Gas v/s diesel for trawlers

Nomad Willy · Dec 22, 2012

POSSIBILITIES

Now your'e gett'in right in there Mark. Lots of possibilities. Possibilities to go astray too. If a boat needs 60 hp to go 7 knots on one engine w DE drive and they but in two 75hp engines the two engines my never get used together. Better to just install one 75hp engine. With two engines 50 to 60% power would have two engines underloaded again. One would need to chose carefully.

Art · Dec 22, 2012

With electric drive motors (energized by whatever means) what would happen to the near instant and near infinite levels of acceleration/deceleration opportunities offered by the throttle on gas/diesel/propane/nat-gas hydrocarbon burning engines? Would the electric motors enable a nearly unlimited inner-range of power to prop adjustments to easily, quickly occur? Just wondering??

Marin · Dec 22, 2012

RickB said:
Those "shifts" are the transitions between series and parallel operation of the traction motors. There is a very short period during the transition when no power is delivered. That is what gives the impression of a gear shift as in a truck.

The "runs" or "notches" are governor limits that control the maximum amount of power available to the traction motors in a given configuration. They reduce the risk of overloading a motor by limiting the amount of power the engine can produce.

Thanks for the explanation, Rick. I didn't think anything was actually shifting gears even though that's what it sounds like. But I don't understand enough about that technology to know that the diesel does not have to run through several gear ratios to power the generator as the load/resistance on the generator increases.

markpierce · Dec 22, 2012

Diesel-mechanical diesel locomotives (usually in small switcher sizes) had/have gear shifts (multiple forward and reverse gears), as well as some geared steam locomotives like the early Climaxes.

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Marin · Dec 22, 2012

markpierce said:
Eric, my builder warned me about changing from forward to reverse saying it must be done at idle/near-idle engine speeds to avoid risk of damage.

That is the recommended procedure for most if not all the drive systems in our boats.

To minimize the "shock" of shifting between forward and reverse we lifted the access hatch in our main cabin many years ago and measured the length of time it takes for our prop shafts to come to a stop when the boat is shifted at idle rpm from forward to neutral and from reverse to neutral. The time will vary with the friction in the driveline, but on our boat it takes about two seconds. So whichever one of us is maneuvering the boat at idle rpm we make sure to wait three seconds or so after shifting a transmission into neutral to shift into the opposite gear.

We did the same thing when the boat was moving at cruise speed. I pulled the throttles to idle and then pulled the shifters to neutral. It took as long for the shafts to stop turning in forward to come to a stop as it did for the boat to decelerate and come to a stop. Which makes sense of course.

So we now know that when the boat is in gear and moving at anything over idle power we need to wait until the boat has come to a near dead stop in the water before shifting into the opposite gear after putting the transmissions in neutral.

Knowing what's going on under the floor with the shafts has demonstrated to us that the folks we see who are frantically sawing back and forth with the shifters on their boats trying to "save" a docking are not doing their marine gears any good as they slam from forward into reverse and then back again. Particularly if they're carrying or adding some power at the same time.

One of my goals when maneuvering our boat to or from a dock or slip is to do it with the minimum number of gear changes I can manage.

psneeld · Dec 22, 2012

Art said:
With electric drive motors (energized by whatever means) what would happen to the near instant and near infinite levels of acceleration/deceleration opportunities offered by the throttle on gas/diesel/propane/nat-gas hydrocarbon burning engines? Would the electric motors enable a nearly unlimited inner-range of power to prop adjustments to easily, quickly occur? Just wondering??

Not positive but I believe electric motors are favored for tight maneuvering/positioning... Many USCG Bouy tenders were diesel/electric for that reason.

bfloyd4445 · Dec 22, 2012

psneeld said:
NOT railroad tech...been around for a LONG time in the maritime industry...big electric motors driven by multiple gensets...I believe the USCGC Glacier 9wwii vintage) had 10 Gensets driving the motors and powering the vessel. She had 2 of the largest electric motors ever built at around 3 stories high.
She was a 15+ knot vessel, designed to break thick ice and ran as many gensets as needed to carry the drive and house load. At any given time one or more were being rebuilt underway.

wow, would be neat to be able to see the Glacier today. Thats about the time the railroads got interested in this technology as well wasnt it? Maybe the marine application was first?...
Thanks psneeld

Art · Dec 22, 2012

Marin said:
That is the recommended procedure for most if not all the drive systems in our boats.

