Replace plywood with marine grade polymer?

jibes138 · Jul 26, 2015

Chances are you also have rot in the deck core around the chainplate. Make sure you fix that while your at it. Can't help with specs on the lumber

woodster · Jul 26, 2015

Re: replace plywood with marine grade polymer

how you going to fasten it to the hull i don't think you can glass it in with that material it wont bond to the plastic on less it is frp......i would go back with more ply wood and stop the source of the leak..it may be strong enough but i don't think it will bond to the hull with fiberglass cloth and resin the poly material that is

jibes138 · Jul 26, 2015

Why not just use marine plywood? Your boat is probably over 30 years old so the plywood will last a long time. Use butyl tape from Maine Sail to seal the chain plates. I doubt you will ever fix it again. Try using an oscillating tool with a wood and metal cutting blade. It will go through the fiberglass and plywood like butter. Then the same tool with an abrasive blade will prepare the hull for the new bulkhead attachment. Good luck with the fix.

rgranger · Jul 27, 2015

I found this at Starboard Marine

Wood vs. Polymer Materials

Some companies use plastic materials as the load-bearing material in replacement transoms, reasoning that the plastic will not rot. While it is true that plastic is more water resistant than bare wood, treated wood encased in fiberglass will resist decay almost as well as plastic.

Wood has a tremendous advantage over plastic materials: Wood will not form stress fractures. Under the constantly fluctuating forces experienced under load, a transom will flex and bend. This movement will cause fatigue in plastic materials but not in wood. As time and usage accumulate, a polymer transom grows weaker but wood remains as strong as ever, perhaps even strengthening with time!
A properly installed wood transom made with treated marine plywood and encased in fiberglass can outlast a plastic one.

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Gunni · Jul 28, 2015

Marine ply, epoxied (not polyester resin), sistered to sound existing bulkhead, or better, a complete bulkhead replacement. This is an important structural element of your boat.

sailhappy20778 · Aug 3, 2015

You need a composite board with high tensile and compression strength plus high modulus. Starbright or other plastics are not adequate with 10% of the modulus of marine plywood. IMHO you need a composite. Search for G10 epoxy-glass laminates. You will need to cut or grind out the old lamination from plywood to hull and then epoxy glass tab the new G10 bulkhead or chainplate knees. Here is how I did it on my boat, an Irwin 31 Citation. It is not cheap or easy, but it is bullet proof (literally). By the way, I replaced the floor stringers with 1" thick G10 and the plywood floor in my shallow bilge with 1/4" pultruded vinyl-glass composite too so I never have to worry about bilge rot.

Knee Replacement

Attach main and spinnaker halyards on side you will replace. Tighten
Loosen main and lower shroud and disconnect from chainplate
Remove all items stored in shelves and lockers
Unscrew berth bottom and remove. Unscrew and remove settee support for berth bottom. Tape in plastic between tank and hull to catch any debris that falls. This will avoid bits of dust and rotten wood from settling in unreachable areas.
Unbolt settee back at both ends. Place bolts in zip lock bag
Remove forward locker door
Reaching through access and doors, cut tabbing between settee back and knees or hull using angle grinder with diamond blade or dremel with tungsten cutter. The most difficult tabbing will be forward of the main shroud. Shelving may be tabbed into the settee back.
Cut bottom of settee back through glass tabbing as high as possible so after settee is returned, you can bolt through it into tabbing rather than re-tabbing
When all tabbing is cut remove settee back. You might need a small crow bar to help.
If you need to create a new settee back, it will not fit through the companionway. Cut about 3” below the bottom of the bottom shelf support. Remove both parts. Create new settee back with the old as a pattern. Use alkyd paint for interior and waterproof inside and edges with alkyd paint or varnish. Create a 6” wide ½” plywood to epoxy the two pieces together after you bring back into the boat. Attach new shelf supports inside and berth support outside.
Remove screws holding shelves into hull tabs. Remove shelves and save for patterns.
Remove any shelf backs. Save for patterns.
Remove any screws holding tabbing to knees
Using angel grinder and dremel, cut tabbing to both knees. It will help to leave 1.5-2” of tabbing on the aft sides to help in aligning new knees. On the forward side you can cut near the hull.
Remove knees and save all parts for patterns. Remove all bolts, ss chainplates, and aluminum backing plates. Wire brush to clean up.
You can cover the deck openings for now to keep rain out. I used Gorilla duct tape. It is strong and leave little residue
Determine if plywood pieces screwed into underside of deck are rotted. If so, you will need to remove the vinyl under the deck to get access. Cut at bulkhead and front of galley and peel back. Cut under bottom edge of inside cabin teak. Keep this piece to estimate how much you need to replace it if desired.
Unscrew all rotted plywood on underside of deck. If you want to replace the vinyl like it was, keep as many of these pieces as you can for patterns.
Clean underside of deck with mold killing agent.
Sand edges of tabbing for knees and shelves and sand with 80 grit where new tabbing will be placed
Clean up
Lay 1” or .75” thick G10 2’x4’ composite on floor and overlay wood knees with straight cabin side of knee along precut edges. Mark outline with indelible ink. Plan cuts with 7 ¼” circular saw with diamond blade to rough cut the knee patterns. Flip composite sheet to finish cuts.
Using multiple circular saw cuts, improve the rough finish. Finally using a 60 grit sanding wheel on the angle grinder, grind to the final shape. Sand with 60 or 80 grit to remove blade chatter and sharp edges.
Remove dust from new composite knees. Mix epoxy with 5% mineral spirits or acetone solvent and paint all cut areas to seal.
When you drill for the chainplate holes with a ½” tungsten carbide bit, place a piece of wood under it to avoid breakout of the back of the hole
Line up the old wood knee with the new composite and clamp in position. Place drill in the first or last hole of the wood knee and drill through the composite. Place a bolt in the hole to keep it aligned. Do the same for the last hole. After this, remove the wood knee and place the ss chainplate over the holes. Insert bolts in the two holes to assure alignment. Drill the remaining 6 holes through the composite and place a bolt in each after it is drilled. Once all holes are complete, place the aluminum backing plate on. If any holes were not perpendicular, the bolts won’t fit. Remove bolts and drill from chainplate through composite and aluminum backing plate to get alignment. If bolts are too long for width of new composite knee, purchase shorter bolts or add ss washers. Leave chainplates installed to align new knee in the boat.
Install knees by first inserting chain plate through deck and then pushing knee into place. Align aft side of knee with what remains of aft tabbing. Wedge into place and attach clamp to chain plate at deck level to keep in place. Check alignment of knees with front and aft braces with a long strait edge. Adjust as necessary to get alignment.
Mix Bondo with short or long fiber following their directions and place between knee and hull and create large radius fillet between knee and hull. Smooth and let set.
Sand bondo fillet smooth with 60-80 grit.
Cut pieces of glass mat 6”-8” wide to fit along knees between shelves. You should use enough to achieve at least 0.10” thick.
Use a board to lay out glass and impregnate with epoxy. Cover board with saran wrap and tape in place. This will release epoxy. Use adequate ventilation. Wear neoprene gloves. Have paper towels or cloth ones available. Have acetone solvent available for clean-up. Have West 105 and 206 components ready with stir devices (large wood tongue depressors). Stir in a figure 8. Mix about 3 pumps of each into a plastic cup and stir. Place mat to be impregnated on saran wrap on board. Pour epoxy over one piece of mat and roll with grooved roller to impregnate until transparent. Pick up impregnated mat and place over knee-fillet-hull and roll with grooved roller to eliminate bubbles.
Repeat until proper tab thickness is achieved.
Continue with next section.
When complete clean roller in acetone. Roll up saran wrap and dispose.
Leave to cure 24-48 hours or more. Wash tabbing with soap and water to remove any residual amines in case you need to adhere or paint in the future.
Sand to eliminate any glass fibers that could be dangerous.
Cut, paint, and fit any shelves.
If you want to replace the vinyl ceiling, do this now.
If you want to replace the backs of
Place shelves in place
Place settee back in place lowering into slot with bottom tabs. Replace fore and aft bolts.
Drill through settee and tabs and bolt with washers and locking washers.
Drill through settee into knees with undersized drill. Then tap and bolt using ss bolts and washers.

