What Is Porposing????
05-31-2011, 12:49 PM
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05-31-2011, 02:45 PM
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I think what's happening is typical of that tyPe of cat. I have owned several and my 25 warlock did the same. Basically ended at high 70's on glass. With a little chop it wouldn't because you are gettnf the hull out of the water consitently. A better prop can help in provided better lift. At 70 things fun start happening and now it's time to tune (; small tabs can help but is just a band aid. What you are describing is pretty normal with a tunnel hull.
05-31-2011, 03:43 PM
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I think what's happening is typical of that tyPe of cat. I have owned several and my 25 warlock did the same. Basically ended at high 70's on glass. With a little chop it wouldn't because you are gettnf the hull out of the water consitently. A better prop can help in provided better lift. At 70 things fun start happening and now it's time to tune (; small tabs can help but is just a band aid. What you are describing is pretty normal with a tunnel hull.
My speed seemed a little low so does this slow you down?
05-31-2011, 04:00 PM
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It sounds like you are right at the point between becoming a true cat and just a twin hulled boat. What is supposed to happen on a cat is you pack enough air into the tunnel and it lifts the weight of the boat off the sponsons and floats the boat on an air cushion. This allows cats to reach high speeds on less power and ride smoother in some conditions than a v-hull. But you have to be going fast enough for the air to build in the tunnel and create positive lift. For many cats that speed is at 70-80 mph. As you near the speed where you pack air you can experience the porpoising you describe because the hull is starting to lift on the air, but as it does some air dumps out the back of the tunnel and you lose lift, so it drops. Then the pressure starts to build back up. And on and on.... In the past some makers added a tunnel tab which allowed the operator to tab down some and close off the back of the tunnel, this would allow more lift at lower speeds and stops or diminishes porpoise. Of course it can also cause the boat to blow over or do other nasty things if not retracted at high speeds. You could also add a small, fixed tunnel tab which may get you past the porpoise, or you are going to need enough power to drive through it (of course once you really pack air.....YEE HAW).
05-31-2011, 04:31 PM
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It sounds like you are right at the point between becoming a true cat and just a twin hulled boat. What is supposed to happen on a cat is you pack enough air into the tunnel and it lifts the weight of the boat off the sponsons and floats the boat on an air cushion. This allows cats to reach high speeds on less power and ride smoother in some conditions than a v-hull. But you have to be going fast enough for the air to build in the tunnel and create positive lift. For many cats that speed is at 70-80 mph. As you near the speed where you pack air you can experience the porpoising you describe because the hull is starting to lift on the air, but as it does some air dumps out the back of the tunnel and you lose lift, so it drops. Then the pressure starts to build back up. And on and on.... In the past some makers added a tunnel tab which allowed the operator to tab down some and close off the back of the tunnel, this would allow more lift at lower speeds and stops or diminishes porpoise. Of
course it can also cause the boat to blow over or do other nasty things if not retracted at high speeds. You could also add a small, fixed tunnel tab which may get you past the porpoise, or you are going to need enough power to drive through it (of course once you really pack air.....YEE HAW).
course it can also cause the boat to blow over or do other nasty things if not retracted at high speeds. You could also add a small, fixed tunnel tab which may get you past the porpoise, or you are going to need enough power to drive through it (of course once you really pack air.....YEE HAW).
