Replacing Cored Chainplate (or Chain Plate) Bulkhead/knee

[mdoyle]

Howdy howdy to all. 'New member here. I have a '79 Hunter 37' Cherubini Cutter & sail out of Providence, RI.

It is necessary to fully replace at least one of the chain plate bulkheads/knees. These have a heavy-glass exterior with a plywood core (or a ply bulkhead with heavy heavy glass/web coating). I discovered at least one of these cores rotted, and it's time for a complete rebuild. I've done a fair amount of glass work - above and below the waterline, but admittedly this will be the most challenging glass project for me to date.

BTW...there are at least a few whispers online that this core may be able to be replaced w/o cutting it out - but I'm dubious that this would be the A-1 job that I plan to do. Disagreements and suggestions to this are welcome!

At any rate, I thought that this would be 1. a great place to get steerage advice and 2. to create a record for anyone who may follow. I have seen pics of ply bulkhead replacements, but I can't seem to find post(s) of exactly what I am contemplating. So, here goes...be gentle.

My preliminary plan is to

1. Loosen and remove the shroud to which the chainplate in play is attached and secure it to my robust toe-rail.
2. Secure main halyard to further ensure rig integrity during project.
3. Remove any/all joinery surrounding the bulkhead/knee to be replaced.
4. Remove chain plate and backing plate from bulkhead
5. Tape off deck to prevent leaks during repair

Then the real work...

6. Cut the entire bulkhead out to the hull. (?Maybe leave a bit of the glass attached to hull, creating a "slot" for new ply?)
7. Grind/sand as necessary to expose the hull's bare glass
8. Out of marine-grade ply, cut the required replacement bulkhead.
9. Glass the edges of the plywood cutout.
10. Heavily glass & web & glass, etc the plywood in place.
11. Mark & drill bolt holes in bulkhead
12. Install chain plate
13. Rebed deck "beauty plate" over chain plate fitting using a Polysulfide sealant.
14. Add a step to post so that my post does not have an unlucky number of steps.

This is a plan in progress, but I respect others' advice who have been there before. I am grateful for any additions/suggestions/etc.

Cheers,
Mike

 

[Ed Schenck]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

Mike, you might find that project in one of the "Owners Mods" like this one: http://hunter.sailboatowners.com/in...&Itemid=267&cat_id=38&page=model&mn=37-cutter . Did you do the Search on Mods? Could be under any model for any boat.

Which chainplate is it exactly? This might help for someone who has actually done a 37-cutter fix. I am fortunate that my bulkheads are all solid.

 

[Don12364]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

Is this a one piece bulkhead right across the boat and will you be able to get a suitably large enough single piece of plywood down the companionway?
If there is a door cutout then this may make it possible to slot it along the coachroof before rotating it down and into the hull.

Good luck with the job.

 

[Bill1565]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

1. somebody has already messed with your bulkheads. They did not come from the factory swathed in fiberglass.

2. while you are tearing up the boat, check the deck for rotted core. If water leaked into the boat, good bet it's in the deck also.

 

[mitiempo]

I understood the original poster to say they were knees that the chainplates were bolted to, not full bulkheads. If that is true they probably were fiberglassed as in many boats.

 

[Ross]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

I don't like deck penetrations if they can be avoided. I moved my chainplates outboard (only about a 6 inch move ) just to avoid going through the deck. The reason they started to penetrate the deck was entirely for sheeting angle. When you consider the stress applied to the chainplates you quickly realize that any uncoupling between deck and bulkhead will create a leak.Better that you bring a plate from bulkhead to deck and a plate from shroud to deck and through bolt them to ensure that everything moves as a single structure.

 

[Ed Schenck]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

I scavenged this picture from "Owners Mods". You can see the chainplate on what could be a knee, I think the upper. I always thought it was on the bulkhead but the owner has already removed the main bulkhead. Then aft and under the cabinet you see what actually looks like a "knee". I think that is where the aft lower chainplate is bolted, up inside the cabinet. Then forward of the sink is where the forward lower would be attached. Again that is a bulkhead on an H37C.

Through the deck chainplates are a PITA to be sure. But after thirty-two years mine are still solid and do not leak. I have only been taking care of them since 1999.

 

[Snotter]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

Many of us here are always interested in following these kinds of projects. Please keep us posted and take many pictures.

 

[mdoyle]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

Monday greetings all,

Thanks so much for everyone putting in their $.02. I am very lucky to have quick access to such brain power and experience.

I have now looked at all the mods forum(s) that may be applicable, and I have yet to find any serious flaws in my methodology from my first post. MiTiempo is correct, I will be replacing what are technically knees, but one area it is kind of a knee/bulkhead hybrid.

I guess I want to focus on the collective opinion on whether I have left out any serious steps and/or methods?

If not, then it's off to the races (the slow, disciplined, measure-twice-cut-once races, that is)

Cheers,
Mike

 

[FourPoints]

13. Rebed deck "beauty plate" over chain plate fitting using a Polysulfide sealant.

I think you may want to use Butyl tape instead of a polysulfide... it will remain permenantly flexable, has much better elongation characteristics than a polysulfide sealant (something like 1000% vs 400%, and will re-adhere / reseal to it's self after it is 'unstretched', even if it is 20-30 years later...

do some searching on this forum, there are lots of posts about it (as well as where to buy it), but here is a great start...

http://forums.sbo.sailboatowners.com/showthread.php?t=117172

 

[mdoyle]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

Thanks FourPoints. I looked at your great research, etc., and I will go w/ Butyl Tape. Why this inexpensive (albeit more labor-intensive) option is not more common is beyond me. BTW, I put a temporary seal under every single beauty plate, and I think it cost me all of $2.50. So worth it.

