I have a 29.5 with the 18hp. Yanmar. What kinds of speed should I expect when cruising? I usually motor at 2800 rpm which yields about 4.7 to 5.1kts depending on conditions. The couple of times that I have exceeded 2800 rpm for an extended period of time (about 2 hours) I have overheated. Last weekend when motoring along with a friend who has a Beneteau 285, I couldn't keep up. She had to reduce her rpm's to 1800 while I maintained 2800 just so I could keep up. She also has a 18hp. Yanmar. She has about a 7000 lbs. displacement vs my 8900. Can that make the difference? What rpm should I be motoring and what speed should I expect? Thank you, Jane "Echo"
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Joe Aquilina
Speed @ RPM
Hi Jane, Join the club. I have been trying to sort out a similar problem for some time. Theoretical boat speed is 7 knots and theoretical engine rpm max is 3600. I changed from the two blade paddle to a three blade Autoprop a year ago. Works fine when sailing as it adds about half a knot when feathered ( gear in forward) and is terrific in giving me control in backing up to the pontoon. I am in Malta and it is Med stern to mooring. The two paddle was a beast and the boat would go anywhere except where I wanted it to point to in reverse. At the moment I get ( with clean prop and clean boat) 5.5 knots on my Autohelm log, and 6.1 knots on my GPS at 2500 knots, at three quarters throttle. More throttle produces more smoke but no more rpm, no more power, and no more speed. I wonder if anybody has really ever seen 7 knots under power with the 29.5 and if so with which prop, the factory original or some other substitute? I will eagerly read replies to your question. Kind regards, Joe Aquilina SY Maverick Valletta - Malta
Hi Jane, Join the club. I have been trying to sort out a similar problem for some time. Theoretical boat speed is 7 knots and theoretical engine rpm max is 3600. I changed from the two blade paddle to a three blade Autoprop a year ago. Works fine when sailing as it adds about half a knot when feathered ( gear in forward) and is terrific in giving me control in backing up to the pontoon. I am in Malta and it is Med stern to mooring. The two paddle was a beast and the boat would go anywhere except where I wanted it to point to in reverse. At the moment I get ( with clean prop and clean boat) 5.5 knots on my Autohelm log, and 6.1 knots on my GPS at 2500 knots, at three quarters throttle. More throttle produces more smoke but no more rpm, no more power, and no more speed. I wonder if anybody has really ever seen 7 knots under power with the 29.5 and if so with which prop, the factory original or some other substitute? I will eagerly read replies to your question. Kind regards, Joe Aquilina SY Maverick Valletta - Malta
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Jane
1800 rpm vs 2800 rpm
How is it possible that someone doing 1800 pm goes so much faster than me doing 2800?
How is it possible that someone doing 1800 pm goes so much faster than me doing 2800?
Of course
Jane: Speed and RPM's have nothing to do with each other on different boats. This would be like a semi and a Porsche. They are both doing 80mph but the semi is doing 1500 RPM's and the Porsche is doing 3500 RPMs. What type of engine does your friends boat have? If it is the same engine, what type of prop do they have (2 blade, 3 blade, folding, feathering etc). Then there are transmission ratios. What about the condition of your bottom (clean or dirty). All of these things come into play. The next thing is your engine running properly. Your Yanmar 2GM should be able to rev to at least 3600 RPM's when it is out of gear, if it do not then you have a problem with your engine. Next you should be able to rev it to 3600 when it is in gear. You do NOT want to run your engine at this RPM for prolonged period of time but you must be able to get it there for brief periods of time. If it will rev to 3600+ out of gear your engine is probably running correctly. If you cannot get it to 3600 when the engine is in gear then you are over propped. If it is under propped then you will be turning your engine very fast and not going anywhere. If you are not sure about any of these items you might have a Yanmar specialist look at your set up for you. Next opinion please!
Jane: Speed and RPM's have nothing to do with each other on different boats. This would be like a semi and a Porsche. They are both doing 80mph but the semi is doing 1500 RPM's and the Porsche is doing 3500 RPMs. What type of engine does your friends boat have? If it is the same engine, what type of prop do they have (2 blade, 3 blade, folding, feathering etc). Then there are transmission ratios. What about the condition of your bottom (clean or dirty). All of these things come into play. The next thing is your engine running properly. Your Yanmar 2GM should be able to rev to at least 3600 RPM's when it is out of gear, if it do not then you have a problem with your engine. Next you should be able to rev it to 3600 when it is in gear. You do NOT want to run your engine at this RPM for prolonged period of time but you must be able to get it there for brief periods of time. If it will rev to 3600+ out of gear your engine is probably running correctly. If you cannot get it to 3600 when the engine is in gear then you are over propped. If it is under propped then you will be turning your engine very fast and not going anywhere. If you are not sure about any of these items you might have a Yanmar specialist look at your set up for you. Next opinion please!
