Air Trap Sponsons

[Marty Davis]

I built a .67 hydro many years ago and it ran really well. Problem was that I set the belly clearance at 5/8" and in race water the bottom of the tub slapped the water.

My remedy was to install 2 strips of 3/16" thick Okume (very light weight) on the bottom of the sponsons. I put one strip on the inside edge and one on the outside. This created an air trap on the bottom of the sponson.

I haden't run the boat in years and when I finally re-rigged it and ran it I noticed something very unusual. The boat was probably the smoothest that I had ever driven. It also had another characteristic that I can not attribute to this change, but it might have some influence. The boat will mill super slow and then accelerate faster than any .67 that I have ever had or seen.

I wonder if the air traps are contributing to these great attributes.

I remember a .67 Boss Boat that Steve and Jack O'Donnell brought to Indy many years ago that also had air traps. That boat was awesome and was super smooth as well.

I would be interested in any opinions on this and think that this is a great topic for further discussion.....

How about it Finch, Andy....

 

[opio]

i have not i repeat have not done this on a rigger, on my vegas a similar set up was installed with the same effects, i have noticed that many hydro, PT 40 for example also have something along the same lines for there sponsons, guess there is something to it.

 

[TomMoorehouse]

How wide are the strips / trap? I'm building a set of sponsons so maybe ill try it out....

 

[jayt]

...i have noticed that many hydro, PT 40 for example also have something along the same lines for there sponsons, guess there is something to it.

The Phil Thomas hydros do not have tunnels in their sponsons, they have offset ride pads instead.

The first time I saw the small tunnels in a rigger sponson was on a Crapshooter from the late 1980s. Lots of claims were made for it, including improved turning and higher speeds. I built a rigger with this feature and found that turning did improve, doubtless from the increased side area from the tunnel sides, but I saw no speed increase that I could identify. I spoke with Ed Hughey about it, and he told me that they were very draggy and only gave improved speed on very flat smooth water, not race water (Greg Hughey sold these hulls at one time, in fact I thought that Marty sold the business to him). This mirrored my experience so I have not used it again. But that does not mean it is a useless exercise - some one may find the right combination of tunnel width and depth and end up with a superior turning hull with equal speed to conventional designs.

..

 

[opio]

...i have noticed that many hydro, PT 40 for example also have something along the same lines for there sponsons, guess there is something to it.

The Phil Thomas hydros do not have tunnels in their sponsons, they have offset ride pads instead.

..

i was speaking of the offset pattern

 

[Charles Perdue]

In 1979 as I was refining the Boss Rigger design, I began to play with different sponson ride surfaces. The final design was with the air trap ride pads.

The pad width in relation to the sponson ride width, was approximately 1/4 to 1/3 of the total width of the ride surface of each sponson, depending on the size and weight of the boat.

The earlier design had a tendency to be sticky on glass smooth water. This was not a problem in heat racing as there is no smooth water, not for very long into the heat anyway. On rough water they were very smooth and allowed the boat to drive very predictable. At about 40 MPH the spray from the sponsons would go away.

A dovetail undercut of about 30 degrees on the insides of the strips helped the sponsons to step up on the ride pads quicker and run cleaner.

The latest design of ride pads consist of the ride pad being made of short strips of carbon fiber about .030 thick laminated together in an overlaping pattern that resembles shingles on a roof. They work very good.

Merry Christmas Y"all....Charles

 

[speakerboy]

intresting ..

any change of a pic of these sponsons ?

Jeroen

 

[Marty Davis]

How wide are the strips / trap? I'm building a set of sponsons so maybe ill try it out....

Tom:

The bottom of the sponsons is divided 1/3, 1/3, 1/3 approximately.

Marty Davis

 

[Marty Davis]

...i have noticed that many hydro, PT 40 for example also have something along the same lines for there sponsons, guess there is something to it.

The Phil Thomas hydros do not have tunnels in their sponsons, they have offset ride pads instead.

