i was thinking

[ek kustomz]

I think the most impotant thing we need to agree on is that the leading sdge of the fin should move rearward as it gets deeper. If the leading edge is perpendicular to the water, the leading edge at the deepest point can search and bend the fin. Like a jet wing, it needs to be raked back to prevent the unwanted flutter. I hope I explained that right. Take a flat blade and run it through a swimming pool with the deepest part forward and you will see that if you turn it in any direction it darts. If you run the same fin or plate metal, rudder, whatever with the deepest part raked back from the direction of travel the turning motion is smooth and there is no flutter.

John:

Are you sure about that?

What happens to a rudder that is lagged? IT LIFTS. Do you really want the fin to lift because of lag in the leading edge?

Marty Davis

Correct me if I am wrong as I do not have a full understanding of this stuff yet, but would it not be different with a turn fin and a rudder?? The rudder pivots against the boat therefore if the rudder lags yes it would creat lift. But the turnfin pivots with the boat not against it so the pressure from the water there would not cause it to do so. Correct?/

Marty is refering only to the leading edge. You are right about the rudder as it pivots, if it is raked back it will cause lift. I never thought about the leading edge causing lift on the turnfin, because it is stationary. I know from experience that a perpendicular leading edge will flutter. Maybe there is a certain degree of rake that works better than another, but maybe a bit of lift would be ok to compensate for the torque that is driving the right sponson downward? any thoughts ?

John:

A couple of things.....

Do you really want the fin to lift as the speed increases? I DOUBT IT. You would have to offset this lifting with something that would be in the same proportion as the amount of lift of the fin. PROBABLY VERY HARD TO SYNCRONIZE.

The leading edge of the fin in a 100% optimum situation would be with zero rake. That way it would cut through the water with no lift. HIGHLY DESIREABLE

A neat way to imagine the effect is to assume that the fin is not sharpened. If you present this flat edge to the water, do you want it with rake? NO, IT WOULD ACT LIKE A WATER SKI. You would want it to be without rake. It would have a lot of drag, but not a lot of lift. I have been moving toward no rake with each new fin I make, and have not had the guts to make one without any rake. Maybe it is time to try that.

Just a thought.... Would you like for me to set up a chat with John and I to discuss this real time? It would move the discussion forward a lot faster than individual posts here. I haven't asked John, but I am sure he is having as much fun as I am with this discussion. Every time that we have gotton together over the years, we both enjoy bouncing things off of each other. Most times we were running on paralell courses with him running monos and me hydros. Now we are both running hydros and the discussion would be even better. Maybe we could get a semi-regular get together to discuss a set item. All kinds of options.

Both John and I love to give back to the hobby and would love to share our findings and experiences. Not sure about John, but the things that I learned the best were from mistakes made rather than from original ideas. Refinement is the way that I like to attack the hobby.

Both John and I have kind of a pet peeve. Things in model boating are much different than when we started. During that time it was necesary to understand the "WHY'S" of boating (to be competitive) rather than the current situation where you can buy a boat that is all set up or with great plans and directions. Now, you don't really have to know the "WHY'S" of model boating. I can tell you that you are missing a satisfying area.

Sorry for rambling on so much....

Marty Davis

Marty,

I think having a live chat wold be great. However I like postin because it allows us to go back an look over what has been discussed. Alot of information here that would be hard to keep track of with a live chat.

Zach

 

[Ray Sametz]

I think the most impotant thing we need to agree on is that the leading sdge of the fin should move rearward as it gets deeper. If the leading edge is perpendicular to the water, the leading edge at the deepest point can search and bend the fin. Like a jet wing, it needs to be raked back to prevent the unwanted flutter. I hope I explained that right. Take a flat blade and run it through a swimming pool with the deepest part forward and you will see that if you turn it in any direction it darts. If you run the same fin or plate metal, rudder, whatever with the deepest part raked back from the direction of travel the turning motion is smooth and there is no flutter.

