View Full Version : going astern question
05-15-2002, 07:52 AM
***********no wooden boat disclaimer**************
writer of the following does not own a wooden boat, he owns a steel one.
I have a little problem when going astern in my 28ft long-keeled sailboat. After a few metres the nose veers of to port FAST, resulting in an elegant pirouette. Needless to say, this has made for some interesting harbour manouvres. The rudder is totally useless at this point. The only way out of it is going forward, and backing up again.
The prop is a three-bladed right turning one, the engine is a 1957 Mercedes 40Hp.
The boat will be pulled in the next week for the first time since I bought it, so I can examine everything more closely.
My question is: how can the boat turn against the wheel-effect of the prop?
To give you an idea of the boat, an old picture (with the old twin-bladed prop which the previous owner replaced).
Sorry about asking this on a wooden boat forum, but you guys seem the most sane lot around on the internet.
[ 05-15-2002, 09:54 AM: Message edited by: barteld ]
05-15-2002, 07:59 AM
<you guys seem the most sane lot around on the internet.>
Sorry I cant help with the problem, but I LOVE the comment!
05-15-2002, 08:10 AM
Long keeled boats are almost completely unpredictable when moving astern. The rudder is wholly useless.
The only predictable thing is that, if there is a wind blowing, the boat will put her stern into the wind, because the bows will "feather" downwind as the boat "hangs" on the prop like a sea anchor.
This technique was actually used as a heavy weather tactic by some steamships early in the last century, and I have known it done by a Japanese containership in the North Pacific in the 1980's.
This may be what is happening.
[ 05-15-2002, 09:12 AM: Message edited by: Andrew Craig-Bennett ]
05-15-2002, 08:30 AM
I had the same problem with no wind to speak of. BTW. my mate had the same problem, so it's not person related.
05-15-2002, 08:44 AM
I'm reading this book on seamanship, and it explains this a little bit. I don't have it with me, here it is from memory:
I think it has something to do with the rotation of the prop causing it to pull to one side or the other, depending on direction of rotation.
Also, going ahead under power gives prop wash over the rudder, while there is not much water passing over the rudder in reverse.
Anyhow, I'm not sure whether I did it justice, but I'll look it up again to see if they mention a solution (I'm guessing that would be more help than just pointing out the problem)
05-15-2002, 08:52 AM
That's just the part I don't get. If it were the wheel-effect (sorry, don't know if this is the right translation), the nose should veer of to starboard, not to port. The nose does go to startboard if, while going forward, I go into reverse to stop the boat. :confused:
I think it may be a gremlin in the engine.
05-15-2002, 08:54 AM
sorry, no one on this forum seems to know much about steel boats. Why not cover it with wood veneer and then I betcha you would (wood) get a good answer...
05-15-2002, 09:12 AM
Now ain't it funny, just got of the phone with my dad, and his folkboat has EXACTLY the same problem. Can you figure the coïncidence? ;)
Any chance of helping my old man?
The veneer doesn't sound too bad, but the purist in me says that an honest heap of rust should stay an honest heap of rust.
05-15-2002, 10:15 AM
Interesting problem! I have absolutely no experience with this sort of problem but do have two questions (the question part is easy!):
Has this boat always done this or is the problem recent?
Have you tried putting the engine in neutral after you're moving? I wonder if the boat behaves the same way when "coasting".
Barteld...it's called "prop walk" Check these websites for more info than I've snipped:
The design of a propeller is such that the thrust it produces does not flow in a perfect straight line for all sorts of reasons too complicated to describe here. As a result the effect that the propeller produces has a tendency to induce a slightly curved course. This can be counteracted by the tiller or wheel and when driving ahead (forward) its effect is only slight.
However when driving astern (backwards) the propeller effect is more pronounced and single screw vessels will have a marked tendency to only turn in one direction with much certainty.
= = = = =
I can't control my boat in reverse! Is there anything
I can do about this?
