Guardian 17, Yamaha 60-HP High Thrust - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  Guardian 17, Yamaha 60-HP High Thrust

search | FAQ | profile | register | author help

Author Topic:   Guardian 17, Yamaha 60-HP High Thrust

koaman posted 06-22-2010 03:31 PM ET (US)
A 1988 Guardian 17 with 2008 Yamaha T60 goes 25.5-MPH 6,000-RPM WOT with 13-1/2 x 13 stock aluminum propeller (16.5% slip), one person, 250-octothorpe, fuel, gear, and Yamaha F8 auxiliary motor. Changed to 13-5/8 x 15 stock aluminum propeller and get 27.5-MPH 5,000-RPM WOT (9% slip). I can[']t figure out why I am losing 1000-RPM with only 2-inch more pitch. Some may say the 13-inch is the correct propeller since I am reaching 6,000-RPM, but I do a fair amount of trolling 7 to 8 [nautical miles per hour] and don't like trolling at over 3,000-RPM. I like the way she trolls with the 15-inch propeller (8-nautical miles per hour 2,800-RPM), but think I should be able to run WOT at at least 5,400 or 5,500-RPM. I don't know if I should by a 14-inch pitch propeller or 13-inch stainless. Thanks in advance for any suggestions. Koaman
number9 posted 06-22-2010 04:52 PM ET (US)
The T50 on my 1984 Outrage 18 is running the black stainless 13.5 x 14 and has hit 28 -MPH at WOT. That's the high end of what Yamaha Rigging Manual says the motor and propeller should do. They say 26-MPH for your 13 and 30-MPH for the 15 pitch propellers. Because my 21-inch long shaft motor is on a 25-inch transom the AV-plate sits almost 3.5-inch above the bottom. Since you have the same 21-inch length you may want to raise your motor mounting position all the way up to increase your WOT RPM and MPH. That would still give you a conservative mounting height.
Bill
bloller posted 06-22-2010 08:20 PM ET (US)
I have a non-commercial 16' hull and a Mercury 60HP Bigfoot Fourstroke. My motor and your motor are very similar with identical displacement but for some reason Yamaha full throttle -RPM range on your motor is 5000-6000-RPMs while my Mercury is 5500-6000-RPMs. Lightly loaded, I get about 5900-RPMs and 34-MPH with a 14 pitch, 5500 with a 15 pitch and well over 6000-RPMs with a 13 pitch. My motor is raised two holes.
A 14 pitch stainless steel is what you want. I am guessing that the added weight of your commercial hull and your large kicker are responsible for the lower -RPMs and speed. You should also raise the engine at least one hole if not already.
koaman posted 06-22-2010 10:13 PM ET (US)
Thanks guys, The motor is two holes up already, I don't know if I want to raise it any more with the water I fish in. I think I will try a 14-inch SS, it should get me close to what I want. Still can't figure why I have 1000-RPM difference in only 2 inch of pitch change. Must be the slip.
Ric232 posted 06-23-2010 08:13 AM ET (US)
koaman,
I think the 1,000-RPM difference actually makes sense. The reason is twofold:
(1) You're dealing with lower pitch props
(2) With the 15P, your motor is not able to reach its peak horsepower RPM
A 2 inch change in pitch from a 13P prop makes a bigger difference than a 2 inch change from a 21P. That's why the smaller pitch props come in 1 inch increments. If all else was equal, in theory a boat running 6,000-RPM with a 21P prop would run 5478 -RPM with a 23P. However, assuming the HP peak is at 5500 -RPM (like your motor), the motor will spin faster than 5478 (say 5600 - 5700) because it is generating more HP at 5478 -RPM vs 6000 -RPM, so the motor is pushing harder in that RPM range. In your case, all else being equal your motor would turn 5200 -RPM with the 15P (vs 6000 with the 13P). However, because your motor is not able to reach 5500 to attain its peak HP, it can't even reach 5200. In short, you are way over-propped with the 15P. Try the 14P as others have suggested. You'll probably end up at 5700 -RPM.
Regarding the slip issue, I recalculated your slip and the slip for your 13-inch prop to be 19.4% (instead 16.5%). Are the props the same brand and both in good condition? As propellers go up in pitch, they gain efficiency (i.e. slip less) but not by that much. I'm talking 1 or 2 percentage points at the most. Are you using a GPS for your speeds? I ask because at the speeds you're running, even a small difference in speed makes a big difference in the slip calculation. For example, if you are actually running 25 -MPH with the 15P (instead of 27.5), your slip would be 17.9%, which makes a lot more sense.
I hope this helps.
