If you need support for a problem you are having with installation or program usage, you may contact us at (321) 725-4115 or via e-mail to:

Please try to resolve your problem by reading the full manual (not just the short 16 page one) and our FAQ section first but if you can’t figure it out, call us or visit our Videos page that demonstrates common operations..

If you are getting a message about WMM.DAT being out of date, see below.

Download the 2021 WMM.DAT file.  This file contains the World Magnetic Model’s magnetic compass variation tables.

The WMM.DAT file is zipped and should be unzipped to the SeaMarks folder.  This file was originally created in 2014 by NOAA and there did not seem to be a replacement on NOAA’s website, so I digitally edited it to change the dates within it.  Since it only applies to magnetic compass variation, it is not of key importance to SeaMarks.

Version Update

This section is only for the use of current owners of Andren SeaMarks who paid for version 10.2 or later less than 2 years ago. This page (History) points to the list of maintenance updates in version 10.2 and the changes since version 7.0.  It is also needed for a Windows 10 upgrade issue where the program quits when you push the OK button on the opening screen.  You can download the maintenance upgrade for free if and only if you purchased a 12.0 or newer version less than 2 years ago. Keep in mind this does mean that each time you update, you reset the clock.  It’s 2 years from the time you last paid for the program or an update.  Our policy is to provide free updates for a period of 2 years after your purchase after which we charge a nominal fee.  Do not download this to upgrade an older version as it may crash for lack of some vital support files.

Update Software to latest version

Download the latest update to the program (2/27/24– 28,557 Kbytes)  The SeaMarks program should be closed to be updated.

If you bought your version more than 2 years ago, you need to purchase the upgrade and get the full installation package.

When you download this file (0_SetupSeaMarks.exe), place it in a convenient location like the Downloads folder because you will need to run it to  place files into the SeaMarks folder. Make sure that the installation is pointed at the correct folder (it is programmed to go to C:\SeaMarks\). After installation, you can delete the installation program if you want.


If you have calibrated your Loran to GPS conversions, the above update will not overwrite that calibration.  If you want to take advantage of our latest pre-calibrations, then  delete the file ASFuser.bin from your SeaMarks folder.  That will erase any calibrations you made, so follow that by either re-running the Calibrate Conversions or just Recalculate LL.

Download the latest ASF tables 6/19/17 Note: If you have calibrated your tables and are satisfied with the results, do not use these or you will need to calibrate again.

Appeal for calibration data

In order to better serve the Loran/GPS community, we need more calibration points for various areas of the country. With this data, we can pre-calibrate more of the ASF tables to make it unnecessary for people in those areas to calibrate the program. Our customers can’t use Loran now and thrash around with inadequate data such as read off maps or the Internet. This makes for bad feelings about the program and many internet postings about how one cannot do a good conversion with a computer program. We will keep this calibration information confidential and only use it to improve the calibrated ASF tables. Your waypoints will not be disclosed. If you want recognition for your efforts, we can post appropriate credits. Please send good calibration data taken with a real Loran and a GPS simultaneously. The more points, the better the calibration will be. For 9960 and 8790 data please indicate whether it was taken before 1/17/07 or after as the station timing changed on that date by about 0.5 microseconds.

The current calibration data was donated by:

Beau Radford- TX
Stephen Shaddock -Lake Charles LA
Tom Littlepage-Mobile AL
Dale Olds, Mike Mahaffey-Destin FL
Bob Stapleton-Mexico Beach FL
Tony Hester, Apalachicola FL
Al Cresse, St Marks FL
Gary Freeman, Tom Brodley-Carrabelle FL
Kirby Klys-Middle Grounds W-FL
Kevin Brewington, Don Busby-St. Petersburg FL
Jim Purdy, Sarasota FL
Carl Andren-Sebastian & Canaveral FL
Jeff Emery-Ponce FL
Jim Netherton, John Lane, Val Thomas-St. Augustine FL
Ron Surrency, Tom Downey-Jacksonville FL
Tommy Thompson, Savannah
Rick Barnhardt-Holden Beach NC
Dave Timpy-Masonboro NC
Uwe Lovas-MD&NC
Joyce Steinmetz, MD
Frank Dorio-Rockaway NJ
Eric Weber, Manasquan NJ
Craig Bates, Cape May NJ
Floyd Carrington, George Steller-LI
John Talen, NY Bight
Joe Mazranni, Nantucket
Al Olsen, LK Michigan
Eric Hodge, Santa Barbara, CA

Click here to see the Modifications and Bugs found and fixed to date versus older versions going back to V7.0 (2008)