i was thinking

[Lay26]

what would the difference of the dead rise angle of the sponson template riding surface on the left do vs the one on the right, would a steeper angle contribute to higer speeds? or if the angle is lower would the boat run faster and handle better? what would be the best compromise take a look at the templates am working with. what are your thougths anybody

 

[John Finch]

View attachment 6312
what would the difference of the dead rise angle of the sponson template riding surface on the left do vs the one on the right, would a steeper angle contribute to higer speeds? or if the angle is lower would the boat run faster and handle better? what would be the best compromise take a look at the templates am working with. what are your thougths anybody

The right flatter deadrise will have less contact with the water and cause less pull on that side of the boat. If you used the flat one on the right side of the boat and the more angled one on the lleft side of the boat it would help prevent propwalk as the left one would drag more, thus making the boat veer to the left. Only if the sponsons are of equal and sufficient size so that they float well on top of the water. The width of the sponson could change everything if the sponsons are dragging IN the water rather than floating on top.

 

[Marty Davis]

View attachment 6312
what would the difference of the dead rise angle of the sponson template riding surface on the left do vs the one on the right, would a steeper angle contribute to higer speeds? or if the angle is lower would the boat run faster and handle better? what would be the best compromise take a look at the templates am working with. what are your thougths anybody

The left flatter deadrise will have more contact with the water and cause more pull on that side of the boat. If you used the flat one on the left side of the boat and the more angled one on the right side of the boat it would help prevent propwalk as the left one would drag more, thus making the boat veer to the left. which compensates for propwalk wanting to make the boat turn right. You can make too much deadrise on the left sponson and boat will dig and not turn well. I prefere a 2 to 3 degree deadrise on the right sponson and a 1 to 2 degree deadrise on the left. The outsides of the sponsons determine how much slide the boat will have when cornering. Flat sides or too much straight up and down angles will make the boat trip and roll over when cornering. Too much angle will let the boat slide too much. The weight and speed of the boat has a lot to do with the angle you choose there.

John:

Interesting analysis.....

It seems that this is a perfect example to show that there are many ways to accomplish something.

First let's define Deadrise: What is deadrise? It's the angle of the boat's bottom (sponsons for an outrigger) relative to the horizontal. A flat bottom boat has a deadrise of 0°, while a deep-V might have a deadrise of 25°.

I do almost the opposite as what you have described. I keep the right sponson flat and the left with 1 degree of dihedral (for racing). The reason is that when the boat slows or goes into the turn, the sponson with the dihedral will penetrate more than the one that has a flat bottom. This penetration creates drag. I don't want more drag on the right sponson since that is the one that gets the pressure from prop torque. On most hydros in the SAW, the sponsons do not penetrate at all because of the speed and attack angle of the sponson. They are effectively only running on a TINY amount of sponson bottom anyway. Once you slow down or reduce the engine speed the prop does not press as hard on the sponson. Once you get back on the throttle, the prop forces the sponson to try to penetrate the water and you get some torque.

Another factor that must be put into the equation is the rudder location. IF the rudder is on the left, any right turn will reduce weight on the left front sponson and add weight to the right (can cause blow off). For a rudder on the right the opposite. The rudder location on an outrigger with wide sponson spacing really does not make a huge amount of difference because of the wide lever arm of the wide sponson stance.

I agree with you about the negative of having a lot of dihedral on the left sponson. It does make the sponson penetrate and you get terrible turning, darting or hooking.

One thing that is very interesting is the width of sponsons on various outriggers. On Stu's Crapshooters, he uses the narrowest sponsons that I have seen. Have you noticed how wet the boat is at launch. That is the reason. He gets a BIG advantage after the boat is up on top of the water with the narrower sponsons because he has much less drag and the smaller sponsons punch a very small hole in the air. As a comparison, the Roadrunner type boat uses a much wider run surface, gets up easily at launch and then pays a penalty with drag and hole punching. Another advantage is that you can run slightly more attack angle on the sponsons because of the narrow running surface (maybe .2 degree or so). That makes a VERY BIG speed difference because of reduced drag. I ran one of his 67 boats for a season and found out about the narrow sponson advantages. I probably would never have figured that out if I hadn't run it that season. In the past I had always run on the wide side.

