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#1
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Prop sizes/performance
I took 3 Aluminium props on the lake today and compared them. No special
hi-tech gear other than a stopwatch and the standard helm instruments. FWIW, I Thaught I would share the results: Boat: 1996 Bayliner 2052 (20' cuddy) 2 adults, 2 children, full fuel tank etc Engine: 4.3 LX mercruiser with Alpha 1 gen II outdrive. Lake: Windemere (fresh water) Weather: Warm, dry, steady breeze Prop 1: 14 1/4" X 22" (originally 21" re-pitched to 22") re-conditioned Prop 2: 14 1/4" X 21" Tiny scrape on tip of one blade. 1/4" sq missing Prop 3: 14 1/4" X 19" good (but not perfect) condition. re-conditioned Engine 22" Prop 21" Prop 19" Prop RPM MPH MPH MPH 4.5K 39 42 38 4.0K 33 38 32 3.5K 30 30 3.3K 22* 3.0K 22* 22* Not Planing * just on plane From rest 7.8 secs 6.7 secs 3.9 secs to plane (approx 22mph) The recommended WOT max RPM is 4800. At WOT the engine will considerably exceed 4800 (max RPM) if allowed to with all props. The 22" is not as fast as the 21". Could this be due to 'slip' or cavitation? There is not much difference between the speeds of the 19 and 22 but the 19 is on the plane in 1/2 the time. Again is this the 22 'slipping'? I cannot percieve any evidence of, or can feel cavitation from the helm. Would a 4 blade prop be better? Is any improvement likely to be only marginal? The speed for a given RPM was 3 MPH lower when travelling into the wind. the above figures were the average runs into and with the wind.. I understand that the boat is supplied with a 19" as standard. Steve |
#2
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Prop sizes/performance
I would bet your re pitched prop has an inefficient shape.
"Steve Lomax" wrote in message ... I took 3 Aluminium props on the lake today and compared them. No special hi-tech gear other than a stopwatch and the standard helm instruments. FWIW, I Thaught I would share the results: Boat: 1996 Bayliner 2052 (20' cuddy) 2 adults, 2 children, full fuel tank etc Engine: 4.3 LX mercruiser with Alpha 1 gen II outdrive. Lake: Windemere (fresh water) Weather: Warm, dry, steady breeze Prop 1: 14 1/4" X 22" (originally 21" re-pitched to 22") re-conditioned Prop 2: 14 1/4" X 21" Tiny scrape on tip of one blade. 1/4" sq missing Prop 3: 14 1/4" X 19" good (but not perfect) condition. re-conditioned Engine 22" Prop 21" Prop 19" Prop RPM MPH MPH MPH 4.5K 39 42 38 4.0K 33 38 32 3.5K 30 30 3.3K 22* 3.0K 22* 22* Not Planing * just on plane From rest 7.8 secs 6.7 secs 3.9 secs to plane (approx 22mph) The recommended WOT max RPM is 4800. At WOT the engine will considerably exceed 4800 (max RPM) if allowed to with all props. The 22" is not as fast as the 21". Could this be due to 'slip' or cavitation? There is not much difference between the speeds of the 19 and 22 but the 19 is on the plane in 1/2 the time. Again is this the 22 'slipping'? I cannot percieve any evidence of, or can feel cavitation from the helm. Would a 4 blade prop be better? Is any improvement likely to be only marginal? The speed for a given RPM was 3 MPH lower when travelling into the wind. the above figures were the average runs into and with the wind.. I understand that the boat is supplied with a 19" as standard. Steve |
#3
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Prop sizes/performance
The 22 is one prop I would toss in the can! But the question is: "What are
you trying to achieve"? Consider this -going with a SS prop may net as much as 5mph... "Steve Lomax" wrote in message ... I took 3 Aluminium props on the lake today and compared them. No special hi-tech gear other than a stopwatch and the standard helm instruments. FWIW, I Thaught I would share the results: Boat: 1996 Bayliner 2052 (20' cuddy) 2 adults, 2 children, full fuel tank etc Engine: 4.3 LX mercruiser with Alpha 1 gen II outdrive. Lake: Windemere (fresh water) Weather: Warm, dry, steady breeze Prop 1: 14 1/4" X 22" (originally 21" re-pitched to 22") re-conditioned Prop 2: 14 1/4" X 21" Tiny scrape on tip of one blade. 