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The previous owner of my mark 11 replaced the atomic 4 with a 13HP Yanmar 2GM. The gear ratio is 2.21:1 and the prop is a three bladed 11" X 9". The problem is I can rarely achieve more than 4 to 4.5 Knots. This seems slow. Does anyone have the same engine installed, and do you have the same gear ration and prop. Boat name is Penny Whistle - thanks Carl Armstrong
Read my query, "Propping a diesel", down the page. Ralph Ainslie's answer should cover you.
Flexofold recommended a 15x 11 or a 14 x 12 two-bladed folding prop, but my gear ratio is 2.6:1. I don't have it yet, so I can't tell you how it will work out.
David Weatherston
Towser, Toronto
C&C 27 Mk IV
Later The 14 x 12 prop is installed and is a great improvement over the size intended for the A4. Reverse thrust is astonishingly good.
Last edited by (2005-08-29 00:46:34)
David Weatherston
Towser, Toronto
C&C 27 Mk IV
Offline
Carl,
I have a 2 GMF on a 74 mk II. Sorry, I don't know what the gear ratio is. My prop is a 13 x 10. This prop does not perform as well as I would like (or as well as the one the yard replaced). I'm planning to replace it with feathering prop. Well maybe after the rigging... and deck... and roller furling...
Mike M
SV Pura Vida
#375
Galveston Bay
Mike M
SV Wind Horse
#375
Galveston, Tx
Offline
Hi Mike - thanks for the reply - I was looking at a picture of a prop on a Mark V and his blades are much wider than mine - I would estimate a good 50% wider. This may be the problem. Like you I would like to go to a folding prop less for speed but for picking up sea weed and cedar bark from log booms. Also I think my prop pitch must be too small. Maybe if I go to the same pitch as yours but with fuller blades it might improve things.
Carl Armstrong in Penny Whistle
After receiving a note from Boatdiesel.com that my registration was about to expire I recalled that they have a prop calculator and tried it out. Also a reread of the survey showed what was on my boat prior to changing over to the PSS shaft seal and changing the prop. The survey stated that the boat came with a 3 blade 14.5" x with 10 pitch. Boatdiesel.com's calculator suggested a 14" with 9.6 pitch. Both 3 blade. The transmission is a 2.62:1 ratio. It looks like the 13 is being replaced sooner rather than later.
The conversion to the PSS Dripless shaft seal has been a great success. It is hard to justify the cost. One could buy a lot of packing for $200 and some of the new packing materials are reliably touted to be dripless as well. But I have to say that my installation has not leaked at all.
Mike M
SV Pura Vida
#375
Galveston Bay
Mike M
SV Wind Horse
#375
Galveston, Tx
Offline
Hi Mike
Thanks for the reply. I have been working with the Campbell Prop people and they are suggesting a 12X6 prop. The difference to your calcs may be the gear ratio. I am at 2.21 and I see yours is 2.62:1. One concern I have is that I have to reverse my rudder when backing out of my slip at the marina I have to back about fifty yards between darn boats with outboards sticking out so I need good control. This one benefit of a tiller. I am not sure if I go to a 14" prop that it would hit the rudder. I am seriously thinking of go to the mark 3 rudder. But one thing at a time. Same with the PSS shaft seal.
Carl in Pennywhistle
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