter information.

Another forum question perhaps is the actual event that creates WOT. Is WOT arrived with the boat pushing against a fixed object (dock) or is WOT arrived with running at WOT free? There is an actual difference. My belief is running free as under actual conditions. The questions is asked from a tug boat application where the power of the wheel is measured by "Bullard Pull". the wheel providing the most pulling power. Different applications for sure, yet efficiency of the wheel is in play. Bullard Pull is determined by pulling or pushing against a fixed object. (I can be corrected on this for sure.)
If this is determined by a forum moderator to be a separate forum, take what action is required. Thanks.
Al

 

[FF]

For most non commercial tug boats the prop is optimized for the boat underway.

The expected Speed of Advance is part of the pitch calculation.

A 7K boat would have the water departing the prop at 14K -16K.

Stopped the 14K prop would overload the engine.This is common for acceleration , just watch the black smoke as operators advance the throttle rapidly to get up on the plane.

An engine usually will be tested in neutral to see if it reaches its rated no load RPM at full throttle .

Then underway again to see if the engine comes within 150 or so RPM of the no load speed.

This is the technique for fast plaining boats like fish killers that operate at or near full RPM for much of their operation.

Not much use for a displacement boat as most operate at such a low percentage of full power.

 

[RickB]

Another forum question perhaps is the actual event that creates WOT.

The governor of a diesel engine has two settings which apply to "WOT."

The "speed stop" or rpm limiter. This is a mechanical barrier or electronically derived signal that is used to limit the maximum rpm of the engine by limiting the amount of fuel delivered.

The "fuel stop" or fuel delivery limiter. This is a process limit that prevents more than a certain amount of fuel to be delivered to the engine. Depending on the type of governor and the engine application, this may be a moving target but there is a maximum level ... the fuel limit may be controlled by manifold pressure (turbo output), rpm, torque, or a larger number of environmental and operating parameters in modern electronically controlled engines.

In normal operation, the "throttle" sets a target rpm. If the load on the engine is below a certain level, the governor will supply more or less fuel to maintain that rpm.

If the throttle is advanced to its mechanical or electrical stop with little or no load on the engine, the speed limiter will prevent the rpm from exceeding the "high idle" setpoint by limiting the fuel delivered.

If the engine is unable to reach the rpm setpoint because of loading, the fuel limiter will reach its maximum delivery point and until the throttle is retarded to the point where the rpm limiter is no longer demanding more fuel delivery, the fuel limiter is controlling.

BTW, it's bollard pull.

 

[kulas44]

It is bollard. And everything rickb said about the "guvna" is correct. Electronic engines are immune to this.

 

[Al]

Thanks Rick,We are leading away from IwillIt's inquiry as often happens. hell of a explanation, lot to learn from your dissertation. Sorry about the terminology. It was not even an mis-spell! Not that you delved into the diesel applications there little application where wheel measurements are valid, though now I believe that it is a separate category of how tug/commercial power is developed. Important, but a different direction. Am I correct?

Al

 

[RickB]

... now I believe that it is a separate category of how tug/commercial power is developed. Important, but a different direction. Am I correct?

I'm not quite sure what you mean. A "properly matched" propeller, red gear, and engine is defined by the type of boat and its intended use.

A harbor assist tug may be "overpowered" for its size and seriously compromised as far as speed and free running economy compared to another vessel the same size intended to take tourists out to watch whales.

A whale watching boat would make a miserable ship assist tug or mid-water trawler.

Horses for courses as they say ...

 

[Al]

It may have been worded incorrectly Bick, however you interpreted correctly. The two words were meant to be inclusive as two classes to be considered not and/or.
Al

 

[IwillIt]

I ended up getting a 19" by 20 P. Thanks for all the good info.

 

[Al]

Butt, butt IwillIt, How did you arrive to the point that this was the purchase? All of us have offered opinions and I am sure all would be interested in the steps you took to come to the conclusion and purchase.

Al
I wondered why the baseball kept getting bigger. Then it hit me.

 

[IwillIt]

I read a lot a literature about pitch, prop size and how work load all play a part in prop selection. I ran a bunch of prop calc ya'll suggested plus ones i found and got my range. so I selected one in the range for max speed keeping in mind I can change pitch up or down 2 pitch degrees. I went to my local salvage yard picked one out saving me $$. with all the money i saved buying used i can get the pitch changed, trued and still be on top. I am putting it on tomorrow so ill have to get back to you on the sweet spot rpm and speed.

 

[123]

Old computer adage: "Garbage in-Garbage out". At the very least you had comparable which in the end gave confidence to the purchase.

One subject that IwillIt may wish to consider is the factors with pitch and diameter changes. I believe the rough computations is: One inch of diameter equals approximately 400 RPM drop or 200 RPM drop per one inch of pitch increase. That based on one inch of diameter increase equals two inches of pitch. (cup blades differ, this is for straight blades computation . Using this one can bring other wheels with different pitch/diameter viewed into perspective of relationship to known pitch and diameter information.

