TBPNews #60 - May 13, 2004
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>>>>>> Tunnel Boat Performance News >>>>>>>>>>>>>> (now over 4800 members!)
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In this issue: 
1) High-speed ferry draws a big crowd on its arrival in Lake Ontario
2) Land N Sea opens Houston center
3) Average price for new boats up in 2003 
4) CAT DRIVER DIES DURING TESTING
5) Jimboat writes Features in HotBoat & World of Powerboats mags
6) 'Powerboat' magazine - Save 52%! 
7) ** NEW ** 'Tunnel Boat Design' Software - Version 7.5
8) FEATURE ARTICLE - What a drag!-Trim angle & engine height reduces drag, increases speed
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1) High-speed ferry draws a big crowd on its arrival in Lake Ontario

ROCHESTER, N.Y. (AP) -- A five-story-tall car ferry will soon be darting across Lake Ontario to Canada at over 50 mph. A few thousand people lined the pier for their first glimpse of the Spirit of Ontario 1, an Australian-built, twin-hulled catamaran that could be the first of several deluxe, high-speed, car-and-passenger ferries plying the Great Lakes.   The round-the-world voyage from a shipyard in Perth, Australia, hit a low point April 1, when the ferry sideswiped a pier while docking in New York City and spent days under repair.  Sometime in May, the ferry will begin carrying as many as 774 passengers and 220 cars three times daily between Rochester and Toronto. Fares are $28, and $40 for most cars.
 
The shipbuilder Austal Ltd. bills it as the world's most powerful, diesel-powered catamaran.  It will make the lake crossing in about two hours and 15 minutes at up to 55 mph. The 171-mile road trip to Toronto usually takes three to four hours and far longer when there are miles-long backups at the border near Niagara Falls.   Two more high-speed car ferries will be launched in late spring -- one in Alaska, the other on Lake Michigan between Milwaukee and Muskegon, Mich. -- and itineraries are under review in Hawaii, Cleveland, Erie, Pa., Racine, Wis., and along the East and West coasts.  

http://www.freep.com/news/statewire/sw96856_20040427.htm
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2) Land N Sea opens Houston center

Land N Sea, the Brunswick-owned, Pompano, Fla.-based marine parts distributor, is opening a new distribution center in Houston.  The 30,000-square-foot facility represents the companys 14th location in North America and provides marine dealers access to Land N Seas selection of general marine supplies and boatyard items, as well as Brunswicks own Mercury and Quicksilver products.
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3) Average price for new boats up in 2003 

The average price of a new boat in 2003 rose 3.3 percent from the previous year, according to the National Marine Manufacturers Associations first Annual Recreational Boating Statistical Abstract, NMMA said in a release.  NMMA said the average price of a new boat was $12,611 in 2003.  The statistical report compiles and organizes data collected by NMMA into a package of market facts and figures that includes analysis of industry activity by sector, annual units and dollar sales. 
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4) Cat Driver Dies During Testing

Randy Linebach, a veteran racer who built and campaigned offshore catamarans, died 4/23/2004 during an unsupervised testing session just one day before the new Offshore Super Series (OSS) kicked off its season in Biloxi, Miss.  Linebach, a 49-year-old boat builder from Michigan, was behind the wheel of the Airborne Big Thunder OSS Cat when the boat flipped in Mississippi Sound at about 11am. Throttleman Charlie Haimes was slightly injured in the accident but still managed to get out of the boat and perform CPR on Linbach on the overturned hull.  The two men, who were running the 40-foot MTI off the designated race course, were found by an off-duty firefighter.

Offshore catamarans are capable of speeds in excess of 130 miles an hour, but can become unstable in high winds or heavy seas. The wind was blowing hard out of the east on Friday when the accident occurred.  Linebach had just recently teamed up with Haimes, a former world champion in the rival American Power Boat Association (APBA) Offshore Super Cat class.  Officials with the OSS declined to discuss the accident and said they would wait the results of an autopsy.  Four classes of race boatsOSS Cat, OSS Vee, OSS Cat Lite and OSS Vee Litewere scheduled to race on Sunday.
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5) Jimboat writes Features in HotBoat & World of Powerboats mags

Check out the NEW high-tech, high performance powerboating feature articles just published:

WORLD OF POWERBOATS (UK) - 'Rocket Science' - "...an article on high performance powerboat design and the technical opportunities for performance improvements in aerodynamic design" [editor-WOP] http://www.aeromarineresearch.com/adverts/WOP_winter04.html

HOT BOAT (USA) - 'Flight Path' - "...Jim Russell explains the aerodynamics of powerboat design" [editor-HB] http://www.aeromarineresearch.com/adverts/HotBoat_April2004.html
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6) 'Powerboat' magazine - Save 52%! 

