Thank you, West. Good morning, everyone, and welcome to the Second Quarter 2021 Tidewater Earnings Conference Call. Joining me in presenting our prepared remarks, as usual, are Piers Middleton and Sam Rubio. I will open the call with some general commentary on the quarter. Piers will cover the markets in the various geographies in which we operate and then Sam will wrap up the prepared remarks with an overview of the income statement, OpEx, G&A and the balance sheet. And then, of course, we'll open it up for questions.
The second quarter is on a seasonal basis, a relatively strong quarter, with the third quarter being the strongest in the year. This year's second quarter followed that pattern. Piers and Sam will provide the details, but globally, average day rate was up, utilization was up, gross margin was up, operating profit was up, the increases are never as swift as we would prefer, but the sequential quarter improvement is a good sign that activities are past the pandemic low.
Industry-wide, what we saw in 2020 were activity levels coming down dramatically in the third quarter with a substantial number of vessels going off higher. As a result of this incremental oversupply, day rates around the world reset downward and as pre-pandemic contracts rolled off, new contracts rolled on with lower day rates in the first quarter. Now as activity levels are picking up again, we are beginning to claw back the day rate that we lost in 2020.
Cash flow for the quarter was again strong. You may recall that accounts receivable bounced up in the fourth quarter of 2020 just as activity levels were coming down, which is not typical. That was due to payment delays from Pemex, which as of June 30, are trending towards normal levels.
In the second quarter, we had strong cash flows from that normalization. We also picked up $18.6 million in vessel and other asset proceeds sales as we continued to high-grade the fleet.
Feel free to pick the metric that best suits your perspective, be it cash flow from operations, free cash flow, free cash flow before vessel disposals, it's all there in the press release. They're all positive, and we have designed the business architecture incentives to keep it that way. Net debt is down to $4.5 million. We do have the maturity of the 2022 bonds in August of next year. The principal outstanding on the bonds is $135 million, and we're currently sitting on $151 million of cash. Currently, the prepayment penalty on the bonds is $10 million. So we're going to be mindful of that as we evaluate refinancing opportunities over the next several months. The prepayment penalty goes down approximately $825,000 per month.
Free cash flow for the trailing 12 months was $84 million, down from the $87.1 million as of last quarter. The slight decline reflects the decrease in activity as the full impact of the pandemic is now in the trailing 12-month figures, offset by a liquidation of working capital related to a decrease in activity.
Quarterly revenue rounds out to $90 million. Operating costs were slightly higher than we were anticipating largely due to direct costs related to the pandemic and vessels reactivated during the quarter. And as a result, margins were 1 percentage point below where we thought they would be for the second quarter, but they still reflected a pickup of more than 3 percentage points during the quarter. We came in at 29% this quarter, but we're still anticipating margins of 30% for the full year. My expectation is that the third and fourth quarters will average just above 30%, but that anticipates a reduction in direct pandemic costs that have proven to be more stubborn than we envisioned at the beginning of the year.
We used the cash generated in the quarter to pay off another $11.4 million of outstanding debt, combined with the build in cash, net debt is down another $21.1 million to $4.5 million.
We spoke a bit on the last quarter call about this business' significant degree of operating leverage. Once the boats are operating, incremental day rate margins and revenue from incremental days work should drop 100% to operating profit. This quarter's incremental operating profit was 95%. Operating leverage has cut against us in the past 6 years and particularly the last year as we dealt with the pandemic, but incremental margins this year were a positive 95%.
It goes up on the same scale as it's gone down. We've spent an enormous amount of effort to signing a culture and a business model that will be cash flow positive in the worst of times and significantly cash flow positive in the best of times. And I look forward to continuing to deliver these positive incremental margins on an increasing revenue base as we proceed through the recovery.
We disposed off 7 vessels and some other assets in the second quarter for $18.6 million, and we have 14 vessels left in the asset held for sale category. We did sell one 260-foot U.S. flag vessel that had been in layup and was facing an approximately $3 million reactivation but which was not classified in the asset held for sale category, I would classify that sale as an opportunistic one.
We sold that vessel for a $4 million book gain. At any point in time, we're willing to sell any vessel if the present value is in excess of our bull market recovery scenario, which was the case in the sale. Based on the recovery in the market that we see beginning to unfold in the second half of 2021, we don't anticipate reducing the vessel fleet any further than what we currently have in asset held for sale. After this lot is sold, we still anticipate everything we own being gainfully employed by the end of 2022.
