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  #16  
Old 03-01-2010, 01:31 PM
portacruise portacruise is offline
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This link will give you most of the information you are looking for:

http://microship.com/bobstuart/spinfin.html

For a 16X16 you need about 8 to 1 gearing, high enough for an athlete. You can drop the prop pitch from there for lower inputs of power from non athletes by switching to a different prop. You would need a huge and expensive prop for 4 to 1 gearing.

One thing I found out many years ago is that cutting the tips of an APC prop really drops the efficiency tremendously. Most of the thrust comes from the higher speed at the tip area. I did careful measurements with a wattmeter using a low power geared down electric motor. I finally just bought a bunch of APCs that were around the size and pitch and honed in on the best one, much like MCDenny did in his posts on the efficient electric boats.

The situation is different that when you have a much higher power reservoir like glow plug engines running in an air medium, IMHO, but I could be wrong....

Enjoy,

Porta

Quote:
Originally Posted by MarkX View Post
Ok, I'm looking at APC Scimitar props here:

http://www.apcprop.com/pindex.asp

Of interest are:
LP16014 16x14
LP16016 16x16

I plan to overprop at first and then cut the prop down gradually to suit. Once I have arrived at a satisfactory effort level by chopping it I'll then guesstimate the nearest size uncut prop. Now it's just a question of suitable gearing... 4 to1 ?
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  #17  
Old 03-01-2010, 01:37 PM
portacruise portacruise is offline
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Oops, make that 10 to 1 on the gearing for 16X16.

Quote:
Originally Posted by portacruise View Post
This link will give you most of the information you are looking for:

http://microship.com/bobstuart/spinfin.html

For a 16X16 you need about 8 to 1 gearing, high enough for an athlete. You can drop the prop pitch from there for lower inputs of power from non athletes by switching to a different prop. You would need a huge and expensive prop for 4 to 1 gearing.

One thing I found out many years ago is that cutting the tips of an APC prop really drops the efficiency tremendously. Most of the thrust comes from the higher speed at the tip area. I did careful measurements with a wattmeter using a low power geared down electric motor. I finally just bought a bunch of APCs that were around the size and pitch and honed in on the best one, much like MCDenny did in his posts on the efficient electric boats.

The situation is different that when you have a much higher power reservoir like glow plug engines running in an air medium, IMHO, but I could be wrong....

Enjoy,

Porta
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  #18  
Old 03-01-2010, 02:43 PM
Tiny Turnip Tiny Turnip is offline
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Some discussion and detailed work by Rick of the seacycle props used on my pedal powered cat Fangle here.
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  #19  
Old 03-01-2010, 03:49 PM
MarkX MarkX is offline
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Thanks Portacruise and T.Turnip but again with both articles, the pitch isn't given or any indication of how it then actually performed in practice.

This is what I mean, there are plenty of people talking at huge length and detail about the vagaries of countless factors but lack of real life, bottom line usable information. Like:
"I found the best prop for my boat (pic) to be one like this (pic), diameter X, pitch Y with a gearing of Z to 1."

Portacruise, the 10-1 gearing with a 16x16 ACP prop suggestion is the kind of useful stuff any budding HPB builder is really looking for to start, thanks.
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  #20  
Old 03-01-2010, 03:54 PM
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gonzo gonzo is offline
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MarkX: the question about how much HP you can produce is the basic data to answer your question. It is right on topic. If you can't tell what power input a propeller will have, all else in nonsense.
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  #21  
Old 03-01-2010, 04:11 PM
Guest625101138 Guest625101138 is offline
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Quote:
Originally Posted by MarkX View Post
Thanks Portacruise and T.Turnip but again with both articles, the pitch isn't given or any indication of how it then actually performed in practice.

This is what I mean, there are plenty of people talking at huge length and detail about the vagaries of countless factors but lack of real life, bottom line usable information. Like:
"I found the best prop for my boat (pic) to be one like this (pic), diameter X, pitch Y with a gearing of Z to 1."

Portacruise, the 10-1 gearing with a 16x16 ACP prop suggestion is the kind of useful stuff any budding HPB builder is really looking for to start, thanks.
Attached shows the prop detail and performance for a slender hull displacing around 130kg doing 6kts.