We have obtained great deals on Powerboat magazine subscriptions. This month we have a great deal on the popular 'Hot Boat' magazine. 

Powerboat Magazine covers performance Outdoor Recreation, technical innovations, marine accessories, water skiing, race events, industry and personal profiles and more.  Issues per Year: 11 Cover Price: $4.50 Regular Price: $49.50 Brandsmall Price: $23.50
 
http://www.aeromarineresearch.com/boating%20magazines%20discounts.html 
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7) NEW 'Tunnel Boat Design' Software - Version 7.5

We've just released the new Tunnel Boat Design Software - version 7.5. This is the best release yet - with the most dynamic and plentiful new features ever! Includes new "Auto BlowOver Check", Design-versus-Design comparison graphics, HeadWind & TailWind feature, Nine (9) new design Wizards!  Check out new features at http://www.aeromarineresearch.com/tbdp6.html, or download the summary of new features at http://www.aeromarineresearch.com/New%20in%20TBDP%20Version%207.zip
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8)  What a drag! - Trim angle & engine height reduces drag and increases speed.

To get the most from your high-performance powerboat setup, motor placement and motor trim angle are as important as horsepower and propeller selection.

The hydraulic drag generated by the motor lower unit or outdrive appendage can make or break your hulls performance.  If you can raise the motor higher, so that there is less unit in the water, then there is less drag - and more speed!  The thrust that propels your hull to the checkered flag is most efficient when if is aimed exactly in direction of boat - so motor trim angles of 1 degree up or 1 degree down can hurt performance. 

** Trim Angle - The most efficient trim angle - as far as engine thrust and drag goes - is exactly neutral.  So, if we can design and/or set up our hull so that it runs properly with the motor/drive unit trim at zero, then we will have the ideal situation.

The difference is not trivial.  Lets consider the effect of even small trim angles.  First, a trim angle of positive 2 degrees - meaning trim creating a bow-up condition of the hull - which means that the lower unit torpedo is angled down at a 2 degree angle.  For a 200hp outboard engine, the difference in forward thrust lost is about 7hp!

The same type of problem can occur with a trim angle of negative 2 degrees - meaning trim creating a bow-down condition of the hull - which means that the lower unit torpedo is angled up at a 2-degree angle.  In this case the power is not being fully applied in the straight-ahead direction, but rather, some of your power is actually being used to raise the aft end of the hull (vertical).  Both of these conditions can be avoided with proper hull design and/or setup.

And thats just power loss - there is also increased profile and induced drag of the lower unit.  At 60mph with this engine, this will amount to another 1 hp for this lower unit angle.

So total, we have experienced a power penalty of 8 hp (4%) resulting from our trim angle.  Translated into speed loss, for a typical performance ModVP hull this will mean a reduced top speed by 2 mph!

** Motor height - Adjusting the height of the motor (lower unit) has a big influence on total hydrodynamic drag.  In an outboard, this is often done with a manual or hydraulic jack plate.  On an IO, this is adjustment is referred to as the X-dimension.  In all cases, when the drive unit is lower in the water, there is more drag generated.

A common starting point for adjusting the setup lower unit height for high-performance hulls is for the torpedo centerline to be level with the trailing edge of the planning surface.  Too high and the propeller can over-cavitate, too low and the setup will generate excessive drag.

Lets consider a setup where the torpedo centerline is one inch (1) below the trailing edge of the planning surface (sponson or pad).  At 60mph, and our 200hp outboard engine, this will generate an additional 9.0 pounds of drag - equivalent to another 1.5hp loss.  

But, theres more.  If your hull setup is using a surfacing propeller (most performance hulls can benefit), then there is an additional propeller drag increase by submersing more of the lower unit (and thus, the propeller) under the water surface.  In the case of an additional 1 below the planning surface, this can affect the thrust transmission efficiency - which can lower your available engine RPM by as much as 5%.  This can easily represent 300 RPM - or another 6hp loss!

Translated into speed loss, for that typical performance ModVP hull this means a top speed further reduced by 2 mph!

In summary, by being able to trim to the optimum angle, and having the lower unit set at the optimum height, we can make a significant improvement on performance!
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See you next time!

/Jimboat

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Note: The articles presented in TBPNews are edited excerpts from the "Secrets of Tunnel Boat Design" book, by Jim Russell, published by AeroMarine Research.  The STBD book explains the theory in full, and outlines example design calculations, step-by-step.  The "Tunnel Boat Design Program", software, does all the force calculations, dynamic force balances at all speeds, and reports the analysis automatically, including complete graphical performance results for any tunnel or modified vee hull design.
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