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Aeromarine Predator 7.5 tunnel hull

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  • Aeromarine Predator 7.5 tunnel hull

    I purchased this boat way back in 1989. It is of fiberglass construction and I can attest to its strength. One day I was moving it along at about 35 to 40 close to the shore when it struck something right under the water. At that point it was thrown into a spin and right into the shore that was lined with big rocks. To my dismay the impact smashed the right sponson tip back extending back about 2 1/2". To repair it I used 2" wide masking tape and roughly formed the original shape of the sponson and after mixing in some gelcoat with the resin and MEK poured the tip solid.

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    Afterward, I sanded it down to shape repainted it and to this day I can't even detect where it ever happened. Oh by the way, that chap you see in the picture is not yours truly, just a future model boater that was happening by the lake that day.
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    Last edited by greenman407; 12-30-2010, 05:21 PM.
    IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

  • #2
    This boat is designed to run with a 7.5 cc size outboard motor. My first motor was rated at a mild two(2) H.P. I then took that motor and modified it with some cyl. porting, an exhaust throttle and a tuned pipe to get about (3) three H.P. Still not satisfied in these pictures you can see the latest motor. It is a K&B .82 (13cc) outboard that is supposed to produce (four) 4 H.P. I am still breaking in this motor but so far the results look promising. In this hobby you are always trying to go faster and turn sharper while still hanging on to some sense of control. I love model submarines but there is much to be said about a gas or glow fuel powered boat. The wonderful smell of burned alchohol and nitromethane, the beautiful yet obnoxious noise, the high pitched cleaver props boiling the water and spewing geysers at the spectaters when you bring it close to shore,give it a hard right turn and gun it! Kind of like SHAMU splashing on cue the addoring spectators. This boat doesnt just turn , it defys your imagination when you watch it. It makes square corners when it turns. Since you are running on the ragged edge sometimes you flip or blowover. Then its time to get in my trusty raft that I always take with me in case of just such an event , paddle out to get it and if no water has made it into the radio box you just blow out the motor , inspect the glow plug and have another go at it.
    Last edited by greenman407; 04-23-2010, 01:03 PM.
    IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

    Comment


    • #3
      Ok , a little more on what makes her tick. Since I lost an earlier boat due to radio problems I upgraded in that department. Here you can see a JR Alpina PCM that is no longer made. What I like about it was way back when it was the only relatively inexpensive radio that had a built in failsafe that would retard the throttle when you lost radio contact.
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      The radio box is a water resistant box with a acrylic see thru tape on lid. You use waterproof tape to seal it up before each run. Inside you have your RX and servos. On this boat I use a big honken 1/4 scale servo to handle the steering duties. Also you will note in these pictures that I use twin fuel tanks, not just to hold more fuel but to provide consistent fuel flow and needle valve settings on a boat that is constantly feeling the effects of inertia due to high acceleration and decceleration. The upper tank is called a header tank. It is plummed so that it always stays full while the lower larger tank empties itself. Because of the venturi effect that most carburetors utilize there is no fuel pump, but exhaust pressure is connected to the tank to give it a little push. On what other class of engine in this world could you hook the exhaust up to the fuel tank and not get an explosion I would like to know? It works well!
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      Also of note is the one large rod used for the steering exiting the radio box thru a bellows seal attached to the engine.

