If you would like to own a new, large, seaworthy convertible that is selling anywhere from $1.8 million to $4 million, and you know you’ll never be able to afford it, recent events may have put that dream – or something close to it – within realistic reach. An interesting thing has happened in the last nine months. First, most convertibles built in the 1980s were powered by (now-obsolete) Detroit Diesel 2-stroke engines which were selling at a discount far greater than their age would indicate on the used boat market. Then, last summer, high fuel prices caused large boats to be discounted farther. Finally, the economic decline the last six months has caused many used boats to fall another 30%. The cumulative effect of this has been to make some classic 1980s convertibles so inexpensive, that they can be repowered with Yanmar diesels and still only cost from 15% to 30% of similar brand new models – and go faster and burn less fuel than they did the day they were new some 20 to 30 years ago. Join us as we show you the dollars and sense of repowering of a 1984 Hatteras 52.

There are over 50 Hatteras 53 convertibles from 1980 to 1990 currently on the market from $195k to $400k.

Many large convertibles and motoryachts built in the 1970s and 1980s were powered by Detroit Diesel 2-stroke turboed and intercooled V-71s. Detroit Diesel WWII-vintage, low-horsepower 2-stroke diesels were hopped-up with Rube Goldberg bolt-ons to produce the energy that the new generation of semi-displacement boats needed. Their blocks were never intended for the tremendous horsepower that they were later required to produce. For example, the DDA 12V71TI rated at 850-hp new in 1986 started life decades before as a 350-hp naturally aspirated engine.

These engines were/are notorious for leaking oil, blowing injector tips, smoking and generally being problematical. General Motors, which owned Detroit Diesel back in the 1970s and ‘80s, refused to spend the money to design and build new engines made for the higher speeds builders wanted to attain in the go-go years of the 1980s. Roger Penske bought the engine maker just as their 4-stroke Series 60 was being introduced, an engine that went on to be very successful.

Repowering With Yanmar

For the last 15 years one of the most popular and successful re-power engine brands in the U.S. has been Yanmar. There are several reasons for that:

First, Yanmar has specialized in repower. It devotes tremendous resources to consumer service which makes repowering happen and be successful. The engineering and sales time that goes into one repowering installation is almost the same that does into selling a builder on using an engine in production for dozens of boats. That is why most engine makers and distributors are simply not willing, or interested, in devoting the time that it takes to this kind of customer service for individual repowering.

Second, generally, Yanmar engines are lighter and often smaller packages. This makes installation easier. Being lighter is always good. Some of its engines have the best horsepower to weight ratios in their class. Generally they are higher speed diesels, which the market and the industry embraced as their reliability was proven over the years and when other companies also came out with higher-speed engines.

Thirdly, Yanmar engines simply cost less in most cases than the engines that they compete with.

Picking the Right Boat To Repower

If you would like to own a large, seaworthy convertible that has been tested over 30 years or more, you can not go wrong with the Hatteras 52. It was built of solid fiberglass which is nearly indestructible. Their topside styling is classic. Its bottom was a classic Jack Hargrave design.

There is nothing like owning a new boat, but they are very expensive, and if you can not afford it, the next best thing is repowering a classic old boat, such as the Hatteras 52. In fact, from our perspective, the Hatteras designs from the 1980s have held up very well from a styling point of view. Obviously the condition of their interiors will vary from boat to boat. Some have been recently rehabbed and are on the market, others can be put in nice condition for as little as $20k and there are yards which will rehab the whole inside of your boat for something on the order of $100k or less.

This week we will look at repowering a Hatteras 52 with data based on actual repowering projects by Mastry Engine Center in Florida. (In two weeks we will look at repowering a Bertram 46, a job done by Mack Boring, in New Jersey, the Northeast distributor for Yanmar.) We’ll give you the total cost for repowering as well as the performance numbers after the project was completed.

Refurbishing a Hatteras 52

The Hatteras 52 was one of the most popular models that Hatteras ever built. We have picked the period of 1980 to ’88 as our sweet spot, but you can go back even farther and find units still cheaper.

Hatteras boats have always been painted rather than have gel coat. Obviously, you will want to find a boat that has been painted fairly recently. A good AWLgrip or Emron paint job should last 10 years and still look good. Hatteras, Bertram and Viking during this eight year period were unquestionably the best boat builders in America and maybe the world. Nevertheless, when buying even one of these brands that old you must have a good surveyor go through the boat and make a close inspection. After the engines, electrical and plumbing are your top concerns.

The New Yanmar Power Package

The 1984 Hatteras 52 in our case study was powered by DDA 12V71TIs of 850-hp and were replaced by Yanmar 8SY-900-hp diesels driving through Twin Disc MGX 5114A 1.92.1 marine gears, turning ZF 32x37x4 props.

Taking the Engines Out

While to the layman it might seem nearly impossible to get the old engines out and new ones in, in fact it is a fairly easy process for those boat yards which are used to doing it. First, the aft bulkhead of the house is removed. Then the galley appliances are taken out along with the settee and furniture. The sole of the salon is then pulled off, or hatches above the engines are removed.

Different yards use different techniques to remove the old iron. Sometimes an “A” frame is constructed in the salon to raise the engines, and sometimes a forklift or some other equipment is used to pull the engines out. New engines beds are installed and then the new engines are “dropped” in. Perhaps the most time consuming work is hooking up all of the plumbing, controls and wiring once the new engines are in. Obviously, this is where the expertise of the yard is of critical importance. To a large degree, the engine room undergoes a major overhaul.

This is another reason why it is important to have an engine distributor that has the personnel, expertise and the enthusiasm to work with individual boat owners.

New Life in the Old Girl

Below is a performance chart of the Hatteras 52 after the new 900-hp Yanmars were installed. While we don’t have performance numbers for the boat with the old engines, we can tell you from our own personal experience with a Hatteras in this size range with 12V71TI Detroits, that the boat runs with the Yanmar 8SY-STP engines about six to eight knots faster top end and burns at least 20 gallons an hour less at 20 knots.



Mastry personnel supplied BoatTEST.com with the numbers above. The test was conducted with 700 gallons of fuel aboard, six people, in calm seas and ambient temperature was 69-degrees F.

The Cost

The complete cost of the repower for the Hatteras 52 with the engines installed, including all installation work would be about $212,000. Assuming a boat in good condition could be purchased for $250,000, then the cost of the boat and the repower would total about $462,000. New convertibles in this caliber of boat generally cost between $1.8 and $2.4 million. That means that the repower project would cost from about 19% to 26% of a new boat.

That price certainly put the fun, seaworthiness, and a lifetime’s dream within reach of many more people.

What Next?

If you have a specific repower installation in mind we suggest that you call a Yanmar distributor and find out their recommendations as to the specific engines should be installed and their cost. We have worked with both Mack Boring and Mastry Engine Centers and can attest to their expertise and knowledge. They can also recommend a yard near you who can do the work in a professional manner.

Central and Northeast U.S.-- Mack Boring & Parts Co. website…

Southeast U.S. -- Mastry Engine Center website…

Next: Repowering a Bertram 46

In the next issue of Offshore Motoryacht we will bring you an actual re-powering story on the Bertram 46. Like the Hatteras 46, there are 50 of them on the market. Check them out and we’ll give you the cost of repowering in two weeks.