rudder were to break how would I get my boat back home?
is a question every boater should ask him or her self.
The next question of course, should be what can I do to prevent this
how to repair any damage or build a replacement?
"A ship is always referred to as "she" because it costs so much to keep
her in paint and powder."
When I began to rebuild
it was clear
that the whole steering mechanism was beyond repair. Mignonne
The simplest solution was to build a transom hung rudder with a tiller
researching the subject I decided it was best to build it from solid
been made quite successfully using plywood sealed with epoxy and glass
However, the blade can be
subject to quite considerable
twist and flex due to water pressure.
Plywood which is constantly
flexing and twisting will
eventually start to
as the bond
between the piles breaks down.
This flexing will also cause
separate from the surface.
The only way to prevent a
plywood from flexing too much
it would to be make it overly thick.
The main problem with usinf
wood is that the
blade can warp.
However this can be countered
if you build the blade up
using several planks of flat-grained timber with the
Although this will not prevent
planks from warping, the bow in one plank will counterbalance the bow
The use of strapping or drift
bolts will also help
prevent warping and strengthen the construction, they can also be used
repair and old rudder.
for rudder building will
be one which doesn’t readily absorb water.
A resinous pine such as pitch
pine would be ideal
otherwise use a well-seasoned hardwood.
If like me, you have to
design a new
rudder the big question
is what size should it be?
If the wetted area is too big
and it will cause
unnecessary drag, too small and it won't have sufficient turning
Finding a happy medium will
depend on the style of hull
and the underwater arrangement.
Below are some formulas which
can be used to give a rough
idea of the optimum size needed for some basic hull configurations.
For a traditional Long
Keel Sailboat with a
full length keel,
the rudder area should be equal to
waterline length x draft.
For a Long
Keel Sailboat where the keel is
less than full length;
0.058 x waterline length x draft.
For a Deep
Narrow Fin-Keel Sailboat ;
0.04 x the waterline length x draft including the keel.
For a Displacement
Motor Boat ; 0.03
to 0.01 x waterline length x draft.
And for a Planning
hull ; 0.018 x
waterline length x draft.
These are however, very
basic rules of
The style of rudder whether it's transom
hung, balanced or
whatever will depend largely on the type and configuration of the hull.
As for the profile of the
blade, there has been much
theorizing about shape.
The predominant thinking is
that the blade should be of
an aerofoil shape, especially for slow and moderate speed boats.
That it should be convex in
cross section rather than
straight and certainly not concave.
This, according to theory,
will minimize drag and
provides lift on the turn as well as reducing chatter or vibration..
It is accepted that a rounded
rather than a sharp leading
edge is more efficient.
It theory, a thin tapering
trailing edge should be
favorite but this is impractical as it would be vulnerable to
However, despite the theory,
wedge shaped rudders with a
fine leading edge are often found on high-speed craft.
And many have a small flat
plate metal blade.
However, that small blade
while being effective at high
speeds will be less effective at slow speed.
Like most things on a boat
there is always a good deal of
For the average cruising boat
less wetted surface and
higher efficiency may not be as important as lower draft.
And there are many designers
and designs which claim all
sorts of advantages for their blade shapes.
The Chinese on their junks
often used a flat blade with a
slot cut through the mid section about a third of the width back from
This, it would seem, allowed
it to create a pressure
difference or perhaps turbulence which apparently increased efficiency
But theorizing aside, the
common ‘classic’ rudder is a flat blade with the leading edge well
rounded and with a small degree of taper towards the trailing
It has also been suggested
that a flat section blade will
give greater control at slow speeds.
And it is when traveling
slowly that accuracy is more
desirable, such as when maneuvering in a restricted area.
There are some other
considerations which will affect the efficiency of a rudder.
The farther aft it is placed, the more turning leverage it will
will respond quicker and be lighter on the helm if the rudder is
balanced, with about 15 percent of its surface area forward of the
For sailing cruisers having the rudder hung from
a skeg or a long keel will offer a cleaner flow of water and thus less
And a deep, narrow, rudder will be more efficient than a wide
It is also worth remembering
that a rudder, once it is
pushed over by more than 35 degrees begins to have more of a braking
than a steering one.
