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Discussion Starter #1
This boat is going to drive me nuts! Had a mechanic kindly nuke a motor for me so I now have a new motor but same dang problem.
16' high tide flats boat
Yamaha 90 sho with a prop tech 18p four blade.
20 gal fuel tank up front. Group 31 tm batt and a motorguide wireless.
Console has a group 24 under it
Smart tabs
So by myself I get about 38-40 mph but when you get the trim about right and the spray at the console it will porpoise with any movement. I cant ever get a decent ride. Motor is mounted in the top hole but the cav plate is right at the top of the cut out. I'm getting 58-6000 rpm. I've tried a 17p alum 3 blade, 17p/3 blade, 19p/3blade and now the 18p/4 blade which will get that rig out of the hole fast enough to snap your neck. I'm just not sure what the heck to do with it. I'm being told it should be running a lot faster.
 

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Discussion Starter #4
I'm on shift tonight I'll post some tomorrow if it's not raining again. The problem with trimming down is by the time I trim down enough I'm only running in the low 30s
 

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some boats do this. I had a mitzi 17, one of the many problems I had with it was chronic porpoising. I tried everything, moving weight around, dif trim angles, moved the motor up hole by hole and back down hole by hole, dif props, wedges, hydrofoils, checked hull for hook. finally put trim tabs on to control it but of course you lose some speed. My Silver King is the same way, won't tolerate much trim up at all.
 

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Discussion Starter #6
Even with the smart tabs you cant tell a difference whether they are deployed or not and I've tried different pressure shocks. I was wondering about raising the motor. I tried with the 19p but didnt do a whole lot
 
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I'm on shift tonight I'll post some tomorrow if it's not raining again. The problem with trimming down is by the time I trim down enough I'm only running in the low 30s
Yes, post up some pics! If you can get a pic of it running from over the transom to see where the water is at on the cav plate that would help too. With the pocket, I am willinh to bet your motor can come up some!
 

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My big flats boat doesn't run right until I push it past 40 mph. At 56 mph I'm trimmed out like crazy and dropping a few psi on the water pressure gauge. I never use my tabs because they kill my top speed. I've learned how to balance my load so it runs just right at high speed.
 

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Zephyr Cove is on FIRE!
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Some boats need adjustable trim tabs to run as fast as possible. Without Lencos my hull would only hit 27-28 but once I trim her out and tab down some I hit 33-34 and throw a roostertail that a bass boat would envy. I’m not a fan of Smart Tabs, if you are going to drill holes in your transom put some Lencos on it so you have full control. Moving crap around all the time gets old, just get in and go.
 

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Discussion Starter #10
I so agree. I wish I would have gone with lencos too. How about the stepback? The recessed area where the drain plug is. Does that have anything to do with motor height? Where should the cav plate be in relation to it?
 

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Discussion Starter #14
Raining pretty good here so I took some pics of the motor height from under the cover and one of the prop to see what you guys think.
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- and toss those "smart tabs" - then install a decent set of either Lencos (electric) or Bennetts (old school hydraulic)... Make sure to contact each trim tab company first with the hull measurements, etc. They'll tell you exactly what model you need...

Hope this helps
 

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Raise it up, n stern lifting prop. I had similar issues with my 18x60 flat boat n added 10x10 trim tabs n adjusted down until porpoise stopped. I think I made about 10 trips to the launch and 2 propeller changes n 2 trim tab sizes n bunch angle changes before it all worked.
 

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Discussion Starter #19
I'm kinda hoping to adjust for the 18p four blade or the 19p three blade as I already have them. The power tech one is supposed to be a good all around prop from what they said but not sure if it's a stern lifting one.
 
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