Friends, When I hear many folks cutting "panels" out of the underside of their decks to remove soft wood, I wonder about the lose of strength. I think of a cored deck as sort of an "I" beam or truss and the strength coming from the whole structure. If you cut the bottom leg off an "I" beam, the beam will lose 75% of its strength. Now in the case of a cored deck, I realize we “glass” back in the lower panel, thus restoring the bottom of the “I” beam,….BUT this glassing back in of the lower panel, is a “secondary” bond and only half as strong as the original skin at best. Now let’s consider the core material that has been reduced to mush. Its only job is to withstand “compression” which of course it doesn’t do as mush. I have come to the conclusion that the best way to repair a soft deck, no matter how bad it is, would be to use the “drill holes and inject epoxy” method. I realize drilling holes in the top surface rubs some of us wrong, as we’ve been fighting water intrusion for years and water intrusion is what caused the problem in the first place! The field of small holes will not significantly compromise the strength of the top skin and sealing these holes should not be an issue. I realize I’m challenging conventional thinking and welcome the opposing explanation from those with more experience. Don .
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Weak deck repair using drill holes and epoxy
Two seasons ago, I used the drill and fill method of repairing a soft deck on my O'Day 22. I found that water intrusion had soften the deck in more areas than expected. Using a drill equiped with a bent 1/4" rod, I removed as much of the "mush" as possible. Since I had drilled many holes, nearly all of the softened material was removed. Use a vacuum to remove the softened balsa core. I decided to refinish the entire deck after the area repaired covered much of the bow, port and starboard deck. I sanded down the anti-skid deck, filled and faired the area. I then used the Interlux Brightside paint system to finish the deck. Non-skid was restored using Interlux beads mixed in with the paint. The result was outstanding. Atfer 2 seasons, no leaks, no problems. The deck is solid as can be. It took me about 6 weeks, part-time, to do the work, but in the process, I gained the respect the many boat owners and workers in the yard for the beutiful work.
Two seasons ago, I used the drill and fill method of repairing a soft deck on my O'Day 22. I found that water intrusion had soften the deck in more areas than expected. Using a drill equiped with a bent 1/4" rod, I removed as much of the "mush" as possible. Since I had drilled many holes, nearly all of the softened material was removed. Use a vacuum to remove the softened balsa core. I decided to refinish the entire deck after the area repaired covered much of the bow, port and starboard deck. I sanded down the anti-skid deck, filled and faired the area. I then used the Interlux Brightside paint system to finish the deck. Non-skid was restored using Interlux beads mixed in with the paint. The result was outstanding. Atfer 2 seasons, no leaks, no problems. The deck is solid as can be. It took me about 6 weeks, part-time, to do the work, but in the process, I gained the respect the many boat owners and workers in the yard for the beutiful work.
Another method.
Don: Another method would be to cut out the deck area where the core needs to be replaced. Then you can replace the core (plywood, balsa etc.). Then the piece of deck could be replaced and sealed with fiberglass resin or epoxy. Then you just need to redo the non-skid if applicable.
Don: Another method would be to cut out the deck area where the core needs to be replaced. Then you can replace the core (plywood, balsa etc.). Then the piece of deck could be replaced and sealed with fiberglass resin or epoxy. Then you just need to redo the non-skid if applicable.
Don
The drill from the deck, vacuum, and fill method is the best one we have used for relatively small bad core areas. For areas that encompass more than 1/4 of the deck area we cut the deck out, epoxy in new core, and replace the deck with epoxy. Don't recommend using polyester fiberglass. As to your question of strength repairing from below, if epoxy is applied correctly it is just as strong either way but much easier to work from above.
The drill from the deck, vacuum, and fill method is the best one we have used for relatively small bad core areas. For areas that encompass more than 1/4 of the deck area we cut the deck out, epoxy in new core, and replace the deck with epoxy. Don't recommend using polyester fiberglass. As to your question of strength repairing from below, if epoxy is applied correctly it is just as strong either way but much easier to work from above.
