A buoy can be tied to the rode
in order to provide the same shock absorbing properties of a kellet, only the orientation of the 'spring' is reversed. Rather than lifting a kellet in order to straighten itself, the rode must instead sink the buoy. An advantage over a kellet is that rather than requiring dead weight, its force is generated by its buoyancy (dictated by its displacement), which means it is lighter to stow onboard.
The ideal position to maximize the buffer effect is, as with a kellet, halfway between the anchor and vessel. However, this effect disappears as the force in the rode overcomes the buoyancy just like it does the catenary from the chain and weight from a kellet. The straighter the rode, the less distance the buoy has over which to provide its effect.
Moreover, the buoy has the drawback of working to disadvantage the anchor in terms of angle of pull: unlike a kellet, the rode is initially kept at a higher angle. However, as with a kellet, by the time the anchor is likely to be troubled, the rode will be close to tight regardless, so the impact on angle of pull and consequent ultimate performance will probably be negligible.
From: Kellets and buoys (Rocna Knowledge Base)
An additional use for such a buoy is an attempt to keep the rode clear of tall obstacles on the sea-bed, such as coral
or dead trees. In this case the buoy can be placed at a point on the rode a distance away from the anchor a little greater than the depth
. In light weather
the buoy will then keep this final section of the rode raised, but will sink to allow the rode to provide scope