Radius ??

Discussion in 'Fiberglass and Composite Boat Building' started by tunnels, May 13, 2012.

  1. tunnels

    tunnels Previous Member

    What it the ideal radius for glassing ??
    not so much over things but internal corners like stringers going down onto the hull and the like where strength is involved !!:?:
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You know better than to make this kind of inquiry. A 1/4" radius is fine for a 1/8" plywood bulkhead, perpendicular to the 1/8" plywood planking in a kayak, if over a structural fillet and covered with 4 ounce cloth. Is it ideal? Probably, considering you'll use less materials and still have a tabbed bulkhead, that will break out the planking before the tabbing, in the event of a hard impact. This same joint would be easier to make if the radius was 1/2", but you'll use nearly twice as much fillet goo in the process, for no real appreciable improvement in strength (the plywood will still fail first).

    Provide some schedule guidelines, say two units of roving and mat (as an example), then you'll have defined the question enough to get a reasonable answer.
     
  3. tunnels

    tunnels Previous Member

    thoughts

    Ok stringers into the bottom of a boat will be
    Cove 18mm radius internal corner
    1x 450 csm over the pu foam as a bedding layer !
    4 x 882 gram double bias that has a 275 gram csm attached !
    1x 450 csm to finish with
    The 2 external corners of the foam should be 10mm radius .:D:p
     
  4. tunnels

    tunnels Previous Member

    Not giving up that easy !!

    The corners that glass goes round is not a place the any one ever gives a second thought to ,specially internal corners !!
    Bogging and coving really is quite important and along with the size and the shape of the cove . , stringers is one place that no one ever takes the care to cove but stick it in and glass it !! usually a small roller and push the glass in and forget it ! over the time the layers of glass are still wet if there is more than one layer of a woven glass unbeknown to you the pressure of being pushed into shape and nothing behind it to hold it there the layers can separate ever so sightly so now you could have glass separation and before it hardens you have a potentually weak place . may not happen all te way along but i could be just a small part , over time the weakness has the age old habit of working slowly little by little the layers move and it will spread !, if its a place that has load like a motor sitting on top and if the stringer has a join again over time little by little the weaknesses are found and the hull movement plays on these areas . a cove of a decent radius will hepl to prevent all this from happening !! Industrial glassing is a place to learn more about glass than you will ever learn in the marine industry .
    The hard roller can be your friend or it can be your enermy . Pushing glass hard in squashes the fibres and so the resin is lost plus you will find there is a hollow with a lump each side . I see it every where i go done by old and new glassing people because they simply dont know . 15 MM RADIUS not diameter is the ideal size !! the glass is easy to roll ! all the layers stay together and theres the proper amount of resin there like the rest of the maninate , always roll into a corner from both directions on the last role go all the way round and leave it at that !. I picked ona stringer because they get so many forces applyed from all diractions up and down side to side . its very important that they stay intact and strong ! once the wood gets wet and starts to rot all the forces get taken by the glass as the timber is now just there and serving no useful purpose !!!A gental curve will take more stress than a 90 degree with all the resin quashed out of it and will be there longer after the wood has turned to mush .
    Its the little unseen things that are important ,care and attenion to detail . :D
     

  5. tunnels

    tunnels Previous Member

    going to keep pushing toll something happens !!

    Disapointed !!
    So no one is in the slightest bit interested in coves and what they can do for you ??:confused:
    I do remember pages of information about coves relateing to size ! what was best shape semi circular and even part of a eliptical shape !! The size was what reallystuck in my mind all these years 50mm diameter or 25mm radius was the best as i recall for places like engine stringers and any where there was load and the possabilites of sideways roll . Getting away from the horrible dead 90 degree sharp bend that glass gets pushed into these days and people think its great when i actual fact its not !!. its a gross weak point !
     
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