Long Keeler going astern

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Carronade

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I have a Colvic MS 31 (same hull as Atlanta 32) My boat is also fitted with bilge keels. The engine is a Thornycroft 90 1.5 ltr. diesel which generates 35 HP @3500 RPM. The prop is 17" X 11" The boat looses steerage going astern and is a nightmare in a marina. It's suggested that the rudder is too small? Rudder design is a complex subject adding another 10% to the length may or may not be the answer. Another point is that when moving ahead slowly the boat can be very skitish. Has any owner of these craft sorted the problem? Would be interested to hear if there is a solution!
 
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Carronade said:
I have a Colvic MS 31 (same hull as Atlanta 32) My boat is also fitted with bilge keels. The engine is a Thornycroft 90 1.5 ltr. diesel which generates 35 HP @3500 RPM. The prop is 17" X 11" The boat looses steerage going astern and is a knightmare in a marina. It's suggested that the rudder is too small? Rudder design is a complex subject adding another 10% to the length may or may not be the answer. Another point is that when moving ahead slowly the boat can be very skitish. Has any owner of these craft sorted the problem? Would be interested to hear if there is a solution!
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Photo of the underwater profile and rudder would help. Expect the rudder is a bit small and may want some balance forward of the pivot point. However, what you describe is typical behaviour of a shallow draft long keel. The rudder actually does very little in slow speed astern. You are more affected by prop walk and the difficulty of getting the long underwater body of the boat to deviate in the way you want it. Use of bursts of throttle to push the boat sideways followed by putting into neutral is one way of improving control.

I have seen all sorts of bits added to the rudder on this type of boat, so clearly a problem. In fact there is an article on exactly this subject in this months PBO.
 
Sophie19 said:
I have the same problem with my gaffer. Does a bucket really help? Can anyone explain how/why?
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When the boat goes astern it will tend to pivot round a point somewhere reasonably near the middle of the boat - I would never try to predict exactly where on a long-keeler as they all have minds of their own. The important point though is that the force that causes the boat to turn is near the back (ignoring wind) and the boat pivots from the "middle" causing the bow to swing in the opposite direction. The bucket is just a drogue that tries to stop the bow swinging - it's hard work to pull the bucket through the water. As the boats pivots round a point anything that stops the bow swinging stops the stern swinging to so the boat goes straighter. In practice it moves the pivot point as well so the effect needs to be tried carefully before you use it to drop sweetly astern into your berth!!

The above is based on logic and having towed boats whilst going astern many times - it makes it makes it much easier to go astern in a straight line, or at least in a more gentle curve. I've never tried using a bucket in the manner described.
 
maxcampbell said:
...and just leave it there? Or have a person throwing it out & pulling?
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On the ones we watch the crew drops the bucket as the helm begins to go astern. The line to the bucket is cleated with the bucket itself a couple of feet from the bow of the boat.

Although we have never used this method it is not too dissimilar from going astern to berth stern-to on anchor. Our boat is pretty poor going astern, especially in crosswinds, but as soon as the anchor is down and chain being paid out the reversing process is far more stable. The rode is not tight but the chain is providing a small amount of drag that helps to keep the bows from drifting away. Grumpy og's explanation seems logical.
 
I suppose this would work just as well with a small canvas drogue, and would enable the use of a trip line to make recovery easier for frail and/or elderly crews. Perhaps single-handers could lead the lines aft to the cockpit . . . . :)

Anyway, an interesting idea and well worth experimenting with
 
Get a bow thruster fitted..... after having had two long keelers it really makes all the difference...... especially on the pocket, I've just had to shell out on a new battery for mine :(

One way of getting control astern with a long-keeler if you have a stiff breeze, is to motor the stern into the wind.

A long-keeler will usually sit there until you sort out something better, .....




a tip given to me by a certain Twister owner ;) ( you'r up early?? )

Did you get the Jag' video I sent you by e-mail?. Off 2France 2moro, sitting at anchor off Bembridge 2nite.
 
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A Kiwi prop transformed my 36' heavy long keeler. Prior to that you would think the gearbox clutch plates were slipping such was the lack of response to engaging astern regardless of revs. It has also enabled faster cruising for the same rpm. (6kts at 2000rpm compared to 5.5kts at the same rpm with the old prop)
The downside is the Kiwi has increased prop walk going astern but this can be mitigated by keeping the rpm down and also using short bursts of power and coasting. In fact due to the kiwis increased pitch when going astern, idle speed is more than adequate unless you want to use the prop walk for a manoeuvre.
Ian
 
Fit a bow thruster or as others suggested, drop a bucket at the bow or a 2ft length of led pipe on a rope dragging on the bottom; these methods will provide a "bow rudder" to give you straight bow steerage. It is not just the long keeler that have the problem, wait until you see me trying to reverse my twin keeler into a berth; you would think that it is driven by a person heavily influence by alcohol.
 
Scotty_Tradewind said:
Get a bow thruster fitted..... after having had two long keelers it really makes all the difference...... especially on the pocket, I've just had to shell out on a new battery for mine :(

One way of getting control astern with a long-keeler if you have a stiff breeze, is to motor the stern into the wind.

A long-keeler will usually sit there until you sort out something better, .....




a tip given to me by a certain Twister owner ;) ( you'r up early?? )

Did you get the Jag' video I sent you by e-mail?. Off 2France 2moro, sitting at anchor off Bembridge 2nite.
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Bow thrusters? Jags?

Ee lad, we're not all made o' money. (Not sure I could even afford a galvanised bucket just now!)

Have a good trip. :)
 
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