Prop walk is also referred to as torque (which is gyroscopic precession). It is one of those facts of life that a C-34 is going to "back to port" (like all single engine boats with a right handed prop). The most important thing is to know it is going to happen and factor it into your maneuvering (Ron Hill).
Some of the problem may be corrected by technique. Inboard boats tend to crab to port when backed. The problem is that you have no steerage until there is water flow over the rudder. The worst condition is at idle, because the prop is crabbing and there is little or no flow over the rudder to establish steerage. The technique that I have found to work best is to accelerate fast (near full throttle) in reverse (i.e. put it in gear and throttle up quickly), until good reward motion is attained, then quickly back off on the throttle and shift the trans to neutral. The forceful reverse action gets the boat moving before severe crabbing affects it. Stopping the prop eliminates the crabbing tendency and water flow over the rudder provides steerage. The momentum will continue to carry the boat in reverse, and positive steerage with the rudder is regained. It takes a little practice, but I find that this technique is the best way to back with as little crabbing as possible and you can even turn to starboard. Just make sure you are clear behind before starting this procedure (Jack Conway).
A three-bladed prop does wonders for reverse control. In my C34, equipped with the stock 2-bladed prop, backing up was out of the question -- even with adequate power, there was not possibility of backing straight. I just installed a three-bladed 15 x 10, and it's a revelation -- straight as an arrow in reverse. Note, though, that all bets are off if the prop gets fouled by barnacles... by the end of the season I was worse off than ever in reverse (Bryan Pfaffenberger)
= = = = =
An inboard engine propeller usually turns clockwise (viewed from astern) and is said to be "right hand", or RHP. In forward gear, with the rudder straight, propeller "crawl" 1 (a weak force) exerted to starboard together with propeller "wash" or "push" (a stronger force) against port causes the stern to move to starboard; in reverse gear the action is the opposite and the stern moves to port. This is "prop walk". The effect is greater in reverse than in forward, and greater in sailboats because of the deeper draft, very large rudder, and other factors. The greater the angle of rudder turn, the greater the presented surface for prop wash, the greater the pressure, the greater the resultant effect.
= = = = =
Asymmetric propeller thrust — The thrust of a propeller is often asymmetric, especially in reverse gear. This is for reasons of inclined propeller shafts, and corkscrewing propeller discharge currents, and other factors which we shall reserve for another forum. Suffice it to say that, while the effect is almost absent in some boats, in others it can be almost overpowering — some will not back in a straight line, because of asymmetric thrust, under any conditions.
The majority of propellers are ‘right-hand’, meaning that they turn clockwise, looking forward, when in forward gear. These right-hand propellers ‘walk’ the stern to port, in reverse gear. At least if you understand how your boat handles, you are less likely to do anything foolish. Furthermore, the asymmetric effect can sometimes even be made to work for you, such as when wanting to swing the stern to port.
Reverse Coasting — The obvious way to get around asymmetrical propeller thrust is not to use the propeller. However, unless you want to sail the boat backwards (some boats can!), or paddle it, or pole it like a Venetian gondola, you’re probably going to need to use power. The key, then, is to minimize using reverse gear — use it very gently, and for the minimum time necessary to produce or to sustain sternway. True, you need enough speed through the water to allow the rudder to steer (unless you have an I/O), but the rudder has more of a fighting chance if it isn’t required to overcome asymmetric propeller thrust.
‘Prop walk’ aside, the hull itself, even if it tracks poorly when going astern, may be more docile when going very slowly, disturbing less water and so experiencing fewer adverse hydrodynamic effects in return.
05-15-2002, 10:51 AM
What you're dealing with is a combination of three, at least, elements: Full Keel, Prop-walk and adaquate flow past the prop and rudder,when in reverse. Your problem has nothing to do with the engine.
At low hull speeds the prop will act more like a paddle-wheel and is pulling the stern to port. Initially, the whole boat will want to slide to port because of the full keel and then it will pivot, clockwise. Since fixed-pitch props are designed to be most efficient in forward, they are notoriously inefficient in reverse so it takes a long time to accelerate and get adaquate water flow past the rudder.
