Boatless------Swept back skegs....which are also "wedged" were designed because the stock "shark finned" Profile becomes unstable at between 130 and 140 mph, due to cavitation and low pressure areas. This robs straightaway control at maximum speeds. However, "spinning in" has nothing to do with this and will create all of the tendencies I noted , with or without the new skegs. Yes boats do barrel roll or spin out with standard rotation, but require much more drastic driver error to do so....
Bottom line..... Boats that spin in assist in the barrel roll....boats that spin out do not.

Magicfloat

Thanks for the link to fibreglassics; fantastic history of the beginnings of the cat design. Looking at the dates, does this mean the cat design appeared before the Hunt deep vee design?

T2x
Regarding the Jesse James 48 Superboat, we did have 5 blade props as well as 3 and 4 blade.

The five blade props are now supports for a coffee table in Chris Lavin's living room (possibly the worlds most expensive coffee table).

As you pointed out the were custom made. The diameter was 22 inches with 36 inches pitch and 15 degree rake, the hubs were 8 inches long and they were rear thrust design like the new #6 Speedmaster props. The shaft dia. was 2 5/8 inches.

Only one pitch was made initially. The gear box custom designed by George Miller (Powertrain Design) provided quick change gear ratios from 1:1 to 1.78:1. The gears provided the equivilent of 1 inch of pitch per gear ratio. It was far less expensive to build gear sets than build a full range of props. By the way the gear boxes were dry sumped and provided counter rotation without the need for counter rotation engines. The design of the drive system was for 3000 hp per side continuous duty. The rudders were equally exotic billet cut cleaver design (Tom Wenstadt) with internal water pickup for engine cooling built by Latham Marine.

These components worked flawlessly, however the engines are another story.

On the subject of prop rotation. There should be no discussion. Those who think inboard rotation is better also think the world is flat! Wake up, the laws of physics cannot be disputed. T2x has covered the basics very well.

During my 6 years (1995 to 2000) as APBA Tech. Chairman I tried in vain to mandate outboard rotation without success. Too many manufacturers and racers have rewritten the laws of physics and are convinced the world is flat.

T2x is right, inboard rotation is a dangerous fix for poor hull design, boat balance and prop selection. Single engine boats also benefit as T2x points out. I found it interesting that the vast majority if not all single engine racers did not have a clue to the advantages of switching rotation depending on the direction of the course and turns. If you are turning left use right rotation and if turning right use left rotation, make the torque and physics work for you and not against you. When you reinvent science to suit your self you are inviting trouble.

George

George:

You're right about the props on JJ...but the castings could have been ground plus or minus 2" as I recall which allowed for a 4" range to choose from if needed...... I forgot about the 5 blade versions.....my age I guess..... Man that thing was ahead of its time.......(sigh)...if only Batten made a decent engine..... The drives and props would be ideal on a range of big sportfishing or performance boats today, and are really the main piece of technology that made that project unique. The loss of that hardware is really a shame. ( of course I think I have a copy of the drawings somewhere..... )I was on an 80' Baia (no not Baja) at the NY Poker Run..... Boy did that need those drives.

Thanks George....now go back to sleep.

[ 09-25-2001: Message edited by: T2x ]

[ 09-25-2001: Message edited by: T2x ]

T2X, GJL

Thanks for the very informative and interesting posts. I have a great Chris Cat that has been restored to "better than new" condition and repowered. It currently runs 117 on GPS (90 degree day), but turns about 500 rpm over peak hp: currently using #3s, 1" above the bottom, no boxes, 4 blade Labs with "tweaked" 17.5 x 33s. Got new tweaked 35s in the works.

With the props spinning out, it had a tendency to porpoise starting at about 90+ mph thru 115. I tried 200# additional weight in the nose and the hop got worse. A well known (to remain nameless) rigger/throttle person suggested trying inboard. I changed to in rotation and although it still porpoises at 90 or so, at 100 it settles down and feels stable. You are correct about turning though: the boats "lifting" with the turn is exacerbated.

What solutions would you suggest to solve the "hop?

Thanks

[ 09-25-2001: Message edited by: Dueclaws ]

Dueclaws
Glad to hear you like your Chris Cat. The best way to control or eliminate the "hop" is to use a tunnel tab. the width of the tunnel and approx 24" long. Use two Merc. trim tabs with one trim pump to activate both tabs and put the plate under the Merc. tabs. There are other ways of doing this but this has proven to be reliable and cost effective if you want to talk call 631-435-8496 office #.

T2x/GJL
Amazing! The technical knowledge that is sitting on this post and the “V” bottom post is truly amazing. I found myself having to print out T2X and George Linder’s posts so I can re-read them to absorb and attempt to understand the technical Info. The amount of knowledge these 2 threads are producing is fabulous. It is clear to see the 48’JJ was, and is still ahead of its time. I am intrigued with the drive/steering/prop combination. Quick-change gear ratios, prop castings that allow for multiple pitch, internal water pickups, one question I have is, why didn’t Mercury pick up on these Ideas? As we all know, the weak link in all of the “current” cutting edge speed demons is the drive, transmission, prop durability and efficiency. What good is making tons of HP and then giving up 15% to induced drag? I would think Cooling water is another problem area, hull pickups can adversely effect a boats performance, At 150, 160 MPH a low pressure area is created around the p/u causing a actual boiling of the water, same thing for the gearcase, Water separation around the gearcase induces slip. Or inefficiency. Quick-change gear sets! What better way to keep the engine in the intended RPM range, while running the most efficient Dia. And pitch. Acceleration for the rough days, top end for the calm days. All out of one Prop Spec.
I hope that all of the proponents of inward spinning props will read and understand how they are tempting fate. I too have tried spinning the props inboard on both of our Skaters, I have never seen any speed or handling gains, only handling losses. On more then one occasion have corrected a high/low sponson condition “way, way, too high on one side” by jumping on the power as a last ditch effort. Luckily it always brought the high side down. I am now glad I was not spinning inboard. Wow 22” Dia. 36” pitch, I would guess the 22” dia was the result of the anticipated HP the engines were going to make? I would think that over 36” pitch, the angle of attack relative to the water flow would cause the blades to “Stall” and water flow to be interrupted just like excessive angle of attack causes a wing to stall. And speaking about wing stall, was the tunnel height relatively constant through the second half of the boat? I would think that there would be little compression needed in the stern sections to produce the necessary stern lift given the speeds this boat was intended to run. And by the way, did the 48’JJ ever get dialed in? If so what were the results?

GJL
OK, tunnel tab is next! And we'll switch rotation (again ).THANKS!

Curious Question...what is the cause of the "Hop" to begin with?

Phillip---- Just a little example of how trick those drives were.... The strut over the drive shaft just ahead of the upper half of the prop was hollowed to allow air holes for aeration of the blades as the boat was planing....... The reason Merc was cool toward the project had to do with the fact that they sold traditional stern drives at that time.....and the K Drive (now the #6)had just been introduced. In retrospect they were in secret negotiations with Fred at the time for the rights to that technology. The last thing they needed to endorse was a fixed surface drive.

The reason the Shadows and Chris Cats hopped was because George used to have a band in College (true story), George Linder and his Blue Knights (sort of a Guy Lombardo meets elevator music group , I think)......and he played a lot of hops.... Or..... maybe it was a lack of aft compression and a porpoise induced by the transition from hydrodynamic to aerodynamic lift. Take your pick... I like the band story better.