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Composite stringer grids
Many manufacturers are touting "no wood/no rot" construction, and some are
using a composite grid system (fiberglass over some type of foam) to replace traditional hull stringers and forms. Several bay boats I am interested in use this type of construction. Of course, from a marketing perspective, it sounds great. But I'd be interested in some real world opinions. Is such a boat less prone to flex? Does it result in a more solid boat? Are there other problems to be aware of? Any pre-purchase inspections that can be accomplished, assuming it's even possible to see the below-deck structure? Comments appreciated. -- Rich Stern www.nitroowners.com - The Nitro and Tracker Owners Web Site www.mypontoon.com - The Pontoon Boat Web Site www.fishingreportdatabase.com - The Fishing Report Database www.mysporttrac.com - The Sport Trac Web Site |
Composite stringer grids
Rich Stern wrote:
Many manufacturers are touting "no wood/no rot" construction, and some are using a composite grid system (fiberglass over some type of foam) to replace traditional hull stringers and forms. Several bay boats I am interested in use this type of construction. Of course, from a marketing perspective, it sounds great. But I'd be interested in some real world opinions. OK Is such a boat less prone to flex? Than what? It is certainly less prone ot flex than the same hull with the same layup and no grid of any type. Is it less prone to flex than the same hull & grid with wood as the grid core? No, because wood is stiffer than foam. In order for the grid to be stiffer due to the foam, then either the hull or the grid (or both) have to be of stiffer construction such as triaxial weave, vacuum bagged, etc etc. Does it result in a more solid boat? Not necessarily. If the grid is not laminated properly then it may not even last longer. Foam doesn't rot but some types can become saturated and all types can delaminate. Some people hate foam core construction, probably because there are so many bad examples that have long term problems. But it can be a great type of construction *if* the details are properly done. Are there other problems to be aware of? Any pre-purchase inspections that can be accomplished, assuming it's even possible to see the below-deck structure? There are a number of things to inspect that indicate good quality work. Without a lot of details plus pictures, it's difficult to compress 'how to do a structural survey' into one usenet post. I'm not the greatest expert anyway. http://boatdesign.net/articles/foam-core-properties/ Some resources on the web, another good place to look would be in your nearest library in books on surveying boats. Some people will say 'foam core = crap' and they probably have some bad experiences with poorly done foam core. Like anything else, there is good and bad. When it's good, foam core construction can be very very good. Fair Skies- Doug King |
Composite stringer grids
Karl Denninger wrote:
2. Cores in decks and hullsides (above the waterline) are acceptable, PROVIDED they are properly encapsulated. This means that there are NO PENETRATIONS without the edges of the core being sealed with epoxy. No way for water to get in, no problems. Note that this means that hardware must be THROUGH BOLTED; screwing it down into a cored structure is NOT ACCEPTABLE. Agreed, but then thru-bolting hardware through a core is also not acceptable. The compression will deform the core, and then of course water gets in, plus some helpful person usually tightens the bolts after a while and that makes it worse. Core should be tapered to a solid laminate where there is hardware thru-bolted. Fair Skies- Doug King |
Composite stringer grids
On Tue, 18 Nov 2003 18:43:02 -0500, DSK wrote:
Core should be tapered to a solid laminate where there is hardware thru-bolted. +++++++++++++++++++++++++++++++++++++++++++++++++ That works of course, but there are other ways. Drilling an over size hole, coating exposed core with epoxy resin, refilling with solid glass, and then redrilling is a perfectly acceptable method of ensuring core integrity and absorbing compression loads. |
Composite stringer grids
If your stringer is relying on the wood core for strength, it's poorly built.
The wood core, foam core, Cheez Whiz core or whatever has served its purpose when it has functioned as a form for the layers of glass and resin that follow. A well engineered stringer can be completely hollow, just like a box beam, and have more than sufficient strength. |
Composite stringer grids
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Composite stringer grids
Wally,
Okay, but were the Silverton's stringers wood core or foam? Paul "WaIIy" wrote in message ... On 18 Nov 2003 21:18:00 GMT, (Rich Stern) wrote: Many manufacturers are touting "no wood/no rot" construction, and some are using a composite grid system (fiberglass over some type of foam) to replace traditional hull stringers and forms. Several bay boats I am interested in use this type of construction. Of course, from a marketing perspective, it sounds great. But I'd be interested in some real world opinions. Is such a boat less prone to flex? Does it result in a more solid boat? Are there other problems to be aware of? Any pre-purchase inspections that can be accomplished, assuming it's even possible to see the below-deck structure? Comments appreciated. My 30ft 1989 Tollycraft has foamed stringers and it's solid as a rock. My friend has a 1989 30ft Silverton and he replaced half the stringers he could get to. Your mileage will vary. |
Composite stringer grids
Chuck,
Okay then why the concern over rotted wood in the stringer? I would imagine that the water got in through a poor job of sealing the wooden stringer, so why not seal it up and not worry about it? But does an older boat like an 89 Sea Ray depend on the wood for its strength or the fiberglass coating? I know a fellow that had his boat (88 Sea Ray 300 Weekender) out of the water for three seasons while he dried out his stringers and checked for moisture with a meter. I think he then bored some holes in the stringer and filled with epoxy. Was he wasting his time? His complaint was that Sea Ray drilled limber holes through the stringers and didn't seal the limber holes causing the water absorption. I'm just trying to determine how wide and important of a problem is this. Paul "Gould 0738" wrote in message ... If your stringer is relying on the wood core for strength, it's poorly built. The wood core, foam core, Cheez Whiz core or whatever has served its purpose when it has functioned as a form for the layers of glass and resin that follow. A well engineered stringer can be completely hollow, just like a box beam, and have more than sufficient strength. |
