rigger pulling to the right ?

[Rigged]

WOW Jeroen you got that rigger honkin. You got a pic of the virginia craftsman turn fin?

I finally got my FF running *decent* with consistent 72.2-72.5 runs w/ stock 6719/3, but had to shim the turn fin a crazy amount to get it to go remotely close to straight without a bunch of left correction. Pretty much giving up on the FF and going to a PHM Viper next season.

 

[impba3548]

One thing I didnt see mentioned that has made quite a difference in mine is to run the left sponson off center, I made extra boom tubes with the holes drilled off center. The boat doesnt look as good but it sure helps with the pulling. Another thing to try is a shorter turnfin, if its straightaway setup you dont need that big of a fin on it and that will reduce the pull as well but it wont work very well in rough water.

My experience is that the gassers seem to pull worse than the nitro boats due to lower rpm and larger diameter higher pitch props.

My two cents worth

mike sr

 

[speakerboy]

Well. after some weekends of bad weather this morning i went to the pond and tryed the rigger again ..tempeture against freezing point . the first 9 feet of water close to the shore was frozen . i cracket the ice a bit so i could launch the boat ..

i didnt changed anything on the main setup . just a longer flex cable with a bigger gap (1/4) between the strutt and dogdrive . mounted a straight carbon turnfin that was 1 inch under the sponson , and 1 inch wide .. just something where i could turn the rigger arround . it worked and i could make some passes . the rigger is still pulling to the right but its minimal . i think the pulling is just coused by propwalk . problem was the pond was too small to let here rev out completely , i needed lots of water to turn here arround . test was good but to less fin ,ore too small pond ..

next fin mounted was the AB fin .. mounted on a good bracket , launched again , boat was great in handling and could turn great , the boat is even acceleration in the turns , its lifting the right sponson at least 1 inch out of the water in full speed turns .. little risky .. in the straights it was pulling more than ever . i needed at least 5 % rudder correction to let her run straight ..

than i put the Virgina craftman fin under the boat ... cracked so many ica allready that i could launch her every where , the boat is amazingly stable in the turns , pulls less then the AB fin but it will slow down just a tat in the turns . but the grip in the turns is amazing .

i could not get more speed than 78 mph .. the water was freezing and the motor was still cold , even after a ty-wrap trick to restrict the ammount of water the motor was still too cold .. not unhappy with 78 in this water , top rpm was 17200 .

i will built another Twister hydro . and will run one for heat racing with the Virgina craftman fin , and ill contignue racing the AB fin on this rigger . i believe the topspeed accelerating in the turns is amazing , i just have to find a way to control the pull and work that out .. concidering i will work with the AB fin , what will couse the boat to lift here right leg up and should i fix that , and what would it be an option if i could angle the fin a bit forward ore backward ?

Rigged , how did you shim your turnfin ? ist that gonna work like a brake there ?

Jeroen

 

[Chris Wood]

you mentioned with the ab fin it was lifting.

losen the bolts and bring the back of the fin up.. if the back is down to much it will lift the sponson out of the water in the straights.. if it is digging or slowing down in the turns with the other pull the back of the fin down as it might be up to much.

you want it parallel with the bottom of the tub or just SLIGHTLY down at the back.. NEVER UP AT THE BACK.

hope i helped

chris

 

[Tom v.d Brink]

chris is absolutely correct lifting and digging in turns is a result of vertical turnfin angle.

normally you align the bend lines of the turnfin to run parallel to the hull

or if your hull is setup incorrectly (and the hull does not run level) you might need a different angle then paralel in which case you will have to experiment to get it right.

but also as chris said don't let it dig!!

 

[speakerboy]

Gentle men , thank you for your answers . i will work with the AB fin to see if it was "out "of line and fix that .. than we run again .

Thanx again !

Jeroen

 

[John Finch]

Gentle men , thank you for your answers . i will work with the AB fin to see if it was "out "of line and fix that .. than we run again .
Thanx again !

Jeroen

jeroen,

I have found that when your boat tracks straight at 75 to 80 mph and then you jump the speed up to the 90's The rudder might have to be either a bit wider front to back or a little longer. I have found just being 1/4 inch longer takes away the pull. Also blade shape.........perfectly rectanglular blades like Andy's work better than tapered blades that are wider at the top and taper to less front to back distance at the tips. I just ran a SAW event a month ago and out of 5 rudders, only one kept the boat running straight. That was with a sport gas hull at 85 mph. The same depth rudder a bit less front to back at the tip made the boat litterally turn right at 85 mph. A blade 1/4 inch shorter made the boat veer right. Look at the rudder carefully and experiment with them. It's as important as the prop and fin if not more so. Also, you can use a fin with no curve and the boat will turn ok at slower speeds when running SAW. You may find you can run without a fin.

