Inhaling water poses the greatest threat of death, far above hypothermia, for someone accidentally falling into cold water.

At a talk on cold-water immersion, a Vineyard doctor warned a gathering of 40 boat enthusiasts that the best way to stay alive is to keep your head above the water at all costs, especially in that first critical moment.

“You can be one of the best swimmers,” said Dr. Michael Jacobs, but unless you can keep your head above water in that first instant of immersion, you could drown.

Earlier this month, Dr. Jacobs spoke at the Sail Martha’s Vineyard offices on cold-water immersion. He gave the talk as part of an effort by Sail Martha’s Vineyard to make boaters safer in the waters around the Island.

Dr. Jacobs was invited to give his talk for the benefit of rowers involved in the Sail Martha’s Vineyard pilot gig rowing club.

For several years, a group of rowers has gathered almost every weekday morning for an hour of rowing in open water. They’ve rowed in the heat of summer and, at this time of year, in the cold of winter.

Rowing Martha’s Vineyard, a community-based club made up of 50 members, rows in two 32-foot Cornish Pilot Gigs. The two boats are moored next to the Black Dog Tavern in Vineyard Haven.

When a swimmer initially falls into the water, Dr. Jacobs said, the first automatic response which can not be controlled is a sudden gasp for air. That inhalation can be deadly, the doctor said.

“It is important to realize that this initial phase of the cold-shock response is brief and that your actions during this time can vastly improve your chance of survival,” Dr. Jacobs said.

After the first gasp, future gasps for air can increasingly come under control. If the swimmer is aggressive, breathing can be brought under control and thus drowning less likely.

It takes less than a glass of water to drown. Being subjected to cold water can cause a heart attack; there is little a swimmer can do if that happens.

“If you fall into cold water, it is imperative to bring your breathing under control immediately — your life depends on it. Try to calm your self,” the doctor said.

Falling into cold water causes violent shivering and intense pain, the doctor added. He then described how a swimmer who has control of breathing will be able to gain control as he becomes acclimated to the water, but only for a short time.

The doctor said a person can have more than 10 minutes of time to move about, maybe less, maybe more, depending on the water temperature and their physical wellbeing.

With temperatures in the ocean around the Vineyard averaging about 40 degrees, and freshwater ponds even colder, falling in could threaten one’s life.

Dr. Jacobs came up with a list of additional suggestions:

• If in a life jacket, place your back to the waves.

• Staying full-clothed in the water can act, to a small degree, as some insulation.

• Swimming to shore isn’t necessarily a smart move, as it depletes the body of its much-needed warmth.

Also, as hypothermia takes over, Dr. Jacobs said, “You can’t assist yourself in your own rescue.”

After the talk, Carol Gannon Salguero, president of Rowing Martha’s Vineyard, said the presentation was helpful for her rowing group, and that it allayed some of their concerns about what is needed should an accident occur.

Of those in attendance at the lecture, she said, half were members of the rowing club. Others were boaters and workers at local boat yards.

Ms. Salguero said the talk would benefit others as much as boaters: “This subject was helpful for anyone who has anything to do with water activities, or the saving of people exposed to cold water.”

She said firefighters, police officers and emergency medical technicians could benefit from the talk, which was videotaped for future showing.

The rowing club is under the umbrella of Sail Martha’s Vineyard, a nonprofit organization promoting safe boat handling for youngsters in the summer sailing season. Ms. Salguero said help in making the rowing program safe has come from the parent organization.

Brock Callen, a program director for Sail Martha’s Vineyard, also participated in the evening program by offering a description of a new $3,000 eight-man inflatable life raft that will be available to the rowing club. The raft is being picked up this week and will be available to the rowing club during the winter. The club has had one on loan for most of this year.

Mr. Callen said the raft will be used in the summer by Vineyard Voyagers, another branch of Sail Martha’s Vineyard maritime programs.

A program and demonstration on the raft’s use will be given in February by the raft’s manufacturer, Life Raft Survival Inc. of Portsmouth, R.I.

Dr. Jacobs is a well-respected teacher and writer about medicine for mariners. He co-wrote Medicine for Mariners: A Comprehensive Guide to Marine Medicine. He frequently teaches a course on safety at sea. He has taught in Seattle, Newport, Kings Point and at Annapolis. He also teaches maritime medicine while on a boat sailing among the British Virgin Islands.

“I have a great affection for the sea, and for medicine,” the doctor told the Gazette after the program. “Not many physicians are into teaching marine medicine. So, I wrote the book.”