- Status
Beta, Vetus & Bukh
Ed S: I believe that you thought that the Bukh was better than these other two engines because it IS a marine diesel and not a Marinized version of a land based engine.
Ed S: I believe that you thought that the Bukh was better than these other two engines because it IS a marine diesel and not a Marinized version of a land based engine.
Replacement
I have been investigating replacements for my 2QM 20 only because it is old, no problems yet. Trying to decide between Beta, Vetus, and Yanmar. Bukh is over built for my needs. The 36 Bukh weighs more than twice as much as the 3GM Yanmar. Leaning again towards the Vetus.
I have been investigating replacements for my 2QM 20 only because it is old, no problems yet. Trying to decide between Beta, Vetus, and Yanmar. Bukh is over built for my needs. The 36 Bukh weighs more than twice as much as the 3GM Yanmar. Leaning again towards the Vetus.
Why replace?
Those things will last forever unless you abuse them or don't maintain them. I go by the old saying "if it ain't broke, don't fix it." I talked to the Yanmar people a few years back before we went cruising. I wanted them to check out my 3QM30 to make sure it was fine. He asked if it was hard starting. "No". He asked if it burned any oil. "No". He said that unless we'd really overheated it, or it had obvious problems, he wouldn't even recommend looking into it. He said they'd torn down many with lots of hours, many still hadn't worn the cross hatch off the cylinders. They're pretty tough, and even if you have a problem, you can fix most anything cheaper than buying new. One problem you'll have if you replace the motor is the transmission. Yanmar doesn't use a standard interface and you'll have to do some machine work, or if the new motor comes with a transmission, you'll have a coupler to buy, maybe a propshaft, and probably a prop. I had to replace my Yanmar transmission with a Hurth. Cost $1000 for the machine work to make it fit, plus modifying all the mounts. What I would strongly recommend you do is change the transmission oil. Few people do, and it's not much work or expense. It cost me about $3000 for not doing it, plus being stuck for a week while I replaced mine.
Those things will last forever unless you abuse them or don't maintain them. I go by the old saying "if it ain't broke, don't fix it." I talked to the Yanmar people a few years back before we went cruising. I wanted them to check out my 3QM30 to make sure it was fine. He asked if it was hard starting. "No". He asked if it burned any oil. "No". He said that unless we'd really overheated it, or it had obvious problems, he wouldn't even recommend looking into it. He said they'd torn down many with lots of hours, many still hadn't worn the cross hatch off the cylinders. They're pretty tough, and even if you have a problem, you can fix most anything cheaper than buying new. One problem you'll have if you replace the motor is the transmission. Yanmar doesn't use a standard interface and you'll have to do some machine work, or if the new motor comes with a transmission, you'll have a coupler to buy, maybe a propshaft, and probably a prop. I had to replace my Yanmar transmission with a Hurth. Cost $1000 for the machine work to make it fit, plus modifying all the mounts. What I would strongly recommend you do is change the transmission oil. Few people do, and it's not much work or expense. It cost me about $3000 for not doing it, plus being stuck for a week while I replaced mine.
To Much Power Problem
One major problem I see with too much engine power is running the engine at reduced power. The Yanmar is susceptible to carboning up if not run at 80 percent power or better according to our local distributor. Hence, if one runs at low rpms it's going to carbon up more. A second problem is the mixing elbow that likes a clean and fast flowing exhaust. Running the Yanmar at a lower RPM is going to cause this "knothole" to clog up sooner. At the above to the prop diameter needed for a larger engine and the clearance to the hull and it's clear that going to a larger horsepower will have definite drawbacks. Larger engines weigh more which ultimately slows you down, a definite disadvantage. Squeezing a larger engine into a small engine room makes it harder to work on. Going to a larger or smaller horsepower engine from optimum I think is a function of a persons boating needs. Even though my cruising grounds have tidal currents that exceed boat speed with any kind of engine my style would tend to err on the side of smaller than larger. My "style" is to wait it out and go with the flow or try tricks like catching the back eddies. On our trip to Alaska, 2222 NM we averaged over 7 knots speed-over-ground, dock to dock and a third of this was under sail, yet hull speed loaded like we were was about 6 knots. In all my years in boating, starting with a 3hp on a daysailor, I can't ever remember actually needing or even wanting a larger engine. Selection of the new power plant is a personal decision after weighing all the facts against ones goals.
