I am considering the possibility of changing my 2 blade prop to a 3 blade. I know much has been discussed on the site ( still cannot get search function to work )
I have Macht Nichts CD 30 MK II with a Weterbeke 21a, and at 2200 rpm we cruise at 5 kts. What can I expect from a 3 blade prop ? What are the pro's and con's. Is there a specific prop that is better than others?
Thanks in advance for the help!!!!!
Michael Heintz
s/v Macht Nichts CD 30 MK II 004
Mzenith@aol.com
3 blade prop
Moderator: Jim Walsh
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Ken Cave
Re: 3 blade prop
I have a Cape Dory 28 and switched to a three bladed prop when I purchased the boat. The local boat yard took my existing prop to a prop shop in Seattle, and they matched the new three bladed prop to this prop and my Volvo MD7A engine.
I run mine at 2200 RPM and usually travel over six knots and use about a half a gallon of fuel an hour.
A friend of mine who also owns a Cape Dory 28 has his in the yard and is doing the same thing as he could not get over five knots running the engine full tilt!!
As we folks use our engines a lot in the San Juan and Gulf Islands, the three bladed prop is the only way to go!!
The change over was not cheap-about $500.00, and that was for the new prop, modifications to the blade, and remounting the prop to the boat.
Ken Cave
bcave@whidbey.net
I run mine at 2200 RPM and usually travel over six knots and use about a half a gallon of fuel an hour.
A friend of mine who also owns a Cape Dory 28 has his in the yard and is doing the same thing as he could not get over five knots running the engine full tilt!!
As we folks use our engines a lot in the San Juan and Gulf Islands, the three bladed prop is the only way to go!!
The change over was not cheap-about $500.00, and that was for the new prop, modifications to the blade, and remounting the prop to the boat.
Ken Cave
bcave@whidbey.net
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mike
Re: 3 blade prop
Mike,
When I took LaVida (CD33) south to the Bahamas from Lake Ontario (and return), I knew I would be motoring more than ever, especially the ICW bits.
So, I went to my local Michigian Wheel dealer and gave him all the specs on my Volvo MD11C along with the boat info. Their engineers came back with a spec and I bought a fixed 3 blade prop from them. I think it was about $250 USD,(I also bought their prop puller which later proved invaluable for another boater, who damaged his prop and couldn't change it out underwater, but that's another story).
I noticed immediate performance increases. I could achieve my hull speed with less rpm's, punch into headseas a WHOLE lot better and most importantly, it gave me a wicked reverse capability, along with better rudder control at low rpm. A quick blast on the throttle and LaVida fairly dances around a pin.
Just my two cents......I won't go back to a two blade, although I do carry it onboard, as a spare, for some unforseen circumstance.
All in all it was one of my better upgrades on the boat.
Good Luck,
Mike
mpr@seascan.com
When I took LaVida (CD33) south to the Bahamas from Lake Ontario (and return), I knew I would be motoring more than ever, especially the ICW bits.
So, I went to my local Michigian Wheel dealer and gave him all the specs on my Volvo MD11C along with the boat info. Their engineers came back with a spec and I bought a fixed 3 blade prop from them. I think it was about $250 USD,(I also bought their prop puller which later proved invaluable for another boater, who damaged his prop and couldn't change it out underwater, but that's another story).
I noticed immediate performance increases. I could achieve my hull speed with less rpm's, punch into headseas a WHOLE lot better and most importantly, it gave me a wicked reverse capability, along with better rudder control at low rpm. A quick blast on the throttle and LaVida fairly dances around a pin.
Just my two cents......I won't go back to a two blade, although I do carry it onboard, as a spare, for some unforseen circumstance.
All in all it was one of my better upgrades on the boat.
Good Luck,
Mike
mpr@seascan.com
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Jerry J Commisso
Re: 3 blade prop
Mike,
I was just wondering how much of a negative impact it has had on the boat while under sail.
Thanks,
Jerry J Commisso
CD30c CHELSEA ROSE
liasboat@aol.com
I was just wondering how much of a negative impact it has had on the boat while under sail.
Thanks,
Jerry J Commisso
CD30c CHELSEA ROSE
mike wrote: Mike,
When I took LaVida (CD33) south to the Bahamas from Lake Ontario (and return), I knew I would be motoring more than ever, especially the ICW bits.
So, I went to my local Michigian Wheel dealer and gave him all the specs on my Volvo MD11C along with the boat info. Their engineers came back with a spec and I bought a fixed 3 blade prop from them. I think it was about $250 USD,(I also bought their prop puller which later proved invaluable for another boater, who damaged his prop and couldn't change it out underwater, but that's another story).
