Friday, March 5, 2021

Michalak's IMB: "Birdwatcher" Style

 Many years ago, Jim built Bolger's Birdwatcher.(Do a Google search on "Bolger's Birdwatcher" for lots of information.) One of the interesting concepts of the Birdwatcher design is that the cabin is almost the full length of the hull and is surrounded by clear waterproof windows on the sides and partially on the ends. The center of the top of the cabin is open as well as the center of the cabin ends. The result is that the boat can be laid over on it's side (on purpose or inadvertently) and no water will get into the cabin. 

The boat is sailed or rowed from inside the cabin and crew is the ballast.

Since his time with Birdwatcher, Jim has designed a number of boats that include its concepts. One of those designs is "IMB". Using Jim's plans, I built this model. 

Jim Michalak's IMB, a "Birdwatcher" Style Sail/Row Cruiser


  • Replaced the designed rudder with a Michael Storer style holster enclosed rudder that I've used on two of my sailboats (and will continue to use in the future).
  • Added racks on the cabin top for spars (mast, boom and yard) for the lug rig sail and oars; required tie-downs not shown.
  • Jim uses ropes to control the leeboard. Based on Jerome Delaunay's Scow 244, I decided to use a  long handle to raise and lower the leeboard.

    One of the advantages of building a model of your boat before you commit to the full sized boat is that you catch your own 'brilliant' ideas before you invest time/money in the full-sized boat.

    For example, the handle on the outside of the lee board (as shown in the photo above) will NOT WORK on IMB. One would not be able to reach the handle without climbing on the cabin top (not a good idea) or by doing an awkward and dangerous stretch from the after deck.

    The handle WOULD work if it were attached on the inside end of the leeboard pivot shaft. Thus the leeboard would be adjustable from inside the cabin.  

IMB Showing Holster Style Rudder in the "Up" Position.
Tiller extends under after deck about 13" into the cockpit.

Oars Extended Through Oar Ports with Covers Removed 


  • Length: 13' 6" (4.1 m)
  • Beam: hull: 5' 3" (1.6 m)
  • Water Line Length: 13' (3.9 m)

  • Cockpit length: 8' (2.4 m) (bulkhead to bulkhead)
  • Cabin top opening: 8' by 2' at midships (2.6 m by 610 mm)
  • Span is 5' 3" (1.6 m); Oar's shown are 8' (2.4 m), which I believe are adequate for the small amount of rowing that would be done with this sail/oar cruiser.  

  • Freeboard: 1' 6" (457 mm),  2" (51 mm) less midships
  • Water Line Width: 5' (1.5 m)
  • WLL/WLW Ratio: 2.6:1

  • Hull Speed: 4.8 Knots, 8.9 kph, 5.5 mph. Given the large wetted surface and low WLL/WLW ratio, sailing in good wind could reach these speeds, but not rowing.


  • Based on the Birdwatcher concept, IMB provides a safe and comfortable sail/oar cruiser.
  • Oar ports enable her to be rowed (from within the cabin) when maneuvering in close quarters or when the wind dies.
  • The lug rig provides a powerful sail that is set with little rigging and hardware.
  • Plenty of dry storage in the 2 under-deck compartments.
  • All sail handling, steering and leeboard control is done from within the cabin.
  • Sailed heeled at 15 to 20 degrees (lee bilge panel is about horizontal), wetted surface would be reduced by approximately half and she would be really fun to sail.
  • Able to be transported with a light trailer.


  • Rowing speed will be lower than "Hull Speed" noted above.
  • Though plans are straight-forward, there are a lot of closefitting parts, especially around the windows and bulkheads, none of which are difficult to create and install, but do take more time to build than an open sailboat such as Jim's Mayfly series.
  • The open top (and ends) of the cabin are really comfortable and safe in sunny/cloudy weather, but would require closures for inclement weather. Such closures are typically made with either waterproof cloth and/or hatches.
If we're looking for a comfortable and safe sailboat for both day-sailing (for a small family) and occasional overnights for one or two (very close friends), this would be an excellent choice that you could build for yourself.