For SAW, high dihedral is a huge advantage because it allows the air to spill out from under the sponson as well as reduce the contact area at speed. It also is good for turning for SAW since the dihedral will act like a turn fin at very low speeds. You can actually run WITHOUT a fin with 5 degrees of dihedral at slow turn speeds.

Much cool stuff at play with hydrodynamics on an outrigger.

Marty Davis

 

[gooycheese]

This is one of the most informative discussions I have read in a long time.

Thank You .

Paul

 

[John Finch]

Marty,

The rudder location is a big ten 4 buddy. I always use the rudder on the left on my gas sport hydros and scale boats to keep the right front sponson planted in the corners. I can't make any left turns what so ever though or the boat flips like you said. Still, I like busting the corners wide open, so I take that option. My riggers have the rudder on the right. I like the right sponson to ride out of the water in the turns and hang on the turn fin. I balance the depth of the fin by adjusting the rear left sponson in the same criss cross pattern you explained about the rudder. Usually 1/16th to 1/8th deeper does the trick. Like you said.....there are many ways to skin the cat and it changes from boat to boat. Interesting hey. I also use the left sponson non trip angle to adjust the slide in the corners because as you know, being one of the roadrunner design gurus, that the turn fin and right sponson are only part of the equasion when it comes to ripping a turn. The left sponson plays a big part in the turns because thats where most of the weight is distributed in the turns. I experimented with sponson width for straightaways. Yes, the boats turn fine without a fin if the sponsons are allowed to dig into the water at slow speed. The problem most modelers had with narrow front sponsons trying for the 100 mph mark a bunch of years ago was using narrow sponsons that dug into the water too much causing the back of the boat to blow out of the water. The first solution came from Don Pinckert who said "not enough wing area" transfered from airplane to boat language that meant float the boat more in the front. Kentley Porter put roadrunner sponsons on a sg tub and presto...103 mph. The next thing that I tried was narrower sponsons, but more forward of the cg so more weight was distributed to the prop and not the front sponsons....111 mph. Yea, smaller profile, less drag, faster speeds. It's funny you mentioned Stu's boat. I am running one very much like it. It runs the more positive angle of attack you mentioned on the front sponsons and rides extremely fast and stable. HMMMMMMMMMM. Got to start thinking about where we have been and where we are headed.

 

[PHM Racing]

I have been playing with a 40 sponson design and the boat is very fast , i haven't had it blow over yet , the turn fin sponson has 3.6 degree's of deadrise and the other side has 8.0 degree's of deadrise and there 2.25" wide at the bottom trailing edge

Attack angle is turn fin side 3.3 and the other side is 3.4 degree's

I raced this boat last weekend at a club race but i kept playing with the needle and didn't finish 1 race but that's what i went there for to see if the boat would stay on the water with the other's while milling and racing and it did , didn't blowoff or show any sighn's of blowing off the water

 

[Tim Kish]

I have been playing with a 40 sponson design and the boat is very fast , i haven't had it blow over yet , the turn fin sponson has 3.6 degree's of deadrise and the other side has 8.0 degree's of deadrise and there 2.25" wide at the bottom trailing edge

Attack angle is turn fin side 3.3 and the other side is 3.4 degree's

I raced this boat last weekend at a club race but i kept playing with the needle and didn't finish 1 race but that's what i went there for to see if the boat would stay on the water with the other's while milling and racing and it did , didn't blowoff or show any sighn's of blowing off the water

Mike

If your boat blows off the water at 53 mph you really have a problem

Tim K

 

