Page 1 of 2 12 LastLast
Results 1 to 50 of 65

Thread: how much strength does fiberglass tape really add?

  1. #1

    Default how much strength does fiberglass tape really add?

    i have searched but found little. im curious, say your building a stitch and glue boat held together w/ epoxy fillets and 6oz tape. does the tape really do all that much? i can see using it on the outside corners where no fillet is possible, but on the inside it seems redundant, at least for anything under about 12'-14'. i made a couple samples just fillet and fillet w/ 2 layers 4" 6oz tape, i couldnt tell the difference when i broke them. how do designers calculate the strength of a joint? help me understand why we do all the extra work. thanks!

  2. #2
    Join Date
    Sep 2011
    Location
    Arizona desert
    Posts
    125

    Default Re: how much strength does fiberglass tape really add?

    Last edited by Frog4; 10-02-2011 at 09:30 PM.

    WEIRD! Because YOUR normal isn't working...

  3. #3
    Join Date
    Jun 2000
    Location
    Madison Wisconsin
    Posts
    6,940

    Default Re: how much strength does fiberglass tape really add?

    I don't see anything in that video that really has anything to do with the question asked. Over an inside fillet, I would suspect that it doesn't really do much. Fiberglass adds strength when put in tension and I can't think of many situations that would do so to the inside of a fillet in normal use. I suppose it might help taper out the stiffness of the fillet at the edges if the tape extends beyond the fillet, reducing the stress riser the fillet could create a bit, and in some cases having tape to smooth out as a final skin might make for a smoother surface. Since most filler blends are fairly brittle, adding some long fibers in the form of the woven tape skin might strengthen the fillet itself (less likely to crack) but whether or not it would noticably strengthen the joint, and the boat, might take some testing to get a feel for.

  4. #4
    Join Date
    Sep 2011
    Location
    Arizona desert
    Posts
    125

    Default Re: how much strength does fiberglass tape really add?

    just added the vid to show the "strength" of fiberglass ...

    this one should be better at answering the question:


    WEIRD! Because YOUR normal isn't working...

  5. #5
    Join Date
    May 2010
    Location
    Sioux City, Iowa (Idiot Out Walking Around)
    Posts
    1,736

    Default Re: how much strength does fiberglass tape really add?

    That video still doesn't have anything to do with the question posed. There are no filleted joints between 2 large panels at a wide angle on a surfboard.

    The use of glass over the fillets on the inside probably doesn't add much to the joint in general use on the water. However...I expect it can and does help in such smaller boats when being handled out of the water. Picking it up, flipping it over, holding the sides together when it accidentally becomes a bath tub... I'd rather have the insurance than not for the small effort it takes put them in.
    Steve Lewis
    Formerly Lewisboats (don't try to change your email address!)

    http://angelfire.com/ego/lewisboatworks

  6. #6
    Join Date
    Sep 2011
    Location
    Arizona desert
    Posts
    125

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by Lewisboater View Post
    That video still doesn't have anything to do with the question posed. There are no filleted joints between 2 large panels at a wide angle on a surfboard.

    The use of glass over the fillets on the inside probably doesn't add much to the joint in general use on the water. However...I expect it can and does help in such smaller boats when being handled out of the water. Picking it up, flipping it over, holding the sides together when it accidentally becomes a bath tub... I'd rather have the insurance than not for the small effort it takes put them in.
    was answering this question: how much strength does fiberglass tape really add?


    WEIRD! Because YOUR normal isn't working...

  7. #7
    Join Date
    Dec 2003
    Location
    Portland, Oregon
    Posts
    18,377

    Default Re: how much strength does fiberglass tape really add?

    I can't quantify it for you, but I've repaired a few runabouts where the fiberglass at the corners was almost the only thing (along with the paint) holding the whole thing together. Without the tape, those boats would have come apart long ago. As Todd mentions, fg is strongest in tension, so if one tapes both the inside and outside of a corner joint, it becomes quite a stout little assembly.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  8. #8
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    fCrickey, I have been saying for years , and catching hellfire for it, that tape in S n G construction is silly.
    I am not one for graphs and theory's, but real world use.
    My lil boat, Wizbang, has about 3000 miles of HARD landing , banging, thumping, pounding, and bone jarring cracking.
    She has NO FG tape . ONLY 403 microfiber filets.
    Her filets are large.
    Wizbang is not the first boat I have forgone tape.
    Long ago , I built a quickee flatiron, (10') that fell of the truck @45mph. and , well, you guessed it, did not break. Later, I carried the same boat through a gale where I frapped the living daylights out of her to where her shape distorted, 5 days later, launched with no leaks.
    Y'gotta make the filets big , and Y gotta use 403, but Y do not need the stinkin' tape.
    The corners are the strongest part of the boat!
    It would take a brazillion miles of rowing or dingy sailing to equal the abuse I have given Wizbang.
    http://www.flickr.com/photos/wizbang...n/photostream/
    Last edited by wizbang 13; 10-02-2011 at 10:26 PM.