Another forum question perhaps is the actual event that creates WOT. Is WOT arrived with the boat pushing against a fixed object (dock) or is WOT arrived with running at WOT free? There is an actual difference. My belief is running free as under actual conditions. The questions is asked from a tug boat application where the power of the wheel is measured by "Bullard Pull". the wheel providing the most pulling power. Different applications for sure, yet efficiency of the wheel is in play. Bullard Pull is determined by pulling or pushing against a fixed object. (I can be corrected on this for sure.)
If this is determined by a forum moderator to be a separate forum, take what action is required. Thanks.
Al

Bollard Pull Rating

This is the traditional calculated measure of merit that was used as a “rating” for tugboats. It is simply the theoretical thrust achieved at zero speed of advance and full engine RPM. Bollard pull rating is an abstract (and somewhat academic) state that cannot be achieved in real operation. This is due to two things – propellers accelerate water as they spin so they never really see water at zero speed, and engines typically do not reach full RPM at towing speeds (as their propellers are “overloaded” at towing since the pitch is typically sized for a speed higher than the towing speed).

The thrust of a bollard pull rating was convenient to calculate since all you needed was one point from a propeller curve (e.g., KT at J=0) and the engine’s rated RPM (with reduction ratio, of course). This calculated thrust – albeit fictional – provided a simple numerical figure to compare one tug’s potential thrust against another in a towing scenario.

 

[FF]

and engines typically do not reach full RPM at towing speeds (as their propellers are “overloaded” at towing since the pitch is typically sized for a speed higher than the towing speed).

This means that IF you tie to a dock , put the boat in gear and look for rated RPM the prop will overload the engine and you will NOT see the book RPM.

You can only check a cruising boat prop underway.

 

[123]

and engines typically do not reach full RPM at towing speeds (as their propellers are “overloaded” at towing since the pitch is typically sized for a speed higher than the towing speed).

This means that IF you tie to a dock , put the boat in gear and look for rated RPM the prop will overload the engine and you will NOT see the book RPM.

You can only check a cruising boat prop underway.

A real example;

Re-powering a twin engine Tug;

Needs a Bollard Pull of 35 Metric Tons or 343,5 kN
Given; 2 Engines 1400 hp @ 1600 RPM


Calculated Bollard Pull - 383,56 kN

Real live Towing at 6 kts - 2800 hp @ 1600 RPM gives a trust of 257,9 kN
Cruising at 10 kts - 612 hp @ 1238 RPM trust of 41,4 kN

The Bollard Pull will never be reached as it cavitates and overloads the propellers.

 

[Al]

Have we come full circle with the information provided by Reiziger,FF,and Rick? The question revolved around a proper "cruising" propeller. The conclusion drawn is to overload the propeller to achieve hull speed or there about, at a 'working' RPM. In other words, free from the dock in a pleasure boat one would not achieve WOT yet at a lower RPM achieve hull speed or there about. The gain is a working engine, higher engine temperature (Not excessive just a tad higher) quieter engine sound (deeper not screaming).
Those factors are involved with a decision to increase the size of our current wheel. The current wheel matches what the conversion formula suggested in the first post to IwillIT. We do achieve WOT running free, (3000 RPM) Hull speed is achieved at 2400 RPM. Engine temp running about 175 degrees. By either increasing diameter or pitch we will lower the RPM, maintain hull speed, and increase operating temperature.
With the knowledge of what increasing diameter and increasing/decreasing pitch can provide the chore of finding a matching wheel begins with confidence.
Been a great thread, thanks to IwillIT and participators.
Al Johnson-Ketchikan (Bridge to Nowhere) Alaska

 

[Tony B]

Try miwheel.com

Michigan Wheel comes highly recommended. Fill out the form completely.
Fortunately, I was on the hard when I dealt with them. They even had a question about the WL beam. No where in the Mainship specs do they give the WL Beam. WL Length - yes. WL Beam - No.
Anyway, they talked me into less pitch then I wanted and I extremely happy with the results. I cruise with one engine at a time (except for docking) and that way I don't underload nor overload the twins.

 

[Nomad Willy]

Al,
If you haven't already done it ... even if you have consider submitting your over propping intentions to Michigan and see what they say.

Re the pics:
For under 15 knots this is an excellent prop. Michigan MP. This one is on my boat. On most boats the MP is slightly less efficient but on some (according to Michigan) it is more efficient. Much better reverse thrust and good smooth running. Ask the Michigan people about this prop.

 

[Al]

Eric-What is 'MP'?

al

 

[Al]

Eric- Okay, I just submitted the information the form requested. It is the same information that I used on the calculator that I have been recommending. Now, the Michigan form DID call for what I wanted to achieve which may or will I suppose because of that, be different from the information submitted on the calculator I used as that calculator ask for specific vessel information to recommend the wheel for the boat, not what I desire. Difference of the two formats.
AMJ