Stepped or pocket transoms?

Discussion in 'Boat Design' started by MIKE I, Sep 30, 2009.

  1. MIKE I
    Joined: Sep 2009
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    Location: Tampa Bay Florida

    MIKE I New Member

    Hi all, I'm newbe here. I've been power boating all of my life, but have taken on a project for the first time.

    I have a vintage 1972 Satelite 14' fiberglass V-hull skiff. It is in, let's just say it is a blank canvas. I will be restoring the transom and changing several other aspects of the boat as I go.

    I will be using the boat to fish the shallow waters of the West Coast of Florida, so shallow water performance is necessary. In that regard, I was considering modifying the transom with a pocket, to allow higher mounting of the engine to allow for shallower running. I had a Sailfish 174 with a pocket transom that performed very well in this regard.

    Does anyone have any experience adding a pocket to an otherwise flat bottom V-hull skiff? I will be using an older Evenrude 25hp 2 stroke long shaft engine. Specifically, I am looking for how large of a pocket would be effective. Also, are there any performance drawbacks with a skiff of this size.

    Thanks in advance for any information.
     
  2. Village_Idiot
    Joined: Oct 2007
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    Location: USA

    Village_Idiot Senior Member

    You will lose speed, performance and efficiency with a pocket. Unless you absolutely need it for running shallow, I would avoid it. If you're set on it, then it will need to be at least three feet in length, four or five feet would be better. Too short and it will not prime properly, too long and you chance sucking in air from the front. With a four-foot length, I would go 4-5 inches high and 12-14 inches in width. Make it five-sided, round if possible. You will need a special tunnel prop, e.g. - blades with a large swept area, lotsa cupping, probably four-blade.

    For a small boat like that, a step might work better. In from the transom 2-3 inches and up 2-3 inches - that will allow you to raise the outboard 2-4 inches from stock position. With a setback bracket you could possibly raise it even more, but not as high as with a pocket. Performance should be better than with a pocket.
     
  3. kmorin
    Joined: Apr 2005
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    Location: Alaska

    kmorin Senior Member

    Terms?

    MIKE I,
    would you mind spending a minute to help me understand what you mean in this question?
    "adding a pocket to an otherwise flat bottom V-hull skiff?"
    I know flat bottom and I've got an idea bout the V-hull but together I guess I don't quite see that image.

    Also I'm totally ignorant about 'pockets', could you take time to help me understand this discussion?

    It sounds like and interesting question, but I'm sorry to be unfamiliar with these terms' use in this way.

    thanks for any time to reply,

    cheers,
    kmorin
     
  4. MIKE I
    Joined: Sep 2009
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    Location: Tampa Bay Florida

    MIKE I New Member

    Sorry, I will clarify.

    The basic hull shape is "v" shaped bow, with a transition to a flat bottom at the transom.

    A "pocket" as I invision it is a cut out area in the hull of the boat, extending in from the transom, sort of an incomplete tunnel. This is to allow water to hit the engine higher than the bottom of the transom, allowing the engine to be installed higher than usual to provide the ability to run shallower than the hull would otherwise permit.

    Without a pocket, to be able to raise the engine's cavitation plate higher than the bottom of the hull would require a set back bracket, something I was hoping not to do, but may consider, especially if a pocket would negatively effect the performance of the boat in other respects.

    According to Village_Idiot, it sounds like the pocket he describes is more than I want to tackle. Cutting in a step is more my speed, possibly adding the set back bracket for fine tuning purposes.

    Thanks for the input thus far.
     
  5. kmorin
    Joined: Apr 2005
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    Location: Alaska

    kmorin Senior Member

    Thanks for the explanation

    MIKE I,

    Thanks for the clarification MIKE I, now I see what is being discussed more clearly and why you suggested these particular methods of shoaling the outboard.

    Hydraulic transom jacks not only move the engine aft about 4 to 8", depending on brand, they allow it to move vertically. So if you move the engine aft, on a jack plate, the wake will rise some, how much I don't think is constant, and the hydraulics can take advantage of that rise in the wake to lift the leg and still keep enough wheel in the water to run.

    If you considered just an additional 6" deep "spacer" of welded aluminum as a means to bolt a hydrualic transom jack to the existing transom, and add the hydrualic jack; I'd estimate the engine would be 12" aft the existing bottom at the stern. This would give a pretty good rise in the wake aft the hull, so the jack could now lift the engine 4-6" vertically and you don't make any hull changes except to bolt a few pieces of aluminum hardware between the engine and the existing transom.

    I realize that I'm spending your money pretty freely since the jacks aren't inexpensive but if it all bolts on, and you don't like it, then you can unbolt it all and list it on eBay.

    just a thought.

    cheers,
    kmorin
     
  6. MIKE I
    Joined: Sep 2009
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    Location: Tampa Bay Florida

    MIKE I New Member

    Thanks for the input. A hydraulic jack plate is far outside the budget for this craft. However, I am tossing around an idea for a manual jackplate, or adjustable setback bracket.

    My former boat, the Sailfish 174 would run with the engine trimmed so high that the skeg was even with the bottom of the hull, allowing very shallow running when necessary. This is why I am considering mimicking that design.
     

  7. Village_Idiot
    Joined: Oct 2007
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    Location: USA

    Village_Idiot Senior Member

    Another possibility is to extend the hull in the form of floatation pods, or sponsons. Here is an example: http://www.explorebeavertail.com/flotationpods.html
    While the commercial pods are a bit pricey, you should be able to 'glass your own pretty easily, especially if you have the 'glassing talents to attempt to tackle creating a pocket. Just use cardboard mockups, then 'glass over them, and 'glass them to the boat. If you don't like them, you can always remove them. Make sure the bottoms of the pods don't angle downward, or you'll have the effect of permanent trim tabs keeping the bow down at all times. Absolutely straight bottom will keep bow down moreso than it is now, and angled up slightly will allow some bow rise, but some loss of floatation from the pods. Just stuff to consider.

    With the pods, you can use a bracket to extend the motor back quite a distance from the transom without significantly affecting your longitudinal CoG (or the boat's "attitude" in the water). This will have the same effect as creating a stepped hull, but with more benefit (essentially creating a longer hull) and probably less work (no modifying of the super-structure of the existing hull).
     
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