The issue is my Atomic 4 is direct drive and I cruise at about 2300-2500 shaft RPM. A diesel will 99% of the time have a reduction gear and cruise at around 1000-1500 shaft RPM. The prop that is correct for me now would be way small for an engine with a reduction gear.
Joe Della Barba From: ALAN BERGEN via CnC-List <cnc-list@cnc-list.com> Sent: Wednesday, May 28, 2025 12:48 PM To: Stus-List <cnc-list@cnc-list.com> Cc: ALAN BERGEN <trya...@alumni.usc.edu> Subject: [EXTERNAL] Stus-List Re: C&C 35 MK 1 Diesel Engine Questions You want the prop to clear the hull, so going to a larger diameter prop isn't the way to go. What diameter prop do other Mk I owners have on their boats? How far does the shaft extend past the cutless bearing on their boats? Instead of going to a larger diameter prop, decide on the right pitch. You should be able to reach the highest rated RPM for your engine at full throttle. If you can't, your pitch is too high. If you can reach the highest rated RPM before reaching full throttle, your pitch is too low. The engine manufacturer can advise you as to the right pitch, based on the prop diameter. Start with your existing prop, and go from there. Alan Bergen 35 Mk III Thirsty Rose City YC Portland, OR On Wed, May 28, 2025 at 9:17 AM Della Barba, Joe via CnC-List <cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com>> wrote: The replacement engine I have is getting ready for final testing once I get the carb fixed. It all looks good so far, but in case it doesn’t work out the salvage shop down the road has a couple of nice diesel engines that may be Plan B. Here is my dilemma – they all suggest 15 or 16 inch props, maybe a 14 inch 3 blade as the smallest. The original prop on Coquina was a 13x7 that BARELY cleared the hull. A 14 inch would be touching the hull. The only way I can see even doing that is getting a longer shaft and/or moving the engine aft. This raises the second issue, I cannot seem to find any 14 inch or larger props made for 7/8” shafts. Do people change the shaft diameter to 1 inch? That would seem to require a new stuffing box and a new strut unless there are 1” cutless bearings that fit the stock strut. Joe Della Barba Coquina C&C 35 MK I Your contributions help pay the fees associated with this list and help to keep it active. Please help by making a small contribution using PayPal at: https://urldefense.com/v3/__https://www.paypal.com/paypalme/stumurray__;!!LIr3w8kk_Xxm!v1yLo-LFd8SQBatMgdH7uMAyI5uY46k7j-0zrsJgShCF3j-j2qGzHxSZr6NZV_w-ucNGOVgg-NoVnwmmIdvAMrM$<https://urldefense.com/v3/__https:/www.paypal.com/paypalme/stumurray__;!!LIr3w8kk_Xxm!v1yLo-LFd8SQBatMgdH7uMAyI5uY46k7j-0zrsJgShCF3j-j2qGzHxSZr6NZV_w-ucNGOVgg-NoVnwmmIdvAMrM$> All contributions are greatly appreciated.
Your contributions help pay the fees associated with this list and help to keep it active. Please help by making a small contribution using PayPal at: https://www.paypal.com/paypalme/stumurray All contributions are greatly appreciated.
