turn fins on tub

[Charles Perdue]

Hello Mike, the first change was the shape of the turn fin itself. Instead of taking a flat fin and bending the angle of inclination (as in the camber to a wheel, leaning it so the bottom of the fin is closer to the tub) into the fin, the fin was left flat and the fin mount was angled. Doing this also made mounting the turn fin and trimming it out much, much easier. Almost "Dummy Proof". The second change was adding 1 to 2 additional degrees inclination to the fin and the third was extending the sponsons farther out from the tub. A fin inclination of about 18 degrees from vertical, taken with the sponson riding surfaces sitting on a flat surface, is a very good starting place for a rigger.

Charles

 

[Charles Perdue]

Guys, let me add a little more info on what kind of turn fin loads that you are dealing with when a boat goes into a turn. Say a 40 rigger that weighs 6 Lbs is going into a 30 foot radius turn 5 feet out from the bouys at 70 MPH. The load on the turn fin is just over 56 Lbs. The same boat going into the same turn at 80 MPH, the turn fin load is just over 73Lbs.

A 14 Lb scale running 60 MPH going into the same turn, the load on the turn fin is just over 96Lb.

If you think that your hull , bracket and fin is rigid enough, just remember that the turn fin needs to have less than .030 deflection at the bottom and less than .030 deflection at the trailing edge under load. If the deflection is at the bottom of the turn fin the fin will try to "Unhook" and let the boat skate out of the turn. If the deflection is at the trailing edge the turn fin will STEER the boat to the left out of the turn.

The first boat that I tried this type of turn fin on twisted so bad that the front radio box bulkhead broke aloose. After repairs, this boat also turned well enough that it won 1st place at the NAMBA Nationals with a perfect score in its class.

While we are on this subject, if you have any questions, fire away and I will try to answer them.

Charles

 

[Chris Wood]

charles,

maybe you can answer this for me.. i made a fin 2 yrs ago that was SO violent.. it would turn inside bouy 1 3 ft off of the bouy. it was absolutly AWSOME.. but i couldn't keep it from wanting to continue to turn out of the turn.

you could hear it cutting the water lol.

what could be done WITHOUT changing the shape size or bend angle. to be able to make that work

thanks

chris

 

[moparbarn]

Martys fishing again!

A turn fin on both sponsons with a small fin on the left and a large fin on the right sponson WILL snap roll, not just theory, tried many combinations years ago. Will not work.

The correct turn fin on the right sponson does not have to pull the right sponson down to make it work. The correct fin holds the sponson in the same position as in the straight -a- way. The boat just does a slow pivot around it. When it is right, the boat "Sweeps" the turns, loosing very little speed. The correct shape doesn't have to be a "Hooked" or a curved turn fin either.

While we are playing with different ideas, what about WHEELS on the sponsons. Don't laugh, they work great in the straights and so-so in the turns. They are just a bear to get up on plane.

Charles

either walt or art arfrons (sp?), of the "green monster" land speed record cars did this back in the late 60's or early 70's - wheels on a boat. but not for turning. was to reduce drag in a quest for a water speed record. theory was that after about 300 mph, water became very similar to a solid surface to the wheels. it worked, he set a record, but it was outlawed for "not being a boat", but rather a car on water. sorry, way off topic, i know. i'm fixing to put my first rigger in the water by next weekend, hope to race it in chesapeake at the end of the month. thank all of you for some VERY interesting info B) . please continue......

 

[Charles Perdue]

charles,

maybe you can answer this for me.. i made a fin 2 yrs ago that was SO violent.. it would turn inside bouy 1 3 ft off of the bouy. it was absolutly AWSOME.. but i couldn't keep it from wanting to continue to turn out of the turn.

you could hear it cutting the water lol.

what could be done WITHOUT changing the shape size or bend angle. to be able to make that work

thanks

chris

Hello Chris, one thing that will cause what you are talking about is some part of the fin assembly (bracket, fin, ect) is flexing a lot. I was trying a very thin fin once and as you would start a turn it would flex under the load and take over the steering. You would never know where the boat was going. It had a mind of its on and it happened VERY quick. Re installed the thicker fin and the problem went away. Your experiennce sounds similar.

Charles

 

[Charles Perdue]

Martys fishing again!

A turn fin on both sponsons with a small fin on the left and a large fin on the right sponson WILL snap roll, not just theory, tried many combinations years ago. Will not work.

The correct turn fin on the right sponson does not have to pull the right sponson down to make it work. The correct fin holds the sponson in the same position as in the straight -a- way. The boat just does a slow pivot around it. When it is right, the boat "Sweeps" the turns, loosing very little speed. The correct shape doesn't have to be a "Hooked" or a curved turn fin either.

