Lake skiff

Discussion in 'Boat Design' started by swamp thing, Jun 2, 2017.

  1. swamp thing
    Joined: Jun 2017
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    Location: louisians

    swamp thing Junior Member

    Hello all,
    I am building an 19' long, 4'6" wide, flat bottom lake skiff. The stern 2/3 is flat then the bow rockers up 10" to a 25* raked bow. I am considering a "bow skeg" that would extend the bow rake down the 10" to even with to bottom and then flare out to flush with to bottom of hull. Kind of like the "cut waters" on the Munson landing crafts. My reason for this is to better handle the chop that I will encounter on the waters I travel. Does anyone think it would help?
     
  2. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    No. If put a "lizard lip" on the boat it will be very difficult to turn.
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    As mentioned, a cutwater will cause the boat to "bow steer" baddly and shouldn't be considered. This assumes the boat is essentially a jon boat type of design and intended for full plane mode operation. As far as handling chop and waves, well this type of hull form is the worst to employ in this regard, so maybe a different choice is necessary if you plan much rough water work. A garvey style of hull is similar to a jon boat and a little better with handling chop, though not by much. How fast will your target speeds be, how much power and what type, are you thinking of using?
     
  4. swamp thing
    Joined: Jun 2017
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    swamp thing Junior Member

    Thanks for the welcome and the thoughts. I will power with 40 tiller steered outboard and will cruse at about 15 k.
    Coastal waters mostly with some crossing open waters to get to islands and marsh fishing.
    Never liked pounding over waves but love skinny water redfishing.
    I had salvaged and rebuild old Lafitte skiff that had a deep bow that did tend to want to trip over her nose with the right wave and speed.
    Part of my thinking is that with my fat ars sitting back tiller steering the bow will ride up and the cut water will mostly engage the waves.
    Locals tend to ride skiffs that way in a chop. Munson must feel it helps but I wonder how much.
     
  5. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    Why don't you consider a Dory hull. Look at the Glen-L dory's for ideas.
     
  6. swamp thing
    Joined: Jun 2017
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    swamp thing Junior Member

    The Wee Hunk dory design a bit longer comes close to what I am thinking.
    Thanks for thoughts. We all know that with any design there are gives and takes.
    Another question, maybe should be a another thread?
    If you had two roughly identical boat but one flat bottomed and one semi-v and you could put "pound"meters in both.
    Would the flat be what % poundery than the v?
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The Glen-L dory series would be about the same in regard to bashing it's way through coastal chop as any other flat bottom hull form. It's not the design, but the hull form that you need to consider, as some are just much better setup to do certain things. For chop and coastal work, you'll want a V bottom with a well thought out entry. Two approaches to this bow shape issue; first and old school is to have some bury, with a fine entry half angle, to part chop as it's encountered. The more modern approuch is to cut the stem back with some rake and make it more bluff, but not so deep. This decreases weight in the forefoot and offers a buoyant entry to help the boat get up on plane and glance over chop. This buoyant bow also doesn't plunge as much, when condisions cause rolling swells or steep chop. Deadrise also can play a big role with deeper hull forms handling chop and coastal condisions more comfortably than shallower hull forms. Of course as always, the tradeoff is the increase in displacement this requires (deeper hull forms) and the power to move them at similar speeds of the flatter versions.
    [​IMG]
    This is the old school approuch with some modifications. A modestly warped V bottom, designed to control the pressure bleed off inherent with this hull form, which permits higher speed potential, sufficient deadrise to make the ride comfortable in rough water, wider than usual chine flats to help get her up on plane faster with less power, taller freeboard so she's drier underway in a rough slosh, etc. This has self bailing decks throughout and loads of storage below the sole, typical for the needs of near shore coastal work.
    [​IMG]
    This is the complete other end of the spectrum a clamming skiff. Stoutly built, flat bottom and about the same length as above. It doesn't have self draining decks, will be wet underway in a slosh, unless the sheer is raised (optional on the plans). She does use a lot less power to get up on plane and is much more shoal than the V bottom, but (again) everything is a tradeoff of some sort. This type of hull is easy to build, but not by as much as you'd think.
    [​IMG]
    In the end, you have to really think about your needs, as it's just as easy to build a boat that's not well suited to your requirements as one that is.
     
