SMALL BOAT RUDDERS
BACKGROUND...
Here is an article I wrote a while back that appeared in the great
paper magazine BOATBUILDER. I've included copies of it in my prototypes
catalog since then. The article shows how I've made rudders for my own
small boats.
Where I sail only a kick-up rudder works well. It's not because once a
year you might strike a ledge and break off a fixed rudder. It's
because our waters are generally shallow and a fixed rudder would
require endless fussing on every trip. With the weighted kick-up rudder
shown here you just blast along without giving the kick-up blade a
second thought.
I have also tried kick-up rudders that weren't weighted, but were held
down by lanyards. Nearing a shore or shallow I had to play the thing
like a puppet and quickly ran out of hands because the tiller, sheet,
and board all needed handling at the same time. The weighted rudder
blade is much better. In this article I'll show you how I build a
kick-up rudder from the ground up from plywood. This sort of rudder can
be suitable for boats up to about 22 feet length.
RUDDER BLADE...
The best way to make the blade is to laminate it from thinner plywood.
I've seen warped blades made from a single piece of 1/2" plywood, but
I've never had a problem with a blade built up from two layers of 1/4"
plywood.
Cut out the plywood blanks and butter one up with glue. I prefer
plastic resin glue. It comes as a dry powder and is mixed with water to
the consistency of regular white wood glue. It's best to spread the
glue with a notched trowel like you use to paste down floor tiles.
Place the glued-up blanks together on a flat surface protected with
plastic or paper, and tap a couple of light nails through them so they
can't slide around on each other. Apply clamping pressure with weights
like concrete blocks placed atop the blanks. Now stay away until the
glue has set good and hard.
Now give the blade a final trimming and streamline the edges where
required. (If your rudder, daggerboard, leeboard or centerboard
vibrates in use, streamline the edges some more. That almost always
cures the ailment.)
SINK WEIGHT...
I called this the "counterweight" in the drawing but "sink weight" is a
better term.
The sink weight should be slightly heavier than the buoyancy of the
immersed blade. Wood is about half as dense as water, and lead is about
11 times denser than water. It works out that the area of the lead
weight should be about 1/16th the area of the immersed blade, or maybe
7 percent of the area to give a slight negative buoyancy. For example,
a blade that is 10 inches by 15 inches immersed is 150 square inches.
The lead weight could be 150 x .07 = 10.5 square inches, which would be
a square 3.24 inches per side. Cut a hole in the blade for the lead to
the proper size, preferably toward the tip and toward the trailing
edge. Bevel the hole's edges so the lead will lock in place by forming
flanges around the blade. Also place some rustproof nails or screws
around the interior of the hole to further lock the lead in place.
Clamp the blade to a flat metal plate and place it level on the floor.
To figure the weight of the lead required, multiply the area in inches
by the thickness in inches and again by .4. In the example, if the
example blade is 3/4" thick, the weight of the lead required is 10.5 x
.7 x .4 = 3.15 pounds.
To melt the lead, I use a propane camp stove. I place it right next to
the job so I woun't have to tote molten lead around the shop. For a
crucible I use a coffee can with a 1/2" pour hole drilled about 3"
above the bottom of the can, with a long metal handle bolted to the
side of the can. The crucible goes on the stove with enough lead wheel
weights inside sufficient for the pour.
Begin the pour as soon as the lead is molten. (The steel clamps on the
wheel weights will float to the top and not pass through the pour
hole.) Take your time and be very careful with the pour, but it must be
done all at once. Overfill the hole in the rudder blade somewhat to
allow for shrinkage on cooling. Shut off the stove and walk away from
the job for a few hours. Lead stays very hot long after it has
solidified.
If the weight gets loose in the blade due to shrinkage, you can tighten
it by placing the weight over an anvil and hitting the lead with a
hammer. That squeezes the center and expands the perimeter.
Now contemplate what it's like to pour a thousand pound keel!
RUDDER STOCK...
Laminate this exactly as you did the rudder blade. You need to add the
downstop and it's amazing to me how sturdy this part needs to be. A
block of hard rubber or phenolic plastic bolted in place might be best.
TILLER/HOIST LANYARD...
Don't make the tiller too short! Make it too long and shorten it later
if needed. The tiller should fold neatly along the back edge of the
rudder for storage.
