Welcome to the Raymarine Technical Forum Terry,
1. The length of NMEA 0183 sentences will vary based upon the type of sentence and the data contained therein. Raymarine's E-Series Widescreen MFDs are designed to support NMEA 0183 v3.01 sentences received at either 4800 or 38400 BAUD. Please refer to the NMEA 0183 v3.01 specification for the detailed format specification for each NMEA 0183 sentence.
2. Raymarine recommends that a NMEA 0183 v2.1 or later 5-10Hz stabilized heading input (ex. E12102 Pathfinder Smart Heading System (retired), S1G/S2G/S3G, etc.) rather than 1Hz SeaTalk non-stabilized instrument heading inputs (ex. ST40/60+, ST80 Active Compass Sensor (M92649)) be used for radar and other features requiring heading input. Accuracy and damping of heading data is critical to several features requiring heading data. Raymarine recommends that accurate 5Hz or greater heading data be supplied to any system using using any of (but not limited to) the following Radar and Chart application features:
It is recommended that customer's regularly check the accuracy of products supplying heading data to the system and perform any calibration/alignment required to provide accurate heading tho the system.
Following the retirement of the Pathfinder Smart Heading Sensor, the T70132 Airmar H2183 Heading Sensor w/NMEA 0183 Cable has been recommended for such purposes. The part number for the heading sensor alone is A92185 and the part number for its NMEA 0183 Cable is A80131.