  9. #9
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    The lilstinker goes 50mph with the 40 , and 39mph with the 25!
    Last edited by wizbang 13; 10-02-2011 at 10:36 PM.

  10. #10
    Join Date
    Nov 2006
    Location
    Seattle, Wa USA
    Posts
    811

    Default Re: how much strength does fiberglass tape really add?

    Sam Devlin specs biaxial tape instead of regular tape because all of the fibers cross the joint, as opposed to regular tape, where half of the fibers don't add any strength.
    -- Tom (boating blog)

  11. #11
    Join Date
    Jun 2000
    Location
    Madison Wisconsin
    Posts
    6,940

    Default Re: how much strength does fiberglass tape really add?

    As mentioned, the "strength" of fiberglass starts to show up when it's put in tension. The only reason that those guys can stand on that airplane part or one of those surfboards is because they use a sandwich of a non-compressible core with fiberglass layers on both sides. When they stand on it, the top glass layers are being placed in compression, not in tension, and are doing very little to take the stress. It's the layers on the bottom of the airplane part or surfboard that are being placed in tension and actually doing the work. A fiberglass fillet isn't really the same sort of thing and doesn't work the same way. The videos simply don't address the sorts of strength and stresses that a fillet is likely to get.

    Picture it this way, for the fillet, you are glass-covering the inside of a fairly small corner radius, on top of the epoxy/fill mixture. For that glass to add a reasonable amount of strength, you have to put it in tension - as in: exert a force that is trying to pull it apart, like stretching a rubber band. That's not a very common force on an inside tight radius on a boat in normal use. Say you make a three plank canoe, with a flat bottom plank and two vertical side planks and you join them together with a glass-taped chine seam on the outside, and a glass-taped chine fillet on the inside. Of all of the various stresses and strains that your canoe might get while in use, about the only one that would put the inner tape in tension would be something like sitting inside the boat and trying to force the gunwales farther apart with your hands, or bridging the boat by setting its ends up on something, suspending the middle and then putting a bunch of weight inside.

    Even so, there is another limit present. A good epoxy bond is stronger than the wood itself, so the weak link in the construction then becomes the grain strength of the wood, not the epoxy work. When a filleted joint fails, it's far more likely that it will fail by breaking away and taking some wood with it, than by the fillet itself breaking. Whether that particular fillet has glass over it, or has no glass and is reasonably tough stuff like Wizbang's epoxy/microfiber fillets probably won't matter. The grain strength of the wood itself is still the weakest part of the equation and the place most likely to fail.

    People also tend to drastically over-estimate the characteristics of fiberglass layers. If you lay up two layers of six-ounce glass with epoxy, let it cure and then peel it off of whaterver you used for a mold, it feels about like the plastic side of a milk jug. It's that thin and similar in stiffness. The only place that it exhibits much "strength" is when you put it in tension, where it does pretty well for such a thin layer of material. If your application isn't putting the glass in tension where it can show its strength, then it's not likely to be contributing much to the project.

  12. #12
    Join Date
    Apr 2009
    Location
    Thames, N.Z.
    Posts
    2,102

    Default Re: how much strength does fiberglass tape really add?

    'Cos that's how it's done. Even the Americas Cup boats I worked on at Cookson's yard in Auckland, the hull/deck joint was only "glassed" (carbon fibre actually) on the inside. But I agree with Todd on this; the amount of glass you are applying and the type & construction of glass you are using won't make much difference over a simple glue fillet.

    Be aware also that 290g boatcloth won't add any appreciable strength if layed over the outside of your plywood boat either. It is for protection only.
    Keep It Simple: KISS it better.

  13. #13
    Join Date
    Nov 2010
    Location
    Melbourne
    Posts
    8,418

    Default Re: how much strength does fiberglass tape really add?

    could someone please explain the term "fillet"
    Do you mean an actual plug of some sort or just the small gaps between the ply panels. as in "What do you do about that gap? -Fillit"?

  14. #14
    Join Date
    Apr 2000
    Location
    Southampton Ont. Canada
    Posts
    5,702

    Default Re: how much strength does fiberglass tape really add?

    "Now Ron,don't you do anything stupid!" - Grandma B.

  15. #15
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    The white stuff are the filets. Concave strip of thickened epoxy .Round putty knife yields a filet.
    Last edited by wizbang 13; 10-03-2011 at 07:24 AM.

  16. #16
    Join Date
    May 2009
    Location
    United Kingdom
    Posts
    104

    Default Re: how much strength does fiberglass tape really add?

    I asked this same question last year, and carried out some brutal tests on a couple of sample joints

    http://forum.woodenboat.com/showthread.php?119666-Beginer-s-Epoxy-plywood-query

    As far as I could see, the fibreglass may add some strength to the epoxy fillet, but the failure in both samples was in the adjoining plywood, which delaminated before the joint failed. My feeling is that even if the fibreglass adds strength, the epoxy fillet is more than strong enough on its own. On my current Portuguese dinghy build I have just filleted inside without glass, and taped the outside, largely to ensure the join is completely waterproof.

    http://forum.woodenboat.com/showthre...e-style-dinghy

    I think if you are building with thin plywood, an epoxy fillet is so much stronger than the plywood, that extra reinforcement is superfluous. If you are building with thick plywood, it may be different.

