Entry deadrise effects on performance.

Discussion in 'Boat Design' started by tuantom, Sep 18, 2007.

  1. tuantom
    Joined: Jan 2005
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    tuantom Senior Member

    I have a 1967 23' cuddy cabin I was out working on tonight - curiosity set in and I started measuring various angles along the bottom.
    I came up w/ 17˚ @ the transom; 38˚ @ the entry and 27˚ @ 6 feet from the entry (the water line is +/- 20 feet. It's a thin hull - only 7 feet wide.

    To me, This sounds like a fairly shallow entry and deadrise - and I remember this boat did slam a bit (I've been in worse) in a heavy chop or on a big wake; but never terribly - though it's been 5 years since it's been on the water and my memory is a little vague.

    How does this compare with more modern hull designs? It seems to me that most of the newer boats of this size have a deeper deadrise @ the entry and transom as well as fewer strakes (I have 2 and 2/3 on either side); while many boats hulls from earlier eras more closely resemble mine. Are the new boats that much lighter that the deeper deadrise doesn't effect speed as much? or is a smoother ride a more marketable trade-off? Maybe they've learned to get the best of both worlds. What are the benefits of having a shallower entry to transom deadrise ratio? Does it plane off easier?
     
  2. GREEKFLEET
    Joined: May 2007
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    GREEKFLEET Junior Member

    i don;t know to many things about the deadrise angle on boats like yours but i can say to you that on ribs that usually have deep-V hulls of the same length the state is 22-26 at transom and 52-56 at entry.Although as i mentioned ribs are deeper i believe your hull it is quite shallow and as i see from the Greek market the market goes to deeper and more comfortable hulls even you will have to spend many $ on gasoline (my opinion is that is wrong).But as it was mentioned before from the forum there is not a perfect boat but perfect boat for specific use-conditions.
     
  3. thudpucker
    Joined: Jul 2007
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    thudpucker Senior Member

    I had a boat like that...I mean a boat that spent most of its life being worked on, rather than in the water.

    Slamming is a way of life up where you are.
    The sharp entry and straight up/down bow line would not salm, but its an awful thing to get any speed out of.
    So the comprimise of a Fair entry and almost planing bottom.
    Enjoy what you have. I wish I had it.
    Why has it been on the beach for so long?
     
  4. Nojjan
    Joined: Sep 2006
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    Nojjan All thumbs...

    I think it sound like a nice hull, for it's size, that variance in bottom angle is not unusual, you can find it on modern boats (the same physical laws apply today as did in 1967). Warp in the bottom is often used to allow for heavy engines and/or better efficiency if the boat is not a true speed demon (then you need a straight run). The combination of resonable deadrise and a slender hull is probably helping you in the chop. I think the alot of boat owners buy boat with 22-26 deg deadrise for no good reason, they don't utilize it and it is costing more in fuel to maintain speed than a lower deadrise. The funny thing is that some boat builders are not really clear on why they have their high deadrise, they pitch words as smooth ride, optimal trim, no snap roll, etc. but ask them to quantify anything and they can't. I think you hit the nail on the head with that high deadrise is marketable.

    I suggest following Dave Gerr's advice and make more slender hulls, combine that with less deadrise and we get boats that may be more efficient and just as comfortable, and we save some fuel. Consider that pleasure power boating is not a friend of the environment.
     
  5. tuantom
    Joined: Jan 2005
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    tuantom Senior Member

    Thank for the replies,
    Greekfleet, that's a good point. I suppose on a calm, inland lake the flatter means better for speed and efficiency, while slamming isn't even a consideration. The Great Lakes can get pretty choppy - though the only time we ever really go out on those days is trolling for salmon (sloooooow). I can speak from experience that 7 - 11 footers are no place to be.

    Thudpucker, I think it's a fine ole boat and had some great times on it; But remember - there's no such thing as a free boat. This one was given to (abandoned to) me as a fixer upper. A new transom, stringers, extra set of stringers, plumbing, engine, outdrive, floor, seating, canvas, deck, paint job (still sanding) and ~$5,000 (time is free) later - and she's almost ready to be close to being ready to float again.
    Nojjan,
    I've spent quite a few hours searching this forum since I started this project 3 years ago, and I'm becoming familiar with a warped plane concept. However I only seem to hear about the positives of having a deeper vee and its ability to cut through waves (aside from what's written above). It's often stated that the deeper the vee, the more power it takes to plane - but it seems quite a few modern boats with equal or less power than mine had would out-perform it in all conditions, despite mine having a shallower hull. Hopefully removing several hundred pounds of wet foam will cure this.

    Is there a rough set of guidelines stating at what rate the hull warps from entry to transom that can determine/predict performance characteristics? How do strakes fit in? I've seen some members break the hull down into 10 stations as reference points on the hull. I'm assuming that experience over the years along with computer models have pushed planing hull technology much further than it was in the 60's. I guess I'm just wondering if there were some basic guidelines as to what station produces what effect.
     
  6. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    Nothing is either simple or straightforward in a planing boat. There will always be compromises to get the desired overall performance. Flat will give fastest and most efficient (less power) planing but, as we all know, flat has major problems in rough water. Warp is introduced to get some of the benefits of a flat(er) stern with better wave and chop cutting of a steeper deadrise bow. How much warp is based on local conditions, speed desired and, yes, personal preference. Try for too much warp like zero deadrise at the stern with a sharp bow entry and the boat will get squirrely at high speed and might even founder.

    Your boat sounds like a conservative approach with a fairly steep deadrise stern. By the way, you don't get to choose all the parameters. Choose a deep V and you get both heavy weight and high power required for planing. You can't have a deep V and light weight at the same time. In order to make the deep V stable, it has to be high displacement. Since it is heavy, it also requires high power. A higher power engine is heavier and so on and on. It's the nature of the beast. Deep V's were made popular by Ray Hunt and the "Moppie" phenomenon on the ocean racing circuit. There are far too many of them on inland lakes where their wave riding advantages are seldom needed.

    Lindsay Lord introduced what he called the monohedron or constant deadrise hull, at least in the aft planing sections. This is generally considered best of the warped plane variants at high speed. It is also used by most deep V designers but also applies at all levels of V.

    Weight is the absolute enemy of planing efficiency. Efficiency defined here as speed vs power. If you can get rid of some, the boat will respond better. I remember going out with a fellow who was so proud of his new deep V inboard on a lake in the 1960's. He invited several others to come along. He was so embarassed when the boat would only plow forward at about 12kts at an uncomfortable trim angle while making lots of noise and a huge wake.

    At the risk of disturbing any professionally trained naval architects who may be lurking about, I offer my own views on planing boats and theory.

    http://www.bluejacketboats.com/planing_boat_theory1.htm
     

  7. Wayne Grabow
    Joined: Aug 2003
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    Wayne Grabow Senior Member

    Slender warped bottom hulls

    I have been playing around with this concept for awhile and plan to start building a 20' hull of my own design next year with 8 degree deadrise at the stern, 15 degree deadrise amidships, and 48 degree deadrise 2 1/2 feet aft of the bow. The beam/length ratio will be 1/3.5. The sheathing is fully developable which will allow the use of a light but strong plywood skin. I realize that such a new design is an experiment, but I have been reading and paying attention to the expert opinions shared here so it hopefully won't be too far off target. Very interested to see what efficiency can be achieved. First we have to finish our new home with a larger shop, which is another fun project. Sorry I don't have results to share yet.
     
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