Go Back  Offshoreonly.com > Technical > General Q & A
Tunnel Hulls, Wings and Ground Effect >

Tunnel Hulls, Wings and Ground Effect

Notices

Tunnel Hulls, Wings and Ground Effect

Old 03-27-2002, 11:35 AM
  #21  
Platinum Member
Platinum Member
 
Join Date: Oct 2000
Posts: 1,297
Likes: 0
Received 5 Likes on 5 Posts
Default

Tomcat-
Good info. I guess that's one reason why George Linder & T2X put driveshafts and engines forward on the Shadows/Chris Cats. They seemed to be less likely to "blow-over" than other designs (of the time).
Dueclaws is offline  
Old 03-27-2002, 12:56 PM
  #22  
Registered
 
Join Date: Apr 2001
Location: Glens Falls, NY
Posts: 131
Likes: 0
Received 0 Likes on 0 Posts
Default

Ahhhhhhhhhh!

Here we go again.

The center of lift of some aircraft may be behind the CG (who knows) but it feels like it is not. When an aircraft is overloaded (people, fuel, cargo) the ones i have flown (5000 hrs.) feel like more down trim is needed. I would have guessed that the center of lift was in the wing section somewhere as it is the structure that is providing the lift. (Fuselage also, but much less)

The reason an aircraft "self corrects" for attitude is when you are going "downhill" the lift increases with speed and picks the nose up. Uphill is the opposite. If it were due to some kind of CG location it would only self correct EITHER going up OR down...not both. But it does both. So much for that theory.

The center of lift of a cat (i can't speak for tunnel hulls like F1 boats) is most likely forward of the center of moment. the problem is that with different attitudes the center of lift migrates. If the nose is high it not only probably moves forward, but much more importantly, it gets very large. Hence a potential blowover.

I talked to Keith Homes after a spactacular blowover in the Supercat "Cat Can Do" in a Washington, NC kilo run and he said "Ted, i backed out as soon as that nose lifted the slightest bit more than normal, and the thing just kept riding on the air cushion pickng the nose up more and more"! Tells me the force got pretty large as simply moving the lift around a bit wouldn't have picked the boat up like it did. Some say it was 40' to 50'in the air at one point, and maybe the highest point was!

Ted
Ted Zoli is offline  
Old 03-27-2002, 08:59 PM
  #23  
Registered
Thread Starter
 
Join Date: Feb 2001
Posts: 1,519
Likes: 0
Received 29 Likes on 8 Posts
Default

Ted - Got your message, no problem. I have a question for you though. I am looking at a 32 SKater rigged for triple outboards, no power. I know the boat and it always rode a little too flat for my eye. What I would like to know is how you would expect this boat to run with a pair of 300x. Is 100mph achievable and would the reduced weight in the stern cause problems?
tomcat is offline  
Old 03-28-2002, 06:19 AM
  #24  
Registered
 
Join Date: Apr 2001
Location: Glens Falls, NY
Posts: 131
Likes: 0
Received 0 Likes on 0 Posts
Default

Hi again,

There are a lot of people on the board more qualified than i am to answer this question. I don't think a 32 with twin 300's will do 100mph...more like about 94 to 96.

32's run very flat...flatter than the 36's just from observation. Whether they really run flat, or it is a visual thing the way the boat is designed i'm not sure.

One thing for sure that by proper rigging you can keep it from "rubbing its tummy", another words get a little bow lift to get some air. It is easier in our experience to do that than lift the stern.

Obviously, triple 2.5's are going to weigh more than two 300's. I would absolutely call Peter H. at Skater and ask him the weight and balance questions. He will talk to you and he will remember the boat. He is amazing! The number is on their web site i believe but they are in Douglas, Michigan. It is possible that fuel tank location will be an issue...not easy to fix but doable.

The 2.5 consumer moters have the same warranty as the 300's in case you want to go with 3 2.5's. There are some good buys out there.

Good luck.

