Anybody know if altitude is a factor at lake Sunapee?

[mjacobydc]

I have a friend who did a charter on lake sunapee NH. The capt. limited the dive to 15 minutes at 70' because of altitude. They said it was at 1000'. My dive computer won't even switch over until I hit 2000'. So I was curious if this is legit or just somebody that really didn't want to go out.

thanks

 

[Charlie99]

The lake is around 1100'. A reasonable altitude adjustment would be to treat the dive as if it were about 5% deeper than actual depth. In other words, a 70' dive should be treated as a 74' dive. An 80' dive NDL in the PADI RdP is 30 minutes. Alternatively, rather than doing a 70' 40 minute dive, one could do a 66' 40 minute dive.

Those are very small adjustments. As you note, many dive computers don't do any altitude adjustment until around 2000'.

Limiting dives to 15 minutes at 70' is unusually conservative, if that was the first dive of the day. Stories sometimes leave out crucial details, such as what dives and surface intervals preceded the 15 minute at 70' dive.

 

[mjacobydc]

Thanks for the info Charlie99. I don't have any training in altitude diving. You are also correct that I probably don't have the whole story.

So I am supposed to dive Winnipesaukee next week- I guess I should do a little research about the elevation there.

 

[Charlie99]

Lake Winnipesaukee is 504' elevation. Low enough to just use sea level tables without compensation. About 75F water temp now.

I'll be headed up to Lake Winnipesaukee tomorrow for 4 days, but no diving. Just sightseeing and some boating with one of my Maui neighbors that is visiting relatives up there. Apparently NH is one of those states that require boating licenses --- he just took his test and got licensed last week. I'm curious whether questions about the diver down flag were on the test.

 

[dave4868]

Lake Winnipesaukee is 504' elevation. Low enough to just use sea level tables without compensation. About 75F water temp now.

I'll be headed up to Lake Winnipesaukee tomorrow for 4 days, but no diving. Just sightseeing and some boating with one of my Maui neighbors that is visiting relatives up there. Apparently NH is one of those states that require boating licenses --- he just took his test and got licensed last week. I'm curious whether questions about the diver down flag were on the test.

The online course covers the diver down flag pretty well.

New Hampshire Boating License and Boat Safety Course - Boating Near Scuba Divers & Snorkelers

Chapter 6: Enjoying Water Sports With Your Boat
Scuba Diving and Snorkeling

Diving is a popular sport, and divers can be found in areas shared with recreational boaters. As diving's popularity increases, it becomes more important for both boaters and divers to take special precautions. Chapter 4 has the legal requirements for your state.


As a vessel operator, you should:

• Be able to recognize a diver-down flag, a red flag with a white diagonal stripe, floating in the area of the divers.
• Stay the legal distance away from a diver-down flag. Chapter 4 has the legal requirements for your state. Do not drive your vessel between a diver-down flag and a nearby shore.
• Watch out for divers surfacing when you see a diver-down flag. Bubbles may indicate that a diver is below.

For their own safety, divers should:

• Always display the diver-down flag and stay close to the flag.
• Use a stable boat that is suited for diving and anchor the boat securely.
• Avoid overloading the vessel with people, equipment, or supplies.
• Never dive or snorkel alone.

Always stay the legal and safe distance away from a "diver-down" flag.

Both divers and vessel operators need to be aware of laws that affect this popular water sport.

​

There appears to be one question in the review section:

8. In addition to a displayed diver-down flag, what indicates that a diver may be below the water's surface?

Dave C

 

[sunapeebob]

I have a house on Sunapee and dive here all of the time. We will make the minor altitude adjustment and as we go later in the season a similar temp adjustment(10%). Agreed that the short dive time needs to be factored in with any prior dives, but I am assuming the only interesting dive at that depth is the Weetamoo at about 67'. That does seem very short.

The other interesting fact is that yes boaters are tested about the "diver down" flag, but rarely obey it. My son and I have been diving and people have passed within about 30 feet of us waving. That is why we almost always have a boat with us or some kayakers (my wife and daughter - not divers). This also allows us to retrieve more glass bottles from the bottom - we put them in a mesh bag, attach them to a small SMB and my daughter or wife pull it up and place them in the kayak. We have retrieved about 100 bottles in the past year, dating from about 1910 to 1950s. We have also removed a tire, other junk and multiple fishing and trolling lines. It is interesting and cleans up the lake. I have been told that there are brass beds that have been thrown in the lake in the past. We are still exploring.