To minimize the "shock" of shifting between forward and reverse we lifted the access hatch in our main cabin many years ago and measured the length of time it takes for our prop shafts to come to a stop when the boat is shifted at idle rpm from forward to neutral and from reverse to neutral. The time will vary with the friction in the driveline, but on our boat it takes about two seconds. So whichever one of us is maneuvering the boat at idle rpm we make sure to wait three seconds or so after shifting a transmission into neutral to shift into the opposite gear.

We did the same thing when the boat was moving at cruise speed. I pulled the throttles to idle and then pulled the shifters to neutral. It took as long for the shafts to stop turning in forward to come to a stop as it did for the boat to decelerate and come to a stop. Which makes sense of course.

So we now know that when the boat is in gear and moving at anything over idle power we need to wait until the boat has come to a near dead stop in the water before shifting into the opposite gear after putting the transmissions in neutral.

Knowing what's going on under the floor with the shafts has demonstrated to us that the folks we see who are frantically sawing back and forth with the shifters on their boats trying to "save" a docking are not doing their marine gears any good as they slam from forward into reverse and then back again. Particularly if they're carrying or adding some power at the same time.

One of my goals when maneuvering our boat to or from a dock or slip is to do it with the minimum number of gear changes I can manage.

Those are good tests you did, Marin. Thanks for posting timed results.

RickB · Dec 22, 2012

bfloyd4445 said:
Maybe the marine application was first?...

The first marine application was in 1903, about 20 years prior to the first rail application.

sunchaser · Dec 22, 2012

ELCO, the boat builder of yore got their name from their activities as the Electric Launch Company. In 1893 they built 55 36' 40 passenger boats to ferry people around the Chicago Exposition. The drive motors were 4 hp and battery driven. Dig deep enough and you may find Thomas Alva Edison involved with all sorts of DC drives setups as the battle between AC and DC for high voltage lines was boiling about this time.

FF · Dec 23, 2012

Aren't pod-drive cruise ships, and the like, diesel-electric driven? Are the pod drives on the new trawlers like this or is it more like a stern-drive system with gears and CV joints?

Pod drives solve problems most yachts do not have.

Their pod drive allow for docking in port with no tug boat assistance.

The house load will at times exceed what could be required for a propulsion load.

With diesels only efficient at high loads the ship can operate with as many of the gen sets on as required .

When there are a dozen , load management and maint becomes easier.

Art · Dec 23, 2012

Art said:
With electric drive motors (energized by whatever means) what would happen to the near instant and near infinite levels of acceleration/deceleration opportunities offered by the throttle on gas/diesel/propane/nat-gas hydrocarbon burning engines? Would the electric motors enable a nearly unlimited inner-range of power to prop adjustments to easily, quickly occur? Just wondering??

psneeld said:
Not positive but I believe electric motors are favored for tight maneuvering/positioning... Many USCG Bouy tenders were diesel/electric for that reason.

Does that mean that marine elect engines’ controls run the electric engines similar to a rheostat switch? Wherein any level of power can be quickly adjusted to all the way through the power range from low to high. Or, are there set phases, i.e. specific multiple levels of power transfer to the prop-shaft? Let’s say... Low / Med Low / Med High / High? One item I enjoy with hydrocarbon burning engines is the nearly unlimited range of power applications that can be instantly adjusted to and that provide great boat maneuverability for nearly any condition. Point in fact: I’ve operated in some pretty hairy following seas with conflicting currents and winds... I sure would not want to be chained to only a few electric engine levels of power thrust! A broaching we might go!!

RickB · Dec 23, 2012

Not to pick too small a nit but sticking to marine drives, the first diesel-electric drive ship was also the first diesel powered ship. It was Russian built and they used D/E because there was no other way to reverse the thing.

