GPS and swell height - no mention of anchors.

[Neeves]

Maybe, although I do do this for a living at one of the largest tech companies on the planet so I feel like my finger is somewhat near the pulse on the subject.

On the contrary, it's looking for about 10 different outputs and had hundreds of input parameters. This is where ML really shines, and humans don't, you just need the right person in the chair to get the ML working, and those people are vastly outnumbered by people pretending to know about ML.

I'm pleased to have offered a thread leading to erudite discussion. A conclusion I come to, from your postings, is that it seems to be possible to measure 'something' (vertical movement of a sensor) and as long as you have an ability to measure the impact of that sensor on your yacht then it should be possible derive swell height, maybe not to the nearest millimeter, but to a decent approximation.

A variable not yet mentioned is that in fact as you surf, or accelerate down the wave the bow will bury itself to a greater of lessor degree when it reaches the bottom - and this will all vary with the swell, or wave.

One reason for asking is that our marine forecasts, needs SSB, voice, or internet access, now include swell height and roughly a direction, or ours do, and if the forecast is different to the actual might indicate to one that the swells might get bigger, or smaller in the near future. In some of our forecasts wave rider buoy data, simply wave height, is also provided. Our forecasts also extend well offshore, eg half the Indian Ocean. Between us an NZ we offer forecast between the 2 countries and NZ marine forecast will extend deep into the Pacific.

But if you cannot measure wave, or swell height, you don't know if its going to get better or worse (on the assumption the swell heights in the forecast are accurate).

Jonathan

 

[Uricanejack]

ST Latia, (320,000 DWT) .... the 'standing' Master for that Vessel was a Fellow of the Natural History Museum and Member of Royal Ornithological Society .....
I was Extra 3rd Mate and was unusually given the 4-8 watch. Junior 3rd Mate had the usual 3rd Mates 8-12.
Anyway - I was asked that when I did 'stars' in the morning - to then alter course for a small island in the Indian Ocean ... Shell had an agreement with the Master that he could divert of course for such if it did not incur too much delay ...
Basically he had rec'd info about an event that occurs periodically near this island .... SWARMING SWIMING CRABS and various birds attracted ... so it was intent to see if we could observe the crabs and what birds ....
Stars plotted ... course set ... of we went ... about 1030 island in view .. 3/O literally panicked and started altering course away from the island ... Master immediately ordered return to course.... the islands such as this are volcanic and have deep water right up close - so there was no danger at all ... and we were still a long way off.
Yes we observed the Crabs ... he even got some Photos from deck level. Birds ? no idea - but there were a lot ! But not apparently not feeding on the Crab.
Master sent in report to NHM and Shell, I was mentioned - but when published I was not mentioned ... only Shell, Ship and Master.

Life !

Wouldn’t have been Aldabra? A funny little mostly uninhabited island a bit to the North of Madagascar.

Somebody high up in BP had a connection with the Royal Geographic and or Oxbridge.
From time to time it would be arranged for one of the big ones on its way round the Cape from the Gulf to Europe to stop by and drop of or pick up a group of mad scientists and some supplies.
It really wasn’t much out of our way, just a slight tweak on the course when leaving the Gulf then another for the Cape. Don’t really remember the details was about 40 years ago.
We dropped a couple off, they joined at the Grey Swift along with a crew change we dropped them off by lifeboat then carried on on our way.
Didn’t get to know them very well they kept themselves to themselves but did come up to the bridge a couple of times after we sighted some sea critter’s. And told me I was wrong about the sea critters.
I think they were zoology students working with somebody studying the local budgies and crabs which apparently were quite distinctive and unique much like the Galapagos.

There was one well known story about one unlucky chap. I didn’t meet he was apparently quite sociable.
who made two trips to the Island. He had been studying some kind of crab which only came ashore on one night per year to mate.
Unfortunatly it was not very precisely know when they did this.
After a couple of month on the island the6 had a bit of a party he imbibed a bit to much and missed the event.
he still had to wait for the next passing ship to make a call.
Then come back again for the next year.

it was an interesting little side trip. I never actually landed on the island, we just lowered the boat went close in shore and transferred everything to a boat the mad scientists had.
then left. Nobody came with us.

