Installing Longitudinal Stiffeners on Sailboat

Discussion in 'Sailboats' started by wesley Sherman, Jan 27, 2020.

  1. wesley Sherman
    Joined: Jan 2020
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    wesley Sherman Junior Member

    I am completely restoring a Alberg 30 1969.

    I have been researching a lot about installing a single row of longitudinal stiffeners (foam under fiberglass) . Some say that they need to be unbroken prow to stern, that breaks at bulkheads cause stress issues. Other things i've read say that you can end them at bulkheads but they need to be attached 1.5 times the size of the stiffener to the bulkhead.

    My main bulkheads are 1/2" off the hull thick tabbed and endless layers of biaxial tabbing.
    In my head the filleted bulkhead off the hull and the foam stiffener well tabbed to the floating bulkhead in my mind seems it should be ok.. but then again scientific knowledge is better than what iffs.

    I would like to install them and continue them prow to stern but have one break at the main bulkhead that supports the mast step beam behind the v-berth and continue on to the stern non stop.

    Comments are appreciated
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Did the boat have any longitudinal stiffeners like these originally or previously at some stage?
    Your hull should already be pretty strong, relatively, with a fairly thick single skin conventional lay-up.
    But if your heart is set on these longitudinals, then your proposed method of tying them into the main bulkheads sounds reasonable.

    Re a previous thread, how is it going re the new bulkheads port and starboard in way of the quarter berths?
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Are there stress cracks at the bulkheads ?
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    Wesley

    The answer to your questions depends upon:
    1) are they for panel breakers, i.e to reduce the load per unit area;
    2) are they anti-buckling stiffeners;
    3) are they design to carry structural loads?

    The answer to your questions depends upon the purpose of them.
     
  5. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Why do you want to install longitudinal stiffeners? Are you trying to correct a problem? Or are you planning to modify the boat? Alberg 30s are generally considered to be well built with considerably more fiberglass than in similar size later boats.
     
  6. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    Just forget the stringers. Build the interior in plywood or sandwich panels and properly fillet and tab everything to the hull and to itself (stich&glue). That way the furniture doubles as internal stiffening structure and it will be way more effective then whatever stringers you install. Not that the hull needs it, but if you are already at it you can just as well do it.
    Stick buildt furniture is for wooden boats. If you want the look of traditional panels you can always glue some nice hardwood onto the ply.

    Just to be sure, inspect the tabbing holding the main bulkhead to the hull. Back in the day that was done with polyester and it does let go of the ply after some time.
     
  7. wesley Sherman
    Joined: Jan 2020
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    wesley Sherman Junior Member

    very good questions. I have removed all interior of the Alberg its a complete restore (Yes labor of Love) I have installed the main bulkhead that supports the mast step beam only so far. The reason I am wanting or thinking of running hull stiffener own the hull side prow to stern is that this boat has seen some slight accidents, (ie car landing on the deck partially) partial grounding many years past. Couple weeks ago I completed removing all paint from starboard side and half the port side.[​IMG]
    The boat hull suffers from some alligatoring of the gel coat in places ( that i feel are from a very long sitting on the hard in the sun, in a few places that I deem not structural flexing. But however there are places, ( 1 were there was an impact of a car on port side looks like flexing, mirror that to the opposite side) looks like flex cracks in gel coat. On both sides I have sanded down to fiberglass and coated with a die kit to see if there was any cracks in hull an there are none. (assuming the die kit works in such a way.. its a kit to find crack in aluminum an the die stays in the crack an rest wipes off. But because of the history of the car impact and the slight grounding many years ago. I would like to for comfort sake run a length from fore to aft about 1 foot above the water line of stiffeners. Have not started this project yet but have the
    [​IMG]
    materials to do it with already purchased. Just because I have them doesn't mean I have to use them.
    I should say however the cracks I ponder about are between the water line stripe and deck attachment seam, mostly they do not run down to the water line stripe only a few here and there.
    One last thing maybe I don't need the longitudinal stiffer in that possibly the 3/4 wiggle wood strips I made for ribs to install closed cell insulation in between and attach slats to will stiffen this areas up as well as they would run vertical across these areas??
    [​IMG]
    If you look at this picture you can see the water line lightly, if you go about about a foot above this area)if you count the boat supports backward from the side its above the second pad between water line stripe an the deck, (between the third and fourth vertical pole) which is behind the bulkheads to the head by about 3 feet. This is one area, mirrored on the port side. Then forward of the main bulkhead it has the same on both sides as well.. they seem to be in the open areas of the hull between bulkheads. There are no stress cracks at any of the bulkhead locations. Being that when I am done with this project I will be blue water sailing I like to feel assured I've covered all bases.

    Thank you all for your input and answers.. there much appreciated. I am not a expert, I just read, read and learn from others and read some more. Then learn from mistakes, then read some more.

    I will add that whoever did the repairs from this event with the car did a beautiful job in the repair, can see were it was reinforced on the inside.
     
    Last edited: Jan 28, 2020
  8. Ad Hoc
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    Ad Hoc Naval Architect

    So the concern is then...???
     
  9. DCockey
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    DCockey Senior Member

    How exactly do you expect the stiffeners to contribute to the structural integrity of the boat? Do you have any experience with structural engineering?

    Adding stiffeners without considering the overall structural design can cause problems by increasing localized stresses.
     
  10. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Wesley, I think you've miss understood.

    It appears you have assumed there is a problem and guided the thread towards what you consider to be a problem and provided your possible solution to it.
    But whether there is a problem or not has yet to be established.

    The questions you are getting are based upon the data/info you have supplied....i.e assuming there is a problem you wish to fix and the replies based upon your - assumed - fix.

    I would suggest you detail up the issues and concerns, and let it be open ended, rather than closed ended, as it is currently. Then you will most likely get the replies you are expecting.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    That is pretty well telling you longitudinal stringers are superfluous. If you have stripped the thing out, it might be worth considering installing a core material with a layer of glass added, to get some insulation and anti-condensation properties, whilst also getting a stiffer and quieter boat. Would not add much weight, but cost a little bit.
     
  12. wesley Sherman
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    wesley Sherman Junior Member

    "Mr Efficiency"That is interesting idea in that other than the main 2 bulkheads it is empty.. I am currently sanding and preparing the hull to start building, If one was to lay a core as you suggest... could i use 1/4 balsa sheets? and how many layers maybe 2? of fiberglass or less? would i need to do the above and below waterline as well? or just waterline and above? interesting idea. Would this cause any stress issues overall ?
    I have about 21 sheet of 1/4 balsa in my shop... 2x4 sheets. Lastly i have the mast beam bulkhead up and the adjoining head bulkhead installed would this be a issue as well since the interior hull floor would be higher?
     

  13. Mr Efficiency
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    Mr Efficiency Senior Member

    I guess it depends where you intend to cruise, but if in colder waters to any degree, it would not be a bad idea. You would need a decent thickness of core to make good installation. You don't need much glass on the inside. If transitioning from cored to non-cored, tapering it over a few inches would avoid stress concentrations, which would not be a problem anyway, in all likelihood. Just an idea, but it could make for a more comfortable living space in cold water areas.
     
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