I've got a 1990 H30 with a Yanmar 2gmf rated at 18 hp at 3200 (or 3400, can't exactly remember) rpm; must be standard for Yanmar 2 cylindars. I've read the rule of thumb for cruising is 80 percent of max rated rpm, or 2560 rpm. I've been running it at about 2700 rpm, which gives me a cruising speed of 5.5 knots. Yet others in the forum are getting 6 to 6.5 knots (hull speed for the H30 is 6.5). I'm curious...what rpms and speeds are people running at with the 2gm?
- Status
- Not open for further replies.
J
Jim McCue
What are you measuring with?
Are you using the old knot/log thru hull impeller for measurement or a GPS? It seems to make a difference. Jim McCue
Are you using the old knot/log thru hull impeller for measurement or a GPS? It seems to make a difference. Jim McCue
T
Tim Op't Holt
rpms and mph
I too have a 2 gmf. At about 2500-2700 rpm, my speedometer reads about 5 mph. But, thats with the impeller style speedometer, not a gps. The previous owner had indicated that the speedometer reads mpk not kph, but I have not been able to verify that with a gps. Tim
I too have a 2 gmf. At about 2500-2700 rpm, my speedometer reads about 5 mph. But, thats with the impeller style speedometer, not a gps. The previous owner had indicated that the speedometer reads mpk not kph, but I have not been able to verify that with a gps. Tim
B
Bruce
My experience
I just checked my boat for speed at various RPM on calm salt water, no wind to speak of, 2 persons, relatively light load and got 5kts @ 2100 and 6 kts @ 2650 or so. Both the GPS and impeller driven knotmeter agreed. Somedays, I get more or less, but have not pushed the Yanmar really more than 2800, and got up to 6.3 Obviously, bottom paint condition means a lot, and we are halfway through the season in Maine. Early on, I could get another couple of points out of it.
I just checked my boat for speed at various RPM on calm salt water, no wind to speak of, 2 persons, relatively light load and got 5kts @ 2100 and 6 kts @ 2650 or so. Both the GPS and impeller driven knotmeter agreed. Somedays, I get more or less, but have not pushed the Yanmar really more than 2800, and got up to 6.3 Obviously, bottom paint condition means a lot, and we are halfway through the season in Maine. Early on, I could get another couple of points out of it.
A
Al Sandrik
Our engine expert at Whitney's Marine
told me to run our 2GM at 2800 rpm's and we make about 5.5 kts in a slack current.
told me to run our 2GM at 2800 rpm's and we make about 5.5 kts in a slack current.
T
Tim Schaaf
sidebar on knotmeters
referring to some of the previous posts on this subject, most knotmeters can (and should) be calibrated, and they can be calibrated for knots, miles, kilometers, or whatever. I was also very surprised, some years ago, to have Datamarine tell me that the impeller should be changed yearly. It has something to do with the lubrication of the little spindle on which it rotates. After changing mine, it worked better. I don't change it every year, but now and then, I do.... Calibrating can be a real pain. Datamarine recommended two passes at a one nautical mile course. If you work out the math, and the built in errors, you have to do quite a few more passes to get the knotmeter to within one tenth of a knot accuracy, and of course you have to time your runs with the tide, so that everything evens out. It is an interesting exercise. But it is invaluable to have a clean, calibrated, knotmeter as well as GPS. One gives you the speed over the bottom, the other the speed through the water. Between them, you know speed of current, etc.
referring to some of the previous posts on this subject, most knotmeters can (and should) be calibrated, and they can be calibrated for knots, miles, kilometers, or whatever. I was also very surprised, some years ago, to have Datamarine tell me that the impeller should be changed yearly. It has something to do with the lubrication of the little spindle on which it rotates. After changing mine, it worked better. I don't change it every year, but now and then, I do.... Calibrating can be a real pain. Datamarine recommended two passes at a one nautical mile course. If you work out the math, and the built in errors, you have to do quite a few more passes to get the knotmeter to within one tenth of a knot accuracy, and of course you have to time your runs with the tide, so that everything evens out. It is an interesting exercise. But it is invaluable to have a clean, calibrated, knotmeter as well as GPS. One gives you the speed over the bottom, the other the speed through the water. Between them, you know speed of current, etc.