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Andy Falls
3 Blade Monster
Could your friend have a 3 blade monster prop? Our 29.5 had a 3 blade and I changed to a folding 2 blade. I gained a knot under light air sailing, lost a knot in heavy air motoring. Go figure! The Beneteau (along with a much lighter displacement) could have a miss-calibrated tachometer! Maybe she THINKS the YM is ginning at 1800 when its really going 2800! And hey, lets "knot" forget, friends have been known to mess and tease fellow sailors! I assume the draft of the Beneteau is deep fin? sparkling clean bottom? PS Joe-did you ever put on a 155?
Could your friend have a 3 blade monster prop? Our 29.5 had a 3 blade and I changed to a folding 2 blade. I gained a knot under light air sailing, lost a knot in heavy air motoring. Go figure! The Beneteau (along with a much lighter displacement) could have a miss-calibrated tachometer! Maybe she THINKS the YM is ginning at 1800 when its really going 2800! And hey, lets "knot" forget, friends have been known to mess and tease fellow sailors! I assume the draft of the Beneteau is deep fin? sparkling clean bottom? PS Joe-did you ever put on a 155?
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Bob Knott
Yanmar 18HP
Maybe the Yanmar 18HP is underpowered for your boat. I had the same engine in my old 280 which weighed 6,800 lbs, and it motored at 6 knots all day long at 2700rpm's. Now your boat is 2 feet er... 1 1/2 feet longer and 2,500 lbs heavier so I would think it would be slower. Smooth sailing Bob Knott
Maybe the Yanmar 18HP is underpowered for your boat. I had the same engine in my old 280 which weighed 6,800 lbs, and it motored at 6 knots all day long at 2700rpm's. Now your boat is 2 feet er... 1 1/2 feet longer and 2,500 lbs heavier so I would think it would be slower. Smooth sailing Bob Knott
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Stephen Ostrander
Yanni
I had a 28.5 with the 2GM20 and standard 2 blade prop and it would cruise all day long at 6 knots @ 2800 rpm.
I had a 28.5 with the 2GM20 and standard 2 blade prop and it would cruise all day long at 6 knots @ 2800 rpm.
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Jay Hill
4.7 to 5.1K?
Sorry to impose on the 29.5 forum, but I have a 31 with the same 2GM20 18 hp engine. With a fresh bottom job and the factory 15X12, two-blade prop I get 5.4k at only 2200 rpm with 9900# displacement and tons of cruising gear and full provisions. I can move up to 6K at 3000 but it starts sucking the fuel then. The boat is 4' shoal draft which helps. I am curious also to hear of the sea conditions. Are you talking about smooth water through a harbor or swells in the ocean? I lose roughly 2/10th knot per foot of swell. Hope you get better speed somehow. Is your log transducer clean?
Sorry to impose on the 29.5 forum, but I have a 31 with the same 2GM20 18 hp engine. With a fresh bottom job and the factory 15X12, two-blade prop I get 5.4k at only 2200 rpm with 9900# displacement and tons of cruising gear and full provisions. I can move up to 6K at 3000 but it starts sucking the fuel then. The boat is 4' shoal draft which helps. I am curious also to hear of the sea conditions. Are you talking about smooth water through a harbor or swells in the ocean? I lose roughly 2/10th knot per foot of swell. Hope you get better speed somehow. Is your log transducer clean?
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Alex
It varries with prop size..