[Marty Davis]

Marty,The rudder location is a big ten 4 buddy. I always use the rudder on the left on my gas sport hydros and scale boats to keep the right front sponson planted in the corners. I can't make any left turns what so ever though or the boat flips like you said. Still, I like busting the corners wide open, so I take that option. My riggers have the rudder on the right. I like the right sponson to ride out of the water in the turns and hang on the turn fin. I balance the depth of the fin by adjusting the rear left sponson in the same criss cross pattern you explained about the rudder. Usually 1/16th to 1/8th deeper does the trick. Like you said.....there are many ways to skin the cat and it changes from boat to boat. Interesting hey. I also use the left sponson non trip angle to adjust the slide in the corners because as you know, being one of the roadrunner design gurus, that the turn fin and right sponson are only part of the equasion when it comes to ripping a turn. The left sponson plays a big part in the turns because thats where most of the weight is distributed in the turns. I experimented with sponson width for straightaways. Yes, the boats turn fine without a fin if the sponsons are allowed to dig into the water at slow speed. The problem most modelers had with narrow front sponsons trying for the 100 mph mark a bunch of years ago was using narrow sponsons that dug into the water too much causing the back of the boat to blow out of the water. The first solution came from Don Pinckert who said "not enough wing area" transfered from airplane to boat language that meant float the boat more in the front. Kentley Porter put roadrunner sponsons on a sg tub and presto...103 mph. The next thing that I tried was narrower sponsons, but more forward of the cg so more weight was distributed to the prop and not the front sponsons....111 mph. Yea, smaller profile, less drag, faster speeds. It's funny you mentioned Stu's boat. I am running one very much like it. It runs the more positive angle of attack you mentioned on the front sponsons and rides extremely fast and stable. HMMMMMMMMMM. Got to start thinking about where we have been and where we are headed.

John:

You sure sunk your teeth into riggers after so many years with the monos. Not many people understand the dynamics of boats as well as you and it is a pleasure to hear your thoughts. Might even be interesting to others to hear a couple of "grey beards" talk about their opinions on the finer points of hull design.

Your drivng style and mine are slightly different (I am somewhat surprised by that). I blip the throttle a little in the turn mostly as a timing mechanism and you are running wide open all the time. The course that I drive is a little different also as I do not run an oval but a distorted oval with a very sharp turn on each end with the rudder bled off as it comes out of the turn. My feeling is that if I turn a super sharp turn and then allow the rudder to bleed off as I come out of the turn, I will be accelerating for a longer distance. It is critical to have a turn fin that is optimized so that it does not take hardly any rudder deflection and the boat does not slow down much. If you can do that, I believe that you can actually run a faster lap by using this method.

I am having a behind the scenes discussion with Terry about SAW sponsons and find that discussion to be of general interest also. Since Oval Heat Racing, Timed Oval Trials and SAW are much different in their demands I believe that to do each to the optimum, you need different configurations.

For SAW I found that a sponson that is fairly wide with 5 degrees of dihedral for the first 4 or 5 inches of the running surface, and an increasing dihedral in front of that to a max of 12 degrees at the tips was by far the best. The reasoning is that you want to spill the air out from under the sponson and you can do that easily with the increasing dihedral. I have not seen anyone use this approach, but is works VERY well. The 5 degrees of dihedral will allow you to be free of a turn fin by reducing speed when turning. The 5 degrees of dihedral penetrates enough to turn easily. As for narrow sponsons for SAW: I think that you can get away with narrow sponsons with no problem IF you make them nearly flat without dihedral. Problem there is that you will then need a small turn fin.