My boat has a left-turning prop and displays the same characteristics as yours, but in the opposite direction.
There is one, very expensive, way of improving the situation and that is a full-feathering prop, such as Max-Prop, Luke, and Autoprop which are as efficient in reverse as in forward. The trouble is, they start at about US$1,800 and you'll find they won't fit in your prop aperture.
Don't change anything until you've had a chance to practice using those characteristics to your advantage. You will find that your docking procedures will be different, depending on which side you're on. Practice with a few buoys, away from the dock. You'll get the hang of it. It isn't hard, but it will take a lot of practice. The first few times, you'll appreciate the steel hull, however.
Don't forget that prop-walk never goes away, not even in forward at hull-speed. You'd hope that you could pick a compass heading and get to your destination. That won't happen! The right-turning prop will pull the boat as much at 15 degrees to starboard.
Congratulations on your new boat, even if it is made of the wrong stuff.
05-15-2002, 11:07 AM
I had similar problems with my 29-footer, always backing out of my slip. I practised backing all over the harbor, and could drive that boat as well backwards as forwards, even in figure eights. But trying to back out of the slip was always a circus.
I switched to a three balde, which improved things a bit, but mostly gave me better 'brakes', something I never had with the two blade (that's another story).
On advice from a guy with more experience than me in long keelboats, he said to use more power in reverse. I had been trying to inch the boat out of the slip, letting the engine idle in reverse. This guy recommended hitting reverse and a full-throttle burst for a few seconds, then neutral as soon as the boat started to move. This gets the boat moving, and the rudder can work (backwards) to direct the boat while you coast out. After trying his technique, it proved to be the answer...more power, not less! But only until the boat starts to move backwards.
There will be a place where the rudder can be placed to back most boats straight under power. On my boat, the tiller had to be offset about five degrees to make the boat back straight in gear, once you got the thing moving, and in the right direction. It takes a lot less rudder to affect the boat in reverse than in forward, coasting or under power.
As said above, all bets are off in any sort of wind. There are some sailboats that simply won't back worth a damn. And backing from a dead stop is a lot different than driving the boat backwards around the mooring field under power. Still, it's good practise, like for setting an anchor or impressing the dock crowd by backing out of your fairway a few hundred yards--Something I did more than a few times, as the bow of the boat got away from me and I had to back all the way out of the place.
If all else fails, you can always simply warp the boat out of the slip, or give it a big push and hop aboard at the last second....both tecniques I employed even after learning to back under most conditions.
05-15-2002, 11:18 AM
I have an 18' inboard power boat. She's powered by a small Perkins which is left handed. The boat very noticably backs to starboard. So much so that the rudder has very little effect even with some sternway on. Granted, I don't have a full keel, which I'm sure changes things. But my point is, why fight it? Use it to your advantage. If you really need back in a straight line, why not just turn around and go forward. ;) Seriously though, putting my boat in reverse and using the prop wash to pull the stern to starboard and using forward to check rearward movement, I can just about turn her in her own length. Some of my fishing buddies with outboards or I/O's have a hard time believing it. Of course it only works that well in one direction. I try to plan ahead to pull up to a dock the way the boat likes to turn. Obviously, that can't always be done. That's my 2 cents.
David Tabor (sailordave)
05-15-2002, 11:56 AM
A couple of comments. The INITIAL question said the BOW swings to port yet several folks have commented that prop walk on a RH prop will swing the STERN to port. That doesn't explain things. I think what is more likely is the prop is a LEFT HAND prop in which case the movement of the bow to port under reverse is correct. And the stern will move to STBD. This is the case on one boat I regularly sail. I use this to great affect when coming into the slip as I tie up on STBD.
Second, prop walk is more pronounced in any boat the steeper the angle the shaft is from horizontal. Has to do with the angle the blade makes at the top of the rotation v. the bottom of the rotation. Others can be more articulate on this than I.