Use light braided line, about 3/16" for the lanyard. Tie it to a small
hole in the rudder's trailing edge. The hole needs to be located about
where the raised rudder meets the aft end of the tiller. Then pass the
lanyard through a hole in the back corner of the tiller, then forward
to a small cleat on the top of the tiller. Pass the lanyard through a
small hole in the base of the cleat and tie and loop for your fingers.
To raise the rudder, yank on the lanyard and belay it around the little
cleat. To lower the rudder, uncleat the lanyard and let the blade drop
kerplunk against the stop.
SHEET FAIRLEAD...
This works very well on smaller sails that don't require multipart main
sheets. Screw a fairlead solidly to the tiller's top face. Place the
fairlead right above the rudder hinges so the sheet loads won't affect
steering. Run the sail's sheet through the fairlead and forward along
the tiller. You can secure the sheet merely by wrapping it a couple of
times around the tiller's grip under your steering hand. Then you can
steer and hold the sheet with the same hand. To release the sheet in a
puff you need only slacken your grip without letting go of the tiller.
You can also belay the sheet around the rudder lanyard cleat if you are
feeling lucky.
HINGES...
I haven't figured out hinges yet. I think the best ones are welded up
from stainless steel, but I'm working towards building boats totally
from lumberyard stuff. Stevenson Projects used barrel bolt locks for
hinges. Payson used eyebolts and rods. Dick Scobbie used door hinges
with big cotter pins for pivots. Seeing those, I tried some door hinges
on a dink rudder and was quite satisfied, especially since they came
from the scrap bin. Most door hinges won't mount as simply as real boat
fittings - check out the angles they swing through and do some head
scratching.
One thing I'm sure of: Don't rely on gravity to keep your rudder on
your transom. In a knockdown the rudder may unship and leave you with a
very wet boat and no rudder. Also, with the sheet fairlead on the
tiller as I've shown it, the sheet can produce a large upward force on
the assembly in strong winds and lift the whole thing out of
conventional fittings. Both of these things have happened to me. Now I
secure conventional fittings against knockdowns and sheet loads by
drilling as small hole in one pintle below the gudgeon and putting a
cotter pin through the hole.
THE CARY HINGE...
I wrote the above a few years ago. But very recently I got letter from
Ted Cary in Florida. He has a way of making effective rudder hinges
from scrap seatbelts.
Here is his description:
"Thought you might be interested in my solution to the rudder pintle
problem. My first experience trying to hit two gudgeons with the
pintles in a big chop, while hanging over the transom, disqualified
that system for me. I came up with a simple track and slide system,
then epoxied up the slide and rudder stock around pieces of connecting
webbing strap. The stap flexes when you steer. You can bend a seat belt
a lot of times before it breaks, and nylon doesn't corrode in salt
water. I found that you must align the strap longitudinally across the
direction of the flex, and you must not allow the epoxy to harden on
the strap where it has to flex. But the ends of the strap have to be
well saturated to hold the slide and the rudderstock halves together.
The most successful way I've used to avoid glue where I don't want it
is to get the parts all glued up and assembled with clamps, keeping the
glue off the flex line as much as possible. Then use a syringe or
squirt bottle to saturate the flex line with vinegar, working it
through the fibers, before the glue starts to set. The acetic acid
neutralizes the amines in the epoxy hardener, so it won't polymerize.
The clamped parts won't allow the vinegar to reach the glue on the
strapping between them, so it goes off where you want it to."
"Dropping the triangular section slide down the transom track installs
the rudder in a fraction of a second.This hinge rig has been working
great on several dinks for over 4 years now."
Well, I must try Ted's system sometime. I think model airplane guys
have been using flexing plastic hinges for a long time. My only comment
might be that I would also lock the slide it to prevent it from
unshipping in a knockdown.
NEXT TIME...
I review the happenings at our last Midwest Messabout.
Contents
PIRAGUA18
PIRAGUA18, SWAMPBOAT, 18' X 3', 90 POUNDS EMPTY
I reviewed the 14' Piragua last issue. Here is the same boat stretched
to 18'. The width of the boat remains at 24" maximum on the bottom
flaring to 30" maximum inside the wales, too narrow to stand up in. It
is intended to be paddled with a double paddle like a kayak. The
stretch creates more weight carrying ability. While the 14' Piragua
will take two adults in a pinch, Piragua18 will float 500 pounds before
its bow and stern start to drag the water. The empty hull should weigh
about 100 pounds leaving 400 pounds for people and gear and that should
be enough for two grown men.
