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Bow lift. VS. stern lift.

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Old 04-27-2008, 09:01 AM
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Littled...
I ran the boat before. Actually not "this" boat but an identical one. The history on this is to frustrating and long for here, and now, but I got the shorties (-1") for speed. Hoping for better bow lift, but I can add spacers easier and cheeper then make a standard "X' dim less with STD lowers. (dont know the dim. I have to measure.)
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Old 04-27-2008, 11:37 AM
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The higher the prop shaft the less bow lift.

I'll explain it the way it was taught to me by Buzzi. The higher the prop shaft the less prop/gear you have in the water to pivot the boat with, your not carring the boat at that point your purely making thrust. This is a good thing. Since we can't pivot the boat to make the bow lift we need to make the boat want to ride with it's bow up naturally. To do that we make the hull with an extreme amount of rocker so it's natural tendency is to ride bow up.

Buzzi used the steps more for the rocker than for a break in the surface tension, not that the steps didn't do that well but he needed lots of bow lift because we ran an extreme negative trim angle on the drives as compared to a stern drive. The drive angles wnated to drive the boat down in front.

Look at all the boats, V or cat that run high drive heights and go fast, lots of rocker created by hull shape or steps? Straight bottom with high drives just doesn't perform the way you want it to?

When you ask about stern lift, I don't think you realy lift the stern as much as loose the bow lift - my opinion only.
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Old 04-27-2008, 07:07 PM
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Didn't want to go into all the theories, but any boat, no matter what bottom.. wants the bow to go down. Friction. Just see what happens when you cut the motors. With all the bottom design some have more bow lift then others. I know many tricks to manupolate the boat, I just wasn't sure what will shorties do on any given boat. (mine in this case)
Habana... FYI .. most of the control of bow up/down comes from the outdrive/prop angle. Thus "trim".. but while the thust is used for lift (bow up, or stern up) then some of the efficiency is lost. IMHO..
Anyway.. thanks. looks like shorties = bow dawn.
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Old 04-28-2008, 12:13 AM
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When I went to shorties, still had plenty of bow lift - but did go to 5 blade props turning in.
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Old 04-28-2008, 02:59 AM
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A deeper prop gives more leverage to lift the bow. I added a 1" bigger spacer to get more bow lift on my Pantera.

That being said, I can't see why a 33' with twin big blocks would need any help with bow lift. It should have plenty unless the props are too high.
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Old 04-28-2008, 10:18 AM
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Quote:
Originally Posted by Griff View Post
A deeper prop gives more leverage to lift the bow. I added a 1" bigger spacer to get more bow lift on my Pantera.

That being said, I can't see why a 33' with twin big blocks would need any help with bow lift. It should have plenty unless the props are too high.
Thanks Griff.

The other 33' hull I had needed a bit of bow lift with 496 mags and STD bravos. Using the trim was ok, but I was wondering what will the SM shorties with ITS wil do.
I have no clue about the props yet. I will start with 4 blade, B's 30" pitch and go from there.
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Old 04-28-2008, 12:30 PM
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The ITS setback should allow you to raise the height an inch with about the same amount of bow lift.
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