Diana Plans PDF

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"DIANA" - 25' classic fantail steam launch, wood. Includes outboard profile, arrangements, lines, table of offsets, framing plans, scantlings, etc. 3 sheets.


The velvety power of steam captures the affection of any man who has monkeyed with it. When boys who have toyed with steam grow up to be men, the size of their toys grows up with them. By informed appraisal, there are 1200 to 1500 of these steam launch buffs in all parts of this country and Canada. Most of the steam “nuts” have engines, boilers, condensers and gauges and whistles, but then have to settle for putting their assemblage of antique machinery into any tub they can find.
It is for these steamboat buffs that Diana has been designed. She is 25 feet overall by 6 feet 6 inches beam over the guards, with a two-foot draft. This is a standard size for a typical high-grade lady of the Gay Nineties. 

I have designed her from personal knowledge of the operation and. understanding of the peculiarities of fan tail launch building. When I was growing up at Rock Harbor on Isle Royale in Lake Superior, my family owned a steam launch of this size, and I ran her for some years. Later, as an apprentice boatbuilder, I worked on this type of hull. You might say, then, that I am very sympathetic with the romance and Cloud Nine stuff of which dreams of steam are fashioned.

Diana has all the goodies demanded by the purist in steam. Her hull is build-able by today’s methods and with today’s materials, but is accurately proportioned to conform with standard practice of 85 years ago.

I have shown two power plants. One is the Semple steam plant, built by the Semple Engine Co. This is a 5 hp double acting, noncondensing engine, steamed by a fire tube boiler fired by anthracite coal. This power plant is available at no more than the cost of an internal combustion power plant.
The other inboard profile shows a sophisticated Gay Nineties power plant. This rig is equipped with all the foo-foo demanded by dyed-in-the-wool frustrated four-stripe steamship Chief Engineers.

In this second power plant you will discover a Kingdon boiler, chosen because the joints of all fire tubes are externally encased in water. At 175 lbs. gauge pressure, she steams a 3-1/2-inch stroke by 3-1/2-inch HP by 6-inch LP compound double-acting engine of Navy type for about 12 hp. This engine exhausts into a surface condenser, which in turn is evacuated by an air pump delivering to a hot well or feed water pan under the boiler. From this pan, a steam injector pokes the water by its own bootstraps back into the boiler when necessary.

This outfit has the works: gauges, whistle, safety valve, bilge-and-water pump, mustard, catsup — all the steak and cole-slaw demanded for simulated steamboat worries. A perusal of the diagram will show this.
The steamboat fan will "grab” this.

The Steamboat fan will "grab" this old-time steam circuitry with giee, so I’ll not dwell on it.

For the uninitiated, let me tell you something about steam power. Perhaps one of the fascinations of steam engines is that they have maximum torque, that is, turning power, at zero revolutions. Any load that steam can start with, it can run with. Another thing that fascinates is the simplicity of the engine, understandable to anybody. Steam is admitted to a cylinder by a sliding valve which cuts off the steam at a pre-designed time, allows it to work by expanding, then opens and exhausts the spent steam. This allows timing by eccentrics and linkage, so that reversing is instantaneous without strain on the engine. The boat becomes highly responsive to backing, filling and surging forward.

Steam must be understood to be skillfully handled. The technology of steam is voluminous, available in any library. But an understanding of the nature of steam, that is, the physics of t, is basic to safe handling of it. Get this set of facts down pat, and you are safe with steam.

The physics of steam have to do with certain peculiarities of water. When water is boiled in confinement in a boiler, it turns, at a certain temperature and pressure, into an invisible gas. This gas is hot, containing enormous heat energy. After doing its work — when released — it condenses to water again, forming the fog which is miscalled "steam.” This is the stuff you see emanating from power plants on a cold day; just condensed water vapor, not steam.

It takes one British Thermal Unit (BTU) to raise one pound of water one degree Fahrenheit. Water boils at 212° F. at sea level. At this point, under what is termed "absolute” pressure (i.e. with 14.7 lbs./sq./in. atmospheric pressure subtracted from "gauge” pressure), the propensity of water to absorb heat is most abnormal. At 212° absolute, water requires an additional 970 BTUs to change its state to steam — the gas. This is an arithmetical equivalent to stating that water requires 5.39 times as much energy to turn it to steam at no pressure increase as was required to bring it to the boiling point.

Under pressure as in a boiler, even more heat must be added until, say at 65 pounds gauge pressure, the temperature is 311.2° and the total heat content per pound of steam is 1181.9 BTUs. This is an enormous energy input.

When the steam condenses back to water at 212°, it gives back this energy in the form of heat. If the boiler ruptures, the heat content built up and contained in the boiler water instantly causes all the water to flash into gas of a high explosive force. That is why boilers must be hydraulically pre-tested to withstand many times the normal operating pressure.

Given that precaution, boilers are safe. The Semple Co. in their brochure states that they test their boilers to 500 pounds static water pressure. They state that there is no Coast Guard restriction for experimental, privately operated steamers, other than the normal equipment requirement of lights, life jackets, etc.

In a small vessel like Diana, a full bodied boat is needed because the power plant is heavy. The hull type is such that wide variations in weight can be handled without materially affecting performance. It takes nearly 500 pounds to set Diana one inch lower in the water.

Nobody is going to win a Harms-worth Trophy with this boat. She is based on the old naptha launch form, which in turn became the form of the electric launch. I had access to the lines and plans for these old electric launches when I was at Elco designing some of their power cruisers prior to World War II. It is on these electric launches that I have based Diana.

Here is some steamboat lore; it is best to run this type of vessel at her natural hull speed, which means that the square root of her waterline length as expressed in knots will be her most easily driven rate for a given power. A 16-foot waterline boat will have a natural speed of 4 knots, a 25-foot waterline vessel will have a natural speed of 5 knots, and so on.

