Uricanejack
Well-Known Member
Forget choosing diesels.
Get a chainsaw and make a well
Get a chainsaw and make a well
Yanmar: why does anyone buy the 2YM15 instead of the 3YM20?
- Thread starter Greenheart
- Start date
JumbleDuck
Well-Known Member
But you have also been saying that the propeller choice is determined solely by the boat and that the engine is chosen to match the propeller.
Tranona
Well-Known Member
No, afraid you misunderstand. The starting point is calculating what size of propeller you can use, but there are choices, depending on how much space you have and whether you want a 3 or 2 blade prop. Then you choose the engine to drive it. You can't always have the perfect prop, nor exactly the right amount of power, nor the reduction ratio to get the shaft speed you would like so it is a question of choosing the best compromise. So, if you have a bigger engine you need a bigger prop, otherwise the engine will not be under load.
When your boat was new the choice was either a 9hp or an 18hp - although the 18 would not physically fit so not really a choice. Ignoring the physical limitations, one is twice as powerful as the other, so it is clear that neither is ideal. Now you could replace your engine with a Beta 14 which would be closer to ideal, but you may well find that there is not enough room to swing the larger prop that would be preferred.
FWB
N/A
Can I jump on the roundabout for a mo?
The prop has to match the engine.
The engine has to have enough grunt to drive the boat.
The engine has to fit in the boat.
The prop has to fit in the aperture/under hull etc.
So go round and round until it fits
The prop has to match the engine.
The engine has to have enough grunt to drive the boat.
The engine has to fit in the boat.
The prop has to fit in the aperture/under hull etc.
So go round and round until it fits
JumbleDuck
Well-Known Member
I think we may be violently agreeing that engine, prop and boat form a system, no part of which can be independently specified and each part of which brings its own constraints to the optimum solution, no?
My boat was only supplied with 9hp, which I find quite adequate. However, if it ever dies on me I shall replace it with something a bit bigger, mainly to get the smoothness of two cylinders. There seems to be no consensus in the owner's club about which to go for ... anything from 12hp to 20hp, apparently.
JumbleDuck
Well-Known Member
Can I jump on the roundabout for a mo?
The prop has to match the engine.
The engine has to have enough grunt to drive the boat.
The engine has to fit in the boat.
The prop has to fit in the aperture/under hull etc.
So go round and round until it fits
Yup. Or, if you like, you are trying to get the power-speed curves for boat, engine and prop all to cross in the same place. Since there is no choice of hull and limited choice of engine, that effectively means choosing a prop to suit the engine/boat combination.
Tranona
Well-Known Member
Do the same as I did. Replace the 1GM with a Nanni 14. Almost direct, although 10mm longer and mounts slightly further apart fore and aft and higher so beds need packing upwards. Exhaust on the other side and 40mm instead of 45mm so you need some form of adaptor if using the same water trap etc. Otherwise relatively easy and well worthwhile. You may need to change the prop depending on your current ratio and the new one to absorb the additional power. your maximum speed would increase from the current 5.3 to just over 6 knots and keep your current cruising speed the same at lower rpm, but still using the same amount of fuel. Would cost you around £3k net of the selling price of your Yanmar.
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JumbleDuck
Well-Known Member
Many thanks - that's very useful. The water trap shouldn't be a problem, as it's a Vetus LP40R which has a swappable inlet spigot ... I still have the 40mm one it came with somewhere, I think. You would put the Nanni over the Beta?
ianc1200
Well-Known Member
I replaced the YSB 8 in my Mk1 Crabber with a 2YM15. I asked about putting the three cylinder in and I was told by the installer it was just wasted power & if anything I should have gone smaller. Have to say it seems very well suited for the boat, my one problem was coming out of the Ore entrance against the flood tide, but that was just me being stupid.
BurnitBlue
Well-Known Member
I chose the 3ym20 beause it runs with less vibration. It is said that an odd number of cylinders run smoother than engines with an even number, excepting single cylinder.
Uricanejack
Well-Known Member
Sorry touther way round.
Even no run smoother they ballance.
propellors on the other hand. odd is often smoother.
I have a yanmar 30gm with a 2 blade prop. oh well it seams to work. locker lid in cockpit allways rattels unless you sit on it. or sail.
Telek
New Member
When I bought my 27 feet Halcyon Clipper and replaced its engine I was given the choice between the 2YM15 and the 3YM20. The advice the engineer gave was wise: "depends on where you go: places with strong currents e.g. but you ain't going to pull a water skier with your boat, is it?".
The prices difference was about a 1000 Euro.
On a small boat weight is an issue as well as accessibility to the engine.
I chose the 2YM15 and think I made the right choice.