Now does everyone know why John (wife opened pool) dropped that in. TEST TEST TEST Keep chuming the water, we will bite. Ray h34r: h34r:

 

[John Finch]

Chat sound great. Never done it before. Or, just keep things going as is. Either way, I'm having a great time. Like Marty said, back in the early days we had to learn things the hard way. Today all the hardware and hulls are pretty much designed for success. It took a long time for that evolution to take place. I have always wanted to know WHY something works or does not work. That's the only way to make progress. When I started model boating there were no books to get info from. Learning came from experimentation. I tried to spread the word thru the 3 books I wrote and Marty did it in his tech articles. Great stuff by the way Marty. Loved those tech articles!

I can see that there is still stuff to learn and always room for improvement. Brainstorming with Marty has been lots of fun. It may even bring us to the next level! Lets do more!

 

[Don Ferrette]

Do you really want the fin to lift as the speed increases? I DOUBT IT. You would have to offset this lifting with something that would be in the same proportion as the amount of lift of the fin. PROBABLY VERY HARD TO SYNCRONIZE.
The leading edge of the fin in a 100% optimum situation would be with zero rake. That way it would cut through the water with no lift. HIGHLY DESIREABLE

I'm going to disagree with Marty just a little on this one. Taking from lessons learned at record trials, a turn fin induces drag which can pull that sponson down. This is one of the reasons we run the left sponson a little tighter, to match what is happening on the right sponson with that curved hunk of metal hanging in the water. It's not just to counter the pulling right the fin can cause from drag but also how it will not let that sponson "free up" like the other side can. Remove the turn fin & then you'll find yourself having to loosen up that left side again. With that being said a small amount of lift generated by the turn fin is not a bad thing, the trick is finding the optimum combination which is why each boat reacts differently. If this was not the case we'd have one design of magic turn fin that worked great on everything, that ain't gonna happen. I did alot of experiments with leading edge rake on scale hulls and found that once you started getting close to zero leading edge rake the boats were more apt to dig too hard in the corner when you would lose that slight lifting property from the fin. You could go right back to the fin with more rake, no other changes & the problem would decrease as the rake increased .... to a point. I cut up alot of aluminum & spent many, many hours at the pond working with fins on the scales. We were trying to stay away from turn fins with any curve in the bottom as on scale boats that hook tended to make for one very unforgiving hull when it came to being able to correct left (ask John about the curved fin on his roundnose). What I would do was try to find the optimum combination of a fixed (bent) angle angle on the flat turn fin that would hold the boat in the corners combined with enough leading edge rake to give enough lift to keep the boat from biting too hard & spinning out. I also would just use an angle ground into the outside edge of the fin, not blend it in, that also affected the lifting characteristics on the fin as well as how it tracked. Man the good 'ol days of being 15 minutes from the pond & it being in the middle of an industrial park next to an interstate, could run whenever for however long you wanted with never a worry about someone complaining. The northern Va. traffic sucked when I lived up there but that Springfield pond sure was nice, funny how you don't know what you got 'til it's gone ........ h34r:

And BTW- the final pattern I settled on for the scales wound up looking a whole lot like the fins on the real ones. B)

 

[Tom w]

.

 

[Marty Davis]

Do you really want the fin to lift as the speed increases? I DOUBT IT. You would have to offset this lifting with something that would be in the same proportion as the amount of lift of the fin. PROBABLY VERY HARD TO SYNCRONIZE.
The leading edge of the fin in a 100% optimum situation would be with zero rake. That way it would cut through the water with no lift. HIGHLY DESIREABLE

