Ask Bob Jackman why he wanted to organize an ultra-marathon in Rhode Island and he’ll give you a simple answer: Because there was none.

When the Nifty Fifty – an ultra-race held for more than two decades in Coventry and then for a couple of years in Middletown – was discontinued a few years ago, he decided to come up with a replacement. His version: The Rhode Island 6 Hour Ultramarathon and Relay. The inaugural event will be Sunday at 8 a.m. at City Park in Warwick.

“I guess I just wanted to put a race on that I would want to do, and the relay worked in well with the event,” said the 27-year-old from Warwick, who has won three ENDURrun 160-kilometer stage races. “There are a lot of longer relays out there now, like Reach the Beach, and there are a lot of marathon relays. So this hits the middle ground –– something a bit longer, but doesn’t take up a whole weekend.”

The object of Sunday’s race is pretty straightforward: The person who completes the most 2.7-mile loops through City Park in 6 hours wins.

“The first ultra I did was a 6-hour, so I liked the distance and thought it was good for beginner ultra-runners because there is no set distance,” said Jackman, who ran cross country and track for Toll Gate in the late 1990s and went on to become an all-conference runner at Johnson & Wales. “Goals can vary greatly without the scare factor of a 50-miler.”

“The usual ultra food will be available,” he added. “There is going to be a certified marathon, 50K and 50-mile marks on the course, and I have been working closely with Ray Nelson and Merrie Nelson on the scoring. Without their help, it would be chaos.”

As of Tuesday, 70 entrants representing 17 states, including California, had registered for the event, which has been chosen to serve as the 2009 USATF New England Ultra Championship.

The top contender appears to be Providence’s own Martin Tighe. The 51-year-old Englishman, who runs for the Tuesday Night Turtles running club, has a number of notable victories to his credit, including the Nifty Fifty and the inaugural North Pole Marathon in 2003.

He gained fame in 2005 by running a world-record 85.83 miles in 12 hours on a treadmill, while setting three other world marks along the way –– for 50K (3:44:48), 50 miles (6:06:19) and 100K (7:39:31). There is a chance that Ben Nephew also will take the starting line. Earlier this year, the 34-year-old from Mansfield, Mass. was selected to compete for the U.S. Team at the IAU World Trail Challenge in Serre Chevalier, France. In September, he won the Gore-Tex 50-Mile race at The North Face Endurance Challenge in Washington, D.C.

“If he is running, it will be a Martin-Ben duel,” said Jackman. “With 50-plus miles possible.”

For those who are either not interested – or not able – to go the whole 6 hours alone, the ultra will include a relay competition. Relay teams may consist of two to six runners, with only one runner allowed on the course at a time.

Twenty-six teams consisting of more than 130 runners have signed up for the challenge.

“I thought a relay aspect would be fun,” Jackman said. “There are a lot of longer relays now (that are) 200 or so miles (and) that take up a whole weekend. I thought this would be a fun way for teams to get together without taking up a whole weekend or having to get 12 runners. Plus, unlike a marathon relay, you can cheer your team the whole way since it is a looped course.”

The entry fee is $60 for those running solo. Relay teams pay $60 for a two-person team, $80 for a three-person team, $100 for a four-person team, $120 for a five-person team and $140 for a six-person team. (Participants are also asked to bring their old shoes, which will be donated to Soles4Souls, an organization that distributes new and used shoes.)

Thursday is the last day for on-line registration at http://www.needtorace.com, and there will be no registrations accepted on race day. For more information, visit the race Web site at http://www.ri6hour.com

cthorn@projo.com