One major problem I see with too much engine power is running the engine at reduced power. The Yanmar is susceptible to carboning up if not run at 80 percent power or better according to our local distributor. Hence, if one runs at low rpms it's going to carbon up more. A second problem is the mixing elbow that likes a clean and fast flowing exhaust. Running the Yanmar at a lower RPM is going to cause this "knothole" to clog up sooner. At the above to the prop diameter needed for a larger engine and the clearance to the hull and it's clear that going to a larger horsepower will have definite drawbacks. Larger engines weigh more which ultimately slows you down, a definite disadvantage. Squeezing a larger engine into a small engine room makes it harder to work on. Going to a larger or smaller horsepower engine from optimum I think is a function of a persons boating needs. Even though my cruising grounds have tidal currents that exceed boat speed with any kind of engine my style would tend to err on the side of smaller than larger. My "style" is to wait it out and go with the flow or try tricks like catching the back eddies. On our trip to Alaska, 2222 NM we averaged over 7 knots speed-over-ground, dock to dock and a third of this was under sail, yet hull speed loaded like we were was about 6 knots. In all my years in boating, starting with a 3hp on a daysailor, I can't ever remember actually needing or even wanting a larger engine. Selection of the new power plant is a personal decision after weighing all the facts against ones goals.
Question on that
I'm no engineer, and I've been trying to figure out all the talk about props for a while. I want to understand this. Re being overpowered = under-running the engine......wouldn't you put the correct prop on to achieve hull speed at 85% RPM on a calm day? So how would end up running the engine at too low RPMs? My understanding was the RPMs are the RPMs, the HP is going to be the ability of the engine to turn those RPMs with added resistance (wind, chop etc ). For example, both engines at 3300 rpm..... you couldn't put a different prop on a 9 HP that would allow it to make hull speed ( or lets say 6 knots ) against a 15 knot headwind on a 10,000 lb sailboat. right? but that would (might) work on a 20HP, because for each revolution, there's more HP to "muscle" the boat ahead. Is the above correct?
I'm no engineer, and I've been trying to figure out all the talk about props for a while. I want to understand this. Re being overpowered = under-running the engine......wouldn't you put the correct prop on to achieve hull speed at 85% RPM on a calm day? So how would end up running the engine at too low RPMs? My understanding was the RPMs are the RPMs, the HP is going to be the ability of the engine to turn those RPMs with added resistance (wind, chop etc ). For example, both engines at 3300 rpm..... you couldn't put a different prop on a 9 HP that would allow it to make hull speed ( or lets say 6 knots ) against a 15 knot headwind on a 10,000 lb sailboat. right? but that would (might) work on a 20HP, because for each revolution, there's more HP to "muscle" the boat ahead. Is the above correct?
engine design.
John: I do not know about the other engines but the Yanmar is designed to run at 70-80% of the max RPM. If you run them higher for extended periods of time you are putting excess wear on them and they will overheat. If you run them at lower RPM for extended periods of time you are going to coke up the engine and put excessive wear on it, which is going to lead to repairs. These are diesel engines and they are different from gasoline. Check out www.yanmarhelp.com about running a Yanmar. Diesels really do best at a fixed RPM range and they can run forever if you keep the oil changed and run them as designed. If you have a 32 hp engine in the boat you are going to have a problem getting the correct prop and still running this at the correct rpm range without burning excess fuel. If you have a 12hp engine on this boat you have to run it at higher RPMs just to keep it at the designed hull speed and when you have head winds or tidal influences you will not have any reserve to push you through it (that is why you want to switch). If you have the adequate tip clearance you could probably accomodate a large engine easier. The largest prop that your boat will accept is about 13". There are many dynamics in prop design that are way beyond my comprehension. This is why you should have someone in this business recommend the correct engine/transmission ratio/prop combination.