  17. #17
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    I thought that rang a bell!

  18. #18
    Join Date
    May 2005
    Location
    Central PA
    Posts
    3,538

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by wizbang 13 View Post
    The white stuff are the filets. Concave strip of thickened epoxy .Round putty knife yields a filet.
    The fibreglass would be good for picking up an outward bend on the sides, but your seat is already catching that load. Same for the corners on the bow and stern.
    It will all be OK in the end...so if it's not OK, you're not at the end.

  19. #19
    Join Date
    Dec 2003
    Location
    on-the-cuyahoga
    Posts
    13,238

    Default Re: how much strength does fiberglass tape really add?

    S&G boats, being a form of monocoque construction, benefit from having large amounts of "glued surface" to spread loads around. The easiest way to get a lot of glued surface in a plywood boat is with a nice strip of fiberglass cloth epoxied into place. If the surface veneer has a large amount of glued surface on the outside any load along the glue line will be transfered to an equally large glued surface between the veneers.
    Trying to get this effect (i.e. a minimum of 2" of glued surface on either side of a joint along it's entire length) with filleting mix only would not only require a huge volume of epoxy, which is heavier than water, it can't possibly have the other advantageous engineering characteristics of fiberglass cloth.
    Filleting is done for two reasons. First you want to get the hull panels locked together before there is a chance of knocking something out of whack. Second, fiberglass cloth has a "memory". It does not cling to sharp interior angles willingly and is inclined to pull away when you are not looking. With the addition of a small amount of epoxy mix in the form of a radiused fillet you can give the tape a surface it is inclined to stick to.
    In short, the guys that figured this out long ago (there were alot of them) knew what they were doing and any attempt to shortcut their findings will not result in an improvement.
    Last edited by Cuyahoga Chuck; 10-03-2011 at 08:53 AM.

  20. #20
    Join Date
    Dec 1999
    Location
    Oriental, NC USA
    Posts
    3,219

    Default Re: how much strength does fiberglass tape really add?

    A basic problem with this question is defining what kind of "strength" is being asked about. Tension, compression, rigidity, peeling, etc? I expect the OP means all of these combined.

    In a angled joint with two sheets of ply, failure from bending the joint usually comes from the thinner plywood part hinging off the thicker plywood at the edge of the filet. Failure will typically include part of the plywood surface where the filet is in tension. If the filet(s) are made really strong, the thinner plywood may fail at the edge of the filet. What the tape adds is peel strength, mainly on the opposite side of the joint away from the bend. If the parts are never going to have any bending of this kind, the tape can often be eliminated with no loss in "strength". Especially true in small boats that do not go fast.

    If the expected load is in tension (one panel being pulled away from the other) the tape is a major contributor to the integrity of the joint. A bulkhead often fits this case and adequate tape should not be omitted.

    In larger boats, especially powerboats that are to run fast in rough water, tape makes much more sense and I use biaxial or triaxial to withstand all the slamming and pounding that the boat will endure. With the thicker scantlings of such a boat, more stress is applied to the joint relative to the thinner scantlings of a smaller boat where the plywood itself can absorb some of the stress before it is transmitted to the joint. In the "Payson" butt joint, the glass does almost all the work and cannot be eliminated. Any joint where the bending puts the joint in tension need the tape on that side. The compression side of the joint can usually avoid the tape.

    No sane amateur builder of small boats is going to get into calculations regarding this issue. The reasonable approach is to follow accepted practice unless you have better data to work from.
    Tom L

  21. #21
    Join Date
    Dec 1999
    Location
    Oriental, NC USA
    Posts
    3,219

    Default Re: how much strength does fiberglass tape really add?

    double post
    Last edited by Tom Lathrop; 10-03-2011 at 09:15 AM. Reason: double post
    Tom L

  22. #22
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    "If the expected load is in tension (one panel being pulled away from the other) the tape is a major contributor to the integrity of the joint. A bulkhead often fits this case and adequate tape should not be omitted."
    heh heh , I dint glass the bulkheads in my big boat either
    Not using glass ,works.
    And cotton fibers do not itch.
    And there is no danger of sanding/chafing through the tape, which is a real world thing.

  23. #23
    Join Date
    Sep 2011
    Location
    Arizona desert
    Posts
    125

    Default Re: how much strength does fiberglass tape really add?

    wizbang, you subbed "cotton fibers" for glass? do you have pics of this process?

    WEIRD! Because YOUR normal isn't working...

  24. #24
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    The WEST 403 microfibers IS cotton. (I think?)