Composite stringer grids
DSK wrote:
Core should be tapered to a solid laminate where there is hardware thru-bolted. +++++++++++++++++++++++++++++++++++++++++++++++++ "Wayne.B" wrote: That works of course, but there are other ways. Drilling an over size hole, coating exposed core with epoxy resin, refilling with solid glass, and then redrilling is a perfectly acceptable method of ensuring core integrity and absorbing compression loads. Sure, but you have to do that yourself. I thought we were talking about fromt the factory. Karl Denninger wrote: Uh, and use a backing plate. Even better, build the backing plate into the hull in place of the core in that spot. But if it's in the center, it's not a backing plate ;) It has to be underneath both the tension & compression skins of the deck structure. I read a description of an uncored but very light & strong boat hull, which had a "subimposed" structural grid. Anybody have any good ideas what that means? Fresh Breezes- Doug King |
Composite stringer grids
On Thu, 20 Nov 2003 03:44:31 +1100, K Smith wrote:
Wood is not a very strong material at all. Tougher hardwoods have very moderate strength in compression, but other than that wood is a very weak material with low resistance to flexing+ ================================================== == Not at all true, wood has a very high strength to weight ratio. You are confusing strength with stiffness. They are two entirely different properties. |
Composite stringer grids
Karl Denninger wrote:
In article , Rich Stern wrote: Many manufacturers are touting "no wood/no rot" construction, and some are using a composite grid system (fiberglass over some type of foam) to replace traditional hull stringers and forms. Several bay boats I am interested in use this type of construction. Of course, from a marketing perspective, it sounds great. But I'd be interested in some real world opinions. Is such a boat less prone to flex? Does it result in a more solid boat? Are there other problems to be aware of? Any pre-purchase inspections that can be accomplished, assuming it's even possible to see the below-deck structure? Comments appreciated. Sure - it sucks. Here's the problem - no access at all to it, But the lack of access applies no matter the stringer materials, so there's no particular disadvantage. and the problem with wood is NOT that its wood. Wood is not a very strong material at all. Tougher hardwoods have very moderate strength in compression, but other than that wood is a very weak material with low resistance to flexing & even worse performance in tension. i.e. bend a piece of wood to simulate a load in the middle; one side is in compression & the other is in tension. The wood will bend easily & a great deal, it will usually then break as the tension side fails. So I'd like to submit the problem with wood is that it's wood. Most anything designed in wood is strength for strength much much heavier than almost any other material, steel, glass, even ferro. This is because the material is inherently weak & this weakness is aggravated by the difficulties of attaching it to anything, even itself (mechanical fastenings, nuts & bolts are about the only real fix) Here's how damage REALLY happens to a cored structu 1. Some small amounts of water get in there due to improper sealing of the core. Closed cell foam, which structural core foams use, don't absorb moisture. There are specific standards & test procedures to verify this, so this can only happen if the wrong foam for the application is used. 2. Wave action and boat motion cause the two panels to compress against the core. This is a NORMAL process. But with that small amount of water in there, it will NOT compress. It thus acts like a hydraulic ram, deforming the core. It might be a "normal" process when you glass over wood because resins will not ever properly bond to wood, but foams are different, the foam material provides an excellent mechanical key to bond with the resin, increasing the notional bonding area many times over AND the foam is a plastic just as the resin in the covering is, giving a chemical bond as well, so again proper choice of materials means there is no so-called "pumping". 3. The panels "relax"; there is now a vacuum in the space. Since it is not cmopletely sealed, it draws in more water. I'm only reviewing this so it's up to whatever you want to make of it, but gees louise; it's a vacuum?? & then water can get in?? This is a good description of how water gets into timber stringers but ....... 4. Complete, just like a jackhammer, until the core integrity is destroyed. 5. If the core is wood, it will EVENTUALLY rot, but the damage to the fiber and bonding - the PRIMARY damage - had nothing to do with that. Note that synthetic cores will delaminate MORE READILY than wood, as they have NOWHERE NEAR the strength of wood in terms of resistance to compression damage. Wood will rot as suggested but it rots because it's wood & wet wood. The foam will never rot even if it gets wet. How do you avoid this? Simple. 1. Don't do that. Specifically, NO CORES IN HULL BOTTOMS. Ever. The racing boats still use full foam construction for ultimate lightness vs strength, however use of cored scantlings below the water have not been in favour for many years as suggested. However in this discussion I thought we were NOT talking the entire skin just a prefab foam cored stringer/frame system?? 