 

[Refueler]

Wouldn’t have been Aldabra? A funny little mostly uninhabited island a bit to the North of Madagascar.

Bang on .... absolutely correct. We were in ballast heading north to the Gulf.

Blimey - never knew people stayed on it ... what a bleak existence !!

I didn't put the name as I always get it mixed up with another island just inside Medi that a Greek ship ran aground on !!

Correction : The Ship was actually ST Linga ... not the Latia ..... Latia (270,000 dwt) was the half size prototype of the B class ships (540,000 dwt) Shell had built in ST Nazaire.

 

[Uricanejack]

I know it was not meant as a bad reply.

The fact was at that time - Inert Gas use was still in pioneer stage - in fact was initiated to reduce in tank corrosion, not to reduce the risk of explosion. The problem was that the Inert Gas either had no effect or even increased corrosion. But the side effect of reducing risk of explosion was noted.
There were a series of catastrophies involving 3 Shell VLCC's (200,000 DWT) ... Mactra, Marpessa and I forget the name of the 3rd ... along with a couple of chartered vessels - one being the King Harcon.... think I have the name right.

At that time - we relied on the TOO LEAN atmosphere for tank cleaning .... we would force ventilate the tank to be cleaned till oxygen level was below 5% ... 2% if possible. Oxygen and Hydrocarbon gas levels were monitored during the wash cycle and if rose above the 5% level - washing would cease while venting continued.
At that time we did not do Crude Oil Washing while discharging as we had no way to ensure risk free operation.

Once Inert Gas (actually exhaust gas from main engine or IG generator scrubbed clean of sulphur) was introduced into tanks to reduce oxygen content - then Crude Oil Washing became common. This then reduced the sediments left in bottom of tanks from successive cargos.

Back to the ships ... the case of the Mactra - this was never completely solved in terms of the explosion that ripped her open for near 1/3rd her deck. Various experiments and inquiries ... such as at Southampton University - could not explain the blast effects ... where not all bulkheads failed in same manner as in a single explosion would have. The deck was literally ripped open and folded back ... a bulkhead blown out ... another blown in ... The damage was such that a completely new hull top was built to repair her .... as with others.

The human cost - People on deck did lose their lives ....wives sunbathing on top of the accommodation were burnt from the flash over and flying metal.

All were during ballast voyages and most when tank cleaning with high pressure sea water. Test conducted by Southampton University showed the Static Electric effect of water droplets falling from the underdeck down to tank floor. It is this that was believed to have been the 'spark' that blew these ships asunder. Prior to this of course - it was easy for blame to be on a crew member on deck at the time.

OK ... sea waves and damage to ships .....

Texaco Oklahoma ... a midships accom MRCC tanker .....

She had undergone USCG periodic inspection as req'd by US Flag rules ... this usually entailed a structural check - but because of it being a repeated inspection through ships life - they alternated tank groups internal checks.
She was checked and cleared ... and she returned to service.
During a subsequent voyage - she encountered heavy seas and the ship actually fractured just aft of the midships accommodation. Sadly - USCG had given permission for decommissioning for repairs to 2 of the 4 ships lifeboats .... as the front half broke away - it veered round and smashed alongside the aft section destroying the only two in service Lifeboats.
The front section immediately sank taking all Navigating Officers and Master with it.
The aft section was left floating .. with Engineers and Seaman Crew. They had the emergency Radio - ships radio stations were midships on such vessels which of course was now sunk. The crew tried using the radio - but after rescue - it was found they still had the test bridge bar in place preventing transmission signal.
Other ships actually sailed past and later when asked said they just thought it was a strange design of ship ...
Finally engineers and crew were rescued and became a lesson for shipping in general.

