Questions about the roof build of a Oday 27 older model likely 1979 or 78

Tally Ho · Friday at 6:40 AM

We should see some photos to help verify what you are looking at, but my understanding is that the deck is a sandwhich consisting of a layer of glass, then some form of core (balsa), and the. A top skin of glass. The balsa gets wet, and rots, causing the laminate to fail. “And so it begins” details the cutting open the top skin, replacing the core, and reglassing the top skin. I don’t recall if he just laid new glass or reused the top skins somehow.

On the inside of the hull, boat builders have used different methods to cover the inside fiberglass.
- Some boats have ”carpet” liners. My 1988 O’Day 322 uses carpet on the upper half of the hull.
- Some boats use wood or other materials for a headliner or wood slats to cover the walls.
- More modern boats use a fiberglass liner that is smooth and finished to cover the roof, walls, etc. My O’Day 322 has a rigid fiberglass headliner overhead covering the entire ceiling of the boat, and a fiberglass hull liner on the bottom 1/2 of the hull.

Carpet can be pulled down (it is glued on). Here I removed the “carpet” liner from the hull in my aft berth…that is the unfinished fiberglass hull. And you can see the fiberglass liner on the lower part of the hull (Below the teak shelf).

My O’Day 322 has some foam core around the hatches…I found this when I pulled the main hatch out to rebed it…
This photo helps explain the sandwich construction. You can see the fiberglass liner (very thin) at the bottom, then a layer of fiberglass, a layer of foam (the green layer) and then the top fiberglass layer.

Here is a shot of the fiberglass headliner that covers the entire top of Tally Ho. It covers the ceiling and the side decks. You can also see more of the carpet liner on both sides where the side shelves are (a blue/gray carpet).

Hope this helps some. Post some photos of what you are looking at and why you want to chop it up…. Replacing the deck is not for the faint of heart, and requires a lot of fiberglass work. Cutting up a fiberglass liner will be hard to repair back to a finished look. Removing carpet is easy enough, and if you are replacing with cloth, it should e too tough….but I still haven’t refinished my aft berth.

Greg

jssailem · Friday at 11:22 AM

Oddvark said:
I have a Oday 27 that I want to experiment with materials, specifically isogrids for reinforcement.

This sounds like fun.
First you might want to understand the way and why your boat was designed. At a basic level is a hull structure that functions as a skin over a skeleton.

In this image the skeleton are the wooden stringers holding the hull skin in shape.

Your O’Day uses some fiberglass ribs attached to the interior of the hull then an interior liner is secured over the hull. This provides strength and interior design function. To the liner are fitted bulkheads and decorative wood / cushions / coverings.

I understand the isogrid benefits, it is not clear how you see those being applied to your boat.

While the hull and liner function to provide a skin and skeleton structure, the salon roof panel provides some stabilization of the deck, but functions more as a covering to hide the under side of the deck.

dlochner · Friday at 6:51 PM

In general when production boats are built there are 4 main pieces, the hull, the pan, the headliner, and the deck. The pan is attached to the hull in a couple of ways, fiberglass tabbing and/or gobs of thickened polyester resin. Once the pan and hull are one, the headliner is lowered in place, it may or may not be glued to the bulkheads and other internal structures. Next the deck is lowered on to the headliner and hull. Gobs of thickened polyester resin are strategically placed on top of the headliner before the deck is lowered. This attaches the headliner to the deck structure and provides additional support and stiffening for the deck.

Deck stiffness is achieved by building thickness with a core between 2 fiberglass laminates. The most common core material is end grain balsa. It is light and adds bulk without weight. Stiffness is also achieved by adding some camber to the flat structures and breaking up the large expanses with the deck house structure, the vertical sides of the house add stiffness.

High end racing boats, like Open 60s, Volvo 70s etc, do use a grid structure for some panels. Search around for honeycomb panels. These provide very strong and very light panels. They are not used in production boats because of cost. Production boats are built to a price and manufacturers do everything they can do to keep material and labor costs low to be competitive.

