I’m in Belhaven, a town I anchored in once but never went ashore and have always passed by since. I walked around enough to get a blister on my foot. It wasn’t actually all that much. This is a pleasant enough place but there isn’t much “there” here so I clearly haven’t been getting off the boat enough.
I had happy hour with some of the boat I passed in the Alligator River. The speed with which Strider passed them led to a discussion of diesel operation, one of my favorite subjects. There’s a post on it in my “Book One” archive:
http://<a href="http://forums....s.com/showthread.php?t=120010&#post728065</a>http://forums.sbo.sailboatowners.com/showthread.php?t=120010&#post728065
(The link to the diagram broke so here is the one referred to in the text)
https://fbcdn-sphotos-h-a.akamaihd....1490921_b3db5c06a9ba78c9562c54187ac36c08[/img
This reminded me of something I should have mentioned in connection with my stopping in the Chesapeake and showing forumite and fellow Endeavour 32 owner “Trasel” how fast he should be running his boat. Like many people, he had been running very slowly under power because of the common belief that your engine will last longer if it doesn’t work too hard and also because he thought the smoke he saw at higher RPM’s meant the engine was overloaded. Part of our test run side by side was my assuring him that the light grey smoke he saw was perfectly normal.
I realized later another trap that may account for some of the sailboats I see creeping along. When I reached the open river after the Dismal Swamp Canal, I opened Strider up and was momentarily alarmed when I looked back. My exhaust looked like the sky over a big city during a temperature inversion. There was a faint slick on the water behind the boat. Uh, Oh!
It only took me a few moments to realize that I had spent a whole day running very slowly behind a large powerboat that was having engine overheat problems due to duckweed clogging is strainers. Once it pulled over to clear them, I then loafed along near idle for an hour so as not to have to wait at the lock. I was making four knots but barely pulling any power out of the engine. What I was seeing was all the crud that built up in the exhaust elbow. I ran up to full power for about five minutes and then nearly full power. The exhaust looked better in ten minutes and was back to normal within half an hour. I can see how someone who habitually runs a diesel at very low power can be alarmed by their exhaust smoke when the bring the RPM’s up into the proper range. It even got me for a moment.
Engines vary but mine is typical. If I take my oil filler cap off when the engine is at idle or running at very low power, air streams out like there was a fan inside the crankcase. It’s almost as strong as a hair dryer. If I do the same thing at cruise power, there is just a hint of air flow, not much more than a baby’s breath. Why this counterintuitive observation? The piston rings are sealed against the cylinder walls by the combustion pressure leaking down into the oil behind them in the grooves and pushing the rings out. If the engine is lightly loaded, the rings float near the bottom of the power stroke and combustion gasses full of acids and other nasty stuff leak down into the crankcase. You do the math. More oil also leaks up into the combustion chambers and, along with less complete combustion (diesels depend on the high pressure and heat to ignite the fuel) contribute to poorly burned fuel and oil building up in the exhaust system.
Strider has a perfect match between engine and prop. (Would you expect anything less from an owner who has designed numerous marine drive trains?) I am not however, running my engine at the optimum 80% power. I used to but the noise, fuel bill, and spray over the bow were too much. I could change the prop but not the engine. Like most boats, Strider should have a slightly smaller engine for optimum operation. Everything sounds good at 2200 and I have a prop that loads the engine up more at that speed than most boats. With the bottom clean and the boat lightly loaded, she comes up to the 2600 RPM for continuous operation at wide open throttle. Loaded, she still gets to 2550. Engine reps on sea trials usually want to see the WOT within 50 RPM to sign off the warranty on a new engine installation so I’m good even with a more aggressive prop than most sailboats have.
As noted in the linked post above, typical propeller characteristics mean that 90% of maximum RPM will pull the optimum 80% power out of the engine. That would be 2340 for mine. I run very hard as people who have watched me pass them in their larger boats often note but my engine would still be happier running a bit faster. However, it will probably outlast my cruising days and 2200 is a good compromise with noise and the fuel bills I pay about once a week the way I’m traveling now.
If my engine was a bit smaller, I could run it optimally. What about reserve power for bad weather, the boogy man that engine salesmen use to get more expensive and oversized engines into boats? Well, I’ve seen some nasty stuff in the over 25,000 miles I’ve run under Strider’s keel. Whenever I’ve been struggling, it has been at less than full power. Even trying to get to anchor in winds over fifty knots in the Alligator River a couple years ago, I was running only at about 2300 RPM because. Boat motion, pounding, and spray usually restrict the power usage to normal if the prop is properly matched to the engine, something all too rare on cruising sailboats.
Speaking of that 25,000 plus miles: I wear the tee shirt that says:
Caveat:
It is possible, although very rare on sailboats, to have too much prop. Having a combination of diameter and pitch that will not let the engine come up to within 50 RPM of its rated horsepower is about the worst thing there is for an engine. If you are seeing black smoke at full power, and are sure it is not just crud being blown out from low power operation; or if you are not coming up to RPM and have verified that your tach is accurate, you need to get some professional advice. Most prop shops now have the software to help you determine the right propeller. You should also verify that your throttle cable is moving the lever to the stop.