The first time I saw the small tunnels in a rigger sponson was on a Crapshooter from the late 1980s. Lots of claims were made for it, including improved turning and higher speeds. I built a rigger with this feature and found that turning did improve, doubtless from the increased side area from the tunnel sides, but I saw no speed increase that I could identify. I spoke with Ed Hughey about it, and he told me that they were very draggy and only gave improved speed on very flat smooth water, not race water (Greg Hughey sold these hulls at one time, in fact I thought that Marty sold the business to him). This mirrored my experience so I have not used it again. But that does not mean it is a useless exercise - some one may find the right combination of tunnel width and depth and end up with a superior turning hull with equal speed to conventional designs.

..

Correct, I did sell to Greg Huey (you even spelled his name right).

In fact, Gregg set the 1/3 mile Oval Hydro Record at that race and Steve broke it with Charles Boss Boat later that day.

 

[Marty Davis]

In 1979 as I was refining the Boss Rigger design, I began to play with different sponson ride surfaces. The final design was with the air trap ride pads. The pad width in relation to the sponson ride width, was approximately 1/4 to 1/3 of the total width of the ride surface of each sponson, depending on the size and weight of the boat.

The earlier design had a tendency to be sticky on glass smooth water. This was not a problem in heat racing as there is no smooth water, not for very long into the heat anyway. On rough water they were very smooth and allowed the boat to drive very predictable. At about 40 MPH the spray from the sponsons would go away.

A dovetail undercut of about 30 degrees on the insides of the strips helped the sponsons to step up on the ride pads quicker and run cleaner.

The latest design of ride pads consist of the ride pad being made of short strips of carbon fiber about .030 thick laminated together in an overlaping pattern that resembles shingles on a roof. They work very good.

Merry Christmas Y"all....Charles

Charles:

YES, the boat that they brought to Indy was your design. WAY before it's time.

I have seen the bottom of race offshore boats with the overlap design. Is .030" enough to get the effect? Reason that I ask, is that I am now building my sponsons from G10 and do not want to add as much trap as the 3/16" that I have on the current 60 boat.

I do suspect that the deep tunnel is important to the super smooth ride. What do you think?

Yes, I did notice the dovetail cut on the insides of the sponsons. Made for a REALLY sharp edge and I suspect some turning enhancement.

 

[SayMikey]

...i have noticed that many hydro, PT 40 for example also have something along the same lines for there sponsons, guess there is something to it.

The Phil Thomas hydros do not have tunnels in their sponsons, they have offset ride pads instead.

The first time I saw the small tunnels in a rigger sponson was on a Crapshooter from the late 1980s. Lots of claims were made for it, including improved turning and higher speeds. I built a rigger with this feature and found that turning did improve, doubtless from the increased side area from the tunnel sides, but I saw no speed increase that I could identify. I spoke with Ed Hughey about it, and he told me that they were very draggy and only gave improved speed on very flat smooth water, not race water (Greg Hughey sold these hulls at one time, in fact I thought that Marty sold the business to him). This mirrored my experience so I have not used it again. But that does not mean it is a useless exercise - some one may find the right combination of tunnel width and depth and end up with a superior turning hull with equal speed to conventional designs.

..

Correct, I did sell to Greg Huey (you even spelled his name right).

Currently Mark Bullard runs the SHINGLE DESIGN. From my observations the boat seems to bounce till it gets on step. A different approach for sure. Ive always figured for speed you need a very small ride surface and thought a tunnel might create unwanted lift. I guess dihedral plays into the equation as well. With all these micro cams these days it might be nice to see what is going on in a full speed turn.......Mike

 

[Charles Perdue]

G 10 works good for the ride pad material also. The .030 material is stacked and laminated. The overall height of the ride pad is about .150. The ride pad looks like a stack of dominos that have been knocked over and lying on their sides giving multible running surfaces with a high attack angle for a short distance with the trailing edges only being about 3/8 of an inch apart getting progressively closer together at the rear of the running pad.

If Tom is talking about his .12 design, he will probably will only need about 1/6 of the ride surface of the sponson running surface for the width of each ride pad. As the size and weight of the boat goes down, the width of the pad needed is considerability smaller. The ideal width is not directly scaled down.

