I have a 1983 Niagara 31 with a
keel stepped
mast,
single spreader rig with navtec rod
rigging and proprietary navtec chain plates. All
rigging and chain plates soundly bedded. The
boat is sitting is nicely on its
cradle with
mast off. When looking at the main bulkhead where the bottom meets the structural molded
fiberglass pan the gap is tight and square. However when the
boat is launched, mast stepped and fully rigged a small gap starts at the bottom about 1/8" then when I fine tune the rig after a few sail days the gap will increase to about 1/2". Everything is just fine the boat
sails well no strange creaking or noises coming from the rig or around the bulkhead, even when sailing in 20n winds and rough waves. The Niagara's have 2
deck ties that connect the top of the bulkhead (inside the boat) to the
cabin top through to the outside bolted securely. The bulkhead at the top where it meets the
cabin top never moves or shows any kind of gap at all. At my marina there are 5 Niagara 31s and 3 of them show no signs of movement the 4th boat shows a small gap about 1/8"max and of course mine at 1/2"max. I have talked to other people about this and they say all
boats flex. The mast step, mast stringer, and
keel sump are solid. Noticed this about 4 years ago and assumed that the
hull was sagging under the rig tension but now thinking perhaps the cabin top is rising?. I have read on other posts that some keel stepped mast
boats have tie rods that go from the mast collar down to the mast step to counter rig loads however this boat wasn't designed that way, the Niagara 31 is a Frers design. When the boat is hauled there are no external signs of cracking or crazing anywhere near the front of the keel where the mast step is located. Any thoughts on how to remedy this?. Attached is a picture of the bottom of the bulkhead when fully rigged and a summer of sailing.