I have a cape dory 30 MkII with a 2 blade 14" 12 prop. The prop shop recommends changing to a 3 blade. Has anyone done this and how did it work? Thanks
Boyd
tern30@aol.com
3 blade prop
Moderator: Jim Walsh
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mike
Re: 3 blade prop
Sort of like asking a car dealer if you need a new car, I guess. We had a CD30 with a 2 bladed prop. I looked and looked, asked and asked, read and read and finally determine what is obvious in retrospect. That is, the increase in oomph would be negligible, the increase in reverse control even less due to the nature of the beast, the increase in resistence under sail negligible. fThe more I looked, the clearer it became that the only benefit would derive to those who pulled the boat so I could install it and those who sold the prop. Mike
michaelconniesmith@home.com
boyd bundy wrote: I have a cape dory 30 MkII with a 2 blade 14" 12 prop. The prop shop recommends changing to a 3 blade. Has anyone done this and how did it work? Thanks
Boyd
michaelconniesmith@home.com
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Andy Denmark
Re: 3 blade prop
Hi Boyd,
I agree with Mike except for the effect of a 3-bladed prop on sailing qualities. On boats < 30 ft it contributes significantly to drag and fairly drastically affects windward ability, especially in light air. Another big disadvantage is the effect of transfering a sizaeable chunk of $$$ from your pocket to the people who sold this prop to you.
It is much more important to match the pitch of the prop to the engine for optimum thrust than to add an extra blade. Your engine manual should give you a max rpm. Wide open, that's what you should be able to turn. Roughly 80% of this number is your "cruising rpm. It's easy to figure if you're turning too fast or too slow and then adjusting the pitch (at haulouts) to bring things within specs. It rarely is a "get it perfect the first time" thing.
Hope this helps.
Andy Denmark
CD-27 "Rhiannon"
trekker@coastalnet.com
I agree with Mike except for the effect of a 3-bladed prop on sailing qualities. On boats < 30 ft it contributes significantly to drag and fairly drastically affects windward ability, especially in light air. Another big disadvantage is the effect of transfering a sizaeable chunk of $$$ from your pocket to the people who sold this prop to you.
It is much more important to match the pitch of the prop to the engine for optimum thrust than to add an extra blade. Your engine manual should give you a max rpm. Wide open, that's what you should be able to turn. Roughly 80% of this number is your "cruising rpm. It's easy to figure if you're turning too fast or too slow and then adjusting the pitch (at haulouts) to bring things within specs. It rarely is a "get it perfect the first time" thing.
Hope this helps.
Andy Denmark
CD-27 "Rhiannon"
trekker@coastalnet.com
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Larry DeMers
Re: 3 blade prop -some experinced views
Ok, this question has popped up twice in the past month, so I thought I would get some actual experience with the fixed, 3 bladed prop. We have a friend that owns "Peace", a 1982 Cape Dory 30, located at Port Superior Marina on Lake Superior. He has used a fixed 3-blade prop for about 6 years.
I asked him if he liked it. A: No. I would trade back for the two blade anytime..or upgrade to a feathering prop, which would eliminate the biggest headache..loss of speed due to more prop hanging out in the flow of water past his keel. He also noted that backing was a larger problem for him, since the prop "P" effect is stronger on 3 bladed props.
He then offered to trade for one year..my 2 blade for his 3 blade. This was said with the kind of grin one associates with Used-Car salesmen of ill repute..the kind of grin that makes me say no thanks.
I would look at the three bladed folding prop..or feathering props for alternatives.
Larry DeMers
s/v DeLaMer
Cape Dory 30
demers@sgi.com
I asked him if he liked it. A: No. I would trade back for the two blade anytime..or upgrade to a feathering prop, which would eliminate the biggest headache..loss of speed due to more prop hanging out in the flow of water past his keel. He also noted that backing was a larger problem for him, since the prop "P" effect is stronger on 3 bladed props.
He then offered to trade for one year..my 2 blade for his 3 blade. This was said with the kind of grin one associates with Used-Car salesmen of ill repute..the kind of grin that makes me say no thanks.
I would look at the three bladed folding prop..or feathering props for alternatives.
Larry DeMers
s/v DeLaMer
Cape Dory 30
mike wrote: Sort of like asking a car dealer if you need a new car, I guess. We had a CD30 with a 2 bladed prop. I looked and looked, asked and asked, read and read and finally determine what is obvious in retrospect. That is, the increase in oomph would be negligible, the increase in reverse control even less due to the nature of the beast, the increase in resistence under sail negligible. fThe more I looked, the clearer it became that the only benefit would derive to those who pulled the boat so I could install it and those who sold the prop. Mikeboyd bundy wrote: I have a cape dory 30 MkII with a 2 blade 14" 12 prop. The prop shop recommends changing to a 3 blade. Has anyone done this and how did it work? Thanks
Boyd
demers@sgi.com
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Greg Kozlowski
Re: 3 blade prop advantage
Boyd,
I had a 3 blade Campbell Sailor on my former Alberg 30 and I liked it a lot. Recently I changed to a 3 blade Machine Works at Essex prop on my CD36, and kept the old 2-blader as a spare. I like 3-blade props on full keel boats because they reduce the engine vibrations. A 2-blader will skip a bit everytime it gets alligned behind the keel and, thus, increase vibes while a 3-blader will not do so. A 3-blader will also give you a bit more juice if it is pitched correctly to your engine and trany, but that is not the main reason I changed.