For Heat Racing, FLAT IS BETTER. I run 1 degree on the left and flat on the right. Gives total stability without ANY penetration. I want the turn fin to load as much as possible by the rudder. This allows me to run the bend line almost paralell with the run atitude. That eliminates a ton of drag. I found that if the right front is not down solid, I had to run a slightly downward angle on the bend line of the fin. That proved to be much slower. As for the non trip on the left sponson, I had Stu change his early models to have a slight amount more angle to soften the effect. The boat was doing a SLIGHT dart because of the higher angle on the non-trip (chine). The narrow sponsons for heat racing seem to be a great thing. You require a turn fin anyway, so you can get away with nearly flat and as long as the boat launches without much problem, the narrower the better. Once it is up and running the mechanical lift of the attack angle will make almost any width sponson be light and up on the top of the water. I believe that Stu is ahead of the pack in this regard. As an example of this working well: Before the Nats in Sarasota, Stu and I worked at getting ready. I was running his old 67 boat. I was able to get that boat to 99mph as a heat race boat with only a fin change and a shorter rudder. The boat was a heavy and large boat for SAW, but was running nearly 100 mph. Flat/Narrow sponsons will work fine for SAW also. The one thing that I don't agree with Stu about is the placement of the rear sponsons. He might as well not have rears, as they are so high above the shaft centerline that they have little effect. I like for the rears to be a pad that will keep the boat from changing attack angle much in all race water conditions.

Here is a really strange comparison: (Talk about our totally different approaches)

You indicated that you ran 98-100 mph on your oval record setting run. I have been helping Brian Callahan with his 67 hydro (my old boat) and turn fin optimizing. He came down to Tampa a short time ago (this Spring) and we put several fins on his boat and optimized the correct one. I drove his boat around the oval for about 6 laps at near the same record time that you currently hold the record. The top speed of the boat was about 82-84 mph. SO, there is obviously more than one way to run fast around the oval. Can you imagine how much different our approaches are??? Looks like I need to find 10 mph to get to an AMAZING time on the oval . I did find out that an "old guy" has a lot of trouble reacting to a boat that fast.

Enough for now...... Your thoughts?

Marty Davis

 

[John Finch]

Marty,

You probably don't remember, but you are the one who told me the football shape course as I call it was giving you a faster lap. I used that technique in setting all three of the last oval hydro records. Thanks for the tip! My oval boat is set up so the rudder right side of the wedge is parallel to the tub going down the straightaway. This gives a large sweeping right hand turn going down the straightaway. When the boat gets to the corner (buoy 2) I give a slight right rudder which puts the left side of the rudder blade parallel with the tub and the tip of the football is carved. Then, as you said, I slowly let go of the steering wheel right after passing buoy 2 so the rudder goes back to being parallel to the tub on the right side of the rudder and the boat is pointed toward the back side of the lake. The arch takes the boat wide at the middle of the course and back into buoy 5 where I again put a slight right rudder adjustment to create the tip of the football again. It is the fastest lap time. Again I agree and appreciate the knowledge you have given me on that driving technique. Note.....the rudder never adds any drag because it never has either side go past parallel with the tub.

Lets keep this thing going. Got to go right now.

 

[Marty Davis]

Marty,You probably don't remember, but you are the one who told me the football shape course as I call it was giving you a faster lap. I used that technique in setting all three of the last oval hydro records. Thanks for the tip! My oval boat is set up so the rudder right side of the wedge is parallel to the tub going down the straightaway. This gives a large sweeping right hand turn going down the straightaway. When the boat gets to the corner (buoy 2) I give a slight right rudder which puts the left side of the rudder blade parallel with the tub and the tip of the football is carved. Then, as you said, I slowly let go of the steering wheel right after passing buoy 2 so the rudder goes back to being parallel to the tub on the right side of the rudder and the boat is pointed toward the back side of the lake. The arch takes the boat wide at the middle of the course and back into buoy 5 where I again put a slight right rudder adjustment to create the tip of the football again. It is the fastest lap time. Again I agree and appreciate the knowledge you have given me on that driving technique. Note.....the rudder never adds any drag because it never has either side go past parallel with the tub.

Lets keep this thing going. Got to go right now.