Friday, February 5, 2021

Michalak's "Marksbark", a Day Cruiser

 Jim's long, narrow "Marksbark" is a fast day cruiser that can carry a passenger safely and yet provide an invigorating single handed row with a hull speed of 5.4 knots. 

Marksbark as a Day Cruiser

The Safety Features of this Day Cruiser

  1. Water proof compartments at each end of the hull, approximately 2' (210 mm) long.
  2. The hull is fully decked except for the cockpit opening.
  3. A 3" (76 mm) coaming surrounds the cockpit opening. 
  4. The deck extends beyond the hull width by 8" (200 mm) midships and then becoming narrow fore and aft. Fastened to the bottom outside edge of the extended deck is a 2" (51 mm) wide 'plank' that runs the length of the hull on each side. Filling the space between this plank and the hull is 2" thick foam. This provides approximately 33 pounds (15 kg) of additional flotation on each side of the hull. Thanks to John Welsford for the idea of extending the deck beyond the hull as he did in his "Kiwi PDR".

    Underside of Deck Extension to Hold Foam Board Flotation 


The cockpit opening is long enough (7', 2.1 m) to accommodate rower and a passenger. Two positions for the oar locks enable a single rower or a rower with passenger without affecting trim. The cross-slotted floorboards enable the rowing seat and foot rest to be shifted as necessary.

Set-up for Rower and No Passenger

Added Passenger Seat & Moved Footrest/Rower's Seat Forward

Two storage compartments (in addition to the water proof compartments at the ends of the hull) provide  dry storage with access through deck hatches. The aft compartment is 2' (610 mm) long and the forward compartment, pictured below, is 3.5' (1069 mm) long. Both hatches are 12" x 18" (305 x 457 mm). The after hatch supports the reverse reading compass

Bow Showing Forward Storage Compartment, Anchor Cleat & Anchoring Fairlead

Use of the 'anchoring fairlead' (see end of post) enables anchoring without going on the deck, which is dangerous in a hull this narrow.


  • Length: 18' (5.5 m)
  • Beam: hull: 3' (0.9 m), edge of deck: 4' (1.2 m)
  • Water Line Length: 16' (4.9 m)

  • Cockpit length: 7.5' (2.3 m)
  • Cockpit opening: 7' by 2.5' midships (2.1 m by 762 mm)
  • Span is 3' 10" suggesting 8' (2.4 m) oars.  

  • Freeboard bow: 12" (305 mm)
  • ... midships: 6" (152 mm)
  • ... stern: 9" (229 mm)

  • Water Line Width: 3' (0.9 m)
  • WLL/WLW Ratio: 5.3:1
  • Hull Speed: 5.4 Knots, 10 kph, 6.21 mph

  • A straight forward build based on Jim's Toto design.
  • Hull is built as Jim designed. The changes noted in The Safety Features in this Day Cruiser are all additions to his design.
  • Fast: A cruising speed of 4 mph (6.4 kph, 3.5 knots) for ten 45" sessions per day results in 30 miles (48 km) a day cruising. Jim states in his write-up for the plans "...she'll hit 6 mph in good conditions and cruise forever at 4 mph."
  • Carries a passenger comfortably without affecting trim.
  • Could be cruised in, but may require shelter. See this post on "Shelters" for alternatives.
  • Abundant dry storage.
  • Seaworthy based on waterproof end-compartments, full decking, coaming and under-deck flotation.

  • Narrow hull at the water line results in a 'tippy' hull which is offset (somewhat) by the under deck flotation.
  • Heavy to car-top, although boats this long are easier to car-top than shorter boats of the same weight. See these posts on car-topping and this one by John Welsford.

    If most of your  rowing is 'day-cruising' and relatively little of over-night cruising, this design, with its ability to carry a passenger and it's speed, is an excellent option.

