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#1
posted to rec.boats.building
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Can 3/8" Balsa Core Go Over 35" Span on Deck Without Structural Bracing?
Does anyone know whether 3/8" balsa core material (sandwiched between
fiberglass skins) can go over a 35" span on a deck without any structural bracing? One area of the deck has some water damage and is "kind of" delaminated. The problem may be coming from an improperly sealed inspection hole. I am trying to drill many holes on the deck and inject thickened epoxy into the core to fix the damage. But I discover that the balsa core is only 3/8" thick (the thickness of the deck with core and skins is only 1/2"), and it needs to go over a 35" span in one direction without any structural bracing (the span over the other direction is around 9 feet without any structural bracing). Before I spend time injecting epoxy and all this, I need to figure out if 3/8" balsa core is strong enough to go over a 35" span. If this is not strong enough, I will have to abandon this project and leave bad enough alone (I don't have access to the bottom of the deck to add structural bracing); the reason is that the problem will come back even if I fix it with injection of epoxy. Any idea? Thanks in advance for any info. Jay Chan |
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#2
posted to rec.boats.building
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Can 3/8" Balsa Core Go Over 35" Span on Deck Without Structural Bracing?
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#3
posted to rec.boats.building
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Can 3/8" Balsa Core Go Over 35" Span on Deck Without Structural Bracing?
rhys wrote:
On 26 Apr 2006 08:04:31 -0700, wrote: Does anyone know whether 3/8" balsa core material (sandwiched between fiberglass skins) can go over a 35" span on a deck without any structural bracing? One area of the deck has some water damage and is "kind of" delaminated. The problem may be coming from an improperly sealed inspection hole. I am trying to drill many holes on the deck and inject thickened epoxy into the core to fix the damage. But I discover that the balsa core is only 3/8" thick (the thickness of the deck with core and skins is only 1/2"), and it needs to go over a 35" span in one direction without any structural bracing (the span over the other direction is around 9 feet without any structural bracing). Before I spend time injecting epoxy and all this, I need to figure out if 3/8" balsa core is strong enough to go over a 35" span. If this is not strong enough, I will have to abandon this project and leave bad enough alone (I don't have access to the bottom of the deck to add structural bracing); the reason is that the problem will come back even if I fix it with injection of epoxy. Any idea? Thanks in advance for any info. A question: Why use balsa core at all, knowing what you know? You could use foam core and encapsulated marine plywood for the deck gear through-bolted spots. Balsa core was a great solution to the overkill, heaviness and structural problems of all glass decks, but there are so many better options these days. R. I am under the impression that the replacement core material for patching is better off to be the same as the original core material. Then the repaired area and the surrounding unrepaired area will have the same rigidity; in case the deck flexes for some reason, we will not have crack along the edge of the patched area. Anyway, I haven't decided on whether I should replace the balsa core in the delaminated area. I am still hoping that I can simply injecting thickened epoxy to re-laminate the balsa core back to the skins -- as long as the 3/8" balsa core can handle a span of 35". Therefore, I was not thinking of replacing the core material. Having said that, do you think a piece of 3/8" marine plywood can go over a 35" span without intermediate bracing? What I am trying to get at is to see if the delamination problem that I have is the result of this situation # 1: Under-strength deck -- Excessive flexing -- Break the seal around the inspection hole -- Water intrusion and delamination Or the situation # 2: Improper sealing around the inspection hole -- Water intrusion and delamination -- Excessive flexing If I have the situation #2, I will attempt to inject thickened epoxy around the inspection hole, and to re-laminate the area. If I have the situation #1, I will have to find a way to strengthen the area, not just re-laminating the area as long as I still want to use balsa core. And that can be tricky because I don't have access to the under-side of the deck, and I cannot add structural bracing in that area. In this case, I will really hope that I can find some core material that is stronger than balsa core. And that brings us to my original question: Can 3/8" balsa core go over 35" span without intermediate bracing? Jay Chan |
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#5
posted to rec.boats.building
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Can 3/8" Balsa Core Go Over 35" Span on Deck Without Structural Bracing?
