Walking a twin-screw boat sideways

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ranger58sb

ranger58sb

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Joined
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Ranger
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58' Sedan Bridge
Art said:
Regarding Steering a Twin Screw:

To properly know how to handle a forward or reverse moving twin screw boat without using helm-wheel steering, via alternating engines’ rpm and shift positions only, it simply takes experience/practice.

In difference to single screw (although with a single screw bow and stern thrusters play well at very slow speeds - i.e. docking, near standstill) twin screw can be maneuvered quite well in forward or reverse via engines alone at nearly any speed... without using helm-wheel steering... as long as rudders are maintained in straight position during the forward or reverse travel. Rudders, as well as per engine alternate rpm and shift positions do come into play on twins when moving boat directly sideways from a standstill, while not trying to simultaneously attempt forward or reverse travel – see #3.

1. At higher speeds the rpm allowed per each engine can alter course as needed as well as maintain the course needed... even for long periods of forward travel if necessary.
2. At very low rpm (docking, slow canal travel and the like) carefully actuated per engine shift positions in coordination with their rpm can keep boat placed where desired or maneuvered into positions desired.
3. For making a standstill twin screw boat to move directly sideways to starboard or port (without thrusters)... the following works well:

“Directly-Sideways” Movement/Handling of Twin Screw Boat

Move boat sideways to port (opposite items for starboard)

- Turn rudders 80% +/- to starboard
- Place starboard in forward and port in reverse
- Starboard kept at idle rpm / Port approx 150 rpm higher

Once rudders in position with engines in the correct gear at idle rpm quickly adjust direction desired engine rpm - higher equivalent rpm for both engines with same %age difference = faster sideways motion – to a point – it can get hairy, go slow! Correction can become a bitch if boat gets moving sideways at too quick a speed... especially in close quarters! Also, depending on rudder size and prop size the numbers mentioned may need to be adjusted. However, the general mechanical/physics properties of thrust and water flow remain the same for described sideways travel.

Take it slow: Gently move a boat laterally. Be careful to not get boat moving too quickly as stopping sideways motion takes considerably more rpm, shift, and steerage adjustment time than simply forward or reverse or circular rotation motion adjustments. Adjust rudder and shift/throttle controls as needed for current and wind conditions to move latterly away from dock. Practice makes perfect. I recommend practice in a completely open area... at least at first!
Click to expand...


Thanks for posting this (in another thread), but I have to admit our results aren't yet promising. Perhaps I just wasn't able to overcome the wind, when I was trying it...

I do assume "turn rudders ... to starboard" means putting the wheel to starboard... which would in turn cause a turn to starboard if going ahead...

-Chris
 
Lock the wheel over to the opposite direction you wish to move the boat. This method even works even on my 36' Nova with a 4' keel and lots of windage.
 
Don't expect to overcome much wind or current. This will vary from boat to boat, and is related to the amount of rudder exposed to your prop wash.

You are using prop wash on the rudder from the engine in forward to push the stern over, and this sideways force must be greater than the sideways force created by the engine in reverse walking the stern in the opposite direction. With the amount of throttle roughly balanced, if your rudders are too small,or not "hard over", that driving force will not be enough, and when you increase power on that side, you will have an excess of forward motion,that will need to be counteracted with additional reverse on the other side.

It is a sometimes tough balancing act, which is always easier in calm conditions.

When you get practiced, folks on the dock will look for your "thrusters" and will wonder out loud why your thrusters don't make the usual rude growling noises they have become used to hearing.
 
If you really want to walk a bigger twin perfectly sideways with negligible fore or aft movement, get a bow thruster. With big winds and currents it really helps.
 
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sunchaser said:
If you really want to walk a bigger twin perfectly sideways with negligible fore or aft movement, get a bow thruster. With big winds and currents it really helps.
Click to expand...
:iagree:
 
koliver said:
Don't expect to overcome much wind or current. This will vary from boat to boat, and is related to the amount of rudder exposed to your prop wash.

