All three products will give you a forecast at your present location and any destination you choose to view. I found it difficult to determine which forecasts are best, but there are clear differences in how they are delivered.
XM is the most straightforward, giving you click access to any location, with further clicking stepping forward in 12-hour intervals. The XM/Garmin was the only system that quickly showed if there would be sun or clouds. The three-hour forecast intervals offered by Sirius are helpful if you want to time your departure or arrival to changing conditions, but the E-80 Sirius interface only moves forward, which is annoying.
ClearPoint provides the most forecast information, as well as sophisticated forecasting models valued by top-notch sailing tacticians, and can easily move forward or backward. All the services, with the exception of XM running on a Garmin 545s, also offer text NOAA marine forecasts you should probably read first, as they include warnings.
Comparison: Forecast Wind/Sailing
Aside from ClearPoint, these live-weather services are not particularly good at forecasting wind conditions. Sirius does offer forecasts at three-hour intervals, but the predictions look like the same generalized model data that XM provides. The velocity and direction forecasts don’t take into account local geography or heat absorbed or released by landmasses.
ClearPoint claims to use an advanced wind model tweaked for local conditions in certain sailing areas where it offers “High Definition” forecasting in 15-, 5-, and 1-mile resolutions. The company is even putting up its own anemometers to validate and improve its model. ClearPoint’s roster of high-end-racing customers may benefit from this, but the average cruiser/racer may find, as I did, that state-of-the-art wind forecasts are often still disappointing.
Hardware prices vary depending on the chartplotter, computer, and receiver method used. The service plans needed to reproduce the benefits in this article, excluding music and high-resolution wind forecasts, are (as of August 2008): XM (Master Mariner package, $49/mo, $50 activation); Sirius (Marine Weather, $29/mo, $50 activation); ClearPoint (HD Weather Edition, $395/six months, or Premium Edition, $10/day + a wireless Internet plan, which starts at about $30/mo).
Dan Corcoran became an electronics enthusiast at 12 and a software company owner at 20. He often sails on Long Island Sound with his family aboard their 39-foot Breeze Pleeze.
ClearPoint Weather, www.clearpointweather.com
Sirius Satellite Weather, www.sirius.com/marineweather
XM Satellite Weather, www.xmradio.com/weather/marine.xmc