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Some Memorandums by Which it is Attempted to be Shewn That an Improved Model May be Adopted in the Construction of Ships by a new Application of Well-known Principles

by Frederick Tudor

Image of page 1 Construction of Ships
Construction of Ships page 1

There are many expert ship builders, who can build a vessel which shall sail fast: but suppose such a man were to build at the same time two vessels, both for sailing. After they are launched and tried together, there is little doubt but one would sail faster than the other. I would then propose to the builder to give the reason why one is the better sailor, and I think he would be unable to tell.

I have thought that a vessel might be made to sail equally well, whether burdensome or not, but I now think that both these qualities cannot be united perfectly in one vessel, but that they can be in a considerable degree.

The form of the main body of the vessel is a very material point to be attended to, but it is not the sole thing. It can only be considered as one point to have correct. It is a very general opinion, and I think erroneous, that the model of the main body is the only important thing; and so it might be if a vessel were impelled forward by a power, acting from stem to stern, as if pulled along by a rope; but this is not the case, except in sailing before the wind. This idea, that every thing depends on the form of the hull, has produced a vast variety of models. Every man has one peculiar to himself, and which he thinks infallible. On this subject there is certainly much want of definite principles; because it has never yet been established what is the form most to be desired.

There is one thing, however, generally admitted, which is, that a vessel having a lean sharp “run” will sail fast; but at the same time it is allowed that a flat-bottomed vessel very “full” aft in a smooth sea and light wind, will sail as well as the other, and in many cases better before the wind.


Image of page 2 Construction of Ships
Construction of Ships page 2

Form of the Hull, or main body.

I mean by the main body that which supports the ship in the water and carries the cargo, not including the keel, or other “dead wood.”

I do not think it necessary to have recourse to experiments to ascertain what is the form which passes with greatest facility through a fluid. It is sufficiently shown in the form of the Dolphin, a fish that moves with great velocity, and whose form is particularly fitted, there is reason to believe, for the purposes intended by nature to be accomplished.

But in addition to this, a form in one point similar to the Dolphin will be met with in all fish, and that is, being largest about the head, or forward part. This may be discovered even in the “flounder”, and this thing is so strikingly marked in all fish, that I think a similar form must be adopted for a vessel. This idea is by no means new, and is continually attempted: but I do not think if has been put in practice in a single instance where it has been intended. This appears a bold assertion, but it must be remembered that a fish not only tapers from head to tail, as cut horizontally in two, but vertically also, or from belly and back to tail.

Many vessels are built with the intention of taking advantage of this shape, and so they look as if they would do, whilst on the stocks; but they are no sooner in the water, than the defects of the model defeat the intention. That is by the leanness aft and fullness forward, the main body sets down much deeper aft than forward; and thus the real form presented to the water is not what was intended, but the vessel has to drag through, deep down in the water, a considerable part of the main body after it is all through forward. It is therefore that vessels which are very sharp forward, having a lean run, generally sail better than those which are full forward and sharp aft, as they by this means sail upon a more even keel, at the same time preserving their hold on the water, which contributes to lessen the defect here stated, otherwise I think an extremely sharp bow is a disadvantage.

Ships intended for swift sailing always draw more water aft, than forward; but on the present construction a very considerable part of the main body is carried down into deep water, where it has to encounter a great resistance, and presents a form of the wedge kind, as it passes through the water; and the advantage of the fish shape is entirely lost in the place where it is most wanted, and in a very considerable degree lost in the form presented to the water nearer the surface. This I think will be found to be the case in all vessels. It is the great impediment, and the desideratum is to avoid it.


Image of plate pages 2-3 Construction of Ships 'Sections of Fish'
Image of plate pages 2-3 Construction of Ships 'Sections of Fish'
Image of page 3 Construction of Ships
Construction of Ships page 3

In opposition it may be stated, that a sharp vessel being loaded by the head, would avoid this shape and preserve the fish shape, still no advantage would arise, but on the contrary a most palpable disadvantage, as the ship would not only become unmanageable, but would not sail so fast.

The answer is, that in restoring the fish shape a great deal of the after part of the keel, dead wood, and rudder, are brought out of the water, and all of it raised nearer the surface, by which means the ship cannot hold so good a wind, and the rudder has less power. Thus, although it is a defect for vessels to carry down aft so much of the main body, they still, in carrying it down, carry also keel and dead wood, so as to take a great hold on the water laterally, which is another important point necessary to fast sailing vessels, and the loss of the fish shape is more than made up by this advantage, the rudder having a great hold on the water, the ship of course is more manageable.

