Rob,

The newer Furuno radars do indeed have this same capability. What RayMarine
calls MARPA, Furuno calls ARP. If you go on the Furuno web site and download the
manual for their radar units, you can read about the ARP setup and use. One such
manual is at:
www.furuno.com/Furuno/Doc/0/EQ45O1VGFNJKVDIUHSF1VBNA45/17x2+17x2C+17x3C+Operator
%27s+Manual.pdf

The MARPA or ARP systems are valuable in that they semi-automatically calculate
CPA and TCPA of a target for you. In just a few sweeps of the radar you get a
quick picture of the collision potential of the target. Caution is needed
however since the angular resolution of our small radar antennas can lead to
very changeable CPA calculations on large targets that are somewhat close. The
calculated CPA on a MARPA system is an aid, but it must be constantly monitored
for updates.

This MARPA or ARP capability is very different from the guard zone feature that
you mentioned. I've found the guard zones to be pretty useless underway since
any sea return within the guard zone will set off the alarm. This means the unit
is always false alarming, and the whole concept of a guarded safety zone with an
alarm then become useless.

Kevin Redden

GYMKIDD319@aol.com
At 12:41 PM 1/3/05 -0500, you wrote:

MARPA is a generic term for target tracking. Furuno has ARPA and MARPA
addons for some of their models.
These tracking systems are not of much use on a vessel under 65 feet. It's
not that the 65 feet has anything really to do with it, but size does
matter or more correctly stability. Yawing of small vessels makes these
addons marginally useful.
The MARPA tracking degrades from the yawing of the vessel, which compounds
the instability of the heading sensor, which  is some kind of compass. Now
that you know it's the compass, you also know from recent posts about rate
sensors and fluxgate compasses used with autopilots that a stable heading
sensor is a tough trick on smaller vessels.

I have had these addons and I don't think they are ready for prime time, at
least on small vessels. The lack of stability leads to loss of tracking of
the target. I suppose if the added cost is little or nothing, this may be
worthwhile, but keep in mind the heading sensor problem.

MIke

Capt. Mike Maurice
Tualatin(Portland), Oregon

At 10:36 AM 1/3/2005 -0800, Mike Maurice wrote:

Manana's 2 year old Raytheon has built in MARPA. I didn't select it for
that feature, but thought what a cool extra to have. Mike is right, on a
smallish boat, in any kind of a seaway, the MARPA is almost useless. I've
watched shrimpers go from a 4 knots to a steady 12 knots, jump up to 28
knots, before settling down to 6, and then going backwards at 3 knots. Not
very usefull! When it is flat calm it works just fine and is a cool extra
feature. Now if we went out and popped for a gyro compass or fluxgate with
heading rate sensors it might make it more usable in a seaway. But I've got
other things to spend the money on.

Jim

Jim McCorison
Starfish Marine
(619) 337-5370
http://www.starfishmarine.com

On Mon, 3 Jan 2005, Jim McCorison wrote:

Hmmm.  Since I've already got a fluxgate in my autopilot, I wonder if
I could feed that to the radar unit via NMEA connection?  Sure would be
a lot cheaper than having a 2nd heading sensor...

MARPA requires heading information at 10 cycles per second, which is faster
than most NMEA compasses produce heading output. (My Comnav will do this,
but the one on my Simrad would not).  A clear advantage of having one
sensor, is that you see the same heading on your radar as on your autopilot
<g>.

Best,

Steve

Steve Dubnoff
1966 Willard 47' Dover Pilothouse
sdubnoff@circlesys.com

At 11:11 AM 1/3/2005 -0800, Paul Goyette wrote:

A simple fluxgate compass isn't enough for this. It needs to be one that
includes... my brain is fading here...heading rate sensors. I'm sure
somebody will correct me if this is the wrong term.

Jim

Jim McCorison
Starfish Marine
(619) 337-5370
http://www.starfishmarine.com

This hasn't been my experience at all.  I've put about 250 hours of
offshore/MARPA use time in on my boat so far.  We always run with radar when
offshore.  In daylight, I'll often track a large target even if I can see it

• it lets me know how close we're going to get - it is often very hard to
  tell visually.  At night during overnight passages, we always track every
  target.  In my opinion, it has been excellent and has rarely, if ever, given
  bad information to us (after the first minute).

In general, when we first lock onto a target, it seems to take about 30
seconds before the target speed is accurate.  After that, I don't see it
varying unless the other vessel is actually varying speed.  When locked onto
a ship, I never see a significant speed change.  We often end up locking
onto a sea buoy from time to time, especially at night when our rule is to
track everything.  I've learned that a speed of under 2 kts generally means
that it is a buoy.

I configured our chartplotter to automatically draw a "lollypop" display on
any locked radar target along with a 6 minute course prediction line.  This
is a very easy-to-understand display and helps to put the target into
perspective with the area we are transiting (you can often see how they are
changing course to enter a shipping channel, etc.).

There are a couple of things on my boat that might be making a big
difference with the quality of data that I'm getting:

1. Active stabilizers.  They are always enabled when we're offshore.  The
   worst weather I've been in overnight was 6 ft. quarter beam seas.  We rocked
   a bit but I noticed no degradation in MARPA.

2. Gyro-stabilized course computer.  This is an extra option for my system.
   You don't have to have it.  It has a gyro for position stability.  I believe
   that it also has 3 accelerometers (OK, I admit to opening it up and looking
   around!).  I believe that all of this helps the MARPA and radar display.
   I'm sure that it makes a difference.

All of my electronics is Raymarine.  It is all integrated together and has
worked without problem.  I've kept the firmware up to date and have found
Raymarine technical support to be excellent and beyond-the-call-of-duty.
I've written 2 paper letters in my life applauding a company's technical
support.  One of them was to Raymarine.  I know others have complained of
problems with them.  I just haven't seen it at all.  I have no affiliation
with Raymarine in any way.

For more information about aCappella's electronics, Voyaging magazine did a
nice article about it at:
http://www.voyagingonline.com/helmshot/fall04helmshot/

================
Jeffrey Siegel
M/V aCappella
DeFever 53PH
W1ACA/WDB4350
Castine, Maine