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01-07-2022, 04:41 PM #1Junior Member
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ENGINES HEIGHT OPINION - X DIMENSION + pictures
Hey guys,
I have the boat in my workshop ready for winter works! My target is to achieve +65MPH with stability.
The boat is a 25ft Tullio Abbate with twin mercs V6 200hp Standard lower units + 23p attwood ballistic (cupped and labed).
It runs in great attitude with no porpoising but over 55MPH it develops terrible Chinewalking.
You can read all about my plan of mods and see pictures of the boat on plane here:
https://www.screamandfly.com/showthr...d-Rails-wanted
*****
In this post I want to know your opinion about the engines height, let me give you all info as possible:
Boat size: 25ft + bracket
weight: 1.300 pounds + 250 in inox. Steel + 850 engines
X dimension: 53,3”
engines distance: 22,8” (11,4” each one to the keel)
V degrees: 145º
Current height: 1,4” (cav. Plate below)
Attending to the 4% calculation, the “standard height” should be 3,8” (9,65cms)
Also I can add at least an other 1,9” (extra distance between cav plate and water intake.
Here is a view of the bracket and engine mounts. The bracket is well built with 3,5” stern wood wall reinforced with kevlar and torsion bars.
My plan is to purchase CMC 5” Vertical extensions and set the engines Cav plates 5,7” bellow.
That means 4.3” higher than now! As the jack plates are inclined, I guess the extra 5” will be a practical increase around de 4.3 needed and still the engines will be bolt in higher position.
Please I want to know your opinions and If you think my numbers are right.
My steps to fight against that chinewalk are:
1ºSteering upgrade (add rear tie bar)
2ºEngines Height adjustment.
3ºTrim Tabs (horizontal + custom keels)
4ºDevelop the surface of strakes (my first option is to install Roca Speed Rails)
**I will not build a pad in this boat or cut the bracket.Last edited by El Español; 01-07-2022 at 04:44 PM.
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01-11-2022, 10:44 AM #2Junior Member
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01-12-2022, 01:36 AM #3
Welcome to the site! It sure looks like your lower units and props are BURIED for your amount of setback. And your description of bad chine walking kind of confirms it. You need water pressure gauges for each motor to watch your pressure as you go up. There are also small scoops that can help if needed when you get the motors up. I could easily see you raising your motors 4” to 6”, plus or minus. Deep motors will chine walk like a bitch. Watch the water pressure as you go up! Good luck and keep us updated.
1990 Shadow bass boat w/ 2.4 200 Merc. Totally resto'd boat and love it!
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David - WI, Jimboat liked this post
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01-12-2022, 01:42 AM #4
For chinewalking, do you have solid motor mounts in both motors? A tie bar on the lowers to tie them together and stabilize things would help also. Steering thoroughly bled out?
1990 Shadow bass boat w/ 2.4 200 Merc. Totally resto'd boat and love it!
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powerabout liked this post
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01-12-2022, 05:48 AM #5Junior Member
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Thanks for your reply guys.
After thinking in your tips, solid mounts is a must. I will change the lower mounts to solids. I think I will not find an extra vibrations if I let the upper rubbers.
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01-12-2022, 09:02 AM #6Team Member
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I don’t remember why, but I thought there was a risk of damage with solid lowe4 and stock upper mounts
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David - WI liked this post
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01-12-2022, 01:37 PM #7Junior Member
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Hey #David, the best for no damage is to leave all rubber stock at they come.
if you change only the lower ones it would be even less damage than if you have all 4 solids.
all solids doesn't allow any any movement, 100% stuck, then you need very good quality parts, steering, tie bars, stern which can manage all raw forces. We are talking about +80MPH boats.
if you change only the lowers, there will be still existing trough the horizontal axel created by the lower solid mounts.
then the lateral movements will gone 80%, but up-down movements will be corrected less. Then tie bar, steering will be suffering less at all.
its very important to apply grease every year to all midsection components, that would be the issue of worm parts
thank you guys.
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01-15-2022, 12:22 AM #8Screaming And Flying!
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Does the hull have a plank bottom, rounded or a vee?
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01-15-2022, 09:57 AM #9Junior Member
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01-15-2022, 10:30 AM #10Screaming And Flying!
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Reminds me of Tunnels
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