05-04-2008, 06:02 PM #1
Stepped sponsons kill speed on a stock boat
I figure that there might be people wondering what certain mods can do for their boat, so Im sharing my experience. I bolted on the cut sposons from my 04 to the 07 before my ride today. I lost 1-2mph on top, but handling difference was noticable. Chine walk is greatly reduced and the ski also feels more playful. Its a good free mod if the speed loss doesnt concern you and you like to play around on the low end
05-04-2008, 06:04 PM #2
Stepped sponsons become necessary when using an aftermarket angled rideplate.
05-04-2008, 06:09 PM #3
05-04-2008, 06:10 PM #4
Maybe the stock plate doesnt generate enough lift to get the tips out of the water. I know that they are pretty needed with an angled plate (I used these with a J-plate on my 04), but wanted to see what happens with a 100% ski
05-05-2008, 07:02 PM #5
05-05-2008, 07:22 PM #6
Eh, not really. Maybe a little bit, but aerodynamics doesn't really apply until 50mph or so, and the sponsons aren't big enough to generate noticable lift.
There's an idea though... buy one of those big aluminum wings and bolt it onto the platform behind the seat 2mph speed secret.
05-05-2008, 08:44 PM #7
Eh, ya really. We're talking about top end here, 65mph and up. I'd say areodinamics have a lot to do with it. Try searching it, there have been a lot of discussion's about it.
05-05-2008, 08:57 PM #8
I don't want to sound like a know it all... but aerodynamics is what i'm going to school for
EDIT: Here's a link to a good discussion on this:
EDIT #2: And here's proof of my airfoil idea above ^^ I had no idea it had actually been implemented... maybe this will be a project for me this summer...
Last edited by cincygpr; 05-05-2008 at 09:06 PM.
05-05-2008, 09:17 PM #9
05-05-2008, 09:50 PM #10
I'm not exactly SURE of how sponsons cure porpoising at speed, but honestly... the sponson isn't that big, and so, won't be causing that much lifting force, even at 70mph. Besides, it's caught in the turbulence between the boat and the water.
With the stock rideplate, the sponsons may still be in the water (because the boat hasn't lifted enough), causing a dragging force that creates a nose-down condition. Without this drag, the hull pitch will be too great, and porpoising will happen.
Now, I don't know about highly modded rideplates. Has there been any testing done on a Jim's FF plate or IR level-4 plate with sponsons in the 'up' position? Or how about the skis running 75+MPH? I'd like to see what happens when they leave their sponsons in the 'up' position.
Really high speed guys probably have their skis dialed in so well that the sponsons most likely don't matter at 80MPH. I just don't want to ask them to make a speed run without the sponsons
EDIT: I did some calcs to help me figure out what i've been saying... if anyone wants some numbers, shoot over a PM!
I just keep thinking about this, and i've come to the conclusion that with a stock ski (NO mods), the stepped sponsons do cure porpoising because they lift the ski out of the water quicker (even though they don't add any lift in the air, they DEFINATELY add lift in the water), and once the ski's on plane, they act as a drag-inducing device that pitches the ski's nose down when it tries to porpoise... but it also slows the ski down.
When going at higher speeds, the aftermarket rideplate, once dialed in correctly, will correct the porpoising problem itself, because like people have told me, the sponsons aren't even in the water. They still help the ski plane faster, but once it's on plane, they're out of the water and add little to the total dynamic of the ski. Other elements come into play to reduce porpoising, such as shimming down the trim tabs, because they do the same thing as the stepped sponsons on a stock ski... they add more drag and thus help to stabilize the nose of the ski from pitching up.
Last edited by cincygpr; 05-06-2008 at 07:21 AM. Reason: I keep thinking of stuff
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