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Thread: fiberglass

  1. #1
    doug@bestnet.org Guest


    I am building a modified version of a Peterborough canoe. I have expanded it by 2", and added another inch to the depth. In order to maintain a low weight, I would like to use a 6 oz cloth on the outside and a 3 oz cloth on the indsides. My question is, do you think I have compromized the structural strength? If so, what would your recommendations be?

  2. #2
    Join Date
    Apr 2000


    We carry 2.3 and 4 oz. cloth. I would not recommend the 2.3, but the 4 will work, if you are a little careful with canoe. The difference in weight between 4 and 6 oz. will be negligible in any case as the resin will be a higher proportion than the glass.

  3. #3
    RandyCates Guest

    Thumbs down

    ...would like to use a 6 oz cloth on the outside and a 3 oz cloth on the indsides. My question is, do you think I have compromized the structural strength??[/B]
    I've just been talking with the folks at Newfound Woodworks on a very similar question. I asked if it would be OK to use 6 oz on the outside and 4 oz on the inside. Their reply was "No". Whe you hit a rock on the outside of the canoe, there is force applied to both the outside (pushing) and inside (pulling apart). According to them fiberglass' best ability is on the inside resisting the pulling-apart force. It's more important to have the strong glass on the inside. The outside is mostly there for abrasion resistance.

  4. #4
    Join Date
    Apr 2000
    Cedar Rapids, IA USA


    I disagree. Fiberglass - cedar strip composites are just like corrugated cardboard. The core provides very little strength. The separation of the fiberglass layers provides your structural strength. Most of the flexural strength comes from the cloth on the outside. THe only situation I can think of where it would be better to have the heavier cloth on the inside is if you were balanced on a sharp rock with a person in each end.

    On the other hand, tou really aren't saving all that much weight. The difference between 3 oz and 6 oz cloth is only 3 ounces per yard. Figure 6 yards on one side = 18 ounces. Add another lb or 2 for epoxy and you have 3 lbs or less by the time you trim the fiberglass. Your water bottle will probably weigh nearly that much. I'd use 6 oz inside and out.


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