Article on Good Old Boat Site
There is an article on that site. It can be copied. You have to go to the archives and search. If you cant find it email me and i can give you more information. The conclusion is basically this. drilling may be fine for small areas but all you are doing is pushing the rotted wood around when you fill. The only real cure is to cut out the section of deck, remove and repair. The hardest part is gaining enough courage to cut a hole in the deck. craig
There is an article on that site. It can be copied. You have to go to the archives and search. If you cant find it email me and i can give you more information. The conclusion is basically this. drilling may be fine for small areas but all you are doing is pushing the rotted wood around when you fill. The only real cure is to cut out the section of deck, remove and repair. The hardest part is gaining enough courage to cut a hole in the deck. craig
I'm not understood, take a look
Steve, Dave, & Craig, you fellows don't seem to be addressing my point. You're maintaining for bad cases, you must cut out a panel (Steve, in your case a top panel?) Either way, you are weakening the structural strength by compromising the integrity of a skin. If you think of the deck as a piece of corrogated card board, perhaps you can invision my concern. Take a look at my picture. Are there any engineers out there who can address this? I believe you are trusting the end grain balsa to have shear strength. There is none! Consider a diving board made from end grain balsa, a 10 pound baby couldn't get on it without it braking...NO SHEAR STRENGTH. Only compression strength. Which means you can stand on it without it compressing/ squeezing. Now if you're talking plywood, that's a different story. Plywood has significant shear strength. The things is, we don't want shear strength from our core. the shear strength comes from the two skins. Does anybody understand what I'm trying to say? Don
Steve, Dave, & Craig, you fellows don't seem to be addressing my point. You're maintaining for bad cases, you must cut out a panel (Steve, in your case a top panel?) Either way, you are weakening the structural strength by compromising the integrity of a skin. If you think of the deck as a piece of corrogated card board, perhaps you can invision my concern. Take a look at my picture. Are there any engineers out there who can address this? I believe you are trusting the end grain balsa to have shear strength. There is none! Consider a diving board made from end grain balsa, a 10 pound baby couldn't get on it without it braking...NO SHEAR STRENGTH. Only compression strength. Which means you can stand on it without it compressing/ squeezing. Now if you're talking plywood, that's a different story. Plywood has significant shear strength. The things is, we don't want shear strength from our core. the shear strength comes from the two skins. Does anybody understand what I'm trying to say? Don
Attachments
It is the UPPER deck skin ...
that is cut to repair an extended rot problem, but this may be beside the point. Your drawing and I-beam analogy calls for a plane (flat) surface that is suspended around the perimeter. Indeed, such a construction would fail and cave in if the lower skin would be weakened for cohesion (as it becomes extended) and/or the upper skin is weakened for lateral compression and/or the core is weakened for vertical compression. Now consider a deck: the hull clamps the perimeter in, so no or very little expansion is possible. In addition, most decks are bowed like an arch (if ever so little). As a result, when putting a load on the deck, the lower skin will have to take predominantly lateral compression forces, the core vertical compression and the top skin mostly distributes the load point over a wider surface of the core (plus maybe aome miner lateral compression). As a result, when you cut the outer (top) skin and peel it off to replace the core (no lateral gaps), then re-seat and seal the cut line with epoxy, all your functionality is back intact. There may be some exception where cutting the lower (interior) skin is easier, but even here the lateral compression stiffness can be reconstituted by sealing the seams with epoxy.
that is cut to repair an extended rot problem, but this may be beside the point. Your drawing and I-beam analogy calls for a plane (flat) surface that is suspended around the perimeter. Indeed, such a construction would fail and cave in if the lower skin would be weakened for cohesion (as it becomes extended) and/or the upper skin is weakened for lateral compression and/or the core is weakened for vertical compression. Now consider a deck: the hull clamps the perimeter in, so no or very little expansion is possible. In addition, most decks are bowed like an arch (if ever so little). As a result, when putting a load on the deck, the lower skin will have to take predominantly lateral compression forces, the core vertical compression and the top skin mostly distributes the load point over a wider surface of the core (plus maybe aome miner lateral compression). As a result, when you cut the outer (top) skin and peel it off to replace the core (no lateral gaps), then re-seat and seal the cut line with epoxy, all your functionality is back intact. There may be some exception where cutting the lower (interior) skin is easier, but even here the lateral compression stiffness can be reconstituted by sealing the seams with epoxy.
