That's a good point - I think our Garmin Map 76 was doing the same. That said, our ground crew timed us from start to finish and the GPS distance measurement is reliable - so our average speed remains the same - 14 mph.

The GPS unit hangs upside down in it's waterproof bagged, stuffed down the crews life jacket - I think this is what makes it loose reception. Next time we'll fasten it to the mast.