The thing to remember is the toot-toot-toot doesn’t mean a hoot.
It’s the chug-chug-chug that makes it go.
Picky detail: The boats one sees on the Mississippi are towboats. The distinction is significant but abstruse, involving boat construction and engine/transmission structure that I am not clear on.
As an IT person I can’t complain, but in things nautical one runs into the second most nit picking bunch of fellows anyone has ever had anything explained by. 
Yeah, they’ve always something to barque about. They should stop being showboats and frigate it and have a schooner of beer, or else someone may smack them. Once they ketch on they’ll be in the pink.
I don’t care how they work, all I know is that if I were ever to get a chance, I’d be a tugboat captain in a NY minute.
You should be ashamed. Does your Mother know you do this?
I heard about a tugboat that was ashamed when it found out its mother was a tramp and its father was a ferry.
Mods! Mods! Hello?
Waiter! Waiter, I’ll have what he’s drinking.
Pretty much answered, but few points:
1/ they are not usually “tiny little”. The first time you see a tug close up that you have, until then, only seen from a distance alongside a large vessel your reaction is likely to be “Great Og that thing is actually freakin’ enormous!*”
2/ Most of the motive force in harbour movements of ships comes from the vessel’s main engine. The tugs are used as thrusters, just pushing or pulling on the bow or stern to enable tighter turns, or to push or pull the vessel bodily sidewards into/out of berth. The former doesn’t require a great deal of force (by ship standards) and the latter occurs very slowly and in calm water.
Moving a large vessel through a channel “dead ship” using only tugs ie without the main engine doing most of the work is very hard and difficult work.
Hey, I haven’t even said anything about “steerage weigh”.
*Insert “that’s what she said” joke here
That would be Linie Akvavit.
Carried twice across the Equator in ships, you know.
EDIT: Ah. I see Princhester has brought the thread back on course.
.
Another point I might add because it’s interesting (at least to me) is that a tug’s pulling power is referred to as its “bollard pull” ie how much force it could exert on a fixed bollard.
A medium harbour tug might have a BP of 50 tonnes. A seriously powerful harbour tug might have maybe 80 tonnes. A group of tugs with total bollard pull of 200 tonnes or a little more might handle a fully loaded capesize with a displacement of several hundred thousand tonnes.
And then, pinnace ensued.
Having grown up on the Lower Mississippi and been around pilots all my life (family members), I’ve never heard one of them use the term “towboat”.
Wikipedia says:
A more proper term for tugboats on the Lower Mississippi would be “pushboat”, but I’ve never heard that one either.
First, the tug boat’s small size is an ADVANTAGE, so let’s get that out of the way right now. Bigger would be worse, because that would be more weight the tug engine would have to move.
Second, the tug boat is mostly engine. It’s a floating engine. A ship is absolutely enormous relative to its own engine(s).
Also, tug boats take advantage of gearing and slip [slip at the prop(s)]. Gear reduction allows the engine to spin a great number of revolutions to increase it’s load. Sort of like how you can use a hand crank winch to move tons of weight. For example, you can hand crank a two ton boat with one arm using a winch that has gears. Your arm goes around 15 times and the boat moves six inches – 6th grade physics.
At the prop(s), if the prop can’t ‘bite’, it slips and this changes depending on prop shape and design. This reduces strain on the engine and gears, and slip allows the engine to come up to its power zone without unduly stressing it.
And they have actually have alot of acceleration. Every year Seattle has tugboat races in Elliot Bay, and one year I was lucky enough to be on one. This was one of the big tugs used on tankers/cruise ships/etc. As one poster said up-thread, you think of them as small when you see them far across the water working with a cargo ship, but up close they are much bigger than you think. Also, the tug we were on was very modern and was driven by thrust pods (not sure what they are really called) underneath that allowed the captain to put all that horsepower into acceleration, as opposed to using older fixed-pitch props. Basically, about 10 tugs line up abreast north of the downtown area and race south to the port. The captain told us to hold on tight when the starting horn blew, and even holding on, I was almost knocked over when he ‘floored it’, so to speak. I’m not sure what the top speeds were that day, but it was definitely faster than you’d expect, too. It was a very cool experience.
Sounds painful.
Better than being “poled” by one.
Wow many thanks everyone. I didn’t know it would draw this much attention but I’m always glad I asked.
One thing I got from it also is that once the tug (http://i78.photobucket.com/albums/j83/dandmb50/Tug_Boat_FR_Le_Four.jpg) starts pulling the ship it is much like pulling/pushing a car, once the tug starts and moves it a bit the momentum of such a large vessel keeps it moving.
Many thanks