As far as I can tell - USCG were never held to account for their part in the disaster.

Sorry for thread drift .....

Interesting, I don’t recall ever hearing about the Texaco Oklahoma.

I do remeber seeing a few Old American T2 which had been lengthened. Both some of the T2 and s one early Liberty‘s had problems with cracking, the cracks would spread past welds.
Problem solved with riveted sheer and bilge strakes. One of the olde tree class product carriers I sailed on had river bilge and sheer strake, She was older than I was. Occasionally we’re in port with the Border Shepherd she was riveted. She carried black oil.

Most of the early history of tank washing issues and the introduction of IG was before my time.
I did sail with a Chief Enginere who was the only British Survivor of the Crown. He was the Junior on watch in the ER, some of the Indian crew survived in addition to the engineering watch. Their accommodations was aft.
(I was shown the wreck still lying on the Shore South of Jeddah about 45 years ago) probably still there.

I have forgotten his name and never did hear him speak of the Crown. I do remember him as a very nice man particularly when I spent some time in the engine room.
The ship the Centaur was an old 69 reputedly at one time the biggest motor ship in the world. B&W 9 Cylinders. They were notorious for shaking themselves to bits. I learned a lot on her. She was fully handaumatic. If something needed doing you had to get of your ass and go do it.
Or send me.
For years I used to win cases of beer from young engineers who doubted I knew how to start and run their engine.
She had an early IG system, it rusted everything. Her lifespan was pre determined and nearing the end. She couldn’t achieve low enough oxygen percentage when the requirements for IG came into effect.
We ran round the N Sea as a very busy shuttle tanker until the deadline.

BP sold and replaced all their midship accommodation crude tankers shortly after the Crown Blew up in the mid 50’s and all new tonnage was fitted with IG. The Centaur was built in the early 60’s before COW. But she did have partially segregated ballast.
We loaded some dirty ballast but always discharged this ashore. In the bad old days it may have go over but that was before my time.
When we tank cleaned as part of the deal to sell her it took weeks. And in the end required shovels.

The older clean Product Ships. Tree class built early 60s didn’t have IG it was believed it would contaminant the cargo.
when I sailed on them we still open loaded and discharged and operated to rich or to lean.
40 some years ago I can’t recal the upper and lower explosive limits, Checking of course was done by me. Along with pretty much anything else which involved standing close to an open sighting port or ullage pipe.

After discharge we would load dirty ballast then tank clean, load clean ballast, discharge the dirty ballast 50 miles offshore.
( it wasn’t very dirty at the time it was legally ok for non persistent oils ie residue from light oils evaporated at ambient temps)
Today you probably get shot a Dawn.
After cleaning we would gas free. Big water turbine fan blowing in from top.
There was a purge pipe on each tank The bottom of which was just above the bottom of the tank so the air was expelled from the bottom.
if we had to do any tank entry we would clean and gas free all adjacent tanks.

Cleaning and gas freeing of other tanks depended on next load. Eg same stuff not required. Or if different depended on compatibility. Some stuff didn’t matter but other did.

With some stuff like ATK we would have to get rid of any left over ballast water. Apparently jet engines don’t like water in thiere fuel.

The tanks which hadn’t been ballasted would be to rich.
The tanks which had been dirty ballast would be almost clean when deballasted and I think were lean, but memory fails. if you pressed them right up they would be virtually gas’s free when deballasted. Water went down fresh air in.

For loading we had sandbags on top of usage pipes.
ues a tape and float to measure the ullage(top of the tank to oil opposite of a sounding)
and an ullage stick to top off.
By the time I’d finished topping off a set of tanks, sometimes I’d be high as a kite.
Possibly part of the reason Tanker men were always considered a bit nutz by pukka seamen.

The mate on one of those ships was one of the hardest working guys at sea. Always busy. I was his go for. He had the worst job. Ussualy we carried two 3mates so he didn’t keep a bridge watch.
The 2nd a 3d just did cargo in port. The mate did cargo nearly 24 7 in port and even more on a short sea ballast passage. He might get a little break on a loaded passage. But he still had other shit to do.