Without knowing the specific engineering that went into the design, it would be prudent to avoid altering the basic structure of the boat. There are large forces on a boat that cause the boat to twist and bend. When the boat is designed these forces are considered, hacking away at structure without knowledge of its function could lead to unintended consequences. Consider for a moment a house, there are load bearing walls and non bearing walls. Ripping out a non load bearing wall is no big deal, ripping out a load bearing wall is different story, the house may fall down. Before attacking the structure of a boat it is essential to know the load paths and how the loads are transmitted.

Project_Mayhem · Friday at 10:12 PM

It will be very difficult and time consuming to remove the good core from a liner. Your lungs and eyes will hate you, especially if it's an enclosed space. I rebuilt the foredeck and part of the stern stern on an O'Day 25.

The composite cores a great until you see the cost. Your boat lasted this long with balsa. New balsa core will outlast the boat.

If you do decide to do this, I would highly advise a full face mask. The double seal helps a ton over a half face mask. It's still far from perfect. You will end up breathing and getting fiberglass dust in your eyes sometimes

dlochner · 2025-12-13T04:30:52-0800

Oddvark said:
Thanks for all the answers and help. I want to make clear, I'm not sure that it is from some responses. I only want the inner fiberglass liner removed. I'm not interested in new cores. My understanding, so far, is there is a outer fiberglass, balsa, inner fiberglass, then a separate fiberglass inner liner. I only want the inner liner gone. I guess the difficulty is, how much thickened, I assume thickened, resin is between the liner and the inner hull. If it's a lot could be really hard to separate the liner. A guess, it's not all over as resin is not cheap so it will be sporadic spots of resin holding in the liner. I, of course, really have no idea. I know that sailing Uma did this to their Pearson 36.

Uma's liner was removed and then they invested a ton of time and money to reinforce the deck and hull structures. Dan and Kika both have engineering backgrounds with degrees in architecture, so they did this understanding the loads and load paths.

The headliner is not just cosmetic, it provides structure. Ripping it out means it will be necessary to replace that structure in some other form. Boats that do not have headliners have deck structures that are designed for the loads they will experience.

Frankly, I wouldn't waste the time and money on an old 27 foot boat.

Tally Ho · 2025-12-13T07:32:08-0800

Oddvark said:
Thanks for all the answers and help. I want to make clear, I'm not sure that it is from some responses. I only want the inner fiberglass liner removed. I'm not interested in new cores. My understanding, so far, is there is a outer fiberglass, balsa, inner fiberglass, then a separate fiberglass inner liner. I only want the inner liner gone. I guess the difficulty is, how much thickened, I assume thickened, resin is between the liner and the inner hull. If it's a lot could be really hard to separate the liner. A guess, it's not all over as resin is not cheap so it will be sporadic spots of resin holding in the liner. I, of course, really have no idea. I know that sailing Uma did this to their Pearson 36.

I don’t know that you told us WHY you want to remove the liner. What are you trying to accomplish?

Get to rotten core from the bottom side? Insulate the deck?

Greg

jssailem · 2025-12-13T10:12:45-0800

I am sitting here sipping coffee in a rain storm thinking about your boat. Maybe you could take a picture of the area you want to remove.

Is there a seam between the hull and the part your calling the inner liner?

Looking at some O’Day 27 images (this one from a 1978 O’Day 27) show what appears to be to be a solid interior fiberglass ceiling to the salon. The deck hardware is through bolted. This would suggest no liner but a solid sandwiched deck.

Trying to remove this surface will expose the filler (balsa wood, plywood, or foam filler) and affect the deck integrity.

Richard19068 · 2025-12-13T10:35:34-0800

Just some observations:

I don't have a 27 but on my 1985 O'Day 31the headliner appears to be very securely attached . When I tap on it in various spots around the cabin ceiling it sounds solid as if there is no space between it and whatever (fiberglass) is above it. See Tally Ho's picture of the sandwich around his deck hatch. The liner is securely attached to the bottom of the deck. I think attempting to remove the headliner would be very very difficult and probably leave lots of roughness and pitting in the remaining fiberglass.

As the liner transitions from the ceiling down the cabin sides (around the windows) there may be some space where it doesn't seem as fully attached. Where the liner folds under (below) the deck out to where the stanchions are bolted there is certainly space between the liner and the bottom of the deck. I have had to cut some of this away to re-bed the stanchions. Also. there is space for wires between the liner and the deck.

