how can I get a flat glossy finish using gelcoat ?

First mistake was to use flowcoat, you would have been better with a two pack polyurethane paint.
However flat it back with coarse grit paper then fine down to about 400 grit. The use one of the excellent Farecla finishing compounds to get a good finish - check out their range for the most suitable.
Finish off with a good quality wax as already advised.

Jonp
November 2009

Hello,
No need to go thru that many grades of paper!
go with dry sanding using the following grits: 120, 320, 600, 800 then polish with professional 2000 grit compound.
You'll need a professional 5mm orbital sander and a polisher to do the job right! (not cheap though)
Also, to maintain a fair hull, make sure you move the sander flat, across the hull at 45 degree strokes. This is most important when using the 120 and 320 grit as these are the most abrasive and will do the most damage!
Alternativley use a fairing board and do it the hard way!

GRP007
July 2009

I think you have given yourself a lot of hard work! The way to do it is to use progressively finer grades of abrasive. I do this on small gel coat repairs. I start rubbing smooth with 80-grade wet-or-dry paper then move on to 120 and so on until I get to 1200-grade (I use 80, 120, 150, 180, 240, 360, 400, 600, 1000 and 1200). At that point I switch to T-Cut and use that to remove the remaining slightly dull surface then finish off with a good wax polish. This gives an invisible repair to small areas but requires a lot of patience. For a 30ft boat - best of luck!

John Renouf
January 2009