sponson shape

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anthony_marquart

Well-Known Member
Joined
Nov 4, 2003
Messages
3,745
I'm thinking of modifying / building new sponsons for my FF.12

I thought about adding a step that runs nearly the full length of the sponson, all the way to the rear, about 1/2 the width and about 1/8 - 1/4 tall. I'm hoping to ruduce the wetted surface at full plane, hoping to get a little faster. Any comments on this?

Also, what's with the bottom cut-away like on the EagleSG sponsons? It seems like the area behind the cut on these would get little use after the boat gets on plane.

Can you tell me what the purpose of these are?
 
anthony_marquart said:
Also, what's with the bottom cut-away like on the EagleSG sponsons? It seems like the area behind the cut on these would get little use after the boat gets on plane.Can you tell me what the purpose of these are?
I saw something on discovery channel about hovercraft and in the early days of hovercraft they relied on a shape not dissimilar to the SG sponson for lift. The idea behind it is that it generates lift / reduces drag.

Later hovercraft used a Skirt and trapped air.

Tim.
 
The preferred hydrodynamic lifting shape is wide and short. For the same wetted area, a short wide planing surface creates more lift. At full out speed the sponson should not be touching the water surface constantly, it should be packing air under the rear edge of the sponson. This is indicated by the absence of spray or much of a wake from the sponsons. I'm not certain that the average .12-powered hydro ever attains this status however.

A longer shape may work better in a corner where the sponson has lost aerodynamic lift and acts like a ski, but for straightaway speed the flatter surface should work best. That doesn't mean that the step as described wouldn't work, but I don't believe it is the "best" for top speeds.

Non-wetted sponson bottoms are usually there to keep the hull from sinking too deeply, supplying additional floatation without adding to the hydro or aerodynamic drag while running.
 
Tim may be right but I just thought the right one is a good place to mount the turn fin farther back and the left one is just to match the right one. :rolleyes: They also would add some flotation.

Also, I do run a step that's 1" wide on the bottom of my 1-1/2" sponsons. They are even with the inside edge and taper in to the bottom about half way up the sponson. I call them ride pads and they are only 1/16" deep at the TE. They seem to work really well for me. The SG sponson bottoms are built pretty much the same way. I have seen many variations of this like two strips with a space between them to trap air, etc., etc.

Don
 
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anthony

one thing to think about. if the boat goes fast enough a smaller top surface compared to the ride surface will make them lift. on the bottom side chines make them small as possible. it gives less surface area for the water to havg onto in the corners. another thing is look at the r/r. the tops slope downward in the front. it takes very little to change the way it rides. it causes downforce. it is eaisier to change the strut to push the nose down. create as much lift as possible and use the strut to set the ride of the boat. this will cause the boat to ride light on the water. just remember the has to be a balance between the tub lift and sponson lift.

jon
 
jayt:

This is an average .12 powered hydro and I do believe they will attain "this status" quite easlly. The sponsons are designed as described above with dihedral built in.

Don ;)
 
... an average .12 powered hydro and I do believe they will attain "this status" quite easlly.
Maybe the average .12 rigger you see, but the average low-powered hydro I see has a lot of problems in setup. Obviously the one in the pic works, but I see 'way too many hydros and riggers not run well. The problem is more prevalent in the lower powered boats, and for nitro .12-power is the lowest. Same problem in electrics too.
Obviously there are 100 different ideas about sponson design, and 20 of them are probably good ones. I do know that removing the 1/16" thick "ride pad" on the bottom of a buddy's rigger increased the GPS speed by 4 mph and it seemed to corner just as well. I also know that the front sponsons with the central tunnel work great in the turns (I've tried them), but not so well on the straights if the water isn't glass smooth. Rough water from leading boats disturbs the air packing and drag is dramatically increased. This isn't just my idea, Tom Prezentka and Ed Hughey agree. But then, they're just a couple of old guys who probably forgot about how to go fast anyway...... ;)
 
jayt:

I don't know Tom but Ed Hughey has been a very good friend of mine for many many years and he certainly is not an old guy who doesn't know how to go fast anymore. Believe me, don't try to get lane one away from him! :lol: I don't disagree with what you have said. I was just at the Hydro Masters and watched a Crapshooter and an SG go at it. The SG had sponsons much like mine (I should say mine are much like the SG) and the Crapshooter, as always, the normal smooth bottom with a bit of dihedral. The only difference I could see in each heat was who drove the best. However, I do have another set of sponsons for my boat that are smooth and who knows, maybe they will work even better. This is actually the first time I have built sponsons this way and the first 12 I have ever built. All my previous experience has been with 67 Crapshooters from years back. Sure wish Donald Campbell was still around. I think he's the one that started all this rigger stuff to start with! :D :D

Don
 
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Well, this started out as a very interesting post.

JayT, I guess being from Humble, TX does not mean that you are humble. Your statement:

(Tom Prezentka and Ed Hughey agree. But then, they're just a couple of old guys who probably forgot about how to go fast anyway) is very disrespectful.

Tom and Ed are pioneers in this hobby and should be treated as such. They have forgot more about going fast then most of us collectively will ever know.

Talk knowledge not smack.
 
Will:

You're right about that but I really think jayt was just talking tung and cheek. ;)

(How the #x%@*! do you spell that thing in your mouth?) :huh:
 
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anthony_marquart said:
I'm thinking of modifying / building new sponsons for my FF.12

I thought about adding a step that runs nearly the full length of the sponson, all the way to the rear, about 1/2 the width and about 1/8 - 1/4 tall. I'm hoping to ruduce the wetted surface at full plane, hoping to get a little faster. Any comments on this?

Anthony,

We tested the ride pads on the FF.21, 1/2" wide 1/16" thick front and rear sponsons.. I can see the boat rides different and seems to be faster. Without radar it's only a guess.

I think you need to test with and without them.

Mike
 
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Will Gallagher said:
Well, this started out as a very interesting post.
JayT, I guess being from Humble, TX does not mean that you are humble. Your statement:

(Tom Prezentka and Ed Hughey agree. But then, they're just a couple of old guys who probably forgot about how to go fast anyway) is very disrespectful.

Tom and Ed are pioneers in this hobby and should be treated as such. They have forgot more about going fast then most of us collectively will ever know.

Talk knowledge not smack.

66759[/snapback]



Will,

The little, winking smilie-face at the end of Jay's post. It means: "I am being sarcastic".

It is a way of "drawing a picture", for those that need it.

Apparently, it doesn't work all of the time.

Jay is not exactly an unknown himself.

While he may not be one of the "Kings of RC Boating", surely he must be the Prince of Carbon Dust :)

KW
 
Will,

Don't worry about that. I would have come back with same thing you did if I had not known that Jayt was saying it in jest! :) Jump in hear anytime.

Don :)
 
Here's a firefighter 12 with pads that Climate runs. After different length/width/position variations were tried, this is what they say worked best for them, so it may be a good place to start with if you want to experiment on yours. 1/16"ply-

View attachment 3328
 
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