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

    I used 3" sill heights on the Skoota, but all aft facing and the deck is quite a bit above water. And there are two massive 15" water exits (boarding doors).

    The way I achieved one of them was by putting a landing on the other side, otherwise, it'd be a 10" drop to get inside. Then you can maintain the grate, increase the coaming to greater than 1.5" above the grate and make the door smaller which is a ducker, but that is boats.

    Now, I realize, this might cause some headaches inside, but you can also take advantage of the landing. Here it is a conduit. The cabin sole is 10" below the cockpit sole. I considered a 5" coaming, but I have quite a few elderly friends I had hoped could ride along.

    652DA0CE-D2DF-447C-9A69-E4F3193574B3.jpeg
     
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  2. Ad Hoc
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    Ad Hoc Naval Architect

    Being aft mitigates most issues to allow the sill/coaming height to be reduced.
    Increased deck height is another.
    Thus 75mm doesn't sound much, but in its location etc..it is probably satisfactory.

    But in both situations, you need to ask yourself this question.

    If a big wave come over crashed through the door, will it fill the cabin and lead to capsize?

    If you have sufficient reserves of buoyancy under the cabin (in the hulls), or raft section or whatever..that is another mitigation.
     
  3. fallguy
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    fallguy Senior Member

    The door is outswinging, to your earlier point.

    A wave crashing through it would be catastrophic. The cabin would be breached and the power of the vessel would have long been disabled.

    A1901978-3694-454F-9124-53E25F91B578.jpeg
    Scuppers..15" by infinity.

    A lot has to do with the potential volumes of water. Have you any idea, DC, about how much water could enter the space?
     
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  4. fallguy
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    fallguy Senior Member

    I actually was a bit nervous about water exiting. But the reality is if we encounter that much water, the outboards will probably have drowned.

    F21C1D75-A53E-4F60-A0D9-847A86A34A82.jpeg
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    Additional freeing ports here:

    upload_2021-4-15_12-22-16.png

    Would help a lot too. As that is a large enclosed deck area to carry water!

    This:
    upload_2021-4-15_12-23-32.png

    Helps a lot, but with only one... it is insufficient for a large stern wave that dumps on you.
     
  6. fallguy
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    fallguy Senior Member

    there are two; one on each side...no good pic I could find--I modified it from the original design just for the safety and dual feature of walking onboard...the cockpit is about 15x7 feet with a 40x40" helm riser..water entering rapidly would crush the cockpit if it did not leave

    but I would like to switch to talking about DC's project...I am wondering how much water could fill his front cargo hold and whether his scuppers are big enough..this also goes to his idea about loading bricks on the sled

    I think if he did a volume calculation, he might find 6" sq times 2 is a bit light, but I am guessing
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Agreed!
    Apologise for the slight digression and deviation... my bad :(
     
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  8. DogCavalry
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    DogCavalry Senior Member

    You fine gentlemen are paragons of virtue! Most threads get hijacked in awful directions, and never come back.

    My uncertainty comes from a couple sources:

    -I find numerous threads on the forum discussing cockpit drains that are served by hoses, and the question is whether a pair of 1¼" drains is enough, or if the builder should go to 1½" to be on the safe side. So my holes, with 20 times the area and probably 50 times the flow rate considering wall and edge effects, seemed plenty. Now I'm less confident.

    - anecdotally, from extensive conversations with Marcus Lee in Sitka Alaska, he found there was such an extravagant amount of volume forward that he never took water over the bow. That, however, is an untested anecdote.

    - I am pretty confident when it comes to my carpenter skills. I imagined I could build a door that could easily keep out a foot of water for the time it took to drain away. Less certain now.

    - I wanted as accessible a door as possible.

    I ain't shy about cutting wood. Maybe I'll build the coaming as high as suggested, then cut it down if it seems like that is possible. Do cracked-ribs' "south tip of quadra on a rough day" test, and see.
     
  9. DogCavalry
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    DogCavalry Senior Member

    I can certainly follow Fallguy's suggestion about the landing, and add Ad Hoc's (see what I did there?) extra coaming height, without making a dangerous step.

    Good calcs on freeing port dimensions found from South African source. Many have been of the 2 square feet plus % of total area of bulwarks. Gives comically large freeing ports. This source gives .168 of H times .4 of L. Much better. And those dimensions are so large that edge effects are mostly absent, so I can use them with confidence.
     
    Last edited: Apr 15, 2021
  10. Lloyd Too
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    Lloyd Too Junior Member

    Maybe look back to the basics, your SOR, and "increase" from there on what's needed or wanted instead of thinking "open/scooped bow crew/rescue/sar that MUST handle everything less than 100mph winds"?
    (I'm not the best at reading the tone of what others are saying/thinking; I could easily be reading my thoughts/biasses into this, anything.)

    Are you willing to dog down the door? Would that ever reasonably be needed?
    Would what works for those in SE AK work for you? Would that (drop ramp, bow picker, ?) be over-kill?
    Door strength compared to planned glazing/windows?
    You're willing to change the design at a later date, would you rather add or remove additional materials?
    Would it make sense to have a fabric cover that you could install to reduce water intrusion into the bow if ever needed? Would that be of use when docked during the rain season(s)?
    Are there other options that would allow/push air into/through the greenhouse when under power?

    I resemble the tall and the fading physical capabilities of occupants descriptions that you've brought up. (Baseball hats had/have been a suitable warning device for my noggin when working in/under vessels and vehicles.)
     
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  11. Ad Hoc
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    Ad Hoc Naval Architect

    Simple ones from Workboat Code

    "..The area of freeing ports should be at least 4% of the bulwark area and be
    situated in the lower third of the bulwark height, as close to the deck as
    practicable..."
     
  12. DogCavalry
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    DogCavalry Senior Member

    That's a great guideline! I'll follow that. I find this forum to be incredible value for the money.
     
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  13. bajansailor
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    bajansailor Marine Surveyor

    Fallguy's Skoota is looking very impressive, with outstanding finish quality.
    Along with DC's multi-purpose sea sled.

    Apologies for the thread drift, but I just saw this photo, taken in the Careenage (the harbour here for small coasters) in 1977 - it shows a traditional timber inter-island cargo vessel discharging bananas and plantains, probably from St Vincent or St Lucia.
    And the apertures in the superstructure reminded me of the discussion on here about windows and doors.....
    I love the 'garden shed' wheelhouse on top of the accommodation.
    And windows / doors like these were the norm on the powered vessels (which generally had a reasonably good safety record) - there were some sailing cargo schooners still trading in 1977 (the last one retired about 15 years ago), but they had much less superstructure, and more traditional companionways and portholes.

    In the background is one of the Barbadian (Bajan) shrimp trawlers - there were about 20 of them, and they would go trawling off the northern coast of South America.
    Two of these trawlers were later converted in the early 80's into patrol vessels for the Coastguard here.

    Careenage - unloading plantains 1977.jpg
     
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  14. fallguy
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    fallguy Senior Member

    bulwark area....

    Let's say the cockpit is 15'x7', using Skoota since I don't know John's. 105 sqft...4%, call it 4.2 square feet, my ports are say 1.4' wide by 1.5' high. 2.1 square feet x 2 of them is 4.2 square feet. Did I do the calc right? My goodness, could my intuition be that close?
     

  15. fallguy
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    fallguy Senior Member

    If the Seasled has two 6"x6" scuppers, then 4% is only 12.5 square feet of bulwark. Am I doing the math right? I have a hard time with more scuppers, and I am confused about the front of the SeaSled. I seem to recall it was big enough for plywood full sheets on their sides. But based on the drawing of the grate, I don't see how it is that big unless the bottom step is down below the forward cockpit. Total confusion here.
     
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