  25. #25
    Join Date
    Apr 2009
    Location
    Thames, N.Z.
    Posts
    2,102

    Default Re: how much strength does fiberglass tape really add?

    Depends how your boat is constructed Wizzbang. I ripped the main ringframe bulkhead loose in a 36ft racing yacht bouncing off a wave in the entrance to Tauranga Harbour. The ply bulkhead was only coved & taped in place in a solid layup f/g hull, and of course in polyester. I think the problem with that boat was that insufficient load-spread for the keel allowed the inertia of the keel to distort the hull enough to spring the bulkhead.
    Keep It Simple: KISS it better.

  26. #26

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by Tom Lathrop View Post
    A basic problem with this question is defining what kind of "strength" is being asked about. Tension, compression, rigidity, peeling, etc? I expect the OP means all of these combined.
    AGREED!

    There has been so much speculation, and so little hard data.

    First, I notice that we hear of very few reports of real world failures of taped seam joints. Reasonable to conclude from this that real world taped seam joints are somewhere between strong enough and too strong.

    Secondly, Tom L. is asking the right question which is: How do we define strength?

    Personally, I have had experience with only one "real world" taped seam joint failure. It occurred to a rowboat I owned, which was crushed during storage by a rock fall/landslide. This event gave me a chance to examine in detail one type of joint failure. It allowed me to learn a lot!

    Most notable, the failure didn't occur in the fiberglass, or the epoxy; but rather the failure occurred in the wood fibers just adjacent to the fiberglass. Telling us that the failure mode was limited by the strength of the wood.

    Wood engineers tell us that wood has variable degrees of strength, depending on the direction of the stress in the wood fibers. Rated in order of strength (from strong to weak) these are:

    1) Pushing (compression) parallel to the grain.
    2) Pulling (tension) parallel to the grain.
    3) Pushing perpendicular to the grain.
    4) Pulling perpindicular to the grain.

    When I looked at the failure I saw that indeed, the point of failure was pulling (tension) perpendicular to the grain. This can be visualized as something like pulling a Band-Aid off of the skin.

    But, when you look close at typical taped seam joints they are two sided. And what you get with that is that in most any situation, the weak 4) "Band-Aid" failure mode is backed up by the opposite side 3) compression perpendicular to grain type of failure.

    You can see this in the photo below. (Look at how the taped seam failed. Don't look at the crushed wood.) The tape pulled away from the wood in tension perpendicular to the grain.


  27. #27
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by Candyfloss View Post
    Depends how your boat is constructed Wizzbang. I ripped the main ringframe bulkhead loose in a 36ft racing yacht bouncing off a wave in the entrance to Tauranga Harbour. The ply bulkhead was only coved & taped in place in a solid layup f/g hull, and of course in polyester. I think the problem with that boat was that insufficient load-spread for the keel allowed the inertia of the keel to distort the hull enough to spring the bulkhead.
    Sure! Racing boats are built as lightly as possible. My 34 footer is strip planked, it is much,much stronger than the average boat.

  28. #28
    Join Date
    Sep 2011
    Location
    Arizona desert
    Posts
    125

    Default Re: how much strength does fiberglass tape really add?

    Bruce, I would love to see that same "failure" with a fillet only seam ... would make a great comparison

    WEIRD! Because YOUR normal isn't working...

  29. #29
    Join Date
    Sep 2011
    Location
    Arizona desert
    Posts
    125

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by wizbang 13 View Post
    The WEST 403 microfibers IS cotton. (I think?)
    quick search, couldn't find anything on WEST 403 microfibers, no MSDS or "ingredients" ...

    WEIRD! Because YOUR normal isn't working...

  30. #30

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by Frog4 View Post
    Bruce, I would love to see that same "failure" with a fillet only seam ... would make a great comparison
    I have given this a lot of thought, at least as a mind experiment. A fillet only seam would have less "square inches" of adhesion to the wood fibers in tension perpendicular to the grain. Hence, it would be less strong. The strength is measured in pounds per square inch, meaning that more square inches means more pounds. Designing joints, you can get stronger by 1) having more square inches, or 2) arranging the geometry so that you avail yourself of wood strength in the stronger direction which is compression perpendicular to the grain versus the weaker direction which is tension perpendicular to the grain.

  31. #31
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by Frog4 View Post
    quick search, couldn't find anything on WEST 403 microfibers, no MSDS or "ingredients" ...
    Cotton flock. I googled "WEST 403 ingredients". A pdf, I could not C n P it.

  32. #32
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by brucehallman View Post
    I have given this a lot of thought, at least as a mind experiment. A fillet only seam would have less "square inches" of adhesion to the wood fibers in tension perpendicular to the grain. Hence, it would be less strong. The strength is measured in pounds per square inch, meaning that more square inches means more pounds. Designing joints, you can get stronger by 1) having more square inches, or 2) arranging the geometry so that you avail yourself of wood strength in the stronger direction which is compression perpendicular to the grain versus the weaker direction which is tension perpendicular to the grain.
    If the filet is BIG, and it had the same square inches , would it be the same? I'm using a 3" knife(rounded) to make em.

