A Question Of Trim & Paddlewheels

Ted,
I'm sure Alan will chime in with more info, but yes, flooding a forward compartment does have a fulcrum effect around the Center Of Bouyancy, and will lift the stern. Almost invariably, over the years, boats get heavier because more stuff is added to them and rarely is that stuff removed. For sternwheelers this can create a problem by putting the bucketboards too deep in the water. I think the DQ and BOL have both had this problem over the years, and work has been done to improve the situation. You can either remove items from the boat until she floats with the draft she was designed for, or chock-up the wheel shaft and bearings to a higher position.

Anyway, getting the bucketboards up to their most efficient "dip" does do wonders for speed. If fact, reducing the dip of the buckets will usually produce some increase in speed, as long as the dip does not become too small.

Ted, I think Steve is absolutely correct...getting the wheel in trim is crucial. I think the fulcrum effect is there, but not as pronounced as one might imagine. As you pointed out, he also probably had the engineers burn from stern tanks, and this works on towboats as well. The boat's design has a LOT to do with it; on the m/v MAGNOLIA, it makes no difference how you burn the fuel, the stern sits down in the water. On the HAL D.MILLER, we could get that stern WAY up, and she would fly! I think also getting the head down helps. One would think that this would increase resistance in the amount of water having to be pushed out of the way, but the extra water that must be pushed out of the way seems to me to have little, if any, practical effect on speed. A good example would be the bulbous bow on many ocean-going ships -- it actually increases the speed.

As to a "square" sternwheel, I think that is not a factor, though Capt. Bates may chime in and tell us otherwise. The BELLE OF LOUISVILLE's wheel is wider than the diameter, and seems to do just fine. The JULIA BELLE SWAIN's wheel is narrow compared to the diameter, and appears to roll slowly -- that is, that boat's wheel carries little water upward, and all the power is used to push the water BACK, not lift it up. The JBS throws very little water up on the wheel, but she is FAST! On the DQ in the 1970's, the boat had become so loaded down with various new systems added that Capt.Wagner felt he had to try to get that wheel out of the water to push forward, not lift water up. I was always told the optimum trim at the wheel was for the circles at the inside of the bucket boards to be just touching the water. In the years before the DQ got her new hull, the wheel sat several feet lower than that, wasting a great deal of energy.

My father told me that on a Mississipi River style paddlewheel steamboat the optimum dip was for three buckets to be in the water at one time. One bucket would be fully submerged, while one of the other two would be heading down into the drink just starting to work and the other would be heading up for air.

The DELTA QUEEN's wheel is a different beast altogether. C.W. Stoll once told me that the wheel we see today on the DQ was heavily influenced by Jesse P. Hughes. Apparently, its California design irked Capt. Jesse, and he had the wherewithal to have it changed. When looking at old photos and movie reels of the DQ's California days, it appears, to me, as if the outside wood and iron circle we see now was made of metal. Perhaps there were other changes made too at that time. The buckets on the DQ's wheel now were repositioned outwards after the new hull was put on. Mike Williams would be the best one to fill us in there.

Even the AMERICAN QUEEN has had her buckets moved around and adjusted trying to improve the wheel's efficiency.

Dad also maintained that the larger the diameter of a boat's wheel the faster she would tend to go. A wheel with less diameter would give a boat more power. He said that this was also the rule of thumb for steam locomotives and their drivers. Therefore steam passenger locomotives had drivers as tall as a man while freight engines had drivers half that size.

When the QUEEN CITY was launched in 1897 her shaft, flanges, wheel arms, wooden and iron circles were all in place. The buckets were put on after she was floating to get their proper placement. I believe that she was known as a fast boat, but a notorious coal hog.

I'm sure Alan Bates can shed more light on how he agonized over the NATCHEZ's and CHAUTAUQUA BELLE's wheel. As we all know, he certainly got those right.

