SpaceX Falcon 9 : Hispasat 30W-6 (1F) : March 6, 2018 - DISCUSSION

[RocketLover0119]

UPDATE: No departure still, however, SpaceX's dock is active and Hawk has been shuffling around some.

[Michael Baylor]

For those following on MarineTraffic, if they are about to move OCISLY, one of the tugs parked to the north west of Hawk and OCISLY will pull up to OCISLY and assist Hawk out of the port. Usually, the tugs Florida or Eagle are the ones to help out, but it could also be someone else.

[Lar]

I can confirm HAWK has attached (or however you want to say this) to OCISLY

Such posts qualify, to me, as an update.
@Lar: do you agree. If so should these be posted in (moved to) update thread?

Not solely my call but it could be. However given the amount of back and forth, it left, no it didn't,  maybe not.

[Johnnyhinbos]

Guys please stop with all this talk of high speed towing. Displacement speed is displacement speed. Let it go. Towing a barge is towing a barge. It’s slow. It’s complicated. It’s displacement speed. Did I say it’s slow? It has to be.

When folks talk about a 400 mile offshore high speed dash it makes this forum look silly. Please just stop.

Here - brush up on this...

http://www.dtic.mil/get-tr-doc/pdf?AD=ADA326849

[Nomadd]

Guys please stop with all this talk of high speed towing. Displacement speed is displacement speed. Let it go. Towing a barge is towing a barge. It’s slow. It’s complicated. It’s displacement speed. Did I say it’s slow? It has to be.

When folks talk about a 400 mile offshore high speed dash it makes this forum look silly. Please just stop.

Here - brush up on this...

http://www.dtic.mil/get-tr-doc/pdf?AD=ADA326849

Naw. You just need to get the barge on plane. I saw it in a cartoon once.

[Robotbeat]

Guys please stop with all this talk of high speed towing. Displacement speed is displacement speed. Let it go. Towing a barge is towing a barge. It’s slow. It’s complicated. It’s displacement speed. Did I say it’s slow? It has to be.

When folks talk about a 400 mile offshore high speed dash it makes this forum look silly. Please just stop.

Here - brush up on this...

http://www.dtic.mil/get-tr-doc/pdf?AD=ADA326849

Be more specific, that's someone's thesis over 100 pages long.

From everyone's favorite source, Wikipedia:

"The concept of [displacement] speed is not used in modern naval architecture, where considerations of speed-length ratio or Froude number are considered more helpful. Though the term "[displacement] speed" seems to suggest that it is some sort of "speed limit" for a boat, in fact drag for a displacement hull increases smoothly and at an increasing rate with speed as [displacement] speed is approached and exceeded, often with no noticeable inflection at [displacement] speed."

(I'm not disagreeing with the claim that high speed towing is a really bad idea that won't happen.)

[Robotbeat]

If ASDS location posted on Google maps is correct, its +-400 miles from the port(and launch site), so either ships depart very soon and reach the location with the average speed around 11 knots, or SpaceX will have to delay launch if they want to land this 1st stage.

Either Hawk has been turbocharged or that's impossible.

We've heard from sailors that tug captains like to go as slow as possible whenever they can to save fuel and reduce wear and tear on their boats.  Given the weather forecast (bad but getting better) this might be an occasion where they wait until the last possible moment to leave then sail at their highest possible speed to arrive "in the nick of time".  The later they arrive on station the better the sea state will be.

The tug is not capable of pulling OCISLY at that speed to make a Tuesday launch.

Given the hull speed of OCISLY (you get enormous drag if you try to exceed hull speed on a non-hydroplaning hull) you'd need a massively powerful tug and special towing gar to even attempt going significantly faster than we've seen ASDS towed before. So, I don't think they'll try that.

Another perhaps possible option, were this not a low-margin mission already, would be a partial boostback, thus allowing OCISLY to be closer to shore. But it's incredibly marginal on recovery already, so I don't think this is possible this time.

My speculation is that SpaceX's silence on a launch date is because they are waiting to see what happens with the sea state (and OCISLY's arrival time on station) before committing. If I had to put money where my mouth is, I'd bet on a Wednesday launch if we see an ASDS sortie in the next few hours.   

