I read with some concern Dorie Cox’s article regarding inclination tests and the stability of yachts [“Procedure, equations define stability,” page B1, April issue].
Although the article highlights an overview of the general procedure involved with obtaining appropriate stability documentation for a motor yacht, I fear that it may instill trepidation in the minds of captains and owners hoping to initiate this process. In most cases the process is painless and relatively cost effective for the owner and vessel’s crew.
The entire process starts with the performance of an Incline Test onboard the vessel. Contrary to the general belief, an Incline Test is not an exercise that results in a “pass” or “fail” upon completion. Instead it is performed to obtain the lightship weight and center of gravity of the vessel.
With these values in hand, the stability characteristics of the vessel can be calculated and an appropriate stability booklet can be generated. This process really only holds the vessel up for a couple of days.
As Will Nock correctly outlined, it takes one day for setup and another for the physical testing onboard atypical motor yacht. The rest of the work is performed in a naval architect’s office and the vessel and her crew do not need to be burdened any further, particularly if the calculations yield positive results.
With the necessary drawings and documentation in hand, a qualified naval architect can turn around an acceptable Incline Test Procedure in a matter of days. There are a number of standards that must be followed and the selection of the standard will be based upon the yacht’s class and flag.
An Incline Test Procedure details how the standard requirements will be carried out for the specific vessel. It is required prior to the physical testing onboard in order to ensure all personnel involved are on the same page.
In addition, the results of testing can be compiled and stability booklets generated in a couple of weeks following the Incline Test. The only scheduling uncertainties are the time associated with statutory review and approval of the document, and whether the calculations document that the required stability criteria are met.
Should the calculations conclude that the stability criteria are not met; the naval architect can propose options to bring the vessel into compliance. Generally, the knee-jerk reaction by the marine industry is to add ballast to correct a stability problem. However, an experienced naval architect can typically offer more cost-effective solutions to solve a stability problem onboard.
In the article, Capt. Paul Stengel was quoted as saying, “Ninety percent of the time you have to add weight.” For reference, Murray and Associates inclines about two vessels a month, and our records indicate that closer to 90 percent of the time we have not recommended the installation of ballast. Our general consensus is that a ballast installation is the last resort, and we go to great lengths to explore all other, less costly options prior to making that recommendation.
As with everything, there are both pros and cons, and the cons of a ballast installation are significant. First, it reduces the amount of usable space onboard, particularly in crucial storage areas like the bilge. Secondly, it adds permanent weight to the vessel that can reduce the vessel’s performance and add to her draft. This draft addition is concerning as the structure of the vessel was initially designed and subsequently reviewed for a design draft. If the ballast installation causes this vessel to sit at a deeper draft, additional structural concerns may arise.
This is particularly concerning for vessels operating with a load line, as is the case for fully commercial yachts. A ballast installation can cause the vessel’s approved load line to be submerged and necessitate a possible relocation of the load line mark. The relocation is never guaranteed, and the review and correspondence with the assigning authority adds significant cost to the project.
Finally, we need to highlight concerns associated with the noted option of adding “usable weight like anchor chain,” to assist with correcting a stability item. The issues with these types of items are two-fold. First, they can be easily removable in the future without proper documentation or foresight. Using anchor chain as an example, a new captain unfamiliar with the stability history of a vessel could come onboard and decide that the extra anchor chain is not necessary and simply remove it from the vessel. If the vessel needed this added weight to comply, she would no longer be compliant with the stability characteristics and there would be no record as to why. A proper ballast installation is semi-permanent where personnel would have to go to significant lengths to remove it in the future.
Secondly, it is not just the addition of more weight, but also the location of the added weight that is crucial for the stability calculations. The lower the better, and anchor chain in a chain locker is not necessarily all that low. Therefore, the overall impact on the vessel’s stability characteristics may be minimal.
In summary, the recipe for a stable yacht should not include fear on the part of captains and owners. With the assistance of an experienced naval architect, it should instead be thought of as an opportunity for the owner and crew to learn about the stability characteristics of the vessel all while obtaining appropriate documentation for the vessel.
Drew Hains is vice president of engineering with Murray and Associates in Ft. Lauderdale. A 1997 graduate of the Webb Institute of Naval Architecture, Hains is a member of a number of professional organizations, including the National Academy of Forensic Engineers. He is also a board certified Forensic Engineer and often provides consulting services to admiralty attorneys regarding technical and engineering issues. He specializes in the analysis of the stability of vessels. Comments are welcome at firstname.lastname@example.org