When we purchased our CD31 last November, it had a 13-10 three-blade prop installed that needed reconditioning. Also in the inventory was a 13-13 two-blade prop that I assume was the original prop that was installed by the manufacturer. The boat has a Universal 25 producing 23 H.P. with a Hurth 2:1 transmission.
As an aside, when I called the 20-year-old number of the original owner, his only specific comment was about the "big" prop that had been installed by a subsequent owner.
The question is, is there any advantage in one or the other, both of which are in the attached photo.
I have also requested a quote for a Campbell Sailer prop and they recommended a 13-9 three-blade version. Does anyone have experience with these props?
[img]http://www.clinedesign.com/prop_photo/Props_CD31.jpg[/img]
Cheers,
Don & Lorraine Cline
"Loon"
Proper Prop
Moderator: Jim Walsh
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barleycopse
- Posts: 11
- Joined: Apr 2nd, '05, 00:51
- Location: CD31
"Loon"
Proper Prop
Last edited by barleycopse on Apr 5th, '05, 15:55, edited 2 times in total.
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Neil Gordon
- Posts: 4367
- Joined: Feb 5th, '05, 17:25
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Re: Proper Prop
I'm not an engineer, but I think the formula is something like "thrust while motoring = drag while sailing."
Fair winds, Neil
s/v LIQUIDITY
Cape Dory 28 #167
Boston, MA
CDSOA member #698
s/v LIQUIDITY
Cape Dory 28 #167
Boston, MA
CDSOA member #698
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Tom
Props
As Neil says, the advantage to the two blade is that there is less drag when sailing and it can be oriented to "hide" behind the keel. The disadvantage is not as much thrust under power. With the three blade you get a noticiable increase in thrust which means more distance per RPM, but you lose a little speed under sail probably less than half a knot. You didn't say what engine you have, but on my 31 with the Universal I took the two blade off and went with a three blade. It depends on the kind of sailing you're planning to do. If you motor much you'll be glad of the three blade and won't mind the slight loss in sailing speed. If you don't motor much or race you'd probably prefer the two blade.
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Cathy Monaghan
- Posts: 3502
- Joined: Feb 5th, '05, 08:17
- Location: 1986 CD32 Realization #3, Rahway, NJ, Raritan Bay -- CDSOA Member since 2000. Greenline 39 Electra
- Contact:
Powerboat prop vs. sailboat prop
Hi Don,
For what it's worth that 3-blade of yours looks like a powerboat prop to me. They are often described as "Mickey Mouse ears". The new 2-blade on the other hand is a proper sailboat prop. Note how narrow the blades are compared to those big "ears".
Anyway, I hope this will help others who feel their boats are improperly propped. Here's what a proper 3-blade sailboat prop looks like. If you've got Mickey Mouse ears, somebody made a mistake.
<img src="http://www.capedory.org/images/misc/Prop072.jpg">
<img src="http://www.capedory.org/images/misc/Prop073.jpg">
<img src="http://www.capedory.org/images/misc/Prop075.jpg">
Cathy
<a href="http://home.comcast.net/~c_m_monaghan/r ... .htm">CD32 Realization, #3</a>
Rahway, NJ
Raritan Bay
For what it's worth that 3-blade of yours looks like a powerboat prop to me. They are often described as "Mickey Mouse ears". The new 2-blade on the other hand is a proper sailboat prop. Note how narrow the blades are compared to those big "ears".
Anyway, I hope this will help others who feel their boats are improperly propped. Here's what a proper 3-blade sailboat prop looks like. If you've got Mickey Mouse ears, somebody made a mistake.
<img src="http://www.capedory.org/images/misc/Prop072.jpg">
<img src="http://www.capedory.org/images/misc/Prop073.jpg">
<img src="http://www.capedory.org/images/misc/Prop075.jpg">
Cathy
<a href="http://home.comcast.net/~c_m_monaghan/r ... .htm">CD32 Realization, #3</a>
Rahway, NJ
Raritan Bay