Tugs.... Coastal

hmm, just want to ask... what is the different between ussual tugs, and the coastal tugs... ( from the design)
thx, forumers... GBU

 

I believe by "usual tugs" you mean harbor tugs. The difference was once fairly simple, with the coastal, or seagoing tugs having more power, greater length, and more freeboard forward. Today it is more complex, as there are a variety of tug designs, with some able to operate equally well in the ship assisting harbor role and in the ocean towing role.

Harbor tugs tend to be designed mainly for manueverability, as their primary task is pushing and pulling to move large ships in close quarters. They are frequently called tractor tugs. Raw power is not critical, although average power has increased as the size of ships has increased. Different drive types , such as azmuthing (rotating) drives and the Voith-Scheider drive, which uses a series of adjustable paddle blades on a circular mount, enable modern tractor tugs to generate almost equal force (Bollard pull is one measure of tug force) regardless of the direction in which the bow is pointed with relation to the load.

Coastal, or seagoing, tugs generally are still longer, with more power and greater freeboard. Their primary function is towing ships or barges on open waters. Again, there are complications. One variation is called ATB (articulated tug and barge). ATB's are specialized tugs and barges in which the barge is built with a notch in the stern, and both the tug and barge have fittings which make a mechanical bond between the tug and barge. In effect, the tug becomes a huge outboard motor mounted on the stern of the barge. The ATB unit combines the economy of barge transport with higher speed and safety of a ship. One example of the overlap in function is Crowley's Invader class of tugs. They are called ship assist tugs, but in 1999 an Invader class tug towed the USN battleship New Jersey (900'/275m, 40,000 tons) 7000 miles/10,500 km from a Pacific ocean berth in the NW part of the US to a berth in Camden, New Jersey, an Atlantic port in the NE part of the US.

Here is some info on harbor/tractor/ship assist tugs: http://www.crowley.com/mediaRoom/images/publications-brochures/ShipAssistnEscort.pdf

and on seagoing/coastal tugs: http://www.crowley.com/vessel-specs/ocean/seavictory.pdf

ATBs here: http://www.crowley.com/petroleum-chemical-transportation/articulated-tug-barges.asp

 

Not to pick at nits, but back in the day, launching some of the first generation of the the Foss tractor tugs, the term referred specifically to the azmuth drive boats. That was one place in the country, others milage may vary.

 

I think you're right, the term tractor is limited to the azmuthing and, more recently, to V-S drive boats. I could have been more precise in my language; I meant that most harbor tugs are called tractor tugs now, because nearly all the new ship assist tugs have either azmuth or V-S drives. A few harbors, like NYC, still have some traditional twin screw tugs performing ship assist, but they're gradually being replaced or converted. Crowley, I believe, uses their Invader class and some other twin screw tugs for ship assist because they have a large investment in them and because they can fill multiple roles as needed.

 

thx, for the answers friends... how about the power range ? my design are
Jenis Coastal Tug
bollard pull 15 kg/bhp
Free speed 12.5 knots
Free speed 6.430555556 m/s
Cruise range 570 SM

what do you think to decided the power...?

 

Can some body help me... thx....

 

I'm not sure what you are asking. Your formula of 15 kg/bhp means 50MT bollard pull would require the equivalent of 3350 hp delivered at the prop. Depending on prop slip and power losses from the drivetrain, your formula would require engine rated power around 4500-5000 hp. Carl Thoresen's Port Designer's Handbook: Recommendations and Guidelines suggests using 10-12 times the needed bollard pull in kN to determine minimum tug engine power required. For estimating purposes, 10 kN=1MT (actually it is 9.8); using Thoresen's guide gives a rating of 5000-6000 hp.

What bollard forces and number of tugs are needed to handle ships is determined by a variety of factors, including the size and type of ship and local weather and current conditions. There are a number of published standards for calculating the requirements, including British Standard BS 6349, Spanish Standard ROM 0.2-90, and OCIMF Guide for the Safe Mooring of Large Ships.

 

hmm, best regards for you Charlie and much thx before...

thats problem made me confused until now.. my lecture just give me thats criteria to built a coastal tugs and this is my first experience to built a vessel.
i never know about Thoresen's guide , my hand book just from Cadwell's hatchinson . Charlie, what is MT in the complete words ? and how to calculate from 15 kg/bhp to 50 MT. my reference from my senior not give me a solution, they are just compare a real vessel with they boat's design.

 

MT is the abbreviation for metric ton. I used it for your benefit because here in the US we still use "short ton" (2,000 lbs). You would probably just call a metric ton a ton, and in your own and most other countries of the world you would be correct.

I selected 50 MT simply as an example. The formula for converting bhp to bollard pull is the formula you gave.

That formula is a good guide. There are many variables in tug design, however. Bollard pull is actually a measure of thrust generated by the tug. Horspower of the engines is the primary component of thrust, but there are other which are significant. Larger propellors operating at lower rpm are more efficient (more thrust/hp or kw), but require greater depth of water to operate. Good in deep harbors, but a tug with large props may not be able to operate further upriver or in other harbors where water is shallower.

Kort nozzles will increase prop efficiency by up to 10% over open prop design. Z drive, azimuth thrusters, Voight-Schneider, and others are all different drive designs intended to increase thrust/hp and to maintain maximum thrust during changes of direction by the tug.

Other key elements of thrust are the location of the propellors and the design of the hull itself.

 

oh, thx mr charlie...

 

Tug Boat Literature

Hi... my name is Andri, I am student university in Indonesia
I need literature for my final project about tug boat.
Where I can read Allan Caldwell's Screw Tug Design book online?
may you help me? Thanks b4 n GBU