RN Minesweepers: Ton Class

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ivorthediver
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Re: RN Minesweepers: Ton Class

Unread post by ivorthediver »

was the cause of the disaster ever determined Harry / Jim ?
"What Ever Floats your Boat"
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Little h
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Re: RN Minesweepers: Ton Class

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from wiki

Sinking

Regularly manned by a combination of Sussex and London Division RNR personnel (from HMS President), she sailed from Shoreham on 11 September 1976 with a crew largely drawn from London Division RNR to take part in Operation Teamwork, a NATO exercise in the North Sea. Following the exercise, on 20 September the ship proceeded in company with six other British minesweepers towards Hamburg for a three-day official visit to the port, after which she was to return to Shoreham. She was detailed to carry out a mail transfer with HMS Mermaid, a considerably larger ship at five times the displacement, 80 miles (130 km) north of the island of Texel.[1] This required HMS Fittleton to steam close behind and to the side of Mermaid at about 3:30pm to pick up a line.

Fittleton was caught in a low pressure area that exists near to the hull of a ship under way and was drawn close to the frigate HMS Mermaid by hydrodynamic forces. A minor collision ensued and the Fittleton moved forward to try and exit the situation but instead was hit amidships by the bow of the much larger Mermaid and turned over within a minute. Thirty-two survivors were picked from the sea and the upturned hull by the accompanying ships,[1] and German and Dutch vessels joined Royal Navy ships in searching for survivors, with divers entering the floating upturned hull. Attempts to keep Fittleton afloat by passing minesweeping cables underneath her propellor shafts failed when the lines parted.[1] The ship sank several hours later, between 9 and 10 pm, in 160 feet (49 m) of water.[1]
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ivorthediver
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Re: RN Minesweepers: Ton Class

Unread post by ivorthediver »

Thank you very much Harry , for you speedy response to my enquiry .

What a tragic event and one that I have never heard of before :?:

What is the nature of these hydrodynamic forces which occurred and what is the prime mover please , is it a form of hydraulic lock between to solid surfaces or some other form of suction caused by compression of water ,

As a diver I have witnessed scouring beneath hull wrecks which can easily pull a human along and under a submerged article but not a surfaced floating unit so confused at this anomaly
"What Ever Floats your Boat"
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Little h
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Re: RN Minesweepers: Ton Class

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From Navy News September 2016 (ISSUU 201609)

Under article titled:- Service Honours Fittleton Victims


Screenshot (4812) - Copy.png
Screenshot (4813) - Copy.png
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Little h
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Re: RN Minesweepers: Ton Class

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ivorthediver wrote: Mon Sep 09, 2019 8:15 pm Thank you very much Harry , for you speedy response to my enquiry .

What a tragic event and one that I have never heard of before :?:

What is the nature of these hydrodynamic forces which occurred and what is the prime mover please , is it a form of hydraulic lock between to solid surfaces or some other form of suction caused by compression of water ,

As a diver I have witnessed scouring beneath hull wrecks which can easily pull a human along and under a submerged article but not a surfaced floating unit so confused at this anomaly
Well Ivor, I have experienced the effects of the hydrodynamic suction on a destroyer during a RAS with an RFA ... result ... emergency break-away for real. That however, fails to answer your question and I have had to research quite a bit to come up with everyday language that might help us out. My olde pal and townie Andy/Ap1 would've pulled a document that explained it perfectly. Meanwhile I offer the following (and links) until I uncover the everyday language version that explains what is going on precisely between the two hulls and the dynamic of various sea states.



hydrodynamics. : a branch of physics that deals with the motion of fluids and the forces acting on solid bodies immersed in fluids and in motion relative to them

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Replenishment at sea demands the very best of helmsmanship from both the guide and approach ships. As the two ships close each other, the hydrodynamic forces will both change and increase noticeably. At a replenishment speed of 12 knots, a one degree course variation will move the ship 20 feet sideways per minute. The best separation alongside during the replenishment depends on a number of factors, but is controlled by wanting to ensure the safest separation while keeping the probes seated. For surface combatants, 140-160 feet seems to work well. Larger ships seem to favor 160-180 feet. Carriers are especially challenging because of the flight deck overhang, but by the time the separation increases to 200 feet, they are probably at the point of unseating the probes.

To commence the approach and begin closing the guide, all that's required of the approach ship is to increase engine speed by 4-5 knots. On Rappahannock, we would normally use about 60% throttle for 13 knots, so from waiting station we will increase speed to 80-85% (17-18 kts engine speed) to commence the approach. While closing the distance to the guide ship, the lateral separation between ships deserves some attention. However, if the approach ship has established good waiting station, it's likely that nothing more than minor course corrections will be required until alongside.

When about 1 ship length astern of the guide, the approach ship can reduce speed to 1-2 knots above base speed. From this point until alongside and settled in position, matching speed will be the conning officer's primary concern.................

