Full-scale air lubrication measurement techniques in use and under development

Air lubrication systems (ALSs) are being installed on an increasing number of vessels. MARIN often receives
requests from clients (ALS producers and shipyards) wishing to quantify ALS effect on the speed/power curve
(i.e. energy saving) or wishing to go deeper into the physics by measuring e.g. the bubble size & concentration
or the distribution of air underneath the hull.

The fundamental problem with measuring full-scale ALSs today is that in order to measure the AL effects one
has to first know what flow configuration (flow regime) the ALS produces; this is because different flow
configurations require different measurement systems to be applied. However, in order to know what gas
configuration is present, one has to first measure it. One way out of this problem is to make an assessment (e.g.
based on gas flowrate) on what the expected flow regime is and to base the measurement system development
on that. Another way is to apply a measurement system that can determine which flow regime is present and
then use this to develop and apply other measurement systems which are geared specifically to measure the
observed flow regime.

An important decision also needs to be made at what scale should the flow be measured. Here, by scale it is
meant ‘level of detail’, not physical scale. Some clients might require only bulk-scale measurements, since they
want to focus on the speed/power curve. Others want to optimise the number and position of air injection points,
so they might be interested in the air coverage (how the air is distributed along/across the hull bottom). Others
still might want to focus on the flow physics and measure the air layer thickness or bubble size/concentration.
At each level of detail, MARIN has either been using or developing a measurement technique which could be
applied not only at lab or basin-scale but also at full-scale.