Technical question regarding speed and nautical stuff

[Neptune's Fork]

Sailing out of Port Canaveral in a couple months and was curious when the ship heads out into the ocean, how long, or far out, until the ship increases engine power to attain cruising speed? Also on the eastern Caribbean leg, between the Tortola and St Thomas stops, that's only about an hour cruising distance, but the ship will take about 12 hours, so how do they kill that time? Are they adrift or actually under motor?

 

[PrincessShmoo]

Sailing out of Port Canaveral in a couple months and was curious when the ship heads out into the ocean, how long, or far out, until the ship increases engine power to attain cruising speed? Also on the eastern Caribbean leg, between the Tortola and St Thomas stops, that's only about an hour cruising distance, but the ship will take about 12 hours, so how do they kill that time? Are they adrift or actually under motor?

They are still under power, just extremely slow, and zig-zag pattern. This was our trip from St Maarten to Tortola, pirate night travel:

 

[Gigi22]

Can't answer the how far/how long to attain cruising speed. A lot of stops in the Caribbean are very close together. The cynical part of me has noticed that ships do a nice sail away from one port and an early a.m. arrival at the next port for the benefit of the paying guests, and then quietly slow down (and maybe stop, not sure) over night.

 

[Neptune's Fork]

Is that a screen shot from your room or somewhere on the ship?

 

[Deb T.]

Is that a screen shot from your room or somewhere on the ship?

That would be from in the cabin. There is a channel on the in-cabin television that constantly show the ship's progress and wind direction. It's pretty cool!

 

[Neptune's Fork]

That would be from in the cabin. There is a channel on the in-cabin television that constantly show the ship's progress and wind direction. It's pretty cool!

Oh wow, that's great. So that would probably answer the questions. Are there monitors around the ship like that? So if you're out and about the ship you can check out the current specs?

 

[Jim Libasci]

The Coffee shop on the Fantasy has a big screen like that. Fun to watch

 

[Mr. Drauer]

there are also monitors in the ships atrium's, and several other locations like deck 4 near the doors to the deck and by the Walt Disney Theatre

 

[Neptune's Fork]

Do these monitors also display the current speed, wind speed and direction, too?

 

[arlopop]

Do these monitors also display the current speed, wind speed and direction, too?

They do. That's how I knew a couple years back on Mexico cruise, that we were dealing with 90knot winds, and 25ft seas. (That was a rockin day)

 

[Neptune's Fork]

They do. That's how I knew a couple years back on Mexico cruise, that we were dealing with 90knot winds, and 25ft seas. (That was a rockin day)

Which ship was that on? Sounds like quite an experience. I'm guessing in conditions like that you can feel it all over the ship?

 

[Neptune's Fork]

I just watched the Dream embark and from my observations it appears that it takes about 30 mins to make it from the terminal thru the channel and into the ocean, and it seemed that even once hitting the ocean it was still at slow speed. So they must wait until they get some distance offshore before starting to increase the speed.

 

[RRB]

Sailing out of Port Canaveral in a couple months and was curious when the ship heads out into the ocean, how long, or far out, until the ship increases engine power to attain cruising speed? Also on the eastern Caribbean leg, between the Tortola and St Thomas stops, that's only about an hour cruising distance, but the ship will take about 12 hours, so how do they kill that time? Are they adrift or actually under motor?

It's a factor of timing and distance. The ship leaves PE at about 5:00 to get to Nassau at about 9:30 the next morning. It's a little over 300 S miles and the ship's cruising speed of +/- 20 MPH, it arrives at the expected time. Other legs are different like the days at sea. The 4 night Bahamas cruise leaves CC in the aftternon and takes its time getting home to PE by 6:00 AM the next morning. Obviously going slower because the last leg of the trip less than th first leg

 

[anna08]

They do. That's how I knew a couple years back on Mexico cruise, that we were dealing with 90knot winds, and 25ft seas. (That was a rockin day)

I can't remember exactly when, but they've dropped the wave height from the cruise "data" page on the ship. I think it freaked people out and folks were posting screen shots all the time back then of what looked like scary numbers. The wind speed and direction of the wind is still there.

 

[arlopop]

Which ship was that on? Sounds like quite an experience. I'm guessing in conditions like that you can feel it all over the ship?

