X-dimension again,...again,...again...

[Len]

If you go to Imco's site you will note that the Bravo set-up raises the X-dimension and leaves the cav plate in same location. A smaller drive with closer to hull bottom prop centerline. Also, here is an explanation by "some" source...

X Dimension - Term applied to the dimension the centerline of the propeller shaft extends below the hull of the boat. The higher the "X Dimension", the less drag imparted to the boat via "Drag" on the "Lower Unit". To high of an "X Dimension", causes hull instability, propeller "Cavitation", and in extreme instances, "Propeller Blowout".

I think GeneD has it right, the first time. Rick, if you measure the relationship of the imaginary line transferred from the cav plate to the transom and measure up from it to the center line of the gimbal housing then how could you ever change the x-dimension in relation to the drive? Raising the motor/drive would only move the package as a whole. Sure it would ventilate easier, blow out the prop and decrease drag but the x-dimension in this case would still be the same as before. The IMCO drives raise the x-dimension by locating the prop closer to the surface in relation to hull bottom without relocating the drive and gimbal location.

One could also say that adding a pad to a former full V "increases" the x-dimension but adds stability at HIGH speeds. Adding a pad to a fromer V would probably require a relocated drive to take full advantage of the benefits. I have seen a pad added to an X-18 copy and the drive was raised 2 inches as well. Runs about the same as you guy's posted speeds with 270hp/350's @ about 67mph but handles differently...My two cents.

[BigGrizzly]

Sorry Len Rick has it right. the X dimention refers to the stock placement of the drive. There was astandard between the cavplate and the imput shaft. Gene has a SS, which is shorter than standard drive. Impco has a shortie which takes the place of the now dead SS, but twice as strong and more hydrodynamic. Part of the problem with raising the X is it raises the motor and the center of gravity of the boat. The ss solves this problem because the X stays the same but raises the prop. This is evident in the speed master also. I have the Volvo setup instructions which are the same as the Merc. Blow out for this situation is fixed with surface piersing prop like a clever or chopper prop. The merc Revolution 4 and the Bavo1 do this well also. The pad if not done correctly will chine walk and ride like a rock. One of our guys here in the Registry did this and is described in a earlier post and didn't like it.

[Owen]

So what's the X-dimension on this?
http://albums.photopoint.com/j/View?u=943763&a=9581405&p=31569282


Gillian Anderson has the only X-dimension I need!

[This message has been edited by Owen (edited 10-26-2000).]

[Jamesbon]

Holy Chr*st!! What's that thing? I think I need one, or two!!

Must be expensive?

Nathan

[rayjay]

Is that one of those Jet Drive to Prop Drive conversions I have heard about but never seen? But it looks cool, wonder how it works and what type of hull it needs to work the best.

Just as a question to pose in this same vein, isn't there a way to build a shorter Volvo drive by combining different uppers and lowers? I seem to remember hearing about this. rayjay

[This message has been edited by rayjay (edited 10-26-2000).]

[GeneD]

So if I am reading this right, X dimension has absolutely nothing to do with prop shaft height, but the relationship between the Cav plate and the hull bottom. Thus putting the engine in proper placement for CG.
Raising the X on a boat would HAVE to mean raising the engine.
The SS's cav plate is identical (pretty sure anyway) in distance from the driveshaft as the Alpha One, it is the bottom half that is short.
That is not to say that the uppers of both are interchangeable, because they are not.
Do I have this right now?
And if so...what do you call it when you install an SS? What kind of mod is it? It wouldn't be called "raising the X dimension", right?

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GeneD
007
Melbourne, Florida

[Len]

one of these I suppose. ZF has a great name behind it... http://www.americanpower.com/geardriv.htm

[GEOO]

Owen, Len, Good find!! SARO Drive?? I've never seen that drive. GEOO

[RickR]

GeneD
You've Got It! http://www.donzi.net/ubb/biggrin.gif

Your SS setup has the same effect as raising the X Dimension without having to raise the entire package. AND your Antiventilation Plate is at the right height to prevent blowout while planing off.

I do not know what raising the propshaft relative to the hull would be called? Fast http://www.donzi.net/ubb/eek.gif?
What do they call it on flats boats with Jack Plates?
Bass boaters say your surfacing the prop.

BTW I sure dissapointed a bass boater on Tuesday, let him borrow my GPS. His Bullet Bass Boat(FAST) with 260HP Merc ran 77.1
Genuine Risk 72.1

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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

[

[This message has been edited by RickR (edited 10-26-2000).]

[This message has been edited by RickR (edited 10-26-2000).]