E
Eric Lorgus
Many, many variables
Dean, You can't always get a set speed-through-water (what your knotmeter tells you) for a given engine RPM, nor can you compare RPM settings and knots among different boats, nor can you judge your knotmeter's accuracy with your GPS (except if conditions of no wind, no waves, and no current). Because, 1) your prop affects your RPM's -- if you're "overpropped", you may never get over 2400 RPM's, even at full throttle. Underpropped, the opposite (you might hit 2800 RPM's at half throttle). Even two boats with identical props may perform differently, especially if one has a fouled bottom or prop. 2) wind affects power required to move a given speed (through water). In a strong headwind, you will probably find your normal RPM's to make 5 kts. isn't enough. 3) Tim's advice about calibrating knotmeters is another reason you can rarely, if ever, compare knotmeter readings between different boats. However, your knotmeter, even if not accurately calibrated, will usually be at least good for indicating relative speed -- after trimming or bearing off, has your boat speed increased or not? Beware other boaters who boast about getting 6.5 knots at 2800 RPM's. The implication is they're at 80% throttle and getting hull speed. Wow! I doubt that, unless it's a really big engine. Calibrate your boat. First, the knotmeter as Tim instructed. Then plot your speed at different RPM settings, including full throttle (preferably in slack current with no wind). If your engine won't hit its rated RPM's, find out why (prop mismatch, fouled bottom, or engine performance). Once you have these benchmarks, you'll know what to expect from your boat, and if you're not getting it, you'll know something's amiss. More power to you. Eric Lorgus
Dean, You can't always get a set speed-through-water (what your knotmeter tells you) for a given engine RPM, nor can you compare RPM settings and knots among different boats, nor can you judge your knotmeter's accuracy with your GPS (except if conditions of no wind, no waves, and no current). Because, 1) your prop affects your RPM's -- if you're "overpropped", you may never get over 2400 RPM's, even at full throttle. Underpropped, the opposite (you might hit 2800 RPM's at half throttle). Even two boats with identical props may perform differently, especially if one has a fouled bottom or prop. 2) wind affects power required to move a given speed (through water). In a strong headwind, you will probably find your normal RPM's to make 5 kts. isn't enough. 3) Tim's advice about calibrating knotmeters is another reason you can rarely, if ever, compare knotmeter readings between different boats. However, your knotmeter, even if not accurately calibrated, will usually be at least good for indicating relative speed -- after trimming or bearing off, has your boat speed increased or not? Beware other boaters who boast about getting 6.5 knots at 2800 RPM's. The implication is they're at 80% throttle and getting hull speed. Wow! I doubt that, unless it's a really big engine. Calibrate your boat. First, the knotmeter as Tim instructed. Then plot your speed at different RPM settings, including full throttle (preferably in slack current with no wind). If your engine won't hit its rated RPM's, find out why (prop mismatch, fouled bottom, or engine performance). Once you have these benchmarks, you'll know what to expect from your boat, and if you're not getting it, you'll know something's amiss. More power to you. Eric Lorgus
B
Bob England
My statistics
The first season (1999) I had my 1989 H30 with the 2GM20F engine, I ran a careful series of speed vs. RPM measurements, using the Yanmar tach and a GPS. I ran about 33 measurements, at 13 different RPM settings (spaced out from 850 to 3200 RPM), run on alternate 180 degree courses to compensate for wind. This was in fresh water with no current. The boat was lightly to moderately loaded with gear. The prop is the standard 2-blade 15x12. I later found on haul-out that the bottom of the boat was fairly dirty, and there was an amazing zebra mussel colony on the wing/bulb keel. The mussels were about 6" thick all over the bottom of the wing, so the data need to be interpreted with that in mind. (The performance is better now that the bottom is clean.) I used "linear regression" analysis to determine a function giving knots per RPM. On this set of measurements, the results were 2.256 knots/1000 RPM. So, for example, at 