Ric232 posted 06-23-2010 08:37 AM ET (US)
I just noticed that your 15P prop diameter is 1/8-inch larger than your 13P. It's normally the other way around. That would further support the dramatic decrease in RPM. It also suggests that the two props are not the same model, which can make a world of difference.
koaman posted 06-23-2010 12:26 PM ET (US)
Thanks Ric232, I had the 19% slip on my notes but posted 16% for some reason. Both props are new Yamaha white aluminum. I reversed the diameter though, the 13p has the 13 5/8 diameter and the other is the 13.5 x 15.
I am using my GPS for my speed #, conditions were the same but there's a chance the current was different. Everybody goes by knots over here and my GPS was set on that and did the conversion when I posted. The 13 pitch barly got 23 knots and the 15 got 24 to 24.5 easier. Thanks for the help, I'm going to try a stock Yamaha black S.S. 13.5 x 14. One person said that my motor is too small for the weight of a S.S. prop, I am hoping that is not the case.
number9 posted 06-23-2010 01:11 PM ET (US)
koaman,
Your T60 should handle the SS weight just fine, my slightly less displacement T50 does. Since you're already mounted two holes may not be worth the effort to raise it. My thought was raising and trying your 15-inch pitch again would be less expensive might get your speed up. If it did and the height worked for your waters a 15-inch SS might be a better investment. Since the actual shaft length is 21-inch your current height is more like one hole up.
Do you have carbs or injection?
Bill
Tom W Clark posted 06-23-2010 01:15 PM ET (US)

quote:
One person said that my motor is too small for the weight of a S.S. propeller..
Whoever said that doesn;t know what they are talking about. A good stainless steel propeller will definitely improve your boat;s performance.
I am puzzled by the speed and RPM data you report.
23 knots at 6000 RPM with a 13-inch pitch prop is 17 percent slip.
24 knots at 5000 RPM with a 15-inch pitch prop is only 9 percent slip.
If both propellers are the same model, and you say they are, then something is fishy, there should not be that much difference.
Was the 13-inch pitch prop damaged in any way or had it ever been repaired?
I agree the 13-1/2-inch x 14-inch Yamaha Painted Stainless Steel propeller would be a good prop to try.
koaman posted 06-23-2010 01:57 PM ET (US)
Thanks Tom, You are correct about the slip. I glad you think the S.S. is a better choice. The 13p was brand new out of the Yamaha box and the 15 came with the motor with less than 50 hrs on it. no dings. Only difference I see is the 15p is stamped on the side between the blades 13.5x15-K and the other is stamped on the hub end 13 5/8 x 13K
Bill, my 2008 T60 is carbureted. I may try a some point raising one more hole to check preformance.
I'm very curious to see where I end up with the 14p S.S. Found a new one on Ebay for $250.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: Guardian 17, Yamaha 60-HP High Thrust
koaman	posted 06-22-2010 03:31 PM ET (US) A 1988 Guardian 17 with 2008 Yamaha T60 goes 25.5-MPH 6,000-RPM WOT with 13-1/2 x 13 stock aluminum propeller (16.5% slip), one person, 250-octothorpe, fuel, gear, and Yamaha F8 auxiliary motor. Changed to 13-5/8 x 15 stock aluminum propeller and get 27.5-MPH 5,000-RPM WOT (9% slip). I can[']t figure out why I am losing 1000-RPM with only 2-inch more pitch. Some may say the 13-inch is the correct propeller since I am reaching 6,000-RPM, but I do a fair amount of trolling 7 to 8 [nautical miles per hour] and don't like trolling at over 3,000-RPM. I like the way she trolls with the 15-inch propeller (8-nautical miles per hour 2,800-RPM), but think I should be able to run WOT at at least 5,400 or 5,500-RPM. I don't know if I should by a 14-inch pitch propeller or 13-inch stainless. Thanks in advance for any suggestions. Koaman
number9	posted 06-22-2010 04:52 PM ET (US) The T50 on my 1984 Outrage 18 is running the black stainless 13.5 x 14 and has hit 28 -MPH at WOT. That's the high end of what Yamaha Rigging Manual says the motor and propeller should do. They say 26-MPH for your 13 and 30-MPH for the 15 pitch propellers. Because my 21-inch long shaft motor is on a 25-inch transom the AV-plate sits almost 3.5-inch above the bottom. Since you have the same 21-inch length you may want to raise your motor mounting position all the way up to increase your WOT RPM and MPH. That would still give you a conservative mounting height. Bill
bloller	posted 06-22-2010 08:20 PM ET (US) I have a non-commercial 16' hull and a Mercury 60HP Bigfoot Fourstroke. My motor and your motor are very similar with identical displacement but for some reason Yamaha full throttle -RPM range on your motor is 5000-6000-RPMs while my Mercury is 5500-6000-RPMs. Lightly loaded, I get about 5900-RPMs and 34-MPH with a 14 pitch, 5500 with a 15 pitch and well over 6000-RPMs with a 13 pitch. My motor is raised two holes. A 14 pitch stainless steel is what you want. I am guessing that the added weight of your commercial hull and your large kicker are responsible for the lower -RPMs and speed. You should also raise the engine at least one hole if not already.
koaman	posted 06-22-2010 10:13 PM ET (US) Thanks guys, The motor is two holes up already, I don't know if I want to raise it any more with the water I fish in. I think I will try a 14-inch SS, it should get me close to what I want. Still can't figure why I have 1000-RPM difference in only 2 inch of pitch change. Must be the slip.
