Sea Going Triloboat Motor Sailor 48'x12'

Discussion in 'Boat Design' started by charlesakeem, Aug 31, 2016.

  1. sharpii2
    Joined: May 2004
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    sharpii2 Senior Member

    Attached are two scow designs of mine.

    One is an 8 ft pdracer, which is 4 ft wide and only about 3.5 inches deep. It is intended for protected water sailing, though some examples of the type have made long coastal voyages.

    As I hope you can see, there is not much room for it to heel before the lee bottom transom corner starts to dig in. So there's not much one can do to form the bottom/side "V", discussed in my previous post.

    The other one is what I call a 'JoeBoat'. it is entirely of my own design. It is 10 ft long and 3 ft wide. It's Hull draft is 5 inches and its Rocker Height is twice that. It is expected to almost always be heeled, even when not under sail. When not under sail, it will be propelled by a short sweep, on the low side, and steered by its rudder, rather than an opposing oar on the other side.

    I don't know if this wacky propulsion method will work, but I see no reason why it shouldn't. It certainly won't be as efficient as real oars, but hopefully not a whole lot less so. The advantage, other than a much shorter, single sweep to stow, is I can move myself closer to the sweep side, and cause some hull inclination, which will lengthen the effective Water Line, while creating a slight "V" to any chop.

    If I were to scale this up to say a 30 footer, and make it a motor-sailor, I would have to dispense with the idea of inclining it while under power.

    What I would do in response to that is to "V" the bottom. I would raise the Chines about half their immersed depth (2.5 inches, with the 10 footer), and place my center line the same amount deeper than the Chines used to be (7.5 inches below the Water Line, with the 10 footer).

    This would accomplish two main things:

    1.) it would lengthen the Waterline, much like inclining the boat would, and
    2.) it would cut in half the amount of bottom likely to slam in a chop.

    With the boat dead upright, as when motoring, I would have a slight "V" to split the chop, plus a full boat length Waterline.

    When the boat heels under sail, it would be able to incline half again as far over as it would have been with the original flat bottom, before the lee corner of the bow transom digs in.

    Also, the added "V" would lower the CB, and the raised chines would subtract from the original initial stability, causing the boat to want to roll less violently in a seaway.

    To be even more fiendishly clever, I could add long, shallow, bilge keels, to get my leeway prevention, under sail, without increasing my motoring draft that much. They would also help dampen any roll.

    I would probably end up with a total draft of about 2 ft, which I would probably need to get adequate rudder depth for sea like conditions.

    I'm not saying this concoction would be adequately seaworthy, but it would certainly be more so than the original.

    The all-up displacement of this creation would be between 4 to 5 tons.
     

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  2. WestVanHan
    Joined: Aug 2009
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    WestVanHan Not a Senior Member

    Maybe they are in protected waters but I wouldn't think of taking such a vessel along the BC Coast, and can't imagine it being calmer than BC.
    I've seen 2' become 6' in about 20 minutes.
    I'd regard a transat trip as being a suicide run.

    My advice,IF it is ever built-spend a bit more money to build a steel tube cradle,and ship it as deck cargo to Europe.
     
  3. charlesakeem
    Joined: Apr 2008
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    charlesakeem Junior Member

    Thank you all who contributed and helped me learn. Hats off to you especially Sharpii2 for the education. Just getting back to reading and researching boats again after a bit of travel. I do like some of those plans you have there. Rocker and a fine bow really make such a difference in the seaworthiness of Loose moose vs the Triloboat. I'm going to have to study and read your posts more to truly grasp everything
     
  4. sharpii2
    Joined: May 2004
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    sharpii2 Senior Member

    Thank you for your kind words, charlesakeem.

    Atttached is a lines sketch of a hull design of mine, intended for offshore work.

    It was intended to be a sailboat, but I see no reason it couldn't work as a motor sailor or even straight power boat.

    As you can see, it has a pronounced 'V' bottom and Chines that are only slightly immersed.

    When I came up with this shape, I was looking for the simplest to build one possible, which would have the capabilities I wanted.

    The first decision I made was to keep the angle of the 'V' consistant for the entire length of the hull. This way, Chine Logs could be cut with a table saw, at just one angle, with no further modification needed.