1/4" sq missing Prop 3: 14 1/4" X 19" good (but not perfect) condition. re-conditioned Engine 22" Prop 21" Prop 19" Prop RPM MPH MPH MPH 4.5K 39 42 38 4.0K 33 38 32 3.5K 30 30 3.3K 22* 3.0K 22* 22* Not Planing * just on plane From rest 7.8 secs 6.7 secs 3.9 secs to plane (approx 22mph) The recommended WOT max RPM is 4800. At WOT the engine will considerably exceed 4800 (max RPM) if allowed to with all props. The 22" is not as fast as the 21". Could this be due to 'slip' or cavitation? There is not much difference between the speeds of the 19 and 22 but the 19 is on the plane in 1/2 the time. Again is this the 22 'slipping'? I cannot percieve any evidence of, or can feel cavitation from the helm. Would a 4 blade prop be better? Is any improvement likely to be only marginal? The speed for a given RPM was 3 MPH lower when travelling into the wind. the above figures were the average runs into and with the wind.. I understand that the boat is supplied with a 19" as standard. Steve |
#4
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Prop sizes/performance
I am thinking in terms of buying a SS prop but I would like to be sure of
getting the right size. As the engine will conbsiderably over-rev, I would like to use this power to get a prop that will give me WOT at 4800 RMP. At the moment the best I can get is 3/4WOT. It seems a shame to have the power and not use it. I agree that an extra 5mph is probably neither here or there but I feel that there is enough unused 'grunt' to get at least 10mph (25%) , or more significantly, better fuel efficency - it costs nearly 100 UKP to fill the tank. (Yes.... I know, the deeper the draught, the bigger the overdraft!). I'm getting quite adept at prop changing in the water, and dropping to the 19" for skiing is not so much of a problem, so getting speed and economy for cruising is probably the order of the day. Steve "Woodchuck" wrote in message ... The 22 is one prop I would toss in the can! But the question is: "What are you trying to achieve"? Consider this -going with a SS prop may net as much as 5mph... "Steve Lomax" wrote in message ... I took 3 Aluminium props on the lake today and compared them. No special hi-tech gear other than a stopwatch and the standard helm instruments. FWIW, I Thaught I would share the results: Boat: 1996 Bayliner 2052 (20' cuddy) 2 adults, 2 children, full fuel tank etc Engine: 4.3 LX mercruiser with Alpha 1 gen II outdrive. Lake: Windemere (fresh water) Weather: Warm, dry, steady breeze Prop 1: 14 1/4" X 22" (originally 21" re-pitched to 22") re-conditioned Prop 2: 14 1/4" X 21" Tiny scrape on tip of one blade. 1/4" sq missing Prop 3: 14 1/4" X 19" good (but not perfect) condition. re-conditioned Engine 22" Prop 21" Prop 19" Prop RPM MPH MPH MPH 4.5K 39 42 38 4.0K 33 38 32 3.5K 30 30 3.3K 22* 3.0K 22* 22* Not Planing * just on plane From rest 7.8 secs 6.7 secs 3.9 secs to plane (approx 22mph) The recommended WOT max RPM is 4800. At WOT the engine will considerably exceed 4800 (max RPM) if allowed to with all props. The 22" is not as fast as the 21". Could this be due to 'slip' or cavitation? There is not much difference between the speeds of the 19 and 22 but the 19 is on the plane in 1/2 the time. Again is this the 22 'slipping'? I cannot percieve any evidence of, or can feel cavitation from the helm. Would a 4 blade prop be better? Is any improvement likely to be only marginal? The speed for a given RPM was 3 MPH lower when travelling into the wind. the above figures were the average runs into and with the wind.. I understand that the boat is supplied with a 19" as standard. Steve |
#5
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Prop sizes/performance
I must admit it don't use it for anthing other than an emergency get me home