  33. #33
    Join Date
    May 2010
    Location
    Sioux City, Iowa (Idiot Out Walking Around)
    Posts
    1,736

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by wizbang 13 View Post
    If the filet is BIG, and it had the same square inches , would it be the same? I'm using a 3" knife(rounded) to make em.
    and a bloody lot of epoxy too. This conversation reminds me of the poly vs epoxy debate. Yep...there have a lot of plywood boats built with poly that have survived but many more that have rotted into oblivion. Yep...there are and are going to be boats built with just fillets on the inside... a lot of those will work...but it remains to be seen if the ratio is in favor of or agin. Personally...for the bit of effort needed to put in tape on the inside...I'll go that route and consider "overbuilt" in this respect a good thing. There is no weight penalty compared to enormous fillets, Glass tape is an order of magnitude cheaper than epoxy and filler and if done wet on wet...no extra effort is involved either.
    Steve Lewis
    Formerly Lewisboats (don't try to change your email address!)

    http://angelfire.com/ego/lewisboatworks

  34. #34

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by wizbang 13 View Post
    If the filet is BIG, and it had the same square inches , would it be the same?
    Conventional taped seam joints are two sided, meaning one side is subject to compression while the other is in tension. A non-taped, plain filleted, joint isn't two sided. That suggests to me (based on my real world test, post #26, above) that plain fillets would be weaker than two sided taped seam joints.

    They still may be 'strong enough', but just a weaker 'strong enough'.

  35. #35
    Join Date
    May 2009
    Location
    Fort Worth, Texas, USA
    Posts
    746

    Default Re: how much strength does fiberglass tape really add?

    Gentlemen,

    The only way to really know is to do a test.

    Make your joint two different ways, weight the test samples, and pull as many different ways as you think the joint is going to be loaded. You have to be able to record the force they break at to prove anything.

    If you don't really care about weight or cost of epoxy, make big fillets and ignore conventional wisdom.

    If you want to reduce the cost and weight of your boat, do the tests.

    Please note you cannot bend a taped join without genertating tension on one side and compression on the other. It doesn't matter if 2 plys of glass after peeling off a mold is just like a milk jug, cause that is not the way you use the material. Fiberglass has significant compressive strength so long as it is NOT standing alone in a thin sheet - that kind of failure is typically "buckling" which does not happen when bonded on one side of a plywood joint.

    FYI I did a design using aerospace carbon fiber precured sheets, with room temp adhesive fillets, which weighed less and broke at a higher load than 2 plys of carbon on each side as a "taped" seam". This was a T joint. For something with double or triple the load we would of made fillets AND added a ply of "tape" which would have significantly upped the strength.

    The real problem even in aerospace is that we all generally can't imagine the actual loads on a joint well enough to be sure of leaving out the glass, which is why I agree with Tom Lathrop and Lewisboater - use the glass on both sides.

    I also support Tom Williamson - do what you want, you will anyway. Just decide if you care about weight and cost. Then prove it as well as you can or - do what you want.

    Most boats are not about the most weight efficient design or build and not really about cost. Except we all like to talk a lot.

    Marc

  36. #36
    Join Date
    May 2009
    Location
    Fort Worth, Texas, USA
    Posts
    746

    Default Re: how much strength does fiberglass tape really add?

    Another suggestion about taped joints. Jim Brown in his Searunner designs used a taped joint where he put a fillet on the inside of the panel intersections, rounded off the outside surface of the joint and then taped both inside and outside. This resulted in minimal wood at the intersection of the joint, probably not a whole lot of epoxy in the fillet and glass on both sides which was required to be structural. It also helped make a "molded" or smooth looking joint instead of sharp edges (one of my personal dislikes).

    This is not joint which might be choosen if you want the clear wood grain look, since it exposes a large area of end grain.

    I just think this is an elegant approach to a smoothly curved plywood boat. Possibly not what is desired by everyone.

    Marc
    Last edited by upchurchmr; 10-03-2011 at 02:55 PM. Reason: correct verbage

  37. #37
    Join Date
    Dec 2003
    Location
    on-the-cuyahoga
    Posts
    13,238

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by Frog4 View Post
    quick search, couldn't find anything on WEST 403 microfibers, no MSDS or "ingredients" ...
    403 is chopped cotton fibers if memory serves me right.

  38. #38
    Join Date
    Sep 2011
    Location
    Arizona desert
    Posts
    125

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by wizbang 13 View Post
    Cotton flock. I googled "WEST 403 ingredients". A pdf, I could not C n P it.
    thanks, sometimes the right combo of search terms is hard to nail, now that google has gone mostly along the
    advertiser way ...

    WEIRD! Because YOUR normal isn't working...

  39. #39
    Join Date
    Feb 2006
    Location
    Pennsylvania
    Posts
    6,012

    Default Re: how much strength does fiberglass tape really add?