    The second decision was to run the chines straight to the stern post, so they would hve to bent in only one plane. This of course came with the requirement of a pointed stern.

    The Chine at the bow had to sweep up to clear the WL, so when the boat was fully loaded the stem post would just touch the water.

    Because of the relatively deep 'V', I felt the sides could be dead vertical. This hull will get its range of stability from the height of its sides, rather than any flair.

    As you can probably guess, based on my previous comments, this boat will not have a lot of initial stability. So the sail plan had to be kept quite low.

    It also requires a considerable amount of ballast, about 25-30% of its design displacement, depending on where it is placed.

    The next attachment shows a sail plan and underwater appendages.

    a 12 x 48 ft version of this shape would displace nearly 18 tons.

    Now imagine it running through a choppy sea, as opposed to a scow.
     

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  5. charlesakeem
    Joined: Apr 2008
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    charlesakeem Junior Member

    Interesting

    I like the lines reminds me a bit of an enlightened pd racer. What type of ballast could be used and is it necessary could it be used for tankage?
    Looking at potentially going for a river boat or maybe converting something to a motor sailor or terminal trawler.
     
  6. sharpii2
    Joined: May 2004
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    sharpii2 Senior Member

    I had four different ballas sytems under consideration for this design.

    The first two were internal ballast, the second two were external.

    The first internal one was simply sea water. Once launched, the tanks would fill up and one-way valves would hold the water in. The only problem with this is it required a LOT of seawater, about 1400 lbs, to get the self-righting capabilities I wanted. With an all-up displacement of around 3,00o lbs, this was not at all attractive. Add to this the tanks hogged up a lot of space in the hull, which encroached on accomodations and gear stowage.

    Next, I considered sand. Sand is about 60% denser than sea water. Re-doing my calculations with sand, I found I not only need less space, but less ballast as well. I found I could get by with around 900 lbs of it, instead of the 1,400 lbs of before.

    The only problem is that I needed some sort of leeway preventer, such as a center board, lee boards, or a keel. What I settled on was a kind of fixed lee board arangment (see first attachment) with the boards permenantly attached at the sheer and a very sturdy guard. If the boat stayed dead level the board's draft would be equal to that of the hull. But the boards were certainly going to weigh something. And much of this weight was going to be above the WL.

    To fix this, I considered an external ballast solution.
    (see second attachment)

    This was to be in the form of two long keels, which extended out from the bottom panels at a right angle. This would be relatively easy to build and probably quite strong. The keels were to be made of concrete and rebar, slathered with a good helping of epoxy, to keep the water out.

    Because the ballast in the keels was deeper, I again found I could do with less of it, only 640 lbs, this time. With this new arrangement the draft would be no deeper, and I gained 260 lbs more payload capcity, not to mention even more stwage space inside the hull. This is the sytem I will probaly stick with, if I ever build the boat.

    Finally, I got to thinking about what if others liked the hull shape, but wanted a single keel. The single keel was to be made opf the same materials as the twin keels, but because it was even deeper it needed less ballast again, this time only 400 lbs.

    So, what started out as a space and payload capacity hogging 1,400 lbs, got reduced to a much more managable 400 lbs.
    (see third attachment)

    This 5 ft by 20 ft boat was intended to cross oceans, under sail. Its likely slow speed (about 3 kts average) meant it had to carry a lot of water, about 50 gallons. It also had to carry a lot of food, cooking fuel, books and cloths, for an estimated 40-60 day voyage. On top of that, because it wasn't going to have an engine, it had to carry real ground tackle. All of this could easily add up to well over 1,000 lbs, one third of the boat's entire displacement.

    As for a large motor vessel of this type, you will probably need some ballast, as I believe the Coast Guard requires an intact stability range of at least 60 degrees. But, in this case, with no large sailing rig to counter balance, the water ballast might work. At the very least, it could be part of the ballast sytem. If it is posible to get the fuel tanks low enough in the hull, the fuel itself could act as ballast. But then water ballast tanks would be needed, so they can be filled, as the fuel is used up, so the boat maintains roughly the same diaplacement (and stability range) throughout its voyage.
     

    Attached Files:


  7. charlesakeem
    Joined: Apr 2008
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    charlesakeem Junior Member

    Reading back over old threads. True quality information Sharpii and glad to see you're still about on the forums.
     
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