Here is a question for the experts, which I am sure I will find on Boatered. A little background first:
I purchased a new 2004 Silverton 39 motor yacht last may and we had a good first season with her. I have twin 425 hp crusader gas 8.1 HO engines in her. My problem is that with full fuel and water, the boat achieves 4600 rpm at WOT and crusader states 4800 to 5200 rpm "under full load" in the manual. Silverton said the boat left the factor 4900 rpm at WOT swinging 24 x 24 inch 4 bladed nibral with a #3 cup. I ordered a spare set of props from michigan wheel last year, figuring I would need to decrease pitch to 22 inches to achieve WOT as stated. Therefore, my spare props are 24 inch diameter, 22 inch pitch, same cup. I would like to be at 5000-5200 rpm with **full fuel and water**. That is how I like to run. Now, silverton said they test their boats with 1/4 fuel and 1/2 water. Silverton said that this was fine with crusader and like I said, it hit 4900 rpm before leaving the factory with the 24 x 24 props. Now, I can confirm that it did get to 4900 with the same fuel and water conditions that silverton tested it with.
Questions:
1. I want to put my new wheels on this in the spring to bring my rpm's up. What will this do to my fuel economy (trust me, I am not looking for anything magical- it sucks now and will always suck--->I don't want it to suck more!
2. Would you leave the original wheels on it and forget about it, swithing to the "spares" only if needed?
3. Am I harming my engines with the current set up. Crusader manual says "must achieve the stated WOT at "normal load" per the manual. The manual does not define "normal load" but does "educate" the consumer stating that a heavier boat decreases top rpm etc. I guess "normal load" is subject to interpretation. Silverton states 1/2 water, 1/4 fuel. I don't know of anyone who will feel comfortable continuing to boat with 1/4 fuel. I certainly don't.
What do you guys think?
I purchased a new 2004 Silverton 39 motor yacht last may and we had a good first season with her. I have twin 425 hp crusader gas 8.1 HO engines in her. My problem is that with full fuel and water, the boat achieves 4600 rpm at WOT and crusader states 4800 to 5200 rpm "under full load" in the manual. Silverton said the boat left the factor 4900 rpm at WOT swinging 24 x 24 inch 4 bladed nibral with a #3 cup. I ordered a spare set of props from michigan wheel last year, figuring I would need to decrease pitch to 22 inches to achieve WOT as stated. Therefore, my spare props are 24 inch diameter, 22 inch pitch, same cup. I would like to be at 5000-5200 rpm with **full fuel and water**. That is how I like to run. Now, silverton said they test their boats with 1/4 fuel and 1/2 water. Silverton said that this was fine with crusader and like I said, it hit 4900 rpm before leaving the factory with the 24 x 24 props. Now, I can confirm that it did get to 4900 with the same fuel and water conditions that silverton tested it with.
Questions:
1. I want to put my new wheels on this in the spring to bring my rpm's up. What will this do to my fuel economy (trust me, I am not looking for anything magical- it sucks now and will always suck--->I don't want it to suck more!
2. Would you leave the original wheels on it and forget about it, swithing to the "spares" only if needed?
3. Am I harming my engines with the current set up. Crusader manual says "must achieve the stated WOT at "normal load" per the manual. The manual does not define "normal load" but does "educate" the consumer stating that a heavier boat decreases top rpm etc. I guess "normal load" is subject to interpretation. Silverton states 1/2 water, 1/4 fuel. I don't know of anyone who will feel comfortable continuing to boat with 1/4 fuel. I certainly don't.
What do you guys think?