Hello G G

Unsure of the boat make, it looks like it has narror low volume bows with hulls that have a built in skeg combined with generous sail area ,-that combination of narrow bow 13 ft Length and proportionately larger sail area lead to the bow down characteristics in higher winds .

Some suggestions to counteract this are -
1 -rake the mast aft more ,--accomplish this by adjusting the stays ,lengthening the forward stay and shortening the sides .-
2 add a roller furler for the jib and roll the jib or take the jib off --per photo ,--when the wind picks up .
3- be sure to move crew and gear weight aft towards the sterns when the wind kicks in .
4 -more drastic ,but you may consider removing the heavier solid deck portion and replacing it with a mesh trampoline -available through your local sail loft or here on Catsailors store , provided the crossbeams are of adquate strength without the deck .The added forward weight of the solid deck is a contributor to the bow down characteristic .

All multihull craft can become overpowered and have this bow down tendancy as the wind increases ,-some much more than others as per this example.
aft mast rake -crew weight aft ,and reduce sail are common to all cats as wind increases proportionately .

Hope this is helpfull --all the best .
Carl