2nd edit because the first one was wrong; opps, missed the upthread confirmation that something may be going on with OCISLY. I'm still sticking with the Wednesday launch guess.

I get a hull speed of 23 knots for OCISLY. It's 300ft long. 1.34*sqrt(300) = 23ish. That means it can go 400 miles in about 15 hours if that's the "limit." Did I make a mistake in my calculation?

What am I missing?

[Robotbeat]

(Never skip a chance to learn something just because you might look silly...)

[Johnnyhinbos]

Well, the issue is, complicated. But to address displacement speed, think of it this way...

For a displacement hull - one that pushes water out of the way (displaced it) instead of riding up and over the water - you create a bow wave of which you are forever living in the trough of - forever trying to climb it. The faster you shove into the water, the bigger the wave and the deeper into the trough you find yourself, ultimately finding yourself in a land of diminishing returns as you then dump more energy into trying to climb the wave you created.

The net is, displacement speed is a factor of hull length (as it relates to wavelength). For recreational sized vessels (30’-60’) that equates to roughly 8 knots (somewhat less). Ships in the hundreds of feet have correspondingly faster displacement speeds - BUT when towing many other dynamics come to play.

Guess my point is - towing is complicated and slow. The physics of the vessels and the environment conspire to reduce speeds to mere knots...

Speaking of environment - here’s the buoy data for buoy 44013 in Boston Harbor for this weekend. I’ve run my boat past it many times, and have dived the area many times. But can’t picture doing either this weekend...

[Robotbeat]

From here:
https://www.boatdesign.net/threads/tug-boat-and-barge-engine-power-calculation.51188/

Probably the best formula for predicting required shaft horse power is Wyman's formula which will work up to SL = 2 as I present it.
W = weight in lbs
Lwl = waterline length (ft)

SHP = (W/1000) * (Kts/Lwl^0.5)^3

Rearrange to determine top speed:
(Lwl^0.5)*(SHP*1000/W)^(1/3) = speed in knots.

So, just a wag, but OCISLY is probably about 1800 tons empty, or 3600000 lbs. 300ft waterline. Tug boats are rated typically 680 to 3400 hp, so:
(300^0.5)*(680*1000/3600000)^(1/3) = 10 knots
to
(300^0.5)*(3400*1000/3600000)^(1/3) = 17 knots

But deep water tugs can be rated for higher (27000hp, up to 34 knots in that simple formula which most certainly wouldn't hold at that speed). What is Hawk's shaft horsepower?

EDIT: Assuming Hawk is this vessel with a gross tonnage of 525:
http://www.marinetraffic.com/en/ais/details/ships/shipid:430027/mmsi:366943250/imo:9103295/vessel:HAWK

...then it is roughly the same displacement as this vessel which has about 3600 hp:
https://en.wikipedia.org/wiki/Valiant-class_harbor_tug

...thus the max towing speed (IN CALM SEAS) of OCISLY with Hawk is likely on the higher end, i.e. 17 knots not counting towing dynamics.

[Robotbeat]

...
The net is, displacement speed is a factor of hull length (as it relates to wavelength). For recreational sized vessels (30’-60’) that equates to roughly 8 knots (somewhat less). Ships in the hundreds of feet have correspondingly faster displacement speeds...

Right. OCISLY is 300 ft long, and thus would have a displacement speed of a crazy fast 23 knots. Likely the tug just can't tow it that fast due to horsepower limitations. Displacement speed isn't really relevant to this conversation since it's not likely the limiting factor.

[Johnnyhinbos]

From here:
https://www.boatdesign.net/threads/tug-boat-and-barge-engine-power-calculation.51188/

Probably the best formula for predicting required shaft horse power is Wyman's formula which will work up to SL = 2 as I present it.
W = weight in lbs
Lwl = waterline length (ft)

SHP = (W/1000) * (Kts/Lwl^0.5)^3

Rearrange to determine top speed:
(Lwl^0.5)*(SHP*1000/W)^(1/3) = speed in knots.

