Cheaper repeater?

[pugwash]

I have a Raytheon Seatalk set-up with antennae GPS and Yeoman plotter in my little ketch, and all the information I need is displayed satisfactorily at the chart table. When I bought the boat it also had a repeater in the cockpit that gave lat/long, COG, VMG, speed, depth, etc, but this has broken and I am being quoted about £360 for a replacement. Really, the only two things I need in the cockpit are speed and depth. Could you suggest a cheaper way of doing it?

 

[Guest]

The key to this one is the language that the repeater and the source use to communicate. Generally most instruments talk NMEA of one type or another.
As long as the source instrument and the repeater are based on same NMEA then you can fit whatever you wish .... the NMEA standard was designed for 'cross-platform' exchange.

You'll probably find Nasa / Echopilot repeater or similar will do the job ... Seatalk is excellent kit, but too pricey for my scrooge pocket !!!! Check your manuals and then check out the shop shelfs for the same NMEA ......

 

[Guest]

Sometime last year pbo published an article about DIY gps-repeaters, using the nmea output from the master unit. If you're interested I'll see if I can find out more from my pile of old mags.

 

[billmacfarlane]

I note that you are using Seatalk. Does your instruments also have NMEA ?

 

[pugwash]

I have been searching through my handbooks and now I'm really confused. The basic Tridata instruments seem to be Autohelm's ST-50 range. One book says: "...can be linked to any of the Autohelm Sea Talk compatible autopilots, or can provide NMEA 0183 data to navigation receivers, chart plotters or to other nav'l equipment..." Another says: "The ST50 Plus GPS and Navdata instruments are repeaters that receive positional fixed via either NMEA or Sea Talk from the GPS satellite system..."
This doesn't really make it clear whether NMEA is part of the existing system or an alternative. So do you think it will take the cheaper repeaters you mention?
What does NMEA stand for, by the way?
Thanks for the input -- gratefully received!

 

[johndf]

Re: NMEA and sea-talk

If I remember correctly, the Autohelm instruments will send whichever you choose out of sea-talk or NMEA, but not both at the same time. On the other hand, I am fairly sure that they can receive both at the same time.

 

[HaraldS]

NMEA stands for something like National Marine Electronics Association. It's a standard for interfacing Marine Electronic devices of different makes and it's been around for many years. The current standard is already ten years old and called 0183 Version 2.0.
There are a large number of so called sentences defined for different boat related data, like speed heading, depth, position and so on. Depending on the instruments, they send out what the have to offer. So the log would give you speed through the water, total miles and trip miles. Generic NMEA repeaters can display about anything that comes in.
From what I gather from your note, you seem to have an ST50 Tridata Log, Depth and Wind instrument, and I'm quite sure it doesn't have a NMEA interface. I have checked Raymarine's excellent Website, but they only have manuals online for the newer generations and the ST60 Tridata, which is the successor of the ST50, definitely doesn't have a NMEA output.
I'm not sure what your Navigator is like, I suppose it's Raytheon too. These often have NMEA output in addition, and in such case would certainly send out the navigator data, but I'm not sure they would also repeat the data that comes in from the tridata via SeaTalk. If it does, the manual of the Navigator would definitely tell you and actually list the sentences it can emit with their three of four letter acronyms.

In your case this would have to be: DBT (Depth below transducer) and VHW (Velocity and Heading).

If neither your Navigator nor your Tridata can send these records, you would need a separate SeaTalk-NMEA bridge from Raymarine which would cost you about 120 pounds and would largely offset what you may gain on the repeater.

If you are into building electronics yourself and would build your own repeater, you can certainly decode SeaTalk directly, it’s not so difficult, especially if you just want some specific data and you’re only listening. But keep in mind that a cockpit instrument has to be quite rugged and waterproof.

Since you only want speed and depth in the cockpit, you may want to check out the Raymarine ST40 Bidata Repeater (Display only), which I think should be about half of what you have been quoted for a Multi Display.

 

[Teddy]

Re: NMEA and sea-talk

Autohelm send NMEA OR Seatalk depending on which model you buy. My ST50 is Seatalk and does not work with the cheap Nasa Clipper repeater. Raymarine tech have confirmed this. The Clipper works fine on my Garmin GPS 12 though.