prop. I'm not very impressed with the finishing. "noah" wrote in message ... On Sun, 20 Jul 2003 17:15:51 -0700, "Bob La Londe" wrote: I would bet your re pitched prop has an inefficient shape. Ditto. The guy who used to rebuild my aluminum props (I fish and run a rocky river), refused a "re-pitch" as a matter of course. He said he could cut and weld it, but it wouldn't be "right", and he didn't want his name on it. noah "Steve Lomax" wrote in message ... I took 3 Aluminium props on the lake today and compared them. No special hi-tech gear other than a stopwatch and the standard helm instruments. FWIW, I Thaught I would share the results: Boat: 1996 Bayliner 2052 (20' cuddy) 2 adults, 2 children, full fuel tank etc Engine: 4.3 LX mercruiser with Alpha 1 gen II outdrive. Lake: Windemere (fresh water) Weather: Warm, dry, steady breeze Prop 1: 14 1/4" X 22" (originally 21" re-pitched to 22") re-conditioned Prop 2: 14 1/4" X 21" Tiny scrape on tip of one blade. 1/4" sq missing Prop 3: 14 1/4" X 19" good (but not perfect) condition. re-conditioned Engine 22" Prop 21" Prop 19" Prop RPM MPH MPH MPH 4.5K 39 42 38 4.0K 33 38 32 3.5K 30 30 3.3K 22* 3.0K 22* 22* Not Planing * just on plane From rest 7.8 secs 6.7 secs 3.9 secs to plane (approx 22mph) The recommended WOT max RPM is 4800. At WOT the engine will considerably exceed 4800 (max RPM) if allowed to with all props. The 22" is not as fast as the 21". Could this be due to 'slip' or cavitation? There is not much difference between the speeds of the 19 and 22 but the 19 is on the plane in 1/2 the time. Again is this the 22 'slipping'? I cannot percieve any evidence of, or can feel cavitation from the helm. Would a 4 blade prop be better? Is any improvement likely to be only marginal? The speed for a given RPM was 3 MPH lower when travelling into the wind. the above figures were the average runs into and with the wind.. I understand that the boat is supplied with a 19" as standard. Steve Courtesy of Lee Yeaton, See the boats of rec.boats www.TheBayGuide.com/rec.boats |
#6
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Prop sizes/performance
One my 21 Scarab which had a 350 Chevy engine was purchased with a 14 x 21
aluminum prop which maxed out at 5000rpm which was too much. I installed a Merc SS 14-3/8 x 21 and rpm dropped to 4700rpm and MPH went up by 4. Do you have any friends with SS props who will let you try them even if they are running more pitch than you need it gives a base line on which way to go in pitch? "Steve Lomax" wrote in message ... I am thinking in terms of buying a SS prop but I would like to be sure of getting the right size. As the engine will conbsiderably over-rev, I would like to use this power to get a prop that will give me WOT at 4800 RMP. At the moment the best I can get is 3/4WOT. It seems a shame to have the power and not use it. I agree that an extra 5mph is probably neither here or there but I feel that there is enough unused 'grunt' to get at least 10mph (25%) , or more significantly, better fuel efficency - it costs nearly 100 UKP to fill the tank. (Yes.... I know, the deeper the draught, the bigger the overdraft!). I'm getting quite adept at prop changing in the water, and dropping to the 19" for skiing is not so much of a problem, so getting speed and economy for cruising is probably the order of the day. Steve "Woodchuck" wrote in message ... The 22 is one prop I would toss in the can! But the question is: "What are you trying to achieve"? Consider this -going with a SS prop may net as much as 5mph... "Steve Lomax" wrote in message ... I took 3 Aluminium props on the lake today and compared them. No special hi-tech gear other than a stopwatch and the standard helm instruments. FWIW, I Thaught I would share the results: Boat: 1996 Bayliner 2052 (20' cuddy) 2 adults, 2 children, full fuel tank etc Engine: 4.3 LX mercruiser with Alpha 1 gen II outdrive. Lake: Windemere (fresh water) Weather: Warm, dry, steady breeze Prop 1: 14 1/4" X 22" (originally 21" re-pitched to 22") re-conditioned Prop 2: 14 1/4" X 21" Tiny scrape on tip of one blade. 