Abstract
This paper describes the SWATH survey ship Jakob Prei and the experiences from the last 2 years of survey activity. The Jakob Prei was built in 2012 by the German shipyard Abeking&Rasmussen (A&R), yard number 6494. The ship’s type is SWATH (Small Water- plane Area Twin Hull) and gives very good seagoing capabilities despite its small size. Surveys can be performed with wave heights up to 3 – 3.5m, which means very few days are lost in most conditions.
Preface
Until 2004, Estonian hydrographers worked only in shallow waters close to the shoreline. However, the HELCOM re-survey scheme demands surveys also in open sea, far from shore and in much deeper waters. There was neither the ship nor survey equipment in possession of the Estonian Maritime Administration (EMA) which could be used for such tasks. Survey equipment could be obtained but the question about the ship remained. As a workaround, a 40 year old buoy-tender EVA-308 was equipped to perform survey tasks. This platform was replaced in 2008 with another buoy-tender Sektori. Both ships were quite big mono-hull steel ships with poor manoeuvrability, low speed and very sensitive to bad weather. If wave heights exceeded 1.5m, both of the ships usually had to stop surveying. This resulted in a large amount of survey time (at least 20-30 %) being lost due to bad weather. Fulfilling the Estonian goals under the HELCOM resurvey scheme was in danger.
New ship
The idea of building a SWATH type survey ship was considered before 2004. SWATH ships have been known to be stable platforms for different works at sea. Also they can be quite small requiring only a small crew. This led to a project of building a new SWATH survey ship for the EMA. The first design was based on an existing 25m pilot tender built by A&R, but was much bigger – around 33m in length. The ship based on this design was never built because of it being too big and costly. The large size of this design was due to the engine room location in the upper structure of the ship. Therefore, in order to have enough space for accommodation and survey tasks, the ship had to be bigger than the 25m pilot boat.
During 2008, the Administration received good news – first A&R had a new 25m SWATH design, with main and auxiliary engines installed into “pontoons“ under the waterline. Second, complete funding of the ship was possible from EU funds.
In October 2009, after a public tender won by A&R, the shipbuilding contract was signed and the ship was delivered to the EMA in April 2012.
Ship’s basic data
The ship had to fulfil these requirements:
1. Unlimited use in sea state 6 with significant wave height of 3.5m;
2. At a sea state of 2m, significant wave height with periods usually met in the Baltic Sea at a speed of 10 to 15 knots in all directions towards the sea, the significant amplitude of both roll and pitch should be less than 4 degrees.
The ship has:
- Aluminium construction with Length 25.65m, width 13m, draft 2.7m, max speed 20 knots.
- Main engines: 2 x 800 kW MAN diesel engines.
- Designed autonomy is 8 days with range of 1550 Nm at a speed of 8 knots.
- Crew is 6 persons (designed for 8), 2 being hydrographers.
- Designed noise levels in wheelhouse and accommodation spaces up to 67 dB(A)
- It has 400V/220V and 24V electrical systems, powered by 2 x 80 kW generators.
- Main engines and generators are installed in “pontoons”.
- The ship has all necessary navigational equipment intended for ships of such class and automatic fin stabilizing system for reducing roll and pitch.
Jakob Prei has been built under survey and to the requirements of Germanischer Lloyd.
Some specific features are a MOB lift on the starboard side of the ship, sauna and 6m long container on fore part of the ship. Also VSAT system is installed on the ship for connecting to the internet in areas far from shore. The container contains equipment for taking sound velocity profiles and a winch for side-scan sonar deployment.
Survey equipment
Jakob Prei is equipped with the following:
- RESON 7125 SV2 multi-beam 200/400 kHz with SVP 70 sound velocity probe and hull mounted transducer
- For multi-beam data collection, Estonian survey software RAN running in linux-based workstation
- Meridata MD DSS 2-8 kHz sub-bottom profiler with hull mounted transducer
- Edgetech 4200 MP side-scan sonar 300/900 kHz with depressor wing, controllable from container, aft part of the ship and wheelhouse
- IXBlue Octans Gyrocompass & motion sensor
- 2 Topcon NET G3A RTK GPS
- Valeport MIDAS sound velocity profiler, controllable from container and connected to survey computer in wheelhouse
- MacArtney Cormac MKI winch for SVP (400 m cable) and MacArtney Cormac MKII winch for side-scan (800 m cable), both installed in container
- All survey equipment except motion sensor, transducers and winches is installed into wheelhouse
- Port side of the wheelhouse is used by hydrographers for performing surveys. Ship’s navigation and operating equipment is installed in the starboard side of the wheelhouse. For guiding the ship on survey lines, the helmsman display is installed in front of the steering wheel
Work results
In Estonia, the survey season lasts usually from May to November although in some seasons, April and December are also possible. There are a total of 13 persons in the Hydrographic Department of the Estonian Maritime Administration who are all performing surveys and processing data.
