Starting a motor with a near flat battery.

[Sybarite]

A tip from a French forum:

If the boat is moving in the water: sails or tow - decompress the motor and start with the forward gear engaged. The speed of the boat turning the propellor turns the motor over and can start the engine.

I haven't tried it and may be it's a technique known by the experts.

 

[johnphilip]

Not with a folding prop you don't.

 

[pvb]

And many newer engines will only start in neutral.

 

[Gwylan]

A tip from a French forum:

If the boat is moving in the water: sails or tow - decompress the motor and start with the forward gear engaged. The speed of the boat turning the propellor turns the motor over and can start the engine.

I haven't tried it and may be it's a technique known by the experts.

That would take 2 people to do and my co-owner could not be relied on to do either with any sort of coordination. That's not why I married her.

Other crew it might be worth a try to see if it can be done.

Easier to hot wire the 'other' battery and get started. Have done that a few times before I admitted that after 10 years the engine start battery needed replacing.

Do carry a modified set of jump leads for just that eventuality. But I also carry a lot of spares that I hope I never need.

 

[William_H]

I would not expect this method to be very successful. As said you must have a non folding propellor and decompression system. However I believe David Lewis in his story of sailing the Southern Ocean in catamaran reported diesel engine starting inadvertently while surfing down a wave I imagine at a speed well in excess of 12 knots. (without decompression)
If the prop is able to drive the engine you may be able to start it by using a joint effort of water flow and electric starter however decompression would be ahuge help to get the rotation speed. You may also be able assist with a belt around ther flywheel if it is accessible to aid the rotation of the engine.
All very dodgy however and no substitute for dual battery system. good luck olewill

 

[Jamesuk]

Not tried it but please do a video and share it when you do ;/)

 

[Uricanejack]

I have done this. sort of. Not under sail. Had an diesel mechanic on board who set things up. He suggested we try bump starting the engine. I was a bit skeptical and we had quite a discussion about which direction we should go in. We eventually decided going ahead and putting into forward gear. I just steered and put in gear.

Twin screw power boat. Nothing wrong with Battery starter had failed on one engine. Engine did not have hand crank.

Left dock under one engine only.
Fixed pitch prop.
Did not decompress.
Once clear of hazards
Increased to full speed under one engine, Other engine out of gear shaft brake off. Propeller spinning out of gear.

Doing about 8 knots. Engaged other shaft and propeller. Lots of throttle.
Engine fired. And ran normally.

Won't work on my boat I have a feathering prop.

I would think to get it to work on a sailing vessel you would have to be sailing quite quickly.

 

[[70521]]

Any indication of the speed that was needed?

 

[skipmac]

Also won't work with some transmissions, like hydraulics. At least the one I have.

Here's another trick. If you're stuck with two 12 V batteries that won't crank the engine but are not totally dead, connect them in series to get 24 Volts instead of 12 and it should do the trick. Reconnect back into parallel 12V configuration after it cranks. Be careful how you do this so you don't fry the alternator or other electrical stuff.

 

[Burnham Bob]

Being the belt and braces type on cruises I always carry a rechargeable jump start unit. I have never needed it yet but for around £30 in a sale it's a good investment

 

[jwilson]

A tip from a French forum:

If the boat is moving in the water: sails or tow - decompress the motor and start with the forward gear engaged. The speed of the boat turning the propellor turns the motor over and can start the engine.

I haven't tried it and may be it's a technique known by the experts.

I have known a 4-cylinder diesel with no decompressors slowly turning over when stopped in gear whilst sailing very fast. Did not start though. I can imagine an engine with decompressors being possible to start this way, but you have to be pushing hull speed plus.

I also once started a big workboat diesel on a mooring by putting 2 flat batteries in series instead of parallel. Turned off again 30 seconds later and reconnected batteries as normal and as it was slightly warmed it started OK and was fine thereafter the weekend I used the boat.

 

[RichardS]

Do carry a modified set of jump leads for just that eventuality. But I also carry a lot of spares that I hope I never need.

I also carry jump leads. I have never needed them to supplement the starter battery but did use them last year to bypass the windlass solenoid which had burned out. That alone was worth the £20!

