I have blogged before on ocean drums, effusively singing their praises. My opinion hasn't changed. This is an instrument with a real wow factor. My earlier post gives you some background information along with my thoughts on the pictorial-versus-plain argument. (Personally I find the illustrations, along with the name of the instrument, too leading. Children are quite capable of deciding for themselves what a given sound suggests. Feeding them ideas before they have a chance to develop their own does nothing to foster their originality or listening skills.)
In the earlier post I mentioned the calming effect of the drum on over-excited children and on those with a short attention span. I repeat that now because I continue to find it a very useful feature.
I have seen these drums on the internet for under £10 (pounds sterling) for a 10" (25cm) model. I don't know what the quality is like but the picture doesn't fill me with confidence - the only good thing about poor quality items is that they tend not to last very long. And I would be inclined to go bigger. Remo make excellent, physically robust, ocean drums of 12", 16" and 22" diameters. If I were buying for a school I would go for the 16" size: small enough to be manageable but big enough to get the impact of all the ball bearings rolling around inside like waves on the beach. My own drum is a 22" example, without the kitsch illustrations. The main problems with a 22" drum are cost and storage: if you can't keep it somewhere safe between use you risk throwing away a lot of money. But it is truly awesome and doubles as a prop in drama situations.
Playing techniques: The usual thing to do is hold the drum horizontally and tilt it so that the ball bearings roll around inside making the characteristic 'waves on the beach' sound. A very dramatic and thunderous effect can be created by holding the instrument firmly in front of, and parallel to, the chest and shaking it vigorously back and forth. This causes the ball bearings to beat with force against both heads of the drum.
A more serene activity is to have one person lie on the ground and two others hold the ocean drum, clear skin down, a few inches above their supine colleague's head. The effect is like lying just below the surface of the water, watching bubbles and foam on the surface. Very calming, it is particularly impressive with the 22" drum. Sadly, I once left my own drum for some time in a cold attic with, unknown to me at the time, a leaky roof. The ball bearings rusted so now my ocean resembles the North Sea rather than the Mediterranean. Store yours in a dry, reasonably ventilated place at room temperature.
The video below shows the drum played very expressively. It can also be played as a conventional hand drum or with a soft-headed beater, often supplied with the instrument and pictured above. The sound is reminiscent of a snare drum.