pullin up the boat ramp
Senior Member
Joined: Jan 2000
Posts: 3,205
Likes: 3
From: Along Lake Erie
Originally Posted by 2stroked
Zaairman,
Nice diagram. Takes me back to my days in Engineering school. Two suggestions though. First, your outboard appears to have a long mid-section (long shaft) where a short shaft is really needed for this particular hull / transom configuration. Running the prop that deep in the water will lead to lower top end and torque steer problems. (Don't force me to draw the diagram for that one!) Second - because this is a boat - you're missing the force of beer. And we all know which way this will drag the boat and trailer!
Nice diagram. Takes me back to my days in Engineering school. Two suggestions though. First, your outboard appears to have a long mid-section (long shaft) where a short shaft is really needed for this particular hull / transom configuration. Running the prop that deep in the water will lead to lower top end and torque steer problems. (Don't force me to draw the diagram for that one!) Second - because this is a boat - you're missing the force of beer. And we all know which way this will drag the boat and trailer!
Force-wise, 7000 lbs of truck and trailer is the equivalent of 31,000 Newtons of gravitational force. If that ramp is 10 ft of rise in 15 ft, that's a 33 degree ramp... pretty steep, but we'll use it. Now, 31,000N * (sin (33))=17,000N which is the equivalent of 3866 lbs trying to drag the truck back down the hill. If the truck and trailer was on a ledge, with a cable running around a pulley to a weight hanging down, that weight would be nearly two tons of force on the cable... it's gonna roll backwards. (It's not quite the same thing on level ground as it is on the hill, because of the traction forces, but that's a whole other discussion.
-Joe
-Joe
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Joined: Mar 2001
Posts: 3,248
Likes: 2
From: Rochester, NY, USA
Joe,
I think you missed the point of me poking fun at the diagram. Besides, I'm a "go fast" guy. The prop shaft on my modified (240 HP) Mercury outboard runs level with the planing bottom in most cases. (adjustable Jack Plate.) We're always looking for ways to go faster and playing with the X dimension works pretty well when you start to exceed 75 MPH. For most of the fishing boats I've played with (on Lake Ontario), outboard height on the transom isn't much of an issue. When the prop comes out - regardless of X dimension - you're in some hellacious rough water. I will agree that the deeper you plant it, the better the boat will handle at low speeds though. Mine's a nightmare around the dock, but it goes like stink.
I think you missed the point of me poking fun at the diagram. Besides, I'm a "go fast" guy. The prop shaft on my modified (240 HP) Mercury outboard runs level with the planing bottom in most cases. (adjustable Jack Plate.) We're always looking for ways to go faster and playing with the X dimension works pretty well when you start to exceed 75 MPH. For most of the fishing boats I've played with (on Lake Ontario), outboard height on the transom isn't much of an issue. When the prop comes out - regardless of X dimension - you're in some hellacious rough water. I will agree that the deeper you plant it, the better the boat will handle at low speeds though. Mine's a nightmare around the dock, but it goes like stink.
Senior Member
Joined: Mar 2005
Posts: 5,843
Likes: 0
From: St. Charles, MO
Originally Posted by 2stroked
Zaairman,
Nice diagram. Takes me back to my days in Engineering school. Two suggestions though. First, your outboard appears to have a long mid-section (long shaft) where a short shaft is really needed for this particular hull / transom configuration. Running the prop that deep in the water will lead to lower top end and torque steer problems. (Don't force me to draw the diagram for that one!) Second - because this is a boat - you're missing the force of beer. And we all know which way this will drag the boat and trailer!
Nice diagram. Takes me back to my days in Engineering school. Two suggestions though. First, your outboard appears to have a long mid-section (long shaft) where a short shaft is really needed for this particular hull / transom configuration. Running the prop that deep in the water will lead to lower top end and torque steer problems. (Don't force me to draw the diagram for that one!) Second - because this is a boat - you're missing the force of beer. And we all know which way this will drag the boat and trailer!
And even though my boat has a short shaft motor, it still sticks out waaaay lower than the boat. And, I'm only good for about 50 MPH at the moment..
Did somebody say 200hp Evinrude? And the beer isn't allowed on my boat, I'm only 18. And GIJoe, on figure 1, it's a 15* ramp that is 50' long...33* ramp
Senior Member
Joined: Aug 2004
Posts: 141
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From: Rudy, AR
Originally Posted by GIJoeCam
Force-wise, 7000 lbs of truck and trailer is the equivalent of 31,000 Newtons of gravitational force. If that ramp is 10 ft of rise in 15 ft, that's a 33 degree ramp... pretty steep, but we'll use it. Now, 31,000N * (sin (33))=17,000N which is the equivalent of 3866 lbs trying to drag the truck back down the hill. If the truck and trailer was on a ledge, with a cable running around a pulley to a weight hanging down, that weight would be nearly two tons of force on the cable... it's gonna roll backwards. (It's not quite the same thing on level ground as it is on the hill, because of the traction forces, but that's a whole other discussion.
Senior Member
Joined: Jan 2000
Posts: 3,205
Likes: 3
From: Along Lake Erie
Originally Posted by 2stroked
Joe,
I think you missed the point of me poking fun at the diagram. Besides, I'm a "go fast" guy. The prop shaft on my modified (240 HP) Mercury outboard runs level with the planing bottom in most cases. (adjustable Jack Plate.) We're always looking for ways to go faster and playing with the X dimension works pretty well when you start to exceed 75 MPH. For most of the fishing boats I've played with (on Lake Ontario), outboard height on the transom isn't much of an issue. When the prop comes out - regardless of X dimension - you're in some hellacious rough water. I will agree that the deeper you plant it, the better the boat will handle at low speeds though. Mine's a nightmare around the dock, but it goes like stink.
I think you missed the point of me poking fun at the diagram. Besides, I'm a "go fast" guy. The prop shaft on my modified (240 HP) Mercury outboard runs level with the planing bottom in most cases. (adjustable Jack Plate.) We're always looking for ways to go faster and playing with the X dimension works pretty well when you start to exceed 75 MPH. For most of the fishing boats I've played with (on Lake Ontario), outboard height on the transom isn't much of an issue. When the prop comes out - regardless of X dimension - you're in some hellacious rough water. I will agree that the deeper you plant it, the better the boat will handle at low speeds though. Mine's a nightmare around the dock, but it goes like stink.
I was talking about that issue literally the day before on a charter fishing trip I went on, so it was fresh in my mind. The first mate on the boat has a salt water motor on his.... he has a 20-ft aluminum hulled center console, and was saying that wen he would troll with it, he would have issues with the motor coming out of the water when cresting the rollers on Lake Erie. The lake blows up a pointy chop that makes it a bear to troll in a following sea. The boat will literally surf down the face of the wave, and if the motor is out of the water, it makes steerage a pain in the butt!-Joe