scale sponsons

[jeff baham]

i've noticed on some scale hydroplanes that the bottom of sponson are cut away, like the whiplash gas hydro and the dumas sport 40 and the i think, the atlas van line are cut too, what effect does this do to the hull .

 

[jeff baham]

i've noticed on some scale hydroplanes that the bottom of sponson are cut away, like the whiplash gas hydro and the dumas sport 40 and the i think, the atlas van line are cut too, what effect does this do to the hull .

40 hits and no one know what i'm talking about. dam. this must be top secret.

 

[Duck899]

The cut-outs are part of the design of course.....Basicly it puts more weight bias on one side of the hull vs the other. More surface area on one side to create more lift on that side. Typicaly the smaller surface area will be on the left side when viewed from the rear on a model boat. This allows little to no weight, (ballast) added to the left sponson to counter-act torque from the engine. A Phil Thomas 82U55 hull is a prime example. The smaller surface area allows the left side to 'sink' easier in the water vs the bigger area on the right side.

Hope this helps.....

My $.02

 

[dschigoda]

The cut-outs are part of the design of course.....Basicly it puts more weight bias on one side of the hull vs the other. More surface area on one side to create more lift on that side. Typicaly the smaller surface area will be on the left side when viewed from the rear on a model boat. This allows little to no weight, (ballast) added to the left sponson to counter-act torque from the engine. A Phil Thomas 82U55 hull is a prime example. The smaller surface area allows the left side to 'sink' easier in the water vs the bigger area on the right side.Hope this helps.....

My $.02

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Interesting - I wonder why the current full sized unlimiteds are designed with the outside sponson much wider than the inside sponson? Maybe the cornering forces and weight shift due to the cornering forces are much larger than the engine torque on the big ones?

Dave

 

[Hydro Junkie]

The cut-outs are part of the design of course.....Basicly it puts more weight bias on one side of the hull vs the other. More surface area on one side to create more lift on that side. Typicaly the smaller surface area will be on the left side when viewed from the rear on a model boat. This allows little to no weight, (ballast) added to the left sponson to counter-act torque from the engine. A Phil Thomas 82U55 hull is a prime example. The smaller surface area allows the left side to 'sink' easier in the water vs the bigger area on the right side.Hope this helps.....

My $.02

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Interesting - I wonder why the current full sized unlimiteds are designed with the outside sponson much wider than the inside sponson? Maybe the cornering forces and weight shift due to the cornering forces are much larger than the engine torque on the big ones?

Dave

You are partially right, but it also involves aerodynamics as well as hydrodynamics. Too bad someone hasn't written a book on this yet

 

[Mike McKnight]

I read an article on unlimited hydro design that was published some years in Powerboat magazine. It was from the mid 80's or so back when asymetrical sponsons were becoming all the rage along with the offset cockpit and center section. It focused on Jones and Lucero since those two were the main schools of thought on sponson design at the time.

They increased the beam or footprint of the outside sponson and offset the tub to the inside for cornering advantage. The larger footprint was to be able to counteract the sudden shift of weight across the lateral balance point of the boat. It was literally designed to "push back" and guide the weight thrust against it. The offset tub was an attempt to keep the longitudinal center of gravity more toward the center of the boat in a turn. The outside sponson usually, not always but usually, has a slightly narrower ride surface than the inside. The recovery pads, the angled surfaces to each side of the ride pad, were wider and had less angle than the inside sponson to deflect water at more of a downward angle. The flatter angles also helped to keep the boat from tripping on that sponson in the turn. The angle kept it from digging in. The non-trip area was also usually fairly shallow compared to the inside sponson as well. The inside sponson typically had a wider ride surface to account for the offset tub which added more weight to that side to plant the turn fin. The recovery pads also had more angle to them as that sponson was intended to literally grip the water in the turn.

Most of the newer boats still employ asymetrical sponson designs, only not as drastic as in the past. More attention is being paid to the angles of the dead-rise pads up front. Plus most of the tubs are back to being centered but lowered into the draft of the hull so that weight is more evently distributed. They also pay more more attention to the aerodynamics of the deck. There are much more longitudinal breaks in the deck and the vertical non-trip areas on the afterplane from the 90's have almost all but been replaced by a rounded joint on the outside.