Third, I saw a reply about using fwd and reverse to turn about in a small radius albeit only in one direction, using the walk. It's called backing and filling. What you do is put your helm hard over to take advantage of the prop walk on that course (RH prop turns boat to left going fwd so hard left helm) then in reverse use full throttle just long enough to get boat moving in reverse, go fwd on throttle when boat starts to react to the rudder instead of the prop walk. Repeat as necessary! You can spin that sucker even if it is a full long keel. Been there, Done that, Got the T-shirt!
Last, speaking of rudders; NEVER let the wheel/tiller go free when going astern. If you have enough way on the rudder will be slammed against the rudder stops and can break the rudder stock or rudder, not a pleasant thing.
When you have the boat hauled let us know what direction prop really is on the boat.
Also, even though you said wind was not a factor, wind and too an even greater degree CURRENT will affect your handling characteristics.... Keep us posted. D
05-15-2002, 01:29 PM
Good question and some good advice. I spend a lot of time going in reverse (literally and figuratively). I keep my boat at a marina whose owner insists that all boats, sail and power, moor stern-to. So I have to back into my tight slip in all kinds of conditions. I have a 30 foot full keel boat with absolutely no steerage in reverse.
My rudder alone will have no effect while the engine is in reverse. What I do is this: when I need to turn around in a tight space, I do the back and fill routine. I can turn my boat in one boat length that way. Most people watching can't believe it. But because my propwash pushes my stern to starboard, I can only do it if I'm turning the bow to port. You need to maneuver the boat in forward to a position where you can use the propwash to your advantage.
When backing into a tight space like a slip, here's what I do. First, I come to a complete stop. Then I run the engine at low throtle in reverse until I just barely have sternweigh on. Then I put it in neutral. If I need to change the direction of the stern, then I use the rudder and throttle in tandem by giving the throttle a very quick and sharp move in forward with the rudder hard in the opposite direction that I want the stern to move. The propwash against the rudder will move the stern to port or starboard, depending on where you have the helm. That way, the stern changes course, but the boat still has some sternweigh. If you run out of sternweigh, just give some very gentle throttle in reverse until you are moving. To stop the boat, a quick shot of forward throttle will do the trick.
The key to getting it right is to go very, very, very slowly. Unlike the fin-keeled boats, you can't come in fast with steerage.
05-15-2002, 02:49 PM
Lot's of great stuff from Donn, Mike, Scott, which I won't repeat.
One more advantage to prop walk is the assist it can sometimes give you when you are docking your boat in a cross wind. You can use that prop walk to advantage when you dock portside-to as it will help keep the bow from being blown off as you finish the maneuver and back down to take way off the boat (assuming that's how you dock). Ceol Mor's wheel goes the other way, so I often try to dock starboardside-to, to get this assist.
I just put a 2-blade MaxProp on her, so I'll probably have to learn all over again. Not that I mind smile.gif
One last note, since you are tiller steered. If you never get up much speed in reverse, this isn't an issue, but beware of losing control of the tiller as your speed increases in reverse. That rudder will want to take control and go to full over if it can, and the forces involved go up as a higher function (between squared and cubed) as boat speed rises. I near as nothing got flung right out of a tiller-steered boat (38') years ago when I didn't pay enough attention.
05-15-2002, 04:19 PM
Well as someone else remarked, the problem is that the opposite to what should be happening is happening. So we either dispute what we're being told about it being a right hand prop or accept another reason.
The boat is cut away forward( like mine)with a full keel and a keel hung rudder. From my experience, yes I can use the propwash to manouvre the boat, but this is easily overridden by a bit of a breeze. Windage on the rig combined with the cut away forefoot.About the only thing I can rely on in reverse is that if there is some wind, the boat will hunt up stern to into it.And then it will hang there ( as Andrew says).
Is it possible that each time you have tried to reverse that the wind has been off your Starboard side?
