Quarterberth "Floating Bulkhead"

When removing the plywood battery tray to reconfigure for my 2 X lithium Group 31 house bank, I was surprised to notice - for the first time - a poor though fairly inconsequential repair job from Windstar's distant past.

   

As constructed - The  bulkhead in this area was trimmed shy of the hull and the 1" or so gap was covered by fiberglass tabbing that was less than 1/8" thick.  Disappointing really, especially as this is in the area where the aft cradle pad supports the boat when on the hard.   This is not unique to Windstar, and fellow 33-2 owner Bruno L had coined this a "floating bulkhead".  this port-side expanse of hull is not supported structurally, as compared to the starboard side, where the galley bulkhead serves this purpose.  My suspicion is the designer did not intend this bulkhead to float.

The thin web of glass is easily crushed if the cradle pad bears any of the boat's weight.  (as it does)  You can see the hull deflection where the pad rests.   

Repair was complicated by the fact that I do not have locating blocks on the cradle so the yard has some latitude as to where the boat sits.   This season the boat is too far aft, so the pad could not be retracted far enough to clear the hull.  As a result I had to raise and support the stern to allow the hull to return to its natural shape.   The correct positioning will be indicated with blocks for next haul out.   

Plan was:

• Remove crushed broken tabbing, (original and repair) clean and prep area 
• Cut hole for access to back (forward side of bulkhead)
• Laminated oak rib to be sprung and wedged in place
• Fill any gaps with glass-loaded putty
• Create epoxy fillet along length of joint
• Laminate heavy tabbing in place  

Prepping the patient.    You can see the gap between the bulkhead and hull. I cut the damaged glass back to the hull and to the bulkhead edge, ground the surfaces then cleaned with acetone.

 How best to fill the  gap between hull and bulkhead?     I decided go old school and to rip some red oak into strips, coat with epoxy and tape into a beam.  While it was still wet I coated the hull below the bulkhead with epoxy putty then I flexed  the laminations   into place, wedging them  it so that the stack pressed against the hull, bedding itself in the putty, and forming a laminated rib.  

Here are the oak strips ready to laminate 

 

 

Each oak strip was coated with unfilled epoxy, then the strips were assembled into a stack and taped with masking tape at each end to hold the bundle together.  The slippery stack was flexed and slid onto the gap, and further wedged with another few shorter strips,  so then new rib pressed against the hull    Any gaps were filled with the thick glass-filled putty, and smoothed along the edges,  and finally the joint was faired with a big fillet of putty over its length to make a fair radius upon which to laminate the tabbing.

With that still wet, I laid up 5 patches of biaxial stitch mat, (cut in advance), each around  12x9”, double in thickness along The middle, and laid them over the joint, tabbing the bulkhead to the hull.  There is a great deal of overlap, with a minimum of  4 thicknesses of material forming the new tabbing.    Strong stuff! For the heck of it I laid in several lengths of high modus carbon fibre tape I happen to have kicking around (as one does...) 

 Because all the work was done solo, and wet on wet, it was too busy and messy there to stop and photograph each stage, but here's the completed repair, prepped for the battery tray then paint.   

            It ain’t gonna crush now. 

 

Mid 1980s C&C keel issues

See below for photos of mid-80s C&C keel deterioration.  This appears to occur where winters are freezing cold and boats are stored on land.   Seems as though water migrates down the keelbolt into the lead casting and freezes each winter, incrementally enlarging any voids or cavities each seasonal cycle.  These photos were shot in a short stroll around one marina yard, near Toronto.

Repair of keel/hull joint, closing unneeded thru hulls, and rudder

Here are some modest sized examples of glass repair- closing two thru hulls, and repairing some small damage (and voids) at the keel/hull joint.

Finishing the job - installing flat support for keelbolts and mast step.

Amazingly the weather cooperated and this job is done!
Here's how the parts created in the previous post were installed.    They were bedded in very thick, glass-loaded epoxy, making a massive (relatively) dead-flat deck for the mast step and foundation to take the compression loads from the keel bolts.  

And this chapter will close with a "before" image!

reinforcing the mast step - Carbon Fibre and Epoxy.

After some discussion with the folks at Composites Canada, I decided to use 9oz unidirectional high modulus carbon fibre and epoxy to stiffen the mast step area.    This stuff is immensely strong and stiff, and is pretty easy to work with.  I used 10 layers in each direction, laid at 90 degrees as you can see.  Each piece was cut to specific and different lengths and widths so that the ends and edges would taper down to a nearly fair landing on the existing glasswork.  It worked out pretty well, and built up to approximately 1/2 thick under the mast step, (20 layers)  just shy of the original thickness of the plywood, putty and liner.   This took 6yd of 12"wide material, with very little scrap.

Partway there

 

Filling the void - too cold or too hot?

After consultation with others I elected tous polyester laminating resin, (AOC Altek HDA-596)   with colloidal silica and long strand chopped glass.  I was able to mix 1 gal at a time, and learned to time the pour so that each gallon could use the considerable heat from the previous gallon's cure to hasten its own cure.  I mixed 1% catalyst to resin.     I mixed the resin with 1% catalyst and was very lucky to have  warm weather into December.The entire job took 15 US gallons of resin and about 6kg of chopped glass (plus a bunch of scrap fabric and other glass I had kicking around.  This weights approximately 150lb, the same as what I removed (slightly more I would guess...) but is much more solid, and should absorb less water.  

Yes.  Messy

Resin heavily loaded with glass.