From the top would be my choice
In the article, the repair was done from the top. I would think replacing the rotted plywood, filling and sealing the area would be as strong as before. In the article the repair has lasted 8yrs without any indication of a problem. I would think the area would be much stonger than before. Personally i think the drill and fill method is a temporary fix and is not addressing the problem but pushing it aside but on the other hand is easier.
In the article, the repair was done from the top. I would think replacing the rotted plywood, filling and sealing the area would be as strong as before. In the article the repair has lasted 8yrs without any indication of a problem. I would think the area would be much stonger than before. Personally i think the drill and fill method is a temporary fix and is not addressing the problem but pushing it aside but on the other hand is easier.
Craig
What kind of material do you have when you take saw dust (dryed, rotten wood)and soak it with epoxy? Can you stand on it? Will it ever get soft again? Does it have shear strength? Who cares, you don't need shear strength! If you replace the core with fresh balsa or plywood, could it get soft again, from water intrusion...especially from all the seams you've now created? I know many have done this type of repair with success. Many have done the drill and fill with success. I've never heard of either repair failing so I guess this is all acedemic!
happy sails!
What kind of material do you have when you take saw dust (dryed, rotten wood)and soak it with epoxy? Can you stand on it? Will it ever get soft again? Does it have shear strength? Who cares, you don't need shear strength! If you replace the core with fresh balsa or plywood, could it get soft again, from water intrusion...especially from all the seams you've now created? I know many have done this type of repair with success. Many have done the drill and fill with success. I've never heard of either repair failing so I guess this is all acedemic!
happy sails!Hans
Hans, I think I see your point, but, I suspect that the "arch" effect is minimal in most cases and we must consider the deck to be more of a plane in which case the lower skin must withstand "streching" as opposed to compression. I do see that the top skin must withstand compression and agree that adhesion is not a problem. So now tell me why this type of repair is supperior to injecting epoxy? I realize it makes us "feel good" to get that rotted woud out and replaced with new wood. Or perhaps the size of the project, time, material ect makes those that have done it that way convinced it must be the best..IE, medicine must taste bad to work. After doing such a project, I can't imagine how bad I would feel when realizing I could have just drilled a few holes and injected some glue to get a comparable or better repair
Hans, I think I see your point, but, I suspect that the "arch" effect is minimal in most cases and we must consider the deck to be more of a plane in which case the lower skin must withstand "streching" as opposed to compression. I do see that the top skin must withstand compression and agree that adhesion is not a problem. So now tell me why this type of repair is supperior to injecting epoxy? I realize it makes us "feel good" to get that rotted woud out and replaced with new wood. Or perhaps the size of the project, time, material ect makes those that have done it that way convinced it must be the best..IE, medicine must taste bad to work. After doing such a project, I can't imagine how bad I would feel when realizing I could have just drilled a few holes and injected some glue to get a comparable or better repair
Thats what makes this fun
There is no one way to fix this problem. Alot depends on the size of the area that is damaged. On a small area the drill and fill method will probably work but on a large area, I believe you need to remove the damaged area and rebuild. You might go to good old boat and search the archives for the article i referred to. It has some pictures and gives you some good information to base a decision. craig The article is written by Bill Sandifer and is titled "Delamination is not spelled d-o-o-m" check it out.It is from the nov/dec issue of good old boat magazine. He is a marine surveyor and has been messing around with boats since the early 50's so i would think he is qualified.
There is no one way to fix this problem. Alot depends on the size of the area that is damaged. On a small area the drill and fill method will probably work but on a large area, I believe you need to remove the damaged area and rebuild. You might go to good old boat and search the archives for the article i referred to. It has some pictures and gives you some good information to base a decision. craig The article is written by Bill Sandifer and is titled "Delamination is not spelled d-o-o-m" check it out.It is from the nov/dec issue of good old boat magazine. He is a marine surveyor and has been messing around with boats since the early 50's so i would think he is qualified.
