Three Meter Discus Buoy
Discus buoys have circular hulls. NDBC’s operational discus buoys are designed in three sizes: 12-meters, 10-meters, and 3-meters. The steel-hulled, 12-meter discus buoys are more sturdy in rough weather than the smaller, steel-hulled 10-meter discus buoy, but are more costly to maintain. The 10-meter buoy has been known to capsize in certain environmental conditions and the overall motion of the buoy is more lively than that of the 12-meter buoy. Due to their size, the 10-meter and the 12-meter buoys generally have to be towed behind a Coast Guard Cutter to their appropriate locations.
The aluminum-hulled, 3-meter discus is very cost-effective but does not offer long-term survivability that the larger discus hulls provide. The transportability of the 3-meter buoy is much improved over that of the larger discus buoys. It easily can be carried on a flat-bed trailer. Since it is constructed of aluminum, it is less likely to corrode, and compass measurements are not affected.
Six Meter NOMAD Buoy
The 6-meter NOMAD is an aluminum-hulled, boat-shaped buoy which provides relatively high cost effectiveness and excellent long-term survivability in severe seas. These buoys are highly directional and have a quick rotational response.
There have been no known capsizings of 6-meter NOMAD hulls. The relatively small size of the NOMAD allows for superb transportability via flatbed trailer, rail, or ship. Like the 3-meter discus, they are less likely to corrode and the magnetic effects on the compass are slight.
(Source: National Data Buoy Center – http://www.ndbc.noaa.gov/hull.shtml)