Cheers,
Mike

 

[Ed Schenck]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

So where are you in the project Mike? Is it just one chainplate and which one(s)? Let us know how the butyl tape works out. I have always used clear silicone and have had no leaks.

 

[mdoyle]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

Quick status and some advice that I've picked up.

The worst knees by far are the two forwardmost knees, port and starboard. As we know, these are also the knees that are connected to the fore bulkhead that runs the entire width of the boat's interior. An entire removal of the bulkhead looked unavoidable.

But I dug deeper, and it appears that I can cut out the knee, and an adequate portion of the bulkhead without removing the entire bulkhead. There is enough access for my grinder. This may not be an A+ job, but I can not afford an entirely new bulkhead right now. I will graft in the exterior ply that is sandwiched in the knee, and that will have to do for now.

After discussing things will several members here, I've also decided to cut out the knee with my angle grinder with a disk that cuts metal. I realize other methods may be better, but I know folks that have done the same and I'm going to try this method first.

Oh, btw I have taken pictures esp of the port-foreward knee, but for some reason (too large?) I can't post them here. Hmph. Let's just say they look very very ugly.

Thanks again to all.
Mike

 

[sandpiper10471]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

Mike, you are absolutely on the right track for repair. I suggest using a 4" diamond blade on the angle grinder for cutting out. Less dust, faster result and easier to control. One of the problems with the original construction is the amount of space between the chainplate and the deck. Far too much caulk required. I would agree that likely the deck coring is gone in the chainplate areas and the compromised knees followed. Rebedding against wet material never works. Once the knees and deck coring have been done, cut only just enough to get the chainplate through the deck. Seal the exposed core. Butyl caulking is recommeneded. The other tool which will be of great use for cutting in close and confined areas is the Fein Multitool. Substitutes are a waste of money except perhaps for the Bosch cordless multitool.
These keel stepped masts are extremely strong and will stand in the boat unsupported. A halliard to the toerail will be just fine for keeping the stick up.

 

[RichH]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

mdoyle - it is of vital importance that any section of 'cored' bulkhead that supports or attaches to a chainplate be SOLID fiberglass where the chainplate bolting goes through the bulkhead. Core material is LOUSEY in supporting 'shear' loads and will easily deform/move under such 'shear loading' as would be caused by such bolting.
Plus if unsupported chainplates/bolts that are properly 'torqued' will compress and deform any 'core' that is between the head of the bolting and the nuts/washers.

Rx: make the area of the bulkhead 'beefier' by putting a solid/filled fiberglass in that section. Otherwise if you must 'cut' open be sure to get long 12:1 tapers on the edges of any cuts you make into the cored, etc. section to affect good bonding of epoxy to any remaining 'old' section.

 

[mdoyle]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

Good morning all,

RichH: Yes, I planned on glassing in the ply core real thick using serious webbing/rove with multiple layers. I want to overdo the structural integrity of the rig, so I'm going to invest in some West System stock before I start buying the materials.

I'm not sure what you meant by a 12:1 taper. I am going to lay up the webbing small-width first with increasing width webbing layer after layer until I have at least a thick 6" overlap on each the hull and the knee. Then I will continue glassing like crazy over the knee to seal in the core. Is this something like you meant?

I have a couple of before pictures, but this system only inserts photos from a link to another site? 'Doesn't make sense, but when I try and insert a photo all I get is a "Please enter the URL for your image" with a partial http: pointer. Confusing. Too bad because they are wonderfully ugly photos.

Cheers,
Mike

 

[Maine Sail]

Then I will continue glassing like crazy over the knee to seal in the core. Is this something like you meant?


Cheers,
Mike

Mike,

I think what Rich meant was to makes the knees solid fiberglass so there is no core to ever rot out again. Many builders do or did this and those boats never have the issues you're addressing.

Here's how Morris does it on their 29 footer. That knee goes all the way from the deck to below the waterline and is over 1/2" of solid fiberglass..

CS Yachts used a similar approach but used hollow solid glass U shaped knees tabbed to the hull with 3/8" thick SS embedded into the knee to bolt the chain plate to. These knees are hollow, no wood to rot, and capped by the hulls inward flange..

 

[mdoyle]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

Maine Sail,

Those are great suggestions. If I did something like that would have to go with fabricating a hefty 1/2-1" thick knee out of glass as in your first example. Any suggestions how I would fabricate a large-ish knee out of glass only? I would guess that I would have to create a wooden form, coat it with wax, and pour/layer glass into that to create the initial knee shape before tabbing it onto the hull?

Cheers,
Mike

P.S. I discovered how to attach photos, above...thanks to Ed Schenck for a post on 9/1/2009!

 

[Ed Schenck]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

1) Not sure why there is discussion of "core". Our chainplates are bolted to solid wood. At least mine are.

2) Wondering about your picture upload problem. I post all of my pictures from my hard drive or from the camera memory. Click on "Upload..." and a new box opens. Click on "Browse" under "Upload from Computer". Find photo, select it, get more photos, when done with selections then "Upload".

Or maybe you are wanting to put the large pictures in line like Maine Sail's above. To use <img> code to imbed then yes, the image has to come from an address.

 

[mdoyle]

Re: Replacing Cored Chainplate (or Chain Plate) Bulkhead/kne

Ed,

My chain plates (at least the for'ward ones) are fiberglass sandwiches around ply. The ply actually the forward bulkhead, but the load and chain plates are bolted to the portion that is heavy glass with ply "core". I was able to attach a couple of thumbnails, above to show what the plate looks like without the ply "core". U.G.L.Y. That space in between the chain plate and the backing plate should be nice dry ply.

All righty, then. I will be making the first cut probably in the next 10-20days. I hope the temperature stays above 50 so I can finish at least one knee this fall.

Cheers,
Mike