Hi need help

We have a broom Gemini 1971. Had it for a few years and it’s been fine. We changed the ply mounts near the transom and since then it takes on water.

Also how can we check the hull is sound as am worried it maybe coming in from there

Sorry to hear this. Do you mean the ply in the pic where the engine mounts? If so, is normally nailed into the grp and plywood underneath, with gripfast nails, which is why the transoms typically rot, f the holes aren't properly plugged and the new ply not glued on, can let water in. Check that the inner drain plug isn't leaking - very often just a captive bolt, I've had that before. And check the area (on the outside of the hull) where the floor is glassed to the hull. The build was never great, nor the layup heavy enough on these - the glassed in plywood floor creates a hardspot at it's most forward edge (on both sides) sufficient to crack the hull.

The old ply was removed all holes filled and sealed and refused and waterproofed. The drain plug seems secure have checked the hull but cannot see any obvious signs of cracking or holes. Am I right in thinking they are doubled skinned so if. Water came in the top (rain or some other method) it wouldn’t be in the hull. If . Do u have any photos of what I should look for on the hull for signs of hard spots or cracking . Am new to this and just finished paying for it so am gutted that something has gone wrong

They are just a hull with a floor moulding, rather than a double skin like a Dory. This means it could be coming in from inside if rained on. I'd check the seats where they bolt to the floor, if they're originals the mounting screws might have rusted below the heads and obviously check for cracks on the floor. Externally the hard spots are often at a point where the floor extends just past the red arrow & check over the top of the moulding black arrow that there is no water in there, or a void to the inner hull. Might be a loose bow eye, or deck hardware, or water spraying up under the deck / hull seam. Look for signs of green mould where there may be damp...is often a giveaway - it's a wheeze I use to check for loose rivets under a Pearly Miss..

Thank you will give it a through check in the areas suggested hopefully we can find the cause missing out on some lovely river boating weather