Race hull design

I race Whitewater Jet boats and am looking for (software, test tank or?) ways to test and/or design and improve our race hulls and propulsion systems. We are jet propelled and the hulls are a modified tunnel design. At times, we race in some big white water and other times we are in as little water as 3 inches deep (or less if we make a mistake and hit a gravel bar). Speeds vary from 90-140 mph so both water and air dynamics are very important. Attached is a link to some video to give you an idea as to what our sport is all about.


http://www.youtube.com/watch?v=IMlw9bcvsFI&feature=youtube_gdata_player

Thanks in advance for any assistance,

Jesse

 

You need to get in touch with Jim Russel. Get a log in to the Scream and Fly forum and look there. His book "Secrets of tunnel boat design" is the bible for what you are doing. He also has a software design program that can do what you need and it takes into consideration aero as well as hydrodynamic lift and drag.

 

Thanks for your reply. I have looked at Jim Russels web site but I wasen't sure how helpful his software would be. Have you or anyone you know had any experience with it?

 

No I haven't but perhaps you should call him or email him. He is very responsive and will tell you if what he has will work for what you want to do.

 

Hi Jesse

Those boats are on the edge of the envelope as such. Therefore existing software will really be of no use. Almost all software available will be using “known” theory/technology. Therefore they would tell you what you already know.

What you really need to do, to progress, is go back to basics. What is the SOR, or design brief…what limitations, owing to rules etc are there…in other words, what is the max and min of everything you are allowed to do under race rules. This is your starting block.

Once you have established this, it provides a platform for further investigation into what technology there is out there that can provide XXX or is an ongoing research field in its own right. If none exists, then how can you create such technology….the usual way, research.

If you wish to go a software only route, you’ll need seriously high end (ie expensive) software but it still needs to be validated, because your at the edge of it limitations. Which means research again.

The type of gains you’re looking for wont come over night and will require a lot of research and looking at ways of improving existing technology, all piecemeal, that once brought together as a whole package…a boat….is an improvement.

Without doing looking at the limitations placed upon you by race rules (and anyone here contributing would need to know them), and doing your own research, the gains you’re after will take much longer.

 

I agree totally with you Ad Hoc. I have seen the video on You Tube: impressive!!! The boats have practically nothing in water except the jet intake with a little piece of hull (that's already known with the racers) but they run on pretty difficult rivers.
I do not see any commercial software able to deal with such designs. Tunnel boats use propellers and that's a very big difference.
It's almost virgin ground. I smell that, within the race rules, there are 2 paths to explore:
-waterjet global efficiency with the hydrodynamics of the intake.
-aerodynamics and stabilisation of ground effect flight as these boats are getting rather similar to a WIG. They could be treated as a a lifting body with aerodynamics controls.
A lot of research in view...

 

Hiya,

This is a really interesting topic and it is right up my alley.

One thing I that will be important is direction of travel and the fact that these boats spend quite a bit of time sideways.

I think efficiency gains could deffinitely be made in the inlet duct to the jet as the flow entering these often separates from the front edge of the duct creating a total pressure distortion entering the impellor. This problem can be aleviated by using boudnary layer trips at the inlet to the duct. I would have though this problem would be made worst when cornering as the ducts will most probably have been designed for straight line travel?

Covering the upper surface of the boat around the engine bay as much as possible to create a flat and smooth surface will help as otherwise you effectively have a re-circulating cavity. Only the exhaust and air intake need to come through.

Creating a 'tear drop' profile begind and prominent structures will reduce drag and improve aero efficiency. This could be done behind the driver/navigator and an engine inlet could easily be encorperated. When doing this you must make sure not to increase the effective frontal area of the boat.

What water is being ejected from the side of the boats? Coolant? Could this be channeld to the rear as pooring out the side will mess up the flow around the side of the boat - increasing its drag.

Anyway just some thoughts, which I can provide more details on if necessary!

Hope it helps

 

Jesse - you might want to check out the AeroMarine Research book and "Tunnel Hull Design" software. I think his work was developed specifically for your type of application. There's alot of guys that seem to have used it for designing on the 'edge' of performance and it seems to account for 'ground-effect' on tunnel applications.