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  1. #1

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    So let me tell ya about a Riva Thru-Hull on a boat.

    We all know that usually a dual exhaust setup on a car is more for looks than for performance (especially the I4s & V6s), and so I assumed would be the case for the boat. WRONG! It turns out that a dual exhaust is about mandatory, given where the thru-hull has to be located. If you look at the first pic, you'll see my thru-hull, located at the only place that will work on the S150 (either side of the transom tie-down).

    I didn't anticipate this, but can anyone guess what I'm experiencing? That right, kids, it's called adverse yaw. As I'm driving the boat, the thrust out the exhaust is constantly trying to move the rear of the boat to starboard, which moves the nose to port. As I'm correcting with the steering to keep a straight path, it is producing extra drag that's actually lowering my top speeds! Even just starting the boat kicks me spinning counter-clockwise. It feels dangerous at WOT, like it doesn't want to turn right.

    The main reason I did the thru-hull was to reduce the clutter aft of the engine, but now I've got to build all new piping to get the exhaust coming out the other side too. I gotta tell ya, I thought it would sound better too.

    The thrust is so great from the exhaust, I bet that's causing the speed gains seen with the skis, because their thru-hull is right out the back, helping with forward thrust.

    I included a picture of Gord's dual thru-hull... that's where I'm headed.
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  2. #2
    iron head's Avatar
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    sound good to me

  3. #3
    ...Lighting The Water On Fire Since '04 duramaxxed's Avatar
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    I don't feel any type of "pushing" effect from my Thru-Hull install. It is however, on the other side of the Strap Hook, so it's closer to the middle of the Boat.

  4. #4

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    I would think the effect would be the same, since it's still at the same angle. I would say that I'm feeling the strong push because I'm sportin' a Rude, but I feel it long before the SC kicks in. Something to keep in mind and watch out for, though.

    Now, I was thinking that with the dual setup, on turns the exhaust in the water will help me spin around faster, but since the other will be out of water with less resistance, I'm sure the gases would be escaping out the other side on turns.

  5. #5
    cyoungesq's Avatar
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    could you just put a clam shell vent on it to redirect the force of the exhaust?

  6. #6

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    It could be an option, but I think it would be hard to get the right shape to redirect correctly at all throttle positions, and then worry if will stay in place. Eh, I'm just doing the dual exhaust, should look and sound better too. I ordered another Riva kit and stainless "Y" splitter last night. Hopefully be done with it by next weekend. I'm testing all new limits of my wife's patience. I knew I shouldn't have told her I was almost done modding.

  7. #7
    Doesn't look like it should effect it at speed? Maybe you need to go faster
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  8. #8
    ...Lighting The Water On Fire Since '04 duramaxxed's Avatar
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    Are you sure you got everything back on good and straight Pump / Control wise when you had to take it off to install the Exhaust Plug?

    It just doesn't seem possible to me that the Exhaust is pushing the back of your Boat off-center.

  9. #9

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    That is a good picture of the back of the boat that shows the exhaust outlet isn't underwater at speed, but the exhaust does point down at an angle towards the water. I'm just reporting what I'm feeling; wounldn't lie to ya. I did create a "T" at the J-pipe that feeds water to a pisser at the exhaust outlet (for sound supppression), perhaps that is creating a force when the exhaust gases are hitting it at WOT. I get into the pump about weekly and have it down to a science, so I don't think I messed that up. Even at idle, it spins the boat counter-clockwise at a pretty good rate, so at WOT, it must produce some serious thrust. Just looking forward to the dual exhaust to balance it all out.
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  10. #10
    Vern's Avatar
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    Scott, something is strange ... Danny put single side exhaust on his RXP, routed it through the area of one of the old OPAS holes, with no effect on handling at all. Same engine, much smaller hull and no impact. I dunno ... just does not seem like it could affect your boat, but not a RXP?

    Here is the link: http://greenhulk.net/forums/showthre...t=side+exhaust
    Last edited by Vern; 08-07-2008 at 02:05 PM. Reason: added link

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