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      Last edited by greenman407; 01-20-2012, 10:54 AM.
      IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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      • #4
        The engine is mounted on a outboard mount that is adjustable for height and angle to the water. Since these props are surface piercing props they are designed to run half in and half out of the water. By thus doing you allow the engine to unload for higher rpms yet acheive good thrust. Infact the boats ride will try to trim itself to just that condition. On a tunnel hull its designed to use air to lift it up out of the water to a certain extent. Thats the secret to speed on a race boat. Instead of plowing through the water as does a submarine or ship the secret is to get as much of your boat out of the water and to skim along the top of the water to minimize hydrodynamic drag. The angle of the prop to the water trims your hulls ride. Angle your prop down and it will push the bow down ,angle it up and it will push your bow up. Its a balancing act as too much of either is undesirable. Because of the direction of rotation of the propellor which most are couterclockwise the boat turns better at speed clockwise. And since the props are surface piercing you run into a problem called propwalk. Since the upper portion of the blade is out of the water at speed and since there is very little hull touching the water the boat has a tendancy to steer to the right. So you find yourself holding your steering somewhat to the left as you go down the straightaway. Its a lot of fun. The fuel tank holds enough fuel for about 8 to 10 mins. at full throttle which is usually where its at all the time, after all, who takes their race boat out to run slow Id like to know???!!! I am anticipating your next question. What keeps the motor cool you say? There is a brass tube just behind the prop that picks up water and circulates it thru the head.
        Last edited by greenman407; 04-23-2010, 01:40 PM.
        IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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        • #5
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          Ok , here we are in 1991 on the water with a stock engine.
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          Youll notice that the boat runs completely out of the water, on top of the water.You can even pop wheelies!
          Last edited by greenman407; 12-30-2010, 05:22 PM.
          IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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          • #6
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            The next step in the evolution of power was the exhaust throttle and stainless skeg.
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            Last edited by greenman407; 12-30-2010, 05:23 PM.
            IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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            • #7
              Then came
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              the Magic muffler(tuned pipe) that is no longer manufactured. I hit upon the idea to combine the exhaust throttle and tuned pipe mods. together. To install a tuned pipe to an outboard
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              you have to cut away some of the lower unit to make room.
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              Last edited by greenman407; 12-30-2010, 05:23 PM.
              IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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              • #8
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                Not to be left out I decided to try a standard inboard style pipe and mate it to the outboard.
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                Last edited by greenman407; 01-20-2012, 10:55 AM.
                IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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                • #9
                  Trying to keep the neighbors at bey I installed a muffler to the pipe. Some people you just cant keep happy!
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                  Last edited by greenman407; 01-20-2012, 10:55 AM.
                  IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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                  • #10
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                    Pictures are worth a thousand words in some cases but what I am trying to show is not as evident in this picture as in real life. The angle that the propellor is at in relation to the bottom of the boat is between 2 and 3 degrees. On this boat it is an absolute necessity , otherwise the boat will be constantly porpoising. With a down angle or negative angle the engine is pushing the stern upwards and the bow downward to make this boat run smooth. With other boats , its a different story.
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                    Notice this detail of the lower unit. The four(4) holes that you see starring you in the face are the exhaust exit holes. To increase the power output of the engine, one of the things you can do is open these up, so that instead of 4 holes turn it into a long slot. The downside to it is that it will increase noise. I once took this boat to a race in Brandon, Florida and the race officials didnt want to let it out on the course with the other boats because of its noise.
                    Last edited by greenman407; 01-20-2012, 10:56 AM.
                    IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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                    • #11
                      This picture is of another manfg. of outboard engines.
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                      It is a Rossi with a tuned pipe included. Its a 7.5cc
                      Last edited by greenman407; 12-30-2010, 05:24 PM.
                      IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

                      Comment


                      • #12
                        I just wanted to dress up this engine a little bit so I resolved to pull of the cooling head and paint it the same Red that the rest of the boat is painted in. When I got it off I was surprised. All of the other K&B outboards and inboards that I own or have owned had a cooloing head that split at the edge so that you could easily clean out the passages. Well this design doesnt allow for that. The actual Cylinder head is pressed into the cooling head. I dont think that I will try to remove it.
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                        IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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                        • #13
                          Heres the finished product. Watch for a video of this boat soon.
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                          IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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                          • #14
                            Took her out today and the moment it started up it kicked parts out the side of the carburator. I retrieved them and then took some pictures. The problem was due to the head of a screw vibrating in two and allowing everything to come out. In the pictures previously posted you can see the screw head missing at that time as well but I didnt notice. Ill call K&B tomorrow and see about a different Carb. I dont care for this one.
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                            IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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                            • #15
                              Turns out after consulting the K&B website that this carburetor is obsolete and has been replaced by a new style. I will try to order one today. Here is their website:http://www.mecoa.com/kb/parts.htm
                              IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

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