My Serious Affair With Semi-Dories
by Mike Hillis

For the novice, semi-dories are attractive, lightweight, easy-planing and fuel efficient little craft. What’s not to love? John Gardner’s The Dory Book includes plans for 4 semi-dories, 12 to 20 feet. I’ve built them all, or at least variations of each. I’ve found each of them to be predictable, mannerly, and fun little craft.

All of Gardner’s semi-dories have narrow flat bottoms, and lapstrake, rounded sides, with a flat run aft for planing. They’re all relatively narrow meaning they plane with a small motor and are mannerly at all speeds, i.e. they don’t have much of a transition between displacement and planing speeds and best of all, they don’t porpoise. Here’s a summary of each:

Photo #1, 12’ semi-dory

The Vacation-Cabin Boat- My friends Gary and Cindy have a vacation home on Montana’s Flathead Lake. They also have the ubiquitous 3000 pound, 200 hp inboard-outboard ski boat, which incidentally has more horsepower than either of my vehicles. They soon discovered that even though Flathead Lake is 30 miles long, it didn’t take them much time to explore the lake at 30 mph. They often found themselves in the dilemma of trying to decide what to do after you’ve circled the lake and it’s still not lunchtime! Worse, the I-O was not comfortable at speeds of anything below a full plane, because its nose was stuck skyward from about 6 mph to about 20 mph, while leaving a wake like an aircraft carrier. They asked me for a “cute, wooden, putt-putt” type of boat. Photo #1 is the 12’ Gardner semi-dory we selected. The boat is built of 6mm Okoume on fir frames. It weighs ~120 lbs. It went together with standard “glu-lap” construction. We tried it out with my 5hp kicker, and it would plane with one person and give an easy 7-8 mph with 2 persons aboard. Gary ultimately powered it with a used 8hp. After one season, Gary and Cindy discovered that the I-O was sitting idle most weekends, while the semi-dory was in constant use. Their teenage sons, however, still needed the adrenalin rush of the I-O. Kids! Photo #2 shows the boat with my wife Lorena and dog Hannah. Lorena’s the one with the cap.

Photo #2, The bow of the 12’ semi-dory

Troy’s Boat- Troy is a social worker in Coeur d’ Alene, Idaho. He’s seriously “boat-struck.” When we first got together, Troy expressed his desires to own a 20’ baby tug, a 20' cruising trailer-sailor, and a number of other fairly pricey boats. Troy also had no real money. Actually, he only had ~$1000 to put towards a boat. So, after much deliberation, we decided on a small, car-toppable motorboat. We took Gardner’s 5-plank, 12’ semi-dory in Classic Craft You Can Build, “stretched” it to 14’, substituted steam bent ribs for the sawn frames from Gardner’s design, and added a foredeck and side decks. I found Troy a 7.5hp Honda with low hours for $475. During construction, I substituted cheap plywood forms for the sawn frames that Gardner specified. I used temporary ribbands to establish the plank shapes. After I pulled the boat off the molds I steam bent in ½” x ¾” ash frames. Photos #3 and #4 show Troy and his boat.

Photo #3, Troy and his 14’ semi-dory

Photo #4, 14’ semi-dory, note the steam-bent ribs and seat riser

The Big Boat- The big boat was conceived while I was camp-cruising in a 16’ square-stern canoe along the southern coast of British Columbia. I wanted to include my wife and dog on the next trip, and take in Chatterbox Falls, and a few other similar destinations in south coastal British Columbia. I selected Gardner’s 16’ semi-dory because it’s fairly cheap and easy to build, requires low horsepower, and is very seaworthy for a 16’ boat. Check out the height of the bow in construction photo #5!.

