5 ms·

I'm not sure what configuration of props a ship like this has, but in my experience with a 40ft sailboat with a single propeller you have absolutely no rudder a

I'm not sure what configuration of props a ship like this has, but in my experience with a 40ft sailboat with a single propeller you have absolutely no rudder authority while reversing. I've read that some large ships also are direct drive--there's no transmission between the engine and the propeller, so "reversing" (if it's even possible) entails shutting down the engine and restarting it in reverse. This can be done with a two stroke engine. And yes, 8.5kt is not slow when you're displacing 100k tons, no correction will happen quickly.

culebron21 3y ago
This reminded me of an old physics book I read where author claimed that Titanic also lost rudder control and yawed because of full reverse.
- qingcharles 3y ago
  Titanic was a “triple screw steamer,” meaning it had three propellers - port, center and starboard. The port and starboard propellers were capable of being reversed, while the center propeller could only propel forward. You can see this in the 1997 movie as they show the props when they throw the ship into reverse. The center prop (that only goes forward) is the one directly behind the rudder, so the theory is partly that they lost some steering advantage when they lost the center prop.
supportengineer 3y ago
No variable-pitch propeller?
wlll 3y ago
> in my experience with a 40ft sailboat with a single propeller you have absolutely no rudder authority while reversing. In general it depends on the rudders and the boat. Longer keeled boats don't respond well in reverse at all but more modern boats (like mine, 1990) will do better but will still need some way to have steerage. I can certainly manouver around the marina in reverse, it's just harder than forwards and I need to be going a bit faster to get the control.
- rightbyte 3y ago
  Long keeled boats don't respond well going forward either, right? Compared to flater boats with a modern keel.
  - wlll 3y ago
    All I really know about long keels is from what people have said. They tend to track well and don't tend to make as much leeway, but perhaps at the expense of speed due to the wetted area, and they are hard to steer backwards. Not being particularly manouverable forwards isn't really an issue if you're spending several hours going mostly in a straight line. Modern flat boats (like the 2017 Dufour I learned on) are highly manouverable at slow speed, we practiced spinning the boat on the spot by using prop wash over the rudder forwards then ticking over in reverse. Could turn the boat in not much more space than the boat length, but may not track as well, may slam more, and make more leeway.
- mcv 3y ago
  Going backwards in the marina I often steer on the engine rather than the rudder (though I keep the rudder aligned with the engine of course). Obviously that's in a tiny sailing boat with an external engine, but I thought large ships also often have a steerable front propeller to assist with steering and mooring. Although maybe these very large ships use tugboats for that.
  - paddy_m 3y ago
    an outboard? that is very very different because you control the direction of thrust also.
  - wlll 3y ago
    My boat has an inboard diesel so no ability to direct the prop. It does have a bow thruster, but it's only really used at slow speed, usually right at the point of docking and undocking in tight spaces, once you get the boat moving in forward or reverse you don't need it. I have no idea about container ship sized boats, though I'd imagine a bow thruster of steerable prop might not be practical at that scale.
rightbyte 3y ago
> my experience with a 40ft sailboat with a single propeller you have absolutely no rudder authority while reversing. I have to protest here. Reversing and using the rudder on a 40ft boat works perfectly fine. I've done it on multiple sailing boats. You need to hold tight so that the rudder wont slap you if using a stick.
- jcgrillo 3y ago
  If you have enough way on to combat the prop walk, yes. But in a situation like backing down trying to come to a stop (at least in my boat, a 1962 Block Island 40) there's a very long "dead time" while transitioning from slowly moving forward to slowly moving in reverse where the rudder just doesn't do anything. The way I maneuver in these situations is to do all my heading corrections in forward gear, where prop wash over the rudder gives it authority. So it's a game of shots of reverse, corrections, rinse, repeat. EDIT: also planning ahead is important, because if I do it right the prop walk in reverse can be used advantageously. Also, with the BI-40's barn door rudder it'll slap you through the wheel if you're not careful. Almost broke my leg that way, not a lesson to forget.
  - rightbyte 3y ago
    Nice boat! Ye it does not look too nimble in harbours. Somewhere over 40ft with "light" boats is where I feel you get into the "you got one chance" harbour manouvers (unless there is some front sideways motor cheating). It happens something that I really can't explain, but I guess it is weight related. Or maybe area. Dunno.
    - jcgrillo 3y ago
      Yeah it's right around 20000lb displacement, so momentum is a real thing ;). The fiberglass is over 2" thick at the keel tapering to a mere 1" at the hull to deck joint. Decks are solid glass as well. At the time it was a newfangled material and they were scared of it so they used a lot. Also, the bow seems to catch the wind really hard so you can get spun around if it's blowing and you head off the wind too much without enough way on. Leave room, plan ahead, have a backup plan, etc.
BWStearns 3y ago
Since they were still moving forward while gunning it in reverse the rudder would still operate normally. They generally have bow thrusters too. I have no idea whether they could have been operational with the broader power/engine failures but if they were available I'm sure they were being used as well.
- jcgrillo 3y ago
  The question is what is the velocity of the water moving over the rudder? If forward velocity and the current due to a reversing prop cancel, then the rudder can't do anything.
esaym 3y ago
>entails shutting down the engine and restarting it in reverse. This can be done with a two stroke engine. Funny, I was starting a 2 stroke chainsaw a couple of years ago. I yanked the cord, it kicked back, pulling my arm back down but the saw started up and ran anyway. But it would not cut at all. I killed it and restarted it and noticed the chain going the other (right) way and it was now cutting fine. It has started in reverse the first time!
- jethro_tell 3y ago
  This is actually common for a 2 stroke type engine and used in things like gas golf carts and snow machines. The direction the engine is started is the direction it runs. So to accomplish this for propulsion, you'd add a reverse polarity switch for your starter and you're good to go.
  - gonzo 3y ago
    You can even get a (2-stroke) Detroit Diesel to run in reverse. You don’t want to do it very long, because they don’t make oil pressure in reverse.
    - jethro_tell 3y ago
      Yeah, in theory, there's not a lot about an engines running direction that matters, its all the stuff that's hooked up to it. As you start getting into more complex engines, where you have fuel injection, timed spark plugs, oil pumps, transmissions it becomes untenable, but not because a v6 can't run backwards but because you'd have to rebuild and time all the support systems.
      - jcgrillo 3y ago
        A low speed marine diesel like you'll find in a large container ship is not your granddaddy's 6V71. They are complicated, yet simple. They are indeed direct drive (possibly through a reduction gear) and they do indeed operate both in forward and in reverse. See e.g. [1]. [1] https://chiefengineerlog.com/2022/06/24/main-engine-fixed-pitch-propeller-reversing-explained https://chiefengineerlog.com/2022/06/24/main-engine-fixed-pi...
AYBABTME 3y ago
I docked in reverse multiple times, same as parking a car in reverse. Just need water flowing along the rudder (from motion, not prop wash), but otherwise it's a great way to turn into tight spaces. Gotta be careful about prop walk, which will dominate the controllability until some reverse speed is established. So until you've decelerated to 0 and re-accelerated in reverse, you don't have much control beyond prop walk.

