BOATBUILDING WITH A DIFFERENCE I
(For Aspiring Amateurs)
by Barend Migchelsen Migchelsen@aol.com
http://ca.geocities.com/bmboats2002/
http://members.aol.com/_ht_a/migchelsen/myhomepage/

Barend Migchelsen, (pronounced Mikkelsen) learned to sail in The Netherlands in 1943. In 1975 he started to build boats and boat models as a hobby.  Today, he organizes and teaches classroom courses in boat building, and has published several books on the subject.  The following is an excerpt from one of these books.  This is the first of four parts.

 
A (Kind of) Philosophical Introduction

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 can’t 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 3 to 1, or 4 to 1, are no good. It does mean that with the 3 to 1 ratio the hull is a bit more stable and slower. With the ratio 4 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. pic1.jpg (11796 bytes)I 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 don’t 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 too-short summertime.

Matryoshkas

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 not change.

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.

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Fig. 1 - 1 Plan and Body view of a Double-Ender

DORY

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.

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Fig. 1 - 2 Tombstone replaces stern stem

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 =15 ft. The modification changed a DOUBLE-ENDER into DORY.

SKIFF

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Fig. 1 - 3 From Double-Ender to Skiff

pic2.jpg (8994 bytes)Figure 1-3A is the Plan and Body view of the original Double-Ender. In figure 1-3B one quarter of the Overall Length ( 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 drawing.

PUNT

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Fig. 1 - 4 From Skiff to Punt

pic3.jpg (9310 bytes)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.

DINGHY

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.

PRAM

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.

CONCLUSION

pic4.jpg (7558 bytes)The 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

To be continued.....

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