You are using prop wash on the rudder from the engine in forward to push the stern over, and this sideways force must be greater than the sideways force created by the engine in reverse walking the stern in the opposite direction. With the amount of throttle roughly balanced, if your rudders are too small,or not "hard over", that driving force will not be enough, and when you increase power on that side, you will have an excess of forward motion,that will need to be counteracted with additional reverse on the other side.

It is a sometimes tough balancing act, which is always easier in calm conditions.

When you get practiced, folks on the dock will look for your "thrusters" and will wonder out loud why your thrusters don't make the usual rude growling noises they have become used to hearing.
Click to expand...


Yeah, I've always understood the theory... but I suspect we've usually bailed early when it didn't seem to work and just used a spring line to warp in...

And we've got small-ish rudders, at least in the grand scheme of things.

Yesterday I decided to really practice, but the situation was windy... so I'll just have to wait for another opportunity...

Certainly a thruster -- or two -- wouldn't be turned down, but oddly enough, I don't see a line of folks queuing up to pay for that :)

-Chris
 
This system definetly does work ..... on some boats !
Hull form, including keel length and depth, propeller pitch, rudder size, maximum rudder angle all make a difference. Throw in some windage, wind and current and it complicates matters quickly.
 
I used to walk our 24' express cruiser sideways, involved a lot of wheel spinning & shifting.
 
If I got a thruster I wouldn't be able to face the "old salts" in our club who say: "thrusters are for people who can't handle a boat."
 
ancora said:
If I got a thruster I wouldn't be able to face the "old salts" in our club who say: "thrusters are for people who can't handle a boat."
Click to expand...

I've never been one to try and impress others..... To each his own though.
 
Like others have said, different boats react to this differently. I've been able to do this a couple of times facing into the current and not fighting too much crosswind. Remove the head current or add a bit of crosswind and all bets are off.
 
ancora said:
If I got a thruster I wouldn't be able to face the "old salts" in our club who say: "thrusters are for people who can't handle a boat."
Click to expand...

Tell the old codgers to go pound sand... they probably once said the same thing about that newfangled black box that gives position from space.

The thing that counts is that you know your boat and are proficient docking... using any tools at hand. I used to bring Volunteer in without using the bow thruster when the conditions were right and the Admiral was not aboard.. she considered it stupid not to use it as it made for a higher percentage of successful landings ( and I didnt want to suffer the harassment of the quiet smirk she gives as I backed out for a missed approach ).

Our new Ocean Alexander is a single and doesn't have a thruster, I figured I would install one this spring but as time goes by I find the boat handles great without one. So far in the thirty or so dockings since August I am 30/30... somewhere there is a major bungled landing waiting to bust my bubble.

HOLLYWOOD
 
ancora said:
If I got a thruster I wouldn't be able to face the "old salts" in our club who say: "thrusters are for people who can't handle a boat."
Click to expand...

:thumb: :dance: :lol:
 
Usually some fwd momentum helps. For a flank (walk) to port, come in slow with a little bit of fwd creep, turn the helm hard to STBD. as the turn starts to STBD, back the port engine and leave the stbd engine in fwd. It takes practice and there is a balancing act of helm and clutches. BE Patient! give the vsl time to react. YMMV
 
I'm glad to hear it's probably a sometime thing.

I've been occasionally trying movements like this since about 2000 after we moved from our single diesel (with no thruster)... in two different twin screw boats... with underwhelming results.

We've always had better results using a spring line...

-Chris
 
ranger42c said:
I'm glad to hear it's probably a sometime thing.

I've been occasionally trying movements like this since about 2000 after we moved from our single diesel (with no thruster)... in two different twin screw boats... with underwhelming results.

We've always had better results using a spring line...

-Chris
Click to expand...

Spring lines can be a boater's best friend in many docking maneuvers!

But, as you can see by posts on this thread from different boaters... a twin screw boat can be made to walk sideways. Every boat's handling qualities are different in various situations, and, a pilot's ways of utilizing each boat's handling qualities are very individual too. As well... current and wind conditions nearly always play a part in what can be accomplished in boat handling maneuvers. As has been mentioned... calm conditions are best for utilizing a twin screw's sideways walking capabilities.