Also of interest would be where and how big the inspection plate hole is.
"Matt Colie" wrote in message ... Jay, You have a lot going on and you have only asked half the question. Can 3/8 balsa core span 35" - yes - but you have not included the weight of the glass on both sides, the expected load on the span and the allowable deflection of the span. Why can't you get on the other side to add structure? Trying to inject epoxy to cause a core that has more than a 5% moisture content is a lost cause and will only make the inevitable future repair more difficult. The fact that it was originally 3/8 balsa core does not mean that this is what it should be. The real problem was caused by the improperly prepared penetration of the cored structure. Because the strength of the structure is a result of both the skin stiffness and the effectiviness of the core to couple the load between the two skins, endgrain balsa is very hard to beat. Marine plywood will make a stiffer structure - all other things being equal- but it is very poor in the area of water intrusion because the grain allows moisture that does enter to flow latterally in the core. I have done a lot of core repairs and am very willing to guide you if you present the whole picture here. Matt Colie wrote: rhys wrote: On 26 Apr 2006 08:04:31 -0700, wrote: Does anyone know whether 3/8" balsa core material (sandwiched between fiberglass skins) can go over a 35" span on a deck without any structural bracing? One area of the deck has some water damage and is "kind of" delaminated. The problem may be coming from an improperly sealed inspection hole. I am trying to drill many holes on the deck and inject thickened epoxy into the core to fix the damage. But I discover that the balsa core is only 3/8" thick (the thickness of the deck with core and skins is only 1/2"), and it needs to go over a 35" span in one direction without any structural bracing (the span over the other direction is around 9 feet without any structural bracing). Before I spend time injecting epoxy and all this, I need to figure out if 3/8" balsa core is strong enough to go over a 35" span. If this is not strong enough, I will have to abandon this project and leave bad enough alone (I don't have access to the bottom of the deck to add structural bracing); the reason is that the problem will come back even if I fix it with injection of epoxy. Any idea? Thanks in advance for any info. A question: Why use balsa core at all, knowing what you know? You could use foam core and encapsulated marine plywood for the deck gear through-bolted spots. Balsa core was a great solution to the overkill, heaviness and structural problems of all glass decks, but there are so many better options these days. R. I am under the impression that the replacement core material for patching is better off to be the same as the original core material. Then the repaired area and the surrounding unrepaired area will have the same rigidity; in case the deck flexes for some reason, we will not have crack along the edge of the patched area. Anyway, I haven't decided on whether I should replace the balsa core in the delaminated area. I am still hoping that I can simply injecting thickened epoxy to re-laminate the balsa core back to the skins -- as long as the 3/8" balsa core can handle a span of 35". Therefore, I was not thinking of replacing the core material. Having said that, do you think a piece of 3/8" marine plywood can go over a 35" span without intermediate bracing? What I am trying to get at is to see if the delamination problem that I have is the result of this situation # 1: Under-strength deck -- Excessive flexing -- Break the seal around the inspection hole -- Water intrusion and delamination Or the situation # 2: Improper sealing around the inspection hole -- Water intrusion and delamination -- Excessive flexing If I have the situation #2, I will attempt to inject thickened epoxy around the inspection hole, and to re-laminate the area. If I have the situation #1, I will have to find a way to strengthen the area, not just re-laminating the area as long as I still want to use balsa core. And that can be tricky because I don't have access to the under-side of the deck, and I cannot add structural bracing in that area. In this case, I will really hope that I can find some core material that is stronger than balsa core. And that brings us to my original question: Can 3/8" balsa core go over 35" span without intermediate bracing? Jay Chan |
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#6
posted to rec.boats.building
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Can 3/8" Balsa Core Go Over 35" Span on Deck Without Structural Bracing?
The inspection hole is 6".