I am very much looking forward to getting out of managing a fleet of layup vessels, in addition to the active fleet vessels and layup, give us the ability to take advantage of improving market conditions. It's an investment in those vessels that do not merit reactivation at this time. But based on our internal forecast of the recovery, they should be reactivated in due course and ultimately more than justify this investment.
Those vessels that don't meet this criteria are classified as assets held for sale. As our perception of the recovery and the cost of reactivation change, vessels will move in and out of the asset held for sale category. During the second quarter, we moved 1 vessel out of the asset held for sale category into the active category.
Vessels in layup cost us $3.8 million in the second quarter, which is down 30% from the first quarter cost, but it's still an annualized cost of $15 million per year. Removing this burden by gainfully employing or disposing of these assets will add that $15 million to cash flow in addition to the operating profit from those vessels that go back to work.
As part of this ongoing work to high grade the fleet, we are also focused on enhancing the connectivity and data capture analysis capabilities of our active vessels, providing our operations team with valuable insight that allows us to operate more efficiently, reducing fuel usage and our Scope 1 emissions. We have demonstrated that shore power systems have also been very effective at reducing emissions while in port. So we are installing several more on vessels, operating in ports that offer the necessary infrastructure to support this technology. This operational data and these positive results are enabling closer collaboration with our customers as we work to identify the most effective methods for reducing our joint carbon footprint.
This data also provides customers with the justification to increase day rates to support those continued investments. Our G&A costs went up for the first time in 10 quarters. Our annualized G&A expense for the second quarter was $67 million. We mentioned on the last quarter call that G&A would begin to rise a bit as we go through the remainder of 2021 as we have begun to fill some open positions, and we anticipate travel expenses coming back as we get further along into the pandemic recovery.
Our big cost focus in 2021 is optimizing the cost of drydocks and minimizing the cost of vessels in layup. As I mentioned earlier, we reduced the annual run rate of vessels in layup by 30% during the second quarter from $21 million down to $15 million. It's a combination of reactivating vessels, disposing the vessels and reducing the cost per day of the vessels in layup. The cost per day of vessel in layup went down 16% and the reduction in the number of vessels in the layup fleet, makes up the remainder to get to the overall dollar reduction of 30%.
We now anticipate drydock costs for 2021 to be approximately $24 million as we are planning to reactivate more vessels than we originally thought we would at the beginning of the year. This is a good development, but it brings with it additional cost. In addition, the second quarter drydock costs came in at approximately $4 million, which was less than the $9 million we were anticipating to spend. The drydock savings in the second quarter isn't a cost efficiency. It's just a cost that has been delayed into the third quarter. So the third quarter will now be our heavy drydock quarter for the year as we reactivate more vessels than we originally budgeted and performed more -- performed drydocks that were originally slated for the second quarter.
We're now anticipating approximately $13 million of drydock costs in the third quarter. Global utilization and day rates are increasing, reactivations are also increasing. The active vessel count prior to the 2020 pandemic, the best quarterly record we had since the 2014 oil price collapse was the second quarter of 2019. In that quarter, we had revenue of $124 million from 163 working vessels with an active utilization of 79% and an average day rate of $10,442. This year's second quarter, we had 118 vessels working average utilization of 78% and an average day rate of $10,435.
We're definitely off the pandemic lows. But to get back to the highest revenue we had prior to the pandemic, we need to put all the remaining vessels back to work and push day rates up another $1,200 per day, which I feel confident will happen as we go through the next 18 months. When we get there, the high grading of the fleet that we have been doing over the past 30 months should demonstrate the revenue and earnings generation capability of the fleet. Similar revenue with 10% fewer vessels results in a higher overall profitability.
I continue to anticipate it will be the first quarter of 2022 before we get back to where we were at from a supply and demand perspective when the pandemic hit and then a year to push day rates and market share. If the market continues at its current pace of recovery, we should see quarterly revenue number by the end of 2022 comparable with that previous record quarter in 2019. Pandemic-driven inefficiencies, which we estimate cost us 5% of revenue are still impacting us. This is factored into our full year margin guidance of 30%. Each wave of the pandemic has created different challenges, although they can all be generalized as increased costs associated with safely moving people around the world.
The latest challenge is the Delta variant and its impact on the Middle East. Last quarter, it was mariners from India. We continue to respond to the circumstances presented, but that 5% of revenue cost still looks like it -- to be with us for the remainder of 2021.
That's a quick overview of the quarter. I will now hand the call over to Piers for an update on the vessel market and the various geographies in which we operate.