I noticed immediate performance increases. I could achieve my hull speed with less rpm's, punch into headseas a WHOLE lot better and most importantly, it gave me a wicked reverse capability, along with better rudder control at low rpm. A quick blast on the throttle and LaVida fairly dances around a pin.
Just my two cents......I won't go back to a two blade, although I do carry it onboard, as a spare, for some unforseen circumstance.
All in all it was one of my better upgrades on the boat.
Good Luck,
Mike
liasboat@aol.com
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Geoff Safron
Re: 3 blade prop
I second Mike's story heartily. I also bought a prop from Michigan Wheel, who did all the math for me. Also paid about $250 for a 3-blade for my MD7A ('78 CD30 Cutter). Much better control in forward, hull speed at about 2000 RPM. I wouldn't exactly categorize my reverse capability as "wicked" (she's still a bit of cow in port), but I have saved my bow several times with the increased braking response. I haven't noticed any tangible drag under sail, but then one doesn't buy a CD to race it (at least I didn't). I imagine you can pull the shaft out of gear and let the prop rotate, which would mean close to no drag at all, though I'll bet there are those amongst us who advise against it in terms of bearing wear. Mike, what did that prop-puller cost, if I may ask?
brainstorm@unidial.com
brainstorm@unidial.com
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mike
Re: 3 blade prop - reply
I haven't noticed much extra drag undersail, although I know there is. My Volvo man says that it is necessary to have the transmission (on my MD11C) in neutral while sailing so it does turn.
I refer to reverse as wicked, because the three blade makes it seem like I didn't have any reverse before.
I think I paid $185 USD for the prop puller which is worth its weight in gold when you need it. Allows you to change props (underwater-I'm a retired commercial diver)without hauling the boat and is much less stressful on the drive train.
mpr@seascan.com
I refer to reverse as wicked, because the three blade makes it seem like I didn't have any reverse before.
I think I paid $185 USD for the prop puller which is worth its weight in gold when you need it. Allows you to change props (underwater-I'm a retired commercial diver)without hauling the boat and is much less stressful on the drive train.
Geoff Safron wrote: I second Mike's story heartily. I also bought a prop from Michigan Wheel, who did all the math for me. Also paid about $250 for a 3-blade for my MD7A ('78 CD30 Cutter). Much better control in forward, hull speed at about 2000 RPM. I wouldn't exactly categorize my reverse capability as "wicked" (she's still a bit of cow in port), but I have saved my bow several times with the increased braking response. I haven't noticed any tangible drag under sail, but then one doesn't buy a CD to race it (at least I didn't). I imagine you can pull the shaft out of gear and let the prop rotate, which would mean close to no drag at all, though I'll bet there are those amongst us who advise against it in terms of bearing wear. Mike, what did that prop-puller cost, if I may ask?
mpr@seascan.com
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Ken Coit
Re: 3 blade prop
Parfait has a three-bladed 15R14 wheel and at approximately 2200 RPM on the Perkins 4-108, Parfait runs about 5.1 Kts. over the ground. Backing is an experience, as usual, but we have power and can turn her around in place if we have to!
I have not had a two-bladed experience with Parfait, so I can offer a comparison. However, yesterday under sail we managed 8.1 over the ground in 10 - 15 Kts. It was a great day for sailing.
Ken
parfait@nc.rr.com
I have not had a two-bladed experience with Parfait, so I can offer a comparison. However, yesterday under sail we managed 8.1 over the ground in 10 - 15 Kts. It was a great day for sailing.
Ken
Michael Heintz wrote: I am considering the possibility of changing my 2 blade prop to a 3 blade. I know much has been discussed on the site ( still cannot get search function to work )
I have Macht Nichts CD 30 MK II with a Weterbeke 21a, and at 2200 rpm we cruise at 5 kts. What can I expect from a 3 blade prop ? What are the pro's and con's. Is there a specific prop that is better than others?
Thanks in advance for the help!!!!!
