hull support when working on bulkheads?

Hi there, am working on a 34ft nelson( motor boat) thats in tidal waters. Am replacing all bulkheads including longitudinal ones. Are they best replaced when the tide is in? When tide is out boat sits on its sea legs putting pressure on the hull, so am concerned about the hulls shape difference when tide is in, or out. Whats the best `state` to do this in? Even if it was out of water, then it would not be in its natural shape i guess. Would guess when the tide is in is best? When tide out there seems to be pressure on hull from outside(sealegs) when tide in the hull is not pushed in so much as when out. Would be grateful of any advice. Presume is best to do when hull is at its ` widest position` so any pressure from outside will hold it together, rather than pull apart If glassed in when hull is under more pressure than its usual sea going shape? Thanks

 

Best to do on land, but if that's not possible, you can use a lot of sticks (boards)----- as if making a pattern------so that the sticks make up a temporary mold ahead or abaft of the bulkhead to be replaced. The webwork of sticks can be drywall screwed together. Leave a crawl-through area so you can access both sides (or get out!). Bond the new bulkhead with epoxy where you can and tab in completely once the temp mold is removed.
Use heavier boards or planks to build the temp mold as you see fit to support shapes you feel would change most when the old bulkheads are removed.
In other words, get a hold of a big pile of various lengths and widths/thicknesses of boards and planks, and a lot of 2"-3" drywall screws.
Drag them into the cockpit along with a jigsaw and a power cord.

Alan

 

thanks, have included a picture for you to see, have replaced the starboard side already, doing port side now. Have replaced smaller port sections and had to remove port longitudinal bulkhead at once, thus leaving no support at once. Have not replaced port longitudinal but not yet glassed it to smaller ones. When tide in there is a gap of about 7mm between them, when tide out there is no gap which is ideal but due to sea leg i think putting pressure on hull, if i glass them in like this, they might pull apart when the boat floats. Guess better to do when tide in? Thanks