That makes a lot of sense, because if the buckets are too close together, the following bucket will be working in the suction of the previous bucket, and not being effective. I think this would also lead to too much carry over.
But I'm just guessing at this.
Steamcerely,
David D.

Trim is the fore-and-aft difference of draft beween bow and stern. It is similar to list, which is lateral. Yes, trim does affect how a paddlewheel performs. It also has some effect on the resistance of the hull, but that is very subtle. You are correct in the see-saw comparison, for trim rotates around a real, but invisible, point called the center of flotation. It is virtually never at the center of buoyancy, which is an entirely different animal.
The proper trim is for the inner edges of the buckets to be at the surface of the water when the boat is at rest. This was a rule of thumb for guidance of builders. During WW I (1916 - 1919) the U. S. Engineers ran a series of tests with several steamboats, notably the Nokomis. Among other things the tests proved that rule to be true. They also proved that if you want speed, a large diameter wheel with relatively shallow dip should be used. For pushing power a smaller diameter with deeper buckets worked better. Since then basin tests have borne out these conclusions.
As for "square" wheels being better, that is a new one to me.
For speed OR power a long stern rake is preferable. The knuckle at a vertical transom should always be well above the loaded draft line or the boat will not back properly.
Steamboats seemed to be crude compared to ocean-going craft, but they were very well suited to the work they had to do and the river conditions with which they had to contend. A lot of subtle design thought went into their design and operation. They held symposia and wrote papers just the same as in other disciplines, a fact that the USCG cannot imagine took place.
Modern western rivers towboats are truly miracles of design. Much thought has also gone into the design of the barges they shove. Here, again, the deep-sea designers are lost.
The Nokomis trials were presented to Congress in a book about the size of an army training manual. They tried seven different paddlewheels on that boat. They also used a dredge, the Tabor, for comparison and tried a couple of feathering paddlewheels. A tunnel-stern propeller-driven boat, the Inspector, was also examined. Several types of barges were tested and a great many different configurations of tows were tried. In addition, dynamometer tests were made to prove the pushing forces. It was an exhaustive test under real conditions. The result is 144 graphs and charts showing speed, horsepower, fuel consumption, slip, drag, overall efficiency, etc.
This book is very rare. My copy was xeroxed from another xerox copy and cannot stand a third reproduction. The title of the book is:
HOUSE DOCUMENTS, Vol. 9, 67th Congress, First Session, April 11 - November 23, 1921.

As for the Natchez paddlewheel, we were obliged to use the machinery, including shaft, cranks, flanges, etc., from the towboat Clairton. I have forgotten the diameter of the Clairton's paddlewheel but it was about twenty feet and had 4 foot deep buckets. We reduced the bucket depth to about 2 1/2 feet (here my memory fails me again) and increased the diameter. The guys on the Natchez can tell you what the dimensions are.

I forgot to answer your "squat" question. Daniel Bernoulli discovered that when a fluid (whether it be liquid or gas) flows through a constricted space a partial vacuum is created and the fluid increases its velocity. When a boat passes over a bar such a condition is created and the vacuum pulls the boat down. This is also why a moving hull, like a flat-sided barge, sucks to a lock wall and is hard to break away. You can also see it when a passing boat "pulls" the water away from the bank.

What is the difference between the center of bouyancy and the center of floatation? What does each affect?

Alan & steamboating colleagues:
The question and answers on this interesting thread amaze me having not progressed beyond school in 101 with a lawn mower, paint brush and broom. Keep it coming. A number on this web have vividly witnessed the 'pull of water from shore' created by a passing sidewheeler or sternwheel vessel. I've witnessed it here and on foreign rivers and other waters. The water drops visibly from the shore followed by the near tsunami flow sending waves up on the bank much to the surprise of those fishing, camping or swimming. Again those fluid dynamics Alan discusses. Years ago there was a mild earthquake in New Orleans. The DELTA QUEEN was docked. Letha Greene and Purser Bob McCann later recalled, among others, the DQ pulled away from the dock with the stage rising and falling. Even a small quake here at the Maysville Fault can create movement in the Ohio River and I've felt it with a boat bumping the dock.

