A topic to think about

[Julio Almazan]

Hi:

I do not mean hooks and such...just simply getting the hydrodynamic lift correct. I found I had too much when going for 80mph. All the aero mods and bandaids did nothing...a few small ride pad tweaks and WOW. Look at how the JAE design has changed riggers. Mainly due to how simple it is and what it going on underneath. Do not get me wrong, aero is important, just expanding the subject a little.

... Kris is right too ...
I think it is the sum of a large number of factors to take into consideration.

 

[Carl Van Houten]

I don't disagree with either of you but you have to consider both or you will leave too much on the table. The Lynx is a round tracker boat and it has seen a single 74mph pass in Elizabeth City VA. with no bottom mods at all so there is a lot left to get out of the class that's for sure. We have recently decided to build a SAW 3.5 O/B tunnel boat.

 

[LohringMiller]

For an example of what aerodynamics does, look at this almost 200 mph boat. The twin rudders make it run straight and the rear wing lifts the prop and rudder out. This force is balanced by the very forward sponson step. If the tail lifts out too much, it looses lift rapidly as its angle of attack decreases and it gets out of the ground effect. The reverse happens as it gets closer to the water. The sponson lifting increases the tail angle of attack, lifting the tail as well.

Stability in tunnels is a lot harder since the wing and sponson step are in the reverse positions. That requires a careful balancing act.

Lohring Miller

 

[dr gary turner]

Need aero when pushing 80 and above with a hydro

For sure with tunnel hulls

 

[Carl Van Houten]

The reason I mentioned the 74 mph pass is to get people thinking about what this means. The Lynx bottom has 18+ degrees of dead rise. Now look at all of the tunnelboats that have been built strictly for SAW. The common thing you will see with all of these boats is the sponson bottoms are FLAT or a degree or two from it. Now, how can you get a boat with a deadrise of 18 degrees up to these speeds? In this case it's mostly done with AIR because in order to reach that speed very little of the sponsons can be allowed to touch the water.

I believe that the key to speed is a transfer of control. Your goal would be to transfer as much hydrodynamic control into aerodynamic control as possible but since we are not building airplanes we have to maintain a minimum contact with the water. I tell people that I want my boat to run like an airplane at the end of the runway. I will end my rant here. It is already proven that Aerodynamics is huge in model boat design and is not just for looks.

 

[Mike Luszcz]

I think the Leecraft SAW hulls were using zero degrees, or something minimal. When we ran the ML Boats in P&Q FE, the 30" tunnel was a stock, 17 degree ride pad, and the 40" tunnel was 15 degrees. I always wanted to try a SAW specific hull, but wanted my customers to have the same opportunity at records if they put their mind to it. Carl, are you planning an FE saw record, or are you talking Nitro 20? Just curious if I need to get out the drawing board, lol. Mike

 

[Wasted wages]

All I can say is that hydro above is SICK !!!!
200 MPH ? Anyone have video of the run?

One thought,,,, I understand physics to a point, but... is it possible that with the size of our boats and what we know about "real world" aerodynamics and hydrodynamics on full size boats, that not all of the laws of physics apply to our scaled down boats as we think they do?

I mean, if a 1/10 scale boat running 200 mph was scaled up to full size would it run 2000 mph ? At what point do things no longer apply as boats are scaled down to our models...?

Oh well, back to the original thread topic...

 

[Carl Van Houten]

Mike, I have always felt as you do and have enjoyed seeing what could be done with what I sell. Me and Talley I did mess around with a smaller version of a round track style pickle fork tunnel a few years ago that we called the STX and ran it in the 3.5 Sport class and although it was impressive for a conventional pickle fork it was by that time running against times set by a purpose specific SAW model. I don't know anything about FE so that is completely out. LOL I have drawn up a SAW 3.5cc tunnel that I would like to try. I am mulling over the final details of the drawings now and soon I will burn it and get started on it. I have a couple of things I need to do for my customers before I can get free enough to start on that project. It won't hurt to have the kit sitting in the shop though.

 

[Kris Flynn]

My SAW boats do not have flat bottoms...they are upwards of 8deg and thin ride pads.

I do have a friend who has a bone stock M11 FE doing 80mph with the same equipment as i used to go 84mph Ave. I have reached over 90mph now, but we have not had a SAW event for over a year, so no way of getting real numbers (timing gates).

A standard hull would have been easier i think, much nicer to get on and off plane and easier to run in less than perfect conditions.

Good luck with the design Carl, look forward to seeing what you guys can do!

 

[Carl Van Houten]

Kris, That is great! 90 is fast. FE has really come a long way over the last 30 years. I have decided to use 12 degrees on my initial boat to see if I can make that work. If I have to drop down I will but maybe I can get that to work well enough to get there. Yea the flatter you go the worse the transition will be. Hopefully we can get past this Covid crap and get back to the way things were.

 

[Kris Flynn]

12deg is a great number I think, for Nitro. FE Can use higher deadrise as they can 'push through' the extra drag.

 

[LohringMiller]

More information on Joerg's record holding hydro:


We spent a lot of time thinking about scaling when we built a model of our proposed full size electric hydro. Things like power and speed don't scale linearly with the size. As an example, horsepower required increases as the cube of the speed.