 

[TomMoorehouse]

Jeron, ive been following this thread closely and you have been working hard to make improvements. I've kept quiet cause everyone has been giving good advice on all the things i'd think to check. I've been thinking about this and "Believe" I have the answer. I have no way to tell for sure as it is just a theory and my water is too hard to test it. This being the biggest rigger i've ever designed I went with some design theories from other people that have more experience than I did with large boats. Maybe I should have stuck with I knew?

Here is what i'm thinking:

I went with a much lower angle of attack than I usually do. I put more belly in to the design cause I thought that would also be better for a larger rigger. I think what i've done with this combination is mess with bernoulli. The camber on the left is 3 and the right is flat. It's making me think that bernoulli is having a stronger pull on the right and hence the problem. Late fall this year I started experimenting on my .21 with different sponson designs to bust bernoulli. I did not get much results due to the pond going hard on me but after my testing and much thought and discussion I think I have a design that will make the boat faster and eliminate the pulling. It's just in my head right now, and I drew a new .12 with the concept. I would love to draw the same concept for the gas rigger if your willing to try it out.... although it sounds like your freezing also..... I'd just draw new sponsons not a whole new boat. a single center rear sponson.

raising the AOA might be an easy way to help? possibly more aoa on just the right side.

what ya think?

 

[speakerboy]

First of all i want to thank everybody here that took the time to post an answer here , all the posts are usefull and have great info . not only for my boat , but for a data base of the How To's .

situation of my rigger right now is that both sponsons are still in line , no toe in no toe out , AOA of both sponsons is 3 degrees . there are no shimms in the boat ore on the turnfin .

the test result with the AB turnfin were pretty good but its till pulling .. and even worse than the VC turnfin . but i made an error with that AB fin ,i took away the 45 degrees angle and smooth her out more . never though abouth the work that the 45 degree angle did .. i found it to be dull ! a fin must be sharp .. and there i messed that one up .. never the less , in the turns the boat is accelrating hard and i like that !

the VC turnfin is a Big turnfin , running it with another prop with less pitch and moroe RPM made the pulling going away , but so did the topspeed .. ended up with 74 mph .. whitch i like for heat racing .. i will built another Twister for heat race and use this VC fin for that ..

so in the SAW ore speed record boat we go back to the AB fin . i just mounted it on the boat last sunday , it was too cold to check if it was alligned perfect .. so it must have be mounted wrong and i might check that so i can get the bend even with the tub .

John .. you might be on to something here. . i use a hydro blade , all straight , no tapered blade , but i did made it shorter than stock .. i checked out the original rudder from Jack .. he is dong close to 70 mph , and i cut my blade at the same lenght that he has .... it might be to short .. ! waterpick ups are in the rudder on the Right side of the blade .. they work perfect .. more drag on the right side of the blade . ?

but if we go back to the first test fin i made from Carbon .. that fin was 1 inch deep under the right sponson and 1 inch long .. sharp .. and it was a handfull to make a turn in slow speeds , but i could accelrate good and even then i have a small amound of pulling to the right . i had to use the steering to let it track straight .

i will try to make some pics tonight of the setups .. just to share ...

Thanx again !

Jeroen

 

[Rigged]

Rigged , how did you shim your turnfin ? ist that gonna work like a brake there ?
Jeroen

Jeroen...just for testing to find where it needed i used an assorment of washers to shim the turn fin. My turnfin is not bolted to the side of the sponson, as i have G10 spur coming out of the back of it that the fin bolts to..not sure if that makes a difference though. Ive ended up with it shimmed about 1/8" to get the boat to run the way it does now (went from 64mph having to hold almost full left to go straight to consistently going 73mph in oval trim with almost no left correction).

Here is hows its shimmed... (btw im using a Crapshooter 90 fin)

This may not be the "right" thing to do...but im not trying to go out and set speed records. Just trying to get the boat consistent and easy to drive for heat racing, which now it is.

 

[Tom Foley]

I can't even imagine how much that Spur is flexing when throwing it into a turn at speed . That fin shouldn't move under ideal setup . I realize of course the lower section of the fin will flex , but the longitudinal backbone of the fin should be rock solid .IMO

 

[John Finch]

Looks like it shimmed the wrong direction. The fin steers the boat like front wheels on a car. To compensate for prop walk you point the front of the fin to the left, not the right.

 

[AndyBrown]

Looks like it shimmed the wrong direction. The fin steers the boat like front wheels on a car. To compensate for prop walk you point the front of the fin to the left, not the right.

Actullay John, much to my own surprise I have expericed the opposite result more times than not and his shim direction is correct to compensate for pulling to the right.

If the fin was much more forward, like on the side of the sponson, the the effect would be as you are thinking.

P.S. I think the longer rudder blade is going to be Jeroen's solution.

I run a much deeper rudder blade on my SAW boats than on my race boats to keep the BIG props from walking to the left.