While we are playing with different ideas, what about WHEELS on the sponsons. Don't laugh, they work great in the straights and so-so in the turns. They are just a bear to get up on plane.

Charles

either walt or art arfrons (sp?), of the "green monster" land speed record cars did this back in the late 60's or early 70's - wheels on a boat. but not for turning. was to reduce drag in a quest for a water speed record. theory was that after about 300 mph, water became very similar to a solid surface to the wheels. it worked, he set a record, but it was outlawed for "not being a boat", but rather a car on water. sorry, way off topic, i know. i'm fixing to put my first rigger in the water by next weekend, hope to race it in chesapeake at the end of the month. thank all of you for some VERY interesting info

. please continue......

Hello Robin, lower drag at higher speeds was what I was trying to accomplish with the wheels on the sponsons. It was just too difficult to get the boat up running on the wheels.

A mechanism to lower the wheels AFTER the boat was on plane would probably work better.

After trying the wheels, I went to tunnels on the sponson bottoms. It took a while to get them figured out, but now on a heat race boat, they are hard to beat. Designing the riding pads on each side of the tunnel with "Shingles" instead of a solid pad helps these to run VERY clean.

If you like a challenge , you will love the rigger.

Charles

 

[Chris Wood]

Hey charles,

i would agree but my only doubt if you will is that i tried two fins back to back using the same thickness material and material make.. just different bends..

i suppose there is such a thing as to much bend hook what have you.

lets assume that is wasn't material thickness.. any other ideas??

i know from testing have spent alot of time on fins and shapes.. alot of work for sure

thanks

chris

 

[Charles Perdue]

Chris, it sounds like too much bend. Some really weird things happen with a curved turn fin that are hard to explain. That is just one of the reasons that I use a totally flat fin. They are very predicitable.

Charles

 

[carlnoki]

Charles;

When we were stationed out in the Phoenix area in the middle 80's, I belonged to the Scottsdale Model Boat club

and we used the angled turn fin on our riggers. I believe i was running around 20-22 degree angle on my 90 riggers at the time.I found out that like yourself, i had to widen the front sponson

footprint to get the boat to stop lifting the left sponson during left corrections if needed. It does work.

I have been using Dicky's fins for quite a while now and maybe i might try to stick an angled one on my new boat i am building to see if it STILL works for me.

And as far as i can remember, the ONLY rigger i have ever seen that could turn left on a dime when he wanted it to

belonged to a gentleman by the name of Jack Oxley out in the L.A. area in the mid 80's. He raced nothing but Wing Dings and they were bullets. I do not remember what type of turn fin he used but it was mounted out on the sponson in back of the wing.

Carl

 

[Charles Perdue]

Hello Carl, the flat turn fin has a lot of advantages and very few disadvantages. The flat fin is sometimes called the California fin and/or the West coast fin. I came up with it and started working out the bugs in the flat/angled design in 1979. They are nothing new. I am just trying to regenerate interest and provide the information to make it useful, that I have learned thru the years playing with it.

On a heavier boat like your 90 it would require slightly more angle to compensate for the flexing and help the boat turn left.

Jack Oxley was a friend of mine that ran out of Legg Lake. The last time that I saw his boat, it had a flat turn fin mounted behind the sponson bracket. He, like myself, needed the boat to turn left to make up for his driving.

Charles

 

[Kim J]

More questions :

What is the best material for fins and which thickness do you recommend ?

How do you sharpen the fin ? Like a chisel in the front and only on the outside - how about the rear and bottom ?

Is there a correlation between the depth of the fin and the depth of the rudder ?

 

[moparbarn]

Martys fishing again!

A turn fin on both sponsons with a small fin on the left and a large fin on the right sponson WILL snap roll, not just theory, tried many combinations years ago. Will not work.

The correct turn fin on the right sponson does not have to pull the right sponson down to make it work. The correct fin holds the sponson in the same position as in the straight -a- way. The boat just does a slow pivot around it. When it is right, the boat "Sweeps" the turns, loosing very little speed. The correct shape doesn't have to be a "Hooked" or a curved turn fin either.

While we are playing with different ideas, what about WHEELS on the sponsons. Don't laugh, they work great in the straights and so-so in the turns. They are just a bear to get up on plane.

Charles

either walt or art arfrons (sp?), of the "green monster" land speed record cars did this back in the late 60's or early 70's - wheels on a boat. but not for turning. was to reduce drag in a quest for a water speed record. theory was that after about 300 mph, water became very similar to a solid surface to the wheels. it worked, he set a record, but it was outlawed for "not being a boat", but rather a car on water. sorry, way off topic, i know. i'm fixing to put my first rigger in the water by next weekend, hope to race it in chesapeake at the end of the month. thank all of you for some VERY interesting info

. please continue......

Hello Robin, lower drag at higher speeds was what I was trying to accomplish with the wheels on the sponsons. It was just too difficult to get the boat up running on the wheels.

A mechanism to lower the wheels AFTER the boat was on plane would probably work better.

After trying the wheels, I went to tunnels on the sponson bottoms. It took a while to get them figured out, but now on a heat race boat, they are hard to beat. Designing the riding pads on each side of the tunnel with "Shingles" instead of a solid pad helps these to run VERY clean.

If you like a challenge , you will love the rigger.

Charles

charles, from what i can remember of the arfrons green monster boat, is that it had VERY wide wheels that only stuck down below the hull about 1/2". the hull completely surrounded the tire at the bottom, so the water flow was not disrupted very much. once at speed, the "boat" was actually rolling on the tires, that is why the record was not allowed. btw, all i have run up 'til now is .21 tunnels. challenges? yeah, a few ..........

 

[carlnoki]

Robin;

come out to the lake Sunday

will bring a pipe for you.

carl

and Charles, i found my old 90 bent fin and will be using it on the new boat.

Carl

 

[Charles Perdue]

More questions :

What is the best material for fins and which thickness do you recommend ?

How do you sharpen the fin ? Like a chisel in the front and only on the outside - how about the rear and bottom ?

Is there a correlation between the depth of the fin and the depth of the rudder ?

Hello Kim John, how is those Zoom carbs doing?

The turn fin material that you use, aluminum, carbon fiber, titanium, ect is base on personal preference, what is avaliable and what tools that you have to work with in shaping and sharpening the fin as long as you take into consideration the stiffness required. The type of material also determines the thickness of the fin.

The finished sharpened shape should be a wedge going from the front edge to the back edge, sharpened only on the right side. The bottom and the rear should be squared off.

The depth of the fin should be the same as the rudder.

Hope this helps, Charles

 

[Kim J]

Thanks for the info Charles.

Have not run them yet - still waiting for parts.

How do you determine where to place the fin - regarding to COG ?

 

[dr gary turner]

Charles: Good discussion. Years ago Mark was running a Pinkert hydro and trying to set the oval record at Huntsville I believe in 40 hydro. I took his straight fin and put a 17 degree bend in the bottom of the fin and he immediately set the record. It is interesting to see that certain numbers really do not change.

Mark has been making our twin turn fins out of THIN tempered steel. It has really reduced flexing. It is a difficult material to work with, but that is part ofthe price to pay. DOC

 

[Charles Perdue]

Thanks for the info Charles.

Have not run them yet - still waiting for parts.

How do you determine where to place the fin - regarding to COG ?

Hello again Kim John, when I set up a new boat, I trim it out so that the center of gravity is at the trailing edge of the turn fin. If any adjustments are needed, I make adjustments from there.

Charles

 

[Charles Perdue]

Charles: Good discussion. Years ago Mark was running a Pinkert hydro and trying to set the oval record at Huntsville I believe in 40 hydro. I took his straight fin and put a 17 degree bend in the bottom of the fin and he immediately set the record. It is interesting to see that certain numbers really do not change.

Mark has been making our twin turn fins out of THIN tempered steel. It has really reduced flexing. It is a difficult material to work with, but that is part ofthe price to pay. DOC

Hello Doc, good to hear from you. Guys, this is the person that talked me into getting back in to boating.

If you will leave the turn fin flat and angle the mount the 17 or so degrees, you get the same advantage of the flat fin without the difficulty of trimming the fin out. Tilting the flat fin up or down on the mount has NO effect on whether the fin pulls down or pushes up. Just one less problem you have to work out.

Charles

 

[Kim J]

More questions Charles :

What are the symptoms of a misplaced fin - too much forward or aft ?

 

[Charles Perdue]

More questions Charles :

What are the symptoms of a misplaced fin - too much forward or aft ?

Kim J, when I build a new boat (most of my boats are scratch built) I make the turn fin mount, with the help of an adjustable bracket, so that I can move it forward or backwards to find the optimum position. The turn fin itself is also sacrificed. Starting with a fin that is to large, I trim it until it is slightly too small, then I back up to the last size that worked well and make a new fin that size.

Considering that everything else is as it should be, a turn fin that is too far forward of the COG will mke the boat turn sluggish using more rudder travel. A turn fin that is too far behind the COG will make the boat turn too snappy, too sensitive in the straights and in the turns. When the turn fin is correct as you put the boat in the turn, you only have to use a small amount of rudder travel and hold the rudder in that position as the boat continues thru the turn. You will know when you have acheived the correct turn fin and position.