Pickel fork design

Discussion in 'Boat Design' started by Lynx_lord, Jul 16, 2019.

  1. Lynx_lord
    Joined: Jul 2019
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    Location: Rock hill

    Lynx_lord New Member

    Hey there, so I'm new to boat building. I understand the basics of hydroplanes, but i want to upgrade a pickle fork/shovel nose hydroplane like the super spartan or tiny titan to fit two people. I understand you cant just scale the plans up to accomplish this. Has anyone done it? Also how is handling in turns on outboard vs inboard and rear vs midset engines? Lastly how can one improve ability to handle wakes/ rougher water? I know its alot but any help or info would he greatly appreciated!
     
  2. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    All hydros are basically a "one man show" the reason is that they are very weight sensitive. Hydros basically ride on a cushion of air that is trapped under the hull with the majority of the weight supported by that air cushion. Adding another 1oo pounds (a very light passenger) or 175 pounds or more is going to badly effect the way the boat performs. Basically that extra weight will turn the hydro into a conventional planing hull. Typical outboard hydros weigh about 100 - 120 pounds and the motor can add another 75 to 120 pounds. The all up weight of even a "D" class boat with driver is around 450 pounds. You're adding almost 40% more weight with a typical male passenger. Consequently the boat will simply come down off of the air cushion and ride on the bottom of the hull and the sponsons. In order to "fly" that much extra weight you'd need to widen the aft hull between the "air traps" to get enough area to get the air to support that extra weight. For an example if you wanted to support 175 pounds at 60 mph you'd need to add about a foot and a half wide area to the 10 foot length between the sponsons. With one person aboard the hull would likely blow over at any speed over 50 mph. That is, if you were to design a two man hydro you couldn't run it at speed with only one person in it.

    As to handling, modern hydros use a side fin on the inside of the turn. That is, they only turn left. If you were to try to turn hard to the right you'd dig the skid fin and would snap roll in an instant. Hydros run down the straights with the skid fin largely in the air. When you want to turn you move your weight forward to get the fin in the water and that gets the boat to turn. If you can't shift that weight you won't get the boat to turn. This would mean that you'd need to have your passenger move forward and aft to help you get the boat to turn.

    Hydros don't handle rough water. Period. The area between the pickle forks determines how much air (and lift) you get between the sponsons. If you raise the lip you add drag and increase lift but it becomes unstable very quickly. For this reason the lip is kept low and you'll only make the boat unstable if you jack it up. If you did a sponson at speed you'll likely tear the boat in half of tear off the sponoson. Hydros race on small inland lakes where no other boats are allowed and can even have disastrous crashes when they encounter wakes from other hydros. You could maybe make your sponsons much higher at the leading edge, but still, you're asking for trouble if you hit the wake of even a small 16 foot ski boat.

    Real hydros aren't toys. If you're going 60 mph or faster in a hydro you should be wearing full safety equipment including a racing life jacket and a suit and a helmet. The "lake racer" boats like the "super spartan" or tiny titan, are mostly just very old designs and aren't very fast anyway, but these are still smooth water boats that would bog down with two people aboard.

    You could maybe do a two place inboard hydro with a mid mounted engine, but that's an order of magnitude greater undertaking than an outboard boat, and it would still not be capable of handling any wakes without digging a sponson and ruining your day.

    If you get the idea that I'm trying to dissuade you from trying to do a 2 man hydro you're catching on. It's a fundamentally bad idea.

    There have been some 2 place tunnel hull boats, and small runabouts like "D" and "E" class boats used to be raced with two aboard, but that was a really cramped situation. You could rework the design of boat like the "C/D" race boat that Glen L sells the plans for if you want a real race boat that would hold two people, scale it up a bit and that would be a good ride.

    The question is, do you really want to go fast, or do you just think a hydro looks sexy? If you want to go fast then you might think about a designing a tunnel hull with the passenger weight centered on the center of gravity so the boat will handle the same with and without the passenger. Another approach to going fast is a padded hull like an Allison, they made some 2 place race 13 foot boats that were neat, handled well and were fast. All of these approaches are fine for inland lakes and places where there aren't 38 foot cabin cruisers throwing 2 or 3 foot wakes like you have in the Detroit river or the Intracoastal Waterway. If you want to go fast and there are wakes and waves around you need to think about the padded V hull like the Allison, they handle rougher water much better than any other approaches.
     
  3. Lynx_lord
    Joined: Jul 2019
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    Location: Rock hill

    Lynx_lord New Member

    THANK YOU SO MUCH! Honestly the reason i wanted to build a hydro was i have had the plans from an old popular mechanics book for years and always wanted to build it. And from the plans it's a fairly sinple affair. My goal was a light, two person boat that could go decent speeds. But was relatively easy to build. Ill research the othe designs and come bakc with any questions if thats okay.
     
  4. Lynx_lord
    Joined: Jul 2019
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    Location: Rock hill

    Lynx_lord New Member

  5. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Could try a "Knife" instead of a "Fork". A Sea Knife has the "cool factor" as well as rough water capability. May need to do a patent search first...unlike 3-point, Gold cuppers, and sea sleds, I'm not sure this is open to public domain yet.
    https://apps.dtic.mil/dtic/tr/fulltext/u2/a081325.pdf
    www.yumpu.com/en/document/read/25454816/introducing-sea-kmfe-powerboat-archive/3
    HIGH SPEED BOAT WITH PLANING HULL http://www.freepatentsonline.com/3763810.pdf

    edited out some clipped text...or tried to
     

  6. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    The Flying Saucer is a very old design, back in the mid 50's. Boat design has come a long way since then. You probably need to first figure out how much motor you want to use and how much you'll spend for the motor. If you want a small runabout that holds two you might look at the DynoMite from Glenn L, it's a small boat for motors up to 25 hp. If you want more power and to go faster, their "Tuffy" is for motors up to 40 hp. The "Bullet" is between the two, smaller than the Tuffy, but with similar power it's faster than the DynoMite. All of these are nice small 2 place runabouts with shallow V hulls that ride better than flat bottoms, but still pound if you get it in rough water. If you look at hull shape of the C/D runabout you'll see that it has a flat planing surface that is about 3 feet wide and then it has angled chines going outboard to the full width of the hull (usually about 60 inches wide at the transom).. When it's going fast a bottom like that will just be riding on the center section and more of it is out of the water. The Diablo is a utility boat, but it has the bottom shape of a race boat and it's considered very fast for that type of boat, and knowing that the bottom is shaped like a race boat it all makes sense. Boats that are flatter aft will be faster, but won't ride as nicely in rough water as a V hull. A padded V will be faster, but isn't as easy to build and I don't know of any plans for a 2 place padded hull . If you look around you can find modern stitch and glue designs that are a lot easier to build than traditional plywood on frame designs. Not that there is anything wrong with ply on frame, but they take more work to build, and are more work to maintain than more modern stitch and glue designs. Clark Craft has some interesting tunnel hulls that are in the 20 to 50 hp range and those will do about 40 mph, which is very respectable for a pleasure boat. They also have a "sport runabout" that is a side by side seating rig that is based on some older racing hulls, but would be a fast setup for the power. The "Madcap" was a successful racing boat back when they required that racing runabouts to seat two people. The best thing you can do is look at all the plans that you think you might want to build and pick something you think you'd want to own and enjoy. As you've seen some of the designs offered by Glen L and Clark Craft are very dated, a lot of them were first designed in the 1950's and they look it. If you want a "classic" looking boat go for it, but remember that we've learned a lot in the last 70 years. Depending on your wood working skills you may want to cut your teeth on an easier to build design and later if you want you can do something more complex.
     
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