As Tally Ho posted, it would be interesting to know what you are attempting to do after you remove your headliner. What does your "experiment" entail?

jssailem said:
While the hull and liner function to provide a skin and skeleton structure, the salon roof panel provides some stabilization of the deck, but functions more as a covering to hide the under side of the deck.

John, is this a generalization or do you have any information on that specific to O'Day's or O'Day 27's?

EDIT: John, I didn't see your last post until after sending this. I think that post answers my question.

Davidasailor26 · 2025-12-13T19:37:19-0800

I don’t know the exact construction, but when it comes to the cutting I think you’d be better served with an oscillating multitool than impacting chisel. The oscillation will probably do a better job slicing through glass and resin, and I’d be worried about collateral damage from too much hammering.

dlochner · 2025-12-13T20:00:39-0800

Part of the confusion is you are using language that is confusing.

The deck has 3 layers, an outer skin, a core, and an inner skin. The deck is laid up in a female mold so the gelcoat is smooth and easily finished. The inner skin is raw fiberglass on the outside. It looks ugly and ugly doesn't sell boats. So builders hide this by using carpet or adding a headliner of some sort. A fiberglass headliner is laid up on a male mold, so the inner surface is gelcoat and not ugly. The ugly side of the headliner faces the ugly side of the deck.

If the inside of your boat looks like the photo in post #11, then you have a fiberglass headliner. In an earlier post I mentioned the design of the headliner also adds support and structure to boat to transfer loads. In the photo you can see a channel where the bulkhead meets the headliner. That channel serves to hold the bulkhead in place, adds support to the deck, and helps to transfer rigging loads to the hull. Between the headliner and the underside of the deck there will be thickened resin of some sort. Expect to find a lot of it where the loads are high such as above the bulkheads and below the mast step. This holds the headliner in place and distributes the loads. The other place you will find it is around the ports, it will fill the gap between the deck and the headliner so the ports can be tightened against the hull. If the original design had deck hardware penetrating the deck the headliner there will be thickened resin in those places.

If I understand your question correctly, you want to remove the headliner and then the inner skin of the deck up to the balsa coring. Next you would install a honeycomb or isogrid of some sort and glass it up against the existing core.

The headliner can be cut out without too much difficulty. Use a circular saw to cut through the headliner. Adjust the depth so that it does not cut into the inner skin of the deck. Cut it out in sections to find where the thickened resin is located.

Once the headliner is removed, remove all the thickened resin to expose the inner skin. The inner skin is probably fairly thin, I'd guess around ⅛" thick. Set the saw blade to that depth and repeat the scoring and sectioning. Now comes the impossible part, removing the inner skin without damaging the balsa core which should be glued to the skin. If the core is wet and rotted, it will be easy and the core needs to come out. If the core is in good shape it will be nigh unto impossible to remove it without damaging the core.

With the inner skin off, the deck will be very weak, don't step on it.

If you go through with this plan, how much weight will you save?

Tally Ho · 2025-12-13T20:19:30-0800

Oddvark said:
That IS my main worry. I do know there are areas that are not attached. I would find it odd if when they built it, they laid fiberglass in the roof mold, added balsa, then immeditely put down the roof liner with no other liner of fiberglass before they added the liner. I believe they have wiring and other stuff and I would think they would let the whole roof mostly set, then add the liner with some sort of thickened resin, though I could be wrong. Be nice if someone had actually done this. All the pictures I see, for the 27' only show the outer top taken off to replace the balsa. Fiberglass below but is that directly the roof liner??? Maybe the best way to find out is to just drill some holes with a hole saw until I hit the balsa and see.

You can certainly take a ‘core sample’ and see what you have.

Have you removed a hatch to see if you can see the construction?

The liner is just that. Covers the rough glass of the deck. It is not the bottom part of the laminate.

You still haven’t said what you are trying to accomplish.

Greg

Rick D · 2025-12-13T20:46:26-0800

OK, I had a 1976 O'Day 27. FWIW, I added a hatch for ventilation on the roof. It was two layers of glass with a balsa core.

Questions about the roof build of a Oday 27 older model likely 1979 or 78

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SBO Weather and Forecasting Forum Jim & John

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SBO Weather and Forecasting Forum Jim & John

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