I'm going to disagree with Marty just a little on this one. Taking from lessons learned at record trials, a turn fin induces drag which can pull that sponson down. This is one of the reasons we run the left sponson a little tighter, to match what is happening on the right sponson with that curved hunk of metal hanging in the water. It's not just to counter the pulling right the fin can cause from drag but also how it will not let that sponson "free up" like the other side can. Remove the turn fin & then you'll find yourself having to loosen up that left side again. With that being said a small amount of lift generated by the turn fin is not a bad thing, the trick is finding the optimum combination which is why each boat reacts differently. If this was not the case we'd have one design of magic turn fin that worked great on everything, that ain't gonna happen. I did alot of experiments with leading edge rake on scale hulls and found that once you started getting close to zero leading edge rake the boats were more apt to dig too hard in the corner when you would lose that slight lifting property from the fin. You could go right back to the fin with more rake & the problem would decrease as the rake increased .... to a point. I cut up alot of aluminum & spent many, many hours at the pond working with fins on the scales. We were trying to stay away from turn fins with any curve in the bottom as on scale boats that hook tended to make for one very unforgiving hull when it came to being able to correct left (ask John about the curved fin on his roundnose). What I would do was try to find the optimum combination of a fixed (bent) angle angle on the flat turn fin that would hold the boat in the corners combined with enough leading edge rake to give enough lift to keep the boat from biting too hard & spinning out. I also would just use an angle ground into the outside edge of the fin, not blend it in, that also affected the lifting characteristics on the fin as well as how it tracked. Man the good 'ol days of being 15 minutes from the pond & it being in the middle of an industrial park next to an interstate, could run whenever for however long you wanted with never a worry about someone complaining. The northern Va. traffic sucked when I lived up there but that Springfield pond sure was nice, funny how you don't know what you got 'til it's gone ........ h34r:

And BTW- the final pattern I settled on for the scales wound up looking a whole lot like the fins on the real ones. B)

Don:

As we said from the beginning, there are a lot of ways top accomplish something.....

I am more interested in the REASONS that something happens rather than, I tried this and ...... There are way to many variables for me to argue your premise... I would much rather just concentrate on one thing at a time rather than the whole package. In order for us to understand the WHY, we must disect each component.

Marty Davis

 

[Marty Davis]

OK, I can believe that we MIGHT want the leading edge to "angle away" like a jet wing. But do we want the fin to be symetrical verically to keep the CP in the same spot when the sponson lifts or bounces?
I wasn't able to open the attached turn fin pictures earlier in the post...so what do your fins look like?

I was just looking at my fin (a skewed upside down shark fin) and can see that the CP could move backwards 3/16 to 1/4 inch rearward if the fin is say 1/2 out of the water vs its normal depth.

I'll try to actually duplicate it in Acad to get an actual delta CP.

Thanks again,

Tom W

Tom:

I do not consider that since I don't think that the fin bounces much. The way that I design my fins, I make the assumption that the boat stays attached to the water almost all the time. If you are turning left, then the fin can come out of the water, but if going straight or in a turn, mu boat won't be coming out of the water.

I agree that the CP can change if the fin is anything except a rectangle or with any swept back of the front edge. Why would that movement of the CP be good or bad?

Marty Davis

 

[Tom w]

.

 

[Don Ferrette]

Don:
As we said from the beginning, there are a lot of ways top accomplish something.....

I am more interested in the REASONS that something happens rather than, I tried this and ...... There are way to many variables for me to argue your premise... I would much rather just concentrate on one thing at a time rather than the whole package. In order for us to understand the WHY, we must disect each component.

Marty Davis

So what's your point Marty?? All I'm referring to is leading edge rake. You said yourself one has to try to see, this is what I tried & found out thru many hours of testing. The REASON that I said some leading edge rake seemed to be needed was to counter how the lack of it seemed to pulled the boat down with no other changes. You said yourself a few posts back "but the things that I learned the best were from mistakes made" so those mistakes you made were because you TRIED something right?

 

[Marty Davis]

I was just curious to see if you took the CP movement into your design(s). I was thinking that if your boat crossed a wake going through a turn you would want to minimize the effect of the CP movement or try to make the change work in your favor (help hold the turn).
Just curious....

Tom W

Tom:

The evolution of my fins with a straighter and straighter leading edge seems to bear out your analysis. That may very well be a valid proposition, but it also might be something else leading me that way... NOT SURE.

