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Speed Rails - fact or fiction?

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Old 12-05-2002, 12:35 AM
  #21
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Guys, this is not hard to figure out. As was stated earlier, the speed will increase when the drag is reduced. Properly installed speed rails direct the water down which will lift the hull, decreasing wetted surface. Every little bit helps.

Now if you really want to lift a hull, try forcing a 42 inch high column of air through an 18 inch opening under the back of Skater or MTI cat. This really helps.

Now the steps.

Next the X goes up and the drives go back (boxes) and the notch, so you can still get on plane.

Now you are broke but fast.


BTW, I tried them on porposing 38 Topgun. Gained 1 or 2 mph and reduced the hopping significantly.

Last edited by John B; 12-05-2002 at 03:04 PM.
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Old 12-05-2002, 10:17 AM
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Wonder if these would help reduce the 'hop' on my 26 Ocean Express, it has a slight rocker to the rear of the sponsons and small 12" pads? My Cat seems to pack air then falls off it, I'm thinking this might trick the hull into a more bow down(i.e.forward C/G as if ballast were added) I have two 250 Yamaha's that are heavier than Merc's. and at WOT it really hops huge on calm water. Any suggestions? Thx,Bill
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Old 12-05-2002, 01:38 PM
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I think a tunnel tab, or flap, would work better and it should be abjustable. JB
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Old 12-05-2002, 02:40 PM
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John B, I agree......or a wedge in the tunnel......

A tunnel, by the way, is the best "speed rail" you can buy.

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Old 12-05-2002, 03:42 PM
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T2X, speaking of packing and unpacking air, I have a 30' cobra single engine which has a tendency to do this or poipose. It sprays out the sides like the steps are venting the tunnel. Did you mention earlier about sealing the tunnel side of the step to keep the air in the tunnel? I guess a thin piece of SS on the inside. What do you think?
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Old 12-05-2002, 03:53 PM
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Try 3/16ths.......aluminum on slide mounts to adjust...Start at 1/4" below bottom at transom, ending flush with the steps. A single engine cat is the toughest bird to tame.

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Old 12-05-2002, 09:28 PM
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Boating Mag. August 1994. Article called "Cutting Edge". If anybody wants to see it, email me and Ill scan it and sent them a copy.
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Old 12-09-2002, 02:16 PM
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Hi!

I have tried them....

I have a Phantom 25 Offshore hull with a Promax 300 outboard. Its bow heavy and need lots of positive trim. It runs fairly quick - 76-78 mph at 6100-6200 rpms spinning a blueprinted Tempest 26. Gearratio 1:1.75. The boat weights approx. 2.500 pounds incl driver and 10 gallons of fuel.

I mounted four speedrails according to the book. Two in front and two 75% towards the stern. This should create bowlift. We used Sikaflex and the speedrails turned to be almost impossible to take off.

It proved to be a great miss. The boat ran higher, but flatter. The top speed decreased approx. 3 mph. Cruise speed increased 1 mph. The boat runs 53 mph at 4.000 rpms. Now it ran 54 mph at 4.000 rpms. It did turn fairly well, but it turned much more precise without.

I pulled off the two speedrails towards the stern keeping the two in front. Top speed increased somewhat, but still 2 mph lower than without. The boat started to porpoise as well at 55 mph - 60 mph.

The speedrails may work on heavier hulls at lower speeds. For me they were a pain in the ****.

I rather advise the following: a) get rid of extra weight; b) rebalance the boat; c) blueprint the bottom; d) play with propheight / x dimension; e) play with props; or buy a Skater...

Good luck!

Cheers, Toffen
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Old 12-09-2002, 05:56 PM
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Way to go Toffen!!!!!!!!


And he comes from Axle Manygimmicks' back yard.

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Old 12-09-2002, 06:15 PM
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I am still Baffled by Swedens answer to Edison Airfoil shaped Tie bar Invention. T2x I would venture to guess it would be used in conjunction with the Helmet wing.
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