Category Archives: Oostvoornsemeer 2015

Oostvoornse meer day 11 and 12: Wrapping up

Having finished most of the mapping and recording of the western side of the wreck yesterday, today we have focused our efforts on the eastern side. In order to map this part of the wreck site we first placed more coded targets before shooting additional video footage for photogrammetry modelling. After every part of the site had been accurately documented, selected timbers were then chosen for dendro sampling.

Dendro sampling also continued on the western part of the site, where our divers faced the time consuming challenge of sawing through the massive keel timber.

Keel with datum point and coded target
Keel with datum point and coded target

There were also some other suitable planks for dendrochronology scattered across the wreck site so we’ve spent most of the day selecting and bringing up more dendro samples.

Day 12

Our final diving day was devoted mainly to ensuring we didn’t miss any measurements or critical construction features and lastly cleaning the site. The coded targets were carefully removed and the last dendro samples were lifted and stored. We have left most of the datum points (numbered points for the basic measurements on site) on sites for future reference measurements.


Back on deck we made sure a full backup of all our data was made; over the course of two weeks no less than 330GB of video footage was recorded. In the following weeks this data should allow us to make an accurate digital 3D reconstruction of both wreck locations.

We finished diving at noon so we could weigh anchor and sail the work barge back to the shore where it will be picked up tomorrow.

The work has finished here. We go back to Amersfoort to process the data and do some further research on the material we gathered. The 3D photogrammetry that we have used to map the OVM 10 and 12 will make this work probably much easier!

Next fieldwork in the Netherlands starts on the 17th August 2015, check our Blog for news on that. In the meantime please keep on following the capacity building project in Vietnam.

Morrison van der Linden (student)

Martijn Manders (Head of the Maritime Programme)

Day 10: The West Site Story

Today we completed 16 dives. We have finished drawing, measuring and filming the western part of the site and have now started on the eastern part of the site OVM10. On the western part of the site we have found a lot of different ship parts. For instance, the stern and the keel. Piece by piece the overall picture of the ship is emerging.

Although the site is harder to interpret with all the scattered fragments of the ship, the photogrammetry process is going a lot faster because of the coded targets we applied. It is much easier to align the different chunks of stills from the videos and this makes it easier to see what has been properly filmed. The photogrammetry experts are then able to tell the divers which parts still need to be filmed to give us a complete picture of the site.

Part of the site that we have processed in Photoscan
Part of the site that we have processed in Photoscan

We took some dendro samples yesterday and today we prepared them for analysis. This requires measuring each individual piece, recording and labelling. We truly hope the samples will be good enough for dating, since many of them do have wide year rings. The samples that were taken may have come from production forests. These forests produced specific trees for the shipbuilding industry from the late 17th century onwards. This is however, problematic for us as it is harder to date the wood using  dendrochronology. We’ll know more when the analysis is done.

Preparing the dendro samples for analysis
Preparing the dendro samples for analysis

Diving will continue this weekend and the pack-up will commence on Monday. The field school is wrapping up and some of the crew are leaving this evening.

Robert de Hoop (intern Maritime Programme)
Bronwyn Hughes (Leiden University)

Day 9: The condition of the OVM 10

We have found a lot of burned wood on the OVM 10. This might be the reason for sinking, but maybe it happened only after the ship was deserted. We will probably never know. The structure however must have burned for quite a while, based on the severity of the burning marks on the individual timbers.

The ship parts emerging from the sediment are quite degraded by Teredo navalis or shipworm. The timbers became exposed after the sand extraction for the Maasvlakte 1, but also other activities in the lake. Some structural elements on OVM 10 only became exposed recently due to illegal airlifting. This wood still hasn’t been attacked by the shipworm but is obviously very vulnerable for future attack.

An example of the burned wood that we found
An example of the burned wood that we found

The site has been particularly difficult to research, because it is not structurally intact and pieces of the ship are strewn about the lake floor. A hypothesis was suggested that this did not occur at or around the time of the ship’s sinking but could be a result of the dredging that took place. This could explain why so many of the planks and beams are sticking up out of the sand. The fact that beams and planks are also cracked and splintered at the ends, supports this theory.