2000 RPM the boat was doing just over 4.5 knots. For the statistically minded thinking about goodness of fit, the R-squared statistic was 0.9678. What really surprised me was that the fit was absolutely linear over the measured range of 850 to 3200 RPM. I had expected the slope coefficient (ratio between RPM and speed) to fall off at the higher RPM values, due to increasing inefficiency of the prop as the boat neared hull speed. But a straight line was the best fit over the entire range, both mathematically and by eye-balling a graphical plot. To verify this, I also tried a quadratic (second order) equation, but there was no improvement in the quality of fit. Therefore no curve in the line. So the value of 2.256 knots per 1000 RPM held over the entire range. By the way, now that the boat's bottom is clean, I can get 3350 RPM under power, and I often cruise at 3000-3200 RPM to keep the mixing elbow clean. But at 3350 RPM the ratio does begin to break down -- I never see the expected 7.5 knots under power. The speed tops out at about 6.9 knots, which is not surprising since the hull speed is listed at 6.8 knots. This implies that exactly 3000 RPM is the optimum cruising speed for this boat/prop/engine/load combination.(Under sail I occasionally see 7 knots <grin>). All speed measurements taken by GPS. Hope this helps. Bob England
The first season (1999) I had my 1989 H30 with the 2GM20F engine, I ran a careful series of speed vs. RPM measurements, using the Yanmar tach and a GPS. I ran about 33 measurements, at 13 different RPM settings (spaced out from 850 to 3200 RPM), run on alternate 180 degree courses to compensate for wind. This was in fresh water with no current. The boat was lightly to moderately loaded with gear. The prop is the standard 2-blade 15x12. I later found on haul-out that the bottom of the boat was fairly dirty, and there was an amazing zebra mussel colony on the wing/bulb keel. The mussels were about 6" thick all over the bottom of the wing, so the data need to be interpreted with that in mind. (The performance is better now that the bottom is clean.) I used "linear regression" analysis to determine a function giving knots per RPM. On this set of measurements, the results were 2.256 knots/1000 RPM. So, for example, at 2000 RPM the boat was doing just over 4.5 knots. For the statistically minded thinking about goodness of fit, the R-squared statistic was 0.9678. What really surprised me was that the fit was absolutely linear over the measured range of 850 to 3200 RPM. I had expected the slope coefficient (ratio between RPM and speed) to fall off at the higher RPM values, due to increasing inefficiency of the prop as the boat neared hull speed. But a straight line was the best fit over the entire range, both mathematically and by eye-balling a graphical plot. To verify this, I also tried a quadratic (second order) equation, but there was no improvement in the quality of fit. Therefore no curve in the line. So the value of 2.256 knots per 1000 RPM held over the entire range. By the way, now that the boat's bottom is clean, I can get 3350 RPM under power, and I often cruise at 3000-3200 RPM to keep the mixing elbow clean. But at 3350 RPM the ratio does begin to break down -- I never see the expected 7.5 knots under power. The speed tops out at about 6.9 knots, which is not surprising since the hull speed is listed at 6.8 knots. This implies that exactly 3000 RPM is the optimum cruising speed for this boat/prop/engine/load combination.(Under sail I occasionally see 7 knots <grin>). All speed measurements taken by GPS. Hope this helps. Bob England
D
D. Riha
F
Frank Walker
5.5 knots
I have a loaded(weight) 88 30. I get 5.5 knots at 2500 RPM with a clean bottom and no wind. I have tried this with a slightly oversized 2 blade and Campbell Sailor 3 blade. Very little difference between the two. Max out at 3300 RPM.
I have a loaded(weight) 88 30. I get 5.5 knots at 2500 RPM with a clean bottom and no wind. I have tried this with a slightly oversized 2 blade and Campbell Sailor 3 blade. Very little difference between the two. Max out at 3300 RPM.
B
Bert Kinyon
D
Daniel Jonas
30K
Bert, If you can get 30K rpm's I think you need to increase the prop pitch just a bit. Aren't typos hell! LOL Dan Jonas (S/V Feije)
Bert, If you can get 30K rpm's I think you need to increase the prop pitch just a bit. Aren't typos hell! LOL Dan Jonas (S/V Feije)
- Status
- Not open for further replies.