One engineer's view . . . why decks are cored
Decks are cored to increase stiffness, i.e. resistance to deformation under load. Other benefits include thermal and acoustic insulation. Deck stiffness depends on several things, including: a) tensile and compressive strength of the skins. Under load (weight), the upper skin undergoes compression (in the plane of the skin, i.e. horizontally) and the lower skin goes into tension, also in its plane. The core goes into compression. There is also some shear, but most of that is taken by the skins. b) the distance between the skins, i.e., the core thickness c) compressive strength of the core material Since this is about the core, I won't discuss skins further except to say that fiberglass is an excellent material for skins. The thicker the core, the farther apart the skins and the stiffer the deck (it's a property called "moment of inertia" which I won't get into). Thicker decks also insulate better. However, a thicker core means more material and more weight. Balsa wood is ideal because of its light weight and surprising compressive strength. It's also affordable and very easy to work. For the deck to remain stiff, the core must retain its compressive strength AND remain bonded to both the upper and lower skin. Rot destroys both properties. Most people inject epoxy in a rotted core because it (hopefully) will fill all the voids (maintaining the distance between the skins) and restore the bond. It's also quick, easy and inexpensive. The penalty is added weight, which is most sailors can live with for small scale repairs. However, if there is a lot of rot, the hassle, cost and weight of injecting epoxy through holes in the skin begin to override the convenience. At this tage, the approach would be to cut a panel out of the upper/outer skin and replace the core. Removing the upper skin makes sense because it's more accessible, the interior of the boat won't get messed up, the watertightness of the lower skin is not compromised and gravity works in your favor when it's time to seal the core with resin and replace the upper skin. When the repaired deck is loaded, compressive stresses in the upper skin also help keep the joint closed between the old and new sections of upper skin. Good Old Boat, BoatUS and other websites have lots of information on the finer points of repairing rotted decks. Good luck. Peter H23 "Raven"
Decks are cored to increase stiffness, i.e. resistance to deformation under load. Other benefits include thermal and acoustic insulation. Deck stiffness depends on several things, including: a) tensile and compressive strength of the skins. Under load (weight), the upper skin undergoes compression (in the plane of the skin, i.e. horizontally) and the lower skin goes into tension, also in its plane. The core goes into compression. There is also some shear, but most of that is taken by the skins. b) the distance between the skins, i.e., the core thickness c) compressive strength of the core material Since this is about the core, I won't discuss skins further except to say that fiberglass is an excellent material for skins. The thicker the core, the farther apart the skins and the stiffer the deck (it's a property called "moment of inertia" which I won't get into). Thicker decks also insulate better. However, a thicker core means more material and more weight. Balsa wood is ideal because of its light weight and surprising compressive strength. It's also affordable and very easy to work. For the deck to remain stiff, the core must retain its compressive strength AND remain bonded to both the upper and lower skin. Rot destroys both properties. Most people inject epoxy in a rotted core because it (hopefully) will fill all the voids (maintaining the distance between the skins) and restore the bond. It's also quick, easy and inexpensive. The penalty is added weight, which is most sailors can live with for small scale repairs. However, if there is a lot of rot, the hassle, cost and weight of injecting epoxy through holes in the skin begin to override the convenience. At this tage, the approach would be to cut a panel out of the upper/outer skin and replace the core. Removing the upper skin makes sense because it's more accessible, the interior of the boat won't get messed up, the watertightness of the lower skin is not compromised and gravity works in your favor when it's time to seal the core with resin and replace the upper skin. When the repaired deck is loaded, compressive stresses in the upper skin also help keep the joint closed between the old and new sections of upper skin. Good Old Boat, BoatUS and other websites have lots of information on the finer points of repairing rotted decks. Good luck. Peter H23 "Raven"
Thanks Peter
Just the kind of explanation I was looking for. Makes sense. You've won me over. I will make sure I don't buy a boat with that much of a problem so I never have to cut up my deck! (Famous last words) Don
Just the kind of explanation I was looking for. Makes sense. You've won me over. I will make sure I don't buy a boat with that much of a problem so I never have to cut up my deck! (Famous last words) Don
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