I had happy hour with some of the boat I passed in the Alligator River. The speed with which Strider passed them led to a discussion of diesel operation, one of my favorite subjects. There’s a post on it in my “Book One” archive:
http://<a href="http://forums....s.com/showthread.php?t=120010&#post728065</a>http://forums.sbo.sailboatowners.com/showthread.php?t=120010&#post728065
(The link to the diagram broke so here is the one referred to in the text)
https://fbcdn-sphotos-h-a.akamaihd....1490921_b3db5c06a9ba78c9562c54187ac36c08[/img
This reminded me of something I should have mentioned in connection with my stopping in the Chesapeake and showing forumite and fellow Endeavour 32 owner “Trasel” how fast he should be running his boat. Like many people, he had been running very slowly under power because of the common belief that your engine will last longer if it doesn’t work too hard and also because he thought the smoke he saw at higher RPM’s meant the engine was overloaded. Part of our test run side by side was my assuring him that the light grey smoke he saw was perfectly normal.
I realized later another trap that may account for some of the sailboats I see creeping along. When I reached the open river after the Dismal Swamp Canal, I opened Strider up and was momentarily alarmed when I looked back. My exhaust looked like the sky over a big city during a temperature inversion. There was a faint slick on the water behind the boat. Uh, Oh!
It only took me a few moments to realize that I had spent a whole day running very slowly behind a large powerboat that was having engine overheat problems due to duckweed clogging is strainers. Once it pulled over to clear them, I then loafed along near idle for an hour so as not to have to wait at the lock. I was making four knots but barely pulling any power out of the engine. What I was seeing was all the crud that built up in the exhaust elbow. I ran up to full power for about five minutes and then nearly full power. The exhaust looked better in ten minutes and was back to normal within half an hour. I can see how someone who habitually runs a diesel at very low power can be alarmed by their exhaust smoke when the bring the RPM’s up into the proper range. It even got me for a moment.
Engines vary but mine is typical. If I take my oil filler cap off when the engine is at idle or running at very low power, air streams out like there was a fan inside the crankcase. It’s almost as strong as a hair dryer. If I do the same thing at cruise power, there is just a hint of air flow, not much more than a baby’s breath. Why this counterintuitive observation? The piston rings are sealed against the cylinder walls by the combustion pressure leaking down into the oil behind them in the grooves and pushing the rings out. If the engine is lightly loaded, the rings float near the bottom of the power stroke and combustion gasses full of acids and other nasty stuff leak down into the crankcase. You do the math. More oil also leaks up into the combustion chambers and, along with less complete combustion (diesels depend on the high pressure and heat to ignite the fuel) contribute to poorly burned fuel and oil building up in the exhaust system.
Strider has a perfect match between engine and prop. (Would you expect anything less from an owner who has designed numerous marine drive trains?) I am not however, running my engine at the optimum 80% power. I used to but the noise, fuel bill, and spray over the bow were too much. I could change the prop but not the engine. Like most boats, Strider should have a slightly smaller engine for optimum operation. Everything sounds good at 2200 and I have a prop that loads the engine up more at that speed than most boats. With the bottom clean and the boat lightly loaded, she comes up to the 2600 RPM for continuous operation at wide open throttle. Loaded, she still gets to 2550. Engine reps on sea trials usually want to see the WOT within 50 RPM to sign off the warranty on a new engine installation so I’m good even with a more aggressive prop than most sailboats have.
As noted in the linked post above, typical propeller characteristics mean that 90% of maximum RPM will pull the optimum 80% power out of the engine. That would be 2340 for mine. I run very hard as people who have watched me pass them in their larger boats often note but my engine would still be happier running a bit faster. However, it will probably outlast my cruising days and 2200 is a good compromise with noise and the fuel bills I pay about once a week the way I’m traveling now.
If my engine was a bit smaller, I could run it optimally. What about reserve power for bad weather, the boogy man that engine salesmen use to get more expensive and oversized engines into boats? Well, I’ve seen some nasty stuff in the over 25,000 miles I’ve run under Strider’s keel. Whenever I’ve been struggling, it has been at less than full power. Even trying to get to anchor in winds over fifty knots in the Alligator River a couple years ago, I was running only at about 2300 RPM because. Boat motion, pounding, and spray usually restrict the power usage to normal if the prop is properly matched to the engine, something all too rare on cruising sailboats.
Speaking of that 25,000 plus miles: I wear the tee shirt that says:
Over 80% of those miles have been under power and my 1979 engine runs like it was new. Oil consumption is about .14 OZ per hour or under a quart per 100 hour change. I rest my case for running hard.
Caveat:
It is possible, although very rare on sailboats, to have too much prop. Having a combination of diameter and pitch that will not let the engine come up to within 50 RPM of its rated horsepower is about the worst thing there is for an engine. If you are seeing black smoke at full power, and are sure it is not just crud being blown out from low power operation; or if you are not coming up to RPM and have verified that your tach is accurate, you need to get some professional advice. Most prop shops now have the software to help you determine the right propeller. You should also verify that your throttle cable is moving the lever to the stop.
