Rodney is correct, of course. But also consider that some C&C models come with different gear ratios for the same boat. Get the ratio off the gearbox name plate before ordering a prop. My PO didn't do that and I got a boat with the wrong prop.
Gary S/V Kaylarah '90 C&C 37+ East Greenwich, RI, USA ~~~~~~~_/)~~~~~~ On Sun, Feb 18, 2018 at 10:06 AM, Rodney Meryweather via CnC-List < cnc-list@cnc-list.com> wrote: > The engine and gear ratio, together with the engine power, are critical > for any propeller sizing. > When choosing an engine &/or propeller for your boat, it is important to > consider the effect of the gearbox ratio on the propeller. Most marine > diesel engines have a reduction gearbox, which makes the shaft turn slower > than the engine, at a speed more suitable for the propeller. > The gear box ratio determines the rotation speed of the propeller in > revolutions per minute (rpm): > Propeller speed (srpm) = Engine rated rpm ÷ Gearbox reduction > ratio > > With an existing engine there were generally several different gear ratios > available to choose from at the time of install depending on shaft angle. > It is best that you get your actual ratio off the gearbox tag. It is > generally stamped on the top or side of the gearbox expressed as a ratio or > number (example: 2.64:1 or A–2.64). > > The best method to get the actual ratio is to use your cell phone camera & > take a photo of the plate on the transmission (beats hanging upside down > reading it with a mirror and a flash light). > > Before selecting a propeller type you should look at the advantages, > features, benefits & differences in performance relative to your sailing > style/boat use so that you can make an informed decision. I know there is a > lot of information below but I want to make sure you choose the correct > propeller to suit your sailing style/boat use. > > I personally am looking at the Variprop Feathering or Gori Folding > The Variprofile feathering propeller is a unique feathering propeller and > the first to incorporate the hi-tec GAWN/KAPLAN profile. The only > feathering propeller with a shaped blade which is 7-11% more efficient than > the std flat bladed feathering propeller. This profile has been used > primarily for high performance power boat applications, but also for rudder > design and in the aircraft industry. > > Normally associated with high-speed power boat and aircraft propeller > blades the Gawn/Kaplan blade profile & slim hub delivers very low drag, > excellent Hydro-dynamics while running extremely more quietly and > efficiently under power than other propellers with the result that the > VariProfile delivers speed normally associated with fixed propellers or the > best folding propellers in both fwd. & reverse with its continuous > independently variable adjustable external pitch control (patented). > Forward and Reverse pitches can be changed independently in just seconds, > even underwater. > > The Gori is a folding propeller with two(2) pitches in fwd & full 100% > reverse thrust, no prop walk. The Gori does not auto-rotate/spin under sail > as does a feathering propeller at higher speeds, or have one blade drop > down and increase drag or not open when coming into the slip. > > The drag for the Gori 3-blade propellers is the lowest of any fixed, > feathering or folding propellers (even less than any 2-blade) giving > increased sailing speeds & less turbulence over the rudder, enabling you to > point higher. The unique folding design prevents seaweed etc from fouling > on the propeller giving increased speed potential. You will see an increase > in sailing speeds over your fixed 3-blade propeller. The drag reduction > will amount to 0.95 + of a knot for a 36 footer. > > The blades of the Gori propeller are designed with both camber, curve & > twist to them, which gives increased efficiency (thrust) throughout the rpm > range, which will always give you better motoring performance > (speed/thrust), especially in heavy seas, or when motor sailing with the > "Overdrive" Function. > The Gori 3-blade "Overdrive" function, by increasing the blade pitch > angle, gives increased thrust and speed - at the same rpm or when motoring > sailing, or the same boat speed at much lower rpms. The result is less > engine noise, less vibration, increased fuel economy & therefore a greater > cruising range. > The Gori 3-blade propeller is the only propeller that will give you > exactly the same performance in reverse as in forward due to the unique > blade folding action of presenting the identical leading edge in reverse as > in forward - resulting in no 'prop walk'. See > http://ab-marine.com/folding/gori/ & http://gori-propeller.com/ > > Rodney Meryweather > > > _______________________________________________ > > 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