John:

I remember... We were in the middle of a "Boring" IMPBA Board Meeting and we were talking and drawing the technique.

Actually, I have changed my approach some from that. I will post a drawing showing the current technique.

Also, here is a tech note that I wrote some time ago that has an AWESOME little Excel Spreadsheet that will allow anyone to test without having to do a complete lap. It is a great way to optimize everything on all areas of the course. Brian Callahan made this up for me and I like to use it when testing for timed oval and also for tuning for a new boat for heat racing. http://rcboat.com/lap.htm There is a link on that to download the spreadsheet. Since your name is on the spreadsheet, Brian must have timed you at the Nats.

The course that I like to use now is like this: http://rcboat.com/course.gif

As you can see, the area where I am turning is in red and is very short. The rest of the time, I am accelerating. I use this course for racing as well as timed oval. Since I use it for racing, I am used to driving this way and I can put down good laps when on the clock.

I am convinced that this approach is TOTALLY dependent upon how well the fin works and how much it takes away from the speed of the boat at the point where you are turning it at MAXIMUM. If you do not have an optimized fin, this probably will cost you more time than a gradual turn around the buoys. Not really sure about that since I spend so much time on maximizing my fins. I KNOW that it is possible to make your turn fin be a pivot point where the rudder is ONLY pivoting the boat around the fin. Very little speed is scrubbed if you can get this pivot action nearly perfect. The amount of rudder deflection is ONLY the amount of the circumference of the turn less how much off the buoys you can run (the circumference becomes larger the more off of the buoys you run).

Your thoughts.....

Marty Davis

 

[Mike Larson]

Awesome post, Marty and John! thanks, keep the info comin..... mike

 

[John Finch]

Marty,

The times Brian recorded were before I started experimenting with riggers and the boat was just average. I was used to driving round corners with my mono hulls at that time. I have since gone to the second method like you have in the drawing for heat racing. Hard to do on the right side of the course though. It is close to what I call the slingshot move where I follow a boat just on the outside, go a bit deep on buoy 4, then do a quick turn followed by an excellerating shot past 4 and 5. I did it at the 97 nats on bouy 4,5,6 in the 1/8 scale consolation race in the final lap to just pass and nudge out by a nose the first place boat. It works great in sneaking up on someone like that because most people go wide on 6. I use your pattern for most of my heats now with the riggers. With the monos there was so much drag in the corners that I just didn't see the advantage of that pattern. I use the pattern with my sport gas boat too. We had different methods of racing back in the 80's, but that's because we ran different boats. About 1997 is when you got me looking seriously at the riggers. Up till then it was all about the Twin Craft monos. As for oval records.....at 103 down the straights the oval I ran was pretty sloppy and wide. It had to be at those speeds. So the boat traveled at lot of distance for one lap. Sort of like an egg shape. If you get the boat down to about 92 to 95 mph the football shape works ok to get a 8.5 second lap. I got a 7 second lap one time with my 60 boat with the pattern in your drawing, but couldn't get the second lap in without nailing a buoy. That was a special boat. I have yet to get another to work as well. I have been measuring the angles with a micrometer and still can't get two boats to work exactly the same. Here's a good one to contemplate. I build a rigger I called the teardrop. I broke the 60 oval record, got the engine tech'd, tried some different sponsons with less non trip. The boat rolled and blew appart. We both know why, because I just told you what I changed. I took another boat that was 1.5 pounds heavier and with a wider tub and sponsons, and broke the record I just set with the lighter smaller boat. The heavier larger boat floated on air, no water coming off the sponsons at all in the straightaway. That proved to me no matter how heavy the boat is, if it floats on air it's faster than a lighter boat that has contact with the water. The reason I can't use the best pattern is that I can't get the boats to track straight enough to do a straight pass from 3 to 4 or 6 to 1. That one boat that would......I don't know why, but it would go straight. The rest need a slow curve down the straights so they are pretty far off the buoys in the front and back straightaway.