This inspection hole is at the highest point of the damaged area. Seem like water got into the core through the inspection hole and went downstream from there. The inspection hole that I suspect is the source of the problem is located right behind the captain-seat/cooler combo. This problem may have to do with the combined weight of the seat/cooler and two persons "may" be pushing the 1/2" deck to the limit. When the boat was pounding in the water, the total force acted on the deck might just exceed what the deck could handle, and caused the deck to deflect. The deck deflection might have cracked the flange of the inspection hole and broke the seal around the inspection hole. That allowed water to get in. When the ex-owner of the boat replaced the cracked flange, he might not have fully sealed the flange (25% of the seal under the flange is missing). That made the situation even worse. And the boat was likely not covered; that allowed rain water to intrude into the core. Thanks for bring the location of the inspection hole to my attention. Now, I need to not only strengthen the area that is damaged, but also I need to strengthen the area under the captain-seat/cooler (that is currently not damaged). That is to prevent its weight from causing the deck to deflect and crack the flange of the inspection hole, and repeat the cycle of this problem. I am glad that I ask around here before I blindly inject epoxy into the core. Otherwise, I might have fixed the symptom, but not the cause. Jay Chan Garland Gray II wrote: Also of interest would be where and how big the inspection plate hole is. "Matt Colie" wrote in message ... Jay, You have a lot going on and you have only asked half the question. Can 3/8 balsa core span 35" - yes - but you have not included the weight of the glass on both sides, the expected load on the span and the allowable deflection of the span. Why can't you get on the other side to add structure? Trying to inject epoxy to cause a core that has more than a 5% moisture content is a lost cause and will only make the inevitable future repair more difficult. The fact that it was originally 3/8 balsa core does not mean that this is what it should be. The real problem was caused by the improperly prepared penetration of the cored structure. Because the strength of the structure is a result of both the skin stiffness and the effectiviness of the core to couple the load between the two skins, endgrain balsa is very hard to beat. Marine plywood will make a stiffer structure - all other things being equal- but it is very poor in the area of water intrusion because the grain allows moisture that does enter to flow latterally in the core. I have done a lot of core repairs and am very willing to guide you if you present the whole picture here. Matt Colie wrote: rhys wrote: On 26 Apr 2006 08:04:31 -0700, wrote: Does anyone know whether 3/8" balsa core material (sandwiched between fiberglass skins) can go over a 35" span on a deck without any structural bracing? One area of the deck has some water damage and is "kind of" delaminated. The problem may be coming from an improperly sealed inspection hole. I am trying to drill many holes on the deck and inject thickened epoxy into the core to fix the damage. But I discover that the balsa core is only 3/8" thick (the thickness of the deck with core and skins is only 1/2"), and it needs to go over a 35" span in one direction without any structural bracing (the span over the other direction is around 9 feet without any structural bracing). Before I spend time injecting epoxy and all this, I need to figure out if 3/8" balsa core is strong enough to go over a 35" span. If this is not strong enough, I will have to abandon this project and leave bad enough alone (I don't have access to the bottom of the deck to add structural bracing); the reason is that the problem will come back even if I fix it with injection of epoxy. Any idea? Thanks in advance for any info. A question: Why use balsa core at all, knowing what you know? You could use foam core and encapsulated marine plywood for the deck gear through-bolted spots. Balsa core was a great solution to the overkill, heaviness and structural problems of all glass decks, but there are so many better options these days. R. I am under the impression that the replacement core material for patching is better off to be the same as the original core material. Then the repaired area and the surrounding unrepaired area will have the same rigidity; in case the deck flexes for some reason, we will not have crack along the edge of the patched area. Anyway, I haven't decided on whether I should replace the balsa core in the delaminated area. I am still hoping that I can simply injecting thickened epoxy to re-laminate the balsa core back to the skins -- as long as the 3/8" balsa core can handle a span of 35". Therefore, I was not thinking of replacing the core material. Having said that, do you think a piece of 3/8" marine plywood can go over a 35" span without intermediate bracing? What I am trying to get at is to see if the delamination problem that I have is the result of this situation # 1: Under-strength deck -- Excessive flexing -- Break the seal around the inspection hole -- Water intrusion and delamination Or the situation # 2: Improper sealing around the inspection hole -- Water intrusion and delamination -- Excessive flexing If I have the situation #2, I will attempt to inject thickened epoxy around the inspection hole, and to re-laminate the area. If I have the situation #1, I will have to find a way to strengthen the area, not just re-laminating the area as long as I still want to use balsa core. And that can be tricky because I don't have access to the under-side of the deck, and I cannot add structural bracing in that area. In this case, I will really hope that I can find some core material that is stronger than balsa core. And that brings us to my original question: Can 3/8" balsa core go over 35" span without intermediate bracing? Jay Chan |
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#7
posted to rec.boats.building
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Can 3/8" Balsa Core Go Over 35" Span on Deck Without Structural Bracing?
