Seakeeping for Autonomous Ship in Heavy Weather

This is spot on. You can have a heading and speed set that is working fairly well and then a front passes and the wind shifts, or the predominant swell is overtaken by another from a different bearing and an adjustment is necessary. There is a lot of it that is just how you feel in the seat of your pants.

Thanks to everyone for your input.

That’s interesting. I wonder if anyone has come up with a measurement system to try to quantify “how badly the ship is moving under your feet”, by which I assume you mean flex and give in the mechanical superstructure of the vessel? There is also the idea of the ship not going the direction it is being steered due to the force of the wind and the waves, but I guess that is more of a heading thing than “under foot”.

Also, you talk about throttle adjustments, but to what end? Is it a matter of trying to keep constant speed and power going up and down these large hills of water?

Luckily, cargo is not a big part of what I am doing, unlike in the merchant navy, though I am sure if they have ammo on board, they will want it tied down very well!

Also I sympathize with the notion that automated ships could loose people jobs. My particular work is all about navigation in high seas for ship safety. As someone who has spent a lot of my career doing machine monitoring and maintenance work, I just can’t see long-run unmanned cargo ships making much sense financially. The ship has to run to make money, and running is when things need maintenance and break down, so that is when tending and fixing them has to happen. So, until we have machines that diagnose and fix themselves, which is a very long way off, I feel like unmanned merchant fleets don’t make much sense. The military, of course, has much different missions, and the main goal of autonomy is keeping men out of harm’s way, like in mined waters. Plus for the Navy, two days in overhaul for every day out is common, but would never be financially viable in commercial shipping.

Thanks for your help!

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They have: “ Although considerable efforts can be made in predictions of ship wave loads during prototype design stage, there is still a real need for real-time monitoring of the stress state of ships during their service life. A set of structural safety monitoring system, which is intended to be used for full-scale ships’ hull stress monitoring and evaluation, has recently been developed by our research team. The stress monitoring system was fitted onboard the large-scale model for a preliminary trial and validation.”

The paper covers a lot of relevant ground to your interests.

thanks!

The Theory and Practice of Seamanship

4 posts were split to a new topic: Storm Oil

What, this must be a joke…

In my experience on a small coast-wise ship while hove-to or nearly hove-to in head seas, as the ship climbs the face of a large wave, when the crest of the wave is reached, or just before, the throttles are pulled back to give the ship more time to pivot over the crest of the wave so as not to slam on the back side of the wave. Once over the crest the throttle can be increased again as needed to maintain steerage to meet the next wave.

On larger, heavier ships, generally speaking the response is more delayed so while rpm might be adjusted to keep the speed within range (between loss of steerage and heavy slamming/pounding) but typically course and speed adjustments would be made less frequently.

This is not a joke. 2 to 1 is something an aircraft maintenance guy told me as a rule of thumb. If you look at something like this:

https://www.globalsecurity.org/military/ops/where.htm

Anywhere it says “home port”, “sea trials”, or “selected restricted availability (SRA)” that means “not deployed”. You will see it is most of the time. Generally beyond 2 to 1 if there is no naval aggression going on.

Now, I don’t want to make the Navy sound bad, if bad things are happening, they can stay active way beyond 2 to 1, I just brought it up to emphasize that applications in the Navy in autonomy does NOT mean much regarding autonomous merchant marine operations.

I see what you mean, quite a difference with the merchant marine where there is sometimes hardly time to spare to carry out necessary maintenance, cleaning/painting of the hull and cleaning of the propellers etc.

BTW, you could search gCaptain with the term ‘unmanned ships’. You will find a number of topics about this subject popping up which could contain useful information for you.

Merchant ships are losing money when not moving. With the military at-sea operations are going to cost more than in-port.

One of ours, not sure if it is the Dauntless or the Daring, has never actually sailed at all. Ever.

I believe two man hours maintenance to one flight hour would be considered a utopian figure for a fighter plane. See below (from user HaveBlue on Fighter Maint. ManHours Per FlightHour Comparison - Airliners.net).

But it’s a lot more complicated for a ship because people live on the thing, and counting man hours maintenance per hour at sea isn’t, IMO, fairly represented by non-deployed time. I imagine it’s a number the Navy could cough up for a given class of ship if it wanted to, once the definitions were settled as to what counts as maintenance. And of course it would be huge, because even little ships are big and Navy ships are jam-packed with fancy gear.

If you’re just counting calendar days, I don’t think it’s fair to count home-port or alongside time as maintenance just because they’re not at sea.