Photo #5, 16’ semi-dory under construction

We powered the boat with a 15 hp Honda. It’s planes the boat at about 10 mph, even with two adults and a dog, and a week’s worth of camping gear. Photo #6 shows the boat in Narrows Inlet, B.C. The kicker on the bracket is for emergency power only. The main engine sits in a tip-up well, and is out of sight. Note the bent coaming at the bow. Chatterbox Falls is at the end of a 30 mile-long Fiord. On the return trip we hit 20-30 knot head winds, which collided with the outgoing tide. We had 3-4’ steep, breaking seas for about 5 hours, during which time we averaged only 4 mph. Eventually, the tide changed, the seas became a lot less steep, and we were able to complete the trip at 6-7 mph. Not bad for a 16’ boat. As steep as the seas were we never really took green water over the bow, although we did have to bail fairly constantly due to the constant spray.

Photo #6, a very filthy and trip-weary 16’ semi-dory. (Note curved coaming)

Emma- You may have seen Emma in a construction photo in DW last June, or in-the-water photos last September. She’s basically a 19’8” Gardner semi-dory with some serious modifications. Photo #7 illustrates the original lines of Gardner’s boat (black) with my modifications (red).

Photo #7, Emma’s lines, original Gardiner lines (black) and my modifications (red)

The major changes include:

  • 1) raising the chine (what used to be the bottom) at the bow;
  • 2) extending the stem aft until it blends into the keel, which is 5” below the old bottom line; and
  • 3) running the keel straight aft from station 3 to the transom;
  • 4) adding a raised deck forward; and
  • 5) cutting out a portion of the sheer strake to give it a broken sheer line.

Step #5 is trickier than it sounds. To establish the true shape of the transom, you have to loft the raised deck line as if there were no “cutout” (dashed red line at the transom in the cross-section profile). The shape of the cutout is established during construction suing battens to make it eye-sweet.

Emma has a lot of carvings, samson posts, wooden cleats, and other “cutesy” features. Her main feature, however, is her performance. This is the perfect “poor mans” yacht. She’s cheap to build, cheap to power (15-20 hp), cheap to run (~12mpg), and cheap to trailer (we tow her behind Asthma, our 14 year-old Trooper). Because of her narrow beam and variable deadrise, there’s absolutely no transition from displacement to planing speed. And, she’ll handle big seas like boats substantially larger.

Incidentally, finding a trailer for Emma was a little challenging. Trailers for 20’ boats typically have capacity for 2000-4000 pounds. Emma only weighs 550 pounds, so with a typical trailer, the wheels would seldom have touched the pavement! I ultimately special-ordered an EZ Loader designed for a 14-17’ boat and had the tongue extended 2’.

I promised several DW readers that I’d send out the Table of Offsets last winter. I’m still procrastinating. During construction, I spent a couple weeks of evenings lofting Emma. Yet, when I set up her frames on the ladder frame, and bent ribbands around them, several were quite unfair and took a lot of manipulating to get the hull sweet and fair. Consequently, I’m a little nervous about sending out offsets and having someone run into major construction problems. Anyone familiar with lofting, and access to Gardner’s semi-dory plans could build the boat assuming they understood lofting and had a good eye. I’m debating re-lofting the boat and constructing/fairing another hull in frame only using throw-away materials so I could get full-size patterns for the molds, stem, and transom. Let me know if you absolutely can’t live without the patterns, and I’ll see what I can do. I’d probably need a few bucks to offset the materials cost. Oh…… and I’d be delighted to build one for somebody on the west coast!

Photo #8, Emma at anchor with Cooter on her stern

Photo #8 is a close-up of Emma. Note our dinghy Cooter sitting upside down on the stern. Cooter is a 6’x 4’, 33 lb Gartside-designed dinghy that my wife built (with me hovering, annoyingly, at her elbow) as a tender for Emma. Cooter also tows wonderfully! Emma has a self-draining chain locker in the bow (which sits atop a floatation tank situated between the stem and a bulkhead at station 1). Also note the walk-thru windshield on the port side of the wheelhouse. The samson posts are super-strong, and are the only feature that is overbuilt on Emma. I tried to visualize being anchored in a strong headwind and 4 foot chop for sustained periods. The motorwell is flanked by watertight compartments and side-decks that makes it very strong, but light (i.e. like an egg-carton). Spilled gasoline fumes drain directly into the well, not into the cockpit.

Mike Hillis