  8. swamp thing
    Joined: Jun 2017
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    swamp thing Junior Member

    Thank you for the clear explanations. The real trick for me at least is deciding what I want the boat to excel at. I tend to want it to do everything well!
    I have built a 30' trailable sailboat that was loosely designed around a Monroe egret sharpie that I found while looking for logs in Castine bayou. I sailed that sharpie for about 10 years before building my trailable version. I wanted it and use it for island camping along the gulf coast but would not consider heading to Cancun!
    I have used flat bottom bluff bow jon boats for marsh fishing but with dreadfull open water crossing ability.
    I hope to improve open water crossing by say 50% and lose only 25% of my marsh ability!
    Likely too much to hope for.
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A modest deadrise V bottom, either warped or monohedron is what you want. Finding a relatively low deadrise monohedron will be difficult, as these hulls typically employ 12 degrees or more and often are 15 or better. This leaves the multitude of warped bottoms which are limited in top speed, but also get up on plane faster, have better shoal draft attributes and need less power to get to speed. Glen-l sells a 15' shallow V bottom called Nimrod, which will be much better in a chop than a jon boat or other flat bottom, but she'll still do shallow water well. She has about 5 degrees at the transom which is pretty darn shallow.
     
    Last edited: Jun 4, 2017
  10. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Another consideration is the tiller steer system. Warped bottom designs want a more forward CG. Even with a tiller extension added, it can be difficult to get the cg far enough forward. You may want to go with a set-forward motor transom and wet well boxes on either side. This is a fairly standard set-up these days. The other option is just get a console. What you are describing sounds like a "lake and bay" boat. Something that is a bit more versatile than a dedicated flats boat. The best I can do is point you back to the original Willie Roberts boats from the Keys. Mako bought the designs when Willie called it quits. These boats are the cat's meow.

    lots of hull pictures here - 1968 Willy Roberts Refurbish http://forums.floridasportsman.com/showthread.php?81976-1968-Willy-Roberts-Refurbish
     
  11. swamp thing
    Joined: Jun 2017
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    swamp thing Junior Member

    Cool boat! Thanks for the link.
    I was going to do the well boxes on the stern but had not seen it done and did not know what they were called.
    I did something like that on the motor/ sail boat that I built. I am grateful to get some confirmation that parts of what I am thinking might be ok.
    Thanks again sharing. It is great to thinking on all this stuff.
     
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Those aft sponsons are only necessary on poorly designed warped bottoms. You usually see them as an addition to an ill handling boat, not out of the box on the origional design. Though some, like Bolger did use them, there are easier and better ways to address the pressure wave concerns on typical warped bottom designs. The Willy linked above is a perfect example of a poor design for this hull form, that was made better with these additions. In plan view you'll note the aft WL's don't "tuck" in aft, but just continue straight aft from just behind midship. This does two things (primarily), first is it limits (often to a great degree) maneuverability and turning diameter, but more importantly causes the pressure wave on the plane patch to increase in volume and intensity, as it moves under the boat. At speed, this wave isolates fore and aft on each side of the centerline, though not at the same rate. Because it's a warped bottom, the gradient ramps up the further it gets aft, eventually causing handling issues (chine walking, pounding, purposing, etc.). Drag goes up exponentially and speeds are limited as a result, along with ill handling. If the LW's are tucked in aft, the pressure can bleed off and delay the drag associated with a warped plane patch. This also lets the boat "dip her hips" in turns, making for crisper maneuvering, especially at speed. This treatment also delays the chines drying out at very high speeds too. I think you need something in between the 2 or 3 degrees of deadrise on the Willy or the 15 - 18 degrees often seen on newer craft. Look around for a hull with about 8 degrees.
     

  13. swamp thing
    Joined: Jun 2017
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    Location: louisians

    swamp thing Junior Member

    Mr. PAR and all thanks very much for your insights. I have greatly enjoyed thinking through all your points on my stuff and other sections of this forum, this is a great resource!
     
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