First-time boat buyers are trending more female than they did in 2020, and Brunswick over-indexes to the industry by approximately 800 basis points.
In Freedom Boat Club, the average Freedom member continues to be almost three years younger than our typical boat buying customer and female Freedom members make up approximately 35% of our member base.
Brunswick received 6, 2021 boating industry top product awards, including for the Mercury Marine V12 600-horsepower Verado and the Sea Ray 370 Sundancer Outboard we highlighted recently, but also for our Bayliner Element M15 entry-level boat, BEP's Smart Battery Hub, Attwood's Sahara Mk2 automatic bilge pump, and MotorGuide's Xi3 Kayak Trolling Motor.
The winners were chosen based on a survey of 50,000 US employees working for companies employing at least 1,000 people in their US operations and only 300 companies made the final list from the thousands of companies that were considered for the honor.
I'm also pleased to announce that we began shipping the new 600-horsepower V-12 Verado engine in late June, and as anticipated, demand has been extremely strong.
We're essentially sold out of the V-12 production slots for the remainder of 2021.
In fact, the sum of our wholesale orders for 2022 model year product is already roughly equal to our projected 2021 full year wholesale Boat Group revenue.
Additionally, we've identified capital-efficient investment options to further raise capacity to approximately 50,000 annual production units by 2023, should this volume of product be required.
With the recently announced acquisition of Fanautic Club and expansion into Spain, Freedom now has 314 locations and 44,000 memberships networkwide, and is closing in on 4,000 votes in the overall Freedom fleet, with an increasing percentage of Brunswick product.
Domestic sales grew 55%, with international sales up 49%, versus prior year.
Despite more difficult year-over-year comparisons in May and June, the main powerboat segments are still up 17% in the first half of 2021 versus 2020 and up 13% versus 2019.
Outboard engine unit registrations were up 5% in the first half of 2021, when compared with the same time period in 2020.
Approximately 40% of the boats leaving our manufacturing facilities are retail sold, which is approximately three times historical averages.
When compared with 2020, second quarter net sales were up 57%, while operating earnings on an as-adjusted basis increased by 126%.
Adjusted operating margins were 17.1% and adjusted earnings per share was $2.52, once again setting new all-time highs for any quarter for which we have available records.
Finally, we had free cash flow of $268 million in the second quarter, with a free cash flow conversion of 135%.
Net sales through the first half of 2021 were up 53% when compared with the first half of 2020, and operating margins of 17% or a 520 basis point improvement from 2020.
This resulted in first half earnings per share of $4.76 and a very robust operating leverage of 27%.
Turning to our segments, revenue in the Propulsion business increased 64% versus the second quarter of 2020 as each product category experienced strong demand and market share gains.
In our Parts and Accessories segment, revenues increased 42% and adjusted operating earnings were 46% up versus the second quarter of 2020, due to strong sales growth across all product categories.
Adjusted operating margins of 23.2% were 60 basis points better than prior year quarter, with significant sales increases driving the robust increase in adjusted operating earnings.
Sales were up 80% and operating margins were 10.5% for the quarter, the second straight quarter this segment has delivered double-digit margins.
When compared to the second quarter of 2019, sales were up 22%, and operating margins were up 160 basis points, further illustrating the foundational improvements that have been made in this business.
Freedom Boat Club, which is included in business acceleration, contributed approximately 3% of the segment's revenue and a margin profile that continues to be accretive to the segment.
Turning to pipelines, our boat production continues to ramp consistent with our plans to produce approximately 38,000 units during the year.
Despite producing almost 10,000 units in the quarter, which is up 5% from the first quarter, retail outsold wholesale replenishment by more than 7,000 units, bringing dealer inventories to an all-time low of approximately 7,400 units.
Our boat brands ended June with under 10 weeks of boats on hand, measured on a trailing 12-month basis, with units in the field lower by 50% versus same time last year.
Without including the potential benefits from the Navico acquisition, we anticipate the US marine industry retail unit demand to grow high single-digit percent versus 2020; net sales of between $5.65 billion and $5.75 billion; adjusted operating margin growth between 150 and 180 basis points; operating expenses as a percent of sales to remain lower than 2020; free cash flow in excess of $450 million; and adjusted diluted earnings per share of approximately $8.
We anticipate expanding top-line in the second half by double-digit percent versus the second half of 2020, which will be more than 40% greater than 2019 with higher earnings as well.
Due to some fantastic branch restructuring work by our tax team and business units, we now believe our effective tax rate for 2021 will be approximately 22%, which is slightly lower than our estimate from our April call.
We extended and expanded our revolving credit agreement, which is now in effect through July of 2026, which now provides for $500 million of borrowing capacity, an increase of $100 million.
In addition, our Board of Directors increased our share repurchase authorization earlier this month, and we now have over $400 million approved for repurchases, which we plan to systematically deploy consistent with our capital strategy.
These moves follow our substantial 24% dividend increase approved in April as we continue to balance desired increases in shareholder return and investment in growth initiatives.
We now anticipate spending $270 million to $300 million on capital expenditures in the year to support and in some cases, accelerate growth initiatives throughout our organization.
In addition to the Navico and Freedom Boat Club transactions, and the start of shipments of the V-12 600-horsepower outboard, which I've already discussed, proof points in the quarter included, the launch of the My Whaler and Sea Ray+ apps for Apple and Android users, which advances the ACES Connectivity strategy by improving the boat ownership experience, reducing friction across the entire ownership journey.
The initial reception of these products is extremely promising, with more than 2,000 accounts created in the first few weeks and a star rating of 4.9 out of five.

Summary:
In fact, the sum of our wholesale orders for 2022 model year product is already roughly equal to our projected 2021 full year wholesale Boat Group revenue.
Adjusted operating margins were 17.1% and adjusted earnings per share was $2.52, once again setting new all-time highs for any quarter for which we have available records.
Without including the potential benefits from the Navico acquisition, we anticipate the US marine industry retail unit demand to grow high single-digit percent versus 2020; net sales of between $5.65 billion and $5.75 billion; adjusted operating margin growth between 150 and 180 basis points; operating expenses as a percent of sales to remain lower than 2020; free cash flow in excess of $450 million; and adjusted diluted earnings per share of approximately $8.