John: I do not know about the other engines but the Yanmar is designed to run at 70-80% of the max RPM. If you run them higher for extended periods of time you are putting excess wear on them and they will overheat. If you run them at lower RPM for extended periods of time you are going to coke up the engine and put excessive wear on it, which is going to lead to repairs. These are diesel engines and they are different from gasoline. Check out www.yanmarhelp.com about running a Yanmar. Diesels really do best at a fixed RPM range and they can run forever if you keep the oil changed and run them as designed. If you have a 32 hp engine in the boat you are going to have a problem getting the correct prop and still running this at the correct rpm range without burning excess fuel. If you have a 12hp engine on this boat you have to run it at higher RPMs just to keep it at the designed hull speed and when you have head winds or tidal influences you will not have any reserve to push you through it (that is why you want to switch). If you have the adequate tip clearance you could probably accomodate a large engine easier. The largest prop that your boat will accept is about 13". There are many dynamics in prop design that are way beyond my comprehension. This is why you should have someone in this business recommend the correct engine/transmission ratio/prop combination.
So..........
In order to get the 70-80% on a 30HP engine, the prop diameter should be larger than 13" which won't fit OR a 13" diameter, with a pitch that I won't be able to find a prop for ( like a 13 X 2 ), which will lead to burning excess fuel for the given knots? OK, I think that makes sense. Thanks. I have consulted with a number of different shops in my area and at the boat show, and all said I should have 1 hp for every ft in length. Actually ( interesting ) Betamarine was the only one that said I should use the 20HP, that their 27 was too much. Thanks all, back to the drawing board.
In order to get the 70-80% on a 30HP engine, the prop diameter should be larger than 13" which won't fit OR a 13" diameter, with a pitch that I won't be able to find a prop for ( like a 13 X 2 ), which will lead to burning excess fuel for the given knots? OK, I think that makes sense. Thanks. I have consulted with a number of different shops in my area and at the boat show, and all said I should have 1 hp for every ft in length. Actually ( interesting ) Betamarine was the only one that said I should use the 20HP, that their 27 was too much. Thanks all, back to the drawing board.
HP
Don't be too concerned about the horsepower, a good prop shop will pitch your prop to get the desired rpms at hull speed. Also, pitch adjustment can compensate for diameter limitations. BTW, Bukhs are designed to run at 100% because they are rated at their continous horsepower.
Don't be too concerned about the horsepower, a good prop shop will pitch your prop to get the desired rpms at hull speed. Also, pitch adjustment can compensate for diameter limitations. BTW, Bukhs are designed to run at 100% because they are rated at their continous horsepower.
Same Boat
I'll add my input. I'm in the process of repowering a 76h30. I found a new Vetus m310 that someone had setting around since 1987. It's rated at 22hp at 3600 rpm. It's a 3 cyclinder engine. I should have it in by Christmas. Mich. wheel suggested if I stay with a two blade prop to go with a 13x12 which I plan to do. Can't afford a feathering prop. My old prop was a 13x11 left hand rotation and my new engine is now rh rotation. I'll let you know how it turns out.
I'll add my input. I'm in the process of repowering a 76h30. I found a new Vetus m310 that someone had setting around since 1987. It's rated at 22hp at 3600 rpm. It's a 3 cyclinder engine. I should have it in by Christmas. Mich. wheel suggested if I stay with a two blade prop to go with a 13x12 which I plan to do. Can't afford a feathering prop. My old prop was a 13x11 left hand rotation and my new engine is now rh rotation. I'll let you know how it turns out.
- Status