Carl; I really suspect that you are approaching this repower from the wrong end. Instead of trying to match the engine to the prop, you should start by picking the engine.
My owner's manuals don't show the prop configurations for the 35-1, but do show the mid-70's 30, 33, and 38. All of which came with an A4 as standard equipment. The 30 had a 12x5 prop standard and a 14" prop for the optional diesel, the 33 and the 38 had 16x10 props standard (with 2:1 reduction on the 38) and also used 16" props on the optional diesel (which was a 25hp Westerbeke on the 38). I'm pretty sure you will find room under your boat for a 14" prop. You comment that the hub of the Martec folder is much longer than on the Flexofold. That's true, and also true for the Gori folding prop. But the length of the taper is the same for all the props, and when you look at the Martec, you will notice that the end of the taper and the attaching nut are way down inside the hub (which is not true for the Gori I have as a spare) and the pivot point on the blades of a Martec are at least 3" BEHIND the end of the shaft. The A4 was rated in its day at 30HP, but if I recall it only produced about 18HP at the prop. A diesel will produce more torque than the A4, so a 20HP diesel will get you to hull speed in flat water. But in chop and headwinds, I suspect it will not be a stellar performer. Increased horsepower will help with performance in adverse conditions. The Beta 20, 25, 30, and 35 are all direct drop ins for the A4 so you could use any of them. Personally I'd consider the 25 or 30 in preference to the 20. My 38 has a 36hp Universal (which is the same block as the Beta 30 and 35) as a replacement for the A4 and I am very happy with the engine performance. Once you have the engine selected and know the shaft size and gear reduction, you can go to the prop manufacturers' websites and ask for a recommendation for a prop. They will ask what model of boat, displacement, waterline length, which engine and reduction gear, max rated RPM of the engine, and some other stuff. Then they will tell you what size prop they would recommend. And the size will vary from manufacturer to manufacturer. I asked for quotes from Martec, Flexofold, and Gori. I was replacing a 16x10 two blade fixed prop. I got recommendations for both 16 and 17 inch diameters and pitches from 10 to 10 1/2 to 12. I understand there are differences in performance between manufacturers base on blade surface area and blade profiles. So my recommendation would be to start by picking the engine and gear reduction, and I would look at 25 to 30HP, then pick which type of prop and manufacturer you prefer and get a prop quote. Rick Brass Imzadi C&C 38 mk 2 la Belle Aurore C&C 25 mk1 Washington, NC -----Original Message----- From: CnC-List [mailto:[email protected]] On Behalf Of Carl Gerstle via CnC-List Sent: Sunday, November 09, 2014 10:00 AM To: [email protected] 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: [email protected] 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: [email protected] To change your list preferences, including unsubscribing -- go bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