I don't know the weight of the glass of the skins. The only thing that
I know is that the total thickness of the deck is 1/2" and the core itself takes 3/8". In other words, the thickness of both skins combined is 1/8". I have a feeling that the skin itself is not thick. I only expect that area to support an adult male (me). As of the allowable deflection, I expect that area to be rigid. The reason is that there are two inspection holes in that area. If the area deflects, the plastic flange of the inspection hole will crack and allow water to get into the core. No, I cannot get to the other side of the deck to add structural bracing. The reason is that the boat is a relatively small boat (18-ft) and there is a gas tank and the bilge area under the deck. The only way to get under the deck is to cut out the deck (the core and both skins), and I will have a hard time to put the bottom skin back. I clearly don't want to do this. No, I will not inject epoxy into the core if I find that the core is still wet. Luckily, I have checked a couple areas in the core material and I find that the core is dry. Having said this, I probably will decide not to inject epoxy into the area; I probably will replace the core completely (mentioned below). You are quite right in saying that there are improperly prepared penetration of the cored. I have checked the area where the screws gets into the core (the screws secured the flange of the inspection hole onto the deck), and I see that each screws was simply screwed into the core material; there is no re-inforcement. No wonder the core material around the inspection hole is totally rotted. When I put the flange of the inspection hole back, I will definitely use through-bolts and use epoxy to replace the core to reinforce the bolts. And I will re-mount all the other inspection holes on the deck to prevent any further problem. Thanks for pointing out that balsa core is a good core material for deck, and thanks for mentioning that the skins also contribute greatly to the rigidity of the deck. Seem like one way that I can fix the problem is to replace the core with a new sheet of balsa core, and add additional fiberglass to strengthen both skins. Hopefully the combined strength of a new balsa core and strong skins will provide enough rigidity to the deck. This means I will need to re-paint the non-skid surface; but this is OK. Sound like I have just got a plan to fix the deck. Great! Jay Chan Matt Colie wrote: Jay, You have a lot going on and you have only asked half the question. Can 3/8 balsa core span 35" - yes - but you have not included the weight of the glass on both sides, the expected load on the span and the allowable deflection of the span. Why can't you get on the other side to add structure? Trying to inject epoxy to cause a core that has more than a 5% moisture content is a lost cause and will only make the inevitable future repair more difficult. The fact that it was originally 3/8 balsa core does not mean that this is what it should be. The real problem was caused by the improperly prepared penetration of the cored structure. Because the strength of the structure is a result of both the skin stiffness and the effectiviness of the core to couple the load between the two skins, endgrain balsa is very hard to beat. Marine plywood will make a stiffer structure - all other things being equal- but it is very poor in the area of water intrusion because the grain allows moisture that does enter to flow latterally in the core. I have done a lot of core repairs and am very willing to guide you if you present the whole picture here. Matt Colie wrote: rhys wrote: On 26 Apr 2006 08:04:31 -0700, wrote: Does anyone know whether 3/8" balsa core material (sandwiched between fiberglass skins) can go over a 35" span on a deck without any structural bracing? One area of the deck has some water damage and is "kind of" delaminated. The problem may be coming from an improperly sealed inspection hole. I am trying to drill many holes on the deck and inject thickened epoxy into the core to fix the damage. But I discover that the balsa core is only 3/8" thick (the thickness of the deck with core and skins is only 1/2"), and it needs to go over a 35" span in one direction without any structural bracing (the span over the other direction is around 9 feet without any structural bracing). Before I spend time injecting epoxy and all this, I need to figure out if 3/8" balsa core is strong enough to go over a 35" span. If this is not strong enough, I will have to abandon this project and