Size of Prop "Ears"...

rpell1@msn.com

rpell1@msn.com

.
Sep 25, 2008
464
Catalina 30 MKIII Varuna Boat Club
Good morning all and Happy July 4th,

Now that I almost have my new boat, '97 Cat30 MKIII, the questions begin.

My '91 MKII had an OEM 13x10 three blade with broad "ears". This new '97 also has an OEM 13x10 three blade but, the "ears" are substantially narrower.

I am assuming that the narrower ears make for less load on the engine allowing higher revs? The wider ears might produce a more powerful thrust at lower rpm.

Since I managed to salvage the older prop, should I change it out and use the newer one as a spare? I deal with a 4-5 knot running tide, as well as close quarter docking regularly.

Any ideas or opinions?

Happy Sailing,
 
C

Capt jgw

.
Feb 8, 2014
1,300
Columbia 36 Muskegon
Probably not a lot of difference in motoring performance between the two props. The narrower blades will give you less drag under sail though. I'd keep the narrower one on.
 
jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
22,085
CAL 35 Cruiser #21 moored EVERETT WA
I would try the new prop before changing.
I had an original prop. Been told it was a Michigan Wheel.
OldProp.JPG
The issue is not the big blades it is the fluid dynamics of the big blades. As they spin at higher speeds cavitation starts at the edges of the blade. This robs the blade of forward thrust. So your boat feels like it is thrashing away but you are not going any faster through the water.
So I changed to a newer design. A Campbell Sailor.
New Prop1.JPG
The blades have a different shape. The prop is a smaller diameter My boat feels more effective in the water. My engine feels like it is working less to achieve a higher speed through the water. I have picked up nearly a knot in boat speed achieving the mathematical hull speed of my boat, not at WOT and without driving the stern down under water.

So try the new prop first. If you do not like it you can always change the prop while the boat is in the water. Or have a diver do it for you.
 
Davidasailor26

Davidasailor26

.
May 17, 2004
5,420
Beneteau Oceanis 37 Havre de Grace
I'm with jssailem. It sounds from your description like the difference between an OEM Michigan Wheel style prop and a Campbell sailor. I've never heard anyone compare about the motoring performance of the Campbell, and I've seen many rave about it. Your boat's PO was evidently satisfied enough with it to not switch back too, so I'd at least try it out before switching.
 
jon hansen

jon hansen

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May 25, 2012
4,338
john alden caravelle 42 sturgeon bay, wis
two bladed "sailing prop" made by michigan wheel. i will never use a three bladed prop in this application.
hows my fifty year old bottom look?
 
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jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
22,085
CAL 35 Cruiser #21 moored EVERETT WA
@jon hansen You need to walk the cat walk a bit baby... Strut your stuff.:what:
We are only getting one profile... :biggrin:
 
kloudie1

kloudie1

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Nov 6, 2006
9,996
Hunter 34 Mandeville Louisiana
Funny you mention ears.. One propeller parameter is E.A.R. which is kinda the % of the disk taken up by the blades.. so a .60 ear has wider blades than a .50 ear prop.. Usually (not always) a larger ear is more efficient than a smaller ear numbered prop.. but at a higher drag under sail .. not a big difference now that we know to leave our transmissions in neutral..
 
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jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
22,085
CAL 35 Cruiser #21 moored EVERETT WA
Oh my? That is pretty... Shake it baby....
 
M

MitchM

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Jan 20, 2005
1,029
Nauticat 321 pilothouse 32 Erie PA
sounds like you'd really enjoy dave gerr's propeller design hand book... !
 
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