Re-Visit Sponson Offset

[Marty Davis]

We had a great discussion about the sponson offset on outriggers last year and I would like to offer some new information.

I have usually offset all of my riggers sponsons to the left (left side further from the tub than the right). On my .21 boat I use 1/2" offset.

I brought out an old 67 boat that had run very well in the past and started running it some. I took it to Charleston with good results.

Thing about this boat is that the sponsons are offset to the right by a little over 1/2".

The boat has ZERO torque into the course and runs totally neutral. AND the sponson spacing is fairly narrow. Wonder what effect making the spacing very wide, very narrow has on this torque effect.

I am not at all convinced that sponson offset is necessary to reduce the torque effect. I believe that the torque effect is because the turn fin, the prop sharpening, or some other thing is incorrect or not optimized.

Would be interested in John Finch and others response to these findings. John had most convinced that the offset was necessary. I am not at all sure that is the case. Give me some more information that will convince me.... Guess that the amount of variables in our hobby are so massive, that it is many times difficult to isolate the effect of one item and its contribution.

Marty Davis

 

[Joe Warren]

We had a great discussion about the sponson offset on outriggers last year and I would like to offer some new information.
I have usually offset all of my riggers sponsons to the left (left side further from the tub than the right). On my .21 boat I use 1/2" offset.

I brought out an old 67 boat that had run very well in the past and started running it some. I took it to Charleston with good results.

Thing about this boat is that the sponsons are offset to the right by a little over 1/2".

The boat has ZERO torque into the course and runs totally neutral. AND the sponson spacing is fairly narrow. Wonder what effect making the spacing very wide, very narrow has on this torque effect.

I am not at all convinced that sponson offset is necessary to reduce the torque effect. I believe that the torque effect is because the turn fin, the prop sharpening, or some other thing is incorrect or not optimized.

Would be interested in John Finch and others response to these findings. John had most convinced that the offset was necessary. I am not at all sure that is the case. Give me some more information that will convince me.... Guess that the amount of variables in our hobby are so massive, that it is many times difficult to isolate the effect of one item and its contribution.

Marty Davis

Marty are you speaking of Roadrunner Hydro Hulls that have center Located engine or Hulls with Off Set motor mounts. Ralph & I have tested many diff combo`s on both center of hull located engine hulls (xtreme) & the Ultralight that has a off set engine mount.

 

[John Knight]

Marty,

One very large variable will be where the engine, hence, the center drive line, is located. Centered, offset to the left or the right, and if so, by how much? Where is yours for the 21 and the 67 that you run? May be a hint for your sponson settings.

Both of mine are centered with no offset and sponsons are the very same.

John

 

[time bandit]

We had a great discussion about the sponson offset on outriggers last year and I would like to offer some new information.
I have usually offset all of my riggers sponsons to the left (left side further from the tub than the right). On my .21 boat I use 1/2" offset.

I brought out an old 67 boat that had run very well in the past and started running it some. I took it to Charleston with good results.

Thing about this boat is that the sponsons are offset to the right by a little over 1/2".

The boat has ZERO torque into the course and runs totally neutral. AND the sponson spacing is fairly narrow. Wonder what effect making the spacing very wide, very narrow has on this torque effect.

I am not at all convinced that sponson offset is necessary to reduce the torque effect. I believe that the torque effect is because the turn fin, the prop sharpening, or some other thing is incorrect or not optimized.

Would be interested in John Finch and others response to these findings. John had most convinced that the offset was necessary. I am not at all sure that is the case. Give me some more information that will convince me.... Guess that the amount of variables in our hobby are so massive, that it is many times difficult to isolate the effect of one item and its contribution.

Marty Davis

Marty,

Great discussion topic, it will be interesting to see what will come out of this.

Just more food for thought, when I designed my .21 boat I spent the better part of a season looking, listening and absorbing all I could.

I ended up putting 1/2" offset to the left (as with your .21). Two out of the norm elements I used though were to widen the front sponson ride base to 18" (about normal for a 40 boat) and raise the overall ride height to 7/8" (bottom of tub to water).

The boat tracks neutral with no torque effects (no trim required) has no tendency to hunt and handles bad water extremely well. It holds it own speed wise and I'm still working on that part of the equation but that's made much easier with good handling.

I think the extra ride width has helped much in the handling department.

Greg Hahn

 

[Joe Warren]

If the engine is Center location.... Do you believe it is better to move the LF sponson OUT? or Move the RF sponson in?? Big difference.......

 

[Marty Davis]

We had a great discussion about the sponson offset on outriggers last year and I would like to offer some new information.
I have usually offset all of my riggers sponsons to the left (left side further from the tub than the right). On my .21 boat I use 1/2" offset.

I brought out an old 67 boat that had run very well in the past and started running it some. I took it to Charleston with good results.

Thing about this boat is that the sponsons are offset to the right by a little over 1/2".