While rudder blades do occasionally
fail most of the load is taken by
the pivot points.
On the majority of transom
hung rudders are attached to
the hull by gudgeons and pintles it is usually the bottom ones which
most load and fail first.
Spade rudders which have no
protection from a skeg or deadwood are particularly vulnerable to
So, the spade requires a stock
of considerable strength
to withstand those rudder forces.
Another issue which is subject
to much theorizing is the
size of the gap between the stern-post and the leading edge of the
Most seem to agree that the
gap can cause turbulence and
drag however, there must be some gap to allow the blade to turn.
One solution is to fit
flexible flaps to cover the
But as I have never seen a
boat with these fitted I
cannot say if it is worth the effort.
Personally I prefer to have
sufficient gap to allow me to
be able to paint all around the stern-post and the blade.
When fitting pintles and
gudgeons it is important that
they are fastened securely.
It is also important that they
are aligned perfectly to
allow the blade to turn and prevent uneven wear.
When I started to rebuild Mignonne
there was very little
of the original steering gear left and most of that was beyond repair.
I decided that the replacement
would be outboard and transom hung, mainly as this would be the simplest to build.
The first job was to work out
roughly the size I would
Next I built a full sized
pattern using scraps of plywood
glued with the
I used thin ply so that the
pattern would be light enough
to be held up to the transom but stiffened with a baton so it didn’t
I then used a variation of the
to get the
leading edge to fit the transom. joggle
I also marked the position of
the pintles and gudgeons on
Next I glued together the
blank using tongue and grove
planks, making sure that it overlapped the pattern.
Once the glue was set the
final shape was marked from the
pattern and the blank cut and trimmed to the marks.
Then I rounded the leading
edge and tapered and rounded
the trailing edge.
When I was happy with the
shape I gave it a good rub down
primed it and gave it a couple of coats of undercoat.
The next job was to add some
strapping to prevent warping
and because I was reluctant to rely on the glued joints even though I
The strapping was wrapped
right around the blade and
through fastened with
The rivets were fitted through
the center of the planks
to allow then to swell across their width.
The strapping was held a tight
as possible with clamps
However, if strapping is
fitted when the wood is dry it
will tighten when the wood takes up and swells.
Another method of
strengthening and preventing warp is to
fit drift bolts through the blade.
The problem with this method
is making sure that the
holes for the bolts are perfectly centered, all the way through.
The external strapping can be
rebated flush however, it
is often left proud on old ships.
And one theory is that the
strapping left proud actually
helps with turning ability.
The final job was to fit the
pintles and gudgeons making
sure that they all aligned perfectly.
The simplest and
therefore the most reliable way to control your rudder is the good old
I personally also prefer
tiller steering as it gives me a
more immediate feel for the trim of the boat.
There are several ways in
which the tiller can be fitted
to the rudder.
Metal cheeks fitted to the
tiller can fit around the
Or the tiller can fit into a
slot in the head of the post.
The tiller doesn’t have to
pivot in the vertical
plane but it will certainly make life for the helms-person much easier
A tiller held in place with a
pin or bolt through the
cheeks will allow the person on the helm to easily steer either
And being able to fold the
tiller out of the way will
free up cockpit space when in port or at anchor.
It’s a good idea to experiment
with some scrap
timber before deciding on the finished length and shape.
And is better to make it over
sized at first, you can
always chop some off later if it needs it.
Unlike steering gear which
uses quadrants, cables or worm
gears there is little to go wrong with tiller and It requires very
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Do you have any back up should your
steering gear break while you are at
There are various methods
which can be employed to steer
a rudderless boat.
A sail boat can be steered by
And the use of a bucket or
other means of applying drag
can be used over the quarter to change direction.
However the simplest, the
oldest and perhaps the most effective emergency form of steering device
large oar hung over the stern quarter.
And that large oar can also be
used as an emergency form
The oar should preferably have
a large blade and if
storage is a problem the stock can be cut and some piping used to
A figure of eight lashing
should be sufficient to attach
pay some thought
to where would be the most suitable attachment
For more detailed questions, tips, photos, etc. go to the in the top menu. Forums
Rudder construction and repair A really well written article which gives loads of facts without being overly scientific.
A real boon to anyone trying to understand the way a rudder …