leave bad enough alone (I don't have access to the bottom of the deck to add structural bracing); the reason is that the problem will come back even if I fix it with injection of epoxy. Any idea? Thanks in advance for any info. A question: Why use balsa core at all, knowing what you know? You could use foam core and encapsulated marine plywood for the deck gear through-bolted spots. Balsa core was a great solution to the overkill, heaviness and structural problems of all glass decks, but there are so many better options these days. R. I am under the impression that the replacement core material for patching is better off to be the same as the original core material. Then the repaired area and the surrounding unrepaired area will have the same rigidity; in case the deck flexes for some reason, we will not have crack along the edge of the patched area. Anyway, I haven't decided on whether I should replace the balsa core in the delaminated area. I am still hoping that I can simply injecting thickened epoxy to re-laminate the balsa core back to the skins -- as long as the 3/8" balsa core can handle a span of 35". Therefore, I was not thinking of replacing the core material. Having said that, do you think a piece of 3/8" marine plywood can go over a 35" span without intermediate bracing? What I am trying to get at is to see if the delamination problem that I have is the result of this situation # 1: Under-strength deck -- Excessive flexing -- Break the seal around the inspection hole -- Water intrusion and delamination Or the situation # 2: Improper sealing around the inspection hole -- Water intrusion and delamination -- Excessive flexing If I have the situation #2, I will attempt to inject thickened epoxy around the inspection hole, and to re-laminate the area. If I have the situation #1, I will have to find a way to strengthen the area, not just re-laminating the area as long as I still want to use balsa core. And that can be tricky because I don't have access to the under-side of the deck, and I cannot add structural bracing in that area. In this case, I will really hope that I can find some core material that is stronger than balsa core. And that brings us to my original question: Can 3/8" balsa core go over 35" span without intermediate bracing? Jay Chan |
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#8
posted to rec.boats.building
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Can 3/8" Balsa Core Go Over 35" Span on Deck Without StructuralBracing?
wrote:
rhys wrote: On 26 Apr 2006 08:04:31 -0700, wrote: Does anyone know whether 3/8" balsa core material (sandwiched between fiberglass skins) can go over a 35" span on a deck without any structural bracing? One area of the deck has some water damage and is "kind of" delaminated. The problem may be coming from an improperly sealed inspection hole. I am trying to drill many holes on the deck and inject thickened epoxy into the core to fix the damage. But I discover that the balsa core is only 3/8" thick (the thickness of the deck with core and skins is only 1/2"), and it needs to go over a 35" span in one direction without any structural bracing (the span over the other direction is around 9 feet without any structural bracing). Before I spend time injecting epoxy and all this, I need to figure out if 3/8" balsa core is strong enough to go over a 35" span. If this is not strong enough, I will have to abandon this project and leave bad enough alone (I don't have access to the bottom of the deck to add structural bracing); the reason is that the problem will come back even if I fix it with injection of epoxy. Any idea? Thanks in advance for any info. A question: Why use balsa core at all, knowing what you know? You could use foam core and encapsulated marine plywood for the deck gear through-bolted spots. Balsa core was a great solution to the overkill, heaviness and structural problems of all glass decks, but there are so many better options these days. R. I am under the impression that the replacement core material for patching is better off to be the same as the original core material. Then the repaired area and the surrounding unrepaired area will have the same rigidity; in case the deck flexes for some reason, we will not have crack along the edge of the patched area. Anyway, I haven't decided on whether I should replace the balsa core in the delaminated area. I am still hoping that I can simply injecting thickened epoxy to re-laminate the balsa core back to the skins -- as long as the 3/8" balsa core can handle a span of 