My recommendation is go to a calm location with plenty open space and practice, practice, practice. I bet you will find what rudder positions and per engine rpm work best for you and your boat to move sideways, in either direction. It's not rocket science, just assertive boat piloting!

Good Luck! :thumb:
 
Art said:

My recommendation is go to a calm location with plenty open space and practice, practice, practice. I bet you will find what rudder positions and per engine rpm work best for you and your boat to move sideways, in either direction. It's not rocket science, just assertive boat piloting!

Good Luck! :thumb:
Click to expand...


Heh... not like I haven't done that practice thing. For 20 years or so, several straight shaft boats. This one has simply eluded me. So far (maybe).

-Chris
 
ranger42c said:
Heh... not like I haven't done that practice thing. For 20 years or so, several straight shaft boats. This one has simply eluded me. So far (maybe).

-Chris
Click to expand...

Yo, ranger

I don't mean to imply that you haven't tried, although I wasn't aware of your 20 yrs successful efforts with other boats... until this post. :flowers:

It could be that location/size/configurations of your current boat's rudders, props, and keel (in combination with the boat's bottom shape – maybe??) might simply make it really difficult to move her sideways via twins. Perhaps bow, stern or a combination of thrusters is in order for your boat?? And, as you mentioned in earlier post - spring lines work well too!

My take on the lateral movement capabilities via twin screw apparatus adjustments is that the screws make it easier the wider apart they are located and rudders make it easier when they are reasonably large. :thumb:

Have you front, back, and side pictures of the running gear while boat is on the hard? :confused:
 
I just choose the "falling leaf" method. It does require you to manage your forward motion/way but it is simpler and seems more natural as I come from a single with bow thruster...which is pretty much what you have to do with a single/thruster set up.

Just approach the dock with a little bit of way and at a 45 degree angle. Use the "outter" engine(furthest from dock) to erase your way and thusly bring the bow away from the dock and the stern towards it. Some times that is all you need if you time it right and have the right amount of speed and the boat will go right up to the dock...sometimes at a slightly alarming rate. If that does not do it, then in and out of forward and reverse until you get the boat alongside....the boat will appear like a "falling leaf". Which engine you use is determined by how much movement you need in the bow or stern and if you need to put way on or take it off. I'm not sure i am making any sense here....hard to explain...easy on the boat though.

I think walking a twin sideways with consistent regularity is somewhat of a myth. Like people have said, the conditions have to be right.
 
Art said:
Yo, ranger

I don't mean to imply that you haven't tried, although I wasn't aware of your 20 yrs successful efforts with other boats... until this post. :flowers:

It could be that location/size/configurations of your current boat's rudders, props, and keel (in combination with the boat's bottom shape – maybe??) might simply make it really difficult to move her sideways via twins. Perhaps bow, stern or a combination of thrusters is in order for your boat?? And, as you mentioned in earlier post - spring lines work well too!

My take on the lateral movement capabilities via twin screw apparatus adjustments is that the screws make it easier the wider apart they are located and rudders make it easier when they are reasonably large. :thumb:

Have you front, back, and side pictures of the running gear while boat is on the hard? :confused:
Click to expand...


Didn't think to mention at first that I'm sort of an old phart :)

And looking back, it might be clearer if I had said by "this one" eluding me, I meant the lateral movement... not just on this boat.

I have pics, but I see this site doesn't do direct upload. In any case, it's just your standard sportfish deep-V configuration... that we putter around on at trawler speeds as often as possible... i.e., when sea states permit, with our hull form. Relatively small props, relatively tiny rudders, decently separated by 15' beam (at widest), with plenty of diesel torque.

FWIW, I've not been worried about not being able to move sideways. Lateral movement would be nifty, though, if I could (eventually) figure it out with no $$$ involved. In the meantime, we just whip out a spring line and get it done. Much cheaper than thrusters :)

-Chris
 
Baker said:
I just choose the "falling leaf" method. It does require you to manage your forward motion/way but it is simpler and seems more natural as I come from a single with bow thruster...which is pretty much what you have to do with a single/thruster set up.