[Scott Pearson]

Raised my X-dimension 1 1/2 inches. I am trying to find an SS drive or will a Imco drive fit on a stock Alpha gimbel housing?

(NJ)Scott

[GEOO]

Scott, Imco is for Bravo's only. GEOO

[Len]

RickR, GeneD,...anyone else listening. I talked this afternoon with the guys at IMCO. Here's their scoop.

The "X" dimension is, in their eyes and calculations, the distance from the actual bottom of the hull to the centerline of the engines crankshaft/gimball. I think that is what Rick said other than the cavitation plate projection, but in reality, none of this matters as it is only a reference to location only. Their goal in life is to reduce the drag of the drive unit underwater and increase performance. They do this by using standard and shorter legs, or Bullet drives below cav plate in themselves shorter(eg.standard bravo, 8" down to drive central axis below cav plate) and optional 1" and 2" shorter legs above cav plate.) In doing this the X dimension remains UNCHANGED technically, drive/gimball/crankshaft remain in same location, no transom or mount rebuilding, no C of G changes, but there are tremendous gains in performance. They use the X dimension as a reference only, in that knowing on a boats transom the location of the engine crankshaft/gimball location in reference to the transom/hull bottom they then know where the stock Bravo props drive is located in the water and can design performance gains around that. eg. Tell me where the centerline of the gimball/crank is in relation to hull bottom, OR tell me where the location of the cavitation plate is in relation to the hull bottom. Simple math (add 8")will then tell them where the Bravo drive is located underwater. None of their components ever actually change the X-dimension. So, in my understanding, after talking with them for 15 minutes, when someone says that they have raised the(increased the number of inches) X-dimension in their boat then they have to have relocated the engine and drive location in the hull and through the transom. The same effect can be accomplished with Alpha SS legs, Imco Bravo parts etc, achieve the same or better (no C of G changes) performance but NEVER actually have changed the X-dimension. Stock leg locations are suggested and templates provided with Mercruiser legs and in general, (hence Rick's Merc bulletins)Medium performance is flush with actual bottom, higher performance is up from that 5/8" or more.

So, here's my take on it. The "X" dimension is nothing more than an "X" as to where you put the supplied template for a gimball housing in relation to the bottom of the hull. Raising the X dimension on an already previously powered boat means you actually rebuilt the transom and put in new mounts to raise the engine, bring the leg out of the water more and brought the cavitation plate up higher in relation to the actual hulls bottom, therfore the propeller as well. With Imco drives, Alpha SS etc. you can do the same thing, but spend more, but you don't require any mount/transom mods. In this case the X-dimension never changed.

This being said, GeneD never changed his X-dimension with the SS but got all the benefits.

[Scott Pearson]

I changed the X-Dimension on my 68'. Once I filled the old Volvo hole in the transom and rebuilt the transom. I raised the template
1 1/2 inches from the stock X-Dimension and cut. You also have to take into account the transom angle. And raise the motor mounts. Even with the 1 1/2 the Alpha SS should work out Great.

(NJ) Scott

[BigGrizzly]

I now you have it, the Imco lower leg looks like a Hydromotive nosecone, no bullet but a knife like entry. Seen a couple at a local hi-Performance shop on triple step Eiminator, a Warlock and a Python. Gary says they work great. all three boats brake 90 on the gps and radar. The all have over 600hp in them. Go by me and I think lost power. what a sight, nothing but rooster tails.

[This message has been edited by BigGrizzly (edited 10-26-2000).]

[RickR]

Len
You've got it except the measurements should be taken from the "True Bottom" not the "Actual Bottom" as discussed in the previous post.

As I said the shorter lower gear units have the same EFFECT as raising the X Dimension.

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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

[This message has been edited by RickR (edited 10-27-2000).]

[Len]

whew!!!...hoo sed eye can't bee tot? http://www.donzi.net/ubb/biggrin.gif

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...look'in for Donzi's in all the wrong places...

[boxy]

It's cold, I'm bored.

I understand x-dim's in relation to single drive applications, how does it relate to dual engine set ups.

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boxy
mailto:sboxma@sprint.casboxma@sprint.ca</A>
Smuggler's Cove
1000 Islands
Ontario

[Len]

Boxy, good point! I have looked at many of these "twins" and outdrive placements on Boat Trader etc, and they all seem to be very high up on the transom. I can't see the above formula's applying to these situations. Can someone shed some light on this topic?

Sorry your cold and bored. You should move out west and help me find one of those 18'single drive applications. http://www.donzi.net/ubb/biggrin.gif or bring one with you from the Great Lakes area.