That was the Wonder. And it was interesting, but not awful. Wasn't quite what you'd call a storm - mostly just spat rain part of the day - but rather a convergence of low and high pressure that set up serious winds blowing from shore to sea. We left Cabo in calm the afternoon before, rounded the point and got hit with full blast of wind. It got progressively worse overnight and by morning it was really moving. It was steady at 70 knots most of that day, with gusts over 90. They closed deck 4. The adult pool I remember washing in big waves across the deck. Very few people out and about (heard there was quite a bit of seasickness on board) and dinner that night was maybe half full with some plates bouncing. You definitely wanted one hand free as you made your way through the corridors. We held up ok and actually enjoyed it - it felt like being at sea rather than on a floating hotel. By late afternoon the sun peeked out and it began to calm, tho the seas were still muddled.

I do remember watching the screen in the cabin and laughing every time I saw a huge gust recorded.

It gave a great sense of confidence in the ship and its capacity to hold up.

 

[Capt_BJ]

WRT when the ship increases speed on leaving port ....

Remember that the ship is under 'control' of the pilot until a point is reached where the 'pilot waters' end and the pilot leaves the ship. This point is typically where the 'dangers' of the port have all been left behind. For US commercial ports this is typically marked by the "sea buoy" . How far this is off shore varies, typically tho it will be where the dredged channel begins/ends. In Canaveral and Miami this point is just a couple of miles off shore. Leaving New Orleans this point is many miles down the Mississippi until 'open water' is reached.

There are only a few places where specific speed limits apply when navigating ships. For the most part the concept is 'safe speed' which is defined in rule 6 of the International Rules of the Road. Safe Speed is defined by
state of visibility
traffic density
maneuverability of the vessel, esp stopping distance and turning 'ability'
state of the weather
draft in relation to depth of water (can significantly impact steering)

(this is about half of what the rules actually list as factors)

Who determines safe speed? The Master/Captain .. altho if a pilot is on board, ignoring the pilot's 'recommendations' carries significant risk....

in a 'legal situation' such as determining fault in an accident, determining whether the vessel was operating at 'safe speed' is a big factor . . .

safe speed in pilot waters is almost always going to be less than safe speed in open waters, if all other factors remain constant . . .

 

[truck1]

Sailing out of Port Canaveral in a couple months and was curious when the ship heads out into the ocean, how long, or far out, until the ship increases engine power to attain cruising speed? Also on the eastern Caribbean leg, between the Tortola and St Thomas stops, that's only about an hour cruising distance, but the ship will take about 12 hours, so how do they kill that time? Are they adrift or actually under motor?

The answers to this question multiple. It varies from ship to ship and distances and time. For the Dream for example, since she is traveling about 200 miles in in 15 hours they take their time getting up to cruising speed. The Fantasy on the other hand ramps us as soon as the pilot is off the ship. The speed the ship travels is dictated by the distance and time available. When the ships run the engines up, they typically do it in fractions. This way no one gets that whiplash feeling when the ship takea off or slows abruptly. For example when they come out of the channel at Port Canaveral their doing around 6- 10 knots. Say for arguments sake the Capt decides the ship needs to make 15 knots to make port on time. They'll do it in rpm increments until the ship is moving at the desired speed. They'll add 50 rpms, wait for the speed to stabilize at the new rpm, then do another 50 until they are moving at the desired speed and from there the computer takes over to keep them at the programmed speed. Same thing slowing down. They know the ship needs how ever much room to come back to 6 knots so they'll reverse the process and reduce the rpm's by 50 or so until they are at the desired speed. It's one of the few times someone actually had a hand on the wheel and a hand on the throttles. Going from say Nassau to CC which is only 90 miles or so, the ships will basically idle over run in a circle or stop. All depends on the weather, conditions, and what's going on that night.

 

[Neptune's Fork]

The answers to this question multiple. It varies from ship to ship and distances and time. For the Dream for example, since she is traveling about 200 miles in in 15 hours they take their time getting up to cruising speed. The Fantasy on the other hand ramps us as soon as the pilot is off the ship. The speed the ship travels is dictated by the distance and time available. When the ships run the engines up, they typically do it in fractions. This way no one gets that whiplash feeling when the ship takea off or slows abruptly. For example when they come out of the channel at Port Canaveral their doing around 6- 10 knots. Say for arguments sake the Capt decides the ship needs to make 15 knots to make port on time. They'll do it in rpm increments until the ship is moving at the desired speed. They'll add 50 rpms, wait for the speed to stabilize at the new rpm, then do another 50 until they are moving at the desired speed and from there the computer takes over to keep them at the programmed speed. Same thing slowing down. They know the ship needs how ever much room to come back to 6 knots so they'll reverse the process and reduce the rpm's by 50 or so until they are at the desired speed. It's one of the few times someone actually had a hand on the wheel and a hand on the throttles. Going from say Nassau to CC which is only 90 miles or so, the ships will basically idle over run in a circle or stop. All depends on the weather, conditions, and what's going on that night.

