Seaboard Marine - Repower Articles | Building “Miss Rebecca” - A 26’ Jack Tar, Designed by Arch Davis

After years of owning and operating boats, reading and studying boat design and construction, and picking up a USCG Masters License, I decided it was time to "take the plunge" - to build a custom boat just for me. After much study I decided on building in wood, specifically plywood epoxy encapsulated, for several reasons:

Modern wood/epoxy construction is strong, low maintenance, and is easily repaired
Materials are readily available
I had the knowledge, skills, and tools to do the work
Literature and plans are readily available for the amateur builder
Wood floats - always a nice thing in a boat
I like wood, my wife likes wood

Selecting the Design

I spent months searching for designs in plywood that were more traditional than contemporary. I knew I wanted a boat in the 25 to 30 foot range, diesel powered, stable, and sea kindly - a boat I could use for fishing, diving, and cruising the offshore islands in Southern California where I live.

At the time, National Fisherman Magazine had just published an article by Arch Davis describing his Jack Tar plywood Maine lobster boat - a boat designed for amateur construction by owner/builders. The Jack Tar design, with its length of 26' LOA, beam of 9'3", and diesel power looked promising.

Having been a fan of lobster boats for years I was very interested in this design. In September 1993 I purchased the plans from Arch. Upon reviewing the 15 pages of plans I realized I'd found my boat - stout construction in materials I understood with a layout perfectly suited for my needs. Construction began in October 1993.

Construction

I quickly settled into a routine centered on building "the boat. Among my family and friends, my identity and the project became one. I've since come to understand this kind of commitment is required if such a project is ever to be completed. Soon, my carefully planned schedule fell by the wayside as I discovered the joy and hard work of building my own boat. One of the challenges of building a boat is finding the suppliers and materials needed for the project.

After turning over the hull I focused on selecting the engine. The design of my boat provided many options for engine selection. I knew I wanted a medium duty diesel engine between 150 and 200 HP. I spoke with owners of boats, both commercial and recreational, about their experiences. I took courses in diesel engine tune up and rebuilding at the local community college. I compared purchase, operating, and maintenance costs. Finally, armed with my collected knowledge I decided on a Cummins B series 6-cylinder engine.

Engine

I purchased my 6BT5.9 M from Cummins Cal-Pacific in Irvine, California. Along with the engine came a recommendation for expert assistance in designing my engine installation - Seaboard Marine in Oxnard, California. Living near San Diego, 150 miles south of Oxnard, I was sure I could find such expertise locally. Prior to installing my engine I had to design my boat's mechanical systems: engine, gear, exhaust, drive shaft, and steering. My search of the local suppliers found several that would do the job, but none that were interested in helping me to do the work. With no success locally I decided to call Seaboard Marine. After talking about my project with Tony Athens, owner of Seaboard Marine, I knew I'd found the help I needed.

Our first project was the design of my exhaust system.During that first phone call I learned more about exhaust systems than I could have ever imagined so I made a trip up to Seaboard.

I arrived at the shop on Saturday at 7:30 AM, blueprints in hand. After sharing boat-building experiences we got down to business. Using my boat's plans, Tony designed an exhaust system that considered operational parameters for backpressure, noise suppression, and preventing seawater backflow. The heart of the system is a 5" exhaust elbow. Built of 316L stainless, it includes a high temperature (loss of raw water) alarm. Another feature, a surge tube for preventing sea water back flow into the engine, was built by myself using directions and materials supplied by Tony. As construction progressed I asked Tony for advice on many other projects, including the boat's fuel system, hydraulic steering, rudder and propeller, and pilothouse windows.

Launch

After six years of effort, construction was completed and the boat launched in the spring of 2000. I found the most nerve-wracking time of a boat building project is the launch and subsequent shakedown. I soon found I had little to be concerned about. Based on the boat's weight and horsepower, the propeller calculations specified a top speed of 23+ knots. On her first run we reached 23.5 - right on the money.

The lobster boat design was everything I'd hoped. She's fast, roomy, incredibly stable, and economical to operate. On the first shakedown run of 70 miles, averaging 20 knots, fuel economy was 2.5 mpg. Subsequent runs at a comfortable cruising speed of 17 knots resulted in fuel economy passing 3 mpg.

Some Final Thoughts

My success with this project can be attributed to many factors, including Tony’s interest in my project. One final note after berthing "Miss Rebecca" at the commercial fishing docks in Oceanside Harbor, my new neighbors stopped by for a visit. Soon we were talking about all aspects of boats, including my shiny Cummins engine. It came as no surprise when three of them knew of Tony's work. One comment sounded familiar too; "He really knows his stuff, he's going to do my new exhaust."Seems good news travels fast on the docks.

Trial Results and Post Trial Follow-up

Based on my performance tests I believe I am over pitched by 1". Although I can reach full RPM, the boat has a hard time staying at full RPM. RPM falls off in turns and fluctuates between 2500 and 2600 RPM. Later this fall I will pull the prop and have it repitched to 20x21.

Weight:

9,000 lbs
(Full)

Transmission:

ZF Marine ZF 63A
(ZF Hurth HSW630A)
Ratio: 1.5:1

Propeller:

4 Blade
20" x 22"
RH

PERFORMANCE

RPM

KNOTS

GPH

1200

7.7

1.5

1800

12.4

3.9

2000

14.5

5.3

2100 (cruise)

15.7

6.2

2200

16.9

7.0

2400

19.7

9.0

2600

22.2

11.2

I've also found that I have insufficient air circulation within the engine box after slowing down from cruise (16 k) to trolling speed (4 k). The air temperature rise within the engine box exceeds the 30 degrees F. recommended by Cummins. I've installed two blowers, one in and one out, connected to a temperature switch that closes at 110 degrees. This has corrected that problem.

Tony Athens | May 1st, 2000