Four survey ships are used – the Jakob Prei, 2x20m catamarans (EVA-320 working at sea and EVA-301 working on inland waters) and a 6m boat EVA-303 working also mostly on inland waters. During mobilisation, 5 persons are working on the ships – 2 on Jakob Prei, 1 on EVA-320, 1 on EVA-301 and 1 on EVA-303. Other staff are processing data if not on vacation. Data processing mainly takes place during winter.
A survey week is from Monday to Friday, 8 hours per day (16 hours on Jakob Prei as there are 2 hydrographers rotating after each 2 hours). During nights, the Jakob Prei usually stays adrift near the survey area and in harbour at weekends. During winter, the ship stays in Tallinn Hundipea Harbour. There are 6 air-bubble making devices installed around the ship to avoid sea ice.
The ship has now worked over 2 survey seasons (2012 and 2013). Surveys have been carried out in HELCOM Cat I and Cat II areas (see https://helcomresurvey.sjofartsverket.se/helcomresurveysite/ ) – being in North-Western and Western sea regions of Estonia. The depth range in this region is usually between 20 and 150m.
The survey speed of the Jakob Prei is usually 11-12 knots. Up to a speed of 12 knots, only half of cylinders of the main engines work. This dramatically reduces fuel consumption. The ship has to stop to take sound velocity profiles but the procedure does not take long as the deployment of the probe is very comfortably done from the container. This also means that bad weather does not make this work unpleasant.
The side-scan sonar cable is guided from a winch in the container over the pulleys on ship’s port side and over the crane in the aft. Deployment of the towfish requires a presence in the aft part of the ship. All real work with the side-scan sonar is done from the wheelhouse. Very few days have been lost because of bad weather. Bad weather for the Jakob Prei means wind speeds of 20 m/s and over and waves higher than 3m. It is also difficult to keep the ship on the survey line if sailing in the direction of the waves when wave heights are close to 3m or higher.
Table 1 is a brief summary of surveys conducted in 2012 and 2013.
Year | Survey period | Survey hours | km² covered | km² per hour | Days lost due to storm | Fuel consumption during survey period (L/hour) |
2012 | Jul – Nov | 399 | 1096 | 2.7 | 7 | 110.4 |
2013 | May – Sept | 534 | 1559 | 2.9 | 4 | 110.6 |
As seen from Table 1, the area covered during working hours is quite good. This is mostly due to more than 50m average water depths. In shallow areas, the coverage is much less. For safety reasons, the Jakob Prei usually does not survey in water with depths less than 10m.
Fuel consumption is the total consumption of the main and auxiliary engines and heating system during the survey period and includes the actual survey time, transfers between harbours and survey area and staying during nights and weekends.
As seen from Table 1, the Jakob Prei could work only 5 months on both years. The testing period in 2012 (setting up equipment, connecting RESON 7125 to Estonian data collection software etc.) took time and the actual surveys started at the end of July. In 2013, the survey season stopped due to a broken gearbox. The gearbox lasted only 2,000 working hours instead of 30,000 as expected. Unfortunately, the warranty period of the ship was already over and the manufacturer refused to cover any repair costs. This gearbox was considered defective as a secondary shaft usually does not break after so little working time. Repairing the gearbox was very costly to the EMA and 2 months of survey time was lost.
Conclusions
Despite the above mentioned technical gearbox problem, the Jakob Prei has already proven itself as a very good ship for hydrographic surveys. Its small draught allows visiting most of the bigger harbours in the Estonian shallow archipelago area. The crew is small and fuel consumption low while maintaining quite high survey speeds. It is quiet and comfortable, survey equipment conforms to the highest standards and finally the ship’s stability in very bad conditions is truly extraordinary – literally it is possible to sail on 3m waves and keep a full cup of coffee nearby without any spill! Fulfilling Estonian goals defined in the HELCOM resurvey scheme in water depths deeper than 10m is now possible even before the expected deadline.
Biography
Peeter Väling was born in Tallinn, Estonia and graduated from the Tartu University in Geology in 1992. He worked as a marine geologist in the Estonian Geological Survey during 1992 – 1994. Since 1994, Peeter has worked in the Estonian Maritime Administration as a Hydrographer. From 2006 he was the Chief Hydrographer and since 2013 he has been the Head of the Hydrographic Department.