oldstuff

Typicallly the "Cat" name came for offshore from Europe. A Cat depends more on Hydrodynamics then aerodynamics, where a tunnel boat is on the "bubble". The offshore Cat has changed into a tunnel boat over the years due to, increased power, advanced construction and materials. I belive if you were to measure the combined width of the sponsons for a Cat, that dimension would be wider then the tunnel width, as opposed to a tunnel boats combined sponson width being less then it's tunnel own width.

There is more details, but the evolution has been outstanding.

glassdave

iTrader: (1)

Thanks, that explains the connection to the newspaper article. I imagine it was a hand full. In the pic it appears to have cable steering running down the sides of the deck to some type of wing plate, a very very long cable arraignment. Its a cool pic to hang in my office and its signed.

T2x

Both are Cats... A catamaran is any twin hulled boat (sail or power....Add a third hull and it's a tri-maran.

A tunnel boat is a catamaran with "assymetrical" sponsons.

The older designs (and one new one, Deep Vee Cats) have/had symmetrical sponsons.

T2x

oldstuff

In the mid 80's, OPC tunnel boats started having 2 different sponson, due to the left turn. Some offshore boats had different sponson due to engine torque.

Don't you think the concept has changed? The Cats today are more like scaled up OPC boats. What do you think?

T2x

There is nothing new under the sun. The original Jones and Cougar hulls back in the 70's were, in fact, scaled up from their earlier OPC designs.....and Jones' OPC designs were merely his cabover hydros with the sponsons lengthened to the stern. I raced a 1977 Molinari with one sponson altered forward to make left turns. it put me in the infield 2 times in the first and only race I tried it in. Later we put it back to its original form. I am not sure about any offshore cats with different sponsons , but I have seen offset cockpits and unequal sponsons in Unlimited hydros.....

Todays Offshore cats are not very different from the early designs with two exceptions.

1. They are MUCH lighter due to newer materials
2. The tunnels tend to be wider

At the end of the day the increase in power and prop technology is the main reason the current cats are going so fast. When we built the original Shadow cat we felt like 115-120 was the absolute maximum speed potential. There's a guy in Louisiana I believe who has brought his up to over 150.... proving it's all about the power and propulsion.......

There's a lot of mumbo jumbo around the "design skills" of some of our current cat builders. Give me a builder with the most years of experience....because in high performance boats .....the top guys in the field learn a lot more from trial and error....then from computers.

T2x

oldstuff

A tunnel hull is a type of boat hull that uses two typically planing hulls with a solid center that traps air. This entrapment then creates aerodynamic lift in addition to the planing lift from the hulls. Many times this is attributed to ground effect. While modern testing has shown that ground effect in aviation is not a matter of air trapped between the wing and the ground, but rather a result reduced drag created by the lift of the wings, this evidence is inconclusive as applied to the marine environment.

Tunnel hulls are distinguishable from other catamarans by the typical close hull spacing and solid deck in between the hulls.

After much real life testing and at the convention in Trondheim, Norway - 1989, ground effects in contained form became an applied science.

There is more about how Reynolds Numbers fall into this subject, but it's a long science. You are 100% correct, All the years of trial and error proved that it is a science and not art form.

Oldstuff

AppSysCons

Reynolds Numbers, that is not something you see every date here on OSO, but that brings me back to my days in fluid mechanics.

It is actually a way to quantitatively compare, as a ratio, the two primary forces, inertial and viscous, in a specific flow condition. I remember lots of pages of discussion in my paper on transport phenomenon, regarding laminar flow, boundary layers, transition layers, and turbulence, all correlated to changes in the surfaces, expressed with Reynolds Numbers.

Very dull tedious stuff at the time...who knew...years latter...knowing this stuff makes you understand how we go so fast.

No question, there is allot of science in how we go fast.

Trial and error or science, they both get my vote.

Cool thread!