As the approach ship's bow crosses the guide ship's stern, but probably not before then, the approach ship can ring up an engine order to match base speed. Before reducing to base speed the conning officer should ensure that he has enough momentum to pass through the pressure wave generated by the guide ship and carry herself into station. At times, the conning officer will match base speed too early and end up stalled out on the guide ship's pressure wave, which can result in a prolonged delay in getting alongside. From this point forward, engine orders to bring the ship into position and match speed are made almost entirely by eye, keeping in mind the base speed determined while in waiting station. The exact matching speed while alongside the guide will probably be very slightly less than the speed required to match while in waiting station. One very effective technique is to order an engine speed somewhat below the matching speed to reduce excess headway, rather than trying to laboriously "glide" into position. However, in using this technique the peculiarities of the ship and the current sea state must be taken into account.

Source of the excerpts above; is section titled Underway replenishment (UNREP) in FAS (Federation of American Scientists) Military Analysis Network; US Navy Ships:

-----------------------------------------

Dynamic Interaction of Parallel Moving Ships in Close Proximity
M. Rafiqul Islam1* and Motohiko Murai2

1.1 Background/significance of the study
Due to the presence of neighboring vessels, the motion
responses of both the vessels are affected significantly.
Study of motion responses for this type of multi-body
system in waves is important in maneuvering and sea
keeping. Hydrodynamic interactions related to wave effects
may result in unfavorable responses or risk of collision in
the multi-body floating system. The physical aspect of this
hydrodynamic interaction is rather complicated and
numerical sound schemes are highly recommended to study
this complex phenomenon

When two ships are moving in parallel, the ship creates an
obstruction, one another to the propagation of waves and
hence the incident waves are scattered. One example is
underway replenishment of naval ships. Replenishment at
sea (RAS) is a method of transferring fuel, munitions, stores
etc., from one ship to another while under way. During this
replenishment both ships travel parallel to each other and
maintain the same speed. This alongside connected
replenishment is a risky operation, as two or three ships
running side-by-side at speed must hold to precisely the
same course and speed for a long period of time and also as
both ships experience combined dynamic effects. These
combined forces include hydrodynamic interactions in a
random seaway, tensioned ropeway resultant forces, and
rudder and propulsion forces required for the ships to
maintain station. A slight steering error or drifting due to
hydrodynamic interaction on the part of one of the ships or
part of the transfer lines and fuel hoses could cause a
collision. For this reason, experienced and qualified
helmsmen are required during the replenishment, and the
crew on the bridge must give their undivided attention to the
ship's course and speed. The risk is increased when a
replenishment ship is servicing two ships at once. In case of
emergency, crews practice emergency breakaway
procedures, where the ships will separate in
less-than-optimal situations. Although the ships will be
saved from collision, it is possible to lose stores, as the ships
may not be able to finish the current transfer. This study is
also important in the context of STCW (1995) which
requires that ‘navigation and watch-keeping simulation
equipment should realistically simulate own ship dynamics
in open water conditions including the effects of interaction
with other ships’.

Source of the excerpt above; Researchgate

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............. and this from shipsnow.com that provides a whole variety of situations in diagramatic form.

Interaction Effects
Pressure distribution around ship hull.
pressure-distribution.jpg

Interaction Effects Between Two Ships

two-ships.jpg

Ships moving in parallel vs opposite course
two-ships-different-size.jpg
_________________________________
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Little h
timlewin
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Re: RN Minesweepers: Ton Class

Unread post by timlewin »

Here is a film of the frigate HMCS Nippigon trying to get up to a position for RAS with the Dutch tanker Zuiderkruiz in a NATO exercise, and struggling. Nippigon looks very light which must have added to his troubles.
This is on YouTube but was sent to me by a friend in Halifax, he is actually down below in Nippigon's engine room. It shows the difficulties of fiding the right spot to refuel/replenish alongside.
Tim

https://www.youtube.com/embed/1pz2Nyr-Xag
timlewin
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Re: RN Minesweepers: Ton Class

Unread post by timlewin »

and here is Jutland, a much bigger destroyer, experiencing the problems of hydrodynamics with RFA Wave Chief.
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ivorthediver
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Re: RN Minesweepers: Ton Class

Unread post by ivorthediver »

Thank you both for your help here lads , and for the dangers of lack of concentration and the possible costs involved :o
"What Ever Floats your Boat"
Brian James
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Re: RN Minesweepers: Ton Class

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Ton Class Minesweeper HMS Buttington.....She was allocated to Severn Division RNR in 1954 and renamed HMS Venturer,built in 1953 at the Fleetlands Yard, Gosport with Mirrlees diesel engines, she was transferred to London Division in 1962 and renamed HMS Thames. Sold for breaking to Metal Recoveries (Newhaven) on June 1st 1970.
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JackW1208
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Re: RN Minesweepers: Ton Class

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My copy of HMS Lewiston M1208 - original photo taken during degaussing runs off Burntisland in Firth of Forth early 1970.
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Raleigh Oct 65, Mercury 66, Gurkha 66-68, Vidal 68-69, Lewiston 69-72, Centurion (HQ Afnorth) Oslo 72-74, CTF345 74-75, Whitehall and Cincfleet for short stints. LRO(G).
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