0.11 litres per nautical mile

[redsky49]

If you have the space, I have always admired these engines, and they seem to do a lot of repowers:



This is a three cylinder Beta, 20 HP. Pic courtesy of Beta Marine US

[GrahamHO]

Originally Posted by Lars_L

One of the problems with my motor is to keep up the oil pressure. I let the motor go at a speed where the oil pressure lamp stops flickering. When the motor gets warm, it is quite high speed. At the moment I have solved that problem with a thicker oil. I know that the problem is the bearing of the oil pump. And the bearing is direct in the motor block. But I think I have found an area in the Sognefjord in Norway where I can dump the motor. It is 1200 m deep.

Yanmar YSB 12 is a four-stroke one-cylinder motor on 510 cc. I can both hear and feel every explosion. With a two cylinders motor I hope that it should go smoother. There are even three cylinders motors with 20 hp. Do they go much smoother? Do they take more diesel than a two cylinders motor with 20 hp?

My Yanmar 2GM 20 sail drive is way smoother than the 10 HP single cylinder engine I replaced in 1998. I do though wish I had replaced it with the then 3 cylinder 27 HP Yanmar. The extra cost of the 3 cylinder engine is minor compared with all the other costs involved changing the engine.

Haul out costs the same, labour and / or personal effort is the same, the propellor costs the same. A new exhaust system costs the same etc. I am though happy with my twin.

I think but am not sure that the new 3 cylinder 20 HP Yanmar may be common rail and likely very efficient. I'm not sure whether I like them having to rely on electricity, and possibly needing more specialist servicing. Generally though newer design motors in any application are much more reliable.

Dumping your old motor in Sognefjord could feature in a possible new Jo Nesbo novel. Got any "friends" you don't like?

[olaf hart]

Nearly thirty years ago (!!) I replaced an old Y series Yanmar with a new 2gm20, it was a very easy conversion, even used the same engine frames. The newer 3 cylinder Yanmars are bigger again, and would be a real squeeze I think.

There is a smallish three cylinder Kubota engine, I think it is in the Beta range, that is smaller than the Yanmar. I have also seen a small Volvo 20 hp three cylinder that might fit.

The 2 gm20 is not a bad engine, but more vibration and noise than a newer 3 cylinder.

You should replace the tank too if it is only 20 l, 60 l is a minimum for a 30 footer.

[GrahamHO]

Originally Posted by a64pilot

Smoothest engine design is an inline six cyl, but an inline three can be surprisingly smooth.
In line fours although very prolific in number is not a smooth running design.
Often packaging drives engine design, a V6 is a terrible design in my opinion, but there is a huge number of them in automobiles.
I'm not including boxers and radials etc as I haven't seen them in boat motors, so not much point in considering them.
But if I had the option, I'd definitely pick a twin over a single, and inline three over a parallel twin, based on smooth running

Now if your using say 6 hp to cruise, using 6 hp from a 20 hp motor will burn slightly more fuel than 6 hp out of a 12 hp motor, but probably not that much.
More cylinders due to frictional losses will consume more fuel, maybe so little more that you would be hard pressed to measure it, but a three cylinder turning slower and making less noise and vibration would probably be a lot more pleasant.
If you can afford an inline three, I think you would be way more happy, even if you had to carry slightly more fuel.


Sent from my iPad using Cruisers Sailing Forum

Quite correct. An inline 6 with its 1,5,3,6,2,4 firing order is in almost perfect dynamic balance. A 4 with it 1,3,4,2 firing order has a couple of strokes at one end followed by a couple of strokes at the other end. ( 2,1 then 3,4 ) A twin must be 1,2 firing order so is trying to oscillate or rock around end to end.

As you say correctly V6 s in cars are for packaging reasons. Nowadays all aspects of a car design work in conjunction with the package including the integral gearbox / FWD, rather than previously a straight 6 cylinder engine might be designed in isolation and dropped into a car.

They all work fine in practice. My previous car was a straight 6 Ford, my present car a V6 Nissan which is turbine like smooth; even more so than the Ford. I also have a 4 cylinder Toyota which runs like the energiser man. My boat motor is a 2 cylinder Yanmar.

