the photo shows up on my post....
my 2 bow u bolts are right through the hull at deck level ,right next to the anchor locker and angled through so that the backing plate (5mm stainless by 20x100) lies flush on the hull.
the angle of the U bolt is slightly off the line of the strop but its strong enough.
i used a 4mm drill bit and took the plunge on the first drill through the hull , lept over the side to make sure it hadnt come through on a spray rail ...Phew ..was just right .
i think the hull was about 18-20mm thick here.
packed the holes with sikoflex and also under the backing plate ,then tightened up.
i do check they are tight each time i lift the boat out.