ISTA Procedures, and other industry-standard packaging test protocols, don’t contain vibration (PSD) profiles for ocean shipment. Several studies have shown that vertical vibration during sea transport is so small that it’s negligible. This is not to say that ocean shipment is benign – there are shocks due to loading and unloading, ship motions can cause the shifting of goods, there is potential damage from extreme temperatures and humidity, and compression forces due to stacking can be large. Since essentially every ocean shipment also involves other kinds of transport (road, rail, air) to and from the port, it has been fairly standard industry practice to simulate those other transport vibrations with the assumption that they envelope any vertical vibration experienced during ocean transport. Regarding shocks related to ocean shipment: there is not a lot of data for loaded sea containers, but what information we have suggests that the shocks are fairly low. The primary shock hazard to ocean-freight packages is probably when they are loaded into the container and unloaded from the container, and are handled at other points during distribution.
The standard practice we see utilized at this time is to select an appropriate test as if the packaged-product were going to be surface-transported only. If you think dockside loading/unloading might be more severe, you could increase the impact velocities and drop heights. You could also add a flat drop or two (to simulate handling with cargo nets), and perhaps some rotational corner drops as well. For stacking, to better simulate the possibly more severe conditions, consider increasing the "F" (compensating) factor above the required value. I'd recommend going to one or more of the atmospheric conditioning extremes (or beyond). You can also consider adding actual water spray to dampen the packages.
The other protocol I would bring to your attention is ISTA 6-Amazon.com-SIOC. This is something to consider if you are doing ecommerce and represents the journey from when a package is received at an Amazon fulfillment center all the way to the end consumers house via either single parcel or LTL. This test combines elements of 3A or 3B depending on the size of the package with other testing elements that represent handling and storage within Amazon.
Utilizing ISTA 4AB to establish a test sequence which includes these additional handling events to your established protocol is another potential path. The ocean freight leg of the journey typically isn’t creating catastrophic failures that are preventable with packaging. However, I do think that the cumulative effects are contributing to the fatigue of a package which then when on land, potential yields failures at a quicker/higher rate. More to come from ISTA on this subject, till then I would love to hear more about your challenges and success with evaluating these hazards against your packaged-products. The real world correlation piece from a variety of product manufactures is always the most useful information in the development & validation of a potential test procedure.
Below are a couple documents talking about the low vertical vibration levels while on a ship.