Stringer repair

Discussion in 'Boat Design' started by Ken Sterback, Jun 19, 2011.

  1. Ken Sterback
    Joined: Jun 2011
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Brantford Canada

    Ken Sterback New Member

    I'm working on a Sunray SV169 which has the floor and stringers rotted out. I have started to fiberglass the new stringers into place and was wondering how many layers of fiberglass would be recommended for this. First picture shows the fiberglassing started. The next 2 show the first layer done.
    Also I can find little information about this boat and would appreciate anything that someone might have about it.

    Thanks:

    Ken
     

    Attached Files:

  2. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 116, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    Ken, Its not the number of fiberglass layers that is so important but getting an adequate bond to the hull and adequate protection for the wood that is most critical. I'd suggest some non woven biaxial or triaxial glass over the filet to the hull bottom. Also, I see quite a number of voids under the glass cloth that is already applied. These can be weak points and entry for water which will find a way in there and cause rot again. You can get a hypo needle and fill these with epoxy resin. A serrated roller is the best way to press the glass down and avoid such voids and a small 1/4" radius on sharp edges is necessary to get the cloth to lie down well. Too late for these precautions now, which is why the hypo solutions is needed.
     
  3. Ken Sterback
    Joined: Jun 2011
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Brantford Canada

    Ken Sterback New Member

    Thank you Tom for your help. I'm now wondering after I do my best to fill the voids, do I need to add another layer of cloth or should I bother. Would another layer of resin be needed? Not sure what you mean by the filet.
    Its all on the job training but I enjoy it. :)
     
  4. keysdisease
    Joined: Mar 2006
    Posts: 794
    Likes: 43, Points: 28, Legacy Rep: 324
    Location: South Florida USA

    keysdisease Senior Member

    Did you use a grinder with very aggressive disc on the fiberglass bottom before you glassed? In the pictures the surface looks clean but not "roughed up." Anytime you are bonding to cured glass you have to grind so the glass can get a "bite" on the surface. This is called a secondary bond. If you are laying layers over wet glass that is a primary bond and the strongest of the typical boatbuilding bonds. There is actually wax on cured resin that will interfere with your bond if you don't grind. Grinding is crucial for a good secondary bond.

    And as Tom suggested, cloth has no strength for this application. If you didn't grind you may want to consider starting over. Did you use any adhesive putty when you set the stringers? This is a thick polyester putty that would fill any voids from an imperfect fit of the new stringer to bottom and then whatever squeezed out would be used as a filet to radius the stringer to the bottom. This eases the tight turn the glass has to make at the stringer to bottom intersection and makes glassing much easier. And as Tom said, if you don't have a rib roller get one, a must have tool for this job.

    Resin has no strength alone at all, with glass cloth not much better. You absolutely need at least some mat and as Tom said even better some bi ax or tri ax to get any real strength in your bond. What you have now with one layer of cloth is inadequate, and putting more resin will not help.

    Typically a filet is putty or resin thickened to a putty that is applied to 90 degree turns like stringer to bottom joints to make a nice radius to glass over rather than a 90 degree turn. This is much stronger and easier to glass than a 90 degree turn.

    Steve
     
  5. Ken Sterback
    Joined: Jun 2011
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Brantford Canada

    Ken Sterback New Member

    Thank you for your help and input. It is very much appreciated.
     
  6. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 116, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    As Steve said, the stringer/joint connection to the hull should be ground or sanded to remove any slick surface. I've seen pieces just pop off a surface that was not sanded. A filet is a curved mass of epoxy (in this case) that smooths a 90 degree internal corner to provide a larger bonding area and one that fiberglass can be molded to. I'm assuming you have been using epoxy resin for this job. Reading some instructional material on use of epoxy is very important before doing any work of this kind. Much is available on the web and what we have offered is just a start..
     
    1 person likes this.

  7. Peter000999
    Joined: Jul 2011
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Brantford, Ontario

    Peter000999 New Member

    Tom/Steve Thanks for your replies to the project Ken and i have been working on. Just a follow up and quick question. We did go through 3 cans of acetone cleaning up the hull each time it was worked on before fiber-glassing.

    After reading both of your comments on bonding the stringers to the hull, can you share any experiences that have led you to this conclusion. Would this be short term deterioration of the vessel or a potential safety concern? This rebuild project has not progressed much more than the pictures shown on the thread.

    In researching a product to bond the stringer to the hull, the 3M-5200 came up first!

    http://multimedia.3m.com/mws/mediaw...uQEcuZgVs6EVs6E666666--&fn=60-4400-5507-1.pdf

    Is this the right type of product, or are there others?

    Peter Liberati
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.