 

[Doug Ashby]

Yea, what he said!!! :blink:

 

[Mike McKnight]

Sorry did I go to technogeek? I got into a conversation with Jim Lucero one time.....he is an extremely smart guy but even I got an ice cream headache before we were done. :blink:

 

[Hydro Junkie]

It's pretty sad that between Ron Brown and Jim Lucero, they have probably forgotten more about hydroplanes than most of us will ever know

 

[dschigoda]

I read an article on unlimited hydro design that was published some years in Powerboat magazine. It was from the mid 80's...

Mike,

Back in the mid '80's I had planned to build and race a 1/8 Scale '83 Miss Renault (simple wood pickle fork hydro with symetrical sponsons and a 3/4" cowl offset). I never built it, but may one day. I always wondered what the effect would be to change the shape and angle of the bottom of the center section.

Picture a longitudnal section drawing - through the center of the boat. Picture a straight line drawn from the bottom of the transom all the way to the sponson transom bulkhead area (parallel to the water). In other words, the after plane would be a constant height above the water for its entire length. Now picture that line continuing forward in a parabolic or eliptical arc, the arc being carried to its end (90 degrees upward) at the front of the tunnel, to meet the deck. So the center section would still have an airfoil shape, but its incidence or angle of attack would be 0 degrees (somewhat like a rigger, only a right side up airfoil shape, with an eliptical front and a tapered rear section).

This design would allow me to set my engine, fuel tank and radio quite low for a lower center of gravity and better cornering, and would give me more clearance for the dummy engine, tuned pipe and driver mounting.

My thinking is that for heat racing 1/8 scale boats - the sponson angle, drive line angle, prop shape, CG, and a light weight boat, would take precedence over center section lift characteristics.

My concerns were: would the bottom of the center section act as a venturi (at the sponson bulkhead area) and suck the boat tight to the water at that point? , which would be about 2" ahead of the CG (not good). Or would there be a build up of air pressure that point and create too much lift? Would it shift the center of lift forward? or back? Would the top of the curve in the top of the deck set the center of lift? Would it be scale appearing and therefore legal? If it becomes wildly successful, will some one propose a rule to outlaw it? If a man speaks, and there is no woman there to hear him, is he still wrong??? Hmmm.

Dave

 

[Mike McKnight]

Ya know the only way to accurately know what those mods would do would be to build it and put it in a wind tunnel. I remember hearing one time that Ron Jones did some wind tunnel testing to some Bud models years ago before the T3 T5 aned T6 came about. Wouldn't that be cool to have those kinds of resources? I'd be in heaven!

Dave most of what you are proposing to do would be legal as long as the bellypan stayed within the 3/4" rule. The venturi effect you describe could go either way. If you are dumping must of your air at the sponson transoms it may very well suck it down to the water. The only way I see it could give you too much lift is if the airtrap and the tub extend the full length. When you look at the bottom of most boats there is couple of options....the airtrap breaks and the tub flattens into the trap...or the tub stops and there is a step back into the trap. The reason for this is so that any compression of air between the belly and the side of the trap has some release or is allowed to expand to relieve pressure from the narrows.

I'm not sure if making the center section more like an airfoil shape would give you enough lift to make efficient use of that airfoil characteristic. I know on the big boats the idea was to trap air but do it in specific ways to allow the rest of the boat, ride pads prop and everything else, to make the best use of the boat riding on air. I'm not educated enough on airfoil angles to be able to give you the magic formula for the curves you would need to get the desired effect you're looking for. However, if it is so drastic that it affects the scale appearance of the boat you may run into a problem there. If you can do it without changing the appearance too much you can probably get that to work. About any rule changes if this goes hog wild.....at the national level it is doubtful...but at the district level that is another story. If you make this work and start leaving boats wrecked in your wake someone may try to legislate you back the rest of the pack. Seems to be a lot of that these days.

By the way Dave you're always wrong whether the woman hears you or not....just ask her she'll tell you!