Your 5 degree deadrise on straightaway boats sounds like something I might want to try. I have been using ride pads like on Andys boats that are 1 inch wide and 1/8 deep. They run light in the straights but fall into the water at slow speed to dig in like your 5 degree sponson would so a turnfin is not needed. As I said earlier in the post I had to move the ride point of the sponsons forward when I went to narrow sponsons. Another reason for moving them forward was to better control the boat at slow speed. With narrow sponsons close to the cg they would dig too much at slow speed and the boat would spin out when I tried to turn it. Taking the weight off the fronts by moving the ride point forward cured that problem. NOTE....I did not move the sponsons forward, but moved the ride point forward. That gave me a roadrunner 60 footprint with an sgx 20 size boat. See the photo in the corner of my post.

 

[John Finch]

Marty,

You got me going! You mentioned turn fins. Wow! Kently porter and myself spent a lot of time playing with widths, depth, curve, when to curve, where to mount in relation to cg, back cut angle to direct water, etc. It's amazing how just changing one of those things changes how the boat goes thru the turns. We could talk about his stuff for hours. We already have. Got to go.

 

[Marty Davis]

Marty,The times Brian recorded were before I started experimenting with riggers and the boat was just average. I was used to driving round corners with my mono hulls at that time. I have since gone to the second method like you have in the drawing for heat racing. Hard to do on the right side of the course though. It is close to what I call the slingshot move where I follow a boat just on the outside, go a bit deep on buoy 4, then do a quick turn followed by an excellerating shot past 4 and 5. I did it at the 97 nats on bouy 4,5,6 in the 1/8 scale consolation race in the final lap to just pass and nudge out by a nose the first place boat. It works great in sneaking up on someone like that because most people go wide on 6. I use your pattern for most of my heats now with the riggers. With the monos there was so much drag in the corners that I just didn't see the advantage of that pattern. I use the pattern with my sport gas boat too. We had different methods of racing back in the 80's, but that's because we ran different boats. About 1997 is when you got me looking seriously at the riggers. Up till then it was all about the Twin Craft monos. As for oval records.....at 103 down the straights the oval I ran was pretty sloppy and wide. It had to be at those speeds. So the boat traveled at lot of distance for one lap. Sort of like an egg shape. If you get the boat down to about 92 to 95 mph the football shape works ok to get a 8.5 second lap. I got a 7 second lap one time with my 60 boat with the pattern in your drawing, but couldn't get the second lap in without nailing a buoy. That was a special boat. I have yet to get another to work as well. I have been measuring the angles with a micrometer and still can't get two boats to work exactly the same. Here's a good one to contemplate. I build a rigger I called the teardrop. I broke the 60 oval record, got the engine tech'd, tried some different sponsons with less non trip. The boat rolled and blew appart. We both know why, because I just told you what I changed. I took another boat that was 1.5 pounds heavier and with a wider tub and sponsons, and broke the record I just set with the lighter smaller boat. The heavier larger boat floated on air, no water coming off the sponsons at all in the straightaway. That proved to me no matter how heavy the boat is, if it floats on air it's faster than a lighter boat that has contact with the water. The reason I can't use the best pattern is that I can't get the boats to track straight enough to do a straight pass from 3 to 4 or 6 to 1. That one boat that would......I don't know why, but it would go straight. The rest need a slow curve down the straights so they are pretty far off the buoys in the front and back straightaway.

Your 5 degree deadrise on straightaway boats sounds like something I might want to try. I have been using ride pads like on Andys boats that are 1 inch wide and 1/8 deep. They run light in the straights but fall into the water at slow speed to dig in like your 5 degree sponson would so a turnfin is not needed. As I said earlier in the post I had to move the ride point of the sponsons forward when I went to narrow sponsons. Another reason for moving them forward was to better control the boat at slow speed. With narrow sponsons close to the cg they would dig too much at slow speed and the boat would spin out when I tried to turn it. Taking the weight off the fronts by moving the ride point forward cured that problem. NOTE....I did not move the sponsons forward, but moved the ride point forward. That gave me a roadrunner 60 footprint with an sgx 20 size boat. See the photo in the corner of my post.