The prop diameter is 400mm nominal pitch is 665mm and gearing is 1:4 at cadence of 75.

I have also added a couple of the screen dumps that allow you to get this answer.

Rick W
Attached Thumbnails
Pedal boat propeller specifications data-picture-19.png  Pedal boat propeller specifications data-picture-17.png  Pedal boat propeller specifications data-picture-18.png  

Pedal boat propeller specifications data-picture-20.png  
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  #22  
Old 03-01-2010, 04:18 PM
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gonzo gonzo is offline
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Is that 75RPM or 75 counting each foot as one? Do you need to be in the same shape as a bicycle racer to acheive that performance?
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  #23  
Old 03-01-2010, 04:29 PM
MarkX MarkX is offline
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Quote:
Originally Posted by gonzo View Post
MarkX: the question about how much HP you can produce is the basic data to answer your question. It is right on topic. If you can't tell what power input a propeller will have, all else in nonsense.
It's pretty obvious. An HPB is almost invariably powered by a person.
The question was: What prop DxP and gearing did you use on your pedal boat (type), and how did it go, please.
One can deduct everything else from that.
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  #24  
Old 03-01-2010, 04:30 PM
MarkX MarkX is offline
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Excellent Rick. Thanks.
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  #25  
Old 03-01-2010, 05:01 PM
Guest625101138 Guest625101138 is offline
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Quote:
Originally Posted by gonzo View Post
Is that 75RPM or 75 counting each foot as one? Do you need to be in the same shape as a bicycle racer to acheive that performance?
It is rpm. The prop is doing 300rpm with 1:4 gearing.

I have attached another prop photo. Prop is 340mm diameter and pitch is nominally 545mm. This one was used to set the 24hr distance record. It was designed for 360rpm with cadence of 90. The boat only displaced 85kg including the pilot. The calculated drag at 12kph was 36N. Power input measured at 11.9kph (about 7kts) was 150W so prop efficiency almost 84%.

The pilot was quite fit. He could do 1000m at 15kph (over 8kts). This requires power of around 270W.

Rick W
Attached Thumbnails
Pedal boat propeller specifications data-picture-21.png  
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  #26  
Old 03-01-2010, 05:18 PM
Guest625101138 Guest625101138 is offline
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I can sustain 130W for about 4 hours when in reasonable shape. This gets me to around 6kts on my best boat. I use the folding prop pictured above on this boat.

Holding 175W as shown in the JavaProp output above requires a reasonably fit cyclist. It is well beyond what a person doing sedentary desk work can sustain unless they have another training regime.

Rick W
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  #27  
Old 03-01-2010, 06:07 PM
Guest625101138 Guest625101138 is offline
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Quote:
Originally Posted by MarkX View Post
Thanks Portacruise and T.Turnip but again with both articles, the pitch isn't given or any indication of how it then actually performed in practice.

This is what I mean, there are plenty of people talking at huge length and detail about the vagaries of countless factors but lack of real life, bottom line usable information. Like:
"I found the best prop for my boat (pic) to be one like this (pic), diameter X, pitch Y with a gearing of Z to 1."

Portacruise, the 10-1 gearing with a 16x16 ACP prop suggestion is the kind of useful stuff any budding HPB builder is really looking for to start, thanks.
One of the most difficult aspects of understanding the nuances of prop performance is defining pitch. I usually give pitch as a nominal value for the props I design. There are at least three ways of defining pitch.

You will see words like "perfect pitch", which I take to mean that the blades are intended to work at the same angle of attack over the entire width. It may be perfect geometry but it does not give the best performance.

I adjust the pitch across my blades so I get a more favourable pressure distribution on the blades. JavaProp also allows you to do this at 4 intervals for the blade. I do it right across the blade.

JavaProp is a bit limited but it will usually be within 2% of actual if you make sure the Re# is in the range. The "Single Analysis" page provides the Re# if you want to check the "Airfoil" selection.

I have made and tested maybe 50 props and designed many more that people have used with success. So you are benefitting from a huge amount of experience when I suggest you give JavaProp a go. I am now working beyond JavaProp but I remain grateful to the person who steered me toward JavaProp - sadly he has since passed away but we had a lot of fun playing with some interesting HPB ideas.

JavaProp is a wonderfully useful tool for designing propellers. It will give hard data you can rely on if you use it with a bit of understanding.

