I've been watching a slight separation at the base of the portside bulkhead toward the center of the boat. An approx 1/2 in opening can be seen from inside the head where the fiberglass meets wood at the base. Exploring deeper I removed the naugahide cover from the mast and found that there was a slight tilt to port applying pressure to the top of the bulkhead and apparently forcing it upward. Anyone experience this or a similar concern? What's the general prognosis?
Thanks for your feedback in advance.
Mast pressure against portside bulkhead
Mon, 08/04/2014 - 11:43
#1
Mast pressure against portside bulkhead
Do you have an interior turnbuckle connecting the mast to the cabin roof? Per our surveyor, the turnbuckle should be lightly tensioned to add structural rigidity and prevent the cabin roof from lifting upwards. If this turnbuckle (and there is a name for it) is loose or not in place, and the bulkhead is more securely fastened to the cabin roof than floorpan, the bulkhead could pull away from the floor.
Paul & Wendy Keyser
"First Light"
Rye NH
2005 C36 MKII #2257
Wing, M35B
Hey Fat Cat,
I don't know exactly what boat you have (hint, hint, please set your .sig with some vitals, thx), but here's the deal on my 1984 C36 MkI:
The port side bulkhead is out of place a few degrees arc to the clockwise if looking at the salon (aft) side. So the misplacement is most visible at the top edge over by where the inside ceiling takes a big turn downwards. The inboard edge of the bulkhead had also commensurately rotated towards the mast and was almost touching it until I recently rewedged the mast.
The turnbuckle mentioned in the previous post has the job of holding the deck down, which in turn holds the bulkheads down. As you tighten the turnbuckle it pulls the deck down towards the eye on the mast to which it is fastened (this cannot move up because the mast is held down by all the shrouds and stays, and so the deck tightens down).
Although the turnbuckle was tight when I bought my boat, the surveyor said he thought someone had previously sailed the boat with the turnbuckle insufficiently tightened, which had allowed the bulkhead to shift. In fact, he said, the whole hull shape can become deformed slightly if this critical rigging step is skipped or missed and the boat is sailed under even moderate load, so the fix he recommends is:
With the boat on the hard and her weight resting on the keel, loosen everything and let the boat slump back into shape. Let the deck fall, let the sides of the hull and the bulkheads move outwards. Then _first_ clamp down the deck with the mast turnbuckle, then tighten and tune everything as normal.
I have not yet tried this technique to shift my bulkhead back into place since I haven't had occasion to haul the boat, but I do know and recommend the surveyor who told me to do it.
Hope this helps.
- nick
Nick Tonkin
*Former* Website Administrator, C36/375IA
*Former* owner, C36 tr/fk #255, Santa Barbara, CA
One additional comment on the cabin roof turnbuckle. I noted on many 36's that we looked at prior to purchasing ours, our surveyor pointed out that he U bolt that ties the turnbuckle to the cabin roof utilizes inadequately sized washers. On some, we noticed the washers could not support the turnbuckle load (maybe the owners over torqued?) without depressing into the cabin roof and cracking the surrounding gelcoat. One 36 had cabin roof damage -water entered through the stress cracks and destroyed the structural integrity of the roof. We replaced the washers with a stainless plate on our 36.
Paul & Wendy Keyser
"First Light"
Rye NH
2005 C36 MKII #2257
Wing, M35B
My boat is on the hard at the moment. I have this problem ie there is a gap underneath the aft head bulkhead between the bulkhead and the fibreglass floor. The gap increases to about 3/8 inch at the head door end. There is no mast to deck underside turnbuckle on my boat at all, which presumably is the cause for this problem. I will be pulling the mast in 3 months time to redo the standing rigging. The boat will be in the water by that time. My thought was that when the mast is out the deck will settle down and the bulkhead should return to full contact with the floor. I will be checking/tightening all bulkhead bolts(perhaps adding some new ones) and I will fit a new turnbuckle to the mast when it is refitted in the boat and hopefully take care of this problem. Has anyone out there already done this and been through this process or is there a better approach than I have outlined above?
Duncan McNeill
1984 Catalina 36 #178
standard rig fin keel M25
Channel Islands
As I mentioned, my surveyor said the proper way to do what you are describing is on the hard with the boat's weight resting on the keel.
Nick Tonkin
*Former* Website Administrator, C36/375IA
*Former* owner, C36 tr/fk #255, Santa Barbara, CA
If the mast is putting so much side pressure against the partner so that it distorts the cabin top or if the cabin top is lifting (not enough downward force via the tie rod -that short turnbuckle) or if the cabin top is depressing (too much downward force via the tie rod), then it should be remediated. All highly loaded forces have some sort of counter. Horizontal coach roof loads are countered by a combination of the sandwich construction and the lower shrouds. Vertical coach roof loads are countered by the the proper adjustment and health of the tie rod and deck attach point. I passed on purchasing a 36 that had the tie rod attach point pulling down into the cabin because moisture had entered the coach roof and softened the sandwich.
I've always done my static rig adjustment with the boat in the water, running and standing slacked, and water tanks filled to simulate provisions, and left like that for a few days so the hull can establish its shape to its natural environment, i.e., supported by water. Any tie rod adjustment (lower chain plates AND mast-to-deck) are best tightened to the correct specifications at that point, before any running or standing rigging is tightened.
Nick Caballero
Retired C36/375IA Mk II Technical Editor