The proportion of the size of the ride pads in the water to the size of the turn fin is very small. I don't know if it is enough to help the boat in the turns, but one thing is for sure, it doesn't hurt.

I am not a good enough a driver to take full advantage of the smooth running and turning ability of this setup but I have seen Steve O'Donnell run less than a foot of off the bouys at full throttle in race water for many laps at a time with the Boss 60.

Charles

 

[Charles Perdue]

...i have noticed that many hydro, PT 40 for example also have something along the same lines for there sponsons, guess there is something to it.

The Phil Thomas hydros do not have tunnels in their sponsons, they have offset ride pads instead.

The first time I saw the small tunnels in a rigger sponson was on a Crapshooter from the late 1980s. Lots of claims were made for it, including improved turning and higher speeds. I built a rigger with this feature and found that turning did improve, doubtless from the increased side area from the tunnel sides, but I saw no speed increase that I could identify. I spoke with Ed Hughey about it, and he told me that they were very draggy and only gave improved speed on very flat smooth water, not race water (Greg Hughey sold these hulls at one time, in fact I thought that Marty sold the business to him). This mirrored my experience so I have not used it again. But that does not mean it is a useless exercise - some one may find the right combination of tunnel width and depth and end up with a superior turning hull with equal speed to conventional designs.

..

Correct, I did sell to Greg Huey (you even spelled his name right).

Currently Mark Bullard runs the SHINGLE DESIGN. From my observations the boat seems to bounce till it gets on step. A different approach for sure. Ive always figured for speed you need a very small ride surface and thought a tunnel might create unwanted lift. I guess dihedral plays into the equation as well. With all these micro cams these days it might be nice to see what is going on in a full speed turn.......Mike

Mark Bullard "Borrowed" the shingle design.

The lift of the tunnel design is not from areodynamic lift but from ground effects. The ground effect degrades very rapidly as the sponson lifts from the water allowing the sponson to glide just above the waters surface.

Charles

 

[AndyBrown]

...i have noticed that many hydro, PT 40 for example also have something along the same lines for there sponsons, guess there is something to it.

The Phil Thomas hydros do not have tunnels in their sponsons, they have offset ride pads instead.

The first time I saw the small tunnels in a rigger sponson was on a Crapshooter from the late 1980s. Lots of claims were made for it, including improved turning and higher speeds. I built a rigger with this feature and found that turning did improve, doubtless from the increased side area from the tunnel sides, but I saw no speed increase that I could identify. I spoke with Ed Hughey about it, and he told me that they were very draggy and only gave improved speed on very flat smooth water, not race water (Greg Hughey sold these hulls at one time, in fact I thought that Marty sold the business to him). This mirrored my experience so I have not used it again. But that does not mean it is a useless exercise - some one may find the right combination of tunnel width and depth and end up with a superior turning hull with equal speed to conventional designs.

..

Correct, I did sell to Greg Huey (you even spelled his name right).

Currently Mark Bullard runs the SHINGLE DESIGN. From my observations the boat seems to bounce till it gets on step. A different approach for sure. Ive always figured for speed you need a very small ride surface and thought a tunnel might create unwanted lift. I guess dihedral plays into the equation as well. With all these micro cams these days it might be nice to see what is going on in a full speed turn.......Mike

Mark Bullard "Borrowed" the shingle design.

The lift of the tunnel design is not from areodynamic lift but from ground effects. The ground effect degrades very rapidly as the sponson lifts from the water allowing the sponson to glide just above the waters surface.

Charles

Who's roof did Mark "borrow" the shingle design from?

Marty,

I have tried the tunnel on the rear sponson with the bevel on the inside edges as Charles described ( I was looking for a certain effect) , but I have not tried it on the fronts. I saw Steve's boss run (1982) and some old Crapshooters also with the tunnel sponson.

 

[carlnoki]

I remember Howard Power in Monterey CA had the tunnel bottom design on his Marlin Hydro. He said it was great on smooth water but he did not see any difference on race water.