I think you have to accept it and learn to exploit it ( as Scott says)I don't think that there is a fix for that rudder /keel design.
Alan D. Hyde
05-15-2002, 04:24 PM
As a boy, I saw a man steer by throwing out a bucket tied to a long line, and then pulling the bucket toward him...
05-15-2002, 04:25 PM
Heh. Say what you will about a steel boat, but I'll be all he has to do is go down and dust the bilge area once a year.
05-15-2002, 04:36 PM
Not much direct experience but I have seen the effect worked to an advantage on US Navy Utility Boats, where the boats were maneuvered "sideways" away from the pier with the rudder cranked full over, by reverse prop walking and forward steering. Youl'd swear they had bow thrusters.
05-15-2002, 07:35 PM
A gentleman not only doesn't sail to weather, but he doesn't back down in a a classic sailboat if he can possibly help it. tongue.gif
05-15-2002, 07:48 PM
Sad to say, there really isn't a solution. I've known this for many years, and take enormous care when backing FII out of a slip, sometimes even just backing out altogether rather than trying to manoeuver to go out forwards. Once you put the helm over any more than a few degrees, the rudder simply acts as a brake - steerage goes out the window. Put wind into the picture and you're hooped.
Capt. Mike, who manages a fleet of (plastic) charter boats, most with fin keels and skeg rudders, kept insinuating it was simply my lack of expertise. So we went for a drive, and he spent over an hour trying to back the boat around at the top end of the harbor where its slack water and no wind, and couldn't make it work at all.
Now he gets ME to teach his members how to handle the three boats in the fleet
Don't worry - slow and easy does it. Just don't expect any immediate or dramatic reaction to the helm.
Any wouldn't you rather have a full keel for seakindliness (is that a word?) and tracking?
05-15-2002, 11:29 PM
This is one of the reasons I love this forum. This is all great education for me. I watched a guy who runs a marina down past Houston spin one of their boats (a 40 or 42-footer) in not much more than its own length. I always wondered how in the heck he managed it ... now I have some idea!
05-16-2002, 08:00 AM
I learned how to deal with that on my european canal boat vacations. The canal boats are deep, long and heavy and underpowered, 40 or 50 horsepower, so they are similar I would think to driving a sailboat under power.
I picked this up watching the professional guys.
The trick is, you do all your steering using forward bursts, even when you are going backward. This was referred to above I think as "back and fill." You get your vessel moving backward, and then you can nudge the stern in the direction you want by turning the rudder the opposite direction and giving a burst of forward throttle. Your momentum keeps you going backward, but that burst of water hitting and deflecting off the rudder acs like a thruster.
The most important thing is not to "drive" the boat. You cannot steer the boat backward in the conventional sense. You cannot leave it in gear and think it will follow your steering. Instead, think of it like docking a spacecraft, you use your momentum and little bursts of thrust. Get going backward, nudge the stern in the direction you want, then a burst of reverse, then correct. Its fun when you get the hang of it,and you can turn a big single screw in is own length, which does impress the onlookers.
05-16-2002, 08:37 AM
If you really need backing control...maybe a bow thruster would be an option. On a steel hull it would be an easy installation.
I was looking around a local boat yard on the weekend and it was full of boats getting ready for the season .A good third of the boats (of all different sizes) had bow thrusters.
[ 05-16-2002, 09:46 AM: Message edited by: JJoohhnn ]
05-16-2002, 04:42 PM
Thanks for all the replies. This boat has done it all the time I had it (but that's only a month or 8). The thing I still don't get is that it goes in exactly the opposite direction of the one you would expect when you just account for prop-walk (what we call the weel-effect). I will be sailing again this saturday, and probably test a bit more.
I have learnt that hitting the throttle hard in reverse makes for better steerability. Thanks for confiming that. I will try steering in reverse by forwarding a little bit (thanks PatCox).
