12

The San Jose Mercury News article Looking like a seagoing Dr. Octopus, SpaceX’s Mr. Steven has added four longer, articulated arms talks about recent modifications to the size of the net on SpaceX's ship Mr. Steven.

Studying Mr. Steven more carefully, I see two sets of markings I don't recognize. The first is what looks like three 4-blade propellors, and the second has a series of horizontal lines and a horse-shoe type shape with antlers.

What do these mean? Are they related in any way to Mr. Stevens' job of catching fairings from the sky?

Full size image can be found at https://www.mercurynews.com/wp-content/uploads/2018/07/0524_nws_tdb-l-mrsteven-05247.jpg

Mr. Steven Markings 1 Mr. Steven Markings 2

enter image description here

uhoh
  • 148,791
  • 53
  • 476
  • 1,473
  • The markings look like 4-blade propellors because they should indicate where additional propellors are mounted. These propellors are used to move the ship to the side and not straight ahead or back. – Uwe Jul 14 '18 at 12:09

1 Answers1

27

The one that looks somewhat like a ladder or staircase is a "load line" or "Plimsoll line" marking. Each line marks how deeply the vessel can be safely loaded under various conditions: winter (W), summer (S), tropical (T), freshwater (F) etc. The circle and line is the primary summer load line for where the vessel was surveyed; any letters on it indicate who did the survey.

enter image description here enter image description here

The symbols that look like Maltese crosses mark the location of thrusters, so that lines et al can be kept clear.

enter image description here

Those are all standard markings for a sea-going ship, not directly related to it's job of catching fairings.

Bob Jacobsen
  • 12,661
  • 2
  • 31
  • 58
  • 2
    Thanks for the speedy and yet thorough answer! I thought those crosses might have been the equivalent of "kill tallies" - maybe they'd run aground three times and wrecked three propellors. I wonder if we will start seeing a tally of fairing-halves once they start catching them regularly! ;-) – uhoh Jul 14 '18 at 07:06
  • 7
    Never expected getting such in-depth naval knowledge from Space.SE :) – SF. Jul 14 '18 at 08:35
  • 4
    @SF. And all I ask is a tall ship and a star to steer her by; 1, 2 Teleplay by Dorothy Catherine Fontana, poem by John Masefield. – uhoh Jul 14 '18 at 09:19
  • These thrusters are called bow thrusters or lateral-thrust units. If the ship in harbor was towed parallel to a quay wall, the bow thrusters may be used to get clear from the quay wall by moving the ship sideways before the tail propellors are used to move frontways. The bow thrusters may help in difficult berthing maneuvers. – Uwe Jul 14 '18 at 12:20
  • 2
    Kinda like RCS. – SF. Jul 14 '18 at 18:42
  • Bow (and stern) thrusters are also useful in station-keeping systems. A ship's main propellers can only drive it forward or backward - only on small drives such as outboard engines can they vary their angle of thrust - and rudders (used to steer a ship) only work when the ship is going forward or backward. So if you want to stay in one place, but you're drifting sideways, neither system will work (without getting out of position along the forward-backward axis). Thus, thrusters. If a ship has both bow and stern thrusters (or two main drives spaced apart), it can also rotate in place. – CBHacking Jul 14 '18 at 22:27
  • 1
    Mr Steven has two diesel engines and dual props, plus three transverse thrusters at the front. She can pivot pretty well, but unlike an RCS can't move sideways with any significant speed. It looks like the track to catch (or practice catching) a fairing is a long, straight run at 9-12 knots: https://www.marinetraffic.com/en/ais/home/centerx:-118.374/centery:33.732/zoom:12 which makes sense if trying to catch something descending under a square parachute. – Bob Jacobsen Jul 15 '18 at 00:30
  • If the link in the prior comment doesn't work, here's an image of a recent Mr Steven track: https://i.stack.imgur.com/FGhwV.png – Bob Jacobsen Jul 15 '18 at 00:36