Duckworks - Projects
The Online Magazine For Amateur Boat Builders

Building Tree Frog Pram
By Terry Lesh


I needed a pram/tender for my 18’ Baymaster Cuddy Dory Sloop when I visit the San Juans or other waters needing shore access. I enlisted the help of my friends on our interest list and got lots of feedback. I wanted a pram as small as possible, as light as possible, yet able to carry 425# safely with adequate freeboard, stable entry from another boat, towable, beachable and salty looking.

I considered a number designs from Bolger, Michalak, Vartalia, Welsford, McCallum and others. These included: The Elegant Punt, Tender Behind, Micro Auray, Minnie Auray, Tween, Nymph, Rubens Nymph, Peanut Pram, Simple Dinghy, and the Tree Frog.

I did a lot of work here: I downloaded all the basic dimensions of each of these boats, rescaled them to a two-dimensional drawing and compared each of them for buoyancy, freeboard, looks, and weight.

The winner is John McCallum’s Tree Frog. It’s dimensions are 7’ 8” x 4” 2”, with a good 14” freeboard. John estimates the weight to be about 75#. It’s an interesting design with a modified garvey style bow and slightly twisted side panels running some tumblehome along the side panels as they run aft toward the bottom of the transom.

What happened here was I liked the Auray Punt redesigns by Hannu Vartiala (Hannu’s Boatyard) so much I tried to rescale his computer design to meet my requirements. But they were a little lacking in my requirements. I rescaled his design to meet my requirements, posted them, and got feedback that I had just designed the Tree Frog! This gave me some ethical issues to think about. Having experience enough in boat building to build from my own sketches, should I go ahead and do it, or should I honor John by buying his plans? Thanks to my buddies, the Coots, I was advised to just go ahead and buy the plans as $38 gets complete instructions, offsets, support and goodwill from a fellow boater. Well advised.

Fortunately John lives in my area so I went out to see him and look at the original Tree Frog he had built. I was quite impressed with the appearance, room, freeboard, buoyancy capacity and general layout for such a small boat. Tree Frog has unique seating arrangements for an 8’ pram, which can get crowded with even one passenger. John says it will fish two adults, and ferry three ship to shore. Tree Frog has a good size transom seat, and a two-position rowing seat amidships, with two strategically placed rowing stations to adjust trim/load requirements.

A perusal of the plans impressed me and of course I bought them. John has gone to a lot of work here. There are some 10 pages of detailed written instructions, materials list, screw schedule, scaled offsets, panel layouts and patterns for the scantlings fitting out. John is hell for stout using some 200 screws and bracings everywhere for stress points like corners, bow and transom, chines and gunnels, seats, floors and skeg. His specs call for the best ¼” marine ply, the best epoxy, the best hardwoods and multiple taping of all joints.

A week after I bought the plans, John was thoughtful enough to bring his prototype of the Tree Frog to the Messabout we had at Fern Ridge Lake in Eugene, Oregon. We all got a chance to try her out on a very windy, stormy day with some good-sized waves hitting our windward beach. I was real curious to see how she handled in the chop, especially with two big guys in her. When I tried her out she handled smoothly on the wind whipped lake after launching off the beach without getting a drop inside. I turned her every which way in the swells, backed her down against them, and rowed her sideways in the troughs. She stayed dry and smooth, no pounding, splashing or crankiness. With two 200# men aboard she still showed good freeboard and kept her manners. An amazing little dinghy!

The Prototype:

Pic # 1: Designer John McCallum Getting Off Windward Shore at Fern Ridge

Pic # 2: John Getting 1st Good Oar Pull

Pic # 3: Two Big Peas In a Punt

Pic # 4: John does an aesthetic Row by

With already 5 boats in my yard, a limited budget, and lots of boat stuff leftovers in my shop, I cheated some (maybe a lot) on Johns quality control. I had some left over epoxy, lots of left over pine, 1 sheet of luan that has been laying out in the rain for two years, a little fiberglass cloth, and about 1000 stainless, bronze and brass screws but hardly two of a kind. I had to order some more cloth and tape from Raka, Coot buddy Pat Pateson promised to mill me some nice fir gunnels.

That left a little more epoxy, paint, hardware and oars I had to get. I have found the Rustoleum latex primer and latex Painter’s Touch colors have worked very well on Toto. Toto is now over 2 years old and, very easy to touch-up and still looks like new. This primer is gray and very tough stuff, easy to sand and seals well. These paints are only about $7 at the local BiMart. Also I found a great price on epoxy from in San Diego. He sells Aeromarine Epoxy, which comes in 1:1 and 4:1 ratios. I got a 5 quart kit for $50 + $9 shipping.