Anyhow, when motoring through the city of Utrecht the prop hit a bicycle or something, and since then vibrates a lot more. So the prop will have to be checked and fixed anyway. I will check for any misalignment then. (By the way if you're ever in Holland, the trip through Utrecht is fun, takes you right through the hart of the old city, going under bridges build in the 1600's of about fifty meters long and just narrow enough for one boat)
Another interesting story I heard just this week: Old Dutch fishing boats were built in pairs, one with a right, the other with a left turning prop. This to makes it easier dragging nets between them.
A bow thruster would be an option, but the purist in me just went of to the bar after reading the suggestion.
Will keep you posted, going to dust out my bilge now.
[ 05-16-2002, 05:48 PM: Message edited by: Barteld ]
05-17-2002, 06:05 PM
Barteld, a quick add-on to all of the above, before engaging astern drive, try and reverse the rudder to counter the propwalk 25-30 degrees or so, then loads of power before you ease off and chugg astern. A lot depends on the surface area of your rudder. If you look at the rudder on the inland waterway barges in Europe you will see what I mean!
01-08-2004, 04:37 PM
Sorry for resurecting this old thread, but I thought I should share some of the things I've leaned in the last few years (including that my boat fits EXACTLY sideways in one of the most busy locks in Holland).
No, I haven't solved it. Whenever possible I simply avoid going more then a few metres astern. I've become quite good at turning it whithin a boat's lenght. Also I've learned that a lot of power in short bursts helps.
I've seen a lot of people in similar boats having the same problems, so I've resolved to learn to live with it.
And finally, I sailed an old dutch iron (no not steel) barge of 25m (75ft), and after that my boat seesm to be a small little dinghy, and a whizz to manouvre.
[ 01-08-2004, 05:38 PM: Message edited by: Barteld ]
01-08-2004, 04:51 PM
It was very nice to hear a follow up on this. So often advice is given and then no feedback returns to let one know if it worked.
Have a picture sideways in the lock? smile.gif
01-08-2004, 04:57 PM
....... going in astern...... yep ..... definately my favorite........
01-08-2004, 05:03 PM
My RH drive,long-keeler swings its stern to port while moving in reverse. But when going forward, and then shifted into reverse, it swings the bow to port, which I use to maneuver in tight spaces. Sounds like this is a case of doing something similar at a standing stop.
01-08-2004, 05:30 PM
well, odd as it may seem, when you're sideways in a lock the first thing you think about isn't your camera. This wasn't even my major goof. That was setting out to sea for the first time with a hangover, and getting into nasty wheater just before one of the nasty ports of Holland (ijmuiden). Then we came to the conclusion we didn't know how the backlight of the GPS worked, our main ligthing didn't work (the backup however did). It's quite scary to be out at sea alone at night in a force six with current against wind. Just steer between the green and the red light. Ah well, learned al lot that day. We didn't feel (and in retrospect weren't) in any danger, but it were a few exciting hours.
btw have got a shot of my boat on the shore (sorry, a tad big, will decrease in the morning). She may not be the most beatiful boat out there, but I've grown to like the sad eyed windows and her sturdiness.
01-08-2004, 05:33 PM
Suddenly, I like steel boats! :cool:
01-08-2004, 06:21 PM
Thanks High C. I've grown up around woodys's. My father mostly had wooden boats. So it's a bit of a blasphemy for me to have a steel boat. anyway. I like it.
01-09-2004, 12:20 AM
Hullo. Until about a year ago I had a 52' steel boat. (The fact that its steel is irrelevant of course, wooden boats behave the same, in fact its only fin keeled flat bottomed plastic boats that you can back around like a car) Anyway, mine of course had prop walk and no steering to speak of in reverse. But its not a problem, any more than leaning over when you hoist a sail is a problem. Its just how it works. Learn to work with it. You can use it to pull up about a yard from a wharf or whatever, then just slide in sideways with a bit of forward and backward thrusting. As someone else noted, you can learn to reverse fairly straight (plenty of throttle, no pussyfooting) and plonk it in forward for a moment to kick the stern one way or tother to steer. Just learn to use it.
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