Indysailor · Aug 3, 2015

jibes138 said:
Why not just use marine plywood? Your boat is probably over 30 years old so the plywood will last a long time. Use butyl tape from Maine Sail to seal the chain plates. I doubt you will ever fix it again. Try using an oscillating tool with a wood and metal cutting blade. It will go through the fiberglass and plywood like butter. Then the same tool with an abrasive blade will prepare the hull for the new bulkhead attachment. Good luck with the fix.

Exactly what I did on my 23. I didn't have nearly this kind of rot and was lucky to have only a few inches diameter of core rotted around the chain plate area. I used okoume marine grade plywood and sealed the edges with CPES. Maine Sail's butyl tape is working extremely well, no leaks after four years.

One big difference is that the bulkheads are not tabbed in on a 23. Most examples I've read in the inter webs have just cut the bulkheads out flush with the hull and then tabbed new ones back in.

cb32863 · Aug 4, 2015

Welcome to O'Day ownership!

I had a 25 for 3 years and redid the bulkheads with marine ply, the next year I recored the deck under the mast, the next year I dealt with a swollen centerboard and sold the boat. This is unfortunately very common on these boats.

Here's how I did it;

http://danssailingblog.blogspot.com/2012/03/project-1-part-1.html

http://danssailingblog.blogspot.com/2012/08/her-come-updates.html

http://danssailingblog.blogspot.com/2012/08/project-1-part-3.html

http://danssailingblog.blogspot.com/2012/08/interior-work.html

Oh yeah, I also rebedded all the mast deck hardware and toe rails, before recoring the deck. So I got to do that twice.

I know I am probably going to be "cursed" by current O'Day owners but... I have lived it.

Indysailor · Aug 4, 2015

cb32863 said:
Welcome to O'Day ownership! I had a 25 for 3 years and redid the bulkheads with marine ply, the next year I recored the deck under the mast, the next year I dealt with a swollen centerboard and sold the boat. This is unfortunately very common on these boats. Here's how I did it; http://danssailingblog.blogspot.com/2012/03/project-1-part-1.html http://danssailingblog.blogspot.com/2012/08/her-come-updates.html http://danssailingblog.blogspot.com/2012/08/project-1-part-3.html http://danssailingblog.blogspot.com/2012/08/interior-work.html Oh yeah, I also rebedded all the mast deck hardware and toe rails, before recoring the deck. So I got to do that twice. I know I am probably going to be "cursed" by current O'Day owners but... I have lived it.

You bought a 30 year old boat that had been poorly maintained. The best advice is to know what you're getting into before you commit.

cb32863 · Aug 5, 2015

Indysailor said:
You bought a 30 year old boat that had been poorly maintained. The best advice is to know what you're getting into before you commit.

Very valid point of course but, I am not the only person that has experienced theses issues with an O'Day. Which, is also a very valid point.

Replace plywood with marine grade polymer?

donandpaula

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