Another gentleman in So. CA, Jack Oxley, raced wing dings with the same set up. his boats were the ONLY riggers i have ever seen that could turn LEFT on a dime when needed.

both of the above boats were very fast and stable on race water.

No matter what the water conditions were, Jacks' boat just ran great.

carl

 

[Charles Perdue]

I lived in Los Angeles and raced in District 19 in the late 70's and the early 80's.

Howard Power was a friend of mine and he also wrote the article in the November, 1981 issue of RC Modeler Magazine covering the NAMBA Nationals in Amirillo, Texas.

He described how the Boss 20 dominated the class ( perfect Score and fast time) and also the confiquration of the front sponson design.

Jack Oxley was, and I suppose still is, a friend of mine that raced Legg Lake and District 19 during this same time. He was also a fierce competitor.

Jerry Dunlap wrote an article for the May 1981 issue of RC Model Builder Magazine in which he described My Boss boat running in a SAW race at Legg Lake (1 MPH of off the record), including the design of the front sponsons.

Charles

 

[Marty Davis]

...i have noticed that many hydro, PT 40 for example also have something along the same lines for there sponsons, guess there is something to it.

The Phil Thomas hydros do not have tunnels in their sponsons, they have offset ride pads instead.

The first time I saw the small tunnels in a rigger sponson was on a Crapshooter from the late 1980s. Lots of claims were made for it, including improved turning and higher speeds. I built a rigger with this feature and found that turning did improve, doubtless from the increased side area from the tunnel sides, but I saw no speed increase that I could identify. I spoke with Ed Hughey about it, and he told me that they were very draggy and only gave improved speed on very flat smooth water, not race water (Greg Hughey sold these hulls at one time, in fact I thought that Marty sold the business to him). This mirrored my experience so I have not used it again. But that does not mean it is a useless exercise - some one may find the right combination of tunnel width and depth and end up with a superior turning hull with equal speed to conventional designs.

..

Correct, I did sell to Greg Huey (you even spelled his name right).

Currently Mark Bullard runs the SHINGLE DESIGN. From my observations the boat seems to bounce till it gets on step. A different approach for sure. Ive always figured for speed you need a very small ride surface and thought a tunnel might create unwanted lift. I guess dihedral plays into the equation as well. With all these micro cams these days it might be nice to see what is going on in a full speed turn.......Mike

Mark Bullard "Borrowed" the shingle design.

The lift of the tunnel design is not from areodynamic lift but from ground effects. The ground effect degrades very rapidly as the sponson lifts from the water allowing the sponson to glide just above the waters surface.

Charles

Charles:

The tunnel packs with air until it lifts a little and vents off the packed air. At that point, the front sponsons will ride just above the water. Maybe that is why the design is so smooth. Since it is so easy for the trapped air to vent, I doubt that there is much of a lifting effect beyond the initial lift to vent.

What do you think that the 30 degree sharp edges on the inside of the pads do for you? Turning edge, cleaner to release the water better?

 

[Charles Perdue]

Hello Marty, I am off of my soap box now.

On the lifting, venting, ground effects, ect.....I think that we are saying the same thing, just using different phrases to describe the same effect.

The undercut of the running pads, by channeling air between them and the full wetted surface, allow the sponsons to transition from the full wetted surface to the ride pads and back to the full wetted surface easier.

When the tunnel sponson design was first tried, the pad to full width wetted surface was as you described, at about 1/3 to 1/3 to 1/3. As I learned more about this design, I found that less pad width was better as it made for more area for the compacted air to lift on the sponson and also less pad surface area to drag during the transition from touching the water to running on a cushion of air.

My next improvement was to go to the shingle type running pad. This allowed the sponson to break clear from the surface of the water easier. The first layered pads that I used were made from 1/32 phenolic. Carbon fiber was unavaliable to me at that time. I also undercut the trailing edges of each of the peices that make up the running pad, to about 30 degrees also.

When the boat was in the turn, the sponsons were running on the full width of the wet surface, and as the boat exited the turn it would transition to the cushion of air. The result were amazing as it looked like it was shot from a cannon. Very little time was lost in the turns.