Im well aware though that real men drive US made 6 litre V8 s.

[Wotname]

Originally Posted by redsky49

If you have the space, I have always admired these engines, and they seem to do a lot of repowers:



This is a three cylinder Beta, 20 HP. Pic courtesy of Beta Marine US

While I have been a fan of Yanmar, I really like these Beta engines. They keep on making small improvements that make the engines easier to work on, easier to maintain etc.

Yanmar seem to say "this is our design, if you don't like it, get over it; we ain't changing it".

I would chose Beta over Yanmar these days!

YMMV.

The biggest issue with re-powering in a small boat (say 30') is (IMO), finding enough space for the new engine

[CSY Man]

. It is not only more efficient in terms of fuel consumption, but you can also slow the engine down while still keeping a reasonable load on it, which makes it much quieter.

If the prop slows the engine down, the it becomes "over propped" and that is a no-no...?

An inboard diesel should get 100 % RPM when running free and 90% tied to the dock using full throttle in both cases. Will the Autoprop allow that?

[GrahamHO]

Originally Posted by CSY Man

If the prop slows the engine down, the it becomes "over propped" and that is a no-no...?

An inboard diesel should get 100 % RPM when running free and 90% tied to the dock using full throttle in both cases. Will the Autoprop allow that?

Isn't the advantage of the Autoprop that it goes into a coarser pitch for motor sailing? That's got to be a good thing. Then there is even less load than "running free". I don't have an Autoprop as I either sail or motor.

I do have a Kiwi Feathering Prop with an adjustable preset pitch which makes it easy to fine tune the maximum revs. Personally I like to only be able to reach about 90% maximum revs running "free". The horsepower curve usually starts dropping away a little at maximum revs and around 90% is close enough to maximum power.

In my opinion there is no "should get". Who says what you should or shouldn't get?

Years ago when I was an aircraft engineering apprentice, the older hands would tell a new apprentice to go to the Prop Bay and get a bucket of fine pitch.

[Lars_L]

It is always a problem to measure how big is the engine room. When the old motor is out its boot easier. I have already had a look at the Beta Marine. I think that 20 hp I enough for my boot and I feel that when I shall bye, then its now or never to get at three cylinders motor. Here in Sweden the three cylinders Beta 20 cost 7% more than the two cylinders Beta 16. I have a straight shaft and therefore the motor needs to tip a little to get it in line with the shaft. Beta has a gearbox where the shaft is angled 7° (price +5%). Does that save much space?

I cannot test if I have the right size of prop. The gearbox is broken and I do not have any instrument to measure the RPM. But even if Autoprop automatically adjusts the pitch, it is made with a pitch that matches the motor power. When you bye the prop you say what engine and what gearbox you have.

About the nature in Norway. It’s always hard to tell what’s the good, but at least it’s not the temperature. I have some pitchers on my blog S/Y Fridas dagbok 2015 1: Dagbok från Januari 2015 och framåt that maybe can give you a feeling of the nature. The blog is in Swedish. I will also say that it’s a large area with long distances.

[a64pilot]

Originally Posted by CSY Man

If the prop slows the engine down, the it becomes "over propped" and that is a no-no...?

An inboard diesel should get 100 % RPM when running free and 90% tied to the dock using full throttle in both cases. Will the Autoprop allow that?

Autoprop is weird, for example tied to the dock, I get full RPM, 3600 or so just like I was in neutral, but as I gain speed, RPM comes down as the prop adds pitch, in my case to full throttle being about 3300 RPM? Not sure exactly as I just don't run full throttle, but it isn't quite full governed RPM, but that can be adjusted by Autoprop, means they use I have assumed to be changing blades, but I don't know, maybe the change the airfoil slightly?
I'm happy with it, so I leave it alone, but the Autoprop at close to zero hull speed seems to provide little thrust, it feels almost like a slipping transmission does in a car, but in my case there is zero prop walk, which I miss as with a lot of prop walk I could turn the boat in pretty much it's own length to Starboard, but not now.
If you have ever driven anything with a constantly variable transmission, that is what an Autoprop acts like.
It shines in motor sailing, where as before I had to turn the engine at 1500 to 1800 RPM to get any thrust out of it at 6 kts of speed, now with the Autoprop I can run the engine at 1,000 RPM and motorsail at 6 kts, in 6 kts of wind.