Diver getting ready
Diver getting ready

The sandy bottom has also been a challenge to our divers who have to be careful not to kick up the sediment when taking measurements as this can decrease visibility. In general, visibility has been reasonable, around 3 meters. This is good enough for our photogrammetry recording.

Good visibility today
Good visibility today

Today divers took some dendro samples from different parts of the ship. These will be taken away for analysis to determine the age of the wood and where the tree was felled. Analysis will also be done to show the effect the shipworm has had on the wood as well as the bacteriological decay.

Degradation of the wood by the shipworm
Degradation of the wood by the shipworm

Most of the measurements have been taken and entered into Site Recorder and the picture of where each and every detected structure element is positioned is becoming clearer every day. The work the divers have been doing is very accurate and we are happy with the results so far.

Tomorrow some of the team members will be leaving us, so they will be wrapping up their work assignments of the project and saying their farewells.

Robert de Hoop (intern Maritime Program)

Bronwyn Hughes (Leiden University)

Day 8: Triangulation and trilateration

Today was already the third day of our campaign on the OVM 10. The whole day we were drawing, measuring and filming. We also tested so called ‘coded targets’ which should make the photogrammetry a lot easier. More on this, see below.

Now that we are familiarized with the site and have an overall picture of what is down there we are able to start taking measurements. We do this by selecting datum points which allow us to work in a precise way. These points correspond to different features or locations of the site. The measurements are made by using a method called triangulation. Measurements are taken between three different points, they are recorded underwater and once the diver brings them up to the surface they are entered into a computer program called Site Recorder. Site Recorder immediately tells you if you measured correctly and what the margin of error is. With all of these measurements we gather we are then able to draw an ever more accurate site plan and they can be used alongside the photogrammetry software.

Entering the measurements in Site Recorder
Entering the measurements in Site Recorder

For the OVM 10 we are trying out coded targets. These coded targets are attached to wood and/or are placed between different objects on the site. The coded targets are necessary for this site as recognition points because the site is spread out over a large area, with frames and deck beams surfacing the seabed.Between areas of sediment there are few features to detect. After stills are taken from the GoPro footage, Photoscan software can detect the coded targets in these photos more easily and align them much faster.

Lots of activity on deck
Lots of activity on deck

Three days ago we started off with a rough sketch of the site. Already we have a much better understanding of what is left on the Oostvoornse lake bed. With the actual measurements of the ship elements and their spread, step by step we are geting a good idea of what is there and what the significance is of OVM 10. The filming underwater is harder to do than on OVM 12 because of the spread of the elements and the visibility that is less here. This is why – as a backup – we will also use the conventional methods to record the site with additional drawing.

A coded target that is placed on the site
A coded target that is placed on the site

A large spread, interesting features, lots of illegal excavation done and wood exposed recently. What can we say about the condition of the site? More about that tomorrow.

Robert de Hoop (intern Maritime Programme)

Day 7: Finding our way on the OVM 10 site

After a test dive yesterday, we have started the archaeological fieldwork on OVM 10 today. The first task for each diver was to orientate on the wrecksite. This is really important in order to be able to execute the next tasks that are essential for the archaeological significance assessment that we want to do.

The site itself is fairly large, with bits and pieces of wreck sticking out of a mound of sediment. Again, like OVM 12, this site was probably hit during sand abstraction for the first extension of the Rotterdam Harbour (Maasvlakte 1) after which the area has been avoided for further abstraction. 

As we said yesterday; we are diving with scuba equipment on the OVM10. We are doing this because the site OVM10 lies at about 20 – 25 meters deep, is spread out over a large area, with frames and deck beams surfacing the seabed (sometimes for several meters) and with a visibility of about max 2 meters. Scuba gives you more freedom moving around than surface supply equipment. With the 300 bar Aga sets we have enough air with us. With a nitrox (40%) mix we can stay down at the site for an hour if we don’t go deeper than 23 meters. So we have a lot more dive time than on the OVM12. After two hours surface interval we can go in for another dive.