With my 29.5 , same engine , with 2 blade folding ("Flex-a-fold"), I do about 5.5 kts at 2700 rpm , my 29.5 being medium loaded but clean hull and prop .(Still cannot get past 3400 in gear.), which is -to my opinion- adequent . But in cruising mode,with hull and prop not so clean and about 1500 above 'formal' displacement , with occasional head sea running,I would prefer an engine one size bigger.. Somehow almost all big manufacturers, except dedicated cruiser or other expensive brands , won't give this even as an option ( except at bigger boats ) With previous fix 3 blade 15*10 (wide blade) 'cruising'-factory delivered optional prop- I did less..on all rpm's.. However I lend it to a friend owning an older European designed fin keel 30 footer-with 1500 pounds less displacement-, and he is doing 6 knots at 2700.. After a lot of 'checking around' and the proffesional advice I got , I would think a 3 blade, medium wide blade, 15*9 would be best suited for the 29.5( taking in account it's higher actual displacement and the high 2800-3000 rpm this engine should be run at , or the "Flex-O-Fold" 2 blade ,15*12,( they have now 3 blade folding ones,it worth cheking this option too) without getting into the much more expensive range of variable pitch etc. propellers. Alex.
With my 29.5 , same engine , with 2 blade folding ("Flex-a-fold"), I do about 5.5 kts at 2700 rpm , my 29.5 being medium loaded but clean hull and prop .(Still cannot get past 3400 in gear.), which is -to my opinion- adequent . But in cruising mode,with hull and prop not so clean and about 1500 above 'formal' displacement , with occasional head sea running,I would prefer an engine one size bigger.. Somehow almost all big manufacturers, except dedicated cruiser or other expensive brands , won't give this even as an option ( except at bigger boats ) With previous fix 3 blade 15*10 (wide blade) 'cruising'-factory delivered optional prop- I did less..on all rpm's.. However I lend it to a friend owning an older European designed fin keel 30 footer-with 1500 pounds less displacement-, and he is doing 6 knots at 2700.. After a lot of 'checking around' and the proffesional advice I got , I would think a 3 blade, medium wide blade, 15*9 would be best suited for the 29.5( taking in account it's higher actual displacement and the high 2800-3000 rpm this engine should be run at , or the "Flex-O-Fold" 2 blade ,15*12,( they have now 3 blade folding ones,it worth cheking this option too) without getting into the much more expensive range of variable pitch etc. propellers. Alex.
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Stephen Ostrander
Yanni part II
I now own a 1988 33.5 with the 2GM20. On smooth water it will push her at hull speed if I red line it. Wind and chop will definetly knock her back. 20 knot breeze with 3' waves will knock her back to 4.5 kn.
I now own a 1988 33.5 with the 2GM20. On smooth water it will push her at hull speed if I red line it. Wind and chop will definetly knock her back. 20 knot breeze with 3' waves will knock her back to 4.5 kn.
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Tim
Answers
Some principles: -The prop pitch sets the maximum RPM of the motor. If the pitch is too high, you will not reach max RPMs, blow lack smoke out the exhaust(does your transom get sooty? Its not supposed to), go slow and overheat. -The motor should be cruised at 80+% of the maximum RPM rating (stamped on the front of the motor) or overtime you are damaging the motor by coking it up. Could all you folks cruising at 2000 RPM please stop? I've always bought used boats and you're not doing people like me a favor. -A 30 foot conventional sailboat is gonna go about 6 1/2 and thats it, no more. The waterline length of the hull sets the upper limit. I can do this in my old H30 with a 13 hp motor. 18hp is more than enough for your boat. -A very little growth on the prop or a small ding will greatly reduce the efficiency of the prop. -The displacement difference doesn't matter much; bottom condition and the correct prop matter a lot. 3 blades will help some, particularly into wind and swells, but the correct pitch will make a bigger difference. Still have doubts? Call Yanmar, Torrenson or Mack Boring and ask for the parts desk.
Some principles: -The prop pitch sets the maximum RPM of the motor. If the pitch is too high, you will not reach max RPMs, blow lack smoke out the exhaust(does your transom get sooty? Its not supposed to), go slow and overheat. -The motor should be cruised at 80+% of the maximum RPM rating (stamped on the front of the motor) or overtime you are damaging the motor by coking it up. Could all you folks cruising at 2000 RPM please stop? I've always bought used boats and you're not doing people like me a favor. -A 30 foot conventional sailboat is gonna go about 6 1/2 and thats it, no more. The waterline length of the hull sets the upper limit. I can do this in my old H30 with a 13 hp motor. 18hp is more than enough for your boat. -A very little growth on the prop or a small ding will greatly reduce the efficiency of the prop. -The displacement difference doesn't matter much; bottom condition and the correct prop matter a lot. 3 blades will help some, particularly into wind and swells, but the correct pitch will make a bigger difference. Still have doubts? Call Yanmar, Torrenson or Mack Boring and ask for the parts desk.
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