07-01-2013, 12:29 PM
If you have the 6.0s, you should have the following props: Michigan EPX-300 18 x 24 .70 DAR #7 cup
If you have the 8.1s, you should have the following props: Michigan EPX-300 19 x 22 #7 cup Nibral
Just because the props are stamped a particular size, does not mean they are correct. Even if you do not hit anything, over time the blades can change pitch. Depending on use, I suggest having your props pulled, scanned, trued and balanced every 3 to 5 years. If you run aground, you should have them done at that time even if there appears to be no damage as it is impossible to see if a blade is out by eye.
The above props are factory original. If you have significantly altered the vessel (via tuna or marlin tower), tow a tender or just carry extra weight above and beyond normal loads, you may need to alter or completely change props to get proper engine loading. Overloading or underloading can both lead to premature engine failure. Jongott listed the proper WOT RPMs for the 6.0s and 8.1s.
Based on your RPM and Speed (3100 RPM @ 22 knots) I'm guessing you have the 8.1s. According to the performance report, your most economical cruise should be at 3200 RPM @ 24 knots - 1.06 MPG.
Notice the #7 Cup for your props. Cupping provides lift. When you have your props checked, make sure the cup is correct. As you stated, you are having issues with bow rise. If your props are under cupped, this could lead to issues with not enough lift causing you to run too bow high. You may also want to run a bit faster (provided condition allow) as 22 knots is a bit slow for wide planning hull with prop pockets. Some hulls like to run faster and are actually more efficient at higher speeds. Optimal running attitude in calm sea-conditions for an inboard planning hull design is 5 to 7 degrees. According to the Tiara performance report for an 8.1 3000 is 7 degrees at 3000 RPM and 6.1 degrees at 3200.
If you have the 8.1s, you should have the following props: Michigan EPX-300 19 x 22 #7 cup Nibral
Just because the props are stamped a particular size, does not mean they are correct. Even if you do not hit anything, over time the blades can change pitch. Depending on use, I suggest having your props pulled, scanned, trued and balanced every 3 to 5 years. If you run aground, you should have them done at that time even if there appears to be no damage as it is impossible to see if a blade is out by eye.
The above props are factory original. If you have significantly altered the vessel (via tuna or marlin tower), tow a tender or just carry extra weight above and beyond normal loads, you may need to alter or completely change props to get proper engine loading. Overloading or underloading can both lead to premature engine failure. Jongott listed the proper WOT RPMs for the 6.0s and 8.1s.
Based on your RPM and Speed (3100 RPM @ 22 knots) I'm guessing you have the 8.1s. According to the performance report, your most economical cruise should be at 3200 RPM @ 24 knots - 1.06 MPG.
Notice the #7 Cup for your props. Cupping provides lift. When you have your props checked, make sure the cup is correct. As you stated, you are having issues with bow rise. If your props are under cupped, this could lead to issues with not enough lift causing you to run too bow high. You may also want to run a bit faster (provided condition allow) as 22 knots is a bit slow for wide planning hull with prop pockets. Some hulls like to run faster and are actually more efficient at higher speeds. Optimal running attitude in calm sea-conditions for an inboard planning hull design is 5 to 7 degrees. According to the Tiara performance report for an 8.1 3000 is 7 degrees at 3000 RPM and 6.1 degrees at 3200.
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