    Whenever I see scraps of plywood along the beach or in the rocks, I have to stop and examine. It's usually the remains of a boat. And almost always, regardless of construction, the chines are more there than the panels themselves -- or the rest of the boat, for that matter. Once the chine is stronger than the adjoining material, adding yet more strength is pretty much a waste of time and money.

    The Gougeon Brothers on Boat Construction has a lot of good information about the various strength properties of wood/glass laminations. For example, cloth on the inside of the hull prevents puncture better than cloth on the outside. But (as I recall this without the book in hand) a sandwich construction with cloth inside and out, while very strong, will spread the damage all over, making for a difficult repair. You may prefer a weaker skin that takes a clean, easily repaired puncture.

    I used to have a Brown Searunner. It had copious amounts of cloth inside and out to form those radiused chines. I think that construction reached the point -- at least in the bottom of the hulls -- where the ply was more of a core material inside a glass structure. Above the waterline, the cloth use was minimal.

  40. #40

    Default Re: how much strength does fiberglass tape really add?

    Thanks for all the response! certainly got several schools of thought. will a dinghy fall apart without tape? very Doubtfull under normal use. does tape add signifigant strength? under certain types of loads, yes. Is its use essential in a dinghy build? i guess thats up to me. thanks again, there is a wealth of info here, and for someone recently addicted to building small boats this forum is a lifesaver!

  41. #41
    Join Date
    Dec 2003
    Location
    Portland, Oregon
    Posts
    18,377

    Default Re: how much strength does fiberglass tape really add?

    And... for dessert... you might want to partake of Mik Storer's interesting article on Rules of Thumb. He touches on the fillet/tape question:

    http://www.duckworksmagazine.com/11/howto/design/index.htm


    Another place I use rules of thumb is in construction. For plywoods under 9mm an epoxy fillet needs to have a radius three times the plywood thickness. Same if you use a piece of timber in the join – the glue cleat needs to be have three times the gluing area to the ply of three times the ply thickness.
    This is another rule that falls apart if taken too far. Testing shows that the fillet radius actually needs to be about 2.2 times the ply thickness, so there is a safety factor already applied (someone is always ready to “add a bit” for safety. But as the ply thickness gets bigger the rule falls apart as you need to add glass cloth to get enough strength – and by that stage if you rely on fillets only then the fillet has so much volume that it has become crazy expensive.
    So, I would suggest that rules of thumb are very useful for professional designers because they know the ramifications – it is easy for Bolger or Chapelle to know what they mean and know when the “rule” breaks down. But a better guide for amateur designers is to look closely at similar sized boats to see which ones perform well in terms of meeting the required use patterns and which ones do not.


    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  42. #42
    Join Date
    Nov 2010
    Location
    Melbourne
    Posts
    8,418

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by Cuyahoga Chuck View Post
    S&G boats, being a form of monocoque construction, benefit from having large amounts of "glued surface" to spread loads around. The easiest way to get a lot of glued surface in a plywood boat is with a nice strip of fiberglass cloth epoxied into place. If the surface veneer has a large amount of glued surface on the outside any load along the glue line will be transfered to an equally large glued surface between the veneers.
    Trying to get this effect (i.e. a minimum of 2" of glued surface on either side of a joint along it's entire length) with filleting mix only would not only require a huge volume of epoxy, which is heavier than water, it can't possibly have the other advantageous engineering characteristics of fiberglass cloth.
    Filleting is done for two reasons. First you want to get the hull panels locked together before there is a chance of knocking something out of whack. Second, fiberglass cloth has a "memory". It does not cling to sharp interior angles willingly and is inclined to pull away when you are not looking. With the addition of a small amount of epoxy mix in the form of a radiused fillet you can give the tape a surface it is inclined to stick to.
    In short, the guys that figured this out long ago (there were alot of them) knew what they were doing and any attempt to shortcut their findings will not result in an improvement.
    Thanks, thats my way of thinking too.

  43. #43
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    Quote from Woxbox" Once the chine is stronger than the adjoining material, adding yet more strength is pretty much a waste of time and money."
    This sums it up for me. For small boats, 4-8mm ply.

  44. #44
    Join Date
    Dec 1999
    Location
    Oriental, NC USA
    Posts
    3,219

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by David G View Post
    And... for dessert... you might want to partake of Mik Storer's interesting article on Rules of Thumb. He touches on the fillet/tape question:

    http://www.duckworksmagazine.com/11/howto/design/index.htm


    Another place I use rules of thumb is in construction. For plywoods under 9mm an epoxy fillet needs to have a radius three times the plywood thickness. Same if you use a piece of timber in the join – the glue cleat needs to be have three times the gluing area to the ply of three times the ply thickness.
    This is another rule that falls apart if taken too far. Testing shows that the fillet radius actually needs to be about 2.2 times the ply thickness, so there is a safety factor already applied (someone is always ready to “add a bit” for safety. But as the ply thickness gets bigger the rule falls apart as you need to add glass cloth to get enough strength – and by that stage if you rely on fillets only then the fillet has so much volume that it has become crazy expensive.
    So, I would suggest that rules of thumb are very useful for professional designers because they know the ramifications – it is easy for Bolger or Chapelle to know what they mean and know when the “rule” breaks down. But a better guide for amateur designers is to look closely at similar sized boats to see which ones perform well in terms of meeting the required use patterns and which ones do not.
    This and Chuck's comments sums it up for me and fits my experience. If Wizbang wants to skip the tape, he probably knows when he can't get away with that with safety. For beginners like the OP, some of the rules of thumb as mentioned should be their guide and its no big deal to err on the safe side. The rule of filet width should relate to the thinner of the two sheets of ply if they are different.