Michael Heintz
s/v Macht Nichts CD 30 MK II 004
parfait@nc.rr.com
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Matt Cawthorne
Re: 3 blade prop
Mike,
Be very careful when ordering a new prop. The prop is part of a system including the hull, engine and transmission. Where a 3 bladed prop will do the most good for you is when the prop is really loaded up. That would be when accelerating/decelerating with lots of power. At cruising conditions you can get better speed with your existing prop without changing engine RPM simply by having a prop shop increase the pitch. That does not mean that the prop or the system is somehow more efficient. What it does mean is that the engine is dumping in more fuel per revolution, but doing fewer revolutions. So why doesn't everyone increase the pitch? It has to do with the power curves for the engine and prop. The engine is capable of delivering more torque (and power) than the prop is capable of using at low rpm's. As the RPM's increase the power that the prop consumes goes up faster than the engine's capacity increases. At some point the power that the engine can deliver equals the power that the prop consumes. Below that RPM the engines governor limits the fuel delivered to the cylinders. If you try and push the system harder, the governor adds extra fuel and it just comes out the exhaust as black smoke.
There are lots of tradeoffs here. If you wish to have the engine run slower and quieter then increase pitch. If you want maximum thrust at low speed, ability to punch through heavy seas and potentially claw off of a lee shore some day, then you want a pitch that allows your engine to just barely reach it's maximum rated RPMs.
How to do this? It is best to start with a calibrated tachometer. Tachs are notoriously inaccurate. I made a correction table with a calibrated strobe and worked from there. Take your boat out under calm conditions and gather test data. RPM's versus speed. If you can not reach maximum RPM's then you need less pitch. If you can, then perahps you could use more. Whoever you get to sort out what your new prop will be should be interested in this info. An outfit like Michigan Wheel should do a reasonably good job without it, but if you wish to get the prop well matched you may have to re-pitch it later.
Most props can be re-pitched about two inches. The big problem is if you do not know the history of that particular prop.
Once you have your new prop you should take it out and do the RPM versus speed thing again. I went through this process on my CD-36 and found that the prop pitch was very high. I could only reach about 70% of the rated engine RPM (at hull speed). I dropped the pitch and got more like 80% of it's capability. The engine runs faster at cruising speed, but the boats ability to power through rough conditions is better. I almost wish that it had a two speed transmission. One to allow the engine to run slow while cruising and one to get every ounce of power if it is ever needed.
Dave Gerr's "propeller handbook" is a good one if you would like to do some reading.
Matt
mcawthor@bellatlantic.net
Be very careful when ordering a new prop. The prop is part of a system including the hull, engine and transmission. Where a 3 bladed prop will do the most good for you is when the prop is really loaded up. That would be when accelerating/decelerating with lots of power. At cruising conditions you can get better speed with your existing prop without changing engine RPM simply by having a prop shop increase the pitch. That does not mean that the prop or the system is somehow more efficient. What it does mean is that the engine is dumping in more fuel per revolution, but doing fewer revolutions. So why doesn't everyone increase the pitch? It has to do with the power curves for the engine and prop. The engine is capable of delivering more torque (and power) than the prop is capable of using at low rpm's. As the RPM's increase the power that the prop consumes goes up faster than the engine's capacity increases. At some point the power that the engine can deliver equals the power that the prop consumes. Below that RPM the engines governor limits the fuel delivered to the cylinders. If you try and push the system harder, the governor adds extra fuel and it just comes out the exhaust as black smoke.
There are lots of tradeoffs here. If you wish to have the engine run slower and quieter then increase pitch. If you want maximum thrust at low speed, ability to punch through heavy seas and potentially claw off of a lee shore some day, then you want a pitch that allows your engine to just barely reach it's maximum rated RPMs.
How to do this? It is best to start with a calibrated tachometer. Tachs are notoriously inaccurate. I made a correction table with a calibrated strobe and worked from there. Take your boat out under calm conditions and gather test data. RPM's versus speed. If you can not reach maximum RPM's then you need less pitch. If you can, then perahps you could use more. Whoever you get to sort out what your new prop will be should be interested in this info. An outfit like Michigan Wheel should do a reasonably good job without it, but if you wish to get the prop well matched you may have to re-pitch it later.
Most props can be re-pitched about two inches. The big problem is if you do not know the history of that particular prop.
Once you have your new prop you should take it out and do the RPM versus speed thing again. I went through this process on my CD-36 and found that the prop pitch was very high. I could only reach about 70% of the rated engine RPM (at hull speed). I dropped the pitch and got more like 80% of it's capability. The engine runs faster at cruising speed, but the boats ability to power through rough conditions is better. I almost wish that it had a two speed transmission. One to allow the engine to run slow while cruising and one to get every ounce of power if it is ever needed.
Dave Gerr's "propeller handbook" is a good one if you would like to do some reading.