Got these from the Air & Space magazine January 2008:

Early F-117…- 113 to 1
Concorde…- 18 to 1

Here’s the compilation from this thread so far:

Saab Draken.- 50 to 1
Eurofighter…- 9 to 1
F-14… - 24 to 1
F-18E/F…- 6 to 1
F-18E/F…- 15 to 1 (different source)
Saab Gripen…- 10 to 1

C-17…- 20 to 1
F-15A/B…- 32.3 here thru f117 stats from (HaveBlue and the F-117A by David Aronstein)
F-15C/D…- 22.1
F-16A…- 19.2
F-117…- 150 (pre 1989)
F-117…- 45 (after improvements, post 1989)
CH-46E…- 19.6 in 1995 GlobalSecurity.org
CH-46E…- 27.2 in 2000
CH-53D…- 24.8 in 1995
CH-53D…- 27.9 in 2000
F-20…- 5.6 (http://www.f20a.com/f20maint.htm)
A-6E…- 51.9 DMMH/FH (FA-18 vs A-6 (Bill DuBois))
F/A-18C…- 19.1 DMMH/FH
B-2…- 124

“The actual B-2 maintenance man-hours per flying hour at Whiteman Air Force Base averaged 124 hours over 12 months ending in March 1997.”
(http://www.fas.org/man/gao/nsiad97181.htm)

Mirage 2000…- 10 Dash 5 (Maintenance)
Gripen…- 12 (Maintenance)

Interesting about the A-7A from a 1964 article…

The contract
between the Navy and Ling-Temco-Vought calls for an 80-per-cent
probability that the aircraft will all achieve mission success, and that
maintenance man-hours per flight hour must not exceed 11.5 or a
penalty will be imposed. If maintenance man-hours per flight hour
reach 13, the contractor must pay the Navy a penalty of $50 per
hour; if the figure reaches 17 the Navy is to receive $700 per hour.
If the maintenance requirement is higher still, then the airplane
will be returned to the contractor for a complete refund of its cost
to the Navy." http://www.flightglobal.com/pdfarchive/view/1964/1964%20-%201850.html

Thanks to everyone for your posts on my behalf. I am working through all the references and old posts on other threads to get myself up to speed, and then I am sure I will have more questions! I have “Theory and Practice for Seamanship” on order from Amazon, and I am sure that will bring up even more questions!

One more question that might be interesting to the group: anybody know of a novel that includes heavy weather trials and decision makings for large-ish vessels? Even age of sail books might be useful if they get into what choices the crew need to make. On the other hand, something like “A Perfect Storm” is more about the drama of the rescue and the weather event (and smaller ships). Wondering if there is a “storm waves classic” out there someone has read!

On 2 to 1, I agree it is oversimplified, but I think there is a good point there that the Navy and merchant missions and cost issues are very different. (also I wanted to correct that I said “aircraft maintenance” when I meant “aircraft carrier maintenance”. I was on the Ronald Reagan carrier between Guam and Hawaii and it was an amazing experience).

On oil calming waves, I don’t really want to jump into that! From the point of view of physics, it is hard to see any surface effect doing much to large waves that have traveled miles to reach a ship. And those are the ones I am interested in.

Thanks again to all for your input.

Into The Raging Sea by Rachel Slade.
Many discussions on here about it.

Thanks, this is very helpful!

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Pugwash

I think the paradigm you’re employing needs to be shifted, you’ve asked about how humans evaluated and made decisions in heavy weather events or how things felt under their feet and decision making. But these all aren’t really relevant to autonomous operation. A human crew will make decisions based on their estimations of risk including and predominantly as it relates to themselves both as life safety issues, human estimation of risk to vessel or cargo/equipment (often unsupplemented by data telemetry beyond an inclinometer) and to some extent even comfort. An autonomous operation suitably informed with extant ability to determine the ‘health’ of the ships’ systems both mechanical and physical against the forces it is experiencing and projected to encounter as well as limitations is an easier equation and will be able to react better since it will have a more comprehensive understanding of the limitations built in. Few to no skippers today have constant telemetry such as described in the sensor web in that paper I linked, DP environmental monitoring systems are close but imagine a linked DP system to hull condition and machinery. Moving thru heavy weather, monitoring the angles of inclination, forecasting them, since the accelerometer data will be able to tell exactly how much the ship will roll at each instant. A master or a Chief will wonder at the angles of inclination that may eventually trip the main engines, designed for a certain limit but the machine will know. And this will then lead to machinery that gets designed for a higher level of inclination. How much of the machinery systems rules are predicated on the idea that humans will be onboard? Class rules for machinery operation at inclination, final angles of stability and lifeboat escape, all not relevant. The machine just has to react to the sensor input, and react to the set points accordingly.

This is an interesting point of view, and I agree with a lot of it. An autonomous system will have to be designed to not NEED to worry about many things a human crew does, and a well-designed autonomous craft would differ significantly from ships intended for human operation. However, it is my experience that there is a lot of wisdom in the small things that a savvy human operator of any system is paying attention to, and it is smart, when deciding WHICH sensors are needed, to pay attention to them and make sure the KEY sensors are there. I think this is reflected in the paper you sent - a sensor web provides more quantitative data, but hopefully its software system would reach the conclusion that the ship is in danger at around the same time a skilled captain would think the same thing. It is also important to remember that no final system ever has ALL the sensors you might hope it would, for cost and complexity reasons. I think it is important to remember we are just at the very start of this. “Autonomy” will probably not mean “full autonomy” for a very long time, if ever. Sea trials and remote control and other stages need to be passed with humans in the loop. I can see, however, that you are thinking forward many years, which is very valuable. Thanks for your post!

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