Take prop manufacturers recommendations with a grain of salt. Years ago I requested a recommendation from Flexofold. The rep at the time was Chuck Angle who was highly regarded. He said he didn't have a good prop recommendation for my 35-1. :) I went with Martec.
In 2011, I repeated the request and got a recommendation for a 15 x 12. In 2016, I again asked and they said 16 x 12. Currently, Touche' is swinging a 14 x 14 Martec which seems a bit under pitched (or too small a diameter). I can run at 6.4-6.5 knots at cruise rpm (80% max, 2450 rpm) and flat water, no wind. On my list for next year's haul out is to measure and document (photograph) the prop tip clearance distance. I will also measure the hub and swing pin location. The swing plane for different props varies. I think prop selection is part science, part art and a bit of voodoo. Dennis C. Touche' 35-1 #83 Mandeville, LA On Mon, Dec 18, 2017 at 9:59 AM, Rick Brass via CnC-List < cnc-list@cnc-list.com> wrote: > The problem that I see with this calculator is that there is no value for > prop diameter (and slip is pretty intangible, though I suspect using .10 > slip might be a good approximation for 90% efficiency). > > > > The rule of thumb that a local propshop told me is that changing prop > diameter by 1” is approximately equivalent to changing the prop pitch by > 2”. So diameter also enters into the calculation. > > > > I believe each prop maker has their own calculator for recommending > initial diameter and pitch, based on boat weight, engine HP and targeted > cruising RPM, transmission reduction ratio, and hull speed. > > > > Rick Brass > > Washington, NC > > > > > > > > *From:* CnC-List [mailto:cnc-list-boun...@cnc-list.com] *On Behalf Of > *svpegasus38 > via CnC-List > *Sent:* Sunday, December 17, 2017 5:56 PM > *To:* cnc-list@cnc-list.com > *Cc:* svpegasus38 <svpegasu...@gmail.com> > *Subject:* Re: Stus-List PROPELLER PITCH > > > > Try this propellor calculator. > > rbbi.com/folders/prop/propcalc.htm > > > > > > > > Sent from my T-Mobile 4G LTE Device > > Doug Mountjoy > > POYC > > Rebecca Leah > > Lf39 > > > > -------- Original message -------- > > From: Bunky via CnC-List <cnc-list@cnc-list.com> > > Date: 12/17/17 14:18 (GMT-08:00) > > To: cnc-list@cnc-list.com > > Cc: Bunky <richard.h.bernst...@uvm.edu> > > Subject: Stus-List PROPELLER PITCH > > > > Luna is a 1984 C&C 35 with a Yanmar 3gm30 engine. Does anyone know what > the proper propeller pitch should be? She has an aftermarket Maxiprop, > and based on engine performance, I believe the pitch may be set too high. > > Richard > Luna, Lake Champlain, VT > > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each > and every one is greatly appreciated. If you want to support the list - > use PayPal to send contribution -- https://www.paypal.me/stumurray > > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each > and every one is greatly appreciated. If you want to support the list - > use PayPal to send contribution -- https://www.paypal.me/stumurray > > >
_______________________________________________ Thanks everyone for supporting this list with your contributions. Each and every one is greatly appreciated. If you want to support the list - use PayPal to send contribution -- https://www.paypal.me/stumurray