Nearly 38 eight years ago I was returning from Russia aboard the steamship ESTONIA in Copenhagen harbor bound for Tilbury Docks just down from London, England. A then Soviet era cargo ship came racing down the channel. Ahead was docked the SAGAFORD [Built 1965]. That 'fluid dynamic action' caused our ship and the SAGAFORD to pull away from the pier with screaming lines and crunching steel gangways pulling away and falling between the ships and dock. The return rush forced the ships back in again with loud grinding sounds. Fortunately passengers and crew had been held back. Later investigations revealed the Russian captain had done it deliberately in a kind of Cold War gesture.

Big 'blue water' ships are not always the best 'backers.' Express liners of the old days were built for full speed ahead. Emergency backings cause no small vibration of the superstructure. Big liners entering New York then and now still carefully calculate the tide and depth of the channel beneath to avoid being pulled down to the bottom not many feet away. No doubt modern dredging has corrected some of these problems. The clearance over the Holland Tunnel in Manhattan was also touchy for the Cunard ships old QUEEN MARY & QUEEN ELIZABETH ['Big Liz'] heading out from the Hudson piers or arriving. May not be 'pure steamboats' but something I had to add.

Cheers,
R. Dale Flick

The center of buoyancy is the center of gravity of the displaced water. The center of flotation is the geometrical center of the waterplane (which is the surface of a plane at a waterline). As draft and trim change, these centers move. Locating them is a nice problem in practical geometry. Calculus helps. Naval architects live with these esoteric points in space and use them to determine how a hull will react to various forces. Any good book on naval architecture will confuse more than it will amuse, so unless you seriously want to design ships and boats, stay far, far away. ABS and USCG examiners want them to agree to the fourth decimal place with their calculations, even though it is impossible to measure hulls to such a fine degree.

Years ago I had an 18 ft. Weaver Yawl built (cost $300) with the idea of powering it with a lawn mower motor and sternwheel. Designing the paddlewheel soon became much more complicated than I ever imagined. Afterall we all know what a paddlewheel looks like, but how do you build one to get a certain amount of desired performance? I found the best was way to "back in to it". I started with the premise that I wanted the boat to go 10 mph.
The first thing I did after getting the yawl was to put it in the water, by standing on the stern transom, I figured that would about equal the weight of the engine, gear, and wheel. I had someone mark the waterline on the boat. I then took the boat home and on a large piece of cardboard I traced the stern of the yawl with the waterline marked. I then drew the fantail I was going to build. That got me the depth from the fantail to the waterline and thus the approximate diameter of the paddlewheel I would need.
Now a boat can go no faster than the speed the wheel rotates. A paddlewheel has a lot of slip so the wheel has to rotate much faster than say a car wheel and the faster a paddlewheel rotates the more slip there is. Using the NIKOMAS test data, which Alan Bates referred to, I figured about a 40% slippage. Once I had firgured out the speed the wheel needed to rotate, I could determine the amount of reduction I needed from the engine RPM to the wheel RPM. I used a 5 hp lawn mower motor. Lawn mower motors idle at about 900 RPMs and go about 3,300 RPM at full speed.
So far I had figured the diameter of the wheel and the speed the wheel would have to rotate in order to achieve 10 mph. Now all I had to do was to design the wheel......width of buckets and number of buckets. Using the NIKOMAS charts again I found that thin buckets on a large diameter wheel created the best speed. Again from the NIKOMAS tests I found that the distance between the wheel buckets should be about 1 1/2 times the width of the buckets. Since I was planning on using 2" buckets, the distance between the wheel arms needed to be about 5 inches, knowing the diameter of the wheel , the circumfrence was easy to determine and dividing that by 5 got the number of wheel arms needed.
Did it work? In one word YES! A 5 hp outboard could not move the boat nearly as fast as that lawn mower engine did. The boat did achieve the 10 mph when the motor was running good (the motor was off an old, old riding mower, cost $5.00, and it had a mind of its own) and the boat was in trim...and it only used about a quart of gasoline per hour.
I took the boat to the Charleston Sternwheel Regatta several years and raced it against Nelson Jones' boat. On the speed run I won easily, but with his wider buckets and smaller diameter wheel Nelson could shove me all over the river.
By the way, I used a single balanced rudder which was about 3 ft long and the boat steered like a dream. It didn't back as well as I had hoped, I think because of the height of the stern transom, but I found if I backed hard for a couple of turns then idled the wheel, the boat would answer the rudder very well while backing.

