The purpose of a stability test is to determine the weight and center of gravity for a vessel. This is very important. When you look at stability assessments and loading conditions, you will notice that the ship’s lightweight is a very large component of those load conditions. It is very important to get this number accurate.
You need a stability test at several times during a vessel life. There should always be at least one stability test when the vessel is first built. And then at periodic times as the vessel ages. When the weight changes beyond a certain percentage, a stability test is required. This is usually any 4% change in weight. But ask you engineer. The exact number depends on who your regulatory body is and the scenario. Basic rule of thumb: anytime you replace, add, or remove a major piece of equipment, you will need a stability test.
A stability test consists of four major procedures:
Stability tests are big, complicated and expensive. They easily cause trouble. Why? Because the stability test a precise scientific experiment. It requires a level of precision that ships rarely ever operate on. Who normally cares if a piece of cargo was one inch to the left? On a stability test, it matters. So pay careful attention to the engineer and follow their advice.
The engineer may seem like the villain in a stability test. They are actually your friend trying to protect your from all the things that can go wrong during a test. The only thing more frustrating than doing a stability test is this: when the regulator refuses to accept the results and you need to do a second stability test. So follow the engineer’s advice and let the protect you from that scenario. A little extra prevention is worth it.
In preparing for this test, there will be plenty of times where you will be tempted to ask the engineer if you can compromise on something. My advice, don’t. The engineer will do it. They want to help you. And they have the methods to work with your compromises and still get the test passed. But say you ask for a compromise right in the planning phase. And then something happens the day of and now you need two compromises. Will the test still pass?
Here is a good rule of thumb: plan to allow no compromises during the planning phase of the test. And allow for only one compromise the day of the test. The engineer should be able to easily accommodate that. Discuss your concerns with the engineer. Go over contingencies. Ask the engineer which things are more risky than others.
There are two major deliverables from the engineer. The first is a stability test plan. This must be submitted to your regulator for review before you do the test. Ask your engineer about this FAR in advance. Some regulators need months to review the stability test plan.
The second deliverable is the stability test report. This is the big one. It tells you the important number that you want to know. And it has lots of math and data to prove that it is correct. All your future stability assessments will be based on this test report.
You can expect 2 – 4 weeks to prepare the stability test plan.
Expect 3 – 6 days for the actual stability test. There may also be preparatory meetings beforehand.
And then expect another 1 – 2 weeks to analyse the test data and prepare the test report.
There are additional costs beyond the engineer’s costs.
Yes, that all sounds very scary and expensive. Find an engineer you trust for this. They will walk you through each step and help you as best as possible. Plan frequent communication with your engineer.
The schedule can be measured in months. Planning will start months ahead of time.
The actual test will only take a few days, weather permitting. Typically the engineer arrives on the vessel a few days beforehand. They perform the deadweight survey on the days leading up to the test. On the day of the incline experiment, all work must stop. The crew must be off the vessel during that day. The galley is not useable. The heads are shutdown. And once an incline experiment begins, it can not be interrupted until finished. The incline experiment typically takes 6 – 8 hours. But if problems arise, it may take much longer. Some take up to 18 to 24 hours in the worst case.
The analysis after the test will take 1 to 2 weeks.
There needs to be a lot of input from the client on this. The engineer will work with you. They will help you as best as possible. But let them look out for your interests. Let them protect you from the risk of doing two stability tests.
One of the major things you need to provide is the vessel, available for the engineer. The vessel will not be useable when the engineers do the stability test. There can still be work done on the vessel, but that work needs to stop on the day of the incline experiment. No workers on the ship during that day. No crew on the ship during that day.
Also, do not expect the vessel to depart for sea the day after your test. It will need refueling. All the stores need to be reloaded onto the vessel. And the day of the stability test may slip a day or two, depending on the weather.