Question for American Pro Boat Builders

[HRTV]

Hey MJR or anyone else,

I need help understanding how the balancing act is carried out on this F-500 Hydro where the motor seems to be set back almost 2 feet from the end of sponsons.

My question is how does the boat balance it self out once on plane if the air dumps at the rear sponsons, what and how does this 2 foot section lift and carry the hull being so far behind the boat.

[PopPop]

Hydro ??

Dan, I am not a builder but I think this boat is a F500 tunnel and not an O500 which is a hydroplane. Unless I am mistaken and the F500 is a four pointer with both front and rear sponsons. Maybe some European UIM racer can set us both straight. I need help here also.

[HRTV]

Dan, I am not a builder but I think this boat is a F500 tunnel and not an O500 which is a hydroplane. Unless I am mistaken and the F500 is a four pointer with both front and rear sponsons. Maybe some European UIM racer can set us both straight. I need help here also.

Hey Phil,

You are correct this is a F500 tunnel my bad but I still need help understanding why the massive set back

[David Weaver]

A Real Tunnel

The F500's are mainly tunnel boats, I believe. A hydro is legal, but not competitive on the one and two bouy turns prefered in Europe.

An APBA 500 Hyrdro is not allowed to utitlize a tunnel design by rule.

[HRTV]

The F500's are mainly tunnel boats, I believe. A hydro is legal, but not competitive on the one and two bouy turns prefered in Europe.

An APBA 500 Hyrdro is not allowed to utitlize a tunnel design by rule.

Yeah I know Dave, my question is about the set back, maybe Marc Johnson will chime in.

[sam]

Dan, you might want to look into Jim Russell's literature on tunnels.

A stable, fast tunnel is all about getting the center of gravity and center of lift the same place. I think these boats tend to use the back of the tunnel sponsons as a fulcrum, the weight of the driver ahead of the fulcrum, the weight of the motor behind the fulcrum. With that set up, you don't need to build much wing/angle of attack into the body of the boat. Wing is aerodynamic drag, if you can design a boat that doesn't need much wing and wing's compromising drag, it should be faster and still stable at speed.

[seaward]

probably needs an extremely high rake cleaver, to lift that much tail.

hal

[sam]

probably needs an extremely high rake cleaver, to lift that much tail.

It might have a high rake prop, but it doesn't need it to lift the tail if the boat is balanced on or ahead of the rear of the sponsons

[HRTV]

Side view

I'm still confused

[Composite Specialties]

Motor Setback

On a tunnel boat, the motor setback has alot to do with the nose of the boat poping up in conjunction with the motor trim. These boats have trim, as most tunnel boats do. The more you set the motor back away from the end of the sponson bottoms, the more it makes the front of the boat lift coming off the turns, thus requiring less trim and horsepower from the motor during this process. The closer the motor is to the back of the sponson bottoms at the end of the boat, the more trim it will take to lift the nose of the boat, thus requiring more horsepower from the motor.

Hope that helps.

[HRTV]

On a tunnel boat, the motor setback has alot to do with the nose of the boat poping up in conjunction with the motor trim. These boats have trim, as most tunnel boats do. The more you set the motor back away from the end of the sponson bottoms, the more it makes the front of the boat lift coming off the turns, thus requiring less trim and horsepower from the motor during this process. The closer the motor is to the back of the sponson bottoms at the end of the boat, the more trim it will take to lift the nose of the boat, thus requiring more horsepower from the motor.

Hope that helps.

Thanks Marc I was waiting for you to chime in I can check this off my list now, any thoughts on my other thread regarding how US drivers will stack up in Lake Alfred

[MN1]

I've noticed that many classes develop a general setback for the class. Is this because of the size of the propeller being used in the class?

Look at it this way, when the boat comes out of the corner and trims up the motor and prop goes deeper into the water with more setback. So, does the smaller propeller need to be deeper in the water to get the best acceleration for a certain weight of boat? I believe this is why many classes find that certain setback. Along with balancing the boat too.
Mark N