    Friday, January 29, 2021

    Bolger's Japanese Beach Cruiser

    Phil Bolger's Japanese Beach Cruiser (JBC) is a 12.5' (3.8 m) seven panel sail boat.  

    The JBC has a transom bow. Ross Lillistone's Whimbrel, Matt Layden's Sandflea and John Welsford's Scamp are three other examples of transom bow boats. Ross wrote a post about transom bows which incorporates some of Bolger's views. They make a case a for transom bows if there is a design constraint of LOA. 

    The plans from Bolger's Boats with an Open Mind (pg. 127)

    Using those plans, I built a 12:1 scale model pictured in the two photos below.

    Bolger's Japanese Beach Cruiser

    Bird's Eye View


    Length: 12.5' (3.8 m)
    Beam: 5.5' (1.8 m)
    Mainsail Sail Area: 89 Sq. Ft. (8.3 Sq. m)
    Mizzen Sail Area: 24 Sq. Ft. (2.25 Sq. m)

    The success of John Welsford's Scamp, which is similar to Bolger's Japanese Beach Cruiser, is a testimony to how successful a transom bow boat can be. Key is that we get a lot of boat for a short LOA.

    Thursday, December 24, 2020

    What Length Oars?

     You built/bought a boat that needs oars. How do you determine what length of oars?

    A rule-of-thumb is to double the span (the distance between the oar locks). However, this may not be the best length for the oars. For example, if the freeboard is greater than normal, then longer oars may be needed.

    Having struggled with deciding what length of oars to make for my Ross Lillistone Flint, I created this worksheet.

    Rowing Geometry Worksheet (Click on image to enlarge)

    (You can download or print a full-sized JPG version of this worksheet from Dropbox.)

    An Example:

    For this Oar Cruiser, the span is 52" (1321 mm). The distance from the oar lock to boat's centerline is 26". The distance from waterline to bottom of the oar lock is 20 " (508 mm). I placed a dot at the intersection of these two dimensions on the worksheet above. 

    Using an 8' 6" (scale) oar with a pencil mark at 7/25ths from the end of the handle. I placed that pencil mark on top of the dot and the blade just under the waterline, as in the photo below.

    Rowing Geometry During the Power Stroke

    This shows that when I'm rowing, the handles will almost touch (about 1" (25 mm) apart.

    I then changed the oar to horizontal for the recovery stroke. Now the handles overlap about 1" (25 mm) which means on the recovery stroke, I'll have to cross my hands.

    Rowing Geometry During the Recovery Stroke

    Using this Rowing Geometry Worksheet, I've been able to confirm that 8' 6" oars will work.

    See this post for additional information on rowing geometry. 

    Friday, December 18, 2020

    Another Oar Cruiser based on the Pacific Troller Dory

    For this Oar Cruiser, I used an unmodified hull of Paul Butler's Pacific Troller Dory. I added decking and another alternative for weather protection while sleeping aboard.

    Another PTD Based Oar Cruiser Buttoned up for Sleeping

    Covering the cockpit are two hatches with fixed skylights. Two mooring/anchoring cleats and a fairlead at the bow facilitate anchoring without climbing on the foredeck. See writeup at the end of this post for details. 

    While Rowing, the the Two Hatches are Stored on Deck

    The hatches are held in place while rowing by side coaming extensions and a tie-down strap (not shown). The reverse reading compass is on the after hatch with a sight line from the rowing seat.

    Top View Showing Slatted Floorboards, Rowing Seat (on left) and Foot Rest 

    The outriggers hook onto the side coamings and are adjustable fore and aft and can be easily removed by sliding them forward and lifting them off the coaming. A detailed description of these outriggers is here.

    Each side of the Hull is Fitted with Two 4" (102 mm) Clear Deck Plates

    Two ports on each topside provide ventilation while sleeping. Oars are shown in racks would include tie-downs (not shown). The coaming is 4" (102 mm) high and includes oak strips enabling movable outriggers.