Richard

 

[jerrytug]

If you really need it to start and only have enough juice in the batteries to turn it over a few times, then you have to get the engine hot hot hot.
First, put all your largest saucepans on to boil.
Drain the coolant into a container.
Fill up the engine with boiling water. (Seawater is fine as you will be draining it soon)
Put the saucepans on to boil again.
Fill up the engine with boiling water.

Repeat until the engine is as as near 100 degrees as possible.

If there is any way you can warm up the starter batteries it will help as well, and connecting 2 in series is a plan as well.
It will start, so rev up and try and warm up the battery and get a bit of charge in it.

When everything is nicely hot, you can drain the seawater and put in your proper coolant back in, which you have obviously also just boiled.

Heating up the engine oil to 120 degrees would help as well.

Horse's mouth info by the way

 

[lydiamight]

Reminds me of the Irishman who wanted to "bump start" his boat----spent weeks looking for a sloping lake

 

[David2452]

And many newer engines will only start in neutral.

Or rather the starter will only engage in neutral, wouldn't stop this working, if it works at all that is.

 

[pvb]

Or rather the starter will only engage in neutral, wouldn't stop this working, if it works at all that is.

Yes, true, but I was thinking of the scenario of motion-induced turning assisting a weak starter battery. Didn't explain it though.

 

[Leighb]

Was there not a story of a long distance yachtsman, French I think?, who faced with this problem rigged up a system of pulleys and lines to a rope wound the flywheel and the other end to the boom, he then gybed the mainsail and this started the engine. Not sure how many times he tried before it started though.

 

[William_H]

The idea of wiring 2 x 12v batteries in series is interesting. Not necesarily a huge advantage if any over 2 x 12v batteries in parallel. The higher initial voltage will drop hugely with the higher intitial current through the starter when in series. Once the engine starts the alternator should not be damaged. It will probably not charge as the batteries in series will recover voltage and probably be more than 14v. If not it soon will be. Some concern however for warning lights pre heaters etc before you crank the engine.
With batteries in parallel the current will be shared by the batteries so only half hence volt drop even for flat batteries will be less.
I think I would prefer to try to start using flat 12v batteries in parallel myself. it also means that they can both be charged immediately without stopping the engine.
Anyone know any better? olewilll

 

[Uricanejack]

If you really need it to start and only have enough juice in the batteries to turn it over a few times, then you have to get the engine hot hot hot.
First, put all your largest saucepans on to boil.
Drain the coolant into a container.
Fill up the engine with boiling water. (Seawater is fine as you will be draining it soon)
Put the saucepans on to boil again.
Fill up the engine with boiling water.

Repeat until the engine is as as near 100 degrees as possible.

If there is any way you can warm up the starter batteries it will help as well, and connecting 2 in series is a plan as well.
It will start, so rev up and try and warm up the battery and get a bit of charge in it.

When everything is nicely hot, you can drain the seawater and put in your proper coolant back in, which you have obviously also just boiled.

Heating up the engine oil to 120 degrees would help as well.

Horse's mouth info by the way

I suppose I could try this if it was cold out.
I have found if there is enough power left to turn the engine over when the compression levers are open. Let it get up to speed, close the leavers and off it goes.

 

[skipmac]

The idea of wiring 2 x 12v batteries in series is interesting. Not necesarily a huge advantage if any over 2 x 12v batteries in parallel. The higher initial voltage will drop hugely with the higher intitial current through the starter when in series. Once the engine starts the alternator should not be damaged. It will probably not charge as the batteries in series will recover voltage and probably be more than 14v. If not it soon will be. Some concern however for warning lights pre heaters etc before you crank the engine.
With batteries in parallel the current will be shared by the batteries so only half hence volt drop even for flat batteries will be less.
I think I would prefer to try to start using flat 12v batteries in parallel myself. it also means that they can both be charged immediately without stopping the engine.
Anyone know any better? olewilll

I read about this trick in some article or book many years ago and filed it away in the memory banks for just in case. Then found myself stranded in the far south Bahamas with 2 very weak batteries and no one with a car or battery within 150 miles.

The engine would just barely turn over with the regular setup IE batteries wired parallel for 12V. Tried several times until it the batteries were so far down the engine wouldn't turn over at all. Hooked the batteries in series for 24V and the engine turned over faster than it did with fully charged batteries at 12V. Started immediately.

So the recommendation based on personal experience, not theory.