 

[Rigged]

Looks like it shimmed the wrong direction. The fin steers the boat like front wheels on a car. To compensate for prop walk you point the front of the fin to the left, not the right.

You're right...the fin steers the boat like the wheels on a car. But i dont turn the wheels left to go right.

When you put input on the rudder to turn right... the leading edge of the blade is to the left of the trailing edge (looking from the back of the boat). So why would i want the leading edge of the turn fin to the RIGHT of the trailing edge if im trying to compensate for a pull to the right? Seems to me, with the leading edge of the turn fin pointing to the left, instead of the trailing edge to the left would just make the boat pull right even worse?

 

[tnrcboatracer]

I think that it matters where the TF CP is relative to the CG of the boat. If you put htat shimmed fin at the front of the sponson, it would pull hte hull to the right, aft of the CG, it pulls it to the left.

 

[Jerry Muro]

Hey Tom I do not think Jerone built a FF. I did build a FF gas rigger and I am having issues with pulling into the course as well. The water got hard around here before I could try what I did. I shimmed the strut 2 degrees to help. Are you saying that the design of the front sponson and rears have to much belly into them? Please explain as to rectify if this is the case. I haven't really had a lot of water time on the boat. It seemed to be okay in speed but as I said the handling issue reduced the speed. Any help will be greatly appreciated.

 

[Rokieboater]

Looks like it shimmed the wrong direction. The fin steers the boat like front wheels on a car. To compensate for prop walk you point the front of the fin to the left, not the right.

You're right...the fin steers the boat like the wheels on a car. But i dont turn the wheels left to go right.

When you put input on the rudder to turn right... the leading edge of the blade is to the left of the trailing edge (looking from the back of the boat). So why would i want the leading edge of the turn fin to the RIGHT of the trailing edge if im trying to compensate for a pull to the right? Seems to me, with the leading edge of the turn fin pointing to the left, instead of the trailing edge to the left would just make the boat pull right even worse?

When you turn left, is the trailing edge of the rudder to the left or right of the leading edge? Is the leading edge the pivot point or the driving/turning point? As the fin goes thru the water does the pressure of the water straighten the fin out and make the boat go left or does the fin drive it to the right? Just a bunch of goofy questions, don't shoot me. Very informative topic.

Robert

 

[John Finch]

yeah, that turn fin is pretty far back from the riding surface of the front sponson isn't it. I didn't see that. Good catch Andy.

 

[John Finch]

Looks like it shimmed the wrong direction. The fin steers the boat like front wheels on a car. To compensate for prop walk you point the front of the fin to the left, not the right.

You're right...the fin steers the boat like the wheels on a car. But i dont turn the wheels left to go right.

When you put input on the rudder to turn right... the leading edge of the blade is to the left of the trailing edge (looking from the back of the boat). So why would i want the leading edge of the turn fin to the RIGHT of the trailing edge if im trying to compensate for a pull to the right? Seems to me, with the leading edge of the turn fin pointing to the left, instead of the trailing edge to the left would just make the boat pull right even worse?

When you turn left, is the trailing edge of the rudder to the left or right of the leading edge? Is the leading edge the pivot point or the driving/turning point? As the fin goes thru the water does the pressure of the water straighten the fin out and make the boat go left or does the fin drive it to the right? Just a bunch of goofy questions, don't shoot me. Very informative topic.

Robert

When you turn left it is because the rudder moved the transom to the right. When you turn right it is because the rudder moved the transom to the left. Like a rear wheel steering car. The turn fin is the pivot point. The turnfin might track straight down the straightaway when it is shimmed, but the boat may actually be crabbing.

 

[Rokieboater]

Looks like it shimmed the wrong direction. The fin steers the boat like front wheels on a car. To compensate for prop walk you point the front of the fin to the left, not the right.

You're right...the fin steers the boat like the wheels on a car. But i dont turn the wheels left to go right.

When you put input on the rudder to turn right... the leading edge of the blade is to the left of the trailing edge (looking from the back of the boat). So why would i want the leading edge of the turn fin to the RIGHT of the trailing edge if im trying to compensate for a pull to the right? Seems to me, with the leading edge of the turn fin pointing to the left, instead of the trailing edge to the left would just make the boat pull right even worse?

When you turn left, is the trailing edge of the rudder to the left or right of the leading edge? Is the leading edge the pivot point or the driving/turning point? As the fin goes thru the water does the pressure of the water straighten the fin out and make the boat go left or does the fin drive it to the right? Just a bunch of goofy questions, don't shoot me. Very informative topic.

Robert

When you turn left it is because the rudder moved the transom to the right. When you turn right it is because the rudder moved the transom to the left. Like a rear wheel steering car. The turn fin is the pivot point. The turnfin might track straight down the straightaway when it is shimmed, but the boat may actually be crabbing.

John, would the boat be any slower if it is crabbing?

Robert