2. Cores in decks and hullsides (above the waterline) are acceptable, PROVIDED they are properly encapsulated. This means that there are NO PENETRATIONS without the edges of the core being sealed with epoxy. No way for water to get in, no problems. Note that this means that hardware must be THROUGH BOLTED; screwing it down into a cored structure is NOT ACCEPTABLE. No bill 3. IF these rules are followed, then wood is a SUPERIOR coring material, particularly, for decks, end-grain balsa. It has inherent rot resistance and is a LOT stronger than PVC or Divynicell cores, and its very light. Plywood makes the best transom cores; nothing else comes close in terms of structural strength. Balsa wood is about the same as other timbers for strength, the devotees pretend it's stronger , but for equal weights of material to carry an equal load, balsa isn't all that special & being timber it's basically a weak material just waiting around a while till it rots. Stringers, ideally, should not have a core in them at all. The best stringer systems are hollow fiberglass "top hat" designs. Those can NEVER rot and, properly engineered, are hellishly strong. They're also rare as hell; only a few production builders have ever used them. Not so rare all benatuas are built on a hollow all glass boxed grid system. The issue is how any stringer or frame system is attached to the skin, again glass or foam will always bond better than any timber. Stringers should not derive their strength from the core; I'd like to also disagree with this if I may. Hollow sections are never as strong as three dimensional webbed or bulkheaded sections. i.e. say in steel a rolled hollow section (RHS) of a given weight is never as strong as as a universal column (RSJ) of the same weight. This is because the top & bottom flanges can better do their respective compression & tension jobs when held apart & kept parallel by the central web. Hollow sections buckle like well... a hollow section:-) In foam construction the foam becomes the "web" it holds the two skins (flanges) apart AND (not hollow) timber beam (or stringer) operates the same way, in any cross section when under load (if you could slice it like bread); (i) one side the wood's cells would be in compression (ii) the outer surface would have the most compression acting upon them, (iii) as you looked further down the slice you'd see the compressive force getting less & less till around the centre there would be no load whatsoever (as if there were no load on the beam at all) then, (iv) as you proceeded further down the wood cells would start to see a tension force trying to pull them apart & (v) this force will increase till at it's maximum at the other outer edge. Hollow uncored beams can work but only if they're wall thickness is excessive OR they're fitted with bulkheads or frames at appropriate intervals, to keep the outer load carrying parts of the beam from buckling or moving relative to each other. (the reason bamboo is so strong relative to it's weight?? it has bulkheads/ring frames & is also better than ordinary wood in tension) should be short and wide rather than tall and narrow. If you have to core them, Marine XL plywood is a good choice, Any sort of wood makes a bad "core" because it can never properly bond to & therefore position & transfer load across to the surrounding load carrying sections; all it can do is act as a spacer & a heavy wet rotting one at that:-) but its not necessary for virtually all boats as a properly engineered stringer doesn't need a core for strength - you can use CARDBOARD - just to hold things in place while the resin cures! If you are using completely hollow stringers or structural members thats fine, however again; you'll need to design them thick walled (& heavy) enough to resist deformation (with glass mostly it's compression force buckling) & if you do that then it will weigh more than the same strength using a closed cell structural foam core or if you choose bulkheading &/or frames. K -- |
Composite stringer grids
Chuck,
Okay then why the concern over rotted wood in the stringer? Depends on the stringer. Did the manufacturer intend to have an FRP stringer that just happens to to have a wood or foam core, or did the mfg put 3/32 inch of glass to "encapsulate" a wooden stringer where the wood was actually bearing the stress? I would imagine that the water got in through a poor job of sealing the wooden stringer, so why not seal it up and not worry about it? See above. I've attended surveys where a decayed stringer core has been detected, and in some cases the stringer is condemned as a result and in others it is not. I know a fellow that had his boat (88 Sea Ray 300 Weekender) out of the water for three seasons while he dried out his stringers and checked for moisture with a meter. Hooooo, boy. Find out whatever it is that guy wants to buy and go into the business of selling it to him. You can't "dry out" decay. Each case is different, but a stringer repair should be doable in a matter of days, not years. I'm aware of situations where the stringer has been sliced open, the old core excavated, new core material substituted, and the whole works glassed back up. Another cure that surveyors have signed off on, (again, depends on the stringer), involves building up the laminate to increase the load bearing ability of the stringer perimeter. I think he then bored some holes in the stringer and filled with epoxy. Was he wasting his time? Three years to do a cheap and dirty Git-Rot fix? Yeah, he was wasting his time. :-) His complaint was that Sea Ray drilled limber holes through the stringers and didn't seal the limber holes causing the water absorption. I'm just trying to determine how wide and important of a problem is this. Paul Unsealed limber holes are fairly common in production boats. :-( It is a bit griping how so many builders, (not just a few) turn out a product that will maintain fair to good structural integrity for 12-15 years, and then price it at $250k or up- and the typical buyer needs a 20-year mortgage to pay for it. |
Composite stringer grids
WaIIy wrote:
On Wed, 19 Nov 2003 10:15:12 -0500, Wayne.B wrote: On Thu, 20 Nov 2003 03:44:31 +1100, K Smith wrote: Wood is not a very strong material at all. Tougher hardwoods have very moderate strength in compression, but other than that wood is a very weak material with low resistance to flexing+ ================================================ ==== Not at all true, wood has a very high strength to weight ratio. You are confusing strength with stiffness. They are two entirely different properties. Well, for the most part, she wrote a great post. How would *you* know that, Wally? -- Email sent to is never read. |
