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New Jersey Scuba Diving

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New Jersey Scuba Diving

Propellers, Shafts, & Rudders

propeller & rudder

modern brass propeller
A huge modern brass propeller ( from the SS United States ) on display.

shipwreck Delaware propeller
Looking down the prop shaft at the iron propeller on the Delaware. The narrow squarish blades indicate that this is a rather primitive 1880's model, unlike the more modern rounded prop on the Macedonia below.

shipwreck Macedonia propeller
The propeller on the Macedonia.

shipwreck Macedonia shaft mount
Propeller shaft bearing and mount on the Macedonia.

reef Venturo propeller
The propeller on the GA Venturo - a completely modern design.
Note the wide, round blades.

Breaking a propeller shaft at sea can be a disaster. The propeller stops turning and becomes a drag, while the vessel's momentum carries it forward. The propeller slams backward, extracting the broken shaft and often mangling the rudder. This leaves a large hole open in the bottom of the vessel, directly into the bilges and machinery spaces. On a large vessel with a deep draft and a large shaft, the water comes in like a fire hose - uncontrollable.

The engine is soon disabled, and along with that the pumps, which in any case are probably not big enough to keep up with this magnitude of flooding. The outcome may take several hours, but it is inevitable, unless maybe the Coast Guard can fly out a special de-watering pump on one of their big helos. Unlike a collision, storm, or rogue wave, there is usually plenty of time for an orderly abandon-ship, and there are seldom casualties if rescue is available.

Shipwreck Emerald
The "Emerald" fell victim to a broken prop shaft in 1873, and the Lady Gertrude sank the same way in 2016.

shipwreck Oregon steering quadrant
The fallen steering quadrant on the Oregon, perhaps 20 ft across.

shipwreck Tolten steering quadrant


The steering quadrant on the Tolten


Paddlewheels

paddlewheel

The paddlewheel predates even the steam engine. Horse-driven paddlewheel ferries have been in use for hundreds of years. Compared to screw-type propellers, the design and construction of a paddlewheel is much simpler, and therefore they remained the dominant method of propulsion through the mid 1800s, with some examples remaining in use until after World War II.

Compared with screw propellers, paddlewheels had a number of disadvantages. Greatest among these was efficiency - early-on it was shown that in a tug-of-war, a propeller-ship would pull a paddle wheeler of equal size and power backwards. Paddlewheels were also much more delicate than propellers, especially in the stormy northern oceans, where waves have actually smashed the paddlewheels off a number of vessels, leaving them to drift, or limp home by sail if they were so-equipped. On a warship, a paddlewheel was likely to be the first thing shot away in a fight.

Paddlewheels also had a few of advantages over propellers. They could operate in very shallow waters where a propeller would strike the bottom. Side-wheel paddleboats could operate in extremely tight quarters, literally spinning in place by putting one wheel in forward and the other in reverse. Most paddlewheels also function equally well in forward or reverse, unlike a propeller which is designed to go in one direction only. This made them ideal for use on ferries and tugboats, which often find themselves needing to go backwards.

shipwreck Mistletoe
The side-wheel excursion steamer Mistletoe. Note the large round box around the paddlewheel, to contain the spray that would otherwise soak the ship. If you look carefully, you can also see that she's going backwards.

shipwreck Champion
The "Inshore Paddlewheeler" - the Champion ?

Stern-wheel paddleboats could operate in debris-strewn waters, since the wheel was protected from damage behind the boat. It was also much easier to repair a damaged paddlewheel than a propeller. Therefore, in the later 1800s, paddle wheelers came to dominate river and inland traffic, while the propeller found greater use in ocean traffic. Ultimately, however, the paddlewheel lost out to the propeller entirely, and today it is only found on antique vessels and a few excursion boats.

side-wheel paddleboat

side-wheel paddleboat

CG illustrations courtesy of the Denbigh Project

Above are two truly superb depictions of a Civil War-era side-wheel paddleboat's propulsion plant and wheels. The large brown object at right is a fairly primitive low-pressure boiler. The gray barrel-like objects at the left are the vessel's two independent steam engines, each with a single cylinder. Horizontal direct-acting engines like this were typically found on European vessels, while American designers preferred upright walking-beam-type engines, as is evident in the photo of the Mistletoe above.

Since the two engines here are completely separate, they may be reversed independently of each other, giving the turn-on-a-dime capability described above. This is done not with a reverse gear as in an automobile, but by reversing the engine itself - a trick that is still used in some marine diesels today. Side-wheelers like this were much preferred over sternwheelers for open-ocean service, and I believe that all of the paddlewheel vessels listed in this website are side-wheelers.

shipwreck Rickseckers
The remains of a paddlewheel are evident in this sketch of the "Rickseckers."


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Disclaimer:

I make no claim as to the accuracy, validity, or appropriateness of any information found in this website. I will not be responsible for the consequences of any action that is based upon information found here. Scuba diving is an adventure sport, and as always, you alone are responsible for your own safety and well being.

Copyright © 1996-2016 Rich Galiano
unless otherwise noted

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