Designing small utility/work boat-skiff rocker question

Discussion in 'Boat Design' started by Murky Deep, Jun 8, 2020.

  1. Murky Deep
    Joined: Jun 2020
    Posts: 3
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    Location: Massachusetts

    Murky Deep New Member

    I have built a few skiffs (8) including a successful one off based loosely on a free design. I have read hundreds of posts from this site, Sucher and Gardner's books. Despite owning a bunch of plans, I site haven't found what I am looking for. I've spend thousands of hours on the water since 1989, everywhere from California to Croatia. I enjoy small boats that can be moved with 1-2 people, low horsepower(5-15), and I rarely go more that a mile or so from shore. Any boat that I own needs to do duty as a light fishing boat, family beach boat, and clamming skiff. Hannu Vartailia has values of efficiency with materials that I admire. Unlike many others, I do not enjoy high speed deep v hulls, and have friends that take me fishing on such boats often enough anyway. If the weather is bad I simply stay home.

    Now, what I plan on doing is building a serious strong back and 3-4 molds (2x6) that will produce a 14-17 foot skiff with a flat bottom out of ply or pine planks. Target weight is around 220-275 pounds. I want to build setup that can be disassembled and put back together, and produces a quality boat that would work well with 8-12 hp, yet still could be rowed home if needed. At least 1 friend and a family member will want one as well. I would build a 14 ft Brockway skiff, however, I am tired of one mold skiff building. Fighting the boat into symmetry takes up far too much time.

    The amount of freeboard forward is easy, as is the beam (just under 4 ft at the chines, 4'8-5' at the shear). Where I am struggling is the amount of rocker aft. In most of the pure rowing skiffs, I see 4-6 inches or so, in many power skiffs, none. I am happy with 6-10 mph under power, so as I try to decide on the height of that last mold to determine the rocker.

    Right now I am thinking 3 " of aft rocker, as it seems a good compromise. Any input?
     
  2. Will Gilmore
    Joined: Aug 2017
    Posts: 98
    Likes: 21, Points: 8
    Location: Littleton, nh

    Will Gilmore Junior Member

    As I understand your intent, you want a skiff that is stable and easy to move with a small outboard and oars. Something that can handle fishing with a friend or two without requiring a ton of materials to build.

    I'm not familiar with your terminology around the use of the word molds (1, 3-4). Is this removable framing? Anyhow, the lines and Web description for this little 17 footer seem like what you are describing. It looks like just enough rocker (I'd guess by the drawing about 3") and 'V' to make achieving hull speed easy with a good rowing setup. The build parameters sounded efficient in both cost and weight.

    Good luck with you hunt. I hope to see the results soon.

    Spira International Inc - Ablemarle Wooden Displacement Boat Plans https://www.spirainternational.com/hp_able.php
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    -Will (Dragonfly)
     
  3. Murky Deep
    Joined: Jun 2020
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    Location: Massachusetts

    Murky Deep New Member

    I was looking through Sucher and found this. It’s not all that different than the one Will posted other than the v.
     

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  4. Murky Deep
    Joined: Jun 2020
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    Location: Massachusetts

    Murky Deep New Member

    Does v make it easier to row?
     
  5. Will Gilmore
    Joined: Aug 2017
    Posts: 98
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    Location: Littleton, nh

    Will Gilmore Junior Member

    It depends on how the bow and the rest of the hull are designed. The less and more gradual you make the water bend around the hull, the less energy is needed to glide through the water. Hard chines can contribute to drag where the direction of water is forced to make a sudden change in direction, but flat bottoms can be better than round ones, where transition areas, like bow, stern, chine and rocker don't have to be accounted for. 3d movement offers more options for water to get out of the way than 2d movement (read here, configurations like plumb bow and no 'v'). Bring that flat bow above the waterline, it might be a different story.

    -Will (Dragonfly)
     

  6. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    A general idea for the aft rocker dimension depends on the displacement of the boat. When the boat is loaded at its intended all up weight, the transom should rise a bit above the static waterline. The boat may be a tiny bit faster if rocker curve is drawn gradually from the lowest point of the bottom upward to the aft end of the boat.

    Forward rocker is also an item of some importance. The forefoot should not be deeply buried for a simple skiff like this. If it is allowed to be too deep when in normal trim, the boat will be inclined to "hunt" when in a chop or when quartering waves or wakes. The term hunt is another way of saying that may not follow the helm steadily. Put the forefoot down into the static waterline but not by more than an inch or so for the small boat that you have described. If you raise the bottom of the stem ( forefoot) above the waterline the boat will be noisy and have more of a tendency to pound.

    The first order of business is to predict the all up weight and then draw the rocker curves to accommodate that figure.
     
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