Composite stringer grids
"Harry Krause" wrote in message news:c3dhc2g=.82627d12784c03afb2097e72f24ffd36@106 9256316.cotse.net... K Smith wrote: Really? Gosh. There probably are 100 million wood frame houses in the united states, some more than 100 years old. I suppose that because of the weakness of wood and the difficulties of attaching it to anyting, even itself, are really problematical, eh? Don't twist those houses or they fall down. Don't suddenly lower the pressure...the nails come out. Don't let the weather barrier get compromised or they rot. Don't compare house construction to boat construction. They don't even come close. |
Composite stringer grids
I suggest you take a look at some standard floor joist simple span tables
and see just what it takes to span 10 feet. Conventional wood is not very resistant to flexing. A lot of other things are stronger. An all composite, no wood boat is a lot better than one with wood in it. Just because a lot of boats have been made with wood does not make it good. It just means it is cheap and easy. "Harry Krause" wrote in message news:c3dhc2g=.82627d12784c03afb2097e72f24ffd36@106 9256316.cotse.net... K Smith wrote: Wood is not a very strong material at all. Bull****. Wood is a very strong material when used appropriately. Tougher hardwoods have very moderate strength in compression, but other than that wood is a very weak material with low resistance to flexing & even worse performance in tension. i.e. bend a piece of wood to simulate a load in the middle; one side is in compression & the other is in tension. Yeah? Tell you what. Envision a wood stringer, say 2"x10"x16'. Tip it on its edge. Now, try to bend it in the up or down plane with any load similar to what you might find in a working hull. Now, build that 2x10 into an eggcrate sort of structure, with cross members of the same or similar material. Now subject that structure to lateral loads. Doesn't bend that way either. This is real world construction here, Karen, not some crap you lifted off a web site. The wood will bend easily & a great deal, it will usually then break as the tension side fails. So I'd like to submit the problem with wood is that it's wood. The problem isn't wood in boats. It is the wood between your ears. Most anything designed in wood is strength for strength much much heavier than almost any other material, steel, glass, even ferro. This is because the material is inherently weak & this weakness is aggravated by the difficulties of attaching it to anything, even itself (mechanical fastenings, nuts & bolts are about the only real fix) Really? Gosh. There probably are 100 million wood frame houses in the united states, some more than 100 years old. I suppose that because of the weakness of wood and the difficulties of attaching it to anyting, even itself, are really problematical, eh? It might be a "normal" process when you glass over wood because resins will not ever properly bond to wood You ought to send your resume to Grady-White. I'm sure they'd be interested in hiring you because in your opinion, the boats they build are likely to fall apart any moment; their stringers are constructed of XL plywood covered in fiberglass. But what could Grady-White know about boat=building, compared to the Australian bull**** artist, Karen Elizabeth Smith? I'd like to also disagree with this if I may. Hollow sections are never as strong as three dimensional webbed or bulkheaded sections. i.e. say in steel a rolled hollow section (RHS) of a given weight is never as strong as as a universal column (RSJ) of the same weight. An important principle to keep in mind when building small boats, eh? More Karen lifts from engineering webpages, but no understanding of materials or applications. -- |
Composite stringer grids
Mole wrote:
"Harry Krause" wrote in message news:c3dhc2g=.82627d12784c03afb2097e72f24ffd36@106 9256316.cotse.net... K Smith wrote: Really? Gosh. There probably are 100 million wood frame houses in the united states, some more than 100 years old. I suppose that because of the weakness of wood and the difficulties of attaching it to anyting, even itself, are really problematical, eh? Don't twist those houses or they fall down. Don't suddenly lower the pressure...the nails come out. Don't let the weather barrier get compromised or they rot. Don't compare house construction to boat construction. They don't even come close. I'm not comparing house construction to boat construction. The point, and perhaps I was too subtle, is that wood frame construction is strong enough for houses, and wood is strong enough for boat stringers, assuming whoever does the design does it properly and the design is correctly implemented and the wood protected. Karen Elizabeth Smith "gets off" on these little tangents of hers, but they mostly are absurd or border on it. Wood is a fine boatbuilding material, and has been for thousands of years. It certainly is "strong enough" to be used as a boatbuilding material. Does wood have shortcomings? Of course it does, but so does every other boatbuilding material. Ms. Smith is quick to castigate for what she perceives to be "problems" in the designs and manufacture of boats generally, and, more typically, boat engines, a position that really is not defensible, if you take a look at the barely floating derelict of a boat she calls her own and the rusting piece of crap "diesel outboard" engine with which she underpowers it. -- Email sent to is never read. |
Composite stringer grids
The problem is that fiberglass is not water proof. Water migrates thru the