Matt
mcawthor@bellatlantic.net
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Catherine Monaghan
Re: 3 blade prop
Mike,
Realization, our CD32, also has a Westerbeke 21A engine. We have a 3-blade prop. She cruises easily at over 6 knots under power at 2200 rpm. We're not in the water yet. If I can remember, I'll attempt to measure the prop and let you know what size it is.
catherine_monaghan@merck.com
CD32 <a href="http://www.hometown.aol.com/bcomet/real ... ization</a>, #3
Rahway, NJ
Raritan Bay
catherine_monaghan@merck.com
Realization, our CD32, also has a Westerbeke 21A engine. We have a 3-blade prop. She cruises easily at over 6 knots under power at 2200 rpm. We're not in the water yet. If I can remember, I'll attempt to measure the prop and let you know what size it is.
catherine_monaghan@merck.com
CD32 <a href="http://www.hometown.aol.com/bcomet/real ... ization</a>, #3
Rahway, NJ
Raritan Bay
Michael Heintz wrote: I am considering the possibility of changing my 2 blade prop to a 3 blade. I know much has been discussed on the site ( still cannot get search function to work )
I have Macht Nichts CD 30 MK II with a Weterbeke 21a, and at 2200 rpm we cruise at 5 kts. What can I expect from a 3 blade prop ? What are the pro's and con's. Is there a specific prop that is better than others?
Thanks in advance for the help!!!!!
Michael Heintz
s/v Macht Nichts CD 30 MK II 004
catherine_monaghan@merck.com
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Ken Coit
Re: 3 blade prop
Catherine,
Parfait's prop size is stamped on the hub.
Ken
parfait@nc.rr.com
Parfait's prop size is stamped on the hub.
Ken
Catherine Monaghan wrote: Mike,
Realization, our CD32, also has a Westerbeke 21A engine. We have a 3-blade prop. She cruises easily at over 6 knots under power at 2200 rpm. We're not in the water yet. If I can remember, I'll attempt to measure the prop and let you know what size it is.
catherine_monaghan@merck.com
CD32 <a href="http://www.hometown.aol.com/bcomet/real ... ization</a>, #3
Rahway, NJ
Raritan Bay
Michael Heintz wrote: I am considering the possibility of changing my 2 blade prop to a 3 blade. I know much has been discussed on the site ( still cannot get search function to work )
I have Macht Nichts CD 30 MK II with a Weterbeke 21a, and at 2200 rpm we cruise at 5 kts. What can I expect from a 3 blade prop ? What are the pro's and con's. Is there a specific prop that is better than others?
Thanks in advance for the help!!!!!
Michael Heintz
s/v Macht Nichts CD 30 MK II 004
parfait@nc.rr.com
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Geoff
Re: 3 blade prop -Anyone tried a folding prop?
They're expensive, and I've heard there's a trade-off in longevity, but there's an instant answer to the drag question. Anybody have one?
brainstorm@unidial.com
brainstorm@unidial.com
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warren stringer
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Brian W.
Re: 3 blade prop -Anyone tried a folding prop?
I've also heard reports from mechanics that some take considerable rpms to get them "opened." One local guy who put one on would put it in gear and go nowhere because the low idle of his engine wasn't snapping the thing opened. I think they figured they might have to up the idle or something. On our "non-race" boats, I wonder whether there would be any noticable gain?
btw, we might have one (possibly 2) three blade props for sale from a CD 33. let me know if interested.
Brian W.
btw, we might have one (possibly 2) three blade props for sale from a CD 33. let me know if interested.
Brian W.
Geoff wrote: They're expensive, and I've heard there's a trade-off in longevity, but there's an instant answer to the drag question. Anybody have one?
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Geoff
Re: 3 blade prop -Anyone tried a folding prop?
Hm, that delay could give one fits doing the "forward-and-back" dance in the harbor. I'd just heard that the bearing that holds each blade one eventually gives, rendering one essentially propless...
brainstorm@unidial.com
brainstorm@unidial.com
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michael soloway
Re: 3 blade prop
I just purchased a CD31 1984 from the original owner. He had removed the original prop and installed a huge 3 bladed prop. I don't know anything about the prop yet except to tell you that it cruises the 31 at 6-7 kts at 2200 rpm - and is impossible to maneover in reverse. Since IO have no comparison with the original prop I don't know if this is a problem, but, I can barelt back out of my slip before she swings way off course in reverse. Stopas very quickl;y, though, when used for that. The original owner said that he installed it because he liked to have good brakes.
m@msoloway.com
m@msoloway.com