A (Kind of) Philosophical
Our whole life is built on certain presumptions. Some of these ideas are facts that are
easy to prove, i.e., the law of gravity. When they cant be proved, they are called
axioms. In the mathematics we learned in secondary school, the axiom is
that the shortest (and fastest) connection between two points is a straight line. This may
be true on earth but it seems to be different in space travel.
Here is an axiom for boat builders: For a Double-Ender, the best compromise between
Overall Length and Beam is expressed by the ratio LOA/Bm = 4/1. This does
not mean that the ratios 3½ to 1, or 4½ to 1, are no
good. It does mean that with the 3½ to 1 ratio the hull is a bit more
stable and slower. With the ratio 4½ to 1 the boat is faster, but also
more tender. It is the designer who makes the decision in the trade-off.
With everything in life, we start out as amateurs. We try to become as professional as
possible as soon as possible. The process is different for every individual.
It is during this process that we form our opinions. This is the reason
so many sometimes-bewilderingly different suggestions turn up on the net when a newbie
asks where and how to start. Recently, one person even called that question: Opening
a can of worms. Also, everybody believes that his/her way is the best. That is good.
Mohammed Ali would never have been world champion had he even for only one moment thought
that he was second best.
In 1975, to work off frustrations, I chose boat building as a hobby. After having built
a couple of hard chined boats, it dawned on me that the shape of that type of hull is
based on some very simple mathematics. That was also the moment that I found out how bad
my memory of mathematics had become.
I live in a suburb of Montreal, Canada. I have relatives in Toronto, Ottawa, and
Halifax. I went to all the public libraries of these cities and scanned all the sections
#623 on building boats. During those years, I read all the magazines that are published on
the subject in the USA, England, and Holland. I collected a substantial library of my own.
suffered from a near terminal case of Boat Building Book and Magazine addiction. It lasted
12 years. After I had overcome that, only one remark had pointed me in the right
direction. The late John Gardner, in The Dory Book, makes that remark when he states,
All Dories are developed from Double-Enders. Their sheer line is part of a circle
arc. In his book, on page 43, he calls that a natural curve.
In addition, there was another piece of advice that has saved me a fortune in
money, time, and effort. It allowed me to pick up a lot of experience without it costing
me an arm and a leg. Harold Dynamite Payson gives this advice in one of his
books. Abbreviated, he states, If you build a model first, you dont have to
buy the wood twice. It made me laugh. Especially later, after the many times I
goofed, I was laughing all the way to the bank.
A to-scale model can be built on the kitchen table in wintertime. No more boat-builders
hibernation period during that time. As a carport-boat-building amateur, I had the
too-long, North-American cold season licked! I had gained a head start on the
Matryoshkas are boxes mostly in the form of a (Russian) doll. Take off the cover; a new
doll of exactly the same shape is fitted in. This goes on until the last doll has become
too small to hollow out further. The principle is applicable to the design of
hard-chined hulls with three exceptions:
1. The new hull has a (slight) change
in form fore, or aft, or both.
2. The reduced form is given a new name.
3. The width of the original sheer line does
Figure 1-1 shows the Plan view and the Body view of a Double Ender. The ratio Overall
Length to Beam is LOA/Bm = 4/1. Because fore and aft are mirror image
identical, it is one of the easiest hulls to build.
Fig. 1 - 1 Plan and Body view of a Double-Ender
In figure 1-2, only one thing changed in the drawing: A raked, triangular
transom board, called the tombstone, replaces the curved,
difficult-to-make-varying-crosscut-angled stern stem. The tombstone has a strong camber.
For the builder, that simplification was a big time saver. For the fisherman, it meant
additional safety. With an oar in the sculling hole, the boat obtains a rudder. What is
more important, if one oar is lost or broken, it is still possible to scull back to the
mother ship, or, for the inshore fisherman, back to land instead of helplessly drifting
out with the wrong current. Little things like that sometimes make the difference between
life and death on a wide ocean.
Fig. 1 - 2 Tombstone replaces
The apex of the V-board starts where the heel of the stem and the chine
lines came together. The only change is that the sheer lines become a bit shorter. The
Overall Length is now: LOA =15¼ ft. The modification changed a DOUBLE-ENDER
Fig. 1 - 3 From Double-Ender to
Figure 1-3A is the Plan and Body view of the original Double-Ender. In figure
1-3B one quarter of the Overall Length (¼ LOA) is lopped. The hole is
closed up with a (vertical) stern board called transom. In this hull the ratio Overall
Length to Beam is LOA/Bm = 3/1.
Although it has not moved, Beam is no longer in the middle of the hull. It
is located at 2/3 of the Overall Length. Again, only the sheer lines are
shortened. Subsequently, the length Overall became LOA = 12 feet. The
boat type is now called a 12' Skiff.
A raked transom board improves the beauty of the lines and increases the
Overall Length. For the untrained eye, it also becomes more difficult to recognize the
origin of the lines. Note the decreased bottom rocker aft and the transom camber in the
Fig. 1 - 4 From Skiff to Punt
In figure 1-4B, a bow board replaces the bow stem of the Skiff of figure 1-4A.
The name Skiff becomes Punt. In figure 1-4B, the
locations of the station lines of the original Double-Ender are placed above the figure in
the drawing. The reason for this is that the Punt does not have to be constructed as
shown. The type of hull allows for great freedom in Overall Length as long as you stay
in the confinement of, and use the original sheer lines of the Double-Ender. The
raking transom board is placed anywhere between stations #12 and #15. The pleasing lines
of the roomy Punt in the picture were obtained by making the ratios between the width of
the sheers of bow board, Beam, and transom board:
Bb / Beam / Tb = 18 / 48 / 30 = 3 / 8 / 5.
Shorten a Punt fore end further. Now it is called a Dinghy.
The 10-ft. M-Dinghy, an English design, is a typical example. It is built and sailed all
over the world.
If a Dinghy is shortened so far that the bow board is against the mast
bench, and the Overall Length does not amount to more than eight feet, the Dinghy
is called a Pram. It is difficult to say exactly at what point a
Dinghy changes over to a Pram. Both types are mainly used as service tenders for bigger
boats and as sail trainers in yacht clubs.
great number of different types of small craft names can sometimes bewilder and frighten
an aspiring amateur. Once you get the drift of how each type of boat is put together,
procrastination about which to build is easy to overcome. Take heart: If you can build a
simple Double-Ender, you can build them all. And this is only the beginning. In the next
posting more simplifications will make designing and building your own boat even easier.
Find out how to draw the first line mathematically correctly without the use of those
*/*&*/* offset tables.
Sheers and Chines, Barend