Backing plate material

[Timm R Oday25]

While installing new hoses ,I noticed the original plywood backing for the through hull was rotted .
I cut out a replacement from plywood and was about to coat it in epoxy, when I noticed I had uhmw plastic the same thickness .
I'm wondering if using bed it tape and the UHMW plastic might be a better choice than expoxy soaked plywood .
The plywood lasted 40 plus years.. Thanks

 

[PaulK]

The plywood is already cut out, but the plastic won't need a waterproof coating and may end up being less work to install. Either can obviously handle the job.

 

[Ralph Johnstone]

A lousy 40 years ? Talk about planned obsolescence. Use epoxy coated plywood and it'll last 140 years. Once the wood is cut to size, 24 hrs and you're finished and the with the epoxy and ready to mount.

Don't use bed it tape to adhese to the UHMW as ther tape has 0.00 mechanical strength. It relies on nuts and bolts to seal. And nothing adheres to UHMW.

As far supporting the plywood to the hull, use more epoxy and glue them anywhere on the hull. No screws required and no
worry of ...............

​

........... you know !

 

[SteveHughessails]

I am a fan of UHMW myself. I don't think I will have to worry about the backing plate, ever.

 

[thinwater]

I've seen fully sealed plywood rot into mulch in 20 years and much less. One crack in the coating, the ply gets wet, and there is no difference. Dry, yes, any amount of time, but that can also be true uncoated. The epoxy helps, but it is not 100% sure.

UHMWPE can crack under sustained load. I've seen it many times. It also does not spread the load the same way because it slowly warps to fit the curve, or in the case of high load, looses pressure on the edges. And nothing bonds for long.

The only permanent solution for through hulls, that I know, is fiberglass. Shape it to the curve of the hull and round the corners (any material), taper a little, and bond it, and it becomes part of the hull.

 

[Ralph Johnstone]

While installing new hoses ,I noticed the original plywood backing for the through hull was rotted .

My bad on that one. I was under the impression that he was looking for hangers for the hose. So much for the speed reading course for the dyslexic.

Ignore post #3.

 

[Timm R Oday25]

The thru hull inquestion is a 3/4" brass unit that allows draining of the galley sink and the ice box.
Only a nut holds the backing plate against the hull .

 

[dLj]

The thru hull inquestion is a 3/4" brass unit that allows draining of the galley sink and the ice box.
Only a nut holds the backing plate againgst the hull .

It's a thru-hull. I certainly hope it's not brass. If it is, you should change it to bronze. Clearly your current installation is sub-par. It doesn't matter what the thru-hull is used for - it's a thru-hull. Thru-hulls should be installed correctly. Failure of a thru-hull can sink your boat.

dj

 

[SteveHughessails]

My bad too. I read backing plate. Immediately thought winches, cleats, blocks etc.

 

[Timm R Oday25]

I'm most likely mistaken as it's more possibly bronze

 

[Ralph Johnstone]

My bad too. I read backing plate. Immediately thought winches, cleats, blocks etc.

Proof positive that great minds think alike !

 

[mermike]

G10 fiberglass plate is the gold standard for through hull backing plates. Costs about as much, too. Here's a very good article:

Seacock Backing Plates - Marine How To

Start by Drilling a Hole Many readers have asked me how to install stronger, flanged seacocks without also drilling extra holes in your hull for the bolts that hold the flange. It can be done, as you will see below. Though this

marinehowto.com

 

[thinwater]

G10 fiberglass plate is the gold standard for through hull backing plates. Costs about as much, too. Here's a very good article:

Seacock Backing Plates - Marine How To

Start by Drilling a Hole Many readers have asked me how to install stronger, flanged seacocks without also drilling extra holes in your hull for the bolts that hold the flange. It can be done, as you will see below. Though this

marinehowto.com

Yup, though a more complex method.

What you DO want to do is make sure that the inside surface of the plate is EXACTLY parallel to the outside, or it the nut won't set well. This can be a challenge where the thickness of the hull varies quickly, such as close to the keel.

 

[mermike]

Anything worth doing is worth overdoing.

Installing through-hulls in a Yamaha 33.

Greetings all. I just spent a lovely month in Port Townsend on the hard, replacing 5 of the 8 though-hulls on my Y-33, along with bottom paint and a topside polish, a new bilge pump and new cockpit drain hoses. Here’s the before picture. Note the lack of backing plates. The hull is thickened...

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