[GrahamHO]

Originally Posted by Lars_L

It is always a problem to measure how big is the engine room. When the old motor is out its boot easier. I have already had a look at the Beta Marine. I think that 20 hp I enough for my boot and I feel that when I shall bye, then its now or never to get at three cylinders motor. Here in Sweden the three cylinders Beta 20 cost 7% more than the two cylinders Beta 16. I have a straight shaft and therefore the motor needs to tip a little to get it in line with the shaft. Beta has a gearbox where the shaft is angled 7° (price +5%). Does that save much space?

I cannot test if I have the right size of prop. The gearbox is broken and I do not have any instrument to measure the RPM. But even if Autoprop automatically adjusts the pitch, it is made with a pitch that matches the motor power. When you bye the prop you say what engine and what gearbox you have.

About the nature in Norway. It’s always hard to tell what’s the good, but at least it’s not the temperature. I have some pitchers on my blog S/Y Fridas dagbok 2015 1: Dagbok från Januari 2015 och framåt that maybe can give you a feeling of the nature. The blog is in Swedish. I will also say that it’s a large area with long distances.

I installed my engine just forward of the bridge deck. Then I made a removable engine cover box. That provides enough engine space for any size motor. It makes the yachts weight distribution better especially going to a heavier motor.
Sailing or at anchor it makes a nice place for someone to sit. It's other important advantage is there is all round accessibility to all parts of the motor. There are a couple of steps on the front of the box into the cabin.

However if you do that with your existing prop shaft it will make the engine too high keeping the alignment straight. You could investigate flexible couplings that allow the engine to be on a different angle to the shaft. As they likely take up some extra space they will also push your engine forward. If I were installing another shaft drive motor I would certainly want to use one of those couplings. (presently I have a sail drive)

You may have to make new engine beds. That's not a hard thing to do and it might avoid the possible complications of trying to fit a new motor on the old beds. If you do, make sure the probably larger weight of the new motor is spread over the hull.

The first thing to do is to remove the old motor. I would do that before I bought a new motor. Then you can join a few bits of say 25 mm X 100 mm timber together to the same dimensions as new engine mounts and the base of the motor. This is before you buy the motor so you might want to measure more than one make. I'm sure an engine dealer will allow you to measure their motors.

Then out of cardboard you can make a pattern of the size of the side and front / rear of a possible new motor and see how it fits your space. If you decide to use a flexible coupling that allows an angle in the alignment, allow for the extra length that might take up.

Its very important to also find out what diameter propellor your new motor should use. A more powerful motor will probably require a larger diameter propellor. From memory the propellor should clear the hull by 10% of the propellor diameter. You can look that figure up to check. You could make it a little closer and just lose some efficiency which may not be noticeable.
Don't push the shaft further back on the underwater strut as the shaft won't properly support the propellor. A very small amount should be OK though.

If you can't fit a larger diameter propellor you can compensate by having a coarser pitch on the propellor. (that is the angle of the blades being greater)
An approximate rule is if you reduce the propellor diameter by 1" you compensate by increasing the pitch by 1". That's theoretically not as efficient though you may not notice the difference.

You might need to do all those things just a little. Maybe; push the shaft back 20 cm, reduce the ideal hull / prop clearance a little, and have a coarser pitch propellor than ideal. Definitely get advice from the propellor supplier.
I don't think that doing all those things just a little will have much effect on fuel efficiency.

I would make those small compromises myself and fit a 3 cylinder motor that fits both your budget and your boat. Beta and Yanmar each have a good following here in NZ. An engine installer tells me they are both good with the Beta cheaper and a little noisier than the Yanmar. The cast iron construction of the Yanmar helps absorb sound.