Steam turbine-electric became popular for propelling cargo ships during WWII because it was faster and cheaper to make generators and motors than reduction gears which were desperately needed for warship use.

The first azimuthing drives were built just before WWII for naval barge propulsion. "Harbormasters" were built by Murray and Tregurtha and used a 6-71 or Graymarine engine. A few of the original Navy units are still in use. We used a pair of war surplus units to drive a submersible support vessel in Nova Scotia and the GOM a few years back.

Modern pod drives are nearly all AC powered via variable frequency drives.

The pods used on smaller vessels such as tugs and the newish yacht drive systems are geared just like a stern drive and connected to the drive engine with a shaft and universal joints. Some smaller units used as azimuthing thrusters in DP applications have an electric motor mounted vertically above the drive leg.

Upper end of pod drive on cruise ship. The red units are the hydraulic motors that rotate the pod.

Cycloconverter cabinets. These change the A/C from the generators to DC then "reassemble" it in the desired voltage and frequency for the drive motors.

They still need and use bow and stern thrusters. This photo shows the center of three units.

Solar - did someone ask if any boat had made long trips on solar alone? The first photo shows the panels on one that made it around the world on nothing but solar power.

Art · Dec 23, 2012

RickB said:
Solar - did someone ask if any boat had made long trips on solar alone? The first photo shows the panels on one that made it around the world on nothing but solar power.

Rick - You know a link to get stats on that solar powered world passage?

RickB · Dec 23, 2012

Art said:
Does that mean that marine elect engines’ controls run the electric engines similar to a rheostat switch?

Far from it.

Rather than waste bandwidth here and bore those who are only interested enough to whine about lengthy explanations, take a look at this http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA417341 for an overview.

There is tons of accurate and relevant information available online from all the manufacturers of marine electric drive systems.

They used to use a rheostat control on the old DC drive systems like on submarines and the old Washington State Ferries. I used to do relief work on the ferries and maneuvering was like juggling eggs controlling two motors in opposite directions with rheostat controls when you couldn't even remember which end of the boat was the front.

RickB · Dec 23, 2012

Art said:
Rick - You know a link to get stats on that solar powered world passage?

Dockwalk - May 2011

Everything you want to know from the source: PlanetSolar

Art · Dec 23, 2012

Quote:
Originally Posted by Art

Does that mean that marine elect engines’ controls run the electric engines similar to a rheostat switch?

Far from it.

Rather than waste bandwidth here and bore those who are only interested enough to whine about lengthy explanations, take a look at this http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA417341 for an overview.

There is tons of accurate and relevant information available online from all the manufacturers of marine electric drive systems.

RickB said:
Dockwalk - May 2011

Everything you want to know from the source: PlanetSolar

Thanks, Rick - I'll delve into both! - Art

AusCan · Dec 23, 2012

There's a boat manufacturer called Greenline who build a 33, 40 & 70 ft "hybrid" diesel electric cruisers. Good to see someone is looking at alternative options.

sunchaser · Dec 23, 2012

Great stuff Rickb.

Closer to the hearts of us trawler owners is electric vs hydraulic for windlass, bow and stern thrusters. Todays electric thrusters have few timeout problems if sized right so that "advantage" is likely moot.

RickB · Dec 23, 2012

Thanks.

Once you get away from thrusters and windlasses powered by converted
DC starter motors, it doesn't much matter if it is electric or hydraulic. I have had no major problems with either AC or hydraulic drives. Both are robust and reliable.

Marin · Dec 23, 2012

Art said:
Those are good tests you did, Marin. Thanks for posting timed results.

Just keep in mind that the time it takes a shaft to come to a stop after shifting into neutral will depend on the friction in the driveline-- the cutless bearings and such. So don't assume that because the shafts in our boat take about two seconds to come to a stop from idle rpm that's how long it will take in your boat. Best to measure it yourself in your own boat.

Art · Dec 23, 2012

Marin said:
Just keep in mind that the time it takes a shaft to come to a stop after shifting into neutral will depend on the friction in the driveline-- the cutless bearings and such. So don't assume that because the shafts in our boat take about two seconds to come to a stop from idle rpm that's how long it will take in your boat. Best to measure it yourself in your own boat.

