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Ultra 23 shadow deck porpoising

Tt020202

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New to RDP and so far awesome, I have a 2007 ultra 23 shadow deck and I am having a porpoising issue, anyone have a fix for this? I trim up just a little and bounce bounce, trim all down and smooth as can be.

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dirtslinger2

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My Placecraft will porpoise sometimes at just the right trim or water conditions, usually a quick bump on the trim will settle it down, or a quick hit on the throttle. I do have trim tabs as well.
 

Nanu/Nanu

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Someone mentioned this hull having an inherent porpoising issue. Sounds like you may have to live with it. Some options to explore.
Tabs may fix this. Prop design could help combat this (i.e. designed for bow or stern lift).
 

98special

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Welcome, and Beautiful boat.
Let us know how this turns out.
 

Ultra912

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I had a 23 for 12 years. Maybe your trimming to soon. Maybe your prop is causing this. Some are saying the hull is inherited to doing that but I never noticed it to be a problem unless everyone sits in the rear at low speed. The bow on that boat is very light. I wouldn't trim up until I reached maybe 30 mph. I ran a 24 Bravo one prop.
 

Tt020202

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I start trimming up around 30 mph and it starts, so far I am changing props to try that then go from 26p to 24p and try that, then try a drive spacer after that.
 

Ultra912

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We had a 496 MAG. 26 is too much prop. The 24 would pop us up on plane in 5 seconds. 24 pitch is 65 mph WOT. I think it's your prop.
 

Tt020202

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I have a 496 HO and it seems to get outa the hole decent but yes I am going to try the 24p prop and see what that does.
 

Tt020202

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Ok no porpoising issues at cruising speeds, another guy told me he has a whale tail also but he is always full speed stop, full speed stop lol
 

razorglow

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New to RDP and so far awesome, I have a 2007 ultra 23 shadow deck and I am having a porpoising issue, anyone have a fix for this? I trim up just a little and bounce bounce, trim all down and smooth as can be.

The design reminds me of a street rod car. Nice.
 

Nanu/Nanu

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Ok no porpoising issues at cruising speeds, another guy told me he has a whale tail also but he is always full speed stop, full speed stop lol
I'm confused. My understanding is porpoising is the word to describe the bouncing motion you get when you hit a bump at speeds while on plane.

When are you experiencing said porpoising?
 

CobraDave

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I'm confused. My understanding is porpoising is the word to describe the bouncing motion you get when you hit a bump at speeds while on plane.

When are you experiencing said porpoising?

It’s more like when there are NO wakes. The boat in calm water will hop rhythmically. Sometimes you are in that sweet spot where the boat wants more air packed underneath. You either have to speed up, slow down, adjust trim or adjust tabs.


Sent from my iPhone using Tapatalk
 

Tt020202

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Yes on flat water trim up a little and it will hop/bounce/ porpoise whatever you wanna call it, trim down it goes away, trim up a little comes back, speed up goes away, but not looking to run balls out all the time
 

Tt020202

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So I traded my 26 p for a 24p and this is where my out drive rookieness comes in. It is a left handed prop and I didn’t notice or figure it out until I went to go put it on. So now after talking with imco and Hill propeller I am going to get a Hill 5 blade 23p prop and try that, hopefully I will get it next week.
 

Ultra912

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Ok so update, trying a 5 blade 23p and it is a night ans day difference. Porpoising has minimized and Rpm has increased by 400 rpm. Still does porpoising but it is 100 times better.
next step is to try one of those whale tail thing.
I know I've asked before but are you running a 496mag? The 23P
Ultra Shadow.JPG
will hit the rev-limiter. Not sure with a 5 blade but I was able to control it but when trimming you just need to hit the button and let go a few times to find your sweet spot. If no one is sitting on the bow it's a fine line.
 

Tt020202

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Yes 496 mag Ho 425 Hp the 5 blade 23p I hit 4800 rpm with 2 adults and 1 kid
 

2FORCEFULL

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the fix is tunnel tabs......... what happining is the boat doesn't go fast enough to pack air and carry the hull, porpoising is when the boat can't decide to run in the water , or on top.. air lifts the hull in the tunnels, but the bow weight brings it back down... if you look at stoker/ schiada... they have tunnel tabs to trap the air in the tunnels,... thats why they will run in the 80's with 500hp.... take the tabs off and they will start hopping........ I would put fixed tunnel tabs ,... and I would put purple ones ( because I have a set) when I prop a boat, I first identify the issue.... that boat will always have a hopping issue with out trim tabs,... unless you just drive it slow.... to get the max out of that hull, it needs to pac air.... cheetah stelleto's have the same problem... but, they made the tunnels so big the speeds under 70 they don't perform well,... I heard , (rumor) theres a guy running one with speeds north of 120 mph, never seen a pic of the boat though...