    I skip the tape pretty often if the joint will not experience much tensile stress on any axis except for the thicker scantlings and heavier loads of fast boats. Trying to estimate the loads that will be seen on larger fast boats is beyond most of us and tape is cheap insurance. Looking at the failures seen on the most advanced boats makes it clear that even the best designers and most sophisticated computer programs can't always do it either.
    Tom L

  45. #45
    Join Date
    Dec 2003
    Location
    on-the-cuyahoga
    Posts
    13,238

    Default Re: how much strength does fiberglass tape really add?

    Quote Originally Posted by rodjr View Post
    Thanks for all the response! certainly got several schools of thought. will a dinghy fall apart without tape? very Doubtfull under normal use. does tape add signifigant strength? under certain types of loads, yes. Is its use essential in a dinghy build? i guess thats up to me. thanks again, there is a wealth of info here, and for someone recently addicted to building small boats this forum is a lifesaver!
    All the major purveyors of S&G boat designs in the US use nothing but the conventional "fiberglass outside/fillet and 'glass in" method. It may have to do with the liability laws. You can do whatever you want but encouraging others to do the same may get you in legal trouble.
    The total engineering view is not just about strength. Every component of a boat has a list of engineering qualities like tensile strength, compressive strength, modulus of elasticity, weight, stifness, density, etc. etc. that come into play in the finished design. Engaging in a home brew "destructive testing laboratory" may be a nice time killer but nobody is going to challenge what has already been published by professionals with all the latest equipment.
    And, in S&G boat technology, an important factor is not how strong this or that component is but about how much glued surface is holding the whole thing together. You don't need anything but a tape measure and a pencil and paper to figure it out.

  46. #46
    Join Date
    Jul 2011
    Location
    Lindstrom, MN
    Posts
    522

    Default Re: how much strength does fiberglass tape really add?

    6oz. plain weave has a tensile strength of 284 x 200 pounds per linear inch of width for style 1528 and 300 x 300 pli for style 7255. Most 6 oz tape should fall somewhere in that range. It is a little harder to find strength at 45 degrees in a composite skin, but as I recall it is about half of the strength in the fiber directions. The strength of fiberglass cloth starts on page 59 of this: http://www.hexcel.com/Resources/Data...s_Handbook.pdf

    West 403 is cotton flock and <20% fumed silica. MSDS is here: http://www.google.com/url?sa=t&sourc...kQlKjw&cad=rja

    Bruce's picture of the crushed rowboat looks more like a peel failure than tension where the taped seam separated. Peel is generally the weakest load for an epoxy joint.

    Todd is mistaken about the lack of contribution that the fiberglass makes on the compression side of a cored panel structure. Something of a first from what I have read of Todd's posts. The core material, plywood, foam etc. provides a lot of support to the skin and the resin matrix prevents the fibers from buckling, so there is quite a bit of compressive strength coming from the fibers. The cores carry shear loads and compression perpendicular to the surface, but not a lot of compression along the surface. If fibers set in an epoxy matrix did not have good compressive load carrying properties, carbon fiber masts would not work. The example of two layers of 6 oz cloth shows how important thickness is to stiffness. The skin of a fiberglass canoe is about 5 times as thick as that two layers of 6 oz cloth and makes a pretty durable boat, which without the compressive strength of the fiberglass would be impossible. I can stand on the bottom of a stripper built with glass on both sides. I wouldn't try it on one with glass on the outside only.

    I am sure that you could demonstrate pretty easily that a thicker fillet is needed for equivalent strength without the fiberglass tape. Dave Carnell http://www.angelfire.com/nc3/davecarnell/epoxy.html talked about 1/4 in fillets and fiberglass on corner joints and the advisability of running a few tests with representative joints. I prefer to glass both sides, and I can't argue with the fact that Wizbang was strong enough as built. It could have been built another way with smaller fillets and glass, maybe, but some of those sharp angles will need a generous fillet radius one way or the other.

  47. #47
    Join Date
    Jun 2000
    Location
    Madison Wisconsin
    Posts
    6,940

    Default Re: how much strength does fiberglass tape really add?