Very few people using pedal boats actually do any useful measurement. If you could tap into the few people who have played with the boats you will get conflicting opinions that lead you no where.

There is some HPB racing for comparison but very few people approached from a sound engineering point of view - it is mostly trial and error. The fastest pedal boat has done over 18kts - it was well engineered. If you look over the WISIL boat pages you will find pictures of boats and some race information but very little of the work is based on a good understanding of the physics involved with boats and propellers:
http://www.recumbents.com/WISIL/hpb/...m#HPB%20Racing
You are asking for information that most people with pedal boats do not bother with.

The Bolly boat prop is about the best commercial prop but it is not as good as you can make with a couple of pieces of flat bar, welder and grinder.

Rick W
Attached Thumbnails
Pedal boat propeller specifications data-props.jpg  Pedal boat propeller specifications data-v6_failed-_prop.jpg  Pedal boat propeller specifications data-v7_outboard-prop.jpg  

Pedal boat propeller specifications data-v7_strutless_prop.jpg  
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  #28  
Old 03-01-2010, 06:50 PM
Tiny Turnip Tiny Turnip is offline
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Dia: 16", 12" (as noted in linked thread) Pitch: unknown, but estimable from pictures and data in linked thread. Gearing: 1:6 (as noted in linked thread)

Almost all the other data, and pictures you ask for in your first post: in linked thread.

How does it go? just fine. How fast does it go? depends on many variables.

Real life bottom line useable information? Prop specs are one tiny part of the experience of building, operating, and fishing from a pedal powered boat in the sea in varying conditions. I know, I've done it. I've reported my experience in some detail in Rick's main PPB thread. I can expand on the difference in performance between 12" and 16" diameter, one or two engines, up to 4 passengers, operating in 6' waves, F6 conditions, detail on the seacycle drives... I wouldn't want to clutter up your thread with 'waffle'; if you would like to know more, please say so. Or search for my posts in that thread.
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  #29  
Old 03-01-2010, 08:19 PM
MarkX MarkX is offline
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Thanks everyone, I now have the info for a starting point:
40cm x 40cm (16"x16") @ 5/6/7 to1

(Rick, chances are I will be doing the refining you suggest in the future, right now there's the a boat to build asap)

I can now concentrate on the drive part. Initial preference is polyurethane covered drive cord as used on machinery and conveyors. This is DIY joinable to any length and available in a range of diameters and strengths (left one in pic):
http://www.par-group.co.uk/rubber-po...xtrusions.aspx

Being round there is no issue in doing the necessary 90 degree twist and guiding them with simple and light pulleys/rollers.
Not sure how slippery they would be when wet but worth a try because the pulleys are dead easy to make in numerous ways. If they slip I could double-wind the cord over the drive pulley/s or make the pulley surface coarser. But that's a different thread...

This thread has served my purpose but it would be good if people kept posting their diameter+pitch+gearing+ boat type etc. for the benefit of other builders.
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  #30  
Old 03-01-2010, 08:43 PM
Guest625101138 Guest625101138 is offline
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Quote:
Originally Posted by MarkX View Post
....
I can now concentrate on the drive part. Initial preference is polyurethane covered drive cord as used on machinery and conveyors. This is DIY joinable to any length and available in a range of diameters and strengths (left one in pic):
http://www.par-group.co.uk/rubber-po...xtrusions.aspx

....
The advice with this is to get the stiffest cord available. Even with this it will still need a slack side tensioner. Use a big pulley on the crank. You also want to increase the angle of wrap on the prop pulley.

The torsional rigidity of the drive train from cranks to prop is a large factor in the smoothness of the drive. It also has some bearing on the efficiency and can severely limit sprint performance if too flexible. I have determined what torsional compliance is acceptable. If you use wire cored cord of 2mm or more with a big diameter driving pulley it will be OK.

I would seal the prop shaft to avoid the cord pumping water back onto the boat. You want to keep the drive leg as narrow as needed to fit the cords.

I have recently been testing a toothed belt with 10mm pitch and 16mm wide. The main pulley is 120mm diameter. I can get it to skip teeth even with a belt tensioner at input power above 250W. It is a nice feel and overcomes a messy chain but limits the top speed to about 14kph.

Rick W
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