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Old 04-10-2007, 16:13   #1
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Join Date: Jan 2007
Location: Perth, Western Australia
Boat: Fountaine Pajot Athena 38
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Optimizing MARPA performance on Raymarine radar systems

Can any body tell me if it is worth spending another $1000 for a fast heading sensor to get the best performance from MARPA ? (Miniature Automatic Radar Plotting Aid)
I find MARPA a nice feature, but is it really worth spending that extra cash ?
How much will I use it ?
How useful is it ?


Question

Is it necessary to install a fast heading sensor for my radar system in order to use the MARPA target tracking feature? My radar already receives COG and SOG from my GPS receiver.

ANSWER

While the MARPA (Miniature Automatic Radar Plotting Aid) target tracking function can operate at a very basic level on a GPS input, it is strongly recommended that all vessels using MARPA also connect a high-speed heading sensor to the radar. This significantly improves the performance of the MARPA's calculated target data at:
Very low speeds.
In high sea states with excessive pitch/roll rates.
During high rate-of-turn manoeuvres such as changing course or tacking.
Raymarine offers several solutions with fast heading output including our Smart Heading System <Raymarine Marine Electronics - Heading Sensors>, and "G" series autopilot core packs. <Raymarine Marine Electronics - Corepacks>
A fast heading sensor updating at 5 Hz (5 times per second) or greater makes your MARPA data more accurate and more reliable under varying conditions. There are 2 primary benefits that make this possible:
1. Low speed heading stability: A properly calibrated compass will tell the MARPA the direction the boat is headed regardless of the boat's speed. Relying on GPS derived COG alone at low speeds is not recommended, as COG readings tend to drift or pinwheel when moving very slowly. In restricted visibility conditions, when moving at bare steerageway, this makes a noticeable performance difference in the quality of the MARPA presentation.
2. Fast update rate during manoeuvring: Because the compass updates the MARPA 5 times per second or faster, the MARPA knows exactly what your boat is doing as you steer through high speed turns. GPS calculated Course Over Ground does not update quickly enough to keep up with the high rate-of-turn that most small vessels are capable of. This tends to cause the MARPA to lose track on contacts while you are changing course, tacking, or manoeuvring.
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