The boat has ZERO torque into the course and runs totally neutral. AND the sponson spacing is fairly narrow. Wonder what effect making the spacing very wide, very narrow has on this torque effect.

I am not at all convinced that sponson offset is necessary to reduce the torque effect. I believe that the torque effect is because the turn fin, the prop sharpening, or some other thing is incorrect or not optimized.

Would be interested in John Finch and others response to these findings. John had most convinced that the offset was necessary. I am not at all sure that is the case. Give me some more information that will convince me.... Guess that the amount of variables in our hobby are so massive, that it is many times difficult to isolate the effect of one item and its contribution.

Marty Davis

Marty are you speaking of Roadrunner Hydro Hulls that have center Located engine or Hulls with Off Set motor mounts. Ralph & I have tested many diff combo`s on both center of hull located engine hulls (xtreme) & the Ultralight that has a off set engine mount.

Joe:

ONLY talking about the front sponson offset not engine offset. Assume engine and drive line in the center of the hull. SEE, that is what I was talking about with all the variables.

Marty Davis

 

[Marty Davis]

If the engine is Center location.... Do you believe it is better to move the LF sponson OUT? or Move the RF sponson in?? Big difference.......

Joe:

As I said, my 20 boat has 1/2" offset to the left and my 67 boat has a little more than 1/2" offset to the right. Both boats are totally neutral. BUT, I want John Finch to convince me that one way is better than the other. Both boats have the engine in the center with no shaft offset. Everything is right down the center.

Joe:

I would say that you have it figured out pretty well. I considered your 40 boat the best handling 40 boat at Charleston, by a very wide margin. In fact, it might have been the most impressive boat at that race.

ALSO, did anyone else notice the sponson spacing on the Japanese Boats in a recent thread? MIght be something to visit. A MUCH wider stance than any of us are currently running.

Marty Davis

 

[dschigoda]

If the engine is Center location.... Do you believe it is better to move the LF sponson OUT? or Move the RF sponson in?? Big difference.......

Joe:

As I said, my 20 boat has 1/2" offset to the left and my 67 boat has a little more than 1/2" offset to the right. Both boats are totally neutral. BUT, I want John Finch to convince me that one way is better than the other. Both boats have the engine in the center with no shaft offset. Everything is right down the center.

Joe:

I would say that you have it figured out pretty well. I considered your 40 boat the best handling 40 boat at Charleston, by a very wide margin. In fact, it might have been the most impressive boat at that race.

ALSO, did anyone else notice the sponson spacing on the Japanese Boats in a recent thread? MIght be something to visit. A MUCH wider stance than any of us are currently running.

Marty Davis

Marty,

This is some interesting info.

What do the full size hydros have for offset? I realize that the forces are much different when scaling up to full size, but I'm not recalling seeing any full size hydros with the weight offset to the outside of the turn. Twenty-five years ago, I recall the Bud Griffon had a huge offset to the inside. The ones running today appear more centered though.

Back in the '60's, when the open wheel cars at Indianapollis went to the rear engine slim tubular profiles (before wings & downforce, in the Jimmy Clark era), many of the cars had a huge offset to the inside.

Offset to the inside just seems to "look right", but I suspect that the turn fin and prop have a much stronger influence on tracking than tub offset.

Dave

 

[Grimracer]

I feel you have to be very carful with offset..

I don’t feel its so much a running issue as it is a landing issue. If the boat happens to take a slight hop and the outer most offset sponson sets first.. it has a lot more leverage to upset the boat as it attempts to finish the landing. I also feel however that “IF” you don’t have your turn fin just right “I never seem to have it right” it has to help hold the boat up in the corner regarding any of the non trip coming into play.. lets face it, we do not want the non trips coming into play unless necessary.

Again.. Too wide on the track width and you run into the same problems as above.. The wider you go the worse it gets. Also I would think the more sensitive to turn fin setup.

As for this having any real effect regarding engine tourk? I don’t know.. I bet its very slight if at all

Just adding…

Grimracer

 

[Grimracer]

If the engine is Center location.... Do you believe it is better to move the LF sponson OUT? or Move the RF sponson in?? Big difference.......

ALSO, did anyone else notice the sponson spacing on the Japanese Boats in a recent thread? MIght be something to visit. A MUCH wider stance than any of us are currently running.

Marty Davis

Marty.. also note the lack of nontrips on there boats.. adding to my post above.

Grim

 

[dschigoda]

We could eliminate a lot of guess work by building a set of sponsons and booms that would allow the tub to be moved left, right, and center. Then time some laps with the tub on the left, right, and then center - without changing anything else on the boat or engine. Then note the changes in lap times, and handling. Then repeat the experiment over several heat races, noting speed and handling. That would answer alot of questions, at least for that hull.

Dave

 

[Marty Davis]

If the engine is Center location.... Do you believe it is better to move the LF sponson OUT? or Move the RF sponson in?? Big difference.......

ALSO, did anyone else notice the sponson spacing on the Japanese Boats in a recent thread? MIght be something to visit. A MUCH wider stance than any of us are currently running.