Thank you. Just curious. Sounds very similar to calculating the various centers for automobile suspension design. I am retired from designing buildings and have no intention of taking up another design career at this stage. The only watercraft I ever designed for actual construction was a cardboard catamaran for a raft race. About all you could say about that was that it floated at its designed waterline and lasted long enough for a second place.

Jim,
Got any photos of your sternwheeler? Sounds like it was a fun project.

Dale,

Your observation about the suction caused by a moving hull in a constricted channel brings to mind one of the most notorious instances of that very situation. At noon on April 10, 1912, as R.M.S. Titanic left Southampton's Ocean Dock on her maiden voyage, that exact scenario was played out as she passed the S. S. New York, moored pierside in the narrow channel leading out to Southampton Water. All of the huge hawsers on the New York snapped, and she was dragged towards the side of the Titanic. Quick action by the harbor pilot stopped the Titanic's engines, and then reversed them pushing the water away from the side of the ship, slowing the drift of the errant ship until Titanic's tugs grabbed onto her and returned her to her pier. They lost about one hour that afternoon during all this maneuvering. Pundits have sometimes wondered if the time expended avoiding that near collision not been used, would the collision with the fatal iceberg have occurred at the time and place which sealed the ship's fate? A moot point, perhaps, since the ship was obviously operated at excessive speed and was driving into a massive ice field that night. But just as Western Rivers steamboat designers learned through experimentation, these naval architects of gigantic Western Ocean liners also were treading uncharted waters with how these massive hulls would behave under various conditions. Alan's point that Bernoulli's principle applies here is well-taken. How that plays out in actual practice was not always so well understood.

Paddlewheel bucket planks should be spaced about 2.5 times as far apart as the dip of the buckets, measured at the half-dip. This is not always possible, of course. Too close together and succeeding buckets are robbed by the preceding ones. Too far apart and they virbrate excessively.
Incidentally paddlewheels have some advantages over propellers. In general, they work with less slip. They work equally well whether coming ahead or backing. They can be repaired without docking the boats. They are not as susceptible to hitting the riverbed as propellers. Their disadvantages are excessive weight and size. They waste much effort lifting water instead of thrusting it. In the major directiion of travel (usually forward) propellers are more efficient.

Fiirst You Have to Row a Little Boat

Simply what is the relationship of a vessel's trim to speed...?[/QUOTE]

Yes, Wagner was right... as usual. And, folks, you can throw away all those gauges, charts, etc. and get yourselves a couple of row boats- one with a model bow (yawl) and the other with the bow of a scow (jonboat) to understand what trim does relative to speed and performance.

Row both boats, separately of course, to understand how each performs without ballast of any sort. Another person or large revetment stones both makes great ballast, but a person is easier to move about the boat than the rocks. My favorite ballast was a beauty called the Fish.

Ballast the bow; then the stern of each boat and row. Your body will act as a better indicator than anything else as you will feel the difference in the way the boats perform according to how they are trimmed, and your senses will also be the best judge concerning differences in speed.