For rowing hardware I ordered the nylon oarlocks and sockets from Duckworks and plain made my own oars. I used sheet metal screws as clamps for all the scantling fittings (knees, braces, seats, etc),then took them out and filled with epoxy putty after cure. I don’t know how much 200 screws weigh but I saved some here.

A word about luan. I get 6mm underlayment from Crosscut Hardwoods for $12 a 4’ x 8’ sheet. Toto is made from this stuff, as is my Windance (Thomson’s Moondance). Both boats have stood up very well. Toto made it through a hurricane sitting on top of my car in Loreto, Baha, last summer. The only damage was 100 mph driven wet sand into some of the deck seams (which I had not glassed) separating the plys for about an inch into the decks. A tough test! It was an easy repair as I just cleaned them up and fiberglass taped them like I should have done. Also I was impressed to find the sheet I had laying out on the woodpile for a couple years that was exposed to the soggy Oregon winters had no damage and no separations. It’s the lightest plywood to use for small boats, and if it's well glued and sealed I see nothing wrong with it. The wood techs at Crosscut tell me they use waterproof glue now in all luan. The panels I got had one very good face, and one face that needed some patching and sanding to smooth. I used Elmer’s exterior wood putty for doing this, it spreads smooth, is tough and sands very well.

Instead of using multiple coats of epoxy to fill the glass weave, I faired the sheathed surfaces with the Elmer’s prior to painting. In the past I have used marine polyester filler to do this and it worked fine. One of the builders of the Redwing 18 used it to fair the hull that had been fiber glassed with epoxy. There is an argument that polyester does not adhere well to epoxy, but the filler fairing compound has worked well for me when the epoxy surface has been well cleaned and roughed up some. It sands well also. I like using the fillers as you just use what you want where you want and you don’t have to remove any epoxy in the sanding.

Building It:

After getting out all the panels for Tree Frog, I sealed them on both sides with two coats of epoxy and tied them together with those nylon electrician’s wire ties. Before assembling the panels (which I had cut out leaving about a 3/16” cut line), I planed them to the line and put in a 1/16” bevel in all seam edges. I have made some 8 boats (including some of my own design) using the sewn seam method and I must say that this one fit together the best of any of them. John’s design measurements are very accurate. The hull assembles easily using no forms or jigs or bulkheads.

Pic # 5: Panel and Oar Layouts (note swept sweep)

(click images to enlarge)

click to enlarge
click to enlarge
Pic #6: Stitching Side Panels to Bottom
Pic # 7: Stitching Bow (yellow line is on a Spanish windlass)
click to enlarge
click to enlarge
Pic # 8: Bending Bow Rail:
Pic # 9: Attaching Transom Rail and Gunnels
click to enlarge
click to enlarge
Pic # 10: Leveling and Truing Hull
Pic # 11: Bottom Glassed and Filled
click to enlarge
click to enlarge

Pic # 12: Attaching Bow Rail

Pic # 13: Bow Rail and Gunnel Detail
click to enlarge
click to enlarge
Pic # 14: Oar Detail
Pic # 15: Completed Oars
click to enlarge

For the oar shafts I selected two 1” x 4” x 8’ bird’s eye pine boards of the lightest color and weight I could find at the local lumberyard. I thought about using doug fir 2” x 2” , but they were so heavy and cost so much, I went for the pine (about $5 worth). I ripped them along the curvature of the grain, glued them in opposite grain runs, watching for the shape (trying to get a spoon type curve to them);* 8 sided shaped them with the angle grinder, then finished them out with an orbital sander to get more or less round.

For the blades I epoxy glued two left over pieces of luan with a glass cloth liner inside. Measured the resulting thickness. Then I ripped a slot in the oar shafts with my bandsaw to fit the blades. Epoxied them in with a thixotropic blend of wood flour. Ground and sanded all to shape and finished them with Teak Oil.

* They turned out beautiful, but this experiment of curving the sweeps did not work well. They gripped and pulled—too well, as they wanted to twist in my hands and was very tiring. Wanting to get going, I broke down and bought some real oars (7'). A note on finishing oars—I talked to a number of drift boat owners trying to determine the best finish. They said oil was the best, as varnish is just too hard to keep nice on these working parts. I finished them with multiple coats of teak oil, and will keep them as spares.

click to enlarge
Pic # 16: Row Seat & Knees
Pic # 17: Tow Bit Inside
click to enlarge
click to enlarge
Pic # 18: Tow Bit Outside
Pic # 19: Skeg & Strakes (note twisted panel)
click to enlarge
click to enlarge
Pic # 20: Seats and Knees (note floor braces, the outside hull strakes are screwed through the hull into these giving a good strong box effect.)
Pic # 21: Skeg and Strakes 2
click to enlarge
click to enlarge
Pic # 22: Finished!
Pic # 23: Author's Maiden Voyage
click to enlarge

© 2004 Terry Lesh, 2nd rights reserved