Your call in the final analysis.
Greg
s/v Sherpa CD36
koz@seijo.ac.jp
I had a 3 blade Campbell Sailor on my former Alberg 30 and I liked it a lot. Recently I changed to a 3 blade Machine Works at Essex prop on my CD36, and kept the old 2-blader as a spare. I like 3-blade props on full keel boats because they reduce the engine vibrations. A 2-blader will skip a bit everytime it gets alligned behind the keel and, thus, increase vibes while a 3-blader will not do so. A 3-blader will also give you a bit more juice if it is pitched correctly to your engine and trany, but that is not the main reason I changed.
Your call in the final analysis.
Greg
s/v Sherpa CD36
koz@seijo.ac.jp
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M. R. Bober
Re: 3 blade prop -another experienced view
We moved from a 14"x10" 2 blade to a 14"x9" 3 blade. This was done in consultation with a highly experienced prop shop. They offered to refund our money or adjust the prop if we were not satisfied. We have been pleased with the extra "oomph" when powering into the short choppy waves of the Chesapeake Bay. We cruise at lower RPM and enjoy the quiet (fuel savings are not significant, to date).
Re: folding props. When they fail to open, it is generally at a memorable moment (e.g. attempting to reverse in a hurry).
To each their own.
Mitchell Bober
RESPITE
CD330
thebobers@erols.com
Re: folding props. When they fail to open, it is generally at a memorable moment (e.g. attempting to reverse in a hurry).
To each their own.
Mitchell Bober
RESPITE
CD330
thebobers@erols.com
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Paul Grecay
Re: 3 blade prop
I have a CD 28 which came with a two blade prop...the boat has a Volvo MD2B (24 hp). I switched to a three blad prop and it was the right thing to do. Reason: I can power effectively into chop...head up in bad conditions. But the best thing about the 3 blade is that when I throttle up with the MDD2B, I can stop the boat immediately when manuvering around in tight places...the ability of the 3 blad prop to stop the boat has saved my boat and others from damage. This is most helpful when jockeying around in high current and wayward wind conditions. The loss of speed to me is acceptable...for me owning a CD was never about speed.
Paul
rfurman@dmv.com
Paul
rfurman@dmv.com
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mike ritenour
Re: 3 blade prop -some experinced views
Prior to my leaving on this round trip from Lake Ontario to the Bahamas and back I called Michigan Wheel and sent them the info on my engine and transmission. They in turn sized a 3 blade prop for me and I installed it before putting LaVida in the water.
After over 450 hours of motoring in all sorts of conditions, I am highly pleased with the results.
The boat is more responsive under power in all directions. I found it was necessary to relearn how to back her down, but that was fortunately only amusing.
Although I carry the old two bladed prop and a prop changer (so I can change the prop underwater without hauling, an cheap alternative to a haulout at 185.00) I have not had any reason to change back.
Michigan wheel dealers have a very good spec sheet to fill out when ordering your prop and their technical staff hit it on the nose.
Good Luck,
Mike Ritenour
LaVida
mritenouru@aol.com
After over 450 hours of motoring in all sorts of conditions, I am highly pleased with the results.
The boat is more responsive under power in all directions. I found it was necessary to relearn how to back her down, but that was fortunately only amusing.
Although I carry the old two bladed prop and a prop changer (so I can change the prop underwater without hauling, an cheap alternative to a haulout at 185.00) I have not had any reason to change back.
Michigan wheel dealers have a very good spec sheet to fill out when ordering your prop and their technical staff hit it on the nose.
Good Luck,
Mike Ritenour
LaVida
mritenouru@aol.com
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Larry DeMers
Re: 3 blade prop -some experinced views
Mike,
How much difference do you see in sailing speed with the 3 blade? Barely noticeable, a bunch..?
I may be tempted to take our friend up on his offer to exchange props for one year (same boat exactly, two CD30's with MD7A/B's). You like the performance boost..but where do you feel the boost has occured?
Larry DeMers
s/v DeLaMer
demers@sgi.com
How much difference do you see in sailing speed with the 3 blade? Barely noticeable, a bunch..?
I may be tempted to take our friend up on his offer to exchange props for one year (same boat exactly, two CD30's with MD7A/B's). You like the performance boost..but where do you feel the boost has occured?
Larry DeMers
s/v DeLaMer
mike ritenour wrote: Prior to my leaving on this round trip from Lake Ontario to the Bahamas and back I called Michigan Wheel and sent them the info on my engine and transmission. They in turn sized a 3 blade prop for me and I installed it before putting LaVida in the water.
After over 450 hours of motoring in all sorts of conditions, I am highly pleased with the results.
The boat is more responsive under power in all directions. I found it was necessary to relearn how to back her down, but that was fortunately only amusing.
Although I carry the old two bladed prop and a prop changer (so I can change the prop underwater without hauling, an cheap alternative to a haulout at 185.00) I have not had any reason to change back.
Michigan wheel dealers have a very good spec sheet to fill out when ordering your prop and their technical staff hit it on the nose.
Good Luck,
Mike Ritenour
LaVida
demers@sgi.com