    • Length:15' 4" (4.7 m)
    • Beam: 48" (1219 mm)
    • Estimated Water Line Length: 13' 9" (4.2 m)

    • Est. Water Line Width: 24" (610 mm)
    • Est. WLL/WLW Ratio: 6.9:1
    • Est. Hull Speed:  5.2 knots, 9.6 kph, 6.0 mph

    • Cockpit length: 6' 6" (2.0 m)
    • Cockpit opening: 4' 6" by 24" (1.4 m by 610 mm)
    • Cockpit headroom with hatches: 24" (610 mm)

    • Two watertight end compartments: 2' 3" long (686 mm) by hull width
    • Two storage compartments (inboard of the two end compartments), with hinged openings, are 2' (610 mm) long by hull width
    • Span is 52" (1321 mm) suggesting 8' 6" (2.6 m) oars.  


    • Plans are in the form of a booklet that describes every step for building the hull and is easy to follow.
    • The full decking and coaming add to the sea worthiness of an already sea worthy hull.
    • The two hatches, when closed, provide a weather proof sleeping cabin that will stand up to high winds from an evening thunder storm. 
    • She has sufficient protected storage for supporting a multi-day cruise.


    • Too heavy to car-top.
    • Windage (top hatches stowed on decks) will be greater than a plain hull. Leave the top hatches at home when you use it as a day boat.
    This PTD Oar Cruiser is, in my opinion, an effective compromise between a fast day boat, such as Gavin Atkins OarMouse, and other Oar Cruisers with temporary shelters.

    Saturday, December 12, 2020

    Andre-Francois Bourbeau's Gorfnik

    Gorfnik  is an 8' (2.4 m) cruiser that is primarily sail propelled and uses a 'stand-up' paddle as auxiliary power. She has been extensively cruised in a wide variety of waters (see the write-up in plans description referenced in "Plans:" below.) Andre-Francois used the PDR hull design and then added a 'cabin' and decking to enable cruising with sleep-aboard accommodations and sufficient storage to be totally self-sustaining for at least a week.

    Gorfnik with Spars, Paddle and Anchor Stored. Leeboard in Raised Position.

    Classic PDR Hull with Rudder Raised in Michael Storer-Style Holster

    Birdseye View Without the Two Hatches of the Cabin Top

    Cabin with the Designed Access Port to Side Storage Compartments


    Free plans are available on the PDRacer site.


    • LOA: 8' 4" (2540 mm)
    • Beam: 4' 2" (1270 mm)
    • WLL: 7' 3" (2210 mm)

    • WLW: 4' (1219 mm)
    • Two side compartments full length of hull, full height of hull and 6" (152 mm) wide
    • Freeboard: 13" (330 mm) to deck

    • Sail: Sprit rigged, 66 Sq. Ft. (6.13 sq. m)
    • Mast: 12' 6" (3810 mm)
    • Sprit: 11' 6" (3505 mm)

    • Boom: 8' 0" (2438 mm)
    • Cabin top without hatches: 2' 5" by 2' 5" (737 mm by 737 mm)
    • Headroom from sleeping platform: 36" (914 mm)

    • Headroom from removable seat: 24" (610 mm)
    • Fore Deck: 4' 0" by 3' 4" (1219 mm by 1016 mm)
    • After Deck: 4' 0" by 1' 3" (1219 mm by 381 mm)

    • Side Decks: 8" (203 mm)
    • Rudder Blade: 3' 3" by 10" (991 mm by 254 mm)
    • Paddle: 7' 9" (2362 mm)

    • Leeboard (starboard side only) 3' 0" by 10 " (914 mm by 254 mm)
    • WLL/WLW ratio: 1.8:1
    • Hull speed: 3.6 knots, 6.7 kph, 4.0 mph

    Possible Modifications:

    • Make the side compartments 8" (203 mm) wide and make them open topped rather than accessible by a port. This would eliminate the 'flotation' that the closed compartments provide, but would provide significantly more accessible storage.
    • Add oarlocks to the forward end of the sides of the cabin at the top (see example in Skow 244) in order to row standing up facing forward, eliminating the 'stand-up paddle'.
    • I would make sure that the removable seat would be low enough and risers long enough that I could sit in both the aft end and the forward end of the cabin without hitting my head on the top hatches. This may require building the hatches with a greater arch than plans show.
    • I would add skylights in the two top hatches so that I could see the sail when the hatches are closed.