That's fascinating, thanks for posting that. I've noticed on the Port Canaveral webcam that the pilot boat seems to pull alongside the ship once it's out in the littoral waters, so that would put it in that first half mile from the coast. I'm assuming based upon your post that at that point they start a gradual speed increase. The only question I'd have on that is about how long is that 'run up' process getting up to full speed?

 

[truck1]

That's fascinating, thanks for posting that. I've noticed on the Port Canaveral webcam that the pilot boat seems to pull alongside the ship once it's out in the littoral waters, so that would put it in that first half mile from the coast. I'm assuming based upon your post that at that point they start a gradual speed increase. The only question I'd have on that is about how long is that 'run up' process getting up to full speed?

Yes. Once the harbor pilot leaves the ship, the ship is free to run the props up. As far as how long it takes to get to full speed, there is no easy answer. It depends on what the conditions are, (Are they fighting a current for example) what the planned speed is, what is the Capt thought process, etc. An off handed guess with all things being equal and assuming that the ship is going for her max speed, Id say prob 30- 60 minutes should be about average from 6 knots to max speed.

 

[Capt_BJ]

This way no one gets that whiplash feeling when the ship takea off or slows abruptly.

When you have a mass of metal that weighs tens of thousands of tons NOTHING WRT speed in the water happens rapidly unless it runs into a very sturdy cliff! (DCL Wonder in round numbers 83,000 tons)

INERTIA!

On a ship the size of a cruise ship, pressing the throttles from 'slow' to 'maximum' does little but produce smoke from exhausts and cavitation from the screws which beat water into froth .... no one is going to experience a head snap of acceleration!

My last command was a vessel of roughly 3500 tons - a LOT less than a cruise ship - and it WAS built for speed. We had a lot of horsepower for our size and could go from zero to 30 knots in about a minute and stop very quickly by reversing the thrust of the prop's rather than the direction of the shaft. No one lost footing from acceleration from 5 to 30 over a minute! .... now executing tight turns at this speed is a different story. At 30 knots a full rudder turn could produce a 30 degree list or more ... this DOES make things fall down and go boom.



(if you want to get technical ... using public data WONDER has a potential of 0.68 hp/ton while my ship had 10.3 hp/ton. For W I say potential because it is a diesel electric setup. The ship has 57000 hp of generating power but this is for both propulsion and hotel services so the # is theory if all the power were sent to propulsion. For the Cutter, the hotel power system is isolated from propulsion. For 'speed' propulsion we had gas turbines which produced 36,000 shaft hp ... there are MANY other factors that impact max speed of a ship and the hp issue is NOT linear but this gives an idea of the factors involved)

Note too that in big ship handling, little happens fast and momentum kills .... ships do NOT stop on a dime. You must anticipate the need to stop WAY WAY in advance. The ship stops either by coasting to a stop because the stop was anticipated or by running the propulsion in reverse (simplified). A 'fast' stop means running HARD in reverse and this burns fuel much more than coasting .... Most of the time you do not want to go ANY FASTER than you must. Going faster works against you.

One of the ways a Captain/Master is 'graded' by the company is their efficiency in operating the ship. As Captain of a CG Cutter I was ranked against my peers in this way and if I used substantially more fuel I was asked why. In my case, sometimes it is easy to explain in my situation - heading for a rescue, chasing a bad guy ... easy to explain. But if in an average 30 days I consistently used more fuel that anyone else and had no 'operation need', my marks reflected my waste of the tax payer dollar. The captain that sails the route and gets "the best gas mileage" is the one who gets the bonuses while the one with the worst often ends up looking for a new job. Running no faster than is necessary .... anticipating ... good planning .... important skills for the master/navigator. A good team of engineer/captain/deck officer will work together to get the ship to the desired speed as quickly as possible while keeping in mind fuel consumption, exhaust (those environmental rules COUNT) and stress on the engines .... and passenger comfort in the case of a cruise ship.