I've also shown on the drawing how I would rig a boat like this with an
electric trolling motor. A typical trolling motor and 100 amphour
trolling motor battery will together weigh around 100 pounds and this
hull will handle the weight of the rig better than the shorter boat.
I'm thinking that is no need to get a large motor. The smallest I've
seen for sale lately was 30 pounds thrust which is usually rated at 1/2
hp. That should drive the boat about 5 mph. Better would be to throttle
to about half power which should give about 4 mph. The battery has to
be a full sized deep cycle trolling battery. There batteries should
never be deeply discharged, in spite of their name, and for long life
they should not be discharged more than 70% of their capacity, and they
should be promptly and fully recharged after use. At full power the 100
amp hour battery should give about 1.25 hours of endurance for a range
of about 6 miles in calm conditions. At half power the battery should
give about 3.5 hours endurance for a range of about 14 miles. Note that
at high rates of discharge a battery has inefficiencies that prevent it
from delivering its full charge. Anyway, power and hull should together
weigh about 200 pounds, still leaving 300 pounds for folks.
This hull might be a good starting point for a beginner's sliding seat
rowing boat. It has the length and light weight and wide open interior
that would take rails for the seat. She's way too narrow for rowlocks
mounted on the wales. You would have to add riggers. No doubt the best
approach would be a drop in unit that has rails and riggers and foot
braces all bolted together. You would have to secure it to the hull
somehow but that could be done in such a way that the unit could be
removed and the boat returned to its canoe configuration.
Anyway this is powered I think it would be a good camper's boat
assuming there is no real rough water about. The ends are boxed in with
buoyancy/storage volumes and the center 9' wide open for sleeping. The
hatches into the storage boxes are small, only 6" wide, in order to
make them less likely to take water in an upset.
Construction is simple nail and glue like the original Piragua. Three
sheets of 1/4" plywood will do it. I don't think these boats need epoxy
coatings if they are stored under cover. The chine corners need to be
armored with fiberglass set in epoxy and the inner seams given a fillet
of epoxy putty to keep water from creeping into the seams.
Plans for Piragua18 are still $15 until one is built and tested.
Contents
Prototype News
Some of you may know that in addition to the one buck catalog which
now contains 20 "done" boats, I offer another catalog of 20 unbuilt
prototypes. The buck catalog has on its last page a list and brief
description of the boats currently in the Catalog of Prototypes. That
catalog also contains some articles that I wrote for Messing About In
Boats and Boatbuilder magazines. The Catalog of Prototypes costs $3.
The both together amount to 50 pages for $4, an offer you may have
seen in Woodenboat ads. Payment must be in US funds. The banks here
won't accept anything else. (I've got a little stash of foreign
currency that I can admire but not spend.) I'm way too small for
credit cards.
Caprice: Chuck Leinweber of Duckworks Magazine has
finished the prototype Caprice. I got a ride and some photos at the
Midwest Messabout and will have a full report soon.
Normsboat: This is an 18' sharpie being built by Cullison Smallcraft
in Maryland. You should be able to check on it by clicking through to
his web site at
Cullison
SmallCraft (archived
copy, actual site no longer active). He is presenting an
excellent photo essay of how to assemble a flattie. This boat has
been launched and I'm waiting for photos and a test report.
Family Skiff: A Family Skiff has been started in Virginia.
HC Skiff: One of these is going together in Massachusetts.
Electron: An Electron has been started in California.
Mayfly: A prototype of the original 14' Mayfly is going together in
New York state.
Contents
AN INDEX OF PAST ISSUES
BACK ISSUES LISTED BY
DATE
SOME LINKS
Mother of All Boat
Links
Cheap Pages
Messing About In
Boats
Duckworks
Magazine
The Boatbuilding
Community
Kilburn's Power
Skiff
Bruce Builds
Roar
Dave
Carnell
Rich builds
AF2
Herb builds AF3 (archived copy)
JB Builds
Sportdory
Hullforms Download (archived copy)
Plyboats Demo Download (archived copy)
Table of Contents