Good thinking .....

Marty Davis

 

[Marty Davis]

Don:
As we said from the beginning, there are a lot of ways top accomplish something.....

I am more interested in the REASONS that something happens rather than, I tried this and ...... There are way to many variables for me to argue your premise... I would much rather just concentrate on one thing at a time rather than the whole package. In order for us to understand the WHY, we must disect each component.

Marty Davis

So what's your point Marty?? All I'm referring to is leading edge rake. You said yourself one has to try to see, this is what I tried & found out thru many hours of testing. The REASON that I said some leading edge rake seemed to be needed was to counter how the lack of it seemed to pulled the boat down with no other changes. You said yourself a few posts back "but the things that I learned the best were from mistakes made" so those mistakes you made were because you TRIED something right? <_<

Don:

Can we keep this simpler....

You made a ton of different statements about things that you have found. Could we discuss one thing at a time so that it is not so overwhelming. For example, your statement that a fin with bend in the bottom is not good for scale boats. I would like to discuss that.....

If you use a fin that is all the same angle all the way from the mount to the bottom, it will lift the boat MUCH more than a fin that has most of it's area 90 degrees to the water. That is something that most scale boaters have found out the hard way. Many have not found the fin with most of it's area 90 degrees to the water because they have not tried it. The outriggers have gone to this system because it is much more effective and the scale boaters have not since the "real boats" are not allowed to use a bent fin. The are required to run a flat plate fin (at least they were the lat time I checked). MAny scale boaters just like to keep the boat as near like the real boat as possible rather than look for the best performance available.

Marty Davis

 

[John Finch]

To have an open brainstorming session like we have, we also have to listen to opinions we may not agree with. Please don't take it personal. Sometimes we think we observe something only to find out later it's not what really happened. You can ask anyone I hang out with. The facts change all the time as we learn more.

The only reason I used rake on a turn fin was to prevent shudder. I had no idea Don had experimented with rake on his scales. The lift in the corners that he sought with a raked fin is just the opposite of what Marty is looking to do, but the cause and effect are the same. Personally, I like the right sponson a bit out of the water in the turn. We can all experiment with the rake now and report back on what we find. By the way, Don........the curved fin on my Bardahl round nose starts to curve before it even hits the water. Not good. I just noticed that. It's been hanging on the wall for nine years. I know that's one fin I need to change. The Circus Circus, that does turn left has a fin that extends straight into the water for quite a distance before it curves. Because of this discussion I can now go back and fix a problems with a boat I have not run in nine years! I might start racing it again if that left turn quirk is gone!

 

[Kelly Miller]

Incredible info, I am reading results to testing that I knew existed but have quite frankly not had the time to test myself. Marty, it is great to know what works but the thrill and enjoyment for me is to know WHY. I have read most all of your technical papers and they have helped me understand "why" quite a few times...just wanted to say thanks. Tom and Ralph got together in 2000 and bulit me a .67 extreeme complete...incredible running boat and had a lot of things done that made me want to know "why exactly did they do that" because I knew it was not LUCK, I have always been just as interested in the failures as the sucessees. I have had a lot of fun keeping it tuned in but have always had the most fun getting the last little bits and knowing why. If my time and $ could handle it I would test 24\7...lots of info you guys have that I love to absorb every chance I get.

Thanks

Kelly

 

[Marty Davis]

Incredible info, I am reading results to testing that I knew existed but have quite frankly not had the time to test myself. Marty, it is great to know what works but the thrill and enjoyment for me is to know WHY. I have read most all of your technical papers and they have helped me understand "why" quite a few times...just wanted to say thanks. Tom and Ralph got together in 2000 and bulit me a .67 extreeme complete...incredible running boat and had a lot of things done that made me want to know "why exactly did they do that" because I knew it was not LUCK, I have always been just as interested in the failures as the sucessees. I have had a lot of fun keeping it tuned in but have always had the most fun getting the last little bits and knowing why. If my time and $ could handle it I would test 24\7...lots of info you guys have that I love to absorb every chance I get.
Thanks

Kelly

Kelly:

I sure miss Tom Grannis. He motivated a lot of people with his knowlege. Wish that we could get Ralph back running a little.