In the mid 60s the Bulldog blew up tank cleaning. ( I sailed with a Capt who was the Mate on the Bulldog) Nobody killed all crew had just left deck for smoko, I never saw pictures, I was told deck was peeled back.
She was the last British Tanker Co. to blow up after this all the mid and late 60s and 70s product ships were built with IG.
Not so sure about the ones they chartered.
The black oil. You would need a flame thrower to get that stuff to burn.
I worked some of the more modern tankers for a while but I liked the old ones better. In many ways life on board was more fun.
I left tankers with the massive down sizing of the mid 80s and quite the sea for a while but didn’t find 9 to 5 life was for me and ended up on other ships again.
It was strange going to other ships. After tankers. I kind of got used to it. Not so sure they got used to me.
More than one interview ended when asked where started out ax soon as I said British Tanker Co.

They might have thought we were all bit nuts. They also knew it meant you knew what you were doing.

 

[Refueler]

"Uricanejack"

I started in 1973 and was right in the Gas Free, portable fans, manual tank cleaning guns ... and 'digging out'. Then of course IG became more widespread.

I left seagoing in 1989 ... basically I was fed up training others to take my job ... and the life was no longer any 'fun' as you said.

With Shell - if you could not stand and run a cargo watch, as an experienced Cadet - you were not suitable ! Mate rarely in those days did chinese watches : Come on and Stop on ... but later when I was with other Co's - that was generally the case that he did all the cargo and juniors just went round making sure Whessoes kept working. When I was 2/O and went 'foreign' - I often ended up on cargo watch alone as Mates soon realised I was old school.

It was embarrassing later as cargo Inspector and then Superintendent - to go on a ship and 3/O 2/O had no clue what to do ... I'd ask - OK - lets go dip the ship ... reply usually - Have to wait for Pumpman.

I hated going onto Brit manned ships ... I'm there as representative of cargo owner - I have authority to refuse discharge / loading etc. but some twatty Brit C/O would tell mme to wait while he did some stupid bit that could be done later ... when I had that - I just sat down and said "Take your time - I'll just have a quick word with client that cargos delayed ...... "

I had some interesting times ..... shuttle tanker for Iran and then changed company and did shuttle for Iraq - during Iran Irag war ...

Alongside Port au Prince, Haiti when revolution going on to oust Papa Doc's son ...

Carrying various items for a certain US 'group' from Miami to Central America ...

In fact going back to 70's .. many people did not know that we ran the Saigon River !! even though officially US had pulled out.

I could keep stories going all night !! Watching M1 Abrahms tanks grinding to halt ... Chieftans just plugging on .... climbing all over captured Iraqi T tanks ...

Thinking about GW1 ... we had an Inspector who exited Terminal and as agreed drove onto a large open area of sand away from everything when Air Raid sirens went off ... He fell asleep in the Toyota pickup ...

He was woken up by a Scud landing in the water just across from him ... it lifted and planted the pickup about 6ft !! He got back to office completely in shock. We had to Medivac him out - he was totally screwed by it.

My sons reckon I should write a booki !!

 

[jwfrary]

It's probobly not possible to get a accurate figure for wave height or swell height from consumer grade electronics availible today.

Most wave buoys use a combination of motion sensors, laser ring gyro and gnss solutions, compasses and some fairly hefty algorithms to come up with a half decent solution.

Hyper accurate GNSS INS solutions found on survey equipment is somewhat temperamental, it doesn't like irregular motions and is so accurate any interference multipath error or any slight error in the dimensions bettween antenna and or the motion reference unit itself will result in poor performance. They are also start around the 80, 000 mark and thr high precision corrections cost anywhere from 5-20k per annum depending on the precision required

Simrad off the HS75 gnss compass which is actually a hemisphere V200n compass, it outputs heave among other things (pitch roll, heading position) , used primarily for adjustment of sonar soudings in the survey world but how or if the simrad gear actually utilises this heave data is unclear.

