02 Oct '12 Keep a close eye on hull fouling and speed percentage drop using Marorka Online
The subject of hull fouling and how to monitor the ensuing speed percentage drop has been high on our agenda for the last few months.
Our partnership with Jotun Hull Performance Solutions has resulted in a straightforward statistical method to estimate the speed percentage drop over time.
High-resolution data logging along with data filtering which excludes bad weather, speed changes and shallow waters together provide a set of points for trending increases in resistance over time.
The Clean Shipping Coalition has proposed this approach to the IMO as a transparent and reliable hull and propeller performance standard ( MEPC 63-4-8 PDF). This document a great deal of underlying research and data supporting the method.
In the Jotun in-depth study it was found that the average speed loss per year across all sailing intervals was 2.36 per cent and that the typical length of the sailing interval was 54 months. This implies a cumulative speed loss of 10.6 per cent over a typical sailing interval. The corresponding vessel efficiency loss would be 16 per cent on average over a typical sailing interval.
The measurements required to generate this report are:
- Log speed
- Shaft power
- True wind speed
- Sea depth
Speed/power curves for a fully loaded and ballasted ship are used to calculate the performance loss.
We plot trend lines between hull treatment events logged within Marorka Online.
Our approach has been to develop and test the method with our customers in partnership with Jotun, and we have reached a point where we are able to deliver the mathematical model and data filtering through Marorka Online. Contact us today for a preview demonstration and start making informed decisions regarding hull treatment and the dry dock priority list for your fleet.