I appreciate the compliment. I like to share what I have learned, and I agree that at least 1/2 of what I learn is from doing it the WRONG way rather than original ideas.

I think that we have about exhausted this topic...

Marty Davis

 

[Don Ferrette]

The only reason I used rake on a turn fin was to prevent shudder. I had no idea Don had experimented with rake on his scales. The lift in the corners that he sought with a raked fin is just the opposite of what Marty is looking to do, but the cause and effect are the same. Personally, I like the right sponson a bit out of the water in the turn. We can all experiment with the rake now and report back on what we find. By the way, Don........the curved fin on my Bardahl round nose starts to curve before it even hits the water. Not good. I just noticed that. It's been hanging on the wall for nine years. I know that's one fin I need to change. The Circus Circus, that does turn left has a fin that extends straight into the water for quite a distance before it curves. Because of this discussion I can now go back and fix a problems with a boat I have not run in nine years! I might start racing it again if that left turn quirk is gone!

Oh boy, what did I just do. John you kicked everyone's butt 2 years straight at the Internats with that Bardahl boat, scale racers watch out if that yellow & black boat comes back out. B)

Marty you asked about curved fins on scales. Ok here goes-

We typically place the rudder on the right side of the transom on the riggers so it's force tends to act upon the left front helping keep the left sponson planted, that big hook of the turn fin has the right sponson handled. Now on the heavier scales that don't have anywhere near as wide a track as an outrigger we tend to place the rudder on the left side of the transom to try to plant the right side and help get that bigger, heavier scale around the corner with less sliding. I've tried the rudder on the right side of a scale & it slid alot even with a heavily curved fin. The down side to the left side mounting is it makes that left sponson easy to lift off the water if left correction is needed. A heavily curved fin seems to accentuate the problem when you try to correct left, rolling that side down into the water & lifting the left side. (FWIW I find my riggers correct left better than my scale boats do at higher speeds). What I found with a flat fin set at an angle was that the boats didn't raise the left so easily when correcting left, I'm thinking that maybe the flat angle might be acting just a little like the non trip angle on a sponson with the water pushing up against that surface (just a theory here). Now the other side to that is the best fin angle seemed to be no more than about 7 degrees. If you went more than that the right sponson would often try to lift some while running straight. One of the things I messed with recently is mounting the flat fin 90 degrees to the water like a typical rigger fin & then putting that 7 degree bend further down, just below the bottom of the sponson ride pad. That seemed to work well on the '94 Joe's boat but much more testing I have yet to & would like to do on that idea on the new '96 hull. Your thoughts please .......

 

[Marty Davis]

The only reason I used rake on a turn fin was to prevent shudder. I had no idea Don had experimented with rake on his scales. The lift in the corners that he sought with a raked fin is just the opposite of what Marty is looking to do, but the cause and effect are the same. Personally, I like the right sponson a bit out of the water in the turn. We can all experiment with the rake now and report back on what we find. By the way, Don........the curved fin on my Bardahl round nose starts to curve before it even hits the water. Not good. I just noticed that. It's been hanging on the wall for nine years. I know that's one fin I need to change. The Circus Circus, that does turn left has a fin that extends straight into the water for quite a distance before it curves. Because of this discussion I can now go back and fix a problems with a boat I have not run in nine years! I might start racing it again if that left turn quirk is gone!

