CPA calculation - ship sizes - closer proximity

[dacust]

Originally Posted by Stu Jackson

Why would you do that for your boat? Compared to shipping, our boats are just gnats. How does this help at all? I understand it for checking large ships, but how does that help THEM to understand YOU?

In some thread somewhere I saw a picture of a laptop running O. Out the pilot house window you could see a few hundred feet of freighter. Us little boats are not the only ones using O. If it doesn't hurt to take ownship into account, why not?

-dan

[rgleason]

Jeff Robbins, Vesper Marine wrote back quickly,

Hi Rick,

Thanks for your email and questions. Yes, it will do as you've suggested and you can use either WiFi or USB to the computer. All our transponders have USB and XB-8000 & Vision also have WiFi. However, it does need a NMEA input rather than SeaTalk, so you'll need to convert that via either existing plotter or Raymarine multi instrument or ST converter.


Very good question on GPS reference location. Currently CPA/TCPA is calculated using GPS antenna positions and doesn't take into account antenna position data. Thus is done for several reasons, but the most significant is the antenna location is not known until vessel static data is received which can be up to 6 mins. Also not all vessels transmit heading so orientation isn't reliable unless that data is included. For most ships it is, but most other Class B transponders don't send it or there is no heading source on-board. In fact, as far as I know Vesper transponders are the only Class B's that do send heading when there is s NMEA 2000 compass or A/P present. [Rick's underlining]


Regarding alarms... this is a function of displays, so it will depend on the capabilities of the display. Ours have a lot of control over alarm scenarios with also the ability to eliminate alarms for stationary targets (eg you are pointed at an anchored or moored vessel) as you go past. All other displays will trigger an alarm in that case.


Hope that info is helpful. If you have additional questions, let me know.


Best regards,


Jeff

On Thursday, October 9, 2014 wrote:
name: Rick Gleason
I was unaware your products acted as a multiplexer for Nmea. Very good!
I have Raymarine Seatalk Instruments would I need a special seatalk converter to Nmea ---> Vesper Equipment ---> USB Computer Port?
Would the wifi version connect via wifi to PC?
Regarding your calcs for close proximity, say less than 1 nm what do you do? What if Target GPS antenna is not placed properly relative to ship? Do you adjust for width of ship too? Or is it simply GPS-GPS? What is conservative enough in close conditions, but not so conservative that alarms are always going?

What is your users experience about close proximity?
Thanks very much.

[rgleason]

Well this sort of leaves with doing nothing because of heading sensors OR doing something

Sent from my SCH-I545 using Cruisers Sailing Forum mobile app

[zengirl]

Originally Posted by barnakiel

THX!

Now I know.

I believe that when sailing a smaller craft, the erratic movement of such a craft (large variations of its speed and heading/course) exact judgement of tight CPA/TCPA scenarios may vary from very difficult to impossible. In fact, when it is a close call, we might be better off by switching off (if only mentally) the AIS dictated clue.

Perhaps the above could somehow be incorporated into the real world coding choices by implementing something along the lines of a "too close to say" warning being displayed along the CPA/TCPA of objects that might pass us by within an X mile(/cable) range.

Thank you again for all your work and tuition.
barnakiel

I am reading everything since I am a newbie. Haven't learned the horthand yet. What is CPA/TCPA? Thanks

[nohal]

zengirl...
CPA and TCPA Alarms Explained | Digital Yacht Ltd - even contains pictures

Pavel

[zengirl]

Originally Posted by zengirl

I am reading everything since I am a newbie. Haven't learned the horthand yet. What is CPA/TCPA? Thanks

haha shorthand

[barnakiel]

Originally Posted by zengirl

haha shorthand

Yes, it was a shortened version of shorthand this time ;-)

As explained above.

Please mind that CPA and TCPA have been, at times, interpreted by various manufacturers in various ways. So do dig into your hardware / software and see how these have been implemented there.

Today it is pretty uniform but older equipment sometimes has its own private and misterious definitions of what is called what.

Sailing instrumentation is full of such phrases (e.g.: TWS AWA COG XTE TTG ETA), etcetera. They nearly always are what they sound (X cross T track E error).

Always mind the same concept may be hidden under various acronyms in different makes (e.g. Garmin vs. Raymarine vs. Silva and so on).

I hope you are having fun ... (?) ;-)

Big hug,
b. (barnakiel)

[zengirl]

Originally Posted by nohal

zengirl...
CPA and TCPA Alarms Explained | Digital Yacht Ltd - even contains pictures

Pavel

Thank you so much. I like pics! haha At this point I am so sick of reading!
Been reading for three years!!