Hi all,
I've been working through a significant moisture issue in the port hull of my 1987 O'Day 40 and wanted to share my findings and planned approach, both to get a sanity check from anyone who's done similar work and to ask for help finding information I haven't been able to track down.
Background
I have a 3ft x 10ft area on the port hull where the outer fiberglass skin has delaminated from the balsa core — confirmed core failure. That section will be cut out and replaced (skin + core), so it's out of scope for the rest of what I'm describing below.
Separately, roughly 50% of the remaining port hull is reading high on moisture meter surveys, which is the larger problem I'm trying to solve.
Survey Methodology
I mapped the full port side using a Klein ET-140 moisture meter on the hardwood setting, with baseline "dry" values established from known-dry areas of the boat. My reading bands:
0–6%: dry baseline
6–9%: dry to the touch when sample-drilled
10–17%: moist to the touch
18–20%: wet
20–27%: dripping
I also tap-tested the hull to delineate the delamination boundary, and drilled exploratory holes every 12" along the lower edge of the affected area. Clear water drained out — fast initially, then slowing after a few minutes, consistent with free water at the skin/core interface draining out before the slower-draining saturated core itself.
Good news on core condition: every sample I've drilled shows good color wood — no black staining, no off-color, no odor. This appears to be wet balsa, not degraded/rotten balsa, which I understand is a meaningfully better starting point structurally.
Planned Drying Approach
For the area outside the cut-out zone, my plan is:
1. Drill a 6x6" grid of holes through the outer skin into the core across the mapped moisture areas
2. Tent the entire port side in sealed 6mil poly sheeting, standoffs to keep it off the hull
3. Run a dehumidifier and heater inside the sealed tent (closed loop — no air exchange with outside) to drive vapor diffusion out through the drilled holes
4.Drill all drainage holes at the bottom of the worst (20-27%) zones first to let gravity clear free water before relying on vapor diffusion for the rest.
5.Monitor with the Klein meter at intervals, and do one consolidated epoxy-fill of all holes at the end once the whole area reads dry — rather than filling zone by zone, to preserve the ability to rework any area that doesn't clear
What I'm Looking For
This is where I'd really appreciate the community's help:
1.Original O'Day 40 hull laminate schedule — ply count, glass weight/type, resin (poly/vinylester/epoxy), and core thickness for the hull skins. I haven't been able to find this published anywhere.
2. I saw a reference elsewhere to Rudy at D&R Marine having been involved in late-production O'Day builds — if anyone has a current contact for him or anyone else with O'Day construction knowledge, I'd appreciate it.
3. Scarf/taper ratio used by others for hull skin patches this size — my new outer skin replacement areas are roughly 2ft x several ft. I'm planning a 20:1 taper on the patch edges; interested if others have done larger structural hull skin patches and what they used.
4.Anyone who has done a similar balsa drying project — particularly interested in real-world drying timelines, what core moisture % you started and ended at, and whether tenting/dehumidifying in place worked as expected versus cut-and-replace.
5.Resin compatibility for the repair — if anyone knows what resin O'Day originally used in '87 hulls (poly vs vinylester), that affects what I can use for the new skin.
6.Anyone with a moisture survey of their own O'Day 39/40 — curious whether this is a known problem area on this hull or specific to mine.
Happy to share more detail/photos of the survey map or drilling samples if useful to anyone dealing with something similar. Will post progress and outcomes as the project moves along — and if anyone has been through this and has lessons learned (good or bad), I'd genuinely rather hear them now than after I've committed resin.
Thanks in advance, Don Evans
ODay 40 Camelot
I've been working through a significant moisture issue in the port hull of my 1987 O'Day 40 and wanted to share my findings and planned approach, both to get a sanity check from anyone who's done similar work and to ask for help finding information I haven't been able to track down.
Background
I have a 3ft x 10ft area on the port hull where the outer fiberglass skin has delaminated from the balsa core — confirmed core failure. That section will be cut out and replaced (skin + core), so it's out of scope for the rest of what I'm describing below.
Separately, roughly 50% of the remaining port hull is reading high on moisture meter surveys, which is the larger problem I'm trying to solve.
Survey Methodology
I mapped the full port side using a Klein ET-140 moisture meter on the hardwood setting, with baseline "dry" values established from known-dry areas of the boat. My reading bands:
0–6%: dry baseline
6–9%: dry to the touch when sample-drilled
10–17%: moist to the touch
18–20%: wet
20–27%: dripping
I also tap-tested the hull to delineate the delamination boundary, and drilled exploratory holes every 12" along the lower edge of the affected area. Clear water drained out — fast initially, then slowing after a few minutes, consistent with free water at the skin/core interface draining out before the slower-draining saturated core itself.
Good news on core condition: every sample I've drilled shows good color wood — no black staining, no off-color, no odor. This appears to be wet balsa, not degraded/rotten balsa, which I understand is a meaningfully better starting point structurally.
Planned Drying Approach
For the area outside the cut-out zone, my plan is:
1. Drill a 6x6" grid of holes through the outer skin into the core across the mapped moisture areas
2. Tent the entire port side in sealed 6mil poly sheeting, standoffs to keep it off the hull
3. Run a dehumidifier and heater inside the sealed tent (closed loop — no air exchange with outside) to drive vapor diffusion out through the drilled holes
4.Drill all drainage holes at the bottom of the worst (20-27%) zones first to let gravity clear free water before relying on vapor diffusion for the rest.
5.Monitor with the Klein meter at intervals, and do one consolidated epoxy-fill of all holes at the end once the whole area reads dry — rather than filling zone by zone, to preserve the ability to rework any area that doesn't clear
What I'm Looking For
This is where I'd really appreciate the community's help:
1.Original O'Day 40 hull laminate schedule — ply count, glass weight/type, resin (poly/vinylester/epoxy), and core thickness for the hull skins. I haven't been able to find this published anywhere.
2. I saw a reference elsewhere to Rudy at D&R Marine having been involved in late-production O'Day builds — if anyone has a current contact for him or anyone else with O'Day construction knowledge, I'd appreciate it.
3. Scarf/taper ratio used by others for hull skin patches this size — my new outer skin replacement areas are roughly 2ft x several ft. I'm planning a 20:1 taper on the patch edges; interested if others have done larger structural hull skin patches and what they used.
4.Anyone who has done a similar balsa drying project — particularly interested in real-world drying timelines, what core moisture % you started and ended at, and whether tenting/dehumidifying in place worked as expected versus cut-and-replace.
5.Resin compatibility for the repair — if anyone knows what resin O'Day originally used in '87 hulls (poly vs vinylester), that affects what I can use for the new skin.
6.Anyone with a moisture survey of their own O'Day 39/40 — curious whether this is a known problem area on this hull or specific to mine.
Happy to share more detail/photos of the survey map or drilling samples if useful to anyone dealing with something similar. Will post progress and outcomes as the project moves along — and if anyone has been through this and has lessons learned (good or bad), I'd genuinely rather hear them now than after I've committed resin.
Thanks in advance, Don Evans
ODay 40 Camelot
