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Fighting Chair plate

  • Thread starter Thread starter Liquid Asset
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Liquid Asset

Liquid Asset

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How are the fighting chair base plates mounted down? Is there a metal plate in the deck that is drilled and tapped? I need to remove mine, but I dont see how there woudl be bolts on the back side since there is a fuel tank there. If there are bolts in the back of the deck, any Idea how to get to them? Thanks.
 
I have heard of backing plates in the fiberglass decking but don't know how far back they go..

My 1980 46C has a very large backing block that fills the opening between the braces under the portion of the deck where the chair is. It looks like two thicknesses of 1" marine plywood that has been sealed (CPES). The plate that the chair pedestal screws into is bolted through both the deck and backing block, with double nuts under the deck for locking purposes. There is evidence of liberal use of 5200 behind the backing block and through-bolts. My set up is easy to get to, so that MAY be why it was done this way.

Never seen one on your model though.

Bernie
 
I just had one made for my boat. I will probably installing it next week. I made a circular plate out of stainless that is flush in size to the pedestal (about 8in center to center of the six bolt holes so the entire plate is about 9inches) The holes in the plate are threaded so I will have it easy when it comes time to take the chair and pedestal off. The mounting plates will remain installed. That same top plate also has a second set of unthreaded holes which are recessed. So when the chair is installed you only see the outer bolts which hold the chair down.

There is then a plate that was made for underneath the deck which is about 12inches in diameter. It will be bolted though with the plate up on top and permanently caulked in with 5200. Everything is fabricated with 316 stainless so there will be no rust.

I was told that the backing plates don't need to be much larger than the diameter of the pedestal base. I hope its enough.

Anyhow, there is nothing fiberglassed into my deck either. Let me know what you find so I can duplicate what has already worked for you.
 
My main concern is how to get to teh back of the chair mounting plate. I dont know how it is bolted down. I will have to get a bigger flashlight and try to look in there tomorow.
 
Mine's bolted through the deck with a backing plate. All the holes are clearance holes, with bolts and nuts. Don't design a sea going part with threaded holes if you can avoid it. Sooner or later the bolts or holes go bad, and you can't repair the mess unless you replace the plate. If the design has through holes with bolts and nuts, in extremis the bolts can be cut in place and new ones installed without losing any parts but the bolts.
I design seagoing hardware for a living, and one of the basic lessons learned is that threaded holes are a no-no. Aluminum plates with threaded holes (with stainless bolts in them!) laminated into hull structures are a design disaster, invented by inexperienced or lazy designers who never actually worked on anything, and have no clue about marine corrosion.
 
Many newer boats have aluminum plates sandwiched into the cockpit sole for mounting of fighting chairs. I believe you should still use a backing plate when through bolting your chair deck plate.

Pat - I am not so sure that Hatteras molded aluminum plates in the cockpit deck back in the 80s. Either way you will have to get in there and see how the deck plate is fastened. If it was done correctly and there was access room I am sure it was through bolted. But since you did not do the work who knows. Is the tank you mentioned a factory tank or could it have been put in after the chair was mounted? I've see some strange stuff including 3M 5200 and screws as a substitute for nuts, bolts & washers.
 
How does all stainless (316) sound? I am not using any aluminum. The only threaded part I wanted to use was to thread the upper plate so that the chair would be easy to remove without removing the mount. The mount is bolted straight through. All stainless plates and stainless bolts. Do you still see a problem? I never did this before so please comment as needed. I figured if a problem occured with the threads later I'd just drill them out and put bolts through. What size do you suggest for a backingplate under the deck for a 130lb class chair?

I never saw signs of a plate glassed into my deck but I will look closer this weekend when I'm in the bilge. Mine Hat is of the 1985 vintage so who knows?
 
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Paul, the tank is definetly factory. It is my rear fuel tank and in the 50C, hatteras put a 768 gallon tank under the rear deck. There is not much clearance between the deck and the tank.

Someone got in there and attached the plate in my boat, and in many others, so I will look tonight when I go to the boat. I just can not figure out how they did it.
 
Jackman said:
How does all stainless (316) sound? I am not using any aluminum. The only threaded part I wanted to use was to thread the upper plate so that the chair would be easy to remove without removing the mount. The mount is bolted straight through. All stainless plates and stainless bolts. Do you still see a problem? I never did this before so please comment as needed. I figured if a problem occured with the threads later I'd just drill them out and put bolts through. What size do you suggest for a backingplate under the deck for a 130lb class chair?

I never saw signs of a plate glassed into my deck but I will look closer this weekend when I'm in the bilge. Mine Hat is of the 1985 vintage so who knows?
Click to expand...
Jack,

Stainless is fine. Just costs more and is a bit heavier. But I think you got a good deal didn't you ;)

You know my feeling on the backing plate is that it simply needs to be the same size or a bit larger than the deck plate. Hopefully the deck plate is a bit larger than the pedestal base. Regarding the treaded holes in the deck plate - that is standard practice. Use at least six (6) bolts to mount the base to the deck plate. The bolts don't have to be long (no need to go through the deck) and probably should be 3/4"-1/2" in diameter. Check with Scopinich, they should be able to tell you.

I doubt if your boat has a plate built into the deck but you never know. Either way I would use your stainless backing plate since you already have it.

My .02......
 
If you are set on using stainless steel for this part type 316 is ok, 316L (low carbon) is better. Keep in mind that "stainless" is only corrosion resistant if there is a steady supply of oxygen to all sides of the part. If oxygen is denied (like where parts are bolted together) ANY stainless wil corrode. This is why you see rust weeping out from under stanchions etc. If you can source it easily, titanium is the best choice, either ti-2 (commercially pure) or ti-5 (6al 4v) will do nicely. As for the size of the backup deck plate, bigger is better. The idea is to spread out the load over a wider area. A fighting chair with a big fish on the line can exert a large bending moment on the deck structure.
 
Jackman: Not that its a big deal, but I'd use a caulk rather than a glue like 5200 because if anyone changes their mind later about that seat base, 5200 does not come apart without taking the deck with it..
 
Yeah...I was thinking about that after I said it...I'll probably use the same thing I will be using to caulk the deck seams around the cockpit.

Okay...The deckplate is due to me in a couple of days according to the machinist. I can still make the bottom one larger. Right now its a diameter of 12" I have the room but is what I have requested of the machinist sufficient?
 
There's no simple answer nas it depends on the stiffness of your deck. All other things being equal, bigger is better than smaller, but you CAN be silly about it.
 
Dave, who is a good source for 316L hardware like bolts, nuts, washers etc. Sometimes I can find this stuff in McMaster-Carr but not always. Whenever I replace exterior bolts I try to use 316 or better yet 316L. 304 does bleed rust and rather easily I find.
 
Allright. I called the machinist and changed the plate that goes under the deck from 12" to 18" 1/4 stainless. That's what I'll have to live with. I don't want to "get carried away" with the size of the plate.

Hopefully everything works out.
 
Jim, as you're in Maryland, I'm at a loss where to send you. Ask at the place where you buy boat supplies, they may be able to steer you to the supplier they use. Have you tried West Marine? They sell Chinese fasteners (not the best material) but if you can't find a local fastener house, give them a try.
The first thing I sould do, however, is look in the yellow pages, or Tomcat, (or on the net) for "industrial bolts"
 
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