Each morning we start with a briefing of what we will do that day. Everybody gets his or her assignment and the situation will be discussed with the help of a hi-resolution multibeam sonar image of the site, printed in A0. Striking is the difference between the current situation on the seabed and the multibeam that was made in 2014. Much more of the shipwreck and e.g. ancient rope are visible: clearly some airlifting has been done before we came to the site. A lot of lines, measuring bars and parts of airlifts, all of which we had also found on OVM 12, have been found. Pieces of ancient rope give evidence to the damage this airlifting must have caused on the site. In the long run the wreck parts may be more vulnerable for shipworm attack if the salinity is not decreased or if the site isn’t physically protected.

The briefing of this morning
The briefing of this morning

Unfortunately we do not know what objects have been taken from the site and we probably will never know…

Today we got one extra student, which makes a total of 5:


Morrison van der Linden
My name is Morrison van der Linden and I’m from the Netherlands. I’m currently in my second year of the Maritime Archaeology Program in Esbjerg, Denmark. Like Robert I also studied archaeology at Saxion University in Deventer. I’m interested in almost every aspect of maritime archaeology and hope to gain some more experience during this fieldschool.

Check back tomorrow for more news on the methodology of mapping the site besides the use of photogrammetry.

Robert de Hoop (intern Maritime Programme)

Day 6: A new week, a new site

Today the ‘official’ fieldschool has started. Four students will work with us on the OVM10. In this blog we will tell you something about the site OVM10 and introduce the students.

The site OVM10 consists of two locations, an eastern and western part. The locations are about 20 meters apart and are on both sides of a hill. On these locations remains of one or two 17th century shipwrecks have been found, this is something we will have to clarify. In 2012 living shipworms were found in wood samples from the wrecksite. The goals of this campaign are more or less the same as with the OVM12. Our first job is to do a significance assessment on the site OVM 10. Secondly we will look at the spread of the shipworm and its effect on the recently exposed wreck parts. As part of the cooperation with the municipality of Westvoorne and current development of a vision for the lake we will also look at the possibilities for dive tourism in the future as part of the management of the underwater cultural heritage in this area. The information we gather will be used in the discussions with different stakeholders on what must happen to the lake.

The students. From left to right: Thomas, Mareille, Bronwyn and Robert
The students. From left to right: Thomas, Mareille, Bronwyn and Robert.

Thomas van Damme

I’m from Belgium and have recently graduated as a maritime archaeologist from the University of Southern Denmark. Professionally I’m mainly interested in underwater photogrammetry – converting 2D images of shipwrecks into accurate 3D models (see blog 3). Having dived with the team on the OVM8 and OVM14 last year I’m excited to test out new hardware and an improved photogrammetry workflow for the three-dimensional recording of the OVM10 during the 2015 campaign!

Mareille Arkesteijn

I studied archaeology at Leiden University and graduated last February. I’m specialised in archaeological leather and started my own small company in conservation and determination of archaeological leather. Last year I joined the project as well and dived on the OVM8 which was really interesting so I am very excited to dive on the OVM10 this week!!

Bronwyn Hughes

I’m from New Zealand and I study archaeology at Leiden University. I have a background in Classical studies but am fascinated by all things maritime. I am a dive master and enjoy sailing. I am looking forward to gaining some practical archaeology experience and learning more about Dutch shipping history.

Robert de Hoop

I have been writing the blogs this past week, but I thought I’d introduce myself as well. I study archaeology at Saxion Deventer where I just turned in my thesis. Next year I will be going to the University of Southern Denmark to study Maritime Archaeology. I’m very interested in digital archaeology, which is also what my thesis was about. Together with Thomas I will be working on the underwater photogrammetry.

The scuba equipment
The scuba equipment

This we week we will be diving using scuba equipment. More on that tomorrow!