Just approach the dock with a little bit of way and at a 45 degree angle. Use the "outter" engine(furthest from dock) to erase your way and thusly bring the bow away from the dock and the stern towards it. Some times that is all you need if you time it right and have the right amount of speed and the boat will go right up to the dock...sometimes at a slightly alarming rate. If that does not do it, then in and out of forward and reverse until you get the boat alongside....the boat will appear like a "falling leaf". Which engine you use is determined by how much movement you need in the bow or stern and if you need to put way on or take it off. I'm not sure i am making any sense here....hard to explain...easy on the boat though.

I think walking a twin sideways with consistent regularity is somewhat of a myth. Like people have said, the conditions have to be right.
Click to expand...


Well said. I can picture it perfectly. I do about the same, just approach the dock at a shallower angle...maybe 30 degrees. If I'm not fighting a wind off the dock, I normally just need to use the 'outer' engine to settle gently alongside the dock.
 
Baker said:
....the boat will appear like a "falling leaf". Which engine you use is determined by how much movement you need in the bow or stern and if you need to put way on or take it off. I'm not sure i am making any sense here....hard to explain...easy on the boat though.
Click to expand...


Yep, that's pretty much what we do... unless conditions warrant use of a spring line to warp alongside.

-Chris
 
Circumstance boaters may encounter... no matter experience or boat capabilities. :D

Some time ago, as usual piloting from our FB, I came to bow-enter our two finger slip in a fair current with more breeze/gusts than usual that were coming from an unusual direction. I made an error in judgment and decided to abort my first try (been years since I needed to fully abort – usually I can get her in even if it's not too pretty - way things were headed this time it could have created big problems). :eek:

We have a 14' 8" tow behind, four seat, 50 hp o/b runabout on short line as I dock... so... not making a clean entry on first try has its problems for direction change in addition to simply needing to start over again. BTW... I have a nice big air filled rubber nose on bow of our runabout so she can butt into transom creating no damage. :whistling:

Anyway, as usual my Admiral was on stbd side deck ready to step off onto our dock steps and fasten side ties. I yelled hold on we're going to try again (as I maneuvered away from collision danger) and she yelled back "What are you doing... you never do this!" :confused:

I turned our Tolly around and went back into position on the canal for getting into dock entry configuration. This time much better knowing how that day’s current and unusual direction wind were interacting. Came in pretty clean this time. The wind and current were a bear though and I did use a rubber corner post on one finger dock as fulcrum to work the boat straight into slip and still hold in position so stbd side came against finger so Admiral could simply step off to secure side ties. :popcorn:

IMHO... every journey or maneuver on a boat has its own set of abnormalities and being able to understand how to “go with the flow” is just part of the game. Cause after all, Pleasure Boating is in actuality nothing more or less than a Big Fun Game! :thumb:
 
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Baker said:
I just choose the "falling leaf" method.

Just approach the dock with a little bit of way and at a 45 degree angle. Use the "outter" engine(furthest from dock) to erase your way and thusly bring the bow away from the dock and the stern towards it. Some times that is all you need if you time it right and have the right amount of speed and the boat will go right up to the dock...sometimes at a slightly alarming rate. If that does not do it, then in and out of forward and reverse until you get the boat alongside....the boat will appear like a "falling leaf". Which engine you use is determined by how much movement you need in the bow or stern and if you need to put way on or take it off. I'm not sure i am making any sense here....hard to explain...easy on the boat though.

I think walking a twin sideways with consistent regularity is somewhat of a myth. Like people have said, the conditions have to be right.
Click to expand...

Good explanation. However, I think the "Sideways" explanation that many boaters refer to while docking a twin confuses a lot of new skippers. The few I've helped that were really having difficulty, failed to grasp the concept that when you are "prop walking" a twin engine boat, as you have explained above, you are really "pivoting" the boat by moving the stern left or right around a pivot point. And even fewer knew where that pivot point was on their boat. Most guessed it was the bow or midship. Once they discover the pivot point and understood the concept, you can see the light come on. :facepalm:

The pivot point on my boat is about 10 feet astern of the bow directly below the helm. I come into my slip a little shallower than you, probably closer to 25 or 30 degrees in neutral and then put the port engine in reverse to break the forward momentum, pushing the stern in and the bow out at the dock.
 
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