Oh boy, what did I just do. John you kicked everyone's butt 2 years straight at the Internats with that Bardahl boat, scale racers watch out if that yellow & black boat comes back out. B)

Marty you asked about curved fins on scales. Ok here goes-

We typically place the rudder on the right side of the transom on the riggers so it's force tends to act upon the left front helping keep the left sponson planted, that big hook of the turn fin has the right sponson handled. Now on the heavier scales that don't have anywhere near as wide a track as an outrigger we tend to place the rudder on the left side of the transom to try to plant the right side and help get that bigger, heavier scale around the corner with less sliding. I've tried the rudder on the right side of a scale & it slid alot even with a heavily curved fin. The down side to the left side mounting is it makes that left sponson easy to lift off the water if left correction is needed. A heavily curved fin seems to accentuate the problem when you try to correct left, rolling that side down into the water & lifting the left side. (FWIW I find my riggers correct left better than my scale boats do at higher speeds). What I found with a flat fin set at an angle was that the boats didn't raise the left so easily when correcting left, I'm thinking that maybe the flat angle might be acting just a little like the non trip angle on a sponson with the water pushing up against that surface (just a theory here). Now the other side to that is the best fin angle seemed to be no more than about 7 degrees. If you went more than that the right sponson would often try to lift some while running straight. One of the things I messed with recently is mounting the flat fin 90 degrees to the water like a typical rigger fin & then putting that 7 degree bend further down, just below the bottom of the sponson ride pad. That seemed to work well on the '94 Joe's boat but much more testing I have yet to & would like to do on that idea on the new '96 hull. Your thoughts please .......

Don:

I agree with you about rudder placement exactly. The narrow front stance of the scale boats makes weight transfer critical so it must be on the left to loat the turn fin.

The angled vs straight with a curve at the bottom, I guess we will have to agree to disagree. Both will lift the left side of the boat on left correction a lot. By putting the straight fin at 7 degrees, you are limiting the lifting to a great extent compared with one of 15 degrees.

I agree with you about the riggers being less prone to lift on left correction. That is due to the very wide stance of the front sponsons and actually will allow you to use a right side rudder (which I do on all my riggers).

I would urge you to try a straight fin with the curve as low toward the bottom as possible on your scale boat. I bet you will love it.... You will also be able to reduce the rudder throw probably in half.

Marty Davis

 

[Don Ferrette]

The only reason I used rake on a turn fin was to prevent shudder. I had no idea Don had experimented with rake on his scales. The lift in the corners that he sought with a raked fin is just the opposite of what Marty is looking to do, but the cause and effect are the same. Personally, I like the right sponson a bit out of the water in the turn. We can all experiment with the rake now and report back on what we find. By the way, Don........the curved fin on my Bardahl round nose starts to curve before it even hits the water. Not good. I just noticed that. It's been hanging on the wall for nine years. I know that's one fin I need to change. The Circus Circus, that does turn left has a fin that extends straight into the water for quite a distance before it curves. Because of this discussion I can now go back and fix a problems with a boat I have not run in nine years! I might start racing it again if that left turn quirk is gone!

Oh boy, what did I just do. John you kicked everyone's butt 2 years straight at the Internats with that Bardahl boat, scale racers watch out if that yellow & black boat comes back out. B)

Marty you asked about curved fins on scales. Ok here goes-

We typically place the rudder on the right side of the transom on the riggers so it's force tends to act upon the left front helping keep the left sponson planted, that big hook of the turn fin has the right sponson handled. Now on the heavier scales that don't have anywhere near as wide a track as an outrigger we tend to place the rudder on the left side of the transom to try to plant the right side and help get that bigger, heavier scale around the corner with less sliding. I've tried the rudder on the right side of a scale & it slid alot even with a heavily curved fin. The down side to the left side mounting is it makes that left sponson easy to lift off the water if left correction is needed. A heavily curved fin seems to accentuate the problem when you try to correct left, rolling that side down into the water & lifting the left side. (FWIW I find my riggers correct left better than my scale boats do at higher speeds). What I found with a flat fin set at an angle was that the boats didn't raise the left so easily when correcting left, I'm thinking that maybe the flat angle might be acting just a little like the non trip angle on a sponson with the water pushing up against that surface (just a theory here). Now the other side to that is the best fin angle seemed to be no more than about 7 degrees. If you went more than that the right sponson would often try to lift some while running straight. One of the things I messed with recently is mounting the flat fin 90 degrees to the water like a typical rigger fin & then putting that 7 degree bend further down, just below the bottom of the sponson ride pad. That seemed to work well on the '94 Joe's boat but much more testing I have yet to & would like to do on that idea on the new '96 hull. Your thoughts please .......

