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prop shaft depth, x-dim

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Old 04-08-2017 | 07:43 PM
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Default prop shaft depth, x-dim

I realize they aren't the same thing though they get used interchangeably. On my little resin bucket the best I can measure the propshaft is 6.5" deep below the bottom of the little delta pad.

What is considered deep? How high can one realistically go? before needing a LWP? I have to take the transom assembly off anyways so I was thinking of going up 2"

Thoughts???
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Old 04-08-2017 | 07:55 PM
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How high can you go before crazy hatch mods or big $$$ custom tail pipes? 3" would be nice, 4.5 will still be a good help over 6.5.
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Old 04-08-2017 | 08:07 PM
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Im already cutting a big hole in the hatch or just making a new one to clear the new blower motor.....so hatch and exhaust holes are a non issue...
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Old 04-08-2017 | 08:21 PM
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I think around 5.5" is the highest you can go with a three blade. I was running 4.25" on a 12" box (so 5.25" at the transom if 12" back = 1"?) and my mirage plus had too much slip, 18-20%+. I had no water pressure issues with a dual water pickup bravo up to my 68-69mph top speed. Some guys take screws and plug upper holes of pickup. I like dual water pickups, upper holes can act as pressure regulator.
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Old 04-08-2017 | 08:40 PM
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Originally Posted by IGetWet
I think around 5.5" is the highest you can go with a three blade. I was running 4.25" on a 12" box (so 5.25" at the transom if 12" back = 1"?) and my mirage plus had too much slip, 18-20%+. I had no water pressure issues with a dual water pickup bravo up to my 68-69mph top speed. Some guys take screws and plug upper holes of pickup. I like dual water pickups, upper holes can act as pressure regulator.
I will definitly be running a 4 blade. THe bottom on this end or Erie is really silty and shallow. LWPs can really suck up some muck around here,
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Old 04-09-2017 | 07:37 AM
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When I converted my Corsa (26x7) to a Bravo, I went with an 18.5" X dimension (3.25" prop shaft depth)

Had no water pressure issues with a standard drive... Also, has NO problems planing with a 4 blade Bravo prop..
and ran 68 mph with a tired 454 mag..






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Old 04-09-2017 | 10:37 AM
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6.5" is pretty deep. Especially if you're putting a big blower motor in it and spinning a big prop, that kind of depth creates a longer torque arm which will make the boat torque roll and chinewalk, etc. You can go to 3-4" no problem and still run a 4 blade and not have any planing issues. Most of the fast single engine v-bottoms (Howard, Lavey Craft, Hallett, etc) all set up their boats 2-3" or higher if the boat has big power. Mine right now (with a -2 lower) is ~4" and I wish I could go up higher.
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Old 04-09-2017 | 10:40 AM
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Originally Posted by phragle
I will definitly be running a 4 blade. THe bottom on this end or Erie is really silty and shallow. LWPs can really suck up some muck around here,
You need the LWP if you're going to raise the x-dimension like that. The other thing you can do is just run a transom mounted pickup to feed the motor and innercooler. An adjustable water pickup like Teague sells would allow you to dial in the pickup depth without too much drag, and it should provide more than enough water for the motor and innercooler.
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Old 04-09-2017 | 02:20 PM
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Originally Posted by ToMorrow44
6.5" is pretty deep. Especially if you're putting a big blower motor in it and spinning a big prop, that kind of depth creates a longer torque arm which will make the boat torque roll and chinewalk, etc. You can go to 3-4" no problem and still run a 4 blade and not have any planing issues. Most of the fast single engine v-bottoms (Howard, Lavey Craft, Hallett, etc) all set up their boats 2-3" or higher if the boat has big power. Mine right now (with a -2 lower) is ~4" and I wish I could go up higher.
I assume they all have notches. I've mentioned before: 19.5" X with a -1 IMCO lower puts me a little less than 1.5" below bottom. 10% slip with B1 4 Blade. 18.5 sounds pretty good for the 24x7 with flat transom. Can find a short lower or add a spacer for +/- 1".

Last edited by TxHawk; 04-09-2017 at 02:28 PM.
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Old 04-09-2017 | 05:08 PM
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Originally Posted by TxHawk
I assume they all have notches. I've mentioned before: 19.5" X with a -1 IMCO lower puts me a little less than 1.5" below bottom. 10% slip with B1 4 Blade. 18.5 sounds pretty good for the 24x7 with flat transom. Can find a short lower or add a spacer for +/- 1".
Good info there. The west coast boats, some do some don't have a notched transom. Mine is notched and I'm still over 4" below, so I'm really too deep. Any issues getting on plane with your setup and a B1? Mine rolls on plane effortlessly which I like because I still ski and tube behind it.
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