Michael I expect you are right about the impeller vs screw analogy, because while the 12x6 is correctly sized going forward given the 2.21:1 gear box, vs the 2:62:1 that is most common in 2GMs, it needs to spin faster in reverse than a prop that was properly sized for a 2.62:1 gearbox.
So its seems that I’ve solved the inability to hit max rpms and cruise at ~80% cont max, but created a different problem. Financial practicality aside, I’m wondering if a feathering prop where the forward and reverse pitch can be set independently might work. Any listers have experience with this style of prop and are they 2 or 3 blade? Martin <mailto:martink...@sympatico.ca> martink...@sympatico.ca 905 848 0925 From: Michael Brown [mailto:m...@tkg.ca] Sent: Thursday, May 14, 2015 5:21 PM To: cnc-list@cnc-list.com Subject: Re: Stus-List Prop Walk C&C 29-2 You could plug your specs in here and see what the recommendation is: http://www.vicprop.com/displacement_size.php I would have guessed a Gori 15X10 to be a little big, maybe the 14X9.5 is OK. The 12X6 seems too small. If it cannot "bite" the water and stay connected it will churn - cavitation - and the effect may be prop walk. Acting more like a centrifugal impeller than a screw. Michael Brown Windburn C&C 30-1 Date: Thu, 14 May 2015 16:10:22 -0400 From: Martin Kane <martink...@sympatico.ca <mailto:martink...@sympatico.ca> > To: <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > Subject: Stus-List Prop Walk C&C 29-2 Message-ID: <blu437-smtp450fc0619106756cf69f2abd...@phx.gbl <mailto:blu437-smtp450fc0619106756cf69f2abd...@phx.gbl> > Content-Type: text/plain; charset="us-ascii" Boat was significantly over-propped when I acquired her. Largely because transmission ratio is 2.2:1 not 2.62:1 as stamped on the casing. While the props that came with the boat (a Gori 15X10 and a 3 blade fixed 14X9) were too big, prop walk was not an issue. Just installed a Campbell Sailor 12x6 and the prop walk is severe (in spite of the additional tip to hull clearance). It is basically impossible to turn the bow to port in reverse . The bow swings to starboard and then once there is some movement through the water will crab sideways, but the bow will not swing around to port. I have not found any combination of throttle and rudder position that makes the situation any better. I need to replace the prop to avoid getting into trouble in close quarters at some point. Question to C&C 29-2 owners: Has anyone found a prop that works well going forward and in reverse. Thanks in advance. Martin Recalculating C&C 29-2 Mimico Cruising Club
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