So, just a wag, but OCISLY is probably about 1800 tons empty, or 3600000 lbs. 300ft waterline. Tug boats are rated typically 680 to 3400 hp, so:
(300^0.5)*(680*1000/3600000)^(1/3) = 10 knots
to
(300^0.5)*(3400*1000/3600000)^(1/3) = 17 knots

But deep water tugs can be rated for higher (27000hp, up to 34 knots in that simple formula which most certainly wouldn't hold at that speed). What is Hawk's shaft horsepower?

Oh, I agree. Hawk has impressive horsepower and has some real giddy-up. I marvel at the incredible power vessels like her possess in order to climb that hill. But it’s not Hawk that’s the problem - it’s her tow. Think of the strain on the towline trying to pull OCISLY out of her own trough...

[Robotbeat]

From here:
https://www.boatdesign.net/threads/tug-boat-and-barge-engine-power-calculation.51188/

Probably the best formula for predicting required shaft horse power is Wyman's formula which will work up to SL = 2 as I present it.
W = weight in lbs
Lwl = waterline length (ft)

SHP = (W/1000) * (Kts/Lwl^0.5)^3

Rearrange to determine top speed:
(Lwl^0.5)*(SHP*1000/W)^(1/3) = speed in knots.

So, just a wag, but OCISLY is probably about 1800 tons empty, or 3600000 lbs. 300ft waterline. Tug boats are rated typically 680 to 3400 hp, so:
(300^0.5)*(680*1000/3600000)^(1/3) = 10 knots
to
(300^0.5)*(3400*1000/3600000)^(1/3) = 17 knots

But deep water tugs can be rated for higher (27000hp, up to 34 knots in that simple formula which most certainly wouldn't hold at that speed). What is Hawk's shaft horsepower?

Oh, I agree. Hawk has impressive horsepower and has some real giddy-up. I marvel at the incredible power vessels like her possess in order to climb that hill. But it’s not Hawk that’s the problem - it’s her tow. Think of the strain on the towline trying to pull OCISLY out of her own trough...

...but OCISLY has a (roughly) 23 knot displacement speed, which is more than Hawk can tow OCISLY anyway using Wyman's formula. So that's not the limiting factor (says me confidently and arrogantly, having just learned about this like 15 minutes ago, LOL... It's okay, I don't mind looking silly).

[Robotbeat]

400 miles at 17 knots is about 20 hours. So still some time, technically...

[Michael Baylor]

There is no way Hawk is getting into position in a day. End of story.

[IanThePineapple]

There is no way Hawk is getting into position in a day. End of story.

The waves are pretty bad out there, I don't blame them.

Godspeed 1044, and thank you.

[Robotbeat]

There is no way Hawk is getting into position in a day. End of story.

Nerd me a story why it can't be done.

[IanThePineapple]

There is no way Hawk is getting into position in a day. End of story.

Nerd me a story why it can't be done.

Hawk isn't exactly a Tesla Model S P100D (meaning it can't just zoom out of port). I think it takes 1 & 1/2 to 2 days to get to the landing spot. Obviously not possible at this point unless Hawk or some other tug can double or triple their usual speed.

[Michael Baylor]

There is no way Hawk is getting into position in a day. End of story.

Nerd me a story why it can't be done.

Hawk isn't exactly a Tesla Model S P100D (meaning it can't just zoom out of port). I think it takes 1 & 1/2 to 2 days to get to the landing spot. Obviously not possible at this point unless Hawk or some other tug can double or triple their usual speed.

In this particular case, they left on Wednesday afternoon for the Sunday morning launch attempt which was then called off.

[Robotbeat]

There is no way Hawk is getting into position in a day. End of story.

Nerd me a story why it can't be done.

Hawk isn't exactly a Tesla Model S P100D (meaning it can't just zoom out of port). I think it takes 1 & 1/2 to 2 days to get to the landing spot. Obviously not possible at this point unless Hawk or some other tug can double or triple their usual speed.

In this particular case, they left on Wednesday afternoon for the Sunday morning launch attempt which was then called off.

But calculations show that Hawk should be able to tow OCISLY at very roughly 17 knots, which means it can get there in ~20 hours. There are about 25 hours left.

The given horsepower and time allow OCISLY to catch 1044.

Sea state is obviously a problem, but that'd be true regardless of horsepower or time. Also, what's the limiting wave height where it's not feasible to tow OCISLY out, let alone catch 1044? And what specifically causes that limit?