    • A mini-cruiser that I can sleep, cook and eat in, protected from rain, without having to set up a temporary shelter.
    • Capable of at least a week-long cruise.
    • Can be sailed and rowed (with the modification).
    • A full set of (free) plans that make it a straight-forward build.


    • Short WLL will keep speed low.

    Friday, November 27, 2020

    Gavin Atkin's OarMouse as a Day Boat

     Gavin's OarMouse is a V-bottom 14 foot row boat made from two 4' by 8' sheets of plywood... one person, fast and easy to build.

    Overview of OarMouse plans by Gavin Atkin

    Plans are free and available at Duckworks.

    Using the plans, I built a concept model (scale 12:1) of a day boat based on OarMouse. 

    The view above shows the 6' 3" (1905 mm) cockpit, 10' (3 m) oars, reverse reading compass, slatted floor boards that enable the foot brace and rowing seat to be adjusted to fit the rower, and the outriggers which are also adjustable and which provide a span of 5' (1524 mm).

    Profile View: Why Windage is Not an Issue

    No technical reason why the reverse transom other than I like the way it looks. And "Roci..." is a "hero" of one of my favorite science fiction series: The Expanse (James S. A. Corey). 

    The Bow Transom Sloped Forward 30 Degrees

    Fitted Out with Sleeping Tent 

    Specifications of the Day Boat:

    • LOA: 15' 6" (4.7 m)
    • Beam: 3' (914 mm)
    • Cockpit opening length 6' 3" (1905 mm)
    • Cockpit width 1' 9" (533)
    • Cockpit length (for sleeping) 7' (2.1 m)
    • Water Line Length: 15' (4.6 m)
    • Water Line Width: 30" (762 mm)
    • WLL/WLW Ratio: 6:1
    • Hull Speed: 5.2 knots, 9.6 kph, 6.0 mph

     Conversion of OarMouse to a Day Boat:

    • Lengthened the LOA from 14' to 15' 6" (4.7 m) by re-spacing the stations to achieve a 15.5' length. 
    • Slanted the aft transom forward by 30 degrees.
    • Slanted the bow transom forward by 30 degrees. Note that these 3 changes were the only changes to the hull shape/size in the original plans.

    • Made the two frames into two waterproof bulkheads 7' (2.1 m) apart providing generous flotation in the two end compartments.
    • Surrounded the cockpit opening by 3" (76 mm) high coaming.
    • Added a 4" (102 mm) V-shaped splash guard to the forward deck.
    • Added a fairlead to the bow. See this article (at the end of the post) for how to anchor from the cockpit without crawling out on the fore deck.
    • Provided outriggers. See this post for a description of these outriggers.
    • Provided demountable hoops for supporting a shelter.


    • A straight forward build from the free plans.
    • She will be one of the fastest boats of all those in this blog.
    • The full-decking, coaming and splash guard will result in a more sea-worthy boat than an open version of the hull. However, she is only designed for protected waters.
    • Very low profile means she will be little affected by cross-winds when rowing.
    • Plenty of storage space in the cockpit for supplies in waterproof bags. 
    • Two waterproof compartments provide flotation.
    • Long boats such as this can be car-topped.  See the comment by John Welsford at the end of this post.


    • The narrow V-bottom hull makes this boat tippy (but fast). Keep weight low and centered. See John Welsford's technique for reboarding long narrow boats such as this.
    • No built-in waterproof storage.

    This boat would be ideal for day trips in protected waters. A boat that moves through the water this easily is a joy to row.