Smooth sailing has all but disappeared underneath the Lagoon Pond drawbridge these days.

Three weeks ago, bridgetender Robert Maciel detected some shaking as cars passed over the 70-year-old bridge.

"I've been the bridgetender for 26 years, and it's worse now than I've ever seen it," he said late yesterday morning from his home in West Tisbury, a time of day he typically spends at the bridge.

The tremors swayed the bridge just enough to displace the bolts by an eighth of an inch, causing it to stick when raising and lowering for tall-masted vessels.

These inevitable signs of aging caused Mr. Maciel to reduce the number of openings from as many as 12 a day to just one. Tall sailboats must pass in and out of Lagoon Pond at 8:30 in the morning or not at all.

For some vessels, day trips to Vineyard Sound are now overnight journeys. These boats have been hooking up to moorings just past the break and using the Vineyard Haven launch service to taxi back to the harbor, Mr. Maciel said.

The veteran bridgetender blames the tremors on the tremendous amount of traffic passing over the drawbridge - a flow that peaks at nearly 16,000 vehicles on any given day in July or August. But he says it's not just the amount of traffic this bridge accommodates that is causing problems.

"The traffic is much heavier - all the trucks and buses," Mr. Maciel said.

The bridge currently poses no safety hazards for traffic, said Steve Young, deputy director of public affairs for MassHighway.

"We're keeping a close eye on it," he said. "If we discover any hazards, we'll close it. In the meantime, we'll keep plugging away."

Of course, some boaters resent the new constraints. To them Mr. Maciel simply passes on the number of the state highway department.

"When I tell them that if we keep raising it, it won't work at all, they're more understanding," he said.

In 1935, the drawbridge that connects Vineyard Haven and Oak Bluffs was considered state of the art. It replaced a ragged 1871 version that shortened the distance between the two towns from more than seven miles to only two. Residents of Tisbury - Holmes Hole at the time - were anxious to make their way to the Camp Ground meetings in Cottage City. Gazette archives report as many as 200 carriages crossing the old drawbridge each summer day.

Having spent $95,000 in the mid-1930s, the state bragged of the first use of Irving decking on the draw for any bridge in the commonwealth.

But the love affair with the Island's new drawbridge faded quickly. Heat proved the biggest enemy - an annual surge in the temperature caused the metal deck to swell and refuse to close. They trimmed an inch of metal many summers to enable the bridge to close properly. The series of technical problems included everything from failed motors to broken road gates. Even a lightning strike in 1988 put the bridge out of commission for a while.

But heat's not the problem this summer. Instead, the sway moved the bridge just enough to prevent the joints from locking.

A team of engineers and repair crew from MassHighway arrived this week to install reinforcement cables underneath the bridge. The team attempted a similar patchwork fix last summer, but they now insist a crisscrossed cable net is needed.

The bridge has been on the short list for replacement by the state Department of Public Works since 1989.

Money is not the reason for the lag. In the last few years, Mr. Young said, MassHighway has spent record amounts even apart from Boston's Central Artery/Tunnel project - the money-sucking Big Dig.

The state recently hired a designer for the project and expects to hold a public hearing by the end of the year, Mr. Young said.

"Once we have the hearings, it moves out of the conceptual phase," Mr. Young said.

A target date has not been set, but Mr. Young estimates construction will begin sometime in the next couple of years.