Ride pad dimension's for .21 size tunnel hull 's ?

[riggerman]

Hi all what size ride pads or a.k.a stumble blocks are required for .21 size tunnel hulls ? The boats i will be using them on are the Dunlap W.O.F 30 and the Dunlap - 27 which is in the process of being converted to UL-1 power and 4s lipo. For location would the front of the ride pad be up against the leading edge? Would using 2 sided servo tape to fasten the ride pads in position be the best method ?

 

[Bill Britton]

1.25 inches is in the ballpark for width to start but could end up +/-. Length should be somewhere in the 5-6 length but like width could end up +/-. This is just an off the top guess. Experimentation with length, width, height,  and placement is to be expected.

Simple rule of thumb. If it still hooks with the pads installed do not add height, You may find that it may try hooking and sliding. Try moving them to the rear .5 to 1 inch at a time until it either works as intended or still has turning issues, or are to far back. If so add 1/8 to height and move to front and start again. Shoot for approx 1/4 between top of pad to edge of sponson for gap. This will be a trial and error sort of thing.

Width, length, height, placement is all yours to play with. Keep at it and you will find the sweet spot.

Good luck

 

[Carl Van Houten]

What Bill has told you is good advise. There is a lot going on when a tunnel boat starts its transition into the turns and there are some boats out there that are ill handling due to a variety of possible design related issues. Not to imply that the W.O.F. boat you are planning to work on is one of these but for a design that is way off, nothing in the way of spin pads will transform it into a great turning boat so just be aware of that and don't get discouraged when trying different things that don't seem to help or that make things worse. You can learn a lot by experimenting with pads. 

-Carl

 

[riggerman]

Thanks for the great replies the turn pads may be a project in itself. Regards Andris Golts.

 

[Kris Flynn]

my personal experience is that if the blocks are doing nothing or too little (too far back or not deep enough) the boat hooks (water sucks tunnel roof down or water comes up over the tunnel/deck) in hard turns or when crossing a wake or rougher water.

If the blocks are too far forward or too deep then the boat 'power slides' once it breaks free while turning (hits a small wake for example) and usually results in the sponson sides digging in and the boat rolling over.  I helped a local racer who thought his boat was hooking, but a close inspection I noticed it was power sliding and dropping the nose, causing the rear end to come around making it appear to be 'hooking'...makign the blocks on his boat smaller/further back improved handling untill he found his next issue

I agree that around 30mm wide is a great starting number.  on my 31" hulls the rear edge of blocks is around 430mm and about 3.5mm from keelson (depth)

 

[Geraghty]

Thanks for the great replies the turn pads may be a project in itself. Regards Andris Golts.

I am probably going to regret this post but here goes.....

Andris......You have no idea how true your remarks are.....  In 1980 I was the idiot that first built and used the "anti-hook" [stumble blocks] on the bottom of the tunnel.... For about a year I chased tunnel boat hooking problems.....I was determined to get a tunnel that would turn left or right without a turn fin on the bottom of the boat.... Tunnels without a turn fins use the "inside of" the sponson inside wall as the turn fin .... The more dihedral you put on the sponson the deeper the sponson will sink in the corner......The width of the sponson bottom also determines how deep that sponson will sink..... [simple water 1.0 specific gravity displacement].......

A good rule of thumb is to place the rear of the anti-hook block 40 to 45% of the length of the boat measuring back from the front of the boat.....Where the rear of the block meets the sponson bottom a 2 to 3 degree positive angle of attack at that point must be maintained.....  1-1/4 in wide block is a good choice but other design parameters must be considered.....  As a general rule of thumb a wider block is better than a narrower block.... The 1/8" depth of the block I used was determined by the NAMBA rule that said no step on a tunnel boat bottom could be deeper than 1/8".....That rule was put in the NAMBA rule book to protect the Prather Lap Cat tunnel which had 1/8"deep  X 5" apart steps in their sponson bottoms...... If somebody wants to make point that any blocks that are more 1/8" deep and are illegal in NAMBA ....they may have a point........oh wonderful politics....

Curved bottom anti-hook blocks will experience Coanda water attachment to a curved surface and will actually pull the block down harder.....That coupled with the curved .....[front to rear] sponson bottoms and the curved  tunnel floor , the Coanda water attachment becomes even more force full holding down the tunnel nose in the corner..... The stumble block is a simple mechanical way to hold up the nose of the boat in the corner...   Without a block a boat will rock up on its nose while in the corner...when it rocks up enough the skeg of the foot comes out of the water and directional control is lost [no rudder]and around she goes so fast you cant even see it.... 

Go to You Tube and look up Coanda and Bernoulli videos and under stand the phenomena of water attachment and high and low pressure areas....You will quickly see how simple it really is.....   If you have boat , whether that be a tunnel , a rigger or a mono and the boat does something stupid in the corner  you can go to where the boat touches the water and find the cause...

There is more to this story but if it hadn't been for a cazillion frame per second TV camera I would probably be still chasing my ass on this subject.... RC tunnels and full scale tunnels are completely different animals ... 

Tommy Lee and yours truly have been all over this subject for years....."everything" in tunnel design is a compromise....

 

[Carl Van Houten]

There is a lot going on when a tunnel boat starts its transition into the turns and there are some boats out there that are ill handling due to a variety of possible design related issues. Not to imply that the W.O.F. boat you are planning to work on is one of these but for a design that is way off, nothing in the way of spin pads will transform it into a great turning boat so just be aware of that and don't get discouraged when trying different things that don't seem to help or that make things worse. You can learn a lot by experimenting with pads. 

-Carl

What Rod has said is correct BUT they will not necessarily make a boat work correctly as I have stated above. Keep testing and I hope you have great results!

-Carl

 

[Bill Britton]

Ya can't polish a tuyd, but you can roll it in glitter! 

 

[Mike Crawford]

Nice buddy say like it is as you DO

 

[Carl Van Houten]

I would say that we have all built a tunnel boat that needed to be rolled in glitter at one time or another...LOL. I remember racing some guys that had really fast boats but they would not make a smooth turn AT ALL! They would drive those silly boats by making three point turns and if you got under them in the turns your chances of getting TEE BONED in the side were really high.

 

[Bill Britton]

Jeeeezzzzzz. I wasn't referring to anyone's boat. It was a line from a movie. 

 

[JimAllen]

I'm just reading this, and I'd like to thank Mr. Geraghty for the education. That is a very good explanation of a no doubt complex subject that gets the point across quite well. I actually did go and watch some YouTube vids, and I get it. Thanks for sharing that.