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Old 12-08-2015, 11:38 PM   #1
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Low Idle Option Detroit Diesel

I could not find this topic under the search function, so I hope it has not been discussed recently.

Can someone explain what the "Low Idle" option does for DD engines? I saw this option on a Hatteras on YW? The photo shows a group of three buttons. One button is labeled "Station Active" and has a light below. The second button is labeled "Sync" and it has a light below it. The third button is labeled "Low Idle" and it also has a light below to indicate when it has been switched on.

I understand the "Station" and "Sync." functions, but what does the "Low Idle" option do? Does it increase the load on the engine at a lower RPM? Is this an expensive option or standard? I have seen a trolling function on some boats. Is this the same as a trolling setting?

Any help to understand this would be appreciated.
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Old 12-09-2015, 07:01 AM   #2
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Can't help you with the low idle option switch, but my second charter boat (25' center console ) had a "Sea State " switch for rough days. Told the customers they could flip it on and the seas would settle down after a while (like back at the dock ).

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Old 12-09-2015, 07:06 AM   #3
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Maybe it turns off the low oil pressure light.
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Old 12-09-2015, 07:49 AM   #4
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Depending on the engine a DD 6-71 or 8V71 will still operate at under 400 RPM.

It will not pick up a load well at that speed .

Perhaps it is just to quiet the engine when idleing or running very slow.

Yes canceling the low oil alarm might be part of it.

On 8V71 coaches the low idle light ON was a requirement to clutch in the 60HP air cond compressor that would rip out if engaged at highway speed.

Ask on the Hat board?
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Old 12-09-2015, 08:57 AM   #5
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Quote:
Originally Posted by Cuttyhunk47 View Post
I could not find this topic under the search function, so I hope it has not been discussed recently.

Can someone explain what the "Low Idle" option does for DD engines? I saw this option on a Hatteras on YW? The photo shows a group of three buttons. One button is labeled "Station Active" and has a light below. The second button is labeled "Sync" and it has a light below it. The third button is labeled "Low Idle" and it also has a light below to indicate when it has been switched on.

I understand the "Station" and "Sync." functions, but what does the "Low Idle" option do? Does it increase the load on the engine at a lower RPM? Is this an expensive option or standard? I have seen a trolling function on some boats. Is this the same as a trolling setting?

Any help to understand this would be appreciated.

Just guessing since I have no experience on the subject, but my best guess would be activating trolling valves.

(edited to remove link to another forum explaining trolling valves. wasn't sure if it was against the forum rules)
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Old 12-09-2015, 09:16 AM   #6
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Low idle switch reduces the idle speed of the engine for maneuvering around docks, etc. Many boats have larger wheels and even at idle propels the boat a fair distance and speed just bumping it in gear. My guess of the Hatteras it has electronic engines to accomplish this. Many older sport fishing boats had what was called a trolling valve. This would allow the gear to turn slower with higher engine RPM's.

Were the engines in question 60 series?
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Old 12-09-2015, 09:23 AM   #7
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You don't say what brand and model of engine controls are involved here. In general this Slow feature is used on electronic controls for to reduce the throttle range, typically 1/2 while doing close quarter maneuvers, both for safety and more precise throttle. Some versions also have a switch to turn on trolling valves if the boat is so-equipped. See page 9 of this Glendinning manual:

http://www.glendinningprods.com/gmp/...s_Guide.v2.pdf
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Old 12-09-2015, 09:36 AM   #8
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It's been a long time since I worked with them (memory dims) but DD did offer a governor with two idle speeds, selected by a switch and solenoid. The usual application was to allow a "high idle" to operate accessories such as air conditioning on a coach, or the exciter on large diesel electric mining trucks. The two idle speeds were adjusted independently so there is no reason one could not have been set very low and the other at normal idle. As noted the old two strokes could idle very slow, as the two stroke fires every revolution.
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Old 12-09-2015, 10:02 AM   #9
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My dock neoghbor and friend has DDECs on his Hatteras. Everyone pretty much explained it properly. It is so you can go slowly around docks and in no wake zones. normal idle in gear yields about a 7 knot(on his boat) and causes enough wake to piss people off. Interestingly, the computer will not allow this option when engine temps are above 175 degress(I think). I guess it needs to keep things rotating quicker to keep things cool if they are heated up.

And yes, trolling valves are the mechanical way to accomplish the same thing. I do believe trolling valves regulate pressure in the transmission to allow the gears to slow down absed on the current throttle setting. The reason they are called "trolling valves" is because you need to go slower than 7-8 knots to properly troll whilst fishing.

Which brings up the question, is a sportfish more of a trawler than a "trawler"???...
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Old 12-09-2015, 12:07 PM   #10
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Thank you for your help on this.

It does appear to be a Glendinning arrangement of switches, although older than the one offered above. The engines are DDEC 12V71. Thanks again.
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Old 12-09-2015, 01:01 PM   #11
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Which brings up the question, is a sportfish more of a trawler than a "trawler"???...
No...it just makes you a 'troller' for asking that question.
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Old 12-09-2015, 01:38 PM   #12
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Quote:
Originally Posted by Capt. Jon View Post
Many older sport fishing boats had what was called a trolling valve. This would allow the gear to turn slower with higher engine RPM's.
Quote:
Originally Posted by Baker View Post
And yes, trolling valves are the mechanical way to accomplish the same thing. I do believe trolling valves regulate pressure in the transmission to allow the gears to slow down absed on the current throttle setting. The reason they are called "trolling valves" is because you need to go slower than 7-8 knots to properly troll whilst fishing.

We have ZF trolling valves. ZF discourages both shifting and throttle levels above idle while the trolling valves are engaged.

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Old 12-09-2015, 04:39 PM   #13
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That's DDEC stuff. Once engine is warmed up hit low idle button and I think it idles at 500. Normal idle is 600. Even higher when engine is cold. Actual rpms vary with what engine it is.
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Old 12-09-2015, 10:14 PM   #14
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That's DDEC stuff. Once engine is warmed up hit low idle button and I think it idles at 500. Normal idle is 600. Even higher when engine is cold. Actual rpms vary with what engine it is.
That looks about right, now that we have the pic.
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