GPS readings for the Cork City Marathon & the Tunnel problem

Someone sent me an e-mail recently about the Cork City Marathon and the GPS readings out along the course. They asked the question..."Do you know if there is there any way to avoid losing the signal on your watch when you go through the Jack Lynch Tunnel?" 

In the Cork City Marathon after passing the 7 mile mark, you run down into the North Bore of the Jack Lynch Tunnel and take a curved route under the River Lee. You do of course lose all the GPS signals once you enter the tunnel and only aquire them again once you exit. No signal, no readings.

Your watch of course has no idea that you took a curved route and just connects the entrance and exit of the tunnel and assumes you took a straight course.


This is just one of the features that causes problems out along the course. If you take sharp corners near tall buildings then your watch can just just record you as having gone through the building. Another issue is the fact that the course is measured by the shortest possible route whereas in a mass of runners, you may well be taking corners wide and not taking the direct route.

The net effect of all factors can be that your GPS watch won't read 26.2 miles and it may seem out by quite a bit.

So my questions are.......
1) What kind of distances have you measured for the Cork City Marathon by GPS?

2) How did you find the loss of signal at the tunnel effected your watch or your race? Was there any issues with the watch going into standby modes when it lost the GPS signal? Any other side effects?

3) With GPS watches that beep every mile, you should find it sounding earlier and earlier as you get near the mile markers. How did the tunnel change this?