John:

It sure was great when you decided to come over from the "dark side" (Monos) to play with hydros. Everyone will benefit from your approach. When someone with the ability to understand hull dynamics gets involved, it benefits everyone. (I know that you like to share with your local guys and keep them fired up and thinking)

You and I are doing things TOTALLY different in regard to timed oval. That is cool and shows that there are many ways to accomplish something. Kind of like the old Tortoise and Hare story.

The 5 degree sponsons were used for SAW, but I can see that they might be really super on a light boat for timed oval. The 5 degrees of dihedral on the outside sponson slipping a little sideways in the turns would lift the sponson (kind of like having attack angle going sideways) and thus place more weight on the right front sponson (a desireable effect to plant the fin).

All the timed oval that I have ever done has been with a heat race boat. I have never done a purpose built timed oval boat. It would be kind of fun to try that sometime. I have always kind of taken the approach of refining my heat race boats to get them optimized and then hopefully they would be close to record performance. I can see that a very light weight, purpose built boat could put down some amazing laps. You indicated that you hit buoys sometimes. That KILLS a boat like that and points out the kind of driving ability that is required. I have seen very few people who could handle that task. (I couldn't)

You stated that you found that a heavier boat was better. For your system, that is the case, but for my system is not. Light weight is highly desireable to me because of the acceleration factor. The Late Tom Grannis always kept telling me about the power needed to accelerate something went up as a square, as the weight increased. I have always raced using a light boat and used acceleration as my race tool. The ability to turn has always been PRIMARY also. A short little story which was responsible for that requirement. Steve and Jack O'Donnell came to Indy to the Hydro Masters Race in the early late 80's or early 90's with a boat that appeared to accelerate in the turns (they set the IMPBA 40 Oval Record at that Race). I was totally amazed! (Boat was designed by Charles Perdue) Ed Lackey and I started to work on turn fins, making HUNDREDS to test. We were able to get to the point that Steve and Jack did after a couple years of intense testing. What a pleasure to drive a boat that would turn like that. The statement that Brian Callahan made about doing a 1.4 second turn shows just how good it is. A side note: He also timed John Brown the next year at the Nats and he also ran in the 1.5+/- turn time. The boat that Jack and Steve used was a Boss which was designed by Charles Perdue who has recently been showing his new ideas on this forum. I would bet that based on his early work, these new boats will be AWESOME.

This thread has kind of gotten into a hodge podge of stuff. (my fault) Maybe we should seperate the topics so that they are not so random?

As for the tracking problem that you talked about.....

I used to really have trouble with that characteristic on the larger hydros. I found that the pulling into the course was related to several things. The prop that you run is a huge contributor because of prop walk. If you choose a prop that lifts a lot where it runs on it's tips, it will pull into the course. Also, if the prop has ANY amount of "non-razor sharpness" in toward the hub, it will also walk badly. I was able to cure most of the pulling by moving the bend line of the turn fin to either lift or pull down the right sponson. Wetting of the right sponson is also a HUGE contributor to this pulling into the course. If you are going to use the fin to lift the sponson, you need to re-design it so that it will still hook up in the turns. A secondary contributor to pulling into the course is the attack angle of the front sponsons and the amount of "belly" that the sponson has. Belly is the amount of non-flat angle on the bottom of the sponson. It is advantageous to use a prop that does not lift a lot for timed oval. The smoothest prop that I ever used was the 4 blade ABC prop for my 67 boat. That prop was designed by Andy Brown while working at Tidewater. The problem with the prop was that the blades were not on the hub equally and one blade bent easily. If one of the prop manufacturers comes up with some similar props for various sizes, it will provide something that will be revolutionary to racing as well as oval record trials. There was ZERO pulling into the course.