Porpoising happens when the center of lift moves aft of the CG. In the normal way of things, the center of lift starts just a little aft of midships. As speed is gained, the lift increases and moves aft as the hull rises out of the water. This cause the classic pitch up seen in most planing hulls. As speed continues to increase, the center of lift moves aft with the decreasing wetted surface. When the lift moves aft of the CG, the boat experiences a rapid pitch down which leads to the wetted surface increasing and a huge increase in drag, which causes lift to be lost which whith the increase in wetted surface forward moves the lift forward of the CG and starts the whole cycle again.

The major reason for jackplates now seen on modern high power OB boats is to get the CG aft enough (i.e. the engine weight) to allow the full power of the engines to be brought into play to achieve maximum speed.
 

Ultra912

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the fix is tunnel tabs......... what happining is the boat doesn't go fast enough to pack air and carry the hull, porpoising is when the boat can't decide to run in the water , or on top.. air lifts the hull in the tunnels, but the bow weight brings it back down... if you look at stoker/ schiada... they have tunnel tabs to trap the air in the tunnels,... thats why they will run in the 80's with 500hp.... take the tabs off and they will start hopping........ I would put fixed tunnel tabs ,... and I would put purple ones ( because I have a set) when I prop a boat, I first identify the issue.... that boat will always have a hopping issue with out trim tabs,... unless you just drive it slow.... to get the max out of that hull, it needs to pac air.... cheetah stelleto's have the same problem... but, they made the tunnels so big the speeds under 70 they don't perform well,... I heard , (rumor) theres a guy running one with speeds north of 120 mph, never seen a pic of the boat though...


Porpoising happens when the center of lift moves aft of the CG. In the normal way of things, the center of lift starts just a little aft of midships. As speed is gained, the lift increases and moves aft as the hull rises out of the water. This cause the classic pitch up seen in most planing hulls. As speed continues to increase, the center of lift moves aft with the decreasing wetted surface. When the lift moves aft of the CG, the boat experiences a rapid pitch down which leads to the wetted surface increasing and a huge increase in drag, which causes lift to be lost which whith the increase in wetted surface forward moves the lift forward of the CG and starts the whole cycle again.

The major reason for jackplates now seen on modern high power OB boats is to get the CG aft enough (i.e. the engine weight) to allow the full power of the engines to be brought into play to achieve maximum speed.

Your a much smarter guy then I and I totally agree with your comments but I was able to plane out my 23 Shadow. Had it for 12 years with a 496 Mag, not a 496 Mag HO. A 24P Bravo One 4 blade. Used it with anywhere between 2 and 6 people. It was happening to us the first summer but I was able to control it with my trim, albeit after some hours of operation . Maybe more time at the helm will find you the sweet spot. I ran that thing at all speeds. WOT trimmed up on top of the water was the only way to get through the chop. Large swells,,,,,not so much. Be careful around the surf boats. They sank mine after 12 years. Low freeboard deck doesn't like flying over 3 foot swells.
 

Tt020202

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I am defiantly learning to drive it and find its sweet spot with trim. I really do like this 5 blade prop. Sorry about your boat, I hope you were able to salvage it?
 

Ultra912

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I am defiantly learning to drive it and find its sweet spot with trim. I really do like this 5 blade prop. Sorry about your boat, I hope you were able to salvage it?
Nope, Went bigger this time. The lake has just gotten too rough for that hull. They offered it back to me for 7k but I passed.
 

King295

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Saw you on the 10 in Beaumont yesterday, boat looks good. Didn't see any tabs on it...... :p
 

Tt020202

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No tabs just yet, I did get a 21p 5 blade and used it this weekend, what a difference. The bounce was 100 times better. It got out of the hole like a rocket, but I did lose some top end speed about 4 mph but it went from 4600 rpm to 5100 rpm
 
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