How do I keep ships in formation?

[CB..]

all of a sudden every convoy i meet seems to have lost it's mind completely...the ships randomly weave in and out of each other stop start sop again change direction -all of which makes the game pretty much un-playable..

i uninstalled and started again with a fresh install to check...same thing...even bit the bullet and patched to 1.4b same thing...

daftest part of all is that the convoys actually seem to stop all together whilst the DD's attack me...only moving again after they have lost contact with me...and then they steam of like ants in a entirely messed up fashion...so much so i can't be bothered trying to attack them as it's just too bizaare to be worth the effort!

i have read that if the lead merchant is faster than the other ships (top speed in the cfg? im assuming here?)
then this creates this issue...but sounds off beat..what i have done is to set all the merchants top speed in the sea/vessel cfg file to 10 knots..in the hope that this will help....what is going on? is this unique to my system (im now running stock SH3 1.4b) or is it a bug?

this game is more frustrating than SH2!!

i can put the occasional glitch of this nature down to me reaching the convoy just as it reachs a looped waypoint --in which case it might double back on it's original course causing some problems--but the percentage chance of this happening four or five times on the run with different convoys at different locations is pretty remote---