Ric232	posted 06-23-2010 08:13 AM ET (US) koaman, I think the 1,000-RPM difference actually makes sense. The reason is twofold: (1) You're dealing with lower pitch props (2) With the 15P, your motor is not able to reach its peak horsepower RPM A 2 inch change in pitch from a 13P prop makes a bigger difference than a 2 inch change from a 21P. That's why the smaller pitch props come in 1 inch increments. If all else was equal, in theory a boat running 6,000-RPM with a 21P prop would run 5478 -RPM with a 23P. However, assuming the HP peak is at 5500 -RPM (like your motor), the motor will spin faster than 5478 (say 5600 - 5700) because it is generating more HP at 5478 -RPM vs 6000 -RPM, so the motor is pushing harder in that RPM range. In your case, all else being equal your motor would turn 5200 -RPM with the 15P (vs 6000 with the 13P). However, because your motor is not able to reach 5500 to attain its peak HP, it can't even reach 5200. In short, you are way over-propped with the 15P. Try the 14P as others have suggested. You'll probably end up at 5700 -RPM. Regarding the slip issue, I recalculated your slip and the slip for your 13-inch prop to be 19.4% (instead 16.5%). Are the props the same brand and both in good condition? As propellers go up in pitch, they gain efficiency (i.e. slip less) but not by that much. I'm talking 1 or 2 percentage points at the most. Are you using a GPS for your speeds? I ask because at the speeds you're running, even a small difference in speed makes a big difference in the slip calculation. For example, if you are actually running 25 -MPH with the 15P (instead of 27.5), your slip would be 17.9%, which makes a lot more sense. I hope this helps.
Ric232	posted 06-23-2010 08:37 AM ET (US) I just noticed that your 15P prop diameter is 1/8-inch larger than your 13P. It's normally the other way around. That would further support the dramatic decrease in RPM. It also suggests that the two props are not the same model, which can make a world of difference.
koaman	posted 06-23-2010 12:26 PM ET (US) Thanks Ric232, I had the 19% slip on my notes but posted 16% for some reason. Both props are new Yamaha white aluminum. I reversed the diameter though, the 13p has the 13 5/8 diameter and the other is the 13.5 x 15. I am using my GPS for my speed #, conditions were the same but there's a chance the current was different. Everybody goes by knots over here and my GPS was set on that and did the conversion when I posted. The 13 pitch barly got 23 knots and the 15 got 24 to 24.5 easier. Thanks for the help, I'm going to try a stock Yamaha black S.S. 13.5 x 14. One person said that my motor is too small for the weight of a S.S. prop, I am hoping that is not the case.
number9	posted 06-23-2010 01:11 PM ET (US) koaman, Your T60 should handle the SS weight just fine, my slightly less displacement T50 does. Since you're already mounted two holes may not be worth the effort to raise it. My thought was raising and trying your 15-inch pitch again would be less expensive might get your speed up. If it did and the height worked for your waters a 15-inch SS might be a better investment. Since the actual shaft length is 21-inch your current height is more like one hole up. Do you have carbs or injection? Bill
Tom W Clark	posted 06-23-2010 01:15 PM ET (US) quote: One person said that my motor is too small for the weight of a S.S. propeller.. Whoever said that doesn;t know what they are talking about. A good stainless steel propeller will definitely improve your boat;s performance. I am puzzled by the speed and RPM data you report. 23 knots at 6000 RPM with a 13-inch pitch prop is 17 percent slip. 24 knots at 5000 RPM with a 15-inch pitch prop is only 9 percent slip. If both propellers are the same model, and you say they are, then something is fishy, there should not be that much difference. Was the 13-inch pitch prop damaged in any way or had it ever been repaired? I agree the 13-1/2-inch x 14-inch Yamaha Painted Stainless Steel propeller would be a good prop to try.
koaman	posted 06-23-2010 01:57 PM ET (US) Thanks Tom, You are correct about the slip. I glad you think the S.S. is a better choice. The 13p was brand new out of the Yamaha box and the 15 came with the motor with less than 50 hrs on it. no dings. Only difference I see is the 15p is stamped on the side between the blades 13.5x15-K and the other is stamped on the hub end 13 5/8 x 13K Bill, my 2008 T60 is carbureted. I may try a some point raising one more hole to check preformance. I'm very curious to see where I end up with the 14p S.S. Found a new one on Ebay for $250.