IMO After using the SCX for a season with #6 shafts above the bottom(surfacing), I believe that there is definitely more work being done spinning the much heavier props. I have had no issues or early indications of wear, but it will be interesting to see how the lowers carrier bearings take the angular loads. I think the weak point that I am the most concerned about lies in the upper and lower swivel pins and their housings. Shifting with the big props was umbelievably good with the SCX's, which is a pretty big task.

That was flat water. For 3-4 footers is simple too.

Simply take the speed at 5400RPM and 14% slip which is 102 MPH. 102 MPH X 5280ft per mi = 538560 ft per hour divided by 60 (minutes in an hour)= 8976 ft per minute divided by 60 (seconds in a minute) = 149.6 ft per second

Now. Average wave height to 3.5' X 2 = average wavelength 7'. This a standing wave. Wind waves are different and can be calculated too....later. Just need to know direction of the wave and wind and speed and depth and fetch and direction of boat travel.

Now the boat is not just touching the crests of the wave. It's actually smashing through to an average depth. A Black Thunder will smash through deeper, say 3/4 the heigth vs a Fountain at 1/4. Since we're going 100+ we must be in a Fountain so I'll use that for practical purposes.

Wave heigth X 1/4 = .875' X length 7 = 6.125' divided by 4 (1/2 crest X 2 + 1/2 trough X 2) = 1.531' length of water propelled through.

149.6' per second divided by 7' swells X 1.531' length = 32.7' amount of water actually propelled through per second

32.7 divided by 149.6 = .22 = 22% of time prop is in water.

The 5 blade props have a blade pulse of 1/300th second X 22% = 1/6000 of a second or average time prop blade is actualy touching water which = even less load on the drive.

Conclusion = Fly that b****, it's easier on the drive!

I do like your saying, not just about this drive but in general. The normal is to baby a overpowered drive and throttle back in the air. But I have seen many people leave the throttle pinned and not break drives! So...

Fly that B****, it's easier on the drive!

Ok, it looks like the original poster is only concerned with the difference between a "deep x" I/O versus a "high x (surfacing)" I/O.

Lots of people have joined in the discussion talking about "real" surface drive systems such as the Arneson, but it looks like the poster doesn't care about those.

So if we're talking about I/O drives, then the whole element comes down to WHERE the propshaft is in relation to the hull pad.

The SCX4 drive is pretty much an SCX drive that is a LOT shorter than a "regular" SCX. This is what the poster is referring to as a surfacing drive.

As has been discussed already, when you raise the X dimension of a sterndrive, you either have to raise the entire motor and cut a new hole in the transom, or you have to bolt on a shorter lower unit. The SCX4 has a shorter lower unit, so the BENEFIT of the SCX4 is that you get to raise your X dimension a lot without moving the motor higher in the hull. That's pretty much the benefit.

Now, when you run a drive way deep in the water, with the anti-cav plate even with the bottom of the hull, that is condered "fully submerged" and the prop only "sees" water regardless of the boat speed. As the prop turns, the blades keep a constant bite on the water, providing a smooth resistance which the gears and shafts also "see".

As you raise the X dimension, the top of the prop becomes exposed when underway, allowing the prop blades to unload when in the "air". This causes the propshaft's loading to become less smooth and more interrupted. The gears and other shafts now see a load that is oscillating.

The more you raise it, the more significant the cycling effect becomes.

Running in this manner requires beefier propshaft bearings, and a stronger propshaft. This is because the thrust load is no longer pushing directly forward on the centerline of the propshaft, but is now offcenter, several inches below the centerline of the propshaft. This is because the lower half of the prop is the only part that is providing thrust.

Now, let's talk blades. If you run a 2 blade prop (late 60's early 70's outboard racers ran 2 blades), and run it with a high X, you will understand the term "vibration" with newfound clarity.

You HAVE to run at least a 3 blade prop when you start exposing the blade tips to the air.

The more blades you run, the less cyclical the loading is.

If you run a fully surfacing setup, then as long as you run lots of blades, you can minimize the vibration on the gears and such.

The SCX4 vs the SCX, as far as my understanding goes - use the same bearings and has the same gears. This means that both drives should be comparably durable.

The shorter vertical shaft in the SCX4 will be less prone to break, but I don't think it is a weak point on the SCX4 - so that doesn't really matter.

As far as shaft lengths, the longer a shaft is, the more it self-dampens torsional vibration.

So in that respect, the SCX may cushion the upper gears better than the SCX4.

Back to your original post, you were also asking if the NXT and Six drives were easier on the gears than a Bravo. That question is not applicable, as the Six has giant gears and two vertical shafts and a huge propshaft with compound bearings.

So the simplest answer will have to be:

The farther out of the water you run the prop, the more vibration you transmit to the drivetrain.

The farther IN the water you run the prop, the more bite it will have.

And any Bravo style drive is a time bomb if you run big power into it.

MC

This was told to me today......Getting on plane the SCX4 setup is tougher on internal parts then the SCX. But once on plane the SCX4 is easier on internal parts. So they almost equal each other out......