The results of these simple, yet reliable, tests should confirm that a yawl with a pointy-bow is best trimmed with the bow down and the stern up. A scow-bow boat is best trimmed with the bow up higher than the stern. Thank you Captain Wagner.

Back in the AVALON days, I challenged two fellows to a boat race who were paddling a canoe from St. Paul to New Orleans and had hitched a ride with us from Memphis to Greenville. It happened that I was rowing alone in the yawl when these fellows came alongside on their way down the placid waters of Lake Ferguson heading toward the mainstream of the Mississippi River to continue their sojurn down-river, and so I invited them to a race. After nearly capsizing their canoe from laughing so hard, they accepted, and I requested their approval to add some heavy revetment stones to the boat. They thought I was really nuts,then, as I hefted enough West Kentucky limestone into the bow to lift up the stern and weigh down the bow.

Their canoe was beaten by more than twice the length of the AVALON's yawl, and were those boys ever peeved over being trounced by a skinny kid pulling on the oars of a sixteen-foot aluminum boat with the pointy bow loaded down with heavy rocks; especially when the two of them, stroking for all their worth in a lightweight canoe with well over a thousand miles of practice and conditioning, were thoroughly humiliated, and there for a few moments I thought I might need some of the smaller stones for protection in case they attempted to board my boat..

They never stood a chance and never understand why.

Hi, David:
Ah, clever you to recall the famous near miss of the RMS TITANIC and the NEW YORK in Southampton, April, 1912. A oft-quoted 'omen' leading to the tragedy of the sinking. Yes, the 'time factor' of that one hour caused a lot of speculation later. A pure case of 'time and place, set and setting.' A pause of one instant can mean all the difference in human existance positive or negative. The ancients opined on the 'mystical force of objects near and far moving around each other in the cosmos.'

An addition to your TITANIC history is this. From roughly 1900 on increasingly new, larger and heavier ships were creating new and in some cases uncharted waters for officers and engineers. Following the TITANIC sinking experts were called to discuss the ship's hull and her failure to experience 'Hull rebound tendency.' Alan and others on this web know and understand this better than me. Basically, in the old days, a steamship of roughly 16,000 tons would, in certain cases, 'bounce or rebound' from relatively minor collision or brushes against surface or submerged objects. The larger OLYMPIC, TITANIC, BRITANIC, etc. of the the new class would, on a collision or brush, not 'bounce or rebound,' but keep right on going with vast tonnage under speed tearing or piercing the hull. One veteran CUNARD officer commented how he'd 'bounced' the CARPTHIA off of wood piers and pilings with no problem in a docking. Nobody knows if the TITANIC had been in a better position she could have brushed off with a rebound or slide. A full collision dead on wouldn't have been so bad and she could have survived. This happened with the STOCKHOLM in the ANDREA DORIA collision when her bow was smashed head on back some 80 feet to a bulkhead.
Not always 'pure steamboats here' but what other excuse can I give?

Cheers,
R. Dale Flick

Jium, you are right. I looked it up and found that the spacing should be from 1.5 to 1.75 times the dip. My remembered 2.5 is wrong.

This thread is great! I am saving it all as a word document, just in case I ever get to build my old dream stearnwheel steam houseboat.
S'
David D.

Thank You Gentlemen , One & All !

Thank You Gentlemen , One & All !
I would like to thank You All ( a Southern term ) for your wisdom , knowledge and insight concerning this question I've carried with me from long ago . This month , I'll be " still above ground " for some 57 years and this " Quenstion " and answer session just goes to show you that , you can still show an old dog a few new tricks and more importantly , if you have the desire of course , you never are really too old to learn something new . In NOBRA's , continueing education courses , we emphasize the " sharing of information , knowlege & personal experiences " so as to better inform and educate our up and coming apprentice pilots and the information that has been passed along on this topice will certainly be shared with them as well ! Thank You Once Again !
Smoothe Sailing !
Ted Davisson