Thoughts......

Marty Davis

 

[Lay26]

wow it only tskes a spark to get fire going. this i great info

 

[Andy Greene]

John, Marty , aboslutly great stuff. Please feel free to keep rambling.

Marty am I going to be able to see you in action this weekend ????

 

[Marty Davis]

OK, for those of you who are dying to start making some turn fins, here is the correct aluminum. The best aluminum that we have found which will hold shape and also bend easily is 2024. You can buy it at http://mcmaster.com The various sizes are on page 3501 of the catalog. I use .063 for 21 and 45 boats and .125 for 67 and up. I would bet that you could use something in between instead of the .125" stuff. They have sizes of .080", .090", .100" which fall in between these sizes. we tried 7075 and it did not bend well and 6061 was too soft.

I will promise you that effort spent with turn fins will reward you about as much as anything that you can do.

Marty Davis

 

[John Finch]

OK, for those of you who are dying to start making some turn fins, here is the correct aluminum. The best aluminum that we have found which will hold shape and also bend easily is 2024. You can buy it at http://mcmaster.com The various sizes are on page 3501 of the catalog. I use .063 for 21 and 45 boats and .125 for 67 and up. I would bet that you could use something in between instead of the .125" stuff. They have sizes of .080", .090", .100" which fall in between these sizes. we tried 7075 and it did not bend well and 6061 was too soft.
I will promise you that effort spent with turn fins will reward you about as much as anything that you can do.

Marty Davis

How about some starting points on fins. Lets get some involvement.

1. The cup at the bottom of the fin. Why?

2. How far into the water should the cup start?

3. Where in relation to the cg should the fin be mounted?

4.. How deep or wide must the fin be?

5. Should you sharpen only the right side of the leading edge or equally on both sides?

6. Why does the fin leading edge need to be raked back?

7. Why is the rear trailing edge raked back?

8. Should the fin be parallel to the tub?

Any takers?

 

[John Finch]

OK, for those of you who are dying to start making some turn fins, here is the correct aluminum. The best aluminum that we have found which will hold shape and also bend easily is 2024. You can buy it at http://mcmaster.com The various sizes are on page 3501 of the catalog. I use .063 for 21 and 45 boats and .125 for 67 and up. I would bet that you could use something in between instead of the .125" stuff. They have sizes of .080", .090", .100" which fall in between these sizes. we tried 7075 and it did not bend well and 6061 was too soft.
I will promise you that effort spent with turn fins will reward you about as much as anything that you can do.

Marty Davis

How about some starting points on fins. Lets get some involvement.

1. The cup at the bottom of the fin. Why?

2. How far into the water should the cup start?

3. Where in relation to the cg should the fin be mounted?

4.. How deep or wide must the fin be?

5. Should you sharpen only the right side of the leading edge or equally on both sides?

6. Why does the fin leading edge need to be raked back?

7. Why is the rear trailing edge raked back?

8. Should the fin be parallel to the tub?

Any takers?

ok, I'll start with number 2....if the cup starts at water level very slightly and continues to get sharper as it desends, the boat will slide towards the outside because the fin will simply slice the top layer of water off the pond and give the boat very little grip. Like pealing a potato. Experience tells me to tell you don't make that mistake. Have the fin go into the water straight up and down with a cup at the bottom of the fin. So, that's one you don't have to build to see what's gonna happen.

 

[tnrcboatracer]

I prefer to make the fin from spring steel. Put the hook in it in the annealed state, and then harden/temper it. A 90 fin is ~0.065" thick and the 21 can be ~0.035" thick. Protect them with either black oxide, or graphite paint. The down side to the spring steel is that it is virtually impossible to adjust the hook once the material is hardened.