Must admit I have never done a time trial such as this on any boat. That said... I never shift into gears unless at low idle and the time from neutral to next gear is a couple to a few seconds, or in an emergency at a bit higher idle, which seldom occurs.

Nomad Willy · Dec 23, 2012

Marin you don't have to wait for the prop shaft to comet a complete stop at all. Just getting the speed of everything fairly close is all that matters. Actually my shaft continues to rotate slowly while tied to the float. And it will survive many reversals at high speed but it's not good for it. In an emergency just shift. Do some idle shifting at rest and observe what the shaft does.

I think ther'e is one point that I don't think is covered yet and that is one should (when reversing) bring the throttle idle and let the engine speed slow before shifting into neutral. The engine will (I think) slow the prop and shaft better than the water over the prop depending on what you're doing of course.

Marin · Dec 23, 2012

manyboats said:
Marin you don't have to wait for the prop shaft to comet a complete stop at all.

You don't have to but it will prolong the life of the transmission if you do. And since in the 14 years we've been running this boat we have yet to feel the need to get into any frantic shifting, pausing a few seconds in neutral before shifting to the opposite gear has never been a problem.

We've never found that things happen so fast in this kind of boating--- even when docking in strong winds--- that we've felt the need to frantically shift between forward and reverse. There has always been enough time to pause in neutral on the way through.

Actually my shaft continues to rotate slowly while tied to the float.

Ours don't.

Do some idle shifting at rest and observe what the shaft does.

Ummm...... that's what we did. As i said, it takes about 2 seconds for our shafts to stop rotating when they are turning at idle rpm.

...one should (when reversing) bring the throttle idle and let the engine speed slow before shifting into neutral. The engine will (I think) slow the prop and shaft better than the water over the prop depending on what you're doing of course.

That is what we do. We NEVER shift a transmission either into or out of neutral unless the engine it's attached to is at idle rpm. The BW Velvet Drive manual says to never shift at an rpm higher than 1,000 but common sense and knowing how this transmission is constructed says the slower the transmission is turning when it's shifted the better.

The other thing that's bad for it is "easing" it into gear. Slamming it suddenly into gear is bad, too, so the way the proper technique was described to me was a "positive, firm movement of the shift lever from neutral all the way forward or back."

bfloyd4445 · Dec 23, 2012

RickB said:
The first marine application was in 1903, about 20 years prior to the first rail application.

really. They had......and why not. Back then all heavy trucking in the USA was done by electric trucks.

Thanks Rick

Merry christmas!!

Britt

RickB · Dec 23, 2012

There were electric road and rail vehicles and a couple of little electric boats but there weren't any diesel-electric boats until 1903 and there weren't any diesel-electric trains until about 20 years later.

bfloyd4445 · Dec 23, 2012

RickB said:
There were electric road and rail vehicles and a couple of little electric boats but there weren't any diesel-electric boats until 1903 and there weren't any diesel-electric trains until about 20 years later.

so looks like maybe we done gone full circle?

Marin · Dec 23, 2012

bfloyd4445 said:
Back then all heavy trucking in the USA was done by electric trucks.

Don't think so. The power and range of electric technology for vehicles was very limiting, particularly back then. When forklifts started appearing in, IIRC, 1927, they were electric powered as were a number of cars.

But look up the history of electric vehicles and while there were a lot of example in the first decade or so in this country, the "craze" had died out by about 1920 and I think you'll find that trucks, at least not the larger ones, were never part of it in any significant numbers. The trucks used in large numbers in WWI were gasoline powered, for example.

Here's a little movie showing some examples of trucking in the first part of the 20th century. Nary an electric powered truck among them.

SomeSailor · Dec 24, 2012

They didn't have lithium polymer / lithium ion battery, AC brush-less motors, or high frequency current controllers back then either.

It's more about money these days. It would be very easy to build a hybrid boat these days (especially a trawler). Assuming your pockets were deep enough.

RickB · Dec 24, 2012

bfloyd4445 said:
so looks like maybe we done gone full circle?

No, but some folks are going around in circles.

Gas v/s diesel for trawlers

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