Slowing down

[Tony Brooks]

13 minutes ago, SiFi said:

Throttle stop, I disconnected the cable.  I need to have a closer look as I don't remember a tick over adjuster stop.

 

It would be rare for the tickover not to have an adjustment. If you can't see one on the engine, post a photo of the engine lever and surrounding area.

[Bee]

A lot of engines only start to run smoothly at something over 1000 rpm, we're not talking about great big old lumps that would frighten the living daylights out of the steerer at that speed but modern motors based on car or van engines, these often have a tickover speed of 6-700 rpm giving a prop speed of about half that with the usual 2:1 gearbox (lots of generalisations here).  I think that to achieve 3.5 mph is a bit hopefull unless the boat/propeller combination is a bit unusual or the arithmetic has gone awry

[SiFi]

Measured tickover of 878 rpm using an app on my phone (measures the exhaust beat).

 

I also had a closer look and found the tickover stop adjuster on the engine throttle. I was able to reduce the tickover a little to about 760 rpm without the engine becoming lumpy.

 

I'm curious to see how this plays out.

[john.k]

maybe engine components that are lubricated by splash and oil mist will wear rapidly for lack of lubrication .............low speed engines have multiple  pumped oil feeds to every bearing and moving part ... injection advance may also need to be reset  to moderate high cylinder pressures.

[MtB]

12 hours ago, SiFi said:

I was able to reduce the tickover a little to about 760 rpm without the engine becoming lumpy.

 

Getting on for 15% reduction in prop speed if my mental arithmetic is right. This will I suspect, make a noticeable  reduction in the speed of the boat at tickover as the power of the blade changes with the cube of the shaft speed IIRC. 

[SiFi]

I'm conscious that the lowest rpm on my build of engine is rated at 850rpm so I may be over egging it!  I will run the boat out and see whether the ~15% helps with the low speed handling of my boat.

Edited September 4 by SiFi

[IanD]

8 hours ago, MtB said:

 

Getting on for 15% reduction in prop speed if my mental arithmetic is right. This will I suspect, make a noticeable  reduction in the speed of the boat at tickover as the power of the blade changes with the cube of the shaft speed IIRC. 

About 15%... 😉 

 

(prop power proportional to rpm^3 + engine power proportional to speed^3 = speed proportional to rpm 🙂 

[NB Alnwick]

I have heard a number of boaters say that they unable slow down for various reasons. That said, our canals and waterways are a valuable asset and there are scarce resources available to maintain them. Excessive speed that causes unnecessary damage is criminally negligent.

If a boat is incapable of being navigated at an appropriate speed at all times and under all circumstances then there must be a serious design fault. As has been said, this could be the size and pitch of the screw, the wrong combination of engine and gearbox, poor commissioning/adjustment etc.

A competent boat builder should not make these mistakes.

Edited September 5 by NB Alnwick
If this was my boat, I would take it back to the builder!

[bizzard]

And engine idle speed tweaked up to cope with enomous electrical loads, ie huge inverters, battery banks, and gready appliancies while on the move.

[IanD]

1 hour ago, bizzard said:

And engine idle speed tweaked up to cope with enomous electrical loads, ie huge inverters, battery banks, and gready appliancies while on the move.

Seems unlikely -- if you have (for example) a Beta engine (very common) these should not be used for heavy charging loads below 1200rpm, but typical cruising rpm is not much above this, and passing-moored-boats rpm is certainly below it.

 

I suspect the problem -- as so often -- is selfish inconsiderate boaters going too fast, nothing to do with onboard electrical loads as such.

 

Or possibly boats with large overpropped -- possibly "traditional"? -- engines which are just plain are too fast even at idle speed... 😉 

Edited September 5 by IanD

[cuthound]

3 hours ago, NB Alnwick said:

I have heard a number of boaters say that they unable slow down for various reasons. That said, our canals and waterways are a valuable asset and there are scarce resources available to maintain them. Excessive speed that causes unnecessary damage is criminally negligent.

If a boat is incapable of being navigated at an appropriate speed at all times and under all circumstances then there must be a serious design fault. As has been said, this could be the size and pitch of the screw, the wrong combination of engine and gearbox, poor commissioning/adjustment etc.

A competent boat builder should not make these mistakes.

 

Not to mention the steerer's inability to observe moored boats and slow down a few boat lengths before them...

 

[NB Alnwick]

Someone asked me today if my engine was always running at "tickover" - my answer was "not really" but I always select "the most appropriate engine speed".

I usually drop to around 100 rpm to pass moored craft (I can go slower) and on most canals I rarely exceed 300 rpm because anything more would be wasted - the boat would just make more wash without moving forward any faster.