The happy effect of a greater draft of water aft in giving power to the rudder, and enabling the ship to hold a better wind, has produced in many persons a misapprehension of the principles on which rest this advantage, so that many think it is not an impediment for the main body to draw more water aft than forward, but this is indisputably an error.

The fish shape may be shewn to be the best for passing through fluids, by observation of various effects in nature. For instance, it may be observed, that a square body passing through a fluid produces before it a dead body of the fluid which it carries with it: this dead or inert mass of fluid opposes a circular front, and advances with the body: there will be found also a mass of dead fluid following after the square body, and tapering away like a fish’s tail. This effect may be seen at one of the square solid piers of Charles River Bridge when the current is rapid. You may there see a still body of water presenting a circular front to the current as it advances, and the still water also trailing away behind very distinct from the current, and shewing clearly that the pier might be nearly twice as large as at present, without opposing additional resistance to the current, provided it were built where the dead water is. It would then present nearly the fish shape. The pier remaining stationery while the current advances against it produces of course the same effect as if the pier advanced through the water.

There is very good evidence, from observation of similar facts, to think the same shape is best; and that similar principles operate on a body passing a fluid perpendicularly as well as horizontally. If, for instance, we take a square block, and force it down hastily in water, we shall find there is a great quantity of water which follows it down; and it is reasonable to think there is some dead water in front and descending with it, the same as at


Image of page 4 Construction of Ships
Construction of Ships page 4

the pier. This is more particularly exemplified by considering the effects of a vessel foundering at sea. In such a case it is well known that those who are on deck, as those who are in the cabin and other parts of the ship, perish equally, and are carried down with the ship. If a considerable portion of water did not trail down with the vessel, what should prevent those on deck from swimming? It will be found that these principles are acted upon by nature in aeriform as well as more dense fluids. For instance, suppose a solid fence is opposed at right angles by a storm of snow: it will then be observed that a body of snow will be deposited in front of the fence, but at some distance from it, and that immediately behind the fence the snow will collect and trail away for some distance, being deepest at the fence. The fence opposes to the wind an inert mass of air, into which the snow cannot be thrown, but (what does not fall before) rises with the wind and falls by its own gravity, and the reaction of the wind on the other side the fence. We see the same thing when a snow storm drives against a hill. The snow is not deposited in front of the hill, but on the other side, from the brow down to the valley. Some crevices in the fence may alter the formation of the snow on the back of the fence somewhat.

From an attentive consideration of the foregoing statement of facts, I think the conclusion may be drawn, that a body of the fish shape may pass through a fluid with as great facility, as a square body of half the size will do it. The square body carries before it, and drags after it, a quantity of fluid to make up for the additional size of the fish shape body which does neither.

The fish shape produces a degree of reaction in the fluid, after the head or largest part has passed through. It recoils in a degree against the tapering part of the fish, and although this recoiling may not aid the fish forward, it certainly prevents any adhesion of the fluid to the tapering part, and therefore this part has only to follow meeting with little or no resistance. In the beginning of this paper, I have assumed the idea as allowed on all hands, that the fish or dolphin shape, was the true one for passing through fluids, but have been led into some attempts to illustrate and strengthen that opinion. It was perhaps useless to attempt to prove what was so evident.

We have now to adopt this shape, having regard to other things and to consider, that a ship is made not only to pass through the water, but on and near the surface of it, which not being the case with fish, we are to avoid some of the disadvantages of the fish shape.

In a ship strictly speaking, there is nothing straight, round, or square: but she is formed out of a compromise and union of all these lines, so as to take the benefit of various principles in nature, many of which are directly opposed to each other.


Image of page 4-5 Construction of Ships 'Effect in a Snow Storm. The form which the wind produces in order to pass the fence is represented below the horizontal line'.
'Effect in a Snow Storm. The form which the wind produces in order to pass the fence is represented below the horizontal line'.
Image of page 5 Construction of Ships
Construction of Ships page 5

The shape of the breast in water fowls, must be considered. This is much of the fish shape, being broadest and deepest near where it enters the water. It is the dolphin shape flattened, wanting however some length, but preserving the same principles in its form, and intended to be as buoyant as possible, so as to avoid as much as may be, the pressure of the water, which increases in a compound ratio, as we descend from the surface.