Ted
Ted Zoli is offline  
Old 05-20-2002, 10:04 PM
  #25  
Registered
 
Jimboat's Avatar
 
Join Date: May 2002
Location: Canada
Posts: 43
Received 1 Like on 1 Post
Default Lift in Tunnel boats

Actually, the lift for a tunnel boat DOES come from the "wing", just like in an airplane. The tunnel boat does it more efficiently due the it's proximity to the "ground" (water surface). The performance of the "wing" is dependent on several parameters, but primarily height above water (h/c); tunnel width/wing chord length (higher aspect ratio is better); and wing thickness (t/c)....and of course the angle of attack. The trick to tunnel boat design is the complex balance of hydrodynamic lift (sponsons) and aerodynamic lift (wing in ground effect).
These references may help: Tunnel Boat Design book
Tunnel boat Design software
Jimboat is offline  
Old 05-21-2002, 09:35 AM
  #26  
Registered
 
Join Date: Jan 2001
Location: PA and MD
Posts: 1,461
Received 2 Likes on 1 Post
Default

JimBoat- Great to see you on OSO. Your website is great. There is a difference between a tunnel/surface wing and an airplane wing. Due to the clossness of the ground the surface wing can only lilft what? max 6' or so. Teach us more.
cobra marty is offline  
Old 05-21-2002, 10:05 AM
  #27  
Registered
 
Jimboat's Avatar
 
Join Date: May 2002
Location: Canada
Posts: 43
Received 1 Like on 1 Post
Default Wings in Surface Effect

A wing in ground effect works exactly the same on an aircraft as it would for a boat. The proximity to the "ground" increases the effectiveness of the Lift/Drag curve - in other words, the closer to the surface, the more lift (also more drag). The proximity is usually measured as a function of the "Height" to "Chord" (wing length) ratio. Most Tunnel boat designs see a h/c ratio of about .04 to .05. Lift will be generated by the "wing" at any Height, but as the h/c increases, the enhanced benefits of ground effect diminish. As the h/c ratio reaches .1 the L/D curves will begin to more closely resemble a wing in "free flight".

There are also other design features that can influence the aerodynamic performance of the "wing" in a tunnel boat - tunnel width, wing camber or shape, wing thickness - all these can impact Lift/Drag significantly even without changing the h/c ratio. A built-in "angle of attack" (sometimes improperly referred to as "packing more air") is an easy way to improve Lift too, but will have equally dramatic effects on the dynamic stability of the hull.
Jimboat is offline  
Old 05-21-2002, 01:38 PM
  #28  
Registered
Thread Starter
 
Join Date: Feb 2001
Posts: 1,519
Likes: 0
Received 29 Likes on 8 Posts
Default

Welcome to OSO, Jim! I live on Lake Simcoe about 2 hours away. I never realized you were so close until I read your ad. I hope you don't mind answering questions. We need a resident expert on this subject. I've got one or two, but I'll post them as new topics sometime.
tomcat is offline  
Old 05-21-2002, 10:53 PM
  #29  
Registered
 
Join Date: Feb 2002
Location: Honeoye, NY
Posts: 763
Likes: 0
Received 0 Likes on 0 Posts
Default

Bob & Dave Switzer of Chrystal Lake Il. built true "wing " hulls, first wooden in the early 60's then glass versions later in the 60's with the last built in the early 70's. They were two narrow step hulls with a small cockpit in each side connected with a true wing with a mechanicaly controlable flap. Twin outboards for power--as much as you could get. They won a lot of marathons and set a lot of records back then. I ran twin worked 135's with SSM's on mine at WELL over 100 mph which was real fast in those days. A truly amazing ride, like nothing else you've ever experienced. Real noisy in the cockpit cause of the water dumming on the hull till you get to a little over 80 then it flys, all the noise stops and you pay lots of attention to flap position. Of course you can't steer it till you drop it back into the water again. I'll see if I can dig up some pics of the old critter. Not exactly what you guys are talking about but it was a TRUE flying boat. --- Jer
jpclear is offline  
Old 05-22-2002, 11:00 AM
  #30  
Registered
 
Jimboat's Avatar
 
Join Date: May 2002
Location: Canada
Posts: 43
Received 1 Like on 1 Post
Default Switzer 'Wing'

JPClear - You're right on target with your example of the Switzer wing from the 60's. I've had alot of good discussions with Bob Switzer about the "good ol' days". The Switzer wing was a true tunnel hull that used aerodynamic lift to the fullest. It was by far, the fastest straight-line hull design in production at the time. It had symmetrical hulls, however, so while it had a nice ride in rough waters, it was very difficult to turn. The introduction of asymetrical hull shapes, that each had a chine and shear, really improved turning ability, and cleared the way for a major breakthrough in acceptance of tunnel boats in more applications. (The book on 'History of Tunnel Boat Design' chronicles all of these developements.) I've got some pictures of Switzer wings that I can post if anyone's interested. I'd love to see your originals, though!

Last edited by Jimboat; 09-19-2006 at 01:49 PM.
Jimboat is offline  

Quick Reply: Tunnel Hulls, Wings and Ground Effect


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.