Lohring Miller

 

[Carl Van Houten]

I never get tired of seeing that. Hydros are just amazing. When you are able to eliminate all but the tub and two sponsons it opens a lot of doors. The tunnelhull however will drive you NUTS because you have all that added surface area that has to go along for the ride too.

Wasted Wages,

If you use a full size boat as a "go-by" you will build a model that will hardly be able to stay on the lead lap with modern round track models.

 

[Julio Almazan]

Hi:

I never get tired of seeing that. Hydros are just amazing. When you are able to eliminate all but the tub and two sponsons it opens a lot of doors. The tunnelhull however will drive you NUTS because you have all that added surface area that has to go along for the ride too.

I think we are mixing things ... one thing is the SAW, magnificent and spectacular but another thing is the tunnels.
Fundamentally two things: the turns and the length of the heats...
When I prepare a boat to compete in Tunnels F1 3.5 cc, I don´t think of only doing one pass in one direction and another pass in the opposite direction.
When I do it, I think about how it will take the curves, how it will behave with one or more of the same boats next to it ...
and the waves produced by the other boat?
Hydrodynamics is very important, but Aerodynamics too ...

 

[john v]

great post, tunnel gods keep on posting

 

[Carl Van Houten]

Julio, You are absolutely right to think that way. Round track boats have a wide range of task to complete to make each lap. Crossing wakes and keeping the boat and prop hooked up through the turns is all part of it but when you are getting ready to build a speed tunnel you can do things differently in some areas because you only have to line it up and punch it in SAW competition. Its fun you should try it if you haven't already.

 

[Kris Flynn]

that's fine mate, go ahead and organize your mount with Vic, and get him to send it with my stuff,

Hi:

I think we are mixing things ... one thing is the SAW, magnificent and spectacular but another thing is the tunnels.
Fundamentally two things: the turns and the length of the heats...
When I prepare a boat to compete in Tunnels F1 3.5 cc, I don´t think of only doing one pass in one direction and another pass in the opposite direction.
When I do it, I think about how it will take the curves, how it will behave with one or more of the same boats next to it ...
and the waves produced by the other boat?
Hydrodynamics is very important, but Aerodynamics too ...

This is a great factor to consider as to why certain hulls and motor packages work better in longer races in Europe/Portugal/Spain and other work better in short track course in Australia, Japan and USA. People do run all sorts of designs and they all do well, but in different parts of the race and depending on the conditions of the day. I know I would not choose a sub 30" boat for longer races (except the HTB 290, that thing handles the rough water SO WELL)...BUT having said that, the length is not the main factor! it just helps get a few of the important (to me!) features in the right spots (ie sponson tip height and also the transition angle/curve from ride pad up to the tips)

SAW and 2-lap boats are different beasts if they are designed to get the maximum speeds for their discipline. i cannot see a 2-lap boat being too much different than a tradition oval racing boat of modern design in the short track courses.

 

[Julio Almazan]

Hi:
Another thing to consider is that many of the hulls we use are not our own design, but rather from people who have spent a lot of time developing a winning hull ... let's see if I can explain myself with this photo ...

 

[Grimracer]

Like other "some" types of model racing it can be inspired by full scale racing.

Tunnel boats were one of those areas.. 1/8 scale RC cars started that way.. 1/10 scale off road... slot cars and many more. As we push for a win.. A lot of that gets tossed aside. (natural progression because I suspect the rules were loose to balance the intent)

Truth is RC tunnel boats were never listed (that I know of) as a scale or semi scale class. so we are where we are today. (not bad.. mind you.. its just hard to compare the two above.. you can easily see one was inspired by a full scale boat and the other not.. Again.. all good.

Having said this at some point we had (still have to I think) have a driver in an open cockpit or a window outline on a closed.. so.. there is that loose intent. (i have old model mags that show bunch's of tunnel boats and they are quite scale looking (in design and paint!).. cool stuff.. "to me"

Merry Christmas all!

Grim

 

[Carl Van Houten]

Good points. I am also glad that scale rules did not and still do not apply to the O/B tunnel class because if they did I would have never gotten interested in it. ( not bashing scale classes its just not for me ) I love the fact that we can explore our models capabilities with very few restrictions. Now that we are down to a couple of new "off the shelf" outboard engines to choose from, I wonder where the next five years will take outboards? Hopefully things will change for Nova Rossi and they will return and be able to once again provide engines and who knows in the meantime this situation may spur some innovational items while people are waiting for things to return to what used to be normal.

I have crested the 60 year mark (62 in June) and I am not sure how many more projects I have left in me. I can say I have enjoyed this sport and I hope that now that there is a vaccine available maybe things can return to the way they were. Who could have ever guessed last fall when we flushed out our engines for the winter that our lives would or could be so drastically changed by something 10,000 times smaller than a grain of salt?

I feel sure that there are enough engines and parts floating around out there to keep things hopping along fairly good through the next couple of years so I look forward to that. I didn't mean to get off the topic so bad but this stuff has been on my mind and well, this is my thread and I guess I could talk about growing tomatoes if I wanted to. LOL

I want to see some new tunnel designs this year how about y'all?