Thursday, October 23, 2003

Chinese Sampan Teaches Much to Designers (中國舢舨啟發現代造船技師)

Chinese Sampan Teaches Much to Designers (中國舢舨啟發現代造船技師)

Chinese Sampan Teaches Much to Designers

C. Andrade, Jr., recently came across an old model of a Chinese sampan. It is an odd piece of work, full of interest and instructive, too. Mr. Andrade lent the model to George B. Douglas, who has taken off the lines, and these lines, pictures of the model and an article written by Mr. Andrade, are given herewith in THE RUDDER.

THE accompanying lines and sail plan illustrate a very interesting model of Chinese sampan. The model from which this was taken is an authentic piece of work, evidently made by a Chinese shipbuilder, as it contains all the peculiarities of design and construction that belong to the Chinese system of naval architecture. It is a fact not generally known that the Chinese are, and for many centuries have been, very successful sailors, and the model shown herewith is a good illustration of their ability as designers. It will be noted that the lines embody many of the refinements which are found in the most up-to-date boats in the United States. For example, the wetted surface of this model is reduced almost to the theoretical minimum for the displacement shown. There is not a single square inch of surface wasted in any projecting keel or skeg or deadwood.

The sheer line of the bottom of the boat also illustrates a peculiarity which naval architects in this country have just begun to appreciate, and that is, that the run can be carried out quite full, almost to the stern, and then come up, with a sharp turn, without hurting the boat's speed in any way. This fact has been known for a number of years to the torpedo-boat builders of England, who carry their displacement curve very full, almost to the stern. The same thing is shown on the Herreshoff small steamers of the type of the Mirage, and other boats of that class, where the keel line is carried out with an easy curve, about to the point where the shaft leaves the hull, and then turns up rather sharply to the stern. This same feature accounts for the very short overhang, with strong upturned buttock lines that are found in the last two or three years' designs of the Herreshoff sailing yachts.

There is no planking across the stern of the boat, but there is a big open space somewhat like a well all the way from the transom to the heavy after bulkhead, which is shown in the sail plan and also in one of the photographs.

I have known of this peculiarity of Chinese construction for many years, but only recently have I been able to evolve any theory which would account for it. This method of construction must have some great advantage, or the Chinese would not have adopted it originally, or having adopted it, would not have adhered to it for centuries, as they have. It is my belief that the purpose of this stern construction is this:

It will be observed that the stern of this model is very full. The half-breadth plan shows that the waterlines are carried out to their full beam, almost to the transom. This, of course, gives the model great stability, and also great ease in driving, but it has the disadvantage of making a stern with too great buoyancy, that is to say, if this boat were planked solid across the transom, and were driven off in a heavy following sea, the enormous surplus buoyancy of the stern would make her pitch to a dangerous degree, and would tend to bury her head. It is at this point that the reason for the peculiar stern construction becomes apparent, for it is obvious that if this boat is running off with a heavy following sea, the instant that a wave strikes her stern, a very large volume of water will be momentarily held in the space between the stern proper and the after bulkhead. In a large boat, this weight of water would probably amount to a ton or more, and the weight of this water momentarily holds down the stern and prevents it from lifting unduly on a following sea.

The effect is just exactly as though a very large weight of ballast were placed in the stem of the boat. Every one knows that this is the only proper and safe way to trim a small boat when running off in a heavy following sea. But the Chinese stern has this advantage over the permanent ballast, and that is, that the moment the sea has passed the water runs out of the space at the stern, and the boat is left light and free to travel with much greater speed than if she were loaded down with a ton or so of ballast at the stern.

There is quite a marked flat portion on the bottom of the hull, so that she can go aground and rest at low tide without heeling over. Indeed, the whole boat appears to be designed for this contingency, because it will be noted that she depends for lateral plane on two features; first, a dagger-board forward, which can be lifted, and, second, a very large rudder aft, which also can be housed entirely within the hull, when not in use. It will be observed that the daggerboard contains the great essential which is necessary in a member of this type, i.e., narrow width with great depth.

