Is the OJ Walker in Lake Champlain a shore dive? It is now.. 🙂 With DPVs anything can be a shore dive it’s just a matter of motivation and perspective. Ok maybe it’s a little more than that but I personally like a good challenge. For those that are unfamiliar with diving in Lake Champlain the OJ Walker is a wreck dive that is north of the Burlington Breakwater in about 60ft. It is typically a dive that you need to a boat to get out to.
When I told my buddy John that I wanted to scooter to it his only question was..when? 🙂 Game on.
The big question – Can we do this dive with my $40 dollar Chinese kayak compass and two $1800 low budget scooters or do I need an $8000 expedition-grade scooter?
There are 3 Parts to this equation. DPV Range/Burntime, Gas Planning and Navigation. I’m sure some pendantic person will come along shortly to correct me and tell me the error of my ways.
DPV Range/Burntime
Do I have enough burntime/range in my scooter? That part was easy. The Dive Xtras Blacktips with 12Ah batteries have a 3.5 mile (123 minute range) at cruising speed. I’ve tested this range thoroughly and it’s a fact that’s not up for debate but there are plenty of variables that can cut this distance much shorter.
You have to account for factors such as drag (diving with doubles + AL80 stage bottle + drysuit and towing a flag) and speed at which you run the scooter. All things that contribute to your drag will cause you to use more watts/power so you need to find a good balance here.
The trick to the Blacktip is not to cruise at higher speeds above say speeds 6-7 which equate to a much higher battery draw. Cruising in speeds 3-5 is the sweet spot here. Most Blacktip users have already found this out themselves or they will at some point. I’m not going to get into proper DPV cave planning since this is not a cave dive but I’m sure somebody is going to tell me what I’ve done wrong and how I’m going to kill myself in the process.
Disclaimer: At some point in your dive planning you either need to have sufficient battery capacity to tow you AND a dive buddy safely, carry a tow scooter OR have sufficient gas reserves to swim back to your entry point.
The big difference here is the Blacktip is an $1800 dollar entry-level technical scooter. It’s not a $8000 Suex or Seacraft or Genesis and it never will be. If you are expecting $8000 scooter performance and range you will be sorely disappointed. It’s like comparing a base model Honda Civic to luxury sports car with all the options (Fan boys will surely argue that BMWs are much better than Mercedes). They both can get you to point A and B but the luxury car is much faster, better engineered has a much larger fuel tank/range. Obviously this analogy is not perfect but a lot of people tend to get a little butt-hurt that $1800 “pool toy” can keep up with their $8000 highly professional and SUPER expedition-level technical scooter.
The truth and cold hard fact is the Blacktip only has a 432Wh battery. (2x 18V12AH ~216Wh batteries in series). It’s simple math. It’s going to have much less range that a scooter with a 1000Wh battery but that doesnt mean it’s useless. It’s still a much better scooter than old school Gavins, Makos, Silient Submersion UV-18 (even UV-26 to some extent) which used to be THE technical scooter. It also doesnt weight 70-90lbs.
Full Disclosure: I found the battery reserve with 9Ah batteries was not sufficient to my liking so I’ve been using the 12Ah batteries lately for most of my dives. Having said that the 9Ah batteres will still do 2 miles 10560ft roundtrip but it’s just going to depend on your speed and drag. This makes the Blacktip with 12Ah batteries a pretty decent ~3500-4000ft cave scooter. It is not a 10,000ft+Manatee scooter nor is it “Let’s scooter every single line and jump inside Ginnie Springs at at full speed 9” scooter.
The other thing to consider here is while this is a long range dive it’s not an overhead. It IS a virtual overhead in the summer with respect to boat traffic..sure but if the shit hits the fan I can surface. It would not be a very fun swimming back but I could activate my PLB (Personal Locator Beacon) that I carry and I’m sure the Coast Guard would not be too happy but I would not drown.
The other nice thing about this dive is the average depth for planning is 40ft. Deco is not really a huge issue.
Gas Planning
This dive is not much different than planning a dive in Peacock Springs doing the grand traverse twice which is about 2 miles of swimming. I’ll just point out that MANY people have done that dive. The gas requirements at this depth are not huge especially if you have a good SAC rate. The good thing here is average depth is 40ft (max of around 65ft on the wreck). I’m also not in a cave so the surface is my last ditch option.
Last year my buddy Tom and I did 90% of this dive on a preliminary exploration dive. I did the dive with HP100 doubles filled to 3400psi and never hit turn pressure. I returned to shore with 2100psi in my doubles with an 81 minute runtime. I used 1300psi in HP100 doubles or 74.2cu/ft. What does this shit actually mean?
40ft (avg depth) is 2.21 ATA. (I rounded up it was closer to 38ft)
100cuft/3500psi = .02857psi per cuft (These are PST 3500psi HP100 tanks)
1300psi x .02857psi x 2 tanks = 74.2cuft used during the dive
74.2cuft / 81 minutes = .916cuft per minute (This is at depth so we need to convert to surface air consumption)
RMV = .916cuft/minute / 2.21 ATA (40ft avg depth)
SAC = .414 cuft/minute
I’ll point out here that most peoples’ SAC rates on scooters are going to be much lower so this isnt always a realistic number to use for planning. This is also actually a pretty high SAC considering we were on scooters (I’ve calculated around .35cuft/minute in Florida) but it’s not terrible considering it’s doubles + drysuit + cold water. You should also plan for a elevated SAC rate to give yourself a little more buffer.
