ENGINES HEIGHT + X DIMENSIONS (With 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.offshoreonly.com/forums/...ls-wanted.html

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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)
https://cimg8.ibsrv.net/gimg/www.off...2f15359b9.jpeg

Attending to the 4% calculation, the “standard height” should be 3,8” (9,65cms)

https://cimg3.ibsrv.net/gimg/www.off...3ce33797e.jpeg

Also I can add at least an other 1,9” (extra distance between cav plate and water intake.

https://cimg8.ibsrv.net/gimg/www.off...5ec777a14.jpeg

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.

https://cimg6.ibsrv.net/gimg/www.off...aced0cf27.jpeg

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 opinion is to install Roca Speed Rails)

**I will not build a pad in this boat or cut the bracket.

I know this isn't part of your plan but have you tried swapping prop rotation from your current set up?

Very interesting #Trash. Now I’m outwards rotation, 1/3 toe out.

https://cimg1.ibsrv.net/gimg/www.off...7f8fd2f63.jpeg

well the first question is did you install solid motor mounts? the stock rubber almost always lead to chine walking

Turn in is faster, carries the bow better.

Hey #BoostBross is exactly what I was discussing today at the workshop. I was shaking the lower units and they have mooovment. I’m afraid solid mounts will lead to a lot of vibrations than can damage the stern and the bracket mounts.

Also If I mount double hydraulic, the problem will be same, as there are rubber mounts between the engines and the steering arms.

As I will mount rear tie bar from head to head, I guess engines will dance together and instead of 4 rubber mounts, will be 8 on “the pack”

I was looking if there exists Teflon made mounts to find a middle point between rubbers and solids, but no find.

I’m 100% Im toe out, but the spinning always I got confused because I exactly don’t know if it is attending to to the top of the props <— —> “outwards” or to the bottom of the props —> <— “inwards”,,, it’s why I post a picture!

if someone can clarify please 🙏

where are the spray rails under the boat? You could move the engines a lot closer.
Toe out? with your props spinning out you should have toe in not out.
I think that Abatte has a 23 degree V, we always put the propshaft 5-6 cm under the boat and 10-12 mm toe in as a starting point

Turning in will lift the stern of the boat more, doesn't work often.
Also not a big fan of those props, Mercury trophy worked always best for us

You’re turning out

No turning out lifts the stern

there are 4 motor mounts changing just the lowers will help a lot you wont see or feel any vibration difference we always said if they are shaking and smoking alls well

dude, turning in takes water outside and pushes in the middle the stern up, turning out takes water in the middle and lifts the nose.

Diesel,

I would think the dynamic in play is prop walk. Turning the props out would work to keep the transom behind the boat, like arrow fletchings.

Thanks. Brad.
(937)545-8991

Thank you very much guys for your replies!

Let me help about the concepts props spinning and toe.

first to talk about the spinning, we have to forget the upper part of the props:

https://cimg3.ibsrv.net/gimg/www.off...c3ee8697b.jpeg

There is not a consensus of how to name Turning in as I will explain (90%) or the opposite (for me is easier the opposite indeed)


- Turning out (Red): it’s a paradox, but most people called it “turn out”, but when you analyse the bite in the water of the prop (the arrows) you realise it works in practice as “turn in”. Any way we call it “turn out”

This is the most common rigging in classical offshore and the reason is because the bite is opposite of the V, and you can achieve cleaner water and lift more the engines.

The direction of the turbulence will go inside.

- Turning in (green): you can use it in some special cases, for example if you have a boat designed for single engine and you have mounted two. (The bite of the props will be closer to the V. In a boat like mine, could be an smart option.

the direction of the turbulence goes outside.

From this point, if you analyse, which option will provide more Sternlift, probably will be turning in (green), but is much less relevant when we think only in the green/red arrows, isn’t it?



