Need to understand

[miyva]

Ok I have a Volvo Penta MD22-L in my Hutner 430. It was fitted a couple years ago with a fettering Max Prop. If i read on the engine it says that the operating speed is 2,600 to 3,000 RPM.

Well i max power it does 2,100 RPM so i cruise like volvo penta recommend that the cruising is 300rpm lower then max rpm, so i cruis between 1,700 to 1,800rpm.

Ok all this said, someone told me that my setup was over prop? i'm trying to see if i'm getting the optimal performance from my boat and if i need to look at adjusting the prop?

Any education on this or tips would be appreciated.

[jamhass]

Check with PYI, as they may well have a pitch recommendation for your boat and engine. You can then reset your MaxProp at your next haulout. There are some divers that can do it in the water.

[Cheechako]

It depends on how much HP you actually need for your boat.

Do you know your hull speed? Do you make hull speed at 1800 rpm?

The normal answer is to make it so the engine RPM is maxed out at maybe 10-15% below engine makers maximum rpm. (you said 3000 rpm, so maybe 2500-2700 rpm) But if you engine has enough HP at lower RPM some people would rather be lower.
It sounds like you may be over propped a bit, but if it doesn't over heat it may be fine. I might rather be 2200 or so at hull speed. Maxing out at 2400-2600 maybe?

[Kokanee]

I'd agree with Cheekako. You're likely overpropped with too much pitch if your hull and prop are clean and maximum rpm is only 2100.

Your Hunter has a hull speed of about 8.2 knots which would require the full 50 hp (3000 rpm) to achieve. Running at 1700 rpm you would only be producing about 15 hp, although the engine would be producing close to maximum torque. This probably gets you 6 or 6.5 knots in speed at 1700-1800 rpm..

If you are happy with this maximum speed under power, and you are not overheating or blowing black smoke, then all is well. Just don't try to run at full throttle. Your engine life will decrease dramatically.

The benefit to being overcropped it lower engine revs at an efficient cruising spread. It is quieter, and may have less vibration.

[a64pilot]

Yeah, but he’s running it 300 off the top, in other words he’s running the snot out of it.
Especially since it’s just a prop adjustment if he’s going to continue to run it like that he needs to get it right, or slow down several hundred RPM.

[Cheechako]

Originally Posted by a64pilot

Yeah, but he’s running it 300 off the top, in other words he’s running the snot out of it.
Especially since it’s just a prop adjustment if he’s going to continue to run it like that he needs to get it right, or slow down several hundred RPM.

He's running it at 1700-1800 right? Max is 3000.

[miyva]

Originally Posted by Cheechako

He's running it at 1700-1800 right? Max is 3000.

Full throttle
operating speed, rpm ........ 2600–3000

But at full throttle i'll get maybe 2,100rpm. and in the owners manual it tells me that cruising speed should be 300rpm less then max. So i cruisse at around 1,700 rpm.

So maybe i need to do more research on prop pitch adjustment for my prop and get it done.

Sorry still learning about props and diesel engines.

[a64pilot]

Originally Posted by Cheechako

He's running it at 1700-1800 right? Max is 3000.

No, his max is 2100. He’s seriously overpropped
But either way, unless an engine is seriously derated recommending it to cruise 300 off the top is going to sell a lot of engines.
Now if this is actually a 3600 RPM motor that has been derated to 3000, then 2700 is different, but if it’s actual designed max speed is 3000, then 2700 is running one awful hard.

[miyva]

Originally Posted by a64pilot

No, his max is 2100. He’s seriously overpropped
But either way, unless an engine is seriously derated recommending it to cruise 300 off the top is going to sell a lot of engines.
Now if this is actually a 3600 RPM motor that has been derated to 3000, then 2700 is different, but if it’s actual designed max speed is 3000, then 2700 is running one awful hard.

Ok i'll be checking this and adjusting the prop.

[a64pilot]

Over propping is very common, and in fact it does work, you see when a boat is propped so that the engine will hit its max RPM. When operated well under that RPM they aren’t loaded very high, so people overprop to get more speed at lower RPM, the issue is when overpropped its very easy to overload an engine, just like pulling a steep hill in a car in high gear can overload an engine, but on a boat that’s overpropped and the engine run hard, that hill never ends. It will shorten the life of an engine.

But people that are overpropped if they understand this and accept that they now have an engine of significantly less power, they can run it forever and not hurt it, because they won’t overload it, they just won’t use the last 1/3 of the power lever or so.
But if you want to run a motor 300 RPM off of its max RPM, it’s important that it’s propped correctly or you will most likely overload it.

[miyva]

Originally Posted by a64pilot

Over propping is very common, and in fact it does work, you see when a boat is propped so that the engine will hit its max RPM. When operated well under that RPM they aren’t loaded very high, so people overprop to get more speed at lower RPM, the issue is when overpropped its very easy to overload an engine, just like pulling a steep hill in a car in high gear can overload an engine, but on a boat that’s overpropped and the engine run hard, that hill never ends. It will shorten the life of an engine.

But people that are overpropped if they understand this and accept that they now have an engine of significantly less power, they can run it forever and not hurt it, because they won’t overload it, they just won’t use the last 1/3 of the power lever or so.
But if you want to run a motor 300 RPM off of its max RPM, it’s important that it’s propped correctly or you will most likely overload it.

Ok i'll do some more research and adjust it to a better setup.

[CassidyNZ]

Having just been involved in a re-power using a new Yanmar 4JH4HTE, the sea trials conducted by the Yanmar dealer required the engine to achieve 3200RPM. If it didn’t, no warranty certificate would be issued. So the ability to achieve max RPM would seem to be a good idea.

But routinely running at that RPM is not efficient. Diesel consumption goes right up with RPM and running a boat with RPM at the upper limits will cost money over time. The power curves (representative only) attached tell the story.

I rarely run our engine over 2000 RPM and at that speed we’re doing 6 - 7kn which works for me. Running at top RPM only achieves 2kn more and uses a whole lot more fuel.

[miyva]

Originally Posted by CassidyNZ

Having just been involved in a re-power using a new Yanmar 4JH4HTE, the sea trials conducted by the Yanmar dealer required the engine to achieve 3200RPM. If it didn’t, no warranty certificate would be issued. So the ability to achieve max RPM would seem to be a good idea.

But routinely running at that RPM is not efficient. Diesel consumption goes right up with RPM and running a boat with RPM at the upper limits will cost money over time. The power curves (representative only) attached tell the story.

I rarely run our engine over 2000 RPM and at that speed we’re doing 6 - 7kn which works for me. Running at top RPM only achieves 2kn more and uses a whole lot more fuel.

Agreed, might have been setup maybe with previous owner and people consulting with was not very good. My engine curves are here http://www.sra-moteur.com/uploads/ca...d22l-md22l.pdf

the learning keeps on going.