Let’s get back to our actual dives. My buddy John decided he wanted to dive it on rebreather but based on my gas planning from my scouting dive last year I knew this dive could easily be done on open circuit. For my actual dive to the OJ Walker I decided to use LP85s doubles (cave filled) and take an additional stage bottle. I would kick the stage bottle first and preserve all my backgas. If I really needed to, once the stage bottle is empty I can drop it and reduce my overall drag but really I just wanted more of a gas buffer.
I calculated that swimmig back to shore would take approximately 96 minutues. 4800ft / 50fpm = ~96 minutes. Do I have gas to swim back if my scooter failed?
This is a simplistic dive plan which I realize doesnt include gas to tow my buddy back (screw them..) but I’m just using it as a very basic example. This also doesnt include any gas in my stage bottle. I’m planning it on pure backgas (doubles) alone with a much higher SAC rate than I use while swimming or scootering. In a cave environment I would add some more conservatism here.
40ft (avg depth) is 2.21 ATA
.7cuft/minute SAC x 2.21 ATA = 1.55cuft/minute RMV
Let’s say my turn pressure is 2400psi (in my set of cave filled LP85s)
85cuft/ 2640psi = 0.0322 psi per cuft
.0322 x 2400psi x 2 tanks = ~154cu/ft of gas (2/3s of my gas left to “exit”)
154cuft / 1.55 = ~99 minutes of available dive time.
This basically means that if my scooter fails right at planned turn pressure (remember I never hit turn pressure) then I have 99 minutes of gas remaining to swim home while my dive buddy John laughes at me and gets on his scooter and waves me goodbye. If my SAC rate were actually .7 and it actually took me 96 minutes to swim back I’d be on fumes hence taking a stage bottle with me.
Actual Gas Used (I’m mostly just including this in here for my own edification for future planning)
We did two DPV dives to the OJ Walker. I recorded how much gas I used in my doubles and stage bottle. I did both dives on double LP85s and an AL72 stage. I had a pretty liberal 3900psi cave fill the first day but the second day my doubles were closer to 3500psi. An AL72 is basically an AL80 but slightly smaller in diameter (6.9″). It’s basically an AL80 stage at 3200psi give or take. I breathed the stage first to preserve backgas.
For a reference – I was able to get to wreck with around 1300-1500psi left in the stage bottle and completely untouched backgas. I basically killed the stage bottle to 600-800psi on the wreck before switching to backgas. This means that at my furthest point of penetration I had a full ~225cuft (not including what was left in my stage bottle) to swim back in the event of a scooter failure.
First Dive (LP85s) start: 3900psi. End pressure: 1800psi. Stage AL72: Start 3200psi End: 700psi.
Second Dive (LP85s) start 3500psi End pressure: 1600psi Stage 72: Start 2900psi End: 600psi 
Navigation (The final part of the equation)
How the fuck do you navigation to a wreck that is 1.2 miles offshore with an extremely silty bottom and manage to find the wreck without ever surfacing? That’s the fun part of this challenge. I really, really wanted to find the wreck without ever surfacing using my trusty $40 Kayak compass mounted on my DPV and some good old fashioned navigation skills but our backup plan was to surface and take compass heading / bearing on the LCMM mooring ball which we suspected would be visible to us if we were within range of the wreck itself. We confirmed the mooring ball was still present. Lake Champlain Maritime Museum (LCMM) usually pulls them out of water in early November.
Thankfully the navigation was actually the easiest part. We were very lucky that 90% of the navigation happens to be following a water intake pipe to the end.
My scouting / preliminary exploration dive with Tom last year proved that the end of the intake pipe was within ~800ft of the wreck of the OJ Walker based on GPS data collected. Last year we towed a dive float with GPS logger and collected very good data to the end of the intake pipe and the actual distance involved. Using the data I collected last year I knew the GPS position of the end of the intake pipe and I knew the GPS position of the wreck itself. From here is was a simple matter of calculating a course to take. The problem is 800ft in poor visibility it could be still very difficult to hit the wreck if our course heading was off.
There are a lots of other variables. I calculated that the true course heading was approximately ~210-215 degrees from the end of the water intake pipe to the wreck of the OJ Walker. I also knew from the GPS coordinates that the distance should be approximately 750-780ft. In theory with an 800′ reel I should run into the wreck if my course heading was correct.
But what course heading do I take? Most of you that are familiar with maritime or aviation navigation know that you need to convert your true course heading to magnetic compass heading
If I remembered anything from my captain’s course it was that “East is least, West is best” 🙂 The magnetic variation in Burlington, Vermont (courtesy of Google is: 13.93°W (WMM2020 magnetic declination)
This means that I need to add approximately ~14 degrees to my heading to get magnetic compass heading. The end result is 230 degrees magnetic. I realize this doesnt account for any deviation my kayak compass that is mounted on my scooter but I wasnt going to exactly make a deviation table for my scooter’s compass.
Actual Dives
The actual dives went without any issues. At the end of the water intake pipe we took a course heading of 225-230 and scootered slowly approximately 8 minutes while running out an 800′ reel (8 minutes x 100fpm = 800′)
Either through my brilliant navigation skills or by pure dumb luck (I’m going with pure dumb luck) we ran directly into the stern of the OJ Walker. The Navionics track line has my true course heading at approximately 219 degrees so I guess I was close enough! We ended the dive with about 50% battery left on our scooters (this is not super accurate as it’s just reading the resting voltage and the blacktip only gives 4 bars rather than percentages) but it’s still a decent battery reserve.
https://webapp.navionics.com/maps/#show/kml/https://social-sharing.navionics.io/upload/1635107861669/1635107861669.kml
Total distance was approximately 2.3 miles (~3.7km) roundtrip with a little over 2 hour runtime for both dives.
So back to the original question..Is the OJ Walker a shore dive? The answer is yes.