Day 5: Last day of our research on the OVM12

Today was the last day of our research on the OVM12 (Oostvoornse meer 12), next week we will be going to the OVM10. We’d like to share our first findings and first (preliminary) interpretation of the ship.

There are two parts of the ship. Both are parts of the same board. Due to the fact that in the southern part we see the start of what may be the bow of the ship we believe both are part of the portside of the ship. Visible are two decks, at least the hanging knees, parts of the deck beams as well as the waterway and the first pinewood deck planks.

The measurements that we took of the ship elements show that the ship had been heavily built. The outer planking is approximately 10 cm thick and the ceiling another 8 centimeter. The frames are, compared to the planking ‘only’, 16 cm thick.  The knees are close to each other and are connected to the ship and deckbeams with iron bolts . Other parts of the construction are joined together with wooden treenails, as is quite normal for Dutch ships. We don’t think it was a warship because we didn’t find any gunports, we think it is more likely a trading ship.

One of the knees with iron bolt
One of the knees with iron bolt.

In what we believe could be the bow, we see heavy curved frames, but also the place where a windlass was fixed to the board. This is also the place where we found an enormous amount of rope. Was this the spare rigging?

The place where the windlass was fixed to the board
The place where the windlass was fixed to the board.
An enormous amount of rope is found at what we believe could be the bow
An enormous amount of rope is found at what we believe could be the bow.

At some places on the ship there are traces of fire on the ceiling, frames and the outer planking. This is on the highest parts of the boards and from the inside out. Was this the reason for the sinking of the ship? A fire on board?

No cargo has been found. We found some leather shoes and a piece of leather of which we don’t yet know what it was for. We have also found a barrel stave. If we can date the stave it can tell us something about the time the ship was wrecked.

Part of the barrel stave
Part of the barrel stave.

Quite a lot of dendrochronological samples have been taken, which can be used for dating the ship. The dendro samples have been taken from different parts of the ship.

Sawing the wood for the dendro sample
Sawing the wood for the dendro sample.

These are just our preliminary findings, because we have recorded the site digitally using photogrammetry we can virtually ‘go back’ to the ship, which can help us to answer the questions we have.

We will keep you informed through

Robert de Hoop (intern Maritime Program)
Martijn Manders (Head of the Maritime Program)

Day 4: The art of archaeology against the silent bubbles

As the OVM 12 wrecksite lies between a depth of 35 to 40 meters, we dive with Surface Supply Equipment (SSE) and surface decompression. Normally scientific divers use scuba equipment, but because of safety regulations and to extend dive times we use SSE. The chamber ensures a safer decompression (as it is in a controlled environment) and allows us to spend more time under water. With SSE the divers are connected with an umbilical cord to the surface. This umbilical has three tubes: one with communication and film, one with air and one with the pneum. We dive with two divers at once.

First the divers put on their suits, jacket and helmet. The divers equipment is then checked. There is always one diver on standby in case something goes wrong.

The divers go through a couple of routine checks
The divers go through a couple of routine checks.

The divers go down to the wrecksite in a cage. On the surface the umbilical cords are tendered.

From the dive control room the dive supervisor can talk to the divers and watch the footage from the cameras on the diver’s helmet. The dive supervisor can measure the depth the divers are at by using the pneum.

The Dive Control Room
The Dive Control Room.

While at the wrecksite the divers have half an hour to take measurements, make drawings and/or film with the GoPro. Due to the relative short time under water the objectives for each dive have to be clear. Each morning all the divers are briefed and the goals for that day are discussed. In the evening there is a debriefing. All the measurements are added into the computer program Site Recorder. This program creates a site plan, based on the measurements from the site.

When the divers are back on the surface they have to get out of their diving gear and be in the decompression chamber in under 3 minutes. When in the chamber they will breathe pure oxygen to get rid of all the excessive nitrogen in their body. Depending on the time and depth spent under water, the decompression process usually takes 30 or 40 minutes. Once out of the chamber the divers have to wait for 4 hours to dive again.

