Design Contest #6 - Entry 2
By Milton "Skip" Johnson - Houston, Texas - USA
Drawings - Statistics - Description - Budget - Bio
(click images for larger views)
WL Beam: 36"
Sail Area: 107 s.f.
Prismatic Coeff: 0.56
Wetted Surface: 31.75 s.f.
Pounds/inch imm: 151
Bruce #: 1.22
Weight on tralier: 300 lbs.
Friend Brendan, actor, free spirit and boat aficionado, is no longer with us but how he would have loved the idea of a solo journey through the Sound. In his memory.
Brendan’s Chariot (BC) is a blend of solo canoe on steroids and Birdwatcher style cabin and an attempt to follow the old maxim “sail when you can, row when you must’. You must row in this case because budget constraints rule out the usual outboard or its electric cousin. My favorite form of human power is a good lightweight doubleblade paddle but this boat wants to be a bit big to doubleblade and paddling in a constant cool drizzle doesn’t sound particularly appealing either. Oars it will be. Power is limited so I would spend the time to make a boat as easy to drive as possible, hence a round bilge canoe shaped hull with low wetted surface. That easily driven hull is nice but won’t hold up very much sail so let’s add some leefoils (buoyant leeboards) spaced out a bit from the hull and pick up some heeled righting moment so now we’re more like a boat with a 48” waterline beam instead of 36”. Tying up to a mooring (not part of the design criteria) can be difficult and we’ll need to remember to put the CE of the sail back a bit to compensate for the offset drag of the leefoil.
40 degrees is pretty cool to a thin blooded old hillbilly so insulation seems like a pretty good idea and positive floatation has its own merits. BC uses foam core for the hull and cabin where possible for the above reasons plus accruing some structural benefits in stiffness and unencumbered interior. The hull is built like a stripper canoe, upside down over forms on 16” centers starting with a keel panel of ¾” plywood and stripping to the cedar gunnel with ¾” PVC foam. The foam strips are surprisingly easy to work with and polyurethane glue makes easy butt joints to get 16’ long 1” to 3” wide strips. Any little gaps or misalignment in the joints are filled up by the expanding glue. Two layers of 12 oz biaxial glass on the outside and one on the inside and we’re ready to put in both bulkheads and the decks.
The two cabintop panels would probably be made first (one at a time) to be able to reuse particleboard formwork. Sandwich panels are made of 5.2mm underlay ply over ¾” blue styrofoam adhered with microballon thickened epoxy. Bottom side of panels and decks are covered with 6 ounce fiberglass. Coaming is laminated in place at same time.
Fairing and finishing is a very personal matter but I would recommend developing an ‘eight foot (or so) attitude’ when looking critically at what you are doing. That and a satin non-glossy finish will get you out on the water quicker and wince less at the first little dings.
The first doodles for BC had a crabclaw rig with bipod mast, a residual bias of playing with proas. But I just couldn’t get the geometry to work. However a balanced lug seemed to just naturally fall into place and, if you held your head just right, could be considered a crabclaw with the tip cut off. Cut from 1 X cedar (birdmouth octagonal mast and diamond shaped yard and boom) spars are light and easy to handle 16# or so maximum for the mast. Sail area’s fairly stout but intended to let the boat move in the lightest puffs. In more reasonable breezes BC will be right at home and well balanced with the first reef in.
32 years separate articles by Phil Bolger and John Welsford on rowing but there’s uncanny agreement in several areas both philosophical and practical. On the practical matters I would definitely consider reshaping the oars as they both recommend though I’d probably use a belt sander rather than spokeshave and plane. Deceptively simple, the oarlocks allow you to keep the oars in place, and use them in a conventional seated position or standing facing forward for approaching or leaving an anchorage or shore. Using a lanyard and choker to position the oar per John Welsfords’ article is a simple way to reposition the oars for standing or sitting.
The least conventional aspect of this proposal, the leefoils are not meant as a halfhearted imitation of a multihull, but as an effective means of leeway resistance in shallow water. The reverse taper puts most of the area in play as soon as BC heels and the upwash helps keep the foil from ventilating. The bits and pieces involved in raising the foils may seem light, but the hard points of connections are well separated and triangulated.
Extending the lexan sides out as a natural extension of the hull flare gives a space that’s natural to lean back and psychologically open. Sloping the cabin top down fore and aft limits accommodations to a solo adult (or adult and child) but minimizes air resistance and materials. I was concerned about visibility but the fairly coarse but geometrically accurate renderings (forward, side and stern) show visibility that is at least as good as most vehicles on the road. When conditions are right (no rain and gentle winds) standing is a great option if you remember to really duck when tacking.
I’m not a real fan of the drag link rudder shown because of the 3 or 4 extra pivot points involved but haven’t yet come up with a better solution that centers our solo sailor. The 11# claw anchor shown might be considered oversized by some for a fifteen foot boat, but I’ve not ever regretted having a slightly oversized anchor. This has been a pleasant exercise and I’m pretty taken with the solution but need to think a bit more before I would invest that much effort on a one-man boat.
Click Here for Spreadsheet
Deciding early that BC would be a fairly ‘evolved’ design rather that a simple box dictated that preliminary pricing would be based on weight rather than number of sheets of plywood. The boats I’ve been involved with have material cost anywhere from one dollar or less per pound (scrap pile specials) to over forty dollars a pound, the latter being kevlar, carbon, foam and epoxy racers where less is truly more (price out a good ultralight carbon bent shaft paddle). In this case a guess of ten dollars a pound on a roughly 200 pound boat puts us in the neighborhood.
In this case pricing is pretty tight so I’ve left a 10% margin for taxes/shipping on priced out materials, in some cases I know I can beat the prices on the spreadsheet but left things priced from generally available sources.
I’m pretty sure that I could build the boat with a 4-½ gallon kit of epoxy but it probably would be tight. I’m not sure where there are any areas for deletion but there are substitutions possible. It might be possible to build the hull with blue foam but I know the PVC foam will make a hull that’s virtually bulletproof, I have however used the blue foam for deck cores glassed on back sides without problems.
The radiata pine ¾” plywood seems to be a current cost effective solution for rigid tough pieces, is a bit heavy though. I would consider using 3mm okume for the cabin and deck pieces if I could afford it, maybe even using a Polytarp kit for the sail to keep in budget. Keep the 5.2mm for the leefoils. The cedar for spars and gunnels is priced as select material from a local supplier, go with whatever is available in your area. It may be that we will soon have to start getting our long straight pieces from cutting up engineered products.
The per diem allowance assumes you won’t be spending a lot of time in coffeehouses or fine restaurants.
I really blew the preliminary weight estimate, by 50% no less. Fortunately cost totals still fell in line being about $6.66 a pound. Preliminary weight estimates were 200# boat, 200# stuff and 200# person. Having a 300# boat leaves 100# for stuff (water, food and gear). Actual design displacement is 611# so going a ¼” deeper will get us 650# displacement and work well enough.
Milton “Skip” Johnson
Deemed “Old and Heavy” by some. Sixty plus and one ninety plus at the moment.
Architect – almost retired
Husband, Father, Grandfather
Lifelong boatnut, built my first full size boat at 16 after a number of models and haven’t stopped yet.
Chuck claims I’ve entered ‘almost every contest’ actually this is the fourth I’ve entered, out of six.