Hi All, Well I started into the mass bulkhead, it has never been touched…factory everything. But very surprising what I uncovered in pulling the old one out. The plywood bulkheads had a clearance of 3/8” all the way around the bulkhead from the hull and deck. So the real loading or down pressure was on the 10/32 little bolts around the bottom of the bulkhead. The legs were carpenter glued and attached with small finish nails into the 3/8” plywood bulkhead. Which I puled off by hand. The bulkhead over the top was 1” mahogany epoxied to the plywood bulkhead. The surprise was the whole bulkhead was under no load? Seeings’ how it was built, the factory packed the open joint above the bulkhead against the fiberglass, filling in the gap with epoxy. The surprise here, the epoxy never bonded to the fiberglass. A raceway for wiring was built in and against the back side the bulkhead head. Once again no real loading properties. From my findings, it seem to me the bulkhead could very well be a secondary support to the main fiberglass hull and deck. There was no deflection in the cabin roof, before or after pulling the bulkhead? I am now wondering if the deflection some folks are having at the mass step, is not the interior bulkhead, but a deck failure? Fiberglass will deflect enough that you can see the difference before stress cracks show up…and if the bulkheads are not loading 100%, by the free floating design to say. I truly thought I was going to have to cut the bulkhead out in pieces. I also thought I was going to have to jack up the deck to hold everything true. But nothing like that was needed? Interesting to say the least. Any thoughts? LarrySV-2761Lilly Too Sent from Windows Mail
Mass Bulkhead:
- Thread starter lewills30
- Start date
Hi All, Well I started into the mass bulkhead, it has never been touched…factory everything. But very surprising what I uncovered in pulling the old one out. The plywood bulkheads had a clearance of 3/8” all the way around the bulkhead from the hull and deck. So the real loading or down pressure was on the 10/32 little bolts around the bottom of the bulkhead. The legs were carpenter glued and attached with small finish nails into the 3/8” plywood bulkhead. Which I puled off by hand. The bulkhead over the top was 1” mahogany epoxied to the plywood bulkhead. The surprise was the whole bulkhead was under no load? Seeings’ how it was built, the factory packed the open joint above the bulkhead against the fiberglass, filling in the gap with epoxy. The surprise here, the epoxy never bonded to the fiberglass. A raceway for wiring was built in and against the back side the bulkhead head. Once again no real loading properties. From my findings, it seem to me the bulkhead could very well be a secondary support to the main fiberglass hull and deck. There was no deflection in the cabin roof, before or after pulling the bulkhead? I am now wondering if the deflection some folks are having at the mass step, is not the interior bulkhead, but a deck failure? Fiberglass will deflect enough that you can see the difference before stress cracks show up…and if the bulkheads are not loading 100%, by the free floating design to say. I truly thought I was going to have to cut the bulkhead out in pieces. I also thought I was going to have to jack up the deck to hold everything true. But nothing like that was needed? Interesting to say the least. Any thoughts? LarrySV-2761Lilly Too Sent from Windows Mail
Many boats have the bulkheads taped to the hull and deck all around with fiberglas cloth/roving and resin. The Vega was built differently, not relying on the bulkhead as a primary support for the deck. It is likely that the filler you found was polyester rather than epoxy. Epoxy wasn't very common when the Vega was in production.
My understanding of bulkhead to hull attachment is that it is good practice to leave a gap between the bulkhead and the hull to avoid creating a "hard spot" or point load on the hull at the bulkhead. The gap allows for some flex and transfer of the load through the fiberglass flange or tab which spreads out the load. I've read the some Vega owners have put in larger bolts, which should be fine, but I wouldn't fill in the gap, unless it was some kind of flexible material.My boat has the same thickened fiberglass putty under the mast step that is not bonded to to both the beam and deck. I expect the movement of the deck ( expansion and contraction from heating and cooling) and flexing of the two dissimilar materials would stress the area if there was not some flexibility.The solid wood trim pieces around the bulkhead door opening aren't designed to support the beam load, but are there to help prevent the bulkhead plywood from bowing under load, which is why they don't touch the floor. My first instinct to make things stronger is to make them rigid and stiff, but like the old saying about the big oak and the flexible sapling in the wind storm, sometimes things that can bend or move a bit do not break. Tim
I guess I should actually answer your questions.On my boat, the deflection at the mast step looked like it was compression of the encapsulated block under the mast, not a mast bulkhead beam deflection. It was only about a 1/4" in a small area.The bulkhead probably doesn't have lots of load on it, unless the rigging is tight or the mast loaded up otherwise. With the mast off, there probably is not much load.I would guess that the bulk head also prevent the hull from creeping and deforming over time under the load of the rigging tension, as well as supporting the mast. It, and the furniture, also add stiffness to the hull to keep it from flexing too much.You probably know that the deck gets a lot of its strength by its cored design.Whether or not you have to jack up the deck to restore it's original shape probably depends on how tight the rig was. An overly tight rig would have caused more deformation. The previous owner of my boat kept the rig adequately loose, and I don't see any significant deflection in the deck or the mast beam. Tim
Larry,There's an excellent article in the Yahoo Vega Files called VODCA_Mast_Beam.pdfIt explains the way the boat was designed for the bulkhead and mast beam to transfer loads to the hull. Beefing up the beam and the doorway stiffeners is great, but transferring loads to places that were not intended to carry them could cause problems. On a lot of Vegas those little bolts that hold the bulkhead to the fiberglass flange have loosened over time and the holes in the bulkhead plywood have become oval from the hull flexing and working.My suggestion is to replace the small bolts with 1/4" or even 5/16"
bolts (with lock nuts) to better attach the bulkhead to the
flange, using larger washers against the plywood to distribute the load. This will take the "slop" out of that area when the boat is working hard, and allow the boat to flex where it was designed t
n my Vega there wasn't a bolt in the whole boat that didn't need tightening!Peter.VODCA_Mast_Beam.pdf
bolts (with lock nuts) to better attach the bulkhead to the
flange, using larger washers against the plywood to distribute the load. This will take the "slop" out of that area when the boat is working hard, and allow the boat to flex where it was designed t
n my Vega there wasn't a bolt in the whole boat that didn't need tightening!Peter.VODCA_Mast_Beam.pdf