If you do’t have a downhaul, I’m sure that’s your problem. I’m traveling now, and wold send a pic, but a line attaches to the bottom of the Boom gooseneck fitting and runs to a cleat on the port side of the mast near the bottom.  It needs no purchase.
When my pop top is up, the down haul pulls the boom down right to the Pop top connector.
Make sure you pull the halyard up all the way.
If you are sailing more seriously, leave the pop top down and adjust your luff tension more carefully.  You can even lower the whole sail on the mast to lower the center of effort when it’s windy by leaving the halyard a foot or so lower and adjusting the downhill accordingly
Fair winds
Ric
Dadventure
HBNY
.
Richard F. Stott, AIA, LEED AP
ric at stottarchitecture.com
O -631-283-1777
C- 516-965-3164

> On Jul 18, 2023, at 10:58 PM, Graham Stewart <gstewart.gm at gmail.com> wrote:
> 
> Thanks Rick. I don’t have a down haul and wondered if that might be the
> problem.. I’ll try that. Thanks again.
> Graham
> On Tue, Jul 18, 2023 at 4:52 AM Ric Stott <ric at stottarchitecture.com> wrote:
> 
>> This looks to me like a halyard/down haul tension issue. It appears that
>> you have a ‘Continental’ rig with a Stack Pc or Lazy Jack system. It should
>> be easy to pull on some down haul to tighten the luff of the sail.
>> Ric
>> Dadventure.
>> HBNY
>> 
>> Sent from my iPhone
>> 
>>> On Jul 18, 2023, at 2:59 AM, Graham Stewart <gstewart.gm at gmail.com>
>> wrote:
>>> 
>>> My mainsail hangs with a diagonal crease that I can't seem to get rid
>> of.
>>> The sail was new a few years ago and was purchased while I was restoring
>>> the boat - which included replacing the inner stay chainplates. I also
>>> changed the furling gear and afterwards it seemed that the inner aft
>> stays
>>> and the aft stays were shorter than before.
>>> Might the rake of the mast create this problem or might it be a
>>> poorly constructed sail? I have attached a picture in case one of the
>>> expert sailors on the list can make a suggestion.
>>> Thanks,
>>> 
>>> 
>>> Graham Stewart
>>> Agile 76
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>> 
> -- 
> Graham Stewart
> gstewart.gm at gmail.com