Don:

I agree with you about rudder placement exactly. The narrow front stance of the scale boats makes weight transfer critical so it must be on the left to loat the turn fin.

The angled vs straight with a curve at the bottom, I guess we will have to agree to disagree. Both will lift the left side of the boat on left correction a lot. By putting the straight fin at 7 degrees, you are limiting the lifting to a great extent compared with one of 15 degrees.

I agree with you about the riggers being less prone to lift on left correction. That is due to the very wide stance of the front sponsons and actually will allow you to use a right side rudder (which I do on all my riggers).

I would urge you to try a straight fin with the curve as low toward the bottom as possible on your scale boat. I bet you will love it.... You will also be able to reduce the rudder throw probably in half.

Marty Davis

Funny you should say that about a straight fin with curve as low as possible, just started messing with that, jury is still out on it but it looks promising.

 

[tnrcboatracer]

I have been following this thread with great interest. I have a question about fins on a SP40. In particular the Betke-Berari I picked up from Norris S that was rigged by Marty. On this hull the rudder was placed on the right, with a straight fin with an angle about 50% down the length. Now granted neither Marty not Norris ever ran this hull to sort it out, but when I first ran it the handling was horrid. Any THOUGHT/ATTEMPT to turn left resulted in an immediate blow over roll to the left. Additionally, the aluminim fin would bend, and not track straight after a fer corners. I added a straight SS fin with a hook at the very bottom with immediate improved results. The fin still tries to pull out a little, so I am in the process of remounting the rudder on the left. (I also plan experiment with air traps to keep the rear up when letting off the throttle, nothing like having it blow over when you back off the trigger, but this shopuld be a separate thread)

Marty, in light of this discussion thread, I wonder about the rudder placement of this particular SP40; was there a specific reason you rigged this hull with the rudder on the right side? Does this hull have a wider track than the other SP40's out there, thus a right side placement would be better? I would like to confirm your intent with the setup on this hull before I carve up the transom and radio box.

Thanks,

Jon

 

[Marty Davis]

I have been following this thread with great interest. I have a question about fins on a SP40. In particular the Betke-Berari I picked up from Norris S that was rigged by Marty. On this hull the rudder was placed on the right, with a straight fin with an angle about 50% down the length. Now granted neither Marty not Norris ever ran this hull to sort it out, but when I first ran it the handling was horrid. Any THOUGHT/ATTEMPT to turn left resulted in an immediate blow over roll to the left. Additionally, the aluminim fin would bend, and not track straight after a fer corners. I added a straight SS fin with a hook at the very bottom with immediate improved results. The fin still tries to pull out a little, so I am in the process of remounting the rudder on the left. (I also plan experiment with air traps to keep the rear up when letting off the throttle, nothing like having it blow over when you back off the trigger, but this shopuld be a separate thread)
Marty, in light of this discussion thread, I wonder about the rudder placement of this particular SP40; was there a specific reason you rigged this hull with the rudder on the right side? Does this hull have a wider track than the other SP40's out there, thus a right side placement would be better? I would like to confirm your intent with the setup on this hull before I carve up the transom and radio box.

Thanks,

Jon

I didn't rig the boat. The rudder should be on the left.

I would suggest that you run a flat bottom strut. Make the turn fin as far forward as possible. The cg is very far forward on that boat.

Marty Davis

 

[tnrcboatracer]

My mistake, I thought that Norris told me that you rigged it for him when I picked it up. The strut is a flat bottom type. I'm already addiing some weight to the front per Mr Betke's suggestion. I have 2 turn fins with slightly different rake. Both are right up at the sponson.

Thanks for the recommendations.