Had similar experience-whilst sailing my boat last summer thru Kyle rea between Skye and mainland Scotland where springs can run well in excess of 10 knots.

So I set of north bound at low tide as reccomended having previosly set a whole load of waypoints in my garmin 152 just in case and duplicated them on  my charts.

Basically you head as I recall NNE up the sound of Sleat into Glenelg Bay-you then turn to just of north to run thru the narrows about half mile wide.

The chart marks the way thru to a lighthouse on the Skye shore with one of those cones of visibility/acceptability as I call them.But I got carried away following a boat in front(I was under power) and using my goto which was set to a waypoint mid chanel off the light house.

As far as my go to was concerned I should have realised I was like a boat on a swinging mooring.I was getting there but the strong current even at turn of tide was pushing me westwards towards Skye.

Suddenly I fely things were wrong and looked at my echosounder 10ft. and rising! and realised I was heading onto a shingle spit which appears at low water.

Luckily as under power did a 90 degree right turn and I only draw about 4 ft.

Phil

I could of course have set up a "road" on my GPS which shows as a road with a centre line edges set to choice EG 10 feet wide etc.-remain on centre line and you are on track all way between two way points and not drifting off-also could have alarmed edges!

Phil

I too remember that gravel spit when heading North through Kyle Rhea. Like Phil I made a 90 degree turn towards Glenelg and breathed a sigh of relief. I had chanced to look over the side and could see the bottom with the seaweed streaming horizontally in the tide. I regularly make that passage now and always keep well into the centre of the channel -- the tide will generally be more helpful there in any case. Kyle Rhea is definitely not a place to cut corners!

One thing that users or gps "repeaters" ought to bear in mind is that although a "road" may have been set up on the instrument at the chart table, which will show a true position of the boat from the original straight line, the repeater will draw a new "road" showing the direction from anywhere the tide has happened to offset the vessel.

I fell victim to this problem once and nearly went aground untill I realised that only the destination waypoint position is relayed to the GPS repeater, and not the original starting position (at least on the Silva and Nasa ones) so a regular check of actual position and bearing should always be made.