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Toeing: the Key is to rigging the bullets as straight to the water as possible. Imagine a Salmon swiming up a river. The fish needs to go straight as possible against flow.

- Toe in (props out): is the most common way. It’s used on heavy boats with the engines just on the stern or I/O. The boat is splitting the water and you have to match the bullets with the flow.

- Toe out (props in): it’s used in special cases, as boats with brackets (long X dimension) or with steps. The boat splits the water but then the water takes an interior direction, and you have to match that flow. If the boat is slow you need to be around 1”toed. If your boat is very fast, you can run almost straight.

- Almost straight: you have to analyse X dimension, V angle, weight and speed. The faster, the less toe in/out you need.

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How to combine Spinning + Toeing.

the idea is that the turbulences of both props have to match in some-point in the rooster.

in my boat 25ft light boat +65MPH the turbulences have to match around 60ft behind.

If your boat is heavier and slower, they have to match before.

- Toe in (props out) + turn out (red): in a heavy boat, I/O or engines just on the stern, you toe in to match the flow with the bullets, but then the turbulences will run to the sides, soo you choose red arrows to impulse the turbulences in, in order to find each other 30-40ft after the boat.

- Toe out (props in) + Turn in (green): in big X dimensions, you match the bullets with the flow, but the turbulences will go also to the middle point very fast, and can meet each other at 15 or 25ft. If you want to increase this distance, you can choose green arrows that will help you to split the turbulences.

- Toe out (props in) + turn out (red): you can replicate the behaviour of a single engine boat, matching the turbulences very close to the boat.

- Toe in (props out) + Turn in (green): imagine if you have an split-hull and you want the turbulences to keep straight and no meeting each other in any moment.

in the end, after all written, most important is:
1.- Toeing: Match the flow, no mater more.
2.- Spinning: In V, red arrows, cleaner water, no mater more.

Forget about stern/bow lifting benefits (you can get is better with other rigging issues), forget about speed gain (bullets straight to the flow=fast), forget about turbulence matching, ect,,

thanks again guys, please I want to know how much you would lift the engines in my case. I have PSI gauges.

The lift vs dig of the prop rotation is caused by the angle of the water hitting the prop coming off the V bottom.

When turning out, the outside of the prop is getting more water than the inside. The outside of the prop which is turning down into the water then pushes the motors up and creates stern lift.

When it’s turning in, the outside blades are pulling the motors down and prying the bow up.

I can switch rotation on my motors by swapping a resistor side to side.

Turning out, I get so much stern lift that I have nearly no perceptible planing speed. The boat just stays flat.

Turning in my min planing speed goes up to about 30 because the stern is getting pulled down so much, picking the bow up a lot. My props are fairly large with a lot of cup so the effect is magnified.

Anyways, if max speed is your goal. Turning in should pick you up 2-3mph. You’ll sacrifice some fuel economy and mid range slower cruising speeds, and docking is much harder.

You can combat with the planing speed issues of turning in with some long tabs. Mine are too short to negate this. So I keep em turning out.

Very interesting #HogieRoll as you could try both spinning type in your boat.

it’s true than in my case, spinning out is bringing to much stern lift, then the boat runs flat as an arrow, I like that attitude, but when cross the 55MPH line it becomes very light and unstable. I can “drive trough” till 62MPH

I will try rising the engines 4,5”, the appropriate rigging by numbers, and I will check if I can maintain the attitude, but gaining in stability with more controlled stern lift.

if I can run till 65 stable then I can improve some MPH, maybe touching 70.

I’m thinking why turn in is faster in your case. Maybe because props are carrying less the weight of the stern? or because the props got closer to the surface, as it bites closer to the V?

V bottoms are virtually always faster turning it.

To go fast in V you need to “carry the bow” by keeping it out of the water. This helps pack air under the boat and reduces your wetted area. All fast non stepped Vs are attempting to ride on only the last little bit of the hull just in front of the transom.

I have done same.

