Every 5 years, lifeboats, release gears and davits are subjected to an 110% overload test to ensure the equipment are still safe for continued usage.
In this post, I like to share how do lifeboat service engineers calculate, pluck the numbers and determine the load for such tests, using a simple formula. This post will be useful for new technicians and ship's personnel whom are interested in how the load test weights are determined.
First, the formula goes like this for the lifeboat and rescue boat:
Lifeboat fully loaded weight x 1.1 - Empty boat weight with equipments = Test Weight
Lifeboat fully loaded weight means the weight of the lifeboat with full equipment and in its full capacity
Empty boat weight is the weight of the lifeboat with full equipment less the people inside
Lastly, the test weight is simply the weight in the form of water balloons, solid weight, etc... that we put inside the lifeboat to simulate the 110% overload situation.
There are several reasons why we carry out this test. First, it is a requirement by the regulation to do this every 5 years.
Another reason is checking the integrity of the fibreglass and/or onload release gear. If there has been a major repair or change of parts to the release gear, it warrants an overload test. Most recently, onload release gears are modified or replaced to meet the requirements of MSC Circ. 1392. Those boats would have required an additional overload test outside of the 5 year cycle.
As for the rescue boat, it is mainly for 5 yearly check on the fibreglass structure since the most common types of rescue boats does not come with release gear installed into the boat.
The next formula is for the lifeboat davit and freefall lifeboat type davit, it is simpler than the lifeboat's:
Lifeboat fully loaded weight x 1.1 = Test Weight
Why we do not use the lifeboat davit maximum SWL is because, a davit of SWL 6000kg, is capable of equipping a range of lifeboats from different manufacturers.Lifeboat weight differs from maker to maker, capacity too will determine the test weight. Hence, if the davit's only function is to launch this lifeboat, it is unncessary to test based on its maximum SWL.
We test the davit every 5 years just like the lifeboat and also when boat falls are replaced or when any load bearing parts for example, davit sheaves are replaced or repaired. Then a overload test is called for to make sure everything is in good order.
Rescue Boat davit & Release Gears for rescue boat and/or life raft
Rescue boat davit / Release Gear SWL x 1.1 = Test Weight
This deserves its own formula because most rescue boat davits are of small SWL than the release gear. Most rescue boat release gears are 15KN while life raft release gears are 25KN. Rescue boat davits SWL are from 12KN onwards, therefore, we never encourage testing release gears with its davit. It is recommended to test the release gear in a workshop or a controlled test environment.
Alternatively, some customers prefer to do a 1-to-1 exchange of release gears due to its low price. In some places, the cost of a brand new release gear might be about the same as a load test.
As for the rescue boat davit, it is tested on site with water balloons.
Some tips:-
The overload tests for the davits are for lowering and never for hoisting, it is meant to test the braking function of the davits. Hoist with excessive loads might burn the electrical motor and cause damage to the winch.
When search for the weights, always look for the lifeboat nameplate first, if the product name plate does not have information on the weight, search from the lifeboat or davit operation manual. Normally there is such data on the first few pages.
For lifeboat on-load release gear tests, make sure the rings are similar shape & sizes to the ones on the davits. We have encountered the hook "catching" the ring and unable to release even though the release gears are already in "release" conditions.
Make sure the overload test is only carried out AFTER boat falls are replaced, otherwise, another load test might be requested.
I hope that the above information has been useful, if you do your load test calculations in another way, please share with me via Linkedin Messages or drop me an email.
If there are any topics on Lifeboat, Rescue boat and Davits that you are interested in, get in touch with me for discussion. I will be happy to write an article on it if possible.
Until then, Stay Safe!