35". Therefore, I was not thinking of replacing the core material. Having said that, do you think a piece of 3/8" marine plywood can go over a 35" span without intermediate bracing? What I am trying to get at is to see if the delamination problem that I have is the result of this situation # 1: Under-strength deck -- Excessive flexing -- Break the seal around the inspection hole -- Water intrusion and delamination Or the situation # 2: Improper sealing around the inspection hole -- Water intrusion and delamination -- Excessive flexing If I have the situation #2, I will attempt to inject thickened epoxy around the inspection hole, and to re-laminate the area. If I have the situation #1, I will have to find a way to strengthen the area, not just re-laminating the area as long as I still want to use balsa core. And that can be tricky because I don't have access to the under-side of the deck, and I cannot add structural bracing in that area. In this case, I will really hope that I can find some core material that is stronger than balsa core. And that brings us to my original question: Can 3/8" balsa core go over 35" span without intermediate bracing? Jay Chan I would bet $ that you have #2 situation. It's far more typical. But if the core is debonded from the skins, then injecting epoxy is a poor substitute for digging out the core and relaminating it. What you're doing with the epoxy is trying to bond the skins together with little puddles of epoxy. But the balsa gets in the way. For small local delamination caused by the core never really bonding to the skins, injecting epoxy works. But if the core is really wet, it won't work. And yes, 3/8" balsa with proper fiberglass skins can easily span 35" Evan Gatehouse |
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#9
posted to rec.boats.building
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Can 3/8" Balsa Core Go Over 35" Span on Deck Without Structural Bracing?
On Wed, 26 Apr 2006 22:53:17 -0700, Evan Gatehouse
wrote: I would bet $ that you have #2 situation. It's far more typical. I concur. As you are getting far more extensive and experienced advice than I could render, I leave you to what will be a messy job (but done properly) with two comments. 1) Consider marine plywood but only if it is entirely encapsulated. This means sealed, coated, encased ENTIRELY in an epoxy that will repeal all water intrusion. I recommend it due to the ease of getting it close to the right size and shape to replace the core you will likely have to dig out. You can precut the inspection holes before you glass it in, and you can adhere the wood to the inner skin with a "mayonaisse" of epoxy and fibres or microballoons. You can carefully take off the top "skin" and replace it later and paint the surface to match. 2) Don Casey's books on hull and deck repair are excellent and easy to follow. I recommend them. I also recommend talking to other people who've done this work. Good luck. R. |
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#10
posted to rec.boats.building
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Can 3/8" Balsa Core Go Over 35" Span on Deck Without Structural Bracing?
rhys wrote:
On Wed, 26 Apr 2006 22:53:17 -0700, Evan Gatehouse wrote: I would bet $ that you have #2 situation. It's far more typical. I concur. As you are getting far more extensive and experienced advice than I could render, I leave you to what will be a messy job (but done properly) with two comments. 1) Consider marine plywood but only if it is entirely encapsulated. This means sealed, coated, encased ENTIRELY in an epoxy that will repeal all water intrusion. I recommend it due to the ease of getting it close to the right size and shape to replace the core you will likely have to dig out. You can precut the inspection holes before you glass it in, and you can adhere the wood to the inner skin with a "mayonaisse" of epoxy and fibres or microballoons. You can carefully take off the top "skin" and replace it later and paint the surface to match. 2) Don Casey's books on hull and deck repair are excellent and easy to follow. I recommend them. I also recommend talking to other people who've done this work. Good luck. R. Thanks for pointing out the various advantage of using marine plywood as core material. It is supposed to be more rigid than balsa core if I understand this correctly. Yes, I have the Don Casey's with me along with the Fiberglass Boat Repair and Maintenance book from West System. They are great. Jay Chan |
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