Sea Sled madness. It’s in my brain.

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

  1. Ad Hoc
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    Ad Hoc Naval Architect

    If you want to go... full on regulations (an over kill), you could use the LoadLine rules:

    upload_2021-4-17_8-59-26.png
    upload_2021-4-17_8-59-40.png
    upload_2021-4-17_8-59-53.png
     
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  2. DogCavalry
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    DogCavalry I aim to misbehave.

    Full of water...
    On land, 7200# of aquacola to fill it up. On water she'd be down by the head so much about ⅔ that. The rest would pour out over the foredeck. The freeing ports obviously have to be at the forward end of the cockpit, or they will only let out half of that before
    they are above water.

    But in the absence of those bricks, even down so the foredeck was awash, it would be level and dry again in about a minute.

    Fallguy asked a while back how much water could realistically enter the cockpit. Not remotely that much unless we motored under a waterfall. How much? Let's see. But with the enormous reserve buoyancy it will be very difficult to scoop much water in the absence of breaking waves 15' tall.
     
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  3. Ad Hoc
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    Ad Hoc Naval Architect

    Final word on the matter.. promise!! :p

    From DNV's small craft rules:

    On craft with bulwark, forecastle, deckhouse or open structures forming wells, the total freeing port
    area on each side of the deck is to be minimum A = 0.02 V m2. The volume V is calculated based on total
    deck area and height to top of bulwark, with deduction of volume of hatches, deck-house etc.
     
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  4. DogCavalry
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    DogCavalry I aim to misbehave.

    Keep'em coming, Ad Hoc. I have at least another psi to go before the top of my head blows off.

    So I have 3.2m³, assuming that it wouldn't dump itself out. 0.064m² of freeing port. Translates to 0.7 square feet in total. My 0.5 in total seems a pretty good guess. Particularly considering that with that weight of water aboard it would be dumping out over the foredeck anyway, so the freeing ports should only need to manage (DC pretends to be doing math for a moment...) and voila! My pair of 6 by 6 ports is perfect.

    Thank god I'm already bald.
     
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  5. DogCavalry
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    DogCavalry I aim to misbehave.

    Just because I like math, I calculated volume by stations, rather than waterlines. Immersed ram first, Serenity would float at about B1. So 3' deep.
     
  6. BlueBell
    Joined: May 2017
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    BlueBell "Whatever..."

    There is no "perfect", don't jinx yourself.

    So my 3 x 10's (30 square inches) isn't that far off your 6x6 (36 squares).
    Both times two, so 1/2 a square foot drainage.
    Glad we got that sorted... or did we...
     
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  7. DogCavalry
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    DogCavalry I aim to misbehave.

    I have my fingers in my ears, going lalalala, so yes.
     
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  8. fallguy
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    fallguy Senior Member

    This means I was right for once in my life and certainly this is the most sensible rule for the application.

    Since most of the water will not usually be the entire volume, someone needs to convince John to scupper aft in a planing hull. An immersed forward scupper in a full on breaking wave won't help much either. And scuppers forward will forever piss him off when that inch of rain is sloshin and he says, that damn Fallguy told me to pass on my nice well I had planned.
     
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  9. Mr Efficiency
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    Mr Efficiency Senior Member

    This is an old formula for "freeing area" of scuppers I have kept, don't know where I got it from though !

    Freeing AREA (square centimetres) = 40 + (cockpit area in square metres x 15)

    The validity of it I can't vouch for, but it must have come from some authoritative source.
     
  10. DogCavalry
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    DogCavalry I aim to misbehave.

    Lets give it a try.
    2.9m x 1.5m=4.35m²
    4.35 x 15 = 65
    So 105cm²

    Seems small, Mr Efficiency. Although to be fair, that's about what I'm actually seeing in the wild.

    This has been an extremely useful meeting Gentlemen. I am grateful. I'm sure forum users in the future will agree.
     
  11. baeckmo
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    baeckmo Hydrodynamics

    I have built to the DNV (old workboat 15 m rules) applied according to post 1218 for many years, and tested the boats in rough conditions. In occasions where we "managed" to take green water on deck, those openings were adequate. But we had a few situations where a customer had installed swinging plates or blocked openings and just barely managed to save the boat. So: the DNV works, stick to it!
     
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  12. Mr Efficiency
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    Mr Efficiency Senior Member

    That would equate to a slot 4" x 2" both sides, and as you say, that is about what you see in actual boats this size, probably more like 4 x 1.5 inches actually. I prefer lightweight flaps on the scuppers angled at about 45 degrees so if you back the boat up in choppy conditions for whatever reason, water won't come flooding in, and neither will it casually wash in when the boat is at rest in a joggle. Planing boats with decent freeboard rarely come to grief from taking large amounts of water on board, self-draining cockpits serve more to allow water to continually escape, rather than build up to the point it represents a danger to stability. This is particularly the case with boats that have cabins and covered foredecks, taking a big wave over the bow seldom sees it flood the aft cockpit, but punching into rough seas can land a lot of spray in there, that builds up gradually to be a potential problem, unless it can escape by gravity, or is being pumped out of the bilge.
     
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  13. fallguy
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    fallguy Senior Member

    DNV

    4.35 sq m
    Times 0.813m high (32"), not sure if this includes the trough..

    3.54 m^3 times 2% is .0708m2 or a whopping 110sqin.

    Two ports each side at 3x8 is about right...

    Did I run it close to right?

    Did the 32" include the trough?
     
  14. DogCavalry
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    DogCavalry I aim to misbehave.

    Yes, my result exactly Fallguy.

    No, the 32" depth did not include the trough. That would increase drainage rate, since it increases the hydraulic head, without significantly increasing the cockpit volume.
     

  15. DogCavalry
    Joined: Sep 2019
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    DogCavalry I aim to misbehave.

    20210417_205417.jpg
    Trough like this. Sliding door omitted for hard-to-draw.
     
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