It must be remembered that the dolphin moves wholly under water, and that its attitudinal pressure is of little consequence to him, the depth of body being so small, but in a ship the attitudinal pressure of the water, must be avoided as far as possible. The fish shape must be preserved, and also as much buoyancy as may be. We must take a medium between a water fowl’s breast and the dolphin. The water fowl gives buoyancy, and the dolphin length.

On the subject of buoyancy it is necessary to keep in mind, that the nearer the surface, the easier is a fluid passed through.

With respect to length, it may be observed that we must give way somewhat to the turbulence of the water, for which reason we cannot make our ship so long, nor taper away aft, so much as we would otherwise. The heavy rolling of the sea will not permit of it. If the ship should taper away so extremely as the tail of a fish, and close nearly together aft in a point, she would be in danger of having the water roll over her, when going before the wind. She must have sufficient transome to lift her out of this danger.

The extreme breadth must be about one quarter of the whole length from the stem, and from thence to the transome must be a regular sweep, or swell, of about nine inches (in a vessel 70 ft. keel) on each side beyond a straight line, in such a manner that the angle from the extreme breadth, shall be continued without any indenture. This is in pursuance of the desired shape.

The Keel (no dead wood.)

The main body being adopted according to foregoing principles, we then have to consider, that we have the form best adapted for passing through the water, and if the power of producing motion existed in the body of a ship, as in that of a fish, nothing more would be necessary, but as this is not the case, and we have to depend on the wind to give the power of moving forward, it becomes necessary that we should give something to the ship, so as to enable the sails to take the greatest possible advantage of the wind.

This is to be done by keel, by which a ship is able to take a lateral or lee hold on the water, without opposing any important impediment to her passage through it.


Image of page 6 Construction of Ships
Construction of Ships page 6

By means of keel, the wind has the greatest effect on the sails, and of course urges the vessel forward with the greater velocity.

Whether a ship is sailing before the wind, or close hauled to it, keel has a good effect: when on a wind it takes a lee hold on the water: when before it, it prevents the ship from yawing and from rolling so excessively, whereby the wind has not that full power on the sails, which it would have. By keel she is enabled to move strait forward without being affected by the irregular motion of the waves.

A vessel without keel falls to leeward for want of sufficient hold on the water, she will not lie near the wind and whatever her form is she passes slowly through the water.

When we bring a vessel without keel near the wind it has less effect upon her sails, she falls to leeward, and the faster she slips from the wind, the weaker of course it strikes on her sails, and in order to keep them full of wind with effect, we must keep her off from it. But when the keel is added, the vessel meets with an immediate impediment which prevents her from falling away from the wind, and the angle which the sails make with the wind, necessarily impels her forward when the force of the wind falls upon them: therefore it may be inferred that a deep keel is the sole cause which enables the ship to lie near the wind, and to sail at the same time.

Many persons think keel will not make a vessel sail faster; but I think I have shewn this to be a mistake, because keel gives additional power to the wind. Proof of this may be seen every day at Martha’s Vineyard, where they employ boats of the same construction as whale boats, with the addition of a keel. Every person who is acquainted with the construction of a whale boat, knows that they will scarce sail at all on a wind, whereas the Vineyard boats sail perfectly well.

The quantity or depth of keel that is proper, is a thing which can be only ascertained by experiment; but without doubt it should be as much, and no more, than will enable a ship, close hauled, to avoid making any lee-way whatever.

If a ship having a keel were detained from advancing ahead, she would gradually fall to leeward, and the reason that this is not the case as she passes through the water ahead, is because she is continually and rapidly changing her position, and of course her keel is perpetually passing a new body of water, and before the vessel has time to slip to leeward, (in consequence of the pressure of the water by the keel to leeward) she has passed into another mass of water which has not been acted upon by the keel, and thus she does not fall to leeward.

If what has been said on keels be admitted, I think it must be allowed that keel is as important for a swift sailing vessel as the form of the main body.


Image of page 7 Construction of Ships
Construction of Ships page 7

We have now to consider how the keel is to be added to the main body so as to have every possible benefit of it. If it is put on so as to be fore and aft at an equal distance from the main body, we shall have a part of its advantages, and lose some of its benefits. Being annexed to the ship in this way, she would be a long time in stays, and the rudder would not have so strong a power.

