|Backing Plates

[Don Crowther]

Mainsail

I've been planing on replacing my thru-hulls this spring. I was wondering if I could use some other material for backing plates? I've read your how to articles and find them very helpful. I have access to 3/8" alunimun plate could I use that for a backing plate? How about 1/2" acylic ? I don't have the materials on hand to make the fiberglass plates.
Thanks

 

[Warren Milberg]

I really like marine plywood impregnated with epoxy resin. Cheap, easy to shape, and easy to install.

 

[Ralph Johnstone]

Another Material .......................

for through-hull backing plates is 3/8" Starboard. Easy to cut out the plate with a hole saw and then drill the centre with a spade bit.

I'd stay away from the aluminum plate for fear of getting into a galvanic couple with the through-hull material.

 

[Capt Fernando Martinez]

That is correct about the corrosion with dissimilar metals, stay away from that solution. Also the acrylic is very brittle an cracks as it takes the shape of the hull. The marine plywood or the starboard solution is good suggestion. Use 5200 for sealant and you will be fine.

 

[Bill1565]

I mis measured, used 1/4" starboard and the seacock bottomed out. hired a diver to hold a tool in the thru hull, backed the sea cock off, slipped in a split 1/4 " starboard piece for 1/2" total and then tightened the sea cock down. Very happy amateur here. No water. Plywood rots in my experience.

 

[mitiempo]

Unfortunately sealants do not stick to Starboard.

My first choice would be either G10 or fiberglass (available from McMaster Carr) or second choice plywood soaked in epoxy.

 

[Maine Sail]

Mainsail

I've been planing on replacing my thru-hulls this spring. I was wondering if I could use some other material for backing plates? I've read your how to articles and find them very helpful. I have access to 3/8" alunimun plate could I use that for a backing plate? How about 1/2" acylic ? I don't have the materials on hand to make the fiberglass plates.
Thanks

I'd use marine ply soaked in epoxy or polyester resin. I would not use acrylic, aluminum or Starboard. Acrylic is brittle and can fracture, aluminum can cause galvanic issues when mixed with bronze and Starboard offers little additional rigidity to the hull and nothing likes to stick to it.

A local power boat owner tried HDPE for backing plates, the new owner now has 6 of them leaking.. I have to re-bed and replace six of the seven backing plates this spring, due to leaks. The other one had already been replaced.

 

[Albanach]

I'd use marine ply soaked in epoxy or polyester resin.

Could you please clarify “soaking in epoxy or polyester” for me? I painted a marine ply cleat bottom plate with 2 coats of polyester, plus flowcoat and the polyester is now splitting off after 2 years.

Many thanks.

 

[Don Crowther]

Thanks Main Sail

I'll try soaking 1/2" marine grade plywood in resin. If i could some how vacum pack it that would probaly work best.

 

[Steve Connell]

Backing options:
http://www.coosacomposites.com/index.html

http://www.strongwell.com/products/pultruded_prod/struc_shapes/

at: hamiltonmarine.com

 

[mitiempo]

The Extren would work well, but the Coosa is compressible and designed as a core material so not a good choice for a backing plate. Great substitute for balsa core though.

 

[SailingHarry]

Coosa, while expensive, is a terrific material. I wish it were in my budget! It is worth noting that Coosa comes in varying densities, and the high end is a replacement for (and stronger than) similar thickness marine plywood and recommended for structural applications. I would very much doubt that the heavier grades would compress appreciably (even steel is "compressible," just not appreciably). I wouldn't hesitate to use the heavier Coosa products for thru-hull backings, deck fitting backings, etc.

Harry

The Extren would work well, but the Coosa is compressible and designed as a core material so not a good choice for a backing plate. Great substitute for balsa core though.

 

[mitiempo]

I;m sure Coosa is good stuff, and also sure it is expensive. Even their strongest and stiffest panel is reinforced polyurethane foam.

The Extren linked to or premade fiberglass panels from Mcmaster Carr (which Extren is) would both be better choices and less expensive than Coosa I think. Or you could use G10, also from McMaster Carr.