Rudder area and bilge keels

C

Carronade

Member
Joined
28 Jan 2003
Messages
28
Location
North East Coast
Visit site
I have a Colvic Motor sailer 31 (same hull as Atlanta 32) the boat has long keel and bilge keels. I have written about the problem of going astern with this boat before without any real solution to the problem apart from fitting a bow thruster. this is a major cost issue and not feasible at this time!.

I note in the Practical Boat Owner March Issue that Irvin Campbell has improved the handling of his Atlanta32 by adding a 4" strip to his rudder adding 25% to the rudder area. I have all the original drawings of the boat and had looked up various calculations of rudder area by different designers and all come out to roughly the same size as the design of the MS 31 (J A Bennett). There seems no logic to increase the size of the rudder but have to admit I have been tempted to follow Mr Campbell and increase the rudder size. I wonder if the triple keel design of my boat has any affect on the proportion of the rudder in relation to handling. The twin keels were added by Colvic as the original design is for a single long keel.
Going ahead the boat does tend to veer off course when moving slowly but going astern it likes to go round in circles!

Would be interested to hear from anyone who has views on this perplexing issue. I have also been reading about the Axiom Propeller which it is claimed improves the handling characteristics of long keelers. Anyone fitted this prop?
 
Carronade said:
I have a Colvic Motor sailer 31 (same hull as Atlanta 32) the boat has long keel and bilge keels. I have written about the problem of going astern with this boat before without any real solution to the problem apart from fitting a bow thruster. this is a major cost issue and not feasible at this time!.

I note in the Practical Boat Owner March Issue that Irvin Campbell has improved the handling of his Atlanta32 by adding a 4" strip to his rudder adding 25% to the rudder area. I have all the original drawings of the boat and had looked up various calculations of rudder area by different designers and all come out to roughly the same size as the design of the MS 31 (J A Bennett). There seems no logic to increase the size of the rudder but have to admit I have been tempted to follow Mr Campbell and increase the rudder size. I wonder if the triple keel design of my boat has any affect on the proportion of the rudder in relation to handling. The twin keels were added by Colvic as the original design is for a single long keel.
Going ahead the boat does tend to veer off course when moving slowly but going astern it likes to go round in circles!

Would be interested to hear from anyone who has views on this perplexing issue. I have also been reading about the Axiom Propeller which it is claimed improves the handling characteristics of long keelers. Anyone fitted this prop?
Click to expand...

Give a short burst of full pwr then out of gear she should then answer to the rudder. It sounds as though you have a lot of prop walk. learn to use it to advantage.
If going astern out of a berth, use a warp to pivot on
 
Last edited:
IIRC, YM tested the Axiom, and were lukewarm about any claimed benefit, although side thrust was reduced a somewhat, so was forward thrust.
 
Last edited:
Thanks for your views on this issue. I have had the boat for 15 years and tried all the tricks of the trade for maneuvering! I'm looking for the impossible .. a Miracle cure! I keep on hoping that someone has found one that is as simple as altering the shape of the rudder or fitting a new design of propeller. The blurb on the Axiom looked very tempting .. I believe that Brunel had a similar propeller shape on his ship design for the Great Eastern, could be he was on to something!
 
There are various ways to increase rudder efficiency but they will not help going astern.
'Attatch' NACA airofoil halves to each side of the rudder to end up with a symetrical aerofoil.
'Attatch' rudder 'fences' at the top and bottom of rudder-these are a bit like the vertical wing tips you see on aircraft.Allthough primiraly intended to reduce rudder 'cavitation' at the surface on fast boats,they are fitted to many relativly slow boats to increase efficiency
Attatch a 'V' at the trailing edge of the rudder.
Allthough all these add on can and do help increase efficiency in certain cases,I have no idea what your rudder is like and so they may not be any use to you,but might give you some food for thought if you havn't allready researched them.
Hope this helps.
Cheers
 
Thanks caiman for your comments. The Rudder Shape is roughly rectangular mounted on a shoe attached to the end of the keel and follows the line of the stern at the top. It is aerofoil section roughly 2" thk at the widest point. I have tried the Vee strips fitted at the after end. The rudder pulsed from side to side with the turning of the prop so had to remove them! It did improve the astern movement but the forward motion was diabolical! The vee fins are a popular fitting with the fishermen but they have very big engines and very big fins and somehow this combination seems to work for them.

Early bird you quoted IIRC, YM not sure what this reference is please help.
 
Carronade said:
.
Early bird you quoted IIRC, YM not sure what this reference is please help.
Click to expand...

Refreshed my memory now! YM did a series of tests May 2009. Flexofold have the article in pdf form on their website. (I wonder why?)
I've re-read it, and perhaps the Axiom is better than I earlier recalled.
Googling YM propeller tests brings up a reference.
Sorry I can't post the link, my IE doesn't seem to let me do this for some reason.
 
Hi.it looks like the only simple options left are -more area,or try the fences at both the top and bottom of the rudder.Apparently they work well with an aerofoil section in that they prevent 'vorticies' from slipping over from one side of the aerofoil to the other and so increases efficiency.As vyv_cox says,a crude and simple bolt on piece of ply ply should be enough to prove if any mods will work before doing a proper job.I have recently bought a transom stern work boat,and when the time comes to restore the rudder I shall be adding aerofoil sections and fences,probably three of them.When I fit my fences I shall be dispensing with area in front of the leading edge so that the chances of catching ropes is not increased.I also intend making the fences robust enough to act as steps for reboarding from the water.(engine stopped of course).A Kort Nozzle is not beyond the realms of self construction.There is also some kind of 'Admiralty' steerable 'nozzle' 'Kitchiner'steering?There is also a 'Becker' type rudder,but these would need quite a major re design.Good luck with fixing your problem,I shall be interested in what your final solution is.Cheers
 
I had a completley different problem with my trailer sailer. When going hard and shy under spinaker it was inclined to round up out of control. I increased the rudder area by making it deeper but also with more ballance area forward of the pintle line. It is a transom mounted swinging rudder normally clamped down so leading edge is forward of the transom.
I added about 2 inches of depth all faired and foil shape. It made a huge difference to control of the round up I can now turn downwind when overpowered rather than losing it and turning upwind.
I would suggest for your rudder an added area at the bottom of the rudder projecting downward with a slot for the lower pintle. Use a polyurethane foam stuck onto the bottom shaped then built up with polyester or epoxy resin. The add on can be made frangible such that it will tear off if it hits anything or it sits on a rock when grounding. I think this area below the centre keel and in clear water will give more control of the boat when moving through the water regardless of prop wash. Just a thought olewill
 
You must log in or register to reply here.

Other threads that may be of interest

Anibal
Garmin GPSmap 1223xsv rudder indicator
Replies
18
Views
420
Anibal
Anibal

Share this page

Top