I propose to have it very shallow forward, and at least five times deeper aft than forward. Thus if it is one foot deep forward, it would be five or more feet aft. I have then all the aid keel can bestow, and by this position of it I give the rudder a strong power, and enable the ship to go about with great facility.

It must be remembered that I call it all keel from the transome down; therefore, although I call the keel five feet deep aft, it does not in fact go down in the water more than two feet deeper than where it is one foot deep; as the main body rises up aft until it comes to the surface of the water, where my keel aft commences descent.

The keel must be as thin as is consistent with the strength it is necessary to give it.

It must be broadest forward and taper away the whole distance until it comes to the rudder, which also must be thinnest on the edge opposite to that affixed to the vessel. The keel must also be continued to be made thickest near the vessel, and taper until it comes to the stern post. In this we take a hint from nature, the part which advances in the water being broadest in the fins of a fish.

On the foregoing principles I take the dolphin, and the duck, and from a union of the two shapes I draw my model of the main body, to which I add the keel according to the plan, and on the principles heretofore stated.

On the opposite side is my model sketched on the principles before stated. The sketch is made so as to be fully understood by other than ship builders.

She is intended to sail faster than other vessels before the wind, close-hauled to it, or with wind free.

To be an excellent sea boat, because on account of her fullness she will live light on the water.

To rise easily on a sea, because she does not present any strait line in her main body from stem to stern.

To be under the perfect command of her rudder, because it has so strong a hold on the water.

To go about with great facility and quickness, because she has so strong a hold on the water aft, and so small a hold forward.

To have sufficient room to stow her cargo, but may be sent to sea without any.


Image of page 8 Construction of Ships
Diagram showing views of ships: stern - between midship and stern - midship (of sailors) - extreme breadth ; and view with water line : 70 feet keel, 8.5 feet hold, 23 beam - draws 4.25 feet water forward, 6.5 feet water aft - depth of keel 7.5 feet aft, depth of keel 1 foot forward - main body, draws 4 feet.
Image of page 9 Construction of Ships
Diagram with three views of fish at water line 1) fish shape on the new construction as it sets in the water; 2 ) fish shape which is commonly attempted as it sets on the water in its best view and 3) the form commonly presented to the water where the fish shape is attempted. Oftener this than the preceding.

Notes and Acknowledgements

This pamphlet is located in the Navy Department Library’s Historical Manuscript Collection, where it accompanies an autographed letter signed by Frederick Tudor, dated 22 December 1812, Boston, to Samuel L. Mitchell.

Frederick Tudor also sent a copy of the pamphlet to former President Thomas Jefferson who responded favorably to it. Jefferson’s letter is transcribed below. The Navy Department Library is extremely appreciative of J. Jefferson Looney, editor in chief of The Papers of Thomas Jefferson: Retirement Series for providing the transcription of Jefferson’s letter which will be printed in the forthcoming volume 5 of the series being published by Princeton University Press. The letter received by Frederick Tudor is located at the Pierpont Morgan Library, New York City, and Jefferson's polygraph copy is at the Massachusetts Historical Society in Boston, Massachusetts.

To Frederic Tudor

Sir Monticello Jan. 8. 13.

Your favor of Dec. 14. has been recently recieved, and I thank you for the pamphlet it inclosed. but of all the subjects on which I could
have been asked for an opinion, that of naval construction is the one on which I am the most ignorant. born & bred among the mountains,
& never having lived in a seaport, I do not understand even the language and phrases of this subject, and am still less familiar with the
different forms of construction. at college indeed I became acquainted with the principles of the solids of least resistance: but your appeal
to the forms of the Duck & Dolphin are more likely to furnish you useful hints. of these two forms I should suppose the former most analogous
to your views, because intended not for immersion, but for buoyancy, burthen, & motion with the least resistance. but to a master in the art,
it would be presumptuous in me to express more than my wishes that this useful art may recieve improvement from you, and the
assurances of my respect.

Th: Jefferson

RC (NNPM); addressed: "Mr Frederic Tudor Boston"; franked and postmarked. PoC (MHi); endorsed by TJ.


Published: Tue May 12 08:38:01 EDT 2020