1/4" sq missing Prop 3: 14 1/4" X 19" good (but not perfect) condition. re-conditioned Engine 22" Prop 21" Prop 19" Prop RPM MPH MPH MPH 4.5K 39 42 38 4.0K 33 38 32 3.5K 30 30 3.3K 22* 3.0K 22* 22* Not Planing * just on plane From rest 7.8 secs 6.7 secs 3.9 secs to plane (approx 22mph) The recommended WOT max RPM is 4800. At WOT the engine will considerably exceed 4800 (max RPM) if allowed to with all props. The 22" is not as fast as the 21". Could this be due to 'slip' or cavitation? There is not much difference between the speeds of the 19 and 22 but the 19 is on the plane in 1/2 the time. Again is this the 22 'slipping'? I cannot percieve any evidence of, or can feel cavitation from the helm. Would a 4 blade prop be better? Is any improvement likely to be only marginal? The speed for a given RPM was 3 MPH lower when travelling into the wind. the above figures were the average runs into and with the wind.. I understand that the boat is supplied with a 19" as standard. Steve |
#7
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Prop sizes/performance
No one I know directly has anything bigger than 19" (I'm talking propellers
here, by the way! ) Our local marina is sail only but I will post a note at the registration office at the launch slipway and generally spread the word. Thanks for your help. Steve "Woodchuck" wrote in message ... One my 21 Scarab which had a 350 Chevy engine was purchased with a 14 x 21 aluminum prop which maxed out at 5000rpm which was too much. I installed a Merc SS 14-3/8 x 21 and rpm dropped to 4700rpm and MPH went up by 4. Do you have any friends with SS props who will let you try them even if they are running more pitch than you need it gives a base line on which way to go in pitch? "Steve Lomax" wrote in message ... I am thinking in terms of buying a SS prop but I would like to be sure of getting the right size. As the engine will conbsiderably over-rev, I would like to use this power to get a prop that will give me WOT at 4800 RMP. At the moment the best I can get is 3/4WOT. It seems a shame to have the power and not use it. I agree that an extra 5mph is probably neither here or there but I feel that there is enough unused 'grunt' to get at least 10mph (25%) , or more significantly, better fuel efficency - it costs nearly 100 UKP to fill the tank. (Yes.... I know, the deeper the draught, the bigger the overdraft!). I'm getting quite adept at prop changing in the water, and dropping to the 19" for skiing is not so much of a problem, so getting speed and economy for cruising is probably the order of the day. Steve "Woodchuck" wrote in message ... The 22 is one prop I would toss in the can! But the question is: "What are you trying to achieve"? Consider this -going with a SS prop may net as much as 5mph... "Steve Lomax" wrote in message ... I took 3 Aluminium props on the lake today and compared them. No special hi-tech gear other than a stopwatch and the standard helm instruments. FWIW, I Thaught I would share the results: Boat: 1996 Bayliner 2052 (20' cuddy) 2 adults, 2 children, full fuel tank etc Engine: 4.3 LX mercruiser with Alpha 1 gen II outdrive. Lake: Windemere (fresh water) Weather: Warm, dry, steady breeze Prop 1: 14 1/4" X 22" (originally 21" re-pitched to 22") re-conditioned Prop 2: 14 1/4" X 21" Tiny scrape on tip of one blade. 1/4" sq missing Prop 3: 14 1/4" X 19" good (but not perfect) condition. re-conditioned Engine 22" Prop 21" Prop 19" Prop RPM MPH MPH MPH 4.5K 39 42 38 4.0K 33 38 32 3.5K 30 30 3.3K 22* 3.0K 22* 22* Not Planing * just on plane From rest 7.8 secs 6.7 secs 3.9 secs to plane (approx 22mph) The recommended WOT max RPM is 4800. At WOT the engine will considerably exceed 4800 (max RPM) if allowed to with all props. The 22" is not as fast as the 21". Could this be due to 'slip' or cavitation? There is not much difference between the speeds of the 19 and 22 but the 19 is on the plane in 1/2 the time. Again is this the 22 'slipping'? I cannot percieve any evidence of, or can feel cavitation from the helm. Would a 4 blade prop be better? Is any improvement likely to be only marginal? The speed for a given RPM was 3 MPH lower when travelling into the wind. the above figures were the average runs into and with the wind.. I understand that the boat is supplied with a 19" as standard. Steve |
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