I know some people will jump up and down and say not to have a smaller coarser pitch prop but life is full of compromises. However I can't see your boat but those are a few things to consider.

To decide on engine power I would first look at what is the "biggest" propellor you can fit and if necessary make the small compromises I suggest. Then see what is the maximum power that propellor can work with.

[GrahamHO]

Just one more idea: if you decide on a more powerful motor than your propellor can use, you could have the engine governor adjusted so it runs at a maximum of perhaps 3000 rpm rather than perhaps 3500, for example, thus reducing maximum horse power a little. It will still have the same maximum torque as the max torque is developed at lower than maximum RPM. This will be an advantage pushing into adverse conditions.

That's what engine manufactures do when they supply the same motor for either recreational use or commercial use. They set the governor to lower maximum RPM for the commercial version that is being used every day. The commercial operator wants maximum reliability and the recreational user wants maximum performance. It also has to do with the warranty for a commercially used engine.

Talk with both your propellor supplier and your engine supplier about that.

I hope all those thoughts help you.

[GrahamHO]

Originally Posted by GrahamHO

I installed my engine just forward of the bridge deck. Then I made a removable engine cover box. That provides enough engine space for any size motor. It makes the yachts weight distribution better especially going to a heavier motor.
Sailing or at anchor it makes a nice place for someone to sit. It's other important advantage is there is all round accessibility to all parts of the motor. There are a couple of steps on the front of the box into the cabin.

However if you do that with your existing prop shaft it will make the engine too high keeping the alignment straight. You could investigate flexible couplings that allow the engine to be on a different angle to the shaft. As they likely take up some extra space they will also push your engine forward. If I were installing another shaft drive motor I would certainly want to use one of those couplings. (presently I have a sail drive)

You may have to make new engine beds. That's not a hard thing to do and it might avoid the possible complications of trying to fit a new motor on the old beds. If you do, make sure the probably larger weight of the new motor is spread over the hull.

The first thing to do is to remove the old motor. I would do that before I bought a new motor. Then you can join a few bits of say 25 mm X 100 mm timber together to the same dimensions as new engine mounts and the base of the motor. This is before you buy the motor so you might want to measure more than one make. I'm sure an engine dealer will allow you to measure their motors.

Then out of cardboard you can make a pattern of the size of the side and front / rear of a possible new motor and see how it fits your space. If you decide to use a flexible coupling that allows an angle in the alignment, allow for the extra length that might take up.

Its very important to also find out what diameter propellor your new motor should use. A more powerful motor will probably require a larger diameter propellor. From memory the propellor should clear the hull by 10% of the propellor diameter. You can look that figure up to check. You could make it a little closer and just lose some efficiency which may not be noticeable.
Don't push the shaft further back on the underwater strut as the shaft won't properly support the propellor. A very small amount should be OK though.

If you can't fit a larger diameter propellor you can compensate by having a coarser pitch on the propellor. (that is the angle of the blades being greater)
An approximate rule is if you reduce the propellor diameter by 1" you compensate by increasing the pitch by 1". That's theoretically not as efficient though you may not notice the difference.

You might need to do all those things just a little. Maybe; push the shaft back 20 cm, reduce the ideal hull / prop clearance a little, and have a coarser pitch propellor than ideal. Definitely get advice from the propellor supplier.
I don't think that doing all those things just a little will have much effect on fuel efficiency.

I would make those small compromises myself and fit a 3 cylinder motor that fits both your budget and your boat. Beta and Yanmar each have a good following here in NZ. An engine installer tells me they are both good with the Beta cheaper and a little noisier than the Yanmar. The cast iron construction of the Yanmar helps absorb sound.

I know some people will jump up and down and say not to have a smaller coarser pitch prop but life is full of compromises. However I can't see your boat but those are a few things to consider.

To decide on engine power I would first look at what is the "biggest" propellor you can fit and if necessary make the small compromises I suggest. Then see what is the maximum power that propellor can work with.

CORRECTION. I MEANT PUSH YOUR SHAFT BACK PERHAPS 20mm NOT 20cm!