Marty Davis

Marty.. also note the lack of nontrips on there boats.. adding to my post above.

Grim

Grim:

An interesting note. I ran one of Stu's Crapshooters for a year and once when I was in Evansville, I had Stu come over and watch it run. I told him that there was a problem with the boat darting. I looked at the chine angle and it was very upright (sharp). I had him reduce the chine angle and the boat didn't dart ony more. I had him make the chine 60 degrees from the bottom of the sponson and it was perfect. That is what I run on my own sponsons and there is no dart. I think that anyhing steeper than 60 degrees and you will have darting.

Marty Davis

 

[Mike Nowicki]

If the engine is Center location.... Do you believe it is better to move the LF sponson OUT? or Move the RF sponson in?? Big difference.......

ALSO, did anyone else notice the sponson spacing on the Japanese Boats in a recent thread? MIght be something to visit. A MUCH wider stance than any of us are currently running.

Marty Davis

Marty.. also note the lack of nontrips on there boats.. adding to my post above.

Grim

Grim:

An interesting note. I ran one of Stu's Crapshooters for a year and once when I was in Evansville, I had Stu come over and watch it run. I told him that there was a problem with the boat darting. I looked at the chine angle and it was very upright (sharp). I had him reduce the chine angle and the boat didn't dart ony more. I had him make the chine 60 degrees from the bottom of the sponson and it was perfect. That is what I run on my own sponsons and there is no dart. I think that anyhing steeper than 60 degrees and you will have darting.

Marty Davis

Marty,

When you say "darting" are you referring to the straitaway or thru the turns. If you are talkin about the straits, why do you think changing the angles was helpful. Do you use a low AOA on your fronts.

Mike

 

[Chris Wood]

the front edge of the tub or nose will cause DARTING as well if the size is wrong.

chris

 

[Marty Davis]

If the engine is Center location.... Do you believe it is better to move the LF sponson OUT? or Move the RF sponson in?? Big difference.......

ALSO, did anyone else notice the sponson spacing on the Japanese Boats in a recent thread? MIght be something to visit. A MUCH wider stance than any of us are currently running.

Marty Davis

Marty.. also note the lack of nontrips on there boats.. adding to my post above.

Grim

Grim:

An interesting note. I ran one of Stu's Crapshooters for a year and once when I was in Evansville, I had Stu come over and watch it run. I told him that there was a problem with the boat darting. I looked at the chine angle and it was very upright (sharp). I had him reduce the chine angle and the boat didn't dart ony more. I had him make the chine 60 degrees from the bottom of the sponson and it was perfect. That is what I run on my own sponsons and there is no dart. I think that anyhing steeper than 60 degrees and you will have darting.

Marty Davis

Marty,

When you say "darting" are you referring to the straitaway or thru the turns. If you are talkin about the straits, why do you think changing the angles was helpful. Do you use a low AOA on your fronts.

Mike

Mike: Through the turns. I run 3.0 on the left and 3.2 on the right on all my boats.

Marty Davis

 

[Grimracer]

Marty..

thats with quite a bit of belly too right?

Grim

 

[AndyBrown]

I have tried all types of sponson offset and engine offset over the past 30 years. The Eagle SGX has everything on center and they seem to run OK.

 

[Marty Davis]

Marty..
thats with quite a bit of belly too right?

Grim

Grim:

I have moved away from a lot of belly. I run hardly any at all now. Boat seems to be much cleaner. I am working on a new design front sponson that will have the best characteristics of a lot of belly and those without. We will see how it works...

Marty Davis

 

[Marty Davis]

I have tried all types of sponson offset and engine offset over the past 30 years. The Eagle SGX has everything on center and they seem to run OK.

Andy:

You don't offset your front sponson spacing?

If the answer is .. you don't, that is really interesting. I wonder about the offset since the two best boats that I run have opposite offset and both don't have any bad characteristics related to that.

Would be interested in your thoughts on this subject.

Marty Davis

 

[Jorgen Andersson]

Hi

I think it is very difficult to find solid anwers to these questions.

Many variables will have effect on the handling.

I have tried many different sponson offset and it can improve handling, like better tracking down the straight, better cornering stability and so on. I have also found that steps on the running surfaces and turnfins in different shapes and sizes can have the same effect on the handling as above.

As Marty pointed out, I have also find that to sharp angle on the chine can give bad effects like darting and nasty handling when cornering very hard.

As for the AOA, this have been the single best area for me to improve speed. The more AOA, the more speed and then you blow off, but I tested many things in order to be able to run higher AOA and still stay on the water.

I can now run 4.0-4.3 degrees and I started on the figures that Marty stated, 3.0-3.2 degrees.

As far as I cen tell, the boats are more "forgiving" when driven hard with higher AOA.

This spring I will test a new system that I hope will help me to run even more AOA, time will tell.

All the best

Jorgen Andersson