Sea Sled madness. It’s in my brain.

Discussion in 'Fiberglass and Composite Boat Building' started by DogCavalry, Nov 11, 2019.

  1. fallguy
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    fallguy Senior Member

    How far above the waterline is the trough bottom?

    Still see no reason for it.
     
  2. DogCavalry
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    DogCavalry I aim to misbehave.

    It's 14" above waterline.

    It allows 2 big freeing ports to be low enough to drain all water. That low they'll get submerged all the time in rough water. I don't want them constantly letting water in and out of the cockpit.
     
  3. DogCavalry
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    DogCavalry I aim to misbehave.

    IMG_2979.JPG
    It's this, but big enough to actually save the boat.
     
  4. fallguy
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    fallguy Senior Member

    So, if you go up 6", doesn't that place them at 20"? Can you also clamshell them on the front side?
     
  5. DogCavalry
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    DogCavalry I aim to misbehave.

    If I go up 6" that makes them a constant source of annoyance, and frequent damage.

    Like the pic I just added of another boat. Those round 2" drains would be much more effective if they were cut into the cockpit sides.
     
  6. fallguy
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    fallguy Senior Member

    Sort of confusing to say raising the port is a problem.
     
  7. DogCavalry
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    DogCavalry I aim to misbehave.

    As designed, they are farther above the water than most boats, and almost impossible to spit into the cockpit. If I raise them, they can't be under the sole anymore. Then they are big holes in the bulwarks. - In the absence of absolutely perfectly sealed covers, they will be spashing water on the legs of paying passengers, and other people's property every time I go to work.

    And a clamshell over them defeats the purpose. They restrict water flow by half or more.

    Oh yes. Flow rate is proportional to hydraulic head. So lowering the ports 6" significantly increases flow rate through them.
     
    Last edited: Apr 18, 2021
    fallguy likes this.
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    The situation that is going to put tonnes of water in this boat at a stroke, are the conditions that are going to overwhelm it anyway, the allusion to motoring under a waterfall seems apt. Large cats used for rescue work in all conditions, simply have a couple of scuppers at the transom, sometimes only one at the centre, they have to go out in conditions you would be foolish to venture out in. You are over-thinking it.
     
  9. fallguy
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    fallguy Senior Member

    We are overthinking it. I think John has the plan.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Planing boats are typically "bouyant", the amount of boat in the water is small compared to the volume above water up to the gunwales, there is little to no chance outside of surf conditions or a breaking bar that will dump large volumes instantly into the boat, unless freeboard has been neglected. So far as I know, bar crossings are not required for this boat. The sort of open water conditions that produce big breaking seas are more likely to blow this boat over in high winds.
     
  11. DogCavalry
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    DogCavalry I aim to misbehave.

    I hope to survive both. The local ferry service has gotten very conservative about bad weather. And when they cancel, some heroic and self sacrificing crew will get them to their critical destination (or assignation, we aren't judgemental) for a nominal fee of course.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    You know what they say, there are lots of old boaties, a lot of bold boaties, but not so many old, bold boaties ! :eek:
     
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  13. DogCavalry
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    DogCavalry I aim to misbehave.

    Lots of glass these last few days, but nothing worth a picture.
     
  14. DogCavalry
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    DogCavalry I aim to misbehave.

    So I'm soon to build the cockpit sole. I'm in the ironic situation where the hull form and power could manage far greater loads than the sole could ever bear.
    But I'd like to get close...ish. The relevant area is where Anne is standing, and the other side of the low bulkhead right in front of her feet.
    My thinking is to install a series of floors, as watertight bulkheads in 12mm plywood with upper and lower flanges/fillets. With a heavy plywood sole bonded down, the hull would function as the lower chord, the sole as the upper chord, and the ply floors between as the web, or triangulation.

    With a 16mm plus glass hull, and a 16mm plus glass sole, the question I come to is, what spacing to set the transverse bulkheads at. Too close is extra work and weight. The sole (or maybe the hull!!) fails first. To widely spaced and they crush, while the sole still is fine. Actually this is a non trivial question. Very dependent on hull form, web depth, and many other factors. 20210408_194738.jpg

    John
     

  15. fallguy
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    fallguy Senior Member

    You have to sample it and decide how much flex you can tolerate.

    The skins add little, so you can test the plywood alone, then the skins just add a wee bit more.

    Don't fall into my friend's fallacy that the other edges support the span...they don't.

    I had a couple pieces here 12mm and I don't like a 19,5" opening, but I do think a 16" opening is okay. Not a span rating. An opening rating, if you will.

    Another thing you can do is make a small i beam. Rip some 12'm stock down to 25-40mm. Bond the 3 pieces into an I. Next day, fillet the channels and lay in a piece of glass about 3" wide.. Next day flip and repeat.

    Then bond those above a small block bonded to the other frames or bulkheads. They split the spans for a bit of weight only. As little as 3" of stock can work. Mine are one inch web, two inch flats in foam. But in ply, you can go more like inch web and inch and a half flats. Make em 30" long or as needed.
     
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