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Old 15-07-2014, 15:03   #1
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Push Start a Sailboat?

I know this is probably another dumb question, but I needed to ask it, before I try it.

We were out Sunday sailing the catamaran around on the Caicos Bank. We have a couple of little 3 cylinder Yanmar diesels in it. The manual says when sailing to just leave the transmission in neutral. I was noticing how fast the props spin the propshafts under sail. And I started thinking...which is probably not the best idea but I can't help myself.

These little 33 hp engines have a compression release on the valve cover. It's not even hooked up, and the Yanmars start right up immediately. I would imagine it would be more of a feature in a really cold climate.

These engines are easy to turn over. My question is whether or not there is any way to use the forward motion of the boat under sail to start an engine. If I put the transmission in forward, and held the compression release open until the engine started turning, would I be able to let go of the compression release lever and use the spinning prop to start the engine? I know the sudden compression would quickly slow or stop the prop, but there must be some speed at which it would have enough kinetic energy or inertia to at least turn the diesel over a time or two.

Or is that, as I suspect, a stupid question for reasons as yet unrevealed ?
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Old 15-07-2014, 15:11   #2
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Re: Push start a sailboat?

You will never ever be able to push start a sailboat or any boat engine. You can't generate enough force on the prop to push start an engine.

Now some have used a rope run to the boom wrapped around the crank pully to start the engine under the right sailing conditions, but push starting is never going to happen.
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Old 15-07-2014, 15:16   #3
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Re: Push start a sailboat?

Sounds like a great way to induce a monster gear lash in the tranny and jump the engine right off its logs.
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Old 15-07-2014, 15:56   #4
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Push start a sailboat?

In answer to your question, if you could get her turning over fast enough with the compression released, yes inertia would likely get it through a compression stroke or two and that may well be enough to get it going.
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Old 15-07-2014, 16:09   #5
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Re: Push start a sailboat?

Nope, the transmissions are not designed to operate in this direction. Torque from the engine is needed to fully seat the clutch, putting the engine in fwd with the props spinning won't do anything except burn material off of the clutch/cone. Putting the gear in reverse tricks the transmission into thinking the torque is coming from the engine, and it stops the prop from spinning.
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Old 15-07-2014, 16:10   #6
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Re: Push start a sailboat?

Part of the issue is the gear ratio in the transmission. Something like 2.4 to 1 or so. Don't think the prop can overcome the torque/stickcion in the engine at 2.4 ish to one, not with a 15" ish prop at a 12/14 pitch.

Maybe with an old atomic 4 that was 1 to 1. But most atomic 4 props are shallow pitch.
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Old 15-07-2014, 16:17   #7
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Re: Push start a sailboat?

Agree, dont think there is a scenario where that is likely to work, but I used to have an older Yanmar with a hand crank. With the compression releases initially open it was relatively easy to start by hand.
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Old 15-07-2014, 16:25   #8
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Re: Push start a sailboat?

If the gearbox is mechanical (Dog clutch or cone clutch) it will stop the shaft. I do this all the time to keep the prop from turning. The engine compression is not overcome by the prop torque.

However... it might be possible to spin the motor over if you use the compression release on all 3 cylinders. (Most diesels do not have them, Yanmar does) I would give it a try. Can't really do any harm. Just put it in gear and use the compression leavers and see if it will spin the motor over. Let us know if it works!
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Old 15-07-2014, 16:36   #9
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Re: Push start a sailboat?

Quote:
Originally Posted by Canibul View Post
I know this is probably another dumb question, but I needed to ask it, before I try it.





We were out Sunday sailing the catamaran around on the Caicos Bank. We have a couple of little 3 cylinder Yanmar diesels in it. The manual says when sailing to just leave the transmission in neutral. I was noticing how fast the props spin the propshafts under sail. And I started thinking...which is probably not the best idea but I can't help myself.





These little 33 hp engines have a compression release on the valve cover. It's not even hooked up, and the Yanmars start right up immediately. I would imagine it would be more of a feature in a really cold climate.





These engines are easy to turn over. My question is whether or not there is any way to use the forward motion of the boat under sail to start an engine. If I put the transmission in forward, and held the compression release open until the engine started turning, would I be able to let go of the compression release lever and use the spinning prop to start the engine? I know the sudden compression would quickly slow or stop the prop, but there must be some speed at which it would have enough kinetic energy or inertia to at least turn the diesel over a time or two.





