Simple Sampan

 

Sampan Bow
Arrow points to the forward end of the straight chine
a.k.a aft end of the bow curve

Simple Sampan met a Boatman,
    With a seaward stare;
Says Simple Sampan to the Boatman,
    “Let me take you there.”

- Olde Mother Sloops

Simple Sampan

Sampan bows have several benefits over western, pointy bows.

They add positive buoyancy at the bow, reducing pitching and helping to ride up and over waves (rather than plow through them). More interior volume is added for forward storage. Forward deck space is widened for better footing and anchor handling. Wide flare at the bow helps toss waves to the side, rather than over the top. The wide forefoot is more stable on a steep beach. It's much easier to roll a cross-log under to protect the bottom on a rough beach.

We LIKE 'em!

With two sampan bows under our belts, I'd like to share some thoughts on dumbing the process down to manageable. This approach uses western design techniques, but leaves the bow to a traditional, 'follow-the-materials' attitude.

In designing your own approach, consider models from paper or cardstock. Fast and cheap compared to plywood!

Simplifying approaches

1. Decide mid-ship's bottom beam
2. Decide bottom beam at the forward end of the straight chine
3. Decide the transition curves between them
4. Decide amount of flare
5. Begin with parallel sides, straight along sheer and chine
6. Use a simple, fair bow curve at the forward end (approaching a circle)
7. Build to forward end of the straight chine with bow extending past
8. Roll bottom upward to plank the bow

Okay, let's unpack that... I'm going to boldface some common boat terms you may have to look up to keep it short...

Decisions - Decide mid-ship's beam and beam at the end of the forward straight chine in the usual manner. Decide the chine and sheer curves in Plan View (chine and sheer on each side will curve in parallel, given these standards). This will determine your beam and station at the forward end of the straight forward chine.

Decide the amount of flare. The simplest case is a constant amount of flare, which produces constant bevels along the chine. We find slope to be the easiest to work with, often 3in of lean-out per vertical foot. A changing amount of flare produces twist, which introduces rolling bevels and generally complicates things.

Parallel, Straight Sides - When laid flat, these are like wide planks. When bent over flared stations that converge toward bow or stern, they develop parallel curvature... 'sheer' along the sheer and 'rocker' along the chine. The more flare and the more the ends are brought inboard, the greater the curvature.

Phil Bolger (TEAL, among others) and Tom MacNaughton (SILVER GULL series) and others have designed handsome, capable vessels with this approach to side planking.

Fair Bow Curve - This curve provides the sampan shape. A curve closer to a circle provides a more blunt entry, while a curve closer to half a parabola makes an easier entry. This is laid out directly on the side planking.

Build from mid-section to fwd end of straight chine - This portion of construction is very easy. Constant bevels and simple, fair curves. Under these assumptions, side heights are all the same. The whole thing pretty much shapes itself! 

Meanwhile, the curved bow ends are sticking out there in space. Depending on your building philosophy, the bottom can be planked to this point with the proviso that you will need to continue bottom planking forward, rolling it up and over the curved, Sampan ends. 

Roll the bottom upward - To make the curve with plywood planking you will likely have to use kerfs.

If not using tape and glue construction, we find 'nailers' to be an easy method. Basically, these are planks along the curve to which the bottom can be mechanically fastened (nails or screