Sea Sled madness. It’s in my brain.

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

  1. DogCavalry
    Joined: Sep 2019
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    DogCavalry Senior Member

    The massive enclosure forward? The hull is so oddly shaped those last 3 feet I just relegated it to storage.

    Okay, I'll skip the stairs. I can always add them. I was inspired by this. 25odyessy_bowstairsXL.jpg
     
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  2. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I just think a bench is nicer. But it is your boat.

    I mean the massive cabin space. What is the goal of the space? Do not be offended too easily here. The adjective is just to offer perspectives. It is your boat; not mine.
     
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  3. DogCavalry
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    DogCavalry Senior Member

    The cabin is for long range travel, in Canada, at night, in the winter. With 8 on board.

    Don't worry about offending me. Speak your mind. I value the input.
     
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  4. fallguy
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    fallguy Senior Member

    You have to resolve weight issues.

    That house is going to need to be ultralight.

    Might I suggest starting with hydrostatics. Understand the displacement; then determine hull weight. Also, knowing ppi might be good because you might end up overweight with 8 pax, but you don't want to be overweight with 2. And if you plan to haul work gear; it lessens the load capacities.

    weight is a big deal in boats...my boat is going to be a bit heavy; hoping not way too
     
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  5. TANSL
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    TANSL Senior Member

    Determine hull weight, then determine displacement.
    Sorry, what is "ppi"?
     
  6. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    PPI is 'pounds per inch' immersion - although Dog Cavalry by being Canadian might be more metric inclined......
    It should be relatively straightforward to calculate approximate ppi's at different drafts, even long hand.

    John, have you worked out any displacements yet, perhaps using Simpson's rules to calculate hull volume?

    And as Fallguy has said, weight is so important - it would be useful to set up a spread sheet showing all the bits that have gone into the boat, with the weight of each item, and ideally the longitudinal distance of the centre of gravity from a suitable reference point (eg the transom) - similarly the vertical centre of gravity above the keel.
    Then take moments, and find out where the overall LCG and VCG is for the boat.
     
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  7. TANSL
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    TANSL Senior Member

    Using Simpson's rules you can calculate the hydrostatic values that will allow you to know the displacement of the ship, and many other things, at different drafts, but with them the weight of the ship cannot be calculated. This data is, indeed, of vital importance and must be calculated as soon as possible, with the greatest precision. The best thing, given the situation in which the construction of the ship is, is to determine the amount of wood used and therefore its weight. For the other items that are part of the ship's displacement, it is easier to obtain the weights.
    Attached is a spreadsheet that can serve as a model for calculating the ship's full load weight.
     

    Attached Files:

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  8. BlueBell
    Joined: May 2017
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    BlueBell . . . _ _ _ . . . _ _ _

    Superstructure weight concerns; agreed.

    Are you any good working with red cedar?
    I know you're fixed on wood.
    Wouldn't that be a nice core with some lighter epoxy/fiber on both sides.
    Domed of course for comfort, strength, drainage and sex-appeal.

    If the windows slide, only 50% can open.
    If they hinge up and hook inboard on the ceiling they raise the CofG but can open 100%.
    If they drop down into the wall they lower the CofG, don't get scratched or broken and open 100%.
    A mix perhaps.
     
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  9. DogCavalry
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    DogCavalry Senior Member

    Gentlemen, I am honored by your attention.

    Based on successful existing designs, I was fortunate enough to speak with designers and owners of, I should be able to safely manage a cargo load of a lot. The numbers quoted by the guys surprised me enough that I don't quite believe them. Winninghoff boats, and Marcus Lee's sleds up in Sitka.

    I calculated ppi at fueled without cargo or passengers, to be 1005#, rising substantially as more of the tunnel fills and the contact area grows.

    Anyway, 3200 pounds dry, but equipped. That much again in cargo is well below their claims.

    I can't work in red cedar. Too toxic, I'm sensitized now, like a guy who works in epoxy for too long.
     
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  10. DogCavalry
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    DogCavalry Senior Member

    As a digression, I was about to phone Fallguy: his suggested technique allowed me to do in 3 hours, what I had previously done in 12. I owe you/him.
     
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  11. fallguy
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    fallguy Senior Member

    yes, a light cedar super could work

    it might be a bit weak for a ton of plastic windows...

    a 1/4" thick strip is light, but not sure it'd support the roof

    figure the available displacement and hull weights first
     
  12. fallguy
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    fallguy Senior Member

    seems high for the ppi based on my gut

    also, 3200 pounds available loading seems wrong, too

    It might be good to challenge those a bit with some of the braintrust here, of which I am not.
     
  13. DogCavalry
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    DogCavalry Senior Member

    I always trust, but verify. I regularly modify my design based on feedback from the group.
    At design waterline, without cargo, surface contact is 10' wide, 21' long, within an inch or 2. There is about 10% loss of total footprint due to the tunnel. Checking the math again, that's pretty close.

    I really won't know about max load, until Bluebell, Anne and I max it out. I do know that contemporary observation and experience of the day related that sleds could still get on the plane at 100# per horsepower. The Winninghoff boats I mentioned were 55', 2x300hp ouboards, commercially harvesting kelp, and planed with 50000# of cargo aboard.

    So truthfully I am not thinking about weight limits, but rather the trade off between weight and fuel consumption.
     
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  14. BlueBell
    Joined: May 2017
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    BlueBell . . . _ _ _ . . . _ _ _

    Why would you use 1/4" strip?

    So, leave the windows out?

    Ppi seems correct to me ~1000.
     

  15. fallguy
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    fallguy Senior Member

    Well, he can't use cedar, so sort of polemics, but it was basically a starting point. And, no, I didn't say leave out windows. But, on the subject, suggesting cedar strip at 12mm is interesting because it is about 4 times heavier than 12mm foam. Sure, more glass on foam, but not that much. So, the only practical advantage to cedar is if ultra-thin. No? Otherwise, foam super seems obvious vs 12mm cedar, okay?

    The only reason I pushed back on the 1000 is because I had a vision the wetted area was not the entire bottom. A crude calculation of ppi would potentially be inaccurate if this was not accounted for. I am only smart enough to raise the question; not the answer. I am still surprised the bottom is in contact for the full width and the tunnel deletion is only 10%. Not saying John is wrong and I am right; jist saying it seems like a pretty high ppi and it seems 'jon boaty'. I had more of a vision of half a cat. But I haven't seen the waterplane eh.

    It sounds like it might pound like hell, too with that much water area. ?
     
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