This rate will give the gentle, graceful glide for which these boats were famous. At above a S/L ratio of unity, or 1, the bow begins to rise and the stern to squat, and heavier wake and resistance is encountered.

It is a fact of naval architecture that these speeds can be attained with 1 hp effectively delivered to the prop shaft per ton of displacement. In engineering parlance, this is termed EHP, or Effective Horsepower. This is the power left from Indicated Horsepower, or IHP, after power lost to friction and auxiliaries is subtracted. Thus, on WL length of 22.5 feet, Diana's natural speed is 4.7 knots— 5.5 mph. Since she weighs at the datum waterline about 4200 pounds or 1.87 tons, she will make 5.5 mph with 2 hp easily. The extra 3 hp put out by the Semple engine would raise this to about 6-7 mph.

Another rule of thumb relates to the size of boiler needed. It requires about 5 square feet of fire exposed surface per engine horsepower for a watertube boiler, or about 6 square feet for a fire-tube boiler. If you conjure your own "patent" boiler, figure on about 40 pounds steam per hp/hour for a simple double acting engine of the same size as the 3-inch by 4-inch Semple 5 hp engine.

The condenser should have about a square foot of condensing surface per hp if of the internal type, and about half that or tt-square-foot per hp if of the keel condenser type.

Your fire is the source of power. The firebox and grate should be of such size as to release 41,000 BTUs per hour per horsepower. Anthracite coal is easiest to manage and burns quietly, producing about 12,000 BTUs per pound per hour. Three and a half pounds of pea coal will steam 1 hp for 1 hour. One cubic foot of bunkering volume will accommodate 40 pounds of pea coal easily.

Wood, as a firing material can be used, but the heat yield is only about 6000 BTUs with spruce, or about 8000 BTUs with birch. The idea of coasting along to Alaska on beach driftwood is nuts. Such stuff is either wet or dry, and burns like gunpowder or not at all.

Good small steam engines have to run at 500 to 600 rpm to deliver efficiency. They thus run at a blur — not the ponderous speed one associates with the big engines in steamships.

Fuel oil, fired in a vapor or Lune Valley burner, will deliver about 19,000 BTUs per hour, but this generally requires some sort of blower to facilitate bringing up to sustaining heat, and these blowers are noisy.

An occasional hunk of lignite or bituminous cannel soft coal will provide the smoke you want for realism — if you favor emulating a tramp steamer hull-down on the horizon, leaving your mark for lurking submarines.

Propellers used on steamers are large in diameter, frequently one and one-half times as large as you*d expect in a gasoline engine installation. The pitch, by motor boat standards, is enormous. Propellers of Vh pitch to diameter will work best. Frequently, in these old fantailers, p/d ratios of 2 were used. I have dressed Diana in a typical Chas. L. Seabury type steam propeller to keep her fashionable as to her times, but any good propeller will work. Doesn’t matter whether right hand or left hand — steam runs equally well in both directions.

A number of things that stem from the best practice in traditional boatbuilding should be mentioned: one is the size and heft of the keel and keelson, another is the material and construction of the horn timber at the stern, and another is the modernization of the old-type dado shaft log alley cut.

The builders of steam, naptha and electric launches found that keels had to be massive in order to handle marine railway haul-outs. There is a lot of weight to the machinery in any of these craft. The keel must be stout enough to provide the main backbone girder effect. If a keelson is used as shown, sided 8 inches and molded 5 inches, tapering to 4-inch siding where indicated, there will be: (1) faying surface in the back rabbet that will give fine fastening faces to the gar board plank and the hood ends of the main planking; (2) the heels of frames can be gained in to the keelson and no floors will be needed. Note the word is "gained." This is correct journeyman lingo for what amateur designers always call "notched." A gain is, in other correct wording, a half mortise. A notch is a nick you cut in a Colt .38 after you have killed the sherriff while heading him off at the pass.

The horn timber is aided 4 inches, molded as shown, and fleshed out with 1-inch oak cheek pieces and proper stop-waters. Oak is preferable, but Englishmen use elm and have for years. There is plenty of white elm available to anyone in this country, and it can be seasoned and sawn to pattern as lofted. Elm weighs but 70 percent of the 54 lbs./cu/ft. of good white oak, but holds fastenings well and is about as easy to work. Wide flitches in elm are easily found.

Note that the fastenings of keel and horn members as assembled go through main members square off the faying, or joining faces. This is proper. I see lots of drawings by green designers that show drifts at every which angle, on the theory that they “key** the timbers together. No such drifting will ever take up tight the second time the boat is launched.

The shaft log is split along the shaft center line, with a square cut made on a dado saw head. After joining with good Vfc-inch line-bored bolts, square to the joint, a PVC pipe (poly vinyl chloride) is centered and locked in place by very hot parafin wax — the white kind available at all supermarkets in one-pound packages of four slabs one-inch-thick. About three pounds will be needed. This provides an absolutely watertight, long lived shaft hole.

Any such work as this always evokes much correspondence for the designer, and since this is time consuming, I must say that if you are a steam “nut** and are serious, I will be glad to supply prints from these drawings if you care to reimburse me for the time and trouble. I state this to discourage the merely curious.

There is much more to this little ship than meets the eye. She is carefully designed, is amenable to wide variations in loading, and could be used even as a motorboat with an engine of the right weight and size.

She is called Diana, because all early steam yacht owners were classicists. They flaunted their expensive erudition by going to Greek mythology for most of the names of their graceful, expensive status symbols. Diana was goddess of the chase, the hunt. Seems fitting for a sleek and silent traveller such as this.

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