Would a Bulkhead Help

Discussion in 'Boat Design' started by Southern Cross, Aug 18, 2013.

  1. Southern Cross
    Joined: Mar 2013
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    Southern Cross Senior Member

    The below article is taken from an Olson 30 website. In lieu of of these modifications, I was wondering if a larger bulkhead, say from the deck to the hull and wider, would help reduce flexing?

    I'm currently in the process of retrofitting the stringer that the mast step sits on. I thought of an alloy but that might be too hard against the hull. The stringers sit in the bilge. The problem in the past has been rot. I could epoxy a piece of hardwood?..

    Any thoughts?

    Olson 30: Beam of Destiny & Jockstraps

    History/Purpose:

    Several Olson 30 owners have added a beam that runs athwartships on the aft side of the main bulkhead. This beam is usually bolted through the chainplates using the top two chainplate holes. This beam has become affectionatley know as the "Beam of Destiny". In addition, "Jockstraps" have been installed from the base of the mast to the chainplates on the forward side on the main bulkhead on each side of the boat.

    The objective of the "BOD" is to reduce the amount of hull flex and to enable the boat to carry more rig tension. The main purpose of the "Jockstraps" is to control mast compression as some boats have fractured the stringer that sits beneath the mast step.

    Both of these items became class legal back in 2000, however, it's important to note that they are not required from a safety point of view. They do, however, stiffen the boat and reduce hull flex which appeals to the serious racer!

    They have been built from stainless steel, laminated hardwood, and carbon fibre.
     

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  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    I have read several threads all along the same lines.

    You are going to have to quantify "flexing".

    So, under a given load which is to be defined, what deflection do you get at bow, midships, stern and at mast base. The deflection given in all 3 degrees of translation.

    Then you're going to need to provide the midship section of the hull and the materials and their mechanical strengths if not readily available.

    Since without such data to actually quantifying your "flexing" is rather difficult to asses whether there is indeed a problem of it is just your perception of a problem; judging by your many threads despite replies from many experience posters. What you see and what you measure are often very far apart and surprising! Thus only facts will tell you if there is indeed an issue to be addressed.
     
  3. Southern Cross
    Joined: Mar 2013
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    Southern Cross Senior Member

    No perception of a problem. A known problem observed by owners who have been racing them for 30+ years.

    The previous thread was about the alloy toe rail. A lot of great input. It answered my questions. This is about beam reinforcement and mast step reinforcement.
     
  4. El_Guero

    El_Guero Previous Member

    I am tired so forgive my rambling, and I am trying to help.

    How is one stringer beneath the mast breaking? One singular beneath the mast?

    Where is it? Directly below? Shouldn't that be a keelson, not a 'stringer?'

    If you need to reinforce, you will need an NA for advice. It is not a safety issue, it is for performance? Are they really saying that? You need your boat inspected.

    Reinforcement should have been (originally) spread across several bulkheads, but I do not know how many, more is always better.

    wayne
     
  5. Southern Cross
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    Southern Cross Senior Member

    Wayne,

    Yes, keelson, I'm sure, except it doesn't run fore and aft. All the other owners have been referring to it as a stringer. You can see it better in the attached picture.

    The original construction used plywood glassed over. So, if water sat in the bilge, the wood became soft on the bottom. When the mast was was loaded the wood compressed and sometimes failed completely. After 30 years, mine sinks about 1/4" (the board dips that much in relation to the surrounding board).

    The keelson/stringer is an easy fix. I'd rather not have a jock strap if I can construct something strong enough to withstand the loads. The jock straps were not part of the original design. I thought a piece of alloy epoxied in might work but I'm afraid of having any hard points on the hull even with something separating the metal from the hull.

    Also, the jock strap seems counter-intuitive to me. Because the jock strap is attached to the chain plate, when the mast is loaded it pulls inwards at the beam. Then the Beam of Destiny was added, for stiffness, but also to keep the beam from flexing? So, doesn't it make sense that reinforcing the stringer/keelson will eliminate all of these extra modifications?

    By the way. These modifications were originally conceived of and approved by an NA for the Class Association.
     

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  6. Southern Cross
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    Southern Cross Senior Member

    The attached picture shows how the beam reinforcement is supposed to be.
     

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  7. Petros
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    Petros Senior Member

    A full bulk head there would help a lot, the other solutions work too. I think an alloy beam or stringer could work if it was well bedded with epoxy where it contacts the hull to distribute the load. You could also build-up a carbon/epoxy beam. It seems wood in cross gain compression, particularly in a wet environment would not be a good choice. Wood only has about 300 to 500 PSI capacity in cross gain compression, so you would need larger bearing plate to keep it from crushing the grain.

    If it were my boat I would design a full bulked for that location, well attached around the perimeter and giving sturdy attachment to the shroud lines. It would make traveling for and aft in the cabin a little troublesome, but at least you will be able to avoid the trip wire problem with the jock strap.
     

  8. Southern Cross
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    Southern Cross Senior Member

    Thanks Petros. Always the thoughtful, helpful and courteous response.

    I think you are right and given the French boats have as many as 10 bulkheads, it seems it wouldn't hurt.
     
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