Tunnel Design Tech

[GTR]

Hi everyone,

Could some of the legends on this forum share their wisdom with us and let us in on design secrets? like the effect that different deadrise angles have - why you have a favourite. Tunnel heights & widths. Oh yeah the benefits of an offset fuselage section.

I know you can't let us know all your stuff or we all go off and be great/prolific designers like you - as if that were possible.

GT ???

 

[Grimracer]

Big G

I don’t know if I fit this question but let me see if I can help. First I do not document every aspect of my hull designs. However I did do a research paper in tunnel hull design and I could e-mail it to you if you can open a Microsoft Word doc. Otherwise this could take quite some time. But lets start with deadrise. First if you are a member of the IMPBA i do an article every quarter called "Tunnel Tech" In the June 2002 issue, here is the link. ( http://www.impba.com/index3.html ) It is just a short blurb but it gets the point across. Also the illustrations in the article do not show up in the web page but shows angles between 13 and 16 degrees.

Overview of design:

Tunnel Depth: I like mine around 5/8" to 3/4" on a 21 boat.

Deadrise: I like 15 degrees

Cant: I like 0 degrees

Sponson Flat Section: I like 30% "By the way I’m anti rocker"

Tunnel width: Undecided

Center Section Offset: If I told you I would have to kill you so that the secret is safe with me!

Grimslayer ;D

 

[billr]

Could you explain center section offset? That is a new term for me.

Billy R.

 

[Slideblues]

To me is like the dirt track cars,the center is moved further to one side to aid in cornering.

Slide 8)

 

[TomMoorehouse]

one of mikes pics:

 

[TomMoorehouse]

one more for ya guys that grim sent a while back....

 

[Ron Olson]

Center section offset was used on the DPI 3.5 tunnel that Jerry Dunlap designed or had his hands in. It is offset to the right to compensate for engine torque. Jerry, correct me if i am wrong. It wasn't very much, like 3/8".

 

[Jerry Dunlap]

Greetings,

All the developments I've made on model tunnel boats, and I built my first one in 1977, were basically trial and error - or "borrowing" an idea from another boat. Over the years, I think a few ideas have proven successful:

1. Sponson dihederal of 15 degress.

2. 30 % flat sponson running surface at back the boat.

3. Not much rise in the floor of the center section.

I don't think there's any real "secrets" in model boat design. Those of us who do design model tunnel boats might have some preferences. When I brought out my Villain to it's first race, guys thought it just another one of my boats. It had a Dumas 7.5 cowling cut to fit and was built from wood.

Since building the Villain, I have built three WOF hulls using the offset motor. The boats all corner great - but then my Dunlap 27 with a centered motor also corners pretty well.

Ron, you might be right about the DPI 3.5 Tunnel. But, I really don't remember. There's probably someone out there who has one.

Jerry Dunlap

 

[TimD]

Since building the Villain, I have built three WOF hulls using the offset motor. The boats all corner great - but then my Dunlap 27 with a centered motor also corners pretty well.

Jerry,

Of the three boats you you mentioned since the Villain, Did you try altering the offset amount at all or built them all the same? I won't ask by how much 'cos I think Grimmy might be unhappy about that little secret getting out there ;D ;D

Tim.

 

[GTR]

Hi guy's,

As a lot of design seems to be preference - I noticed JD likes spray rails and the villian doesn't have them have you guy's noticed any real differences with or without. JD in your hotshot sprint 7.5 design you have included ramps/steps on the sponson tips - do you think they help?

How about crown on the top of the sponsons - any noticeable effect in cross winds? Not trying to steal all your great ideas but very interested in the evolution of design ideas. I have a heap more questions but can't pester you all to much.

Grim being in Australia I don't have access to your information published. Maybe you could post it in the articles area for all to find.

cheers

GT 8)

 

[Jerry Dunlap]

GTR,

I don't think those front steps/pads on the sponson tips of the Hotshot 7.5 Sprint do anything. I'm not even sure why I did that :-. I probably haven't run a 7.5 Sprint hull in 10 years or more.

Jerry Dunlap

 

[TimD]

Hi guy's,

How about crown on the top of the sponsons - any noticeable effect in cross winds? Not trying to steal all your great ideas but very interested in the evolution of design ideas. I have a heap more questions but can't pester you all to much.

GT, Yes it does make a difference - so does cowl height. Played with this a little as the earlier f1-11's were affected by cross winds. When we used to race at Cables Waterski Park in Penrith :'( :'( the wind always seemed to blow down the course so you would really notice any changes we made within a lap or two.

my 2 cents.

Tim.

 

[GTR]

Hi guy's

I just asked about deck crown as the earlier JD designs - original WOF, Sprints, Dunlap 27 all have considerable crown. Newer design WOFs are almost flat across top, villian somewhere in between. Cowlings on models are much lower proportionally than 1:1

GT ;D