Or is that, as I suspect, a stupid question for reasons as yet unrevealed ?



Considering that you'd have the gearbox ratio working against you in addition to the low torque produced by the prop w.r.t. the engine torque required to overcome compression strokes - the only viable way I could foresee this working is if you were sailing on a sea of Mercury, but then your newly-awful B/D ratio would be giving you more of a headache anyway!
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Old 15-07-2014, 17:08   #10
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Re: Push start a sailboat?

Good question.

I would have tried it already in the time it took you to write the post.
But it won't work.

Think of push starting a car. Especially if the engine is cold, when you engage the clutch of a moving car, the compression of the engine will stop the car unless the car is going more than 5 mph and many times more.

Now,that's a car with rubber tires on a road that produces a lot of friction.

In your boat, your prop on the other hand, has none of those advantages. Then add the fact that a diesel engine has a compression ratio that is at least double that of a gasoline engine.


having said all that, if you rally want to know, try it, but I would start with a hot engine.

Have fun.
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Old 15-07-2014, 17:53   #11
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Re: Push start a sailboat?

I think I remember Bob and Nancy Griffith talking about doing just this in their book water sailing">Blue water sailing IIRC he got her up to 7 knots and threw the decompression levers one by one.

And I have heard of a few old fishing boats being tow started as well like this. But in both cases probably old heavy flywheels engines and simple gearboxes.

Why not give it a go? Having decompression levers is a huge bonus for easy starting. Maybe help it by using the hand start crank to ease the load on the clutch cones.
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Old 15-07-2014, 17:57   #12
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Re: Push start a sailboat?

For the past six years we owned two 2005 Land Rover Defenders with the 2.5 l TDi diesels in them. I often would bump start these on a slight hill just to do it. Put it in second gear, with the ignition on, push in the clutch to start rolling and let the clutch out. Unlike every gasoline engine I've ever push started, these fired right up easily every time and as soon as they started turning over. I could start the little Defender 90 in a level parking lot just by pushing it, if I had someone inside to handle popping the clutch.

These Yanmars seem similar. I mean, these are not big powerful diesels. We're pushing the seagoing equivalent of a small three bed, two bath flat along with less horse power than a Harley Sportster.

But those are some good thoughts about the transmission issues. I hadn't considered the ratio and I don't know exactly how the clutch works on those things. Yet.

You can see my thinking though, right? Would be nice to have a way to start an engine manually, just in case. The compression release makes it real easy to spin the crank and pistons on this little thing.

These didn't come with a hand crank, but I wish they did.


Maybe wrap a pull line around a pulley and get the boat up to 7 or 8 knots and throw the line out with a big drogue on it.....
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Old 15-07-2014, 18:04   #13
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Re: Push start a sailboat?

Quote:
Maybe wrap a pull line around a pulley and get the boat up to 7 or 8 knots and throw the line out with a big drogue on it.....
If you should try this, be REALLY sure that the line will come free from the pulley if the engine should actually start. The repercussions of having it jam and then wind around the pulley with the engine running are pretty, uhh, interesting!

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Old 15-07-2014, 18:07   #14
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Re: Push start a sailboat?

Quote:
Originally Posted by Snowpetrel View Post
I think I remember Bob and Nancy Griffith talking about doing just this in their book Blue water sailing IIRC he got her up to 7 knots and threw the decompression levers one by one.

And I have heard of a few old fishing boats being tow started as well like this. But in both cases probably old heavy flywheels engines and simple gearboxes.

Why not give it a go? Having decompression levers is a huge bonus for easy starting. Maybe help it by using the hand start crank to ease the load on the clutch cones.


I too recall them talking about this. I believe it worked so well for them that they did it for quite some time before bothering to fix it. Clearly remember them talking about being unable to make port once because there wasn't enough wind to start the engine.
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Old 15-07-2014, 18:14   #15
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Re: Push start a sailboat?

I'll look into the transmission situation to be sure I'm not going to break anything but I do plan to try it to see what happens.

I guess that if gearing was an issue, it would be possible to put a pulley and belt on the free turning shaft , parallel another shaft up the length of the engine, and come up with a way to use the turning prop to crank the engine from the end with the belts and pulleys on it. A water driven reverse PTO?

I guess with enough pulleys and a Rube Goldberg imagination, one could start a small diesel by dropping an anchor.
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