Removing the deck of a 46' express cruiser Ultimate Dive Boat

Discussion in 'Boat Design' started by cgoodwin, Jan 1, 2018.

  1. gonzo
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    gonzo Senior Member

    That was my observation too.
     
  2. JSL
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    JSL Senior Member

    To Baekmo's comment I would add that allowing for sea-state, speed, duration, you could be putting the 'divers' into a very uncomfortable situation. You are also exposing them to possible injury (back/spinal)... especially with the athwartships facing seats. To top it off, it also gives a better chance of getting sea-sick.
    But, if the speed is limited to 20 knots, waves to 18", you might be okay
     
  3. ondarvr
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    ondarvr Senior Member

    This was my thought also, this type of hull may not respond well to a heavy load being moved forward that far.

    The concerns about strength can all be taken care of.
     
  4. TANSL
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    TANSL Senior Member

    Not always.
    In addition to trimming, there are aspects of safety and stability that are likely to be a serious problem. Almost everything can be solved but many times the high cost does not compensate the transformation.
     
  5. ondarvr
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    ondarvr Senior Member

    What I meant was the strength issue is far easier to solve than the wrong hull shape. Once the boat has been dismantled to the point where he wants to take it, it's not hard to add the needed support structure. There is no resolution to the problem of a hull design that can't handle the load.
     
  6. TANSL
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    TANSL Senior Member

    Yes, I believe that we are all talking about the same thing or about different aspects of a problem that the OP raises and that probably does not have a cheap solution. But with that said, even a poor weight distribution can be corrected, much more easily than a structural failure. As to whether the boat can support the 20 divers with their equipment, the draft will increase by 25 or 30 cm but, surely, if the minimum freeboard allows it, the ship will be able to support it. It is more a question of the regulations on the minimum allowed freeboard than on the capacity of the hull, its buoyancy reserve, to support it, imo
     
  7. ondarvr
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    ondarvr Senior Member

    It's fiberglass, anything can be done to make the structure strong enough, and it really doesn't cost that much more than just making it slightly stronger. Around here people are constantly repurposing commercial boats, so turning this into an open bow isn't that insurmountable of a task.

    If the bow is fairly narrow and can't support the load of 20 divers and gear, then it makes no difference about strengthening it, that aspect trumps everything else. From the look of the hull the freeboard doesn't appear to be an issue, it has high sides, but it may become very unstable with that load up there if it's narrow.
     
    Last edited: Jan 2, 2018
  8. TANSL
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    TANSL Senior Member

    Everything is possible, in effect, it is what I am saying for a long time.
    As for the freeboard, this is not measured to the upper point of the boat's side but to the deck. If you remove the deck and replace it with a lower floor, the freeboard decreases a lot.
    The sides are very high and, therefore, very weak, since they do not have deck or transversal beams that supports them. This greatly diminishes the longitudinal strength of the hull as well as its resistance to torsion.
    Precisely, for being reinforced plastic, the addition of new elements and their union to existing ones is, in my opinion, more problematic than with other materials.
    I repeat that everything is possible but what you have to check is whether the cost is worth it.
    Going back to what the OP is interested in, I think he should explain in more detail what he wants to do, with dimensions included, for an expert to make a technical and economic assessment.
     
    Last edited: Jan 4, 2018
  9. PAR
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    PAR Yacht Designer/Builder

    As drawn, I seriously doubt he'll find enough foot well volume to have the seating in the positions indicated. They'll likely be much farther in board, just to have some foot well room around the table/storage area. This places the CG higher and well forward, though given the mass of these puppies in general, I think it can be handled. You have to remember she's likely powered by twin Cat's, with associated tankage, so plenty of mass to counter a couple of tons forward, even if well up and out on the forward end of the LWL. She looks to be a 5 bulkhead boat, likely with considerable longitudinal stringers bracketing the engines, below the sole. Again, it's possible for this to work, though a lot more effort and cost than likely initially envisioned.
     
  10. SamSam
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    SamSam Senior Member

    Boat Review by David Pascoe - Sea Ray 39 Express http://www.yachtsurvey.com/boatreviews/SeaRay39.htm
    Sea Ray and Balsa Core Bottoms - by David Pascoe, Marine Surveyor http://www.yachtsurvey.com/searay_balsa_core_bottoms.htm
    Are They Fiberglass Boats Anymore? by David Pascoe, Marine Surveyor http://www.yachtsurvey.com/Fiberglass_Boats.htm
    Cored Hull Bottoms http://www.yachtsurvey.com/cored_hull_bottoms.htm
     
  11. ondarvr
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    ondarvr Senior Member

    If it's balsa cored then it could change everything.
     
  12. fallguy
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    fallguy Senior Member

    Gear for’d, riders aft; keep more bowdeck; fly the helm above the head. Avoid cutting doors-not the ideal rig-probably need integral benches-way outta my league.


    Why so many headcount? Hard to care for that many. Are you always full?
     
    Last edited: Jan 3, 2018
  13. gonzo
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    gonzo Senior Member

    Gear forward is a really bad thing for divers. The gear is always aft next to the transom door and ladder. Moving from the bow to the stern with all the diving gear on is likely to cause injuries.
     
  14. fallguy
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    fallguy Senior Member

    Shows you what I know. You know with 20 divers he is going to be cutting doorS. Not sure the hull can take that. Also outta my league.

    I think the whole thing is a bad idea. Think I shudda stuck with that. It is like a test where you change the answer; then get it wrong, but the question was lousy in the first place or at least one you weren’t prepared to answer.
     
    Last edited: Jan 3, 2018

  15. fallguy
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    fallguy Senior Member

    Pretty likely balsa to the bottom if early 80s per Pascoe.
     
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