Jerry's 1/4 Scale Tunnel

[ggillman]

Hi Jerry,

Just read your article in the August 2002 RCBM, Final Moorings on page 74.

Man that is one WILD lookin tunnel, the real one and the 44 inch scale version. Must have been very cool to hang out with the race team also. The cockpit is very different looking and the boat just turned out GREAT

Bet she really boogies with that 11cc K@B

You and Terry Rinker and the team look like ya got a couple winners there for sure!!!!!

Gene ;D

 

[Jerry Dunlap]

Gene,

The 1/4 Scale Rinker Tunnel has proven to be a really fun endeavor . The crew chief, James Chambers, and I correspond by e-mail quite often.

The boat is not true scale in tunnel width or amount of pickle fork. A 17' tunnel boat has about a 4' tunnel width, which scales to about 12" in 1/4 scale. The first 1/4 scale tunnel I was involved with was the DPI 1/4 Scale and it was very close to true scale. It was much too wide, trapped too much air and would blow off easily. The 1/4 Scale Rinker is 8 3/4" wide in the tunnel.

The pickle fork on the full size Rinker Tunnel is 18" that would scale at about 4 1/4" in 1/4 Scale. The pickle fork on my model is 11 1/2" - again to decrease the amount to air being carried under the boat.

This year I am running the boat with a K&B 91 with tune pipe. It runs a 1455 prop and I'm hoping to improve on my second place finish at last year's NAMBA Nationals. The boat was the fastest 1/4 Scale at last year's NAMBA Nats, but I had a receiver pack go dead and that cost me one heat and first place.

Jerry

 

[Kris Flynn]

Jerry,

Sounds like a great experience...cant say i have read it yet because over here in Aus it takes a few extra weeks to get over here so hopefully i will see it soon

Also do you have any pics of the boat at all, or of the real thing you are talking about?

Kris

 

[Jerry Dunlap]

Kris,

I have some color prints of the model and the full size boat. If you'd like me to mail a few to you, contact me using my e-mail address and I send you some.

Jerry

 

[GTR]

Hi Jerry,

With your years of practical experience designing and building tunnels do you think full-size tunnels don't scale down because of the tunnel width/tunnel depth aspect ration, or is it more to do with the light weight our models are for the power used to propel them that upsets the stability?

1200lbs v 300hp = 4lbs/hp or

8lbs(Guess) v 3.75hp(K&B .67 quoted figure) = 2lbs/hp

GT 8)

 

[Jerry Dunlap]

GTR,

I think it's probably more power to weight. I have no training in tunnel boat design - just lots of years of building model tunnels. Our first attempt at a 1/4 Scale Tunnel was the DPI Rolla Propeller boat - it was based on a Seebolt Tunnel. It looked great and ran like stinky stuff. It just packed too much air. My new Dunlap 29.5 WOF Tunnel has less tunnel width by 1/2" than the Dumas 3.5 Sprint - a 24" boat.

Jerry

 

[GTR]

Jerry,

Could you get the same result by keeping the tunnel full width but making it shallower? Does the deadrise angle on the sponson bottoms have an influence on how deep/shallow the tunnel is?

GT 8)

 

[Martin]

Hello Jerry

I have a Dunlap 27 built and running very nicely with a mod 3.5ss and want to build another, but this time 2 inches longer for CMB or Nova Rossi power. While I am altering the plans to add the length at the rear I was wondering if I should change some other things. It seems that with your experience with Mikes Villian S1 you might have changed the tunnel depth , width and deadrise for your new wof 29.5sc . Do you recommend changing these dimensions on the dunlap 27 plans and what are the optimum numbers do you think at this point. Thanks alot ........Martin

 

[Zach]

Jerry,

I bought the Predator 2 tunnel hull from aeromarine, I'm using the O.S. outboard .21, how would you set the angle of the outboard,

-Zach

 

[Jerry Dunlap]

Zach,

I'd recommened setting the c/l of the prop about 3/16" above the bottom of the sponsons with a neutral thrust angle. If the boat is too light in the bow, try adding a couple of ounce of lead to the front sponson tips. It the boat rides stuck to the water, kick the thrust angle back slightly to loosen the hull. I've never owned a Predator, but those suggestions work on most tunnel boats.

Jerry