culebron21 3y ago

This reminded me of an old physics book I read where author claimed that Titanic also lost rudder control and yawed because of full reverse.

qingcharles 3y ago
Titanic was a “triple screw steamer,” meaning it had three propellers - port, center and starboard. The port and starboard propellers were capable of being reversed, while the center propeller could only propel forward. You can see this in the 1997 movie as they show the props when they throw the ship into reverse. The center prop (that only goes forward) is the one directly behind the rudder, so the theory is partly that they lost some steering advantage when they lost the center prop.

supportengineer 3y ago

No variable-pitch propeller?

wlll 3y ago

> in my experience with a 40ft sailboat with a single propeller you have absolutely no rudder authority while reversing. In general it depends on the rudders and the boat. Longer keeled boats don't respond well in reverse at all but more modern boats (like mine, 1990) will do better but will still need some way to have steerage. I can certainly manouver around the marina in reverse, it's just harder than forwards and I need to be going a bit faster to get the control.

rightbyte 3y ago
Long keeled boats don't respond well going forward either, right? Compared to flater boats with a modern keel.
- wlll 3y ago
  All I really know about long keels is from what people have said. They tend to track well and don't tend to make as much leeway, but perhaps at the expense of speed due to the wetted area, and they are hard to steer backwards. Not being particularly manouverable forwards isn't really an issue if you're spending several hours going mostly in a straight line. Modern flat boats (like the 2017 Dufour I learned on) are highly manouverable at slow speed, we practiced spinning the boat on the spot by using prop wash over the rudder forwards then ticking over in reverse. Could turn the boat in not much more space than the boat length, but may not track as well, may slam more, and make more leeway.
mcv 3y ago
Going backwards in the marina I often steer on the engine rather than the rudder (though I keep the rudder aligned with the engine of course). Obviously that's in a tiny sailing boat with an external engine, but I thought large ships also often have a steerable front propeller to assist with steering and mooring. Although maybe these very large ships use tugboats for that.
- paddy_m 3y ago
  an outboard? that is very very different because you control the direction of thrust also.
- wlll 3y ago
  My boat has an inboard diesel so no ability to direct the prop. It does have a bow thruster, but it's only really used at slow speed, usually right at the point of docking and undocking in tight spaces, once you get the boat moving in forward or reverse you don't need it. I have no idea about container ship sized boats, though I'd imagine a bow thruster of steerable prop might not be practical at that scale.