My boatbuilder Dad  and others suggested I simply use concrete to fill this space, and I could not bring myself to do it for some reason, the additional 130-180 lbs being part if it, vague concerns about adhesion being another.  In the end, I think it may be an excellent choice, possibly the best, and would certainly be less expensive.

  Trial fitting 

Ground to slightly undersized, with beveled edges, and fitted flush at the same height as built.

Epoxied in place with a dime for luck - Canadian of course, the Bluenose visible.  

the worst is over!

Putting it back together. Compresson posts.

After getting the keel box excavated I had to figure out how to make this repair permanent.  Which material to fill with?  How to manage the compression loads?  There have been several approaches.  Some, like Doug A have made stainless posts sleeved over the keel bolts, some have installed posts adjacent to the keel bolts, and perhaps most elegant is Bristol Marine's approach where they do not excavate the keel stub anymoe, but have developed a tool which bores a hole into the keel stub co-axial with the keel bolt, and extracts the filler.   they then install a built up fibreglass post over the keel bolt in that hole.  By the way, Nick at Bristol was also very helpful in this.  It was clear this  would be a DIY job, and he offered a great deal of encouragement and advice.  (and offered me a job...lol)  Thanks Nick!

So, I made a couple of very sturdy compression posts, laid up over 1.25" ABS pipe.

Work in process.

Posts were cut at the correct angle and had sheet fibreglass feet attached with massive poxy fillets, and these were then set into epoxy on the bottom of the keel box.   More glass filled epoxy was used to secure the posts in place.  Killer stuff.  
Ready for filling....

The excavation begins.

My home away from home.  That vac was totally inadequate, and I needed my huge shop vac.  

The patient prepped - I elected to cut out the side of the settee for access.  I will replace the panel, but leave the oval slot you can see for ventilation.  

Here is a "core sample" of the top of the keel stub, in the area where the bolts bear.   Glass is 3/8 thick.   A bit thicker under the forward keel bolt.

You can see the top of the keel stub cut away, and the first few holes drilled into the putty with a spade bit.  The stub is 24" deep, around 7" wide and around 24" long.  I ended up drilling holes about 3" deep, then using a 4-foot crowbar bashed into the hole to lever and break away the putty.   Repeat for two full weekends...

A few inches down and a long way to go.  See the black. moldy fault lines, and the piles of rubble accumulating on the deck.  You can almost see the starboard side of the keel box, which had separated from the putty block.  This is where the water would accumulate, though there were cracks throughout, and the putty itself was damp throughout even the pristine solid parts.  Talc-filled I think.  Ugly, but I don't think it was deteriorating badly - certainly not like I've heard from others.  

Are we there yet?

Almost done.  the bottom was in surprisingly good shape, and the putty was difficult to remove.

How bad is the problem? How major the repair?

So, you can imagine what happens.  


A 1" bolt torqued to 300 ft/lbs exerts a tremendous amount of clamping force.   On the first bolt, the mast step spreads this load somewhat but on the second keel bolt, standard fender washes are used to distribute this load.  See below.

http://www.engineersedge.com/calculators/torque_calc.htm


When torqued, the  keel bolts exert 18000lbs compression on the fibreglass top of the keel stub and if that deflects, on the putty beneath.  The mast and rig exerts its own additional load, as do hard groundings.   If the putty has shrunk, is crushed, damaged or deteriorated, it compresses to some extent.  You run aground, things get jarred, maybe fracture a bit.  Torque is lost, things move, the mast step sinks a little, the smile opens, more water enters, etc....  You re-torque, things compress....   Etc.


When it hits this stage, the typical repair is major:

• Cutting out any interior parts which hinder access
• opening the keel stub, 
• removing all of the putty (hardened polyester resin, aka "bog".  basically cheap marine bondo), 
• ideally adding some structure to take the compression lead of the bolts, 
• refilling the cavity with... something, 
• repairing the glass that was cut for access.
• reestablishing some sort of structural integrity as this is a major stress-bearing region of the boat.  
• Replacing the interior.

A pro repair of this type would certainly exceed $10,000.  (Bristol Marine has developed a slick repair that involves drilling a hole coaxial with the keel bolts, and replacing the putty removed with a fiberglass compression post.   this minimizes much of the work described above.  I have no idea what they charge for this.)  

On the other hand....a boat that had not yet exhibited any signs of failure or significant deterioration could be perfectly fine.  Keep the water out, improve the load bearing surfaces to better distribute the compression, and it would likely be fine for another 30 years.

Windstar had no significant signs of structural degradation, although the fiberglass supporting the second keelbolt had sunk a bit.   After a lot of thought and discussion with others, I elected to simply do a thorough job of reinforcing the mast step area, and anywhere else subjected to the keel bolt torque.  I feel that the factory could have done better than simply using washers, and I think most builders skimp in this.

So, I was all set to move ahead with this strategy, and bounced it off Doug A who at first agreed, then in a later email he echoed my own lingering doubts:

I would hate to have you go through the same experience. [he had invested considerable time in a reinforcement strategy, only to have to remove it and fully excavate the keel stub]  Especially after doing glass work under the mast step making a much more difficult job if you decide to do some digging. Think about it. I know that we have different boats, but a good friend of mine at the club has a 84 C&C 33 who warned me about the problem. He had excavated his cavity several years prior for the same reason. Which is why I knew what to expect.

Again, I can't thank Doug enough for the time he took to share the details of his own excellent repair, and as a sounding board for my own.

I thought also about eventually having to sell the boat and I did not want to be in a position of having to be less than transparent about what may have been a latent issue.  Life's too short for that.