SPACE & HEAT
The engine space is well filled with this engine and at least there is now some air around the engine to absorb the heat that isn't taken away by the cooling system. The engine does not come with a heat probe. The only indication of overheating is a red light on the dashboard and an audio signal when it is all too late. I know this as on first trial of the engine a belt damaged the cooling hose as it all had been installed too close to the access door that had pushed the hose against the belt resulting in the cooling liquid leaking away. I couldn't place the engine more to the back of the boat but did manage with some bending and a metal shield in place to avoid this "confined spaces disaster" from happening ever after. Space is very much an issue.
TANK - CONSUMPTION & ENDURANCE
The original engine had been something like a 9HP engine. It was fed from a tank that holds about 20 liters - only.
Bigger engine = more fuel consumption and with a small thank that means less endurance unless filled up while at sea. We have to fill up every couple of hours when running the engine at 75 percent. We now got some battery operated hand pump to transfer the diesel as quick and smooth as possible from the jerrycan to the tank. Quite a task and if the engine had been bigger that had been one core more to do all to often.
BACKUP BOOSTER POWER
With all 14HP of the 2YM15 at full throttle we couldn't get into Cardiff marina against the tide in the Bristol Channel. The solution was to lower the 4HP outboard that we carry on a dedicated bracket. The extra 4HP pushed us slowly up to Cardiff barrage and into Cardiff Bay.
Our aim has always been to have at any time at least 2 power sources available at all times: wind, onboard engine and outboard are our options. It's the relative small outboard, used regularly on the dinghy, that saved us that night. Installing the larger 3YM20 just for these cases wouldn't weigh up to the disadvantages of overpowering the boat; especially not as the outboard can provide extra punch if needed.
NO NEED TO OVERPOWER
With the 2YM15 on full throttle and in spite of a heavy anchor, 50 meters of chain, a dinghy and the about 100 liters of drinking water tank upfront the bow goes up and the cockpit gets flooded up to the ankles with water flowing in from the holes that are supposed to drain the place. The 3YM20 in our case would have been overkill; an expensive error that could not have been corrected.
The prices difference was about a 1000 Euro.
On a small boat weight is an issue as well as accessibility to the engine.
I chose the 2YM15 and think I made the right choice.
SPACE & HEAT
The engine space is well filled with this engine and at least there is now some air around the engine to absorb the heat that isn't taken away by the cooling system. The engine does not come with a heat probe. The only indication of overheating is a red light on the dashboard and an audio signal when it is all too late. I know this as on first trial of the engine a belt damaged the cooling hose as it all had been installed too close to the access door that had pushed the hose against the belt resulting in the cooling liquid leaking away. I couldn't place the engine more to the back of the boat but did manage with some bending and a metal shield in place to avoid this "confined spaces disaster" from happening ever after. Space is very much an issue.
TANK - CONSUMPTION & ENDURANCE
The original engine had been something like a 9HP engine. It was fed from a tank that holds about 20 liters - only.
Bigger engine = more fuel consumption and with a small thank that means less endurance unless filled up while at sea. We have to fill up every couple of hours when running the engine at 75 percent. We now got some battery operated hand pump to transfer the diesel as quick and smooth as possible from the jerrycan to the tank. Quite a task and if the engine had been bigger that had been one core more to do all to often.
BACKUP BOOSTER POWER
With all 14HP of the 2YM15 at full throttle we couldn't get into Cardiff marina against the tide in the Bristol Channel. The solution was to lower the 4HP outboard that we carry on a dedicated bracket. The extra 4HP pushed us slowly up to Cardiff barrage and into Cardiff Bay.
Our aim has always been to have at any time at least 2 power sources available at all times: wind, onboard engine and outboard are our options. It's the relative small outboard, used regularly on the dinghy, that saved us that night. Installing the larger 3YM20 just for these cases wouldn't weigh up to the disadvantages of overpowering the boat; especially not as the outboard can provide extra punch if needed.
NO NEED TO OVERPOWER
With the 2YM15 on full throttle and in spite of a heavy anchor, 50 meters of chain, a dinghy and the about 100 liters of drinking water tank upfront the bow goes up and the cockpit gets flooded up to the ankles with water flowing in from the holes that are supposed to drain the place. The 3YM20 in our case would have been overkill; an expensive error that could not have been corrected.
jwilson
Well-Known Member
From experience on a previous boat I can say that a bit under 1 hp per ton is just a trace low-powered. The boat sailed well though..... Current boat about 5 hp per ton, plenty of power even with a two-bladed prop.
RichardS
N/A
The thread's an oldie but goldie ....... but just because you have more power available doesn't mean you have to use it, of course.
Richard