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Old 07-10-2019, 09:50 PM
ryangraham's Avatar
ryangraham ryangraham is offline
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Join Date: Aug 2006
Boat: 1986 Stars and Stripes, 351W PCM
Location: Southeast
Posts: 45
Prop to reduce bow rise (porpoising) in 2003 X9

I'm looking for a new prop to reduce bow rise and eliminate the porpoising affect in a 2003 X9 with the MCX. I've talked to a couple sources, Acme, Nettles, and I've read various forum posts here and elsewhere. There's no real consistent information and clear answer. And maybe that's the answer. But I'll ask here in a new thread all the same...

I've tried to load up weight in the bow and remove all weight from the stern. Still does it.

I don't have the "hook" in the transom. Would rather not spend $1K+ to have that installed.

Acme recommends their 1581 model which is 13x11.5 with 0.060 cup.

Nettles recommends the Acme 843 which is a 13x12 with 0.080 cup.

Both are 3 blades.

The current prop on there is an OJ 345 which is a 3 blade 13x11.5 with 0.090 cup.

In addition to insight on solving my porpoising problem with a prop change, if anyone knows what specific specs on a prop can create stern lift, or bow drop, I'm all ears. I'm skeptical that such a small change from what I'm currently running will make enough difference to correct the problem. But I also know small changes can make huge results. So let me know what you think.

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Old 07-10-2019, 11:24 PM
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Miss Rita Miss Rita is offline
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Join Date: Jul 2009
Boat: 1992 ProStar 205, 1991 Ski Pro
Location: Black Hills
Posts: 1,491
I'm surprised that you have any bow rise at all in a DD, because the vector of the prop thrust is always angled downward.

In stern drives you can play around with it a little more: adjust trim, get props with more or less rake, different diameters, three or four or five blade props, etc.

My opinion, FWIW, is that changing props isn't going to change any problems with bow rise in a DD boat.

Last edited by Miss Rita; 07-11-2019 at 08:22 AM.
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Old 07-11-2019, 01:06 AM
Tsumi Tsumi is online now
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Join Date: Feb 2012
Boat: 2001 X-star 5.7L LTR, 2000 Prostar 190 5.7L LTR, both dark green
Location: Pacific
Posts: 862
Some sort of wake plate is probably your best bet. A prop really isn't going to change anything IMO.
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Old 07-11-2019, 06:17 AM
waterlogged882 waterlogged882 is offline
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Join Date: Dec 2004
Boat: 93 190
Location: lake
Posts: 12,854
In agreement with other comments so far; a prop will not solve the issue. I can say that from having had this issue myself on an older model I owned several years ago. Like you, I tried everything you mentioned...the only thing (last resort) that resolved the issue was a lip (hook) on the back of the hull. Doesn't take much to make the change but that took the porpoise out of the hull.

Your mileage may vary.


John 14:6
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Old 07-11-2019, 08:19 AM
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epnault epnault is offline
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Join Date: May 2010
Boat: 2016 ProStar 6.2L
Location: Maple Grove, MN
Posts: 1,823
Prop has nothing to do with this, been down that path. We didn’t have the hook on ours either. The only time I experienced it was with a full tank of fuel, no passengers, and going above 30 mph. Usually on long runs from the boat launch back to the cabin. I never experienced during towing. I did run about 100lbs stuffed in the bow. If I kept the boat I probably would have added a plate but MC engineering cautioned against it as you could end up in some dangerous situations.

What situations are you seeing porpoising?
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Old 07-11-2019, 09:21 AM
88 PS190 88 PS190 is offline
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Join Date: Aug 2005
Boat: 1988 MC Prostar 190, 351 Ford
Location: Midwest
Posts: 4,732
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At what speed is this occurring on your x9?
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Old 07-11-2019, 07:54 PM
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ryangraham ryangraham is offline
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Join Date: Aug 2006
Boat: 1986 Stars and Stripes, 351W PCM
Location: Southeast
Posts: 45
From 30 to 35 mph is the porpoise zone. If I can manage to get through it quickly Iím smooth water it settles down as it approaches 40 mph, but it doesnít go away. Itís never that buttery smooth ride at WOT Iím used to in my old 19í S&S. If I let the porpoising get out of control, or hit rough water, forget it, I have to throttle down or else it gets uncomfortably bouncy and dangerous.

Iíve yet to run the gas tank down much below half. Iíve tried to offset with water in the ski locker (front) ballast only as well as 200-300 lbs of humans in the bow. None of that solves the problem.

Iím not mad, I boat this boat with eyes wide open regarding this issue. Iím just exploring all my options (if any) before pursuing the expensive hook install.

Love the comments. Keep them coming!
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Old 07-12-2019, 05:51 AM
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CantRepeat CantRepeat is offline
Join Date: Jul 2008
Boat: Passively looking for a CSX 265
Location: Roll Tide!!
Posts: 15,185
Add a trim tab?
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Old 07-14-2019, 09:30 PM
foil dude foil dude is offline
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Join Date: Apr 2019
Boat: 2001 X9 2019 NXT20
Location: Norcal
Posts: 20
Mine did it also. The one thing I hated in that boat. I tried more ballast in the nose and that helped but didn’t cure it by any means. I alway thought adding a Lenco trim tab would be the best fix. That said I just sold if after 18yrs of great time with it. Our new boat has one and what a difference it makes depending on the water you can really load up the nose and watch it smooth out in rough water.
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Old 07-14-2019, 10:24 PM
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CruisinGA CruisinGA is offline
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Join Date: Jun 2009
Boat: '01 X9 330HP
Location: Georgia
Posts: 2,363
Ryan, thinking more about this I basically go two speeds in our X9
21.4 to foil and ~40 to barefoot. Spend very little time at any other speed, might be why this has been less of an issue for me.
'02 X-9
Lake Blue Ridge
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