I usually use the aux Yanmar YSE12 as little as possible, and don't usually depend on it for speed. I have noticed that for about 5 years it seems to have lost it's ability to push the boat at anywhere near hull speed, even in flat, currentless water and no headwind. I do not have a knotmeter and my GPS broke about the same time so I can't give an accurate speed. I knocked the rudder skeg into a rock and had to replace it about that time and even though I used a Hunter provided exact replacement and the job came out seemingly good as new, it seems that may have been the moment when the boat got noticeably slower under power.
Last weekend (even though the issue is years old) when I couldn't come close to staying with a friends boat I thought maybe I ought to kick around some possibilities for the loss of speed here. Unfortunately the boat lacks some of the most rudimentary of instruments, so I may have to first get some ideas on what to use to check current performance before I can even start thinking about causes for the slowness. Like I said, no knotmeter and also no tach. I think I'll get a new gps so I can get speed over ground, can anyone suggest a tach I might be able to hang on the engine for low cost?
The boat has the original 1 cylinder 12 hp Yanmar, never rebuilt besides stuff that broke and nothing replaced that would effect max power output that I can think of. Original prop (looks undamaged), shaft, tranny and throttle/ gear shift. I put the throttle to the same position as I have for 35 years for full speed, about 100 degrees rotated forward from straight up and down, I stop there because the engine lugs down a bit and the exhaust starts to get darker and makes more of it noticeably if I go past that spot. The motor sounds and acts the same, but the boat just goes way slower. I used to have one of those hand knotmeters (graduated plastic tube with a 90 degree elbow you stick in the water and a float that rose to indicate speed) in the 80's and I remember getting the float to indicate right at 6 knots under power, which is close to hull speed. I'm guessing it doesn't go over 4 knots now.
Can I find out what the propeller pitch is and the original recommended full power RPM is from anyone here?
Other thoughts and observations:
I've always used the regular cheapo albative bottom paint, the hull looks and feels about the same as always, and the powered speed seems just as slow the day I drop her in (May each year) compared to October, so I don't think hull resistance has changed much over her lifetime or affected by seasonal fouling build-up much.
In 14+ knots of wind I still match up speed and pointing wise to other boats the way I remember. She was always pretty slow in light air. But I guess to be honest I can't be 100% sure speed under sail hasn't fallen as well, and since I don't have any old info on her speed in certain conditions sailing prior to this motoring speed issue, I just don't know if the sailing speed is similarly affected. Does anyone with a shoal draft 30 have any info on how fast you can sail at various wind speeds? I have a 100% foresail and a 170% gen.
To me it seems that the dropoff in speed is so severe that if some mechanical resistance (a tight bearing, or other other rubbing/component malfunction) was being placed on the output drive components between engine crank and hull exit that that amount of robbed power would exhibit itself in the form of heat and ruin something.
Noise and vibration seem similar to always, but these one cylinder Yanmars are notoriously obnoxious in that regard. If I had some looseness or something that caused the prop and shaft to oscillate around, do you think that could kill the speed this much yet still survive mechanically after a bit of motoring over 5 years?
I guess a general wearing of the rings or cylinder liner may cause some loss of power over the years. What's anyone's opinion on whether that type of wear related power loss could be this severe without affecting the motors ability to make enough compression for starting and running? It always starts right up.
Last weekend (even though the issue is years old) when I couldn't come close to staying with a friends boat I thought maybe I ought to kick around some possibilities for the loss of speed here. Unfortunately the boat lacks some of the most rudimentary of instruments, so I may have to first get some ideas on what to use to check current performance before I can even start thinking about causes for the slowness. Like I said, no knotmeter and also no tach. I think I'll get a new gps so I can get speed over ground, can anyone suggest a tach I might be able to hang on the engine for low cost?
The boat has the original 1 cylinder 12 hp Yanmar, never rebuilt besides stuff that broke and nothing replaced that would effect max power output that I can think of. Original prop (looks undamaged), shaft, tranny and throttle/ gear shift. I put the throttle to the same position as I have for 35 years for full speed, about 100 degrees rotated forward from straight up and down, I stop there because the engine lugs down a bit and the exhaust starts to get darker and makes more of it noticeably if I go past that spot. The motor sounds and acts the same, but the boat just goes way slower. I used to have one of those hand knotmeters (graduated plastic tube with a 90 degree elbow you stick in the water and a float that rose to indicate speed) in the 80's and I remember getting the float to indicate right at 6 knots under power, which is close to hull speed. I'm guessing it doesn't go over 4 knots now.
Can I find out what the propeller pitch is and the original recommended full power RPM is from anyone here?
Other thoughts and observations:
I've always used the regular cheapo albative bottom paint, the hull looks and feels about the same as always, and the powered speed seems just as slow the day I drop her in (May each year) compared to October, so I don't think hull resistance has changed much over her lifetime or affected by seasonal fouling build-up much.
In 14+ knots of wind I still match up speed and pointing wise to other boats the way I remember. She was always pretty slow in light air. But I guess to be honest I can't be 100% sure speed under sail hasn't fallen as well, and since I don't have any old info on her speed in certain conditions sailing prior to this motoring speed issue, I just don't know if the sailing speed is similarly affected. Does anyone with a shoal draft 30 have any info on how fast you can sail at various wind speeds? I have a 100% foresail and a 170% gen.
To me it seems that the dropoff in speed is so severe that if some mechanical resistance (a tight bearing, or other other rubbing/component malfunction) was being placed on the output drive components between engine crank and hull exit that that amount of robbed power would exhibit itself in the form of heat and ruin something.
Noise and vibration seem similar to always, but these one cylinder Yanmars are notoriously obnoxious in that regard. If I had some looseness or something that caused the prop and shaft to oscillate around, do you think that could kill the speed this much yet still survive mechanically after a bit of motoring over 5 years?
I guess a general wearing of the rings or cylinder liner may cause some loss of power over the years. What's anyone's opinion on whether that type of wear related power loss could be this severe without affecting the motors ability to make enough compression for starting and running? It always starts right up.