fiberglass and soaks the stringer. You can not seal a wood stringer with fiberglass. Epoxy is more likely to keep the stringer dry but it is a lot more expensive so nobody uses it. Even with epoxy any compromise is going to let the water thru. Most are laying enough fiberglass on the stringers to provide the majority of the strength even after the wood gets soft. Some have figured out that they don't really need the wood for strength and switched to foam. The foam is just there to as a form for the glass. I'll bet if you drill a hole around those motor mounts on your Tolly you'll find quite a bit of fiberglass. "WaIIy" wrote in message ... On Wed, 19 Nov 2003 08:40:18 -0500, "Paul Schilter" paulschilter@comcast,dot,net wrote: Chuck, Okay then why the concern over rotted wood in the stringer? I would imagine that the water got in through a poor job of sealing the wooden stringer, so why not seal it up and not worry about it? But does an older boat like an 89 Sea Ray depend on the wood for its strength or the fiberglass coating? I know a fellow that had his boat (88 Sea Ray 300 Weekender) out of the water for three seasons while he dried out his stringers and checked for moisture with a meter. I think he then bored some holes in the stringer and filled with epoxy. Was he wasting his time? His complaint was that Sea Ray drilled limber holes through the stringers and didn't seal the limber holes causing the water absorption. I'm just trying to determine how wide and important of a problem is this. Paul I know the mid 80's Wellcrafts - 34 ft or so- were famous for rotten stringers. It would be interesting to know how much some og the boatmakers rely on the wood in a stringer for strength and just pretty it up with epoxy. I know in my little Tollycraft, it would take a wrecking ball to move the stringers my engines are mounted on. |
Composite stringer grids
Lawrence James wrote:
I suggest you take a look at some standard floor joist simple span tables and see just what it takes to span 10 feet. Conventional wood is not very resistant to flexing. A lot of other things are stronger. Well, of course, but that's not the point, is it? The point is that properly designed, implemented and installed, wood floor joists are strong enough. And that's all they have to be. As to the flexing issues, my house has built-up "truss" joists of wood, and my floors don't flex to the point you'd notice it. Further, large areas of the main and second floors of my house are covered in ceramic and marble tile, installed the usual way, and we have no cracks in the mortar or tile. If there were substantial flexing of the wood subfloor (held up by wood trusses), we'd have some mortar cracks. An all composite, no wood boat is a lot better than one with wood in it. Again, I suggest you take that up with Grady-White and other manufacturers of small pleasure boats who continue to use wood in the construction of their boats. GW can build boats any way it chooses, without worrying too much about price points, since it already is at the top of the price chart. It chooses wood. Just because a lot of boats have been made with wood does not make it good. It just means it is cheap and easy. It's easier to build a small boat's structure of composites or foam. The stuff can come out of a mold and be glued into the boat. No special skills required. -- Email sent to is never read. |
Composite stringer grids
Lawrence James wrote:
The problem is that fiberglass is not water proof. Water migrates thru the fiberglass and soaks the stringer. You can not seal a wood stringer with fiberglass. Epoxy is more likely to keep the stringer dry but it is a lot more expensive so nobody uses it. Even with epoxy any compromise is going to let the water thru. What's the impact of water on XL plywood? -- Email sent to is never read. |
Composite stringer grids
On Wed, 19 Nov 2003 21:28:57 -0500, Harry Krause
wrote: if you take a look at the barely floating derelict of a boat she calls her own and the rusting piece of crap "diesel outboard" engine with which she underpowers it. =============================== Be kind Harry. We all know that the best boat in the world is the one that we own (particularly if its also paid for). |
Composite stringer grids
But there are better materials and most of them are not subject to water
intrusion or rotting. The biggest weakness in most fiberglass boats is the wood. If it was not for the wood a properly constructed fiberglass boat would last forever. Anyone buying a new boat today should be considering no wood models seriously. "Harry Krause" wrote in message ... Lawrence James wrote: I suggest you take a look at some standard floor joist simple span tables and see just what it takes to span 10 feet. Conventional wood is not very resistant to flexing. A lot of other things are stronger. Well, of course, but that's not the point, is it? The point is that properly designed, implemented and installed, wood floor joists are strong enough. And that's all they have to be. As to the flexing issues, my house has built-up "truss" joists of wood, and my floors don't flex to the point you'd notice it. Further, large areas of the main and second floors of my house are covered in ceramic and marble tile, installed the usual way, and we have no cracks in the mortar or tile. If there were substantial flexing of the wood subfloor (held up by wood trusses), we'd have some mortar cracks. An all composite, no wood boat is a lot better than one with wood in it. Again, I suggest you take that up with Grady-White and other manufacturers of small pleasure boats who continue to use wood in the construction of their boats. GW can build boats any way it chooses, without worrying too much about price points, since it already is at the top of the price chart. It chooses wood. Just because a lot of boats have been made with wood does not make it good. It just means it is cheap and easy. It's easier to build a small boat's structure of composites or foam. The stuff can come out of a mold and be glued into the boat. No special skills required. -- Email sent to is never read. |
Composite stringer grids
We're talking about years and years once water has intruded. And it will
intrude. It never drys once soaked. "Harry Krause" wrote in message ... Lawrence James wrote: The problem is that fiberglass is not water proof. Water migrates thru the fiberglass and soaks the stringer. You can not seal a wood stringer with fiberglass. Epoxy is more likely to keep the stringer dry but it is a lot more expensive so nobody uses it. Even with epoxy any compromise is going to let the water thru. What's the impact of water on XL plywood? -- Email sent to is never read. |
Composite stringer grids
Wayne.B wrote:
