The recommendations I made are about engine RPM, not shaft RPM. Alan
On Wed, May 28, 2025 at 9:59 AM Della Barba, Joe via CnC-List < cnc-list@cnc-list.com> wrote: > 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> 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$> > All contributions are greatly appreciated. > > Your contributions help pay the fees associated with this list and help to > keep it active. Please help by making a small contribution using PayPal > at: > https://urldefense.com/v3/__https://www.paypal.com/paypalme/stumurray__;!!LIr3w8kk_Xxm!rLLBcnda0xQ4RH9S3izX_0vDI-wdnACgUIovKgFPVL4NjBrCinJB8KWTB7bZKvYN0yuIky-8cUyWzjpHY_H7uDI$ > 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.