    I have no problems with glassing both sides and generally tend to follow the designer's directions to the letter, mostly because I've seen some real doozies of mistakes made by builders who thought they knew better and didn't. If a plan said to glass over the fillet, I'd do it, if for no other reason than it might make for a smoother job. In this case though, my point was that I'm not convinced that the glass on the inside of a good fillet, out in the real world, would ever be put in either enough tension (or compression) for the glass covering layers to make much difference - especially when the bond, whether glassed or not, is critical to the joint and limited mostly by the grain strength of the wood. Unless you're using something quite unusual for your filleting blend and resin, I have a lot of trouble picturing the fillet ever flexing enough to put the fiberglass covering layers in compression. By that time, you're into the realm of impact or flex that has the potential to blow any joint apart and/or destroy the boat - and nobody ever said boats can't be destroyed.

    My reference to the two layers of glass was made simply to point out that a layer or two of light fiberglass is hardly the bomb-proof armor plating that a lot of folks seem to think it is. One good, and somewhat surprising, way to understand this is to isolate a couple layers of glass as I indicated and get a real look at what it can do and what it doesn't do. I just get the feeling that some people tend to equate a couple layers of 6 oz. with typical, non-wood, fiberglass boat construction and assume that they're getting or adding that same sort of "strength" to their wooden hulls. This is not the case and the two layer example was in reference to that - and in my opinion, still well worth doing for anyone using fiberglass cloth to cover parts or all of a wooden boat. I'd been working on both fiberglass and wood/glass boats for better than 20 years before I tried it and it was pretty shocking. I decided at one point to lay up some tapered fiberglass sail battens using epoxy and leftover 6 oz. glass cloth. I simply couldn't believe how many layers of the stuff it took to start getting something substantial enough that it might actually do the job in the non-cored areas of the battens. Maybe I'm the only person on earth that wasn't aware of this aspect of 6 oz. cloth, but I doubt it.

  48. #48
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    9,187

    Default Re: how much strength does fiberglass tape really add?

    Here is another. A carvel boat originally. Glued back together with no frames or fastenings, only 403 in the seams and gaps. The stem, stern and keel are gone.
    She is only a little sailing dinghy, the hardest abuse she gets is the deck frapping at sea, carried on deck.But no glass. The "floors" are temps.

  49. #49
    Join Date
    Sep 2011
    Location
    Arizona desert
    Posts
    125

    Default Re: how much strength does fiberglass tape really add?

    cool project

    WEIRD! Because YOUR normal isn't working...

  50. #50
    Join Date
    Jul 2011
    Location
    Lindstrom, MN
    Posts
    522

    Default Re: how much strength does fiberglass tape really add?

    [QUOTE=Todd Bradshaw;3150655
    My reference to the two layers of glass was made simply to point out that a layer or two of light fiberglass is hardly the bomb-proof armor plating that a lot of folks seem to think it is. One good, and somewhat surprising, way to understand this is to isolate a couple layers of glass as I indicated and get a real look at what it can do and what it doesn't do. I just get the feeling that some people tend to equate a couple layers of 6 oz. with typical, non-wood, fiberglass boat construction and assume that they're getting or adding that same sort of "strength" to their wooden hulls. This is not the case and the two layer example was in reference to that - and in my opinion, still well worth doing for anyone using fiberglass cloth to cover parts or all of a wooden boat. I'd been working on both fiberglass and wood/glass boats for better than 20 years before I tried it and it was pretty shocking. I decided at one point to lay up some tapered fiberglass sail battens using epoxy and leftover 6 oz. glass cloth. I simply couldn't believe how many layers of the stuff it took to start getting something substantial enough that it might actually do the job in the non-cored areas of the battens. Maybe I'm the only person on earth that wasn't aware of this aspect of 6 oz. cloth, but I doubt it.[/QUOTE]

    I don't think many people are aware of that. Your posts are generally very reliable and I didn't like taking exception to something you wrote. It is hard to believe how a flimsy layer like that can add as much strength and stiffness as it does to a sheet of plywood or a strip canoe.

    There are a few websites that have some good information for anyone interested in more detail: http://www.oneoceankayaks.com/Sandcore.htm and http://boatdesign.net/articles/foam-core/

    Payson's plywood butt joints are a good example of the effect of a shallow angle and small fillet. It would take a pretty big lump of filled epoxy to make a tapeless butt joint. Since the fillet size is less conspicuous when there is an angle between the boards, the 'glass tape may be less important. It may not be the easiest experiment to set up, I think that you could demonstrate that there is a minimum fillet size for a given filler, epoxy, thickness of plywood and joint angle below which tape makes a big difference and above which the tape is not so important. The implication would be that you need to be very careful to keep the entire tapeless fillet size above the minimum needed. Fiberglass tape will reduce the minimum fillet thickness needed, but by how much and at what angle is hard to say without a well designed test. Taping both sides will also compensate for any undersized fillets. OK, my prejudice is definitely on the tape both sides side. Sanding the taped seams is a pain that I could do without, so I cut off the selvage and try to fray the edges a bit to reduce the sanding.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •