Best set-up for best cornering speed

[John Finch]

Don,

I had the same problem and fought it for 4 years before I figured it out. If it is happening just before the apex of the turn and the boat just blows off the water for no reason......I may know what it is. Raise the right rear sponson a quarter inch and the problem may go away. Never saw this problem with nitro but gas is a different deal with those heavy gas engines and pipes sitting up high on the tub. Let the boat lean into the corner. I made the change and never had the boat do it again. Again.....it is not a fix for every boat. Try it. You may like it.

John

 

[DON MAHER]

John,

I would if I could, but this is a true 3 point, no rear sponsons or center shoe. And yes it is at the apex of the turn or very close.

I am going to try moving the fin back and a little more tuck and see if that will help? I think this may allow the front to "Float" a little more freely. We'll see!

John, just want to thank you for all your input on this and a lot of other subjects over the years!

Don

 

[dwilfong]

https://youtu.be/cbTWd6kJYjQ

look at this testing video and look rely close at the 3 min mark in the middle of the corner and in the same corner next time around.

Tell me what you see?

 

[Marty Davis]

If you are looking for "proof" of flexible turn fin working just look at a SGX turn fin.

Also take note of the boom tubes that also flex.

When testing this thin flexing turn fin. I also made it longer front to back making the pressure point larger on the fin.

I did a test buy putting a backer on the fin as I was under the impression that it needed to be stiffer.

I did this at a race in west palm beach. Well the boat was very dartey and not controllable as I would like.

Those watching me run the boat asked what happened to the boat it was so obvious.

That was a small pond to say the least as those that have run there know.

Well I put the boat back to the original set up with out the backer and took 1st place for the weekend.

The next step was the rudder. I had a problem the boat was FAST. When coming in to a corner at full tilt and letting off the throttle it would stop turning. No mater what I did it would just not turn if you let off the throttle if you ran in the corner fast.

Marty and many there at the race witnessed this at one race in Brandon first hand. The boat was smoking fast but was unpredictable in the corners if you had to throttle down.

Hence the large rudder idea. Steve wood was able to make me a very large rudder at my request. After installing this on the boat it was like night and day.

So this is what I have done to get my boat to drive as I like it.

This may not work on a different style boat or a marginally fast boat may not need this to run.

But on a FAST SGX with my driving style this is what has worked for me.

David:

I think that the reason that the boat was unpredictable in the turns is because of the flex of the fin.

I want my fin and support system to be as RIGID as possible with zero flex if possible. When you change the angle of the working part of the turn fin, strange things happen and you get unpredictable results.

 

[Marty Davis]

What was the Boss boat Ron Hubbard and Norris Sparks were running? Different boat same name? Just asking.

It was not one of mine. I am not aware of anyone else using the Boss boat name except one guy in the LA area that was building gas boats some years back. Maybe Marty will chime in and help us on that one....he is from the area where those guys ran.

Charles

As Norris Sparks said, he was a VERY successful Rat Airplane Racer and he called his planes Boss Planes. He always built and designed his own riggers (20 and 40) and sold some to others. The boats were very successful and won a lot of races. He is from Cincinatti and still occasionally goes to the lake to test. He is one of the VERY best engine people that I know and I consider him one of my best friends. We talk all the time about ideas. He is also the machinist that built our physical dyno at Ackerman's shop in Indy.

As for the West Coast Boss boat, I also know a good deal about it. Steve and Jack O'Donnell came to Indy many years ago with 60 and 40 boats. The race that they came to was one of the first Hydro Masters Events. I remember that on first hitting the water, everyone was amazed at how well the boats turned. They looked like thy picked up speed in the turns. Gregg Huey set the 40 oval record during qualifications with his Crapshooter. About an hour later Steve broke the record with his Boss. Steve qualified for the A Main with both boats.

His ability to turn made me get to work. Along with Ed Lackey and some of my other close friends we started on a plan to design and develop our own turn fins. That took years to get to the level we wanted to be, but the physics principles were repeatable and could be documented. Brian Callahan was very helpful in the repeatability by calculations of the correct fin depth, width, angles, etc.

One additional thing that nobody has touched on is the angle of attack of the boat/sponsons. If the boat runs super loose, the turn fin won't work well. The boat needs to be down on the water in a snug condition. Not tight, but also not very loose. If the boat is very loose the only way to get the effect that you want is to make the fin bigger = DRAG.

 

[Chris Wood]

I know when testing boats i built before production I tried many turnfins and size and thickness. And I can tell you the thickness for me played a huge part

I always wanted to make one out of spring steel but never found a way to bend it. I know it rust but I take care of stuff enough it would be ok. And I truely think that stuff would work great for fins. But that is just me. Personal opinion

I also know when doing fins the more I heated up to soften the alum to bend the worse boat became in darieness. I later quit heating and found a way to make them without.

Sent from my iPhone using Tapatalk

 

[Terry Keeley]

Ran CF fins for years but have discovered Ti, works great. Biotch to bend tho!

Very stiff and super light hanging on that right sponson where you really don't want the weight.

 

[John Finch]

John,

I would if I could, but this is a true 3 point, no rear sponsons or center shoe. And yes it is at the apex of the turn or very close.

I am going to try moving the fin back and a little more tuck and see if that will help? I think this may allow the front to "Float" a little more freely. We'll see!

John, just want to thank you for all your input on this and a lot of other subjects over the years!

Don

Thanks Don. Let us know.

John

 

[gil sonsino]

Thanks guys for such informative thread! Gill

 

[Scott Tonak]

Ran CF fins for years but have discovered Ti, works great. Biotch to bend tho!

Very stiff and super light hanging on that right sponson where you really don't want the weight.

Thin titanium fins I'm sure work really well with smaller/lighter boats. However, for large gas boats like the Backlash sport hydro, I found that the titanium fin @ .060 thickness flexed way to much for my driving style to the point of letting the boat unhook, barrel roll, and eventually bent the fin beyond repair.

Gonna try a new Randy Rapedius "Titan" fin on a smaller gas sport this year. See you at the time trials Terry!

 

[dwilfong]

Scott

Was the fin a curved bottom fin or just a strait angle bent fin?

 

[Terry Keeley]

Ran CF fins for years but have discovered Ti, works great. Biotch to bend tho!

Very stiff and super light hanging on that right sponson where you really don't want the weight.

Thin titanium fins I'm sure work really well with smaller/lighter boats. However, for large gas boats like the Backlash sport hydro, I found that the titanium fin @ .060 thickness flexed way to much for my driving style to the point of letting the boat unhook, barrel roll, and eventually bent the fin beyond repair.

Gonna try a new Randy Rapedius "Titan" fin on a smaller gas sport this year. See you at the time trials Terry!

Ya we sure saw that up close and personal didn't we!

I use 0.050" for my 40 boat and 0.063" (1/16") in my single 90 but for a heavier gas hydro I bet 0.075" to 0.090" would work better.

I think Randy's gone a little thicker, no?

 

[Randy Rapedius]

Ran CF fins for years but have discovered Ti, works great. Biotch to bend tho!

Very stiff and super light hanging on that right sponson where you really don't want the weight.

Thin titanium fins I'm sure work really well with smaller/lighter boats. However, for large gas boats like the Backlash sport hydro, I found that the titanium fin @ .060 thickness flexed way to much for my driving style to the point of letting the boat unhook, barrel roll, and eventually bent the fin beyond repair.

Gonna try a new Randy Rapedius "Titan" fin on a smaller gas sport this year. See you at the time trials Terry!

Ya we sure saw that up close and personal didn't we!

I use 0.050" for my 40 boat and 0.063" (1/16") in my single 90 but for a heavier gas hydro I bet 0.075" to 0.090" would work better.

I think Randy's gone a little thicker, no?

Originally I made my Titanium fins from .063 however many did not like the flex so I switched to a slightly thicker material.

My current fins are .071 which appears to be perfect.

 

[Scott Tonak]

Scott

Was the fin a curved bottom fin or just a strait angle bent fin?

It was a curved bottom fin.

Ran CF fins for years but have discovered Ti, works great. Biotch to bend tho!

Very stiff and super light hanging on that right sponson where you really don't want the weight.

Thin titanium fins I'm sure work really well with smaller/lighter boats. However, for large gas boats like the Backlash sport hydro, I found that the titanium fin @ .060 thickness flexed way to much for my driving style to the point of letting the boat unhook, barrel roll, and eventually bent the fin beyond repair.

Gonna try a new Randy Rapedius "Titan" fin on a smaller gas sport this year. See you at the time trials Terry!

Ya we sure saw that up close and personal didn't we!

I use 0.050" for my 40 boat and 0.063" (1/16") in my single 90 but for a heavier gas hydro I bet 0.075" to 0.090" would work better.

I think Randy's gone a little thicker, no?

Yeah, I've tested Randy's new very slightly thicker titanium fin and it performs really well on the Backlash.

 

[John Finch]

I have a Randy fin to test this spring and they are sharp! Ok, we have talked about turn fins but what else is involved in making a boat turn faster? I will start out by saying weight distribution. I have experimented a lot with moving the front sponsons forward and back on the tub to see what the results are. First off, I found that the more weight on the sponsons the more they stick to the water and the more the prop walks the boat into a right turn. Simple fact of physics. If the front sponsons stick the prop blows out of the water walking the transom to the left. In one experiment I ran a rigger that veered into the course badly on acceleration from the start line during heat racing. I moved the sponsons forward to move the weight off the front sponsons to see the boat track straight on acceleration as the prop stayed where it should be. That is what we do for SAW trials by the way. We run the sponson more forward. Mostly to get more weight on the prop. So, the same weight distribution forward and aft affects turning as well. Too much weight distribution to the rear of the boat makes the front sponsons dance and they don't plant well for cornering. There is also sponson width, AOA, rudder placement, rudder design and size, and props we could talk about.

John

 

[Mike Hughes]

I have build a few tit fins. The nice thing about the tit is that when it does flex, it comes back to the orginal shape. It very hard to bend. The larger boat need the thicker material. I did a .90" one once. Needless to say a vice and sledge hammer was involve and getting it to bend. I prefer to build them out of 7075 now. Since boeing surplus closed I have not been able to get the tit real cheap. Still have a little stash for my use.

 

[Mike Hughes]

John,

How much distance did you have to move them forward? Just curious, because built a new set for my twin with this in mind. Have not been able to do any testing with them yet.

 

[dwilfong]

You can get Ti sheets on Ebay for a good price.

 

[John Finch]

I tried one inch more forward with the sponsons then 2 inches forward. The best setup for that boat was 2 inches more forward on the front sponsons. The boat then tracked straight on the course on acceleration. You could get the same results with wider sponsons to keep them from sticking. It was Don Pinckert who gave me the tip on wider sponsons years ago. I now prefer wider sponsons with the engine more forward for better turn speed. During that testing I also tested the tapered rudder and noticed if using a tapered rudder that the leading edge must be perpendicular the water. If the trailing edge is perpendicular then the rudder is in effect tilted back, which lifts the prop and makes the boat turn into the course.

John

 

[DON MAHER]

John,

You are right about the wide sponsons. The boat in my earlier post has a very wide stance (21-1/2") with alum tubes (5/8"x.058 wall) that are mounted "old school" bolted in the tub with slotted tub sides for adjustment. This boat is 12-1/2lbs. When I went from 18 to 21-1/2" the alum tubes would bend after 2-3 laps and the boat would not handle right at all!! The fix for this was to lnstall 1/2" solid rod inside the 5/8" tubes and extend 2" beyond the tub. Fixed the bend, but added about 4oz to the front and as you know changed everything again! LOL

Don