Here we go again. Not complaining but so many misunderstand the concept. I'll respond in no particular order/importance.
The P-1 is more accurate than internal GPS. It operates at the fastest refresh rate but so does the G3 internal HDS's. G1 internal = 1/sec; G2 internal = 5/sec; G3 internal and P1 = 10/sec. If using P1 with G1 it will improve to 5/sec; P1 with G2 = 10/sec. Refresh remains the same for G3/P1.
Visit this BBC
thread. It will explain all you need about the P! with an amazing differences of advice and opinions. Understanding these different views, which are to a fault (almost) true, will allow you to move forward with a P1 or not.
Personally, I use the P1 to the point (no pun intended), when mine broke (not physically), I purchased another P1 via the Lowrance discount program. Mine is basically over the transom ducers for the most accurate reading. What does this do? Simply, my waypoint is spot on less the inaccuracies of # of satellites, weather or other interference are out of my control. I set the majority of my wpts from the console.
Now here comes the part most get wrong with the Xi5. If I come upon a BP while at the console and set the wpt (console unit set to use P1) and then move off the area say 50 yards, turn off the big motor, deploy the Xi5, let GPS register (look at status lights), and with the HDS G3 at the bow set to use the P1, and direct the Xi5 from the console unit OR the bow, the Xi5 goes directly to the BP where the wpt was set from the P1 (stern)!!!!! A wpt is a wpt regardless to the Xi5 given environmental conditions remain the same. Think about it.
Ethernet is not necessary to transfer wpts from one HDS to another if you have NEMA. But NEMA transfer is slow. I load wpts by lake only. So before going to the lakes, my unit are cleared of all wpts/trails (after saving of course), then the lake being fished is loaded separately onto both units: console HDS 10 G2 and HDS 9 G3 on the bow because of the slow loading via NEMA. If you use Ethernet, it is fast. I do not have my two units ethternet connected by choice, but that's just me. If I set a wpt from the console using just NEMA, it pops up on the bow unit. If I delete a wpt from either unit, the other unit is not updated unfortunately. This is true of Ethernet too. Also the reason I load wpts/trails to each unit is the NEMA doesn't transfer trails at all. I'm not sure if Ethernet does, but I think it does. It's been a long time since I used Ethernet connected units to recall.
If you don't believe the wpt discussion consider this.
Xi5 with gateway connected to NEMA
HDS 9 G3 at bow NEMA connected set to use P1
HDS 10 G2 at console NEMA connected set to use P1
P1 at stern NEMA connected
From anywhere with TM deployed, (driveway, lake, wherever SAT is available) set a wpt from the console. Go the the bow unit and check what the coords are for the newly created wpt from the console LAT/LONG is, Viola, they are the same. Or, set it from the bow, and check the console, the coords are the same as the bow. Now, think where would the Xi5 go if using the GO TO wpt function. The same damn wpt. It is that simple and easy. So the TM would be sitting on top of the wpt created by the P1 at the STERN!
Understanding this, setting units to use what is the best GPS for your use, is paramount to understanding accuracy. And of course, we all know there is a built in gov't inaccuracy for military purposes, but it is rather small. The units can even tell you the approximate error range. That's another discussion, which can be helpful to understand why sometimes you can't get on the wpt exactly or near exactly, which is mainly caused by # of satellite receptions the unit is able to lock onto.
In your setup, if I didn't get a P1, I would change the bow HDS (GPS non-functioning) to use the console GPS. You will either be spot on or off 6-8'. You'll know wpts are always set at the console. By having the Xi5 as the GPS on the bow you will not know which wpts are set where. Now, if you only set wpts using the TM (highly unlikely), then I'd change the console to the Xi5 GPS. If you elect to get the P1 and set it at the stern because the console is used mainly for wpt creation, then follow the above.
I hope they 'sticky' this. I'm worn out. LOLs - enjoy.