Horsepower versus design

[galeonis]

Firstly, let me say that this site great! I've been land-locked all my life, but have recently discovered a interest in tugboats. Incredible vessels!

But I have a question regarding the ships themselves. Is towing simply a matter of horsepower? Or are the craft designed specifically for the task?

Or to phrase it differently could any ship with enough horsepower tow any other much larger ship?

Thanks!

[xenophon]

It's the ratio of size to horsepower. A ship and a tug could turn the same energy out, but a tug's small package makes it more powerful in terms of the lesser of it's own weight it has to move along with its tow.
Also, try to move a ship in that close without bashing something up.

[mtalarino]

I need to find information on tugs, and how they work. Is there any place where I can get information on how a tug works in different conditions?

[Fleet Super]

That's a very broad question with a wide range of answers.

Could you be more specific?

Then we could branch off form the short answers into a deeper conversation.

[wafinator]

the hull design, placement of the wheels, type of wheels, etc, all play important roles as well. A good example would be Moran's ATBs and new ASD tractor boats. Similar horsepower from similar engines (the same engines in some cases). However, the tractor will put out nearly twice as much bollard pull (static pulling power measured in tons) than the similarly powered ATB. This is because the wheels and engine configuration on the tractor were designed for maximum power at a static condition, ship docking conditions, where it will be used most. Therefore at the drop of a hat it can generate alot of thrust without needing to move ahead. The new class of ATBs on the other hand have new generation rolls royce "speed" wheels which are more efficient turning ahead, and engines configured to produce maximum power at their cruising speed pushing a loaded barge at around 10 knots. That on demand power of the z-drives, despite having the same HP, isn't really there with the ATBs, they don't need it, but there is sufficient power once it gets up to speed. Handling characteristics are of course drastically different. Aside from the tractor boats having twin asmiuthing stern drives, their hull form allows vastly greater manueverability and are inherently directionally unstable to allow for this. The ATB designed solely to push a specific barge is really only concerned about moving ahead in a straight line most of the time and as a light boat will comparably handle like a hog.

To attempt to answer to your question more specifically, sure any vessel could tow another vessel, but it won't do it very effieciently if its not designed for that. It more has to do with the engine design and wheels than anything. You'll notice tugboat propellers that are meant to move other things, ie. ships, barges, are usually big, fat, and rounded. This large surface area to move large amounts of water will give them that low speed or static power, when paired correctly with an engine designed for that. They will also generate good power rotating astern than other wheels might, which a tug doing ship docking will oftentimes need as well. On the flip side, say a navy destroyer, its wheels are thin, sharp, and turbine like, with usually more blades. These are designed for speed, but would mostly just chop the water if it had to push or tow astern anything other than itself. Landlubbers might compare a tractor-trailer to a ferrari. On paper they might have the same hp and torque, but dont count on the ferrari to tow a trailer very well.

Many large ocean towing vessels will further maximize towing power by designing their wheels to sit inside nozzels. This will greatly direct the thrust more efficiently for towing and theoretically add 20-30% more horsepower ahead. It will detract from their manueverability compared to other tugs (a good deal of manueverability is derived from the momentum of the wheels turning, which the nozzels block), but they aren't concerned much with that as they'll usually be towing point to point. So again, its that pushing power that makes the tug boat unique, and when talking about ship docking boats, that static pushing power makes them even more unique.

Thats kind of a scattergun response, hopefully you'll find something somewhat useful in there.

Regards.