This is why I got another A4. I could not figure out how to get a decent prop for a reduction gear engine without extending the shaft.
Joe Della Barba j...@dellabarba.com Coquina C&C 35 MK I -----Original Message----- From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Carl Gerstle via CnC-List Sent: Sunday, November 09, 2014 10:00 AM To: cnc-list@cnc-list.com Subject: Stus-List 35-1 drivetrain replacement (prop, engine HP, transmission ratio) Having searched the archives and not found this info, I feel the need to ask... I am committed to a re-power this winter and am surprised at the difficulty in choosing an appropriate prop which then leads to the appropriate engine HP and transmission choices. I already have input from two other 35-1 owners but am looking for a wider array of input. My old engine/tranny/prop is the venerable Atomic-4, 1:1 tranny, 12x6 folding prop. The new engine will be a BetaMarine... but either 20 or 25 HP depending on how much power a prop that FITS can absorb through a choice of a 1.45:1, 2:1, or 2.6:1 transmission. As I really don't want to face the added expense of upsizing the shaft from 7/8" to 1" (even a 14" prop can be safely driven on a 7/8" Aquamet shaft) or worse - moving and replacing the strut to gain prop diameter - please provide whatever real-world info you have on the prop (make, diameter, pitch); engine HP, and transmission ratio that you are using on your 35-1. It turns out that the prop make/model is critical due to the effective hub length. For instance, my current folder places the blades 5 5/8" behind the strut (5" hub, with 5/8" exposed shaft). The prop I am considering (Flexofold 13") has only a 4.5" hub length, while a Martec 14" appears to be a beefy 9" from hub to blade pivot. So the length of the hub has a large effect on tip clearance. As Dave Gerr (The Propellor Handbook) recommends an absolute minimum of 10% clearance (a 14" prop thus needs 7" + 1.4" clearance from shaft center to hull) - I only have 8" clearance with a 4.5" hub) - a longer prop hub allows for greater prop diameter (a very good thing). So real-world experience - including your experience with speed, prop noise, and vibration from using a small blade tip to hull clearance would be invaluable to me. The problem is complex enough that Flexofold actually refused to recommend a prop, tranny drive ratio, and HP requirement; and recommended that I work with a boat-builder to work out these choices. Your actual numbers and knowledge will be greatly appreciated. Thanks, Carl Gerstle Impulse C&C 35-1 #149 Portsmouth, RI _______________________________________________ This List is provided by the C&C Photo Album Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com _______________________________________________ This List is provided by the C&C Photo Album Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