On Wed, 19 Nov 2003 21:28:57 -0500, Harry Krause wrote: if you take a look at the barely floating derelict of a boat she calls her own and the rusting piece of crap "diesel outboard" engine with which she underpowers it. =============================== Be kind Harry. We all know that the best boat in the world is the one that we own (particularly if its also paid for). No argument from me, but if I were casting aspersions on the boat or engine designs or construction of others, I'd want to be sure that mine was or were of at least standard quality and in reputable condition. Further, the one photo I've seen of her boat, and it isn't a very good photo, shows a craft that looks carvel-built to me, or, maybe clinker-built. Though it could have popped out of a mold that way, it may well be a wood-hulled boat. Looks to be a planing hull, too, or at least semi-displacement. If so, it is grossly underpowered with that rusting hulk of a "diesel" outboard. -- Email sent to is never read. Visit Yo Ho, our Parker fishing boat: http://f1.pg.photos.yahoo.com/hakrause |
Composite stringer grids
Lawrence James wrote:
But there are better materials and most of them are not subject to water intrusion or rotting. The biggest weakness in most fiberglass boats is the wood. If it was not for the wood a properly constructed fiberglass boat would last forever. Anyone buying a new boat today should be considering no wood models seriously. Hmmm. So, I guess no one should be considering boats from Grady, Hatteras, Buddy Davis, Parker and about a ka-zillion others...at least not seriously. Water permeates fiberglass, by the way. And it sure can play havoc with the gel coat. You've not seen a blistered fiberglass boat? That isn't wood popping off the surface. Or foam that has become waterlogged? Now, steel, that's a boatbuilder's material. Treat it properly and keep it properly coated, pay attention to galvanic action and voila! A boat that will last a lifetime. -- Email sent to is never read. |
Composite stringer grids
Harry Krause wrote:
Lawrence James wrote: But there are better materials and most of them are not subject to water intrusion or rotting. The biggest weakness in most fiberglass boats is the wood. If it was not for the wood a properly constructed fiberglass boat would last forever. Anyone buying a new boat today should be considering no wood models seriously. Hmmm. So, I guess no one should be considering boats from Grady, Hatteras, Buddy Davis, Parker and about a ka-zillion others...at least not seriously. Water permeates fiberglass, by the way. And it sure can play havoc with the gel coat. You've not seen a blistered fiberglass boat? That isn't wood popping off the surface. Or foam that has become waterlogged? Now, steel, that's a boatbuilder's material. Treat it properly and keep it properly coated, pay attention to galvanic action and voila! A boat that will last a lifetime. One correction. Hatt converted to all-composite stringers a couple of years ago. Less labor involved. -- Email sent to is never read. |
Composite stringer grids
Wayne.B wrote:
On Thu, 20 Nov 2003 03:44:31 +1100, K Smith wrote: Wood is not a very strong material at all. Tougher hardwoods have very moderate strength in compression, but other than that wood is a very weak material with low resistance to flexing+ ================================================== == Not at all true, wood has a very high strength to weight ratio. You are confusing strength with stiffness. They are two entirely different properties. With respect I don't think so indeed wood is of such low structural strength at any sort of unsupported span is usually limited by the weight of the wood itself. i.e. if you get the books out & design a wooden beam to carry a heavy load over spans that are commonplace with say RSJs, composites or even ferro, the problem with wood becomes that the beam sags under it's own weight, without any load!!! It's reasonably good at holding leaves up, flexible enough to survive wind storms (maybe sometimes) & porous enough to allow them some water etc, so long as those leaves a manufacturing food to keep it in good working order. As soon as it's removed from it's roots & leaves life support it just become mulch indeed even trees throw those limbs off rather than risk the rot spreading. As a structural material it's not much good. Add a moist boat type environment & that's why boats are built these days of almost anything other than wood. I love my old wooden boat, but ....... K |
Composite stringer grids
Harry Krause wrote:
K Smith wrote: Wood is not a very strong material at all. Bull****. Wood is a very strong material when used appropriately. Not according to any rational analysis. It's cheap & renewable to some extent & still has some traditional uses but in actual structural situations it's about the worst choice. However you are certainly entitled to put your opinion, just so long as you don't deny me the same right. Tougher hardwoods have very moderate strength in compression, but other than that wood is a very weak material with low resistance to flexing & even worse performance in tension. i.e. bend a piece of wood to simulate a load in the middle; one side is in compression & the other is in tension. Yeah? Tell you what. Envision a wood stringer, say 2"x10"x16'. Tip it on its edge. Now, try to bend it in the up or down plane with any load similar to what you might find in a working hull. Now, build that 2x10 into an eggcrate sort of structure, with cross members of the same or similar material. Now subject that structure to lateral loads. Doesn't bend that way either. This is real world construction here, Karen, not some crap you lifted off a web site. Gee now if only websites could give some understanding I could lead you to one, however you are just babbling because it's me delivering the news, sorry don't shoot me I'm just the tea girl delivering the mail. The wood will bend easily & a great deal, it will usually then break as the tension side fails. So I'd like to submit the problem with wood is that it's wood. The problem isn't wood in boats. It is the wood between your ears. Dear dear dear you can't help yourself, tell you what why don't you make up a lie about how you're a structural engineer & specialise in these things, or how about the jetski lie, this time what?? you won a hammer & nail in a raffle??? Most anything designed