***Hydrofoil Barge***
Regarding the suggestions to get a larger / faster tug to give faster turnaround on 1 ASDS, two thoughts / suggestions for comment - a) Are multiple tugs an option? Seems like E3 is already at the large end of the spectrum though certainly not the biggest.b) It seems to me that the easiest way to speed up the tugging is to have the ASDS unballasted during towing. IIRC, there is 12' of water in the tanks to enhance stability during landing. Or was it enough water to cause 12' of draft? Whichever way, without ballast the ASDS drafts about 3'. That's a lot less drag and a lot more speed. Is this ballast needed for towing? Assuming that the F9 can handle more rocking motion during tow? If yes to all of the above then fit the ASDS with a built in ballast pumping system.
...ya but can they get on plane to go faster? Actually 15kt is significantly fast.
Won't make any difference you are fighting two facing two large limiting factors:1) Drag- goes up exponentially till it starts to plane---Not going to happen Don't need to do the math typical drag plot attached.2) Propeller efficiency. Propellers are designed for specific working limits. See the Wageningen B series curves below. We call these the fishhook curves. (thrust & torque-vertical axis, and speed-horizontal are dimensionless coefficients) Back in the day you could figure out which pitch by looking at you motor torque and drag numbers to match them to the best pitch on this chart. If you have controllable pitch propeller you get all the curves just set you operating point. Notice how the lines drop sharply after they reach a maximum; these correspond to the torque coefficient. This is what happens when you over power a propeller; it cavitates and stops pulling.The fastest we have seen the tugs is about 7 Kts(J=1.0). So Assuming these curves and controllable pitch propeller ( we get all the pitch lines) J / speed maxes out at 1.2 or 8.4 Kts. Less than a knot and a half.That's if you have enough power to overcome the drag.
The tugs have been seen towing an ASDS at 7 knots? Any idea where? If it's in a strong favoring current, that's not a true speed, but if that's actual speed through the water, that's actually quite an improvement from 5 knots. To go out 400 standard miles, 69 hours at 5 knots, 49 hours at 7kt. Shaving off 20 hours each way might be quite useful in case of a scheduling bottleneck necessitating a fast ASDS turnaround.
Quote from: CJ on 04/29/2016 01:15 amI wonder how fast a Coast Guard Cutter could tow an ASDS??
A lot more interesting is how fast a Burke class Destroyer can towed the ASDS. Considering they are fitted to tow an active sonar array.
Quote from: CJ on 04/29/2016 01:15 amThe tugs have been seen towing an ASDS at 7 knots? Any idea where? If it's in a strong favoring current, that's not a true speed, but if that's actual speed through the water, that's actually quite an improvement from 5 knots. To go out 400 standard miles, 69 hours at 5 knots, 49 hours at 7kt. Shaving off 20 hours each way might be quite useful in case of a scheduling bottleneck necessitating a fast ASDS turnaround.Nope. The issue, pure an simply, is fuel economy.From Doesitfloat's graphs we see drag increases exponentially with speed and, generally speaking, fuel consumption follows a similar curve. There is a limit to the amount of fuel each of the Support Tugs can carry (ASDS on-station duration is similarly constrained), so whether or not they can do the tow at 7kts becomes kinda irrelevant if they'll run out of fuel when they get there and need to call the USCG to tow them back.I wonder how fast a Coast Guard Cutter could tow an ASDS??
OK spacefans...er, barge fans...get ready for OCISLY to head out tonight.
Quote from: Kabloona on 04/29/2016 12:23 pmOK spacefans...er, barge fans...get ready for OCISLY to head out tonight.So soon?
As I mentioned earlier, usually we have a static fire schedule (even if only in L2) before the ASDS leaves port.
Quote from: Kabloona on 04/29/2016 12:23 pmOK spacefans...er, barge fans...get ready for OCISLY to head out tonight.So soon?Anyway, I sincerely hope that this will bring back this thread to the quality of the old one. Since resetting, this thread has become way worse than the old one. First time I see that happening on this forum, usually its the other way around.