RUNNING ENGINES NOT UNDER LOAD

[Guest]

I have a cat in the med and I find it necessary to run my engine/s when at anchor to maintain battery charge. My batteries drop quite quickly from 13.25V to 12.6V. I don't have a generator or solar panels. I have been told that running the engines for prolonged time not under load will cause harm. Is this correct?

Also I am being given ocnflicting advice on whether it is harmfull to leave one's propellers running freely when under sail. The resistance caused by placing the engines in gear so as to fix the props can decrease boat speed by .5Knot.

 

[Chris_Robb]

Battery Voltages

You should expect battery Voltages to drop quickly down to 12.6. ir even 12 V if you are drawing power. A fully charged battery that has been left for several hours will show around 12.8V. If your batteries drop to 11.5 V then they are badly discharged.

Running engines without load is bad for them. As you are in the Med and especially with a Cat, get some Solar Panels. They may well cut out the requirement to charge other than underway totally. Light running causes polishing of the bores, which in turn causes loss of oil retention and loss of compression.

Freewheeling Props: Whether it is OK to Freewheel props or not entirely depends on the type. Some hydraulic boxes eg Paragon are quite OK - mine is 30 years old and original. Others will wear bearings that are meant to be bathed in oil from running the gearbox. So refer to the manufacturer.

 

[steve_cronin]

This voltage drop when off charge is normal> Our boat is in the med too and we have the same problem. I would recommend solar panels or even a wind genny to keep the fridge going.

AS to running the motor out of gear for long periods, this will result in the cylinder bores becoming glazed which will reduce compression and increase ring wear. You should discontinue it immediately. When we are charging up we moor stern-to a quay and run at around 1100rpm IN GEAR pulling against the mooring warps. So long as you're not annoying the neighbours with the wash (it won't be much) or the noise & smell you will achieve a good charge in about 90 mins - especially if you have one of the new "intelligent" voltage sensed alternator controllers. (Sterling etc) Incidentally "Mr" Sterling's motoryacht "Electromarine" is a common sight around the eastern med. Nice bloke, he will put you right if you get to talk to him.

As to "drag when pulling a stationary prop through the water" Well it's actually LESS than when it is free-wheeling. Have you noticed how a sycamore seed falls slowly to the ground? Also ask a chopper pilot about free falling against a controlled auto-gyrate descent after loss of power. It is right though that some manufacturers don't recommend it. Our Volvo saildrive needs to be left free-wheeling whereas on our previous boat Yanmar recommended that the shaft be locked to PREVENT rotation.

Steve Cronin

 

[oldharry]

Definitely the quickest way to destroy your diesels is to run them off load. Bore glazing is only the beginning. Off load, although the coolant reaches running temprature, other parts of the engine may not as the engine is not working hard enough. Injectors will be damaged by cold erosion, because of insufficient combustion heat, similarly heater plugs if fitted. The cylinder head will not warm through properly and can become distorted resulting in gasket failure, or may even crack. The valve springs will remain cool and may attract condensation causing erosion to the spring steel which will lead to them breaking with the risk of dropping the valve into the engine with extremely terminal results.

I've not finished yet! The lubricating oil will not reach working temprature, nor will it circulate properly, so that combustion products will not be effectively purged from the engine resulting in accelerated wear to bearing surfaces, and contaminants from the exhaust gases will remainin the oil to be carried to the bearing faces causing further damage.

And theres more! The combustion chambers, exhaust ports and turbochargers if fitted will rapidly get clogged up with carbon and soot, reducing engine efficiency and causing rapidly increasing environmental pollution as it gets worse.

Solar Panels are MUCH cheaper than new engines - and of course are totally environmentally friendly.

If you have a real problem with high power consumption on board then install a portable generator - modern ones can be incredibly quiet, and are vastly more fuel and cost effective per kw of electrical output than your main engine can ever be!

Battery voltage at rest (i.e without any discharge is normally around 12.8 volts, and the measured voltage will drop in direct proprtion to the electrical load. A 'charge held' voltage reading is only accurate after batteries have remained disconnected for at least 10 minutes to allow internal voltage to stabilise - which is why 'percentage charge' graded voltmeters are largely a waste of money!

As to the conundrum of rotating versus locked props while under way - a freewheeling propellor presents less resistance to the water so gives a very small gain in speed under sail, but the shaft and gearbox parts are constantly moving. so there is a small bu significant degree of wear taking place all the time. A fixed prop causes more drag, but nothing is being worn down! So it depends how many hundred hours a year you spend under sail as to whether the wear is significant or not. The answer of course is a folding prop which gives the best of both worlds.