On my first twin OB 24’ Sonic I switched the gear cases to test rotation.

They we’re turning out and the boat ran perfect.

25” V-6 JohnRudes on 6” manual Jack plates on a 19” bracket.

After reading all the reports of turning in giving me 2 - 3 mph, I switched to turning in.

W/no other changes, one motor (I think port) now cavitated coming on plane and would no longer carry the bow at speed.

I think I lost 2 -3 mph.

That was an old Donzi design w/a round keel and not a straight vee.

That build taught me to listen to everyone but try it yourself anyway.

That rig proved most theories wrong.

Also tested toe in vs toe out and saw/felt nothing.

And as it was running the magic 80 mph that the industry said you needed nose cones, so I added them too.

Went from being fastest w/neutral trim to requiring full up trim just to fly the bow and lost 3 mph!
Knocked the cones off and got it all back!

Thanks again guys,

#TwinO/BSonic your information is very useful for me, I guess my boat has similar wet area as yours, 25ft, but angled stern and peaky bow. Also my keel is rounded, not straight.

As you mention, with out-spinning our attitude is nice, no reason to change, same as if you can run with standard lower units in a nice height and you are not in surface props, is not necessary lower pick ups.

You are in the nice height when the water of the roosters grows till the top of the engine cages.

What props are you running?
I’m 23P (infamous) attwood ballistic cuped and label.
V is 145º rounded and X dimension is 53,3”

How much height is your cav plate below?
my calculations is 5,5” below +or-

Maybe I will plug the upper two (of 8) lower unit intakes. I guess I will have like 1” security distance from the water intakes, plugg-in the two upper will give an other 1” extra security distance if Im running in choppy seas.

Thanks again.

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.

There is also a steering method to counter act chine walk in a vee bottom.

Its called steering chop.

When the hull starts to rock left, turn the wheel slightly to the right.

When the hull starts to rock to the right, crank in some left wheel.

All rigs are different and you’ll have to figure out what yours wants.

Some it’s fairly aggressive, some are very mild.

When you get used to it, you’ll almost sense what it’s going to do before it does it.

The 24’ Sonic I referred to above was the first of two I’ve owned/rigged.

I now have a twin OB 25’ Checkmate and it is way more difficult to drive fast/straight than the Sonics we’re.

When it starts to chine walk, it is so violent it is trying to throw you out of the boat!
W/steering chop, I can still drive it straight.

I am still working on set up on it.

None of the three have had solid mounts which does not help.

BTW, the Checkmate is 6” narrower than the Sonics were.
This aggravates the situation.

Setting motor height on a twin engine vee is complicated.
You have to guesstimate how much your hull lifts at speed to know where your props/gear cases will be.

My target is to have prop shafts even w/water at speed.

#Twin O/B Sonic

Thanks mate!

Yes, I’m improving my “drive trough the wild” skills, as I have been reading eeeverything about.

What works good for me is the “chop chop” technique. Your left hand at 10 and vertical chops like cutting carrots.

My boat use to unbalance to starboard, soo I chop to correct to portside. I drive from begging of chinewalk (55MPH) till 62MPH, more I can’t.

My plan with the mods is run stable till 62-64 (with tabs and negative trim) then improve driving trough to get closer to 70.

Which props have you been running and top speed? If you have a post with the characteristics of that boat and your experience, please let a link here.

Thanks again

Here you go.

This is on my current Checkmate build.
Unfortunately not much performance info as I’m just finishing it up.

https://www.facebook.com/marketplace...tory_type=post


You can go to screamandfly.com and search “Sonic twin o/b” there and get much more info.

Be aware, I did threads on builds on two different twin OB 24’ Sonic builds.
Tons of info between the two on there.

OSO is 99.9% IO only.

Scream and fly is 99.9% OB.

Thanks mate! I also have profile at screamandfly, I will study all info in your posts and if I have any questions, I will DM you!

Thanks my friend