Accurate Motion is the biggest issue with high resolution sonar, as weather conditions increase the data quality reduces and the motion is unable to reconcile the movement of the ship. Hence our consumer stuff might give a reasonable result in calm and moderate conditions but as the wave hight increases the data probobly won't make much sense.

1 cm in the horizontal and 2 cm in the vertical is achievable with top notch survey grade kit at Sea with high quality corrections via iridium satellite.

 

[boomerangben]

I'm pleased to have offered a thread leading to erudite discussion. A conclusion I come to, from your postings, is that it seems to be possible to measure 'something' (vertical movement of a sensor) and as long as you have an ability to measure the impact of that sensor on your yacht then it should be possible derive swell height, maybe not to the nearest millimeter, but to a decent approximation.

A variable not yet mentioned is that in fact as you surf, or accelerate down the wave the bow will bury itself to a greater of lessor degree when it reaches the bottom - and this will all vary with the swell, or wave.

One reason for asking is that our marine forecasts, needs SSB, voice, or internet access, now include swell height and roughly a direction, or ours do, and if the forecast is different to the actual might indicate to one that the swells might get bigger, or smaller in the near future. In some of our forecasts wave rider buoy data, simply wave height, is also provided. Our forecasts also extend well offshore, eg half the Indian Ocean. Between us an NZ we offer forecast between the 2 countries and NZ marine forecast will extend deep into the Pacific.

But if you cannot measure wave, or swell height, you don't know if its going to get better or worse (on the assumption the swell heights in the forecast are accurate).

Jonathan

We use forecast significant wave height charts at work and indeed base our go/no go decision based on those charts alone. There are wave meters at various places in our area of operation but are not used for go/no go due to “calibration”. We can observe them and use them to build a more holistic picture of what is going on. Anecdotally I would say the forecasts are pretty accurate based on comparing the forecast and the meter readings.

I don’t know how those wave meters work, but many of them are located on fixed structures and others on large moored tankers.

Having said all that, when sat in a small boat (or indeed quite a big one for that matter) it’s not just wave height that matters

 

[lustyd]

not just wave height that matters

Maybe we're all looking at this wrong. What if there were a sensor that showed sea impact. Large boats that are not affected as much may show an impact score of 5 in a F8 while a 20 footer would show an impact score of 11. Easier to measure, more directly interpreted too. It could relate to decelleration, slamming, any violent G force.

 

[Neeves]

The actual swell heights that I know of are described as Wave Rider Buoys, the one of important to us is off the west coast of Tasmania. If there were fixed structures (oil rigs) it would be easy to measure swell height - but you have to be there to do it. We have an oil rig forecast for Bass Strait (where the rigs are located) but I have not listened to it for some time now, the pandemic and I'm sure they will include forecast swell - but I don't recall if the include actuals

A nice idea, which I like.

My understanding is we can measure acceleration, easily - using the sensors in out phone/iPad or tablet.

However if we have lots of accelerations surfing down a wave the rise and fall in, long wave length, swells, and the impact of short wave length waves (or big chop). They might all be caused by wind, your F8, but they will still exist if the wind is no longer F8 (the swells may be big but you might never experience the winds that produced them).

The problem with the idea is correlating what we can measure, for our yachts, with what is included in a forecast or an actual reading from a wave ride buoy.

Jonathan

 

[kdot]

ML can't overcome physical reality, and a sensor at a single position can't determine the direction of wave trains; there is insufficient information. It might manage for short period waves with a strong circular motion at the surface, but it won't for swell, where there is only vertical motion.

Utilising Doppler shift, a single GPS-receiver can give not only the position but velocity (speed, direction) of a wave buoy and hence wave direction.

As I read "Research on the Algorithm Model for Measuring Ocean Waves Based on Satellite GPS Signals in China"