POINTER94
Vice Admiral
- Joined
- Oct 12, 2003
- Messages
- 5,031
Re: East coast verses West coast
Efficiency and Angle of Attack<br />The graph in Figure 4-30 (above) shows how propeller efficiency increases and then decreases as angle of attack is increased. In the example, in Figure 4-30, efficiency peaks at approximately 80% (3 degree- 4 degree angle of attack) and begins to decline as the angle of attack increases beyond the optimum.<br /><br />Efficiency and Pitch / Diameter<br />In a given propeller series, the maximum possible efficiency decreases as pitch decreases. For example, a 23" pitch propeller with 13-1/2" diameter can have a peak efficiency of 80%, but a 13" pitch propeller with a 16" diameter can have a peak efficiency of only 65%. <br /><br />If all other variables remain unchanged, propeller efficiency increases as the pitch/diameter ratio increases.<br /><br /> <br /><br />© 2004 Mercury Marine<br /><br />--------------------------------------------------<br /><br />Speed criteria Synchronous Variable Vapor pressure, rated psi.a <br />Speed set @ rpm Material <br />Impeller diameter, rated set @ 3.91 in Material requested AutoNot specifiedCast iron-BronzeCast iron - Stainless steel <br />Impeller diameter, maximum : 3.91 in Material selected : Not specified <br />Impeller diameter, minimum : 3.91 in Pressure Data <br />Efficiency : 73.34 (0.00) % % Maximum working pressure : 103.8 psi.g <br />NPSH required / margin required :N/A (0.00) / 0.00 N/A / 0.00 Working pressure limit : 606.0 psi.g <br />Ns / Nss : N/A Suction pressure limit : N/A <br /><br />I am entering this a little late. but if you can read through the goop posted above you will see that mercury states that the best efficiency that can be attained is 80%, the mess posted below is from Berkeley. It states that the best that can be attained from an impeller is 74%. I can state for a fact that this can be increased by backfiling the impeller or by coating it.<br /><br />Efficiencies over 80% can be achieved. I would assume that they are about the same as far as efficency is concerned. <br /><br />The efficiencies of the impeller refer to BEP (best efficiency point).<br /><br />I would have to assume that it would be somewhat equal in terms of milage.<br /><br />By applying the affinity law you can have a condition where the engine is producing far more horsepower than is required at low rpm, there lies your inefficiency with regards to the high fuel consumption and also why they level off at higher speeds where the engine hp equals the impeller potential.
Efficiency and Angle of Attack<br />The graph in Figure 4-30 (above) shows how propeller efficiency increases and then decreases as angle of attack is increased. In the example, in Figure 4-30, efficiency peaks at approximately 80% (3 degree- 4 degree angle of attack) and begins to decline as the angle of attack increases beyond the optimum.<br /><br />Efficiency and Pitch / Diameter<br />In a given propeller series, the maximum possible efficiency decreases as pitch decreases. For example, a 23" pitch propeller with 13-1/2" diameter can have a peak efficiency of 80%, but a 13" pitch propeller with a 16" diameter can have a peak efficiency of only 65%. <br /><br />If all other variables remain unchanged, propeller efficiency increases as the pitch/diameter ratio increases.<br /><br /> <br /><br />© 2004 Mercury Marine<br /><br />--------------------------------------------------<br /><br />Speed criteria Synchronous Variable Vapor pressure, rated psi.a <br />Speed set @ rpm Material <br />Impeller diameter, rated set @ 3.91 in Material requested AutoNot specifiedCast iron-BronzeCast iron - Stainless steel <br />Impeller diameter, maximum : 3.91 in Material selected : Not specified <br />Impeller diameter, minimum : 3.91 in Pressure Data <br />Efficiency : 73.34 (0.00) % % Maximum working pressure : 103.8 psi.g <br />NPSH required / margin required :N/A (0.00) / 0.00 N/A / 0.00 Working pressure limit : 606.0 psi.g <br />Ns / Nss : N/A Suction pressure limit : N/A <br /><br />I am entering this a little late. but if you can read through the goop posted above you will see that mercury states that the best efficiency that can be attained is 80%, the mess posted below is from Berkeley. It states that the best that can be attained from an impeller is 74%. I can state for a fact that this can be increased by backfiling the impeller or by coating it.<br /><br />Efficiencies over 80% can be achieved. I would assume that they are about the same as far as efficency is concerned. <br /><br />The efficiencies of the impeller refer to BEP (best efficiency point).<br /><br />I would have to assume that it would be somewhat equal in terms of milage.<br /><br />By applying the affinity law you can have a condition where the engine is producing far more horsepower than is required at low rpm, there lies your inefficiency with regards to the high fuel consumption and also why they level off at higher speeds where the engine hp equals the impeller potential.