The divers in the decompression chamber. Photo: Paul Voorthuis/
The divers in the decompression chamber. Photo: Paul Voorthuis/

This morning a filmcrew from RTV Rijnmond came by to see what we are doing. See:

RTV Rijnmond Oostvoornse meer

Check in tomorrow to find out what all this diving has led to: our first findings and interpretation.

Robert de Hoop (intern Maritime Program)

Day 3: Computer Vision Photogrammetry

During the fieldwork, we will be implementing some new archaeological techniques to do our research. One of these new techniques is Computer Vision Photogrammetry for underwater archaeological site recording. Computer Vision Photogrammetry allows us to load a series of overlapping pictures of the shipwreck into dedicated software in order to automatically generate an accurate three-dimensional model.

The process is as follows. Divers film the site with a GoPro in a lawnmower pattern, thereby ensuring overlap. The video footage is then loaded into a program that takes still pictures from the footage. Finally the pictures are then loaded into software called Agisoft Photoscan.

As soon as the GoPro’s are back at the surface the photogrammetry processing begins using the on-site laptop.

Agisoft Photoscan uses a so-called ‘feature detection algorithm’ to automatically identify and match features in overlapping pictures. Based on the detected features and the camera calibration parameters, Photoscan aligns the pictures relevant to one another. The result is a so called sparse point cloud, which is a 3D approximation of the scene in the pictures. The software now knows the original camera positions and the camera calibration. With this information it can calculate where the pictures overlap. The additional feature points that are then created, are added to the existing sparse point cloud. This creates a much more detailed dense point cloud.

The dense point cloud with all the detected feature points.
The dense point cloud with all the detected feature points.

Using the dense point cloud Photoscan creates a surface mesh from the dense point cloud.

The surface mesh
The surface mesh.

Finally Photoscan ‘imposes’ parts of the original pictures onto their corresponding points in the surface mesh.

The final textured result
The final textured result.

Computer Vision Photogrammetry reduces underwater recording time and produces an accurate, detailed and objective three-dimensional result. The created model does not only look good, but can also be used for measurements and further research. The pictures in this blog are off course just a small part of the ship. We are looking forward to the final results and will keep you updated! Check our blog tomorrow for more information on the diving techniques used in this campaign.

Robert de Hoop (intern Maritime Program RCE)

With special thanks to Thomas van Damme

Day 2: Salination of the Oostvoornse meer

We ended the blog yesterday with the problem of the salination of the Oostvoornse meer. Oostvoornsemeer is now a freshwater lake and the wrecks are a popular destination for the thousands of divers who take to the deep here every year. The easy diving conditions, good visibility, and the interesting wrecks make this one of the most frequently visited diving spots in the Netherlands.

After years of desalination, the salinity in the lake is being increased again in the hope of improving the water quality and biodiversity. However, this has also reintroduced one of the greatest threats to wooden shipwrecks – Teredo navalis, the naval shipworm. The shipworm damages the wood by eating it. To investigate the salination and the reintroduction of the shipworm, multibeam sonar, water quality research, underwater observation and sampling are being used to obtain the clearest possible picture of the current spread of shipworm, and the imminent threat. During this fieldwork campaign we want to assess the speed of degradation of the wooden shipwrecks by the shipworm. The municipality of Westvoorne is bringing together stakeholders to discuss how to manage the underwater cultural heritage in relation to the vision that is being developed for the lake. We are providing the information for the discussion and the decision making process.

Martijn explains the situation in the lake to the filmcrew
Martijn explains the situation in the lake to the filmcrew

Today a filmcrew from the Dutch television came by to film for a program called ‘De Kennis van Nu’ (Current Knowledge), presented by Diederik Jekel. The program focuses on the underwater archaeological research that is being conducted on the shipwrecks at the Oostvoornse meer and the implementation of new archaeological research techniques. We will keep you updated on the airing time and date of the television programme! Tomorrow we will tell you about the implementation of those new archaeological research techniques. So check it out!

Robert de Hoop (intern Maritime Program)

Martijn Manders (Head of the Maritime Program)