Offshoreonly.com - What Is Porposing????

Offshoreonly.com (https://www.offshoreonly.com/forums/)

- General Boating Discussion (https://www.offshoreonly.com/forums/general-boating-discussion-51/)

- - What Is Porposing???? (https://www.offshoreonly.com/forums/general-boating-discussion/254725-what-porposing.html)

I thought it's what happens when your GF is on top of you on a waterbed.

[QUOTE=Sydwayz;3416302]A dozen things could be causing it. If you have a problem with it on your boat, we need to know:
What hull? 2008 Lightning Custom Boats, 27 Strike (like a Elim. Dayton)
What props? (this is often the culprit) Right now I have a bravo 1 24p (starting to work with Bblades now for a labbed prop)
How long are the tabs? No tabs, I was told they are dangerous on my size boat
If cat, do you have a tunnel tab? No, single engine
What is the X-dimension? I have no idea
Do you have a notched transom? (this is often the culprit) I have no idea
Has the bottom been modified? (hook or rocker added/removed, or anything else done) Not that I know of
Has the center of gravity been changed on the boat from original?
(ballast) No
Do you have extension boxes? No I do not
Have the engines been moved? (forward or back) No

Here is the link to info on my boat
http://vtesinla.org/Lightning2010/models.asp?id=27st

Is it a splash of an Eliminator hull? Or an previous Eliminator hull/mold/model?

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.

Quote:

Originally Posted by Sydwayz (Post 3416480)

Is it a splash of an Eliminator hull? Or an previous Eliminator hull/mold/model?

Not really sure what the story is on the hull just someone that use to work at Eliminator told me it was or like an Eliminator hull

Quote:

Originally Posted by Poker~N~Run (Post 3416504)

Ok, so the main thing I need is more power for more speed then it will go away? Or stay away from glassy water:) My speed seemed a little low so does this slow you down?

Its when your boat screws the water:drink:

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).

Quote:

Originally Posted by Ted G (Post 3416584)

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).

LOL, thanks for all the great info