It is well known that the former edge of the keel, or centerboard, is what does most of the work, and the Chinese apparently have grasped this fundamental principle. Therefore, while the daggerboard seems to have a very small lateral area, it will be noted that its area is of very high efficiency, particularly as the board is located right under the fore-foot, where it works in solid water, which is undisturbed by any portion of the hull, and which is not affected by any lateral movement that would be gathered by the hull further aft. This daggerboard has two different holes and a stop, so there are three different adjustments at which it could be carried, thus changing the balance of the boat very materially, as desired.

The rudder, as is common with Chinese rudders, has five diamond-shaped holes in the blade, and the blade itself is of very thin wood. The purpose of these diamond-shaped holes is undoubtedly to permit dead water to run through to the back of the rudder blade and prevent the accumulation of dead water along the after edge of the rudder. As already stated, the rudder can be completely housed in the hull, simply by setting it straight fore-and-aft, and then drawing it up through a slot, which is cut for the purpose in the deck. This construction is shown in detail at the stern of the hull in the sail plan.

"Transom" timbers removed for clarity to show end of planks. The grey bulkhead is partially hidden behind the ends of the planks since it is located at the second section line in from the stern. A sampan will typically have a flat bow timber, often tapering from small at bottom to wider at the top - COD

It will be observed, on reference to the buttock lines, that the boat carries a long and very efficient floor practically from station No.2 to the very stern of the boat. This feature will, of course, make the boat very fast on a reach, and will make her very easy to drive.
It is quite apparent from a glance at the body plan that the boat will have to be weighted with a generous amount of inside ballast before she will acquire much stability, but as she is built for carrying weight, that feature is really an excellent one.

The anchor is an interesting detail, as it will be noted that it is quite large, in comparison with the rest of the boat, and is made entirely of wood, the only metal being on the single fluke. It will also be noted that the stock is placed at the end of the anchor, next to the fluke, and not at the cable end. As soon as the anchor strikes the bottom, the weight of the metal fluke brings it down, and as soon as it takes hold, the stock lies flush with the bottom, and makes an anti-fouling anchor.

There are a couple of little hand windlasses of primitive type, one on each side of the mast, as shown in the half-deck plan. The mast is set in a tabernacle, so that it can be lowered when going under bridges, etc.

It will be noted that the rig is very simple, and very efficient. The mainsheet rigging is quite interesting, consisting of a single length of sheet, which is rove in an unusual manner, as will be noted from the sail plan. The wooden block through which all the parts of the sheet run has a little becket at its lower end, and this becket runs along the wooden traveler on the extreme stern.

I believe that a boat built exactly on these lines, including the unusual stern construction, would make a very comfortable and useful small boat for cruising. I can see no objection to building such a small cruiser with a jib set on a stay running to the stem-head, and a mainsail which might hang over the stern a foot or so, so as to be easily reefed.

As the lines are drawn, it shows the stern a little higher than the bow. This is a peculiarity of Chinese construction, and is a feature that was common on ail old types of sailing ships, as it will be recalled that Columbus's ships, and the Half Moon, and all the sailing vessels of that time had the stern considerably higher than the bow. Many theories have been advanced for this, but modern practice, of course, has gone the other way. I suppose one reason for making the stern higher was so as to give the steersman a better view; second, so that the vessel would ride head to the wind, in case she was left to drift in a gale; and, third, to avoid the danger of being swamped by overtaking waves in a heavy sea. With this high stern, and the daggerboard down all the way, this sampan should lie head to the wind in any kind of a gale, without any sail at all. I will be glad to hear of any boat built to these lines.

Editor's Comments:

The invention of the Chinese junk/sampan hull and sail archetypes required creativity and originality. Their subsequent evolution over the centuries that followed required patience and perseverance. Modern sailing enthusiasts are the happy beneficiaries of both processes.

-- Bevin Chu

Explanation: Chinese Sampan Teaches Much to Designers
Author(s): C. Andrade, Jr
Affiliation:The Rudder
Publication Date: July 1917
Original Language: English
Editor: Bevin Chu, Registered Architect

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