Originally Posted by Brian Dinsley
The Garmin 550S does show wrecks on the chart, but in my experience I have navigated to them only to find that the wrecks are not actually located at this position. I'm not sure if the given coordinates are the reported wreck position. What you need to do, is to buy wreck guides. There are two excellent books that I have bought for my area. They are;
1.Shipwrecks of the North East Coast - Vol 1. ISBN 0-7524-1749-5
2. Shipwrecks of the North East Coast - Vol 2. ISBN 0-7524-1750-9
I'm sure if you search the internet there'll be other similar books. Try scuba dive guides.
The problem with the positions could well be the inaccuracies of the chart relative to the datum the GPS uses (WG something or other).
I frequently anchor in a small bay in which there is a smaller island, about 200m x 50m. I can assure you I remain afloat, yet the plotter always puts me fair and square right in the middle of the island. That's because the chart is wrong by about 50m in that area. (My plotter is set up using the correct datum, before anyone mentions that.)
I would think that most wrecks on charts are old and their positions found using coastal compass bearings, horizontal sextant angles, or even astronomical observations. From small boats these observations are not all that accurate. I think there will be such discrepancies with all plotters, not just Garmin ones.