Lightweight but strong backing material

[Terra Nova]

Now it makes sense.

[estarzinger]

Originally Posted by zboss

This is a lesson for when I put the new backing on- use several pieces rather than one big piece, use epoxy, and separate by a very small bead of 3M 4200 or 3M 4000. Also, fill the screw/bolt holes with sealant.

All surfaces and edges of the plywood, including the fastner holes, should be well sealed with epoxy.

[jamhass]

Were it me, I would use a 'composite' approach.

1. Make a frame of g10 or other properly structural and truly waterproof material around each port. If, say, you need a 1/2 inch thickness, you can build it up from say 1/4 or 1/8 material alternating the joints, thus getting the best efficiency from standard stock materials.

2. Fill the areas between the ports with lighter weight non-structural materials (foam, ply, etc) properly sealed, of course.

This approach minimizes the use of the most expensive materials, while keeping moisture-sensitive materials away from leakage prone exterior penetrations.

With some forethought, you can plan for your eventual upgrade to NFM ports and reuse the inner frames.

[zboss]

Originally Posted by jamhass

Were it me, I would use a 'composite' approach.

1. Make a frame of g10 or other properly structural and truly waterproof material around each port. If, say, you need a 1/2 inch thickness, you can build it up from say 1/4 or 1/8 material alternating the joints, thus getting the best efficiency from standard stock materials.

2. Fill the areas between the ports with lighter weight non-structural materials (foam, ply, etc) properly sealed, of course.

This approach minimizes the use of the most expensive materials, while keeping moisture-sensitive materials away from leakage prone exterior penetrations.

With some forethought, you can plan for your eventual upgrade to NFM ports and reuse the inner frames.

I was thinking of that as well. We have teak decorative spacers that are just slightly larger than the port so I could use them as a template for the g10 and for the ply. How tough is G10 to cut? Will it cut well with a Fein tool?

G10 is very very expensive so this would allow me to buy less material.

Is West Systems Six10 Epoxy a good enough binding agent between the old fiberglass and the G10?

[Terra Nova]

G10 (or virtually any fiberglass) cuts well with grit blades, particularly on a saber saw. The Fein blades won't last long, even the bi-metal.

Six10 is fine--sand and clean surfaces with acetone, first.

[jamhass]

Originally Posted by zboss

I was thinking of that as well. We have teak decorative spacers that are just slightly larger than the port so I could use them as a template for the g10 and for the ply.

Assuming your ports are rectangular, I don't see why you would need a template. Let's say your ports are 6x10 inches and you want a 1-inch frame around them 3/4 inch thick. Thus, the outside dims of the frames are 8x12. Lets also say you use 1/4 inch material. For each frame make 6 1x11 and 6 1x7 strips. These will make up 3 1/4 inch thick subframes, which you assemble and glue like a stack of bricks so no joints overlap.

If not nearly rectangular, use wider strips then trim as needed to shape, probably need to trim the ID only.

I have good success using an inexpensive dry diamond wheel in a 4-1/2 inch grinder to cut fiberglass, G10 etc.

[Ziggy]

Instead of G10, you might consider using structural or electrical grade fiberglass. While not quite as strong as G10, I think they're more than adequate for backing plates, and half the cost of G10. See http://www.mcmaster.com/addlcontent/...sp?doc=8549KAC

[zboss]

An update...

We ended up using FR-4 (the successor to G10) as Evan suggested instead of marine ply. It worked out really well but that stuff is HARD to cut!

To get the sizing just right - because nothing is straight on a boat - we used patterning material from Sailrite that my wife had some extra of. It worked exceedingly well at transferring the pattern over to the FR-4 for cutting. We then used a diamond grit blade in our jigsaw to make the cuts.

Once the part was set, we used West Systems Six10 to glue to board to the existing fiberglass hull. We now have 1/2" of fiberglass around the port holes.

We glued the teak to the FR-4 using life-calk (it didn't need to be strong).

We did not yet buy new portholes but that is definitely on the plan for next year - we could use the extra air flow and light plus the New found Metal port holes seem more robust. The ports were then bedded into the holes using the existing fitting parts and Butyl rubber. That rubber is very very sticky and strong - its squishing out very well into all the gaps. I'd be very surprised if these port holes leak anywhere than the window gaskets.

[Terra Nova]

You'll absolutely love the Newfound Metals stainless portholes. Have them on TN. Good people too.

[exMaggieDrum]

I'll give a strong second to what Terra Nova just said about NFM portlights. We used them to replace all our portlights on our Whitby. Make sure you get the right size and do some cutting if needed as you can't add very well, at all. They are great people. However, you can't say their products are cheap. Sometimes you get what you pay for. Have fun with your projects and thanks for you update.