[C320-list] Subfloor for cabin sole

[Jeff Hare]

If you're interested, you should check out my photo album where I did this project (but on another boat).

https://c320.org/mediagallery/album.php?aid=296

I would recommend using BS-1088 grade marine plywood (google it).  It has many layers, quality glue and very smooth surfaces.  Surface imperfections in the plywood will project through the finish flooring.  You will not find marine plywood in most lumber yards, although they will try to pass off exterior grade and pressure treated as marine grade.  What you're looking for is essentially cabinet grade plywood with marine glue.

Of particular note, with this plywood, you can make a cut anywhere in the sheet and the cut edge will never have a void in the interior layers and that's really important.  Pat Tormey can probably speak to the material's durability.

On the east coast, we buy from Bolter Plywood in Somerville MA.  If you're looking for technical info on the project, I had numerous conversations with LonSeal's technical team and have quite a few application docs and such I can share.

We made luan plywood templates for the entire floor and fit/screwed them in place and with basic alignment transfer marks. Then these luan templates were used to trace/cut the plywood flooring.  The actual flooring parts were then cut and fit in place, using sanders to get the fit near perfect. When these were screwed down, alignment marks were drawn to ensure that the stripes could be placed to line up perfectly across all pieces.

Making luan plywood templates is necessary if you don't have really good existing boards to work from.  They also come in very handy during the laminating step for protecting the lonseal from damage when weighing it down and are alot easier to trim to size during the initial fitting.  For the 320, you could probably use the original floor panels for templates if they fit really well and are in good shape. Might even be able to laminate lonseal over the original floorboards, but they'd want to be free of any surface dings that would project through, and you'd still want to epoxy seal all the edges again.

My opinions.  I planned to do this job at some point for our boat.

-Jeff Hare
2001 #809 Woodbine II

-----Original Message-----
From: C320-list <c320-list-bounces at lists.catalina320.com> On Behalf Of David Veeneman
Sent: Tuesday, April 14, 2020 11:44 PM
To: C320 Assn Forum <c320-list at lists.catalina320.com>
Subject: [C320-list] Subfloor for cabin sole

I’m getting ready to replace my cabin sole with Lonseal vinyl flooring. I’m going to replace my subflooring with 3/4 plywood.

Here’s my question: What sort of plywood is considered acceptable in this application? I know that I need a smooth-surface plywood, but beyond that, what should I look for for in a plywood? Home Depot doesn’t list any plywoods as ‘marine grade’, and just about the only feature they list is pressure-treated. As a result, I’m a bit at sea on this, and any advice would be helpful and appreciated.

--
David Veeneman
SV Adelante, Hull #131
Dana Point, CA