in wood is strength for strength much much heavier than almost any other material, steel, glass, even ferro. This is because the material is inherently weak & this weakness is aggravated by the difficulties of attaching it to anything, even itself (mechanical fastenings, nuts & bolts are about the only real fix) Really? Gosh. There probably are 100 million wood frame houses in the united states, some more than 100 years old. I suppose that because of the weakness of wood and the difficulties of attaching it to anyting, even itself, are really problematical, eh? Gees louise you really think a house frame is the same thing??? You have no concept do you, try picking a wooden house up say 4ft by one corner then drop it as you pick the opposing side up the same 4 ft. You'll have barbie fuel for longer than it would take for you to tell the truth about the time. Timber house bearers weight almost as much as the highest loads they're ever likely to see & again if you stopped & thought about things you'd realise whenever timber is used as a structural load bearing materieal it's in compression, never in tension, because in tension it will fail usually where the tension force is applied. Boats aren't static they get constantly attacked by forces from all angles, not to mention the regular tangles with a wharf or sandbar at varying speeds. It might be a "normal" process when you glass over wood because resins will not ever properly bond to wood You ought to send your resume to Grady-White. I'm sure they'd be interested in hiring you because in your opinion, the boats they build are likely to fall apart any moment; their stringers are constructed of XL plywood covered in fiberglass. But what could Grady-White know about boat=building, compared to the Australian bull**** artist, Karen Elizabeth Smith? Gee now there's a killer rejoinder, some people still use wood therefore wood must be good??? Harry if you had any education whatsoever you'd never come out with these childish arguments. I'd like to also disagree with this if I may. Hollow sections are never as strong as three dimensional webbed or bulkheaded sections. i.e. say in steel a rolled hollow section (RHS) of a given weight is never as strong as as a universal column (RSJ) of the same weight. An important principle to keep in mind when building small boats, eh? Yep absolutely if you can understand the general principles of how materials are used you can use that in all sorts of innovative new ways, do you want a link to the rec boats page for a classic example?? More Karen lifts from engineering webpages, but no understanding of materials or applications. Harry that was just a quick off the cuff answer to what I saw as a sweeping statement about cored beams which I tried to counter & actually explain why I disagreed. It's no surprise you can't understand it but as with so many other things here at least I've tried. As for the rest of your comments I guess all I can say is tell me where I can even see let alone inspect other reasonable HP diesel OB motors, I mean even Yanmar gave up at 40 HP so till you find the latest diesel OBs in the same HP range as mine ............ The boat?? yep; she's old & yes she works for her keep but it's my boat independently verifiable to anyone, which is more than can be said of you or your made up fantasy boats K -- |
Composite stringer grids
Chuck,
I guess this is the issue, I'm considering getting a late vintage 1980's, 30 foot Sea Ray and I'm not sure how important the wood's integrity is. I'm under the impression it played a vital role rather than a place holder for the glass. Paul "Gould 0738" wrote in message ... Chuck, Depends on the stringer. Did the manufacturer intend to have an FRP stringer that just happens to to have a wood or foam core, or did the mfg put 3/32 inch of glass to "encapsulate" a wooden stringer where the wood was actually bearing the stress? |
Composite stringer grids
Thanks Wally, kind of figured that's what you meant. Sounds like they put
some thinking into those Tolly's. Paul "WaIIy" wrote in message ... On Wed, 19 Nov 2003 08:05:26 -0500, "Paul Schilter" paulschilter@comcast,dot,net wrote: Wally, Okay, but were the Silverton's stringers wood core or foam? Paul Wood... I don't have the exact details. I'm guessing water got in there and turned the wood to mush and things got wiggly. "Where's the beef?" |
Composite stringer grids
On Thu, 20 Nov 2003 08:02:38 -0500, "Paul Schilter"
paulschilter@comcast,dot,net wrote: I guess this is the issue, I'm considering getting a late vintage 1980's, 30 foot Sea Ray and I'm not sure how important the wood's integrity is. I'm under the impression it played a vital role rather than a place holder for the glass. ============================================== That's a good assumption, the wood is almost always there as a structural element. Hire the best surveyor you can find and have him check everything out carefully. Some of the 20 year old Sea Ray's have not held up particularly well, but there are always exceptions. |
Composite stringer grids
On Thu, 20 Nov 2003 22:45:08 +1100, K Smith wrote:
As soon as it's removed from it's roots & leaves life support it just become mulch indeed even trees throw those limbs off rather than risk the rot spreading. =========================================== Since your trees are upside down, where do the limbs fall? Once again you are confusing stiffness (flexibility) with strength. And the structural properties of rotted wood are not at issue either, since that relates to durability, not strength. Properly protected from the elements, wood lasts a verrry lonnnng time. |
Composite stringer grids
K Smith wrote:
.. With respect I don't think so indeed wood is of such low structural strength at any sort of unsupported span is usually limited by the weight of the wood itself. Yep, that must be why so many hi-tech racing sailboats are built with wooden hull structures. It's hard to pick between carbon fiber and this mushy unfastenable stuff that will barely even hold up its own weight. K.Smith your credibility was already low, but it's sinking even further. DSK |
Composite stringer grids
Lawrence James wrote:
