News and features of interest….
J1674 – Report of the Withern Wreck – 7th October 2019
Langstone Harbour Authority contracted Shoreline Surveys Limited to execute a multibeam bathymetric survey of the Withern wreck within Langstone Harbour. The purpose of the survey was to chart the wreck extents together with the lost isolated danger marker pile. These two elements of the survey have been addressed in two parts in this report. Survey data collection took place on the 7 th October 2019 onboard Shoreline Surveys Limited survey vessel Shoreline. Details of the data collection parameters have been provided at the end of this report.
Extract 2 – The Bruce, thought to be of similar design to the Withern.
- THE WRECK
Extract 1 – Birds eye view of Withern extent.
Extract 1 presents a north up plan view of the overall extent of the wreck multibeam data. The Withern is centered on the location 50 48.13011 N 001 1.81751 W (WGS84). It has been annotated with interpreted features:
‘a’ marking a wheel like structure
‘b’ marking a possible derrick
‘c’ which appears to be the vessels funnel
‘d’ marking the broken navigation pile (top balls also present).
The eastern face of the Withern would now appear to be collapsed. There is little information available of the Withern prior to its loss in 1926. Images of similar vessels can be found, for example Extract 2 is an image of Bruce a bucket dredger built in 1905. It is clear from the multibeam data that the Withern has collapsed and degraded significantly but appears to be three possible main coincidental features in the multibeam data. These have been annotated onto Extract 2 below:
Extract 2 – The Bruce, thought to be of similar design to the Withern.
Extract 2 was taken from Shipwrecks for walkers Vol2: Explore Britain’s beaches for these 50 shipwrecks by Tom Bennet.
Extract 3 – Presenting the Withern from approximate north.
Extract 3 presents multibeam coverage annotated with ‘a’, ‘c’ and ‘d’. ‘b’ is omitted for it is not entirely clear in this extract. The interpreted inside of the funnel can be seen (‘c’).
Extract 4 – Side view from west side of the Withern.
Extract 4 presents the side view of the Withern (Z axis is amplified) with shallowest point marked (small red arrow) with the shallowest interpreted point being 2.97 metres below Chart Datum. There are several other points along the length of the wreck which are almost as shallow as this. However, the only feature observed as being higher than this is the remaining upright of the navigation post at 2.64 metres relative to Chart Datum (small green arrow). More information on this aspect of the survey is provide within section 2.
Extracts 5 – Presenting the western wreck face from an elevated view.
Extract 6 – Presenting the eastern face from an elevated view.
Extract 7 – Presenting the southern end from an elevated view.
- THE NAVIGATION PILE
The second purpose of the survey was to locate and determine the condition of the missing isolated danger beacon.
The beacon was clearly identified in the data, situated at the northern end of the Withern. It is evident from the records that the beacon has broken off with approximately 10 metres of its length now lying flat on the seabed, pointing more or less due north. The central position of the pile (which has been interpreted as being 0.4 metres wide) is
50 45.142465N, 01 1.816363W (WGS84).
Extract 8 – Presenting the interpreted broken pile:
Close to the base of the fallen pile a broken upright section of pile remains rising from the seabed by 4.1 metres with a shallowest depth of 2.64 metres below Chart Datum (note: higher than the highest interpreted section of the wreck which is 2.97 metres). The location of the post is 50 48.142465N, 01 1.816363W (WGS84). It is presumed that the post has broken at this point and therefore would have originally been approximately 13m in length. The ball marks which would have originally been at the top of the beacon are clearly visible in the data.
Extract 9 – Presenting a side view of the fallen together with the presumed original base section of the pile.
Extract 10 – Presenting a further image of the pile.
The three dimensional aspect of the remaining upright pile and associated balls can be clearly seen, together with its proximity to the north of the wreck.
The Norbit iWBMS high resolution multibeam system provided an excellent tool for clearly mapping the extent and features of the Withern wreck and broken navigation pile residing in its the locality. The confidence level in determining the shallowest point of the wreck and pile is high. However due to the specific nature of wrecks and their associated debris (possible thin angular metal work which may remain undetected using sonar techniques) we strongly advise that no vessel should navigate over or within close proximity of the wreck.
J1609 – Multibeam Survey report of the West Pole Wreck – 15th October 2019
In June 2019 whilst surveying the usual harbour surveys for Chichester Harbour Conservancy Shoreline Surveys Limited were contracted to execute a side scan sonar survey of the wreck laying in the vicinity of West Pole Beacon. The results of the side scan sonar survey were limited.
In October 2019 we were working in the locality of West Pole Beacon once again undertaking survey work for Hayling Beach Replenishment Scheme. We had our high resolution multibeam system installed so took the opportunity to gather more data. Survey data collection took place on the 15th October 2019 onboard Shoreline Surveys Limited survey vessel Shoreline. Details of the data collection parameters have been provided at the end of this report.
Extract 1 – Birds eye view of West Pole wreck extent.
Extract 1 presents a North up plan view of the overall extent of the wreck multibeam data. The wreck is located on the West Pole Sands, a sand shoal extending South along the Western edge of the channel entrance to Chichester Harbour. With a central position of 50° 45.409428N, 0° 56.677432W (WGS84), it lays approximately 125m South-West of the West Pole Beacon.
At the time of writing, there is no information available pertaining vessel type, date or cause of wreckage on West Pole sands. It is clear from the multibeam data that the wreck has degraded significantly over a long timescale, including burial by sediment. This is to be expected due to its location on shallow shoals undergoing influences from tide & wave action.
Remnants of the wreck include: side boards (hull), bow & stern debris, central rib/ frame, keel. There are also two main forward & aft structures of the wreck, of which the latter is dominant.
Approximate horizontal wreck dimensions are as follows: length 21m, beam (at midships) 7m.
Extract 2 – Profile view from South-West side of the West Pole wreck.
Extract 2 presents the profile view of the West Pole wreck (Z axis is amplified) with the shallowest point marked ‘A’ which was interpreted as 2.28m below Chart Datum. From this view ‘B’ ‘C’ structures are also clear.
Extract 3 – Presenting the West Pole wreck from approximate North-West.
Extract 5 – Presenting the West Pole wreck from approximate East.
The Norbit iWBMS high resolution multibeam system provided an excellent tool for clearly mapping the extent and features of the West Pole wreck. The confidence level in determining the shallowest point of the wreck is high. However due to the specific nature of wrecks and their associated debris (possible thin angular metal work which may remain undetected using sonar techniques) we strongly advise that no vessel should navigate over or within close-proximity of the wreck and that any dimensions provided within this report are treated with caution, specifically the interpreted shallowest depth.