rightbyte 3y ago

> my experience with a 40ft sailboat with a single propeller you have absolutely no rudder authority while reversing. I have to protest here. Reversing and using the rudder on a 40ft boat works perfectly fine. I've done it on multiple sailing boats. You need to hold tight so that the rudder wont slap you if using a stick.

jcgrillo 3y ago
If you have enough way on to combat the prop walk, yes. But in a situation like backing down trying to come to a stop (at least in my boat, a 1962 Block Island 40) there's a very long "dead time" while transitioning from slowly moving forward to slowly moving in reverse where the rudder just doesn't do anything. The way I maneuver in these situations is to do all my heading corrections in forward gear, where prop wash over the rudder gives it authority. So it's a game of shots of reverse, corrections, rinse, repeat. EDIT: also planning ahead is important, because if I do it right the prop walk in reverse can be used advantageously. Also, with the BI-40's barn door rudder it'll slap you through the wheel if you're not careful. Almost broke my leg that way, not a lesson to forget.
- rightbyte 3y ago
  Nice boat! Ye it does not look too nimble in harbours. Somewhere over 40ft with "light" boats is where I feel you get into the "you got one chance" harbour manouvers (unless there is some front sideways motor cheating). It happens something that I really can't explain, but I guess it is weight related. Or maybe area. Dunno.
  - jcgrillo 3y ago
    Yeah it's right around 20000lb displacement, so momentum is a real thing ;). The fiberglass is over 2" thick at the keel tapering to a mere 1" at the hull to deck joint. Decks are solid glass as well. At the time it was a newfangled material and they were scared of it so they used a lot. Also, the bow seems to catch the wind really hard so you can get spun around if it's blowing and you head off the wind too much without enough way on. Leave room, plan ahead, have a backup plan, etc.

BWStearns 3y ago

Since they were still moving forward while gunning it in reverse the rudder would still operate normally. They generally have bow thrusters too. I have no idea whether they could have been operational with the broader power/engine failures but if they were available I'm sure they were being used as well.

jcgrillo 3y ago
The question is what is the velocity of the water moving over the rudder? If forward velocity and the current due to a reversing prop cancel, then the rudder can't do anything.

esaym 3y ago

>entails shutting down the engine and restarting it in reverse. This can be done with a two stroke engine. Funny, I was starting a 2 stroke chainsaw a couple of years ago. I yanked the cord, it kicked back, pulling my arm back down but the saw started up and ran anyway. But it would not cut at all. I killed it and restarted it and noticed the chain going the other (right) way and it was now cutting fine. It has started in reverse the first time!

jethro_tell 3y ago
This is actually common for a 2 stroke type engine and used in things like gas golf carts and snow machines. The direction the engine is started is the direction it runs. So to accomplish this for propulsion, you'd add a reverse polarity switch for your starter and you're good to go.
- gonzo 3y ago
  You can even get a (2-stroke) Detroit Diesel to run in reverse. You don’t want to do it very long, because they don’t make oil pressure in reverse.
  - jethro_tell 3y ago
    Yeah, in theory, there's not a lot about an engines running direction that matters, its all the stuff that's hooked up to it. As you start getting into more complex engines, where you have fuel injection, timed spark plugs, oil pumps, transmissions it becomes untenable, but not because a v6 can't run backwards but because you'd have to rebuild and time all the support systems.
    - jcgrillo 3y ago
      A low speed marine diesel like you'll find in a large container ship is not your granddaddy's 6V71. They are complicated, yet simple. They are indeed direct drive (possibly through a reduction gear) and they do indeed operate both in forward and in reverse. See e.g. [1]. [1] https://chiefengineerlog.com/2022/06/24/main-engine-fixed-pitch-propeller-reversing-explained https://chiefengineerlog.com/2022/06/24/main-engine-fixed-pi...

AYBABTME 3y ago

I docked in reverse multiple times, same as parking a car in reverse. Just need water flowing along the rudder (from motion, not prop wash), but otherwise it's a great way to turn into tight spaces. Gotta be careful about prop walk, which will dominate the controllability until some reverse speed is established. So until you've decelerated to 0 and re-accelerated in reverse, you don't have much control beyond prop walk.