I suggest you take a look at some standard floor joist simple span tables and see just what it takes to span 10 feet. Conventional wood is not very resistant to flexing. A lot of other things are stronger. I suggest you educte yourself about wood boat construction. http://www.westsystem.com/webpages/u.../composite.htm Floor joists notwithstanding, wood is one of the best boatbuilding materials. It's only in the past ten years (or a bit less actually) that carbon fiber has become predominant over cold molded wood. Boats are not built like houses. Fresh Breezes- Doug King |
Composite stringer grids
Wayne,
Good advise, I definitely plan a survey. Paul "Wayne.B" wrote in message ... On Thu, 20 Nov 2003 08:02:38 -0500, "Paul Schilter" paulschilter@comcast,dot,net wrote: I guess this is the issue, I'm considering getting a late vintage 1980's, 30 foot Sea Ray and I'm not sure how important the wood's integrity is. I'm under the impression it played a vital role rather than a place holder for the glass. ============================================== That's a good assumption, the wood is almost always there as a structural element. Hire the best surveyor you can find and have him check everything out carefully. Some of the 20 year old Sea Ray's have not held up particularly well, but there are always exceptions. |
Composite stringer grids
On Thu, 20 Nov 2003 10:07:49 -0500, DSK wrote:
Yep, that must be why so many hi-tech racing sailboats are built with wooden hull structures. It's hard to pick between carbon fiber and this mushy unfastenable stuff that will barely even hold up its own weight. ================================================== ====== Yes, and I guess we could also cite the use of balsa wood by model airplane builders where high strength to weight ratios have made it the construction material of choice for many years. I'm never quite sure where "K" is coming from with some of these assertions. If she is playing devils advocate in the hope of drawing people into the fray with more information, good job. Otherwise, yikes. |
Composite stringer grids
Oh and that's why there are so many old boats still around. Because wood is
such a good material to build boats with. "WaIIy" wrote in message ... On 20 Nov 2003 21:20:36 GMT, (Karl Denninger) wrote: The key is to keep the water out of it. Which isn't impossible, but sometimes difficult. I like the Alfred E. Neuman philosophy for stringers.. "I use foam, What, Me Worry?" |
Composite stringer grids
I don't disagree with you that wood is an acceptable material for boats. It
brought Columbus here...the vikings, etc. lol So it's proved itself. I got the impression you were comparing wood framing in construction to boat framing...that's all. By the way...that's a nice looking boat of yours. Parker is also on my list for the next boat. If they didn't mistreat me here at the local dealer I probably would have one right now. But the dealer was arrogant. When I asked if he had one for me to look at (the 21' Sport Cabin) his only answer was "I have a yard full of boats". Ok...like I didn't know that? And he refused to get up off his as* to show me around. lol So I left. But I'll give him a second chance in two years. "Harry Krause" wrote in message ... Mole wrote: "Harry Krause" wrote in message news:c3dhc2g=.82627d12784c03afb2097e72f24ffd36@106 9256316.cotse.net... K Smith wrote: Really? Gosh. There probably are 100 million wood frame houses in the united states, some more than 100 years old. I suppose that because of the weakness of wood and the difficulties of attaching it to anyting, even itself, are really problematical, eh? Don't twist those houses or they fall down. Don't suddenly lower the pressure...the nails come out. Don't let the weather barrier get compromised or they rot. Don't compare house construction to boat construction. They don't even come close. I'm not comparing house construction to boat construction. The point, and perhaps I was too subtle, is that wood frame construction is strong enough for houses, and wood is strong enough for boat stringers, assuming whoever does the design does it properly and the design is correctly implemented and the wood protected. Karen Elizabeth Smith "gets off" on these little tangents of hers, but they mostly are absurd or border on it. Wood is a fine boatbuilding material, and has been for thousands of years. It certainly is "strong enough" to be used as a boatbuilding material. Does wood have shortcomings? Of course it does, but so does every other boatbuilding material. Ms. Smith is quick to castigate for what she perceives to be "problems" in the designs and manufacture of boats generally, and, more typically, boat engines, a position that really is not defensible, if you take a look at the barely floating derelict of a boat she calls her own and the rusting piece of crap "diesel outboard" engine with which she underpowers it. -- Email sent to is never read. |
Composite stringer grids
DSK wrote:
K Smith wrote: .. With respect I don't think so indeed wood is of such low structural strength at any sort of unsupported span is usually limited by the weight of the wood itself. Yep, that must be why so many hi-tech racing sailboats are built with wooden hull structures. It's hard to pick between carbon fiber and this mushy unfastenable stuff that will barely even hold up its own weight. K.Smith your credibility was already low, but it's sinking even further. DSK Our Ms. Smith thinks if she throws enough badly written b.s. at the wall, some of it will stick. -- Email sent to is never read. |
Composite stringer grids
On Fri, 21 Nov 2003 01:47:44 GMT, "Lawrence James"
wrote: Oh and that's why there are so many old boats still around. Because wood is such a good material to build boats with. ================================================== ==== More baloney. Those wood boats that have received the proper care and maintenance over the years ARE still around. It's well understood that they do require more care and maintenance, and that is the issue for most people. We have a sailboat boat at my club in Connecticut that was built from epoxy saturated cedar strips back in the early 70s. It requires almost no special maintenance because of the encapsulation, and it is still one of the lightest, fastest 30 footers in our region. |
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