 

[TomMoorehouse]

Hello Marty, I am off of my soap box now.
On the lifting, venting, ground effects, ect.....I think that we are saying the same thing, just using different phrases to describe the same effect.

The undercut of the running pads, by channeling air between them and the full wetted surface, allow the sponsons to transition from the full wetted surface to the ride pads and back to the full wetted surface easier.

When the tunnel sponson design was first tried, the pad to full width wetted surface was as you described, at about 1/3 to 1/3 to 1/3. As I learned more about this design, I found that less pad width was better as it made for more area for the compacted air to lift on the sponson and also less pad surface area to drag during the transition from touching the water to running on a cushion of air.

My next improvement was to go to the shingle type running pad. This allowed the sponson to break clear from the surface of the water easier. The first layered pads that I used were made from 1/32 phenolic. Carbon fiber was unavaliable to me at that time. I also undercut the trailing edges of each of the peices that make up the running pad, to about 30 degrees also.

When the boat was in the turn, the sponsons were running on the full width of the wet surface, and as the boat exited the turn it would transition to the cushion of air. The result were amazing as it looked like it was shot from a cannon. Very little time was lost in the turns.

do you have a picture of this? So if my sponson bottom is 1.25" wide.... i would take roughly 2 sets of .25" wide 1/32" thick "shingles" and attach them to the sponson bottom with the overhang or visible shingle gettting smaller toward the trailing edge?

 

[Marty Davis]

Hello Marty, I am off of my soap box now.
On the lifting, venting, ground effects, ect.....I think that we are saying the same thing, just using different phrases to describe the same effect.

The undercut of the running pads, by channeling air between them and the full wetted surface, allow the sponsons to transition from the full wetted surface to the ride pads and back to the full wetted surface easier.

When the tunnel sponson design was first tried, the pad to full width wetted surface was as you described, at about 1/3 to 1/3 to 1/3. As I learned more about this design, I found that less pad width was better as it made for more area for the compacted air to lift on the sponson and also less pad surface area to drag during the transition from touching the water to running on a cushion of air.

My next improvement was to go to the shingle type running pad. This allowed the sponson to break clear from the surface of the water easier. The first layered pads that I used were made from 1/32 phenolic. Carbon fiber was unavaliable to me at that time. I also undercut the trailing edges of each of the peices that make up the running pad, to about 30 degrees also.

When the boat was in the turn, the sponsons were running on the full width of the wet surface, and as the boat exited the turn it would transition to the cushion of air. The result were amazing as it looked like it was shot from a cannon. Very little time was lost in the turns.

Charles:

So, you are using a combination of the air trap and the shingles?

Have you settled on the width of the run surface as a percentage?

Do the shingles run all the way to the front of the sponsons? Full width of the inside and outside run surface?

What kind of spacing on the shingles have you arrived at?

I have seen this shingle approach on the full sized offshore boats but the spacing is big and they are very deep.

Do you think that there is an optimum depth for the air trap? As I remember, Steve's Boss 67 was about 1/8" deep with the 30 degree angle on the insides.

VERY interesting discussion that is helping me understand what I stumbled upon.

The shingles are something that kind of confuses me a little. I wonder how much space you can use between the shingle tips. It would seem that the wider the space the less contact patch and the less drag, BUT also the less the induced attack angle.

The minimum thickness of the shingle to get optimum performance is an important consideration for a couple reasons. The thicker = the heavier (important on a .21). The thicker the shingle the more attack angle the shingle imparts to the bottom of the sponson and thus the better the result toward acceleration AND maybe launch??? The wider the shingle space = less drag by the shingle. If you can tell us your findings, I can lay this out on CAD and be able to determine the induced attack angle of the shingles.

At first thought, I can see a big advantage to having BOTH the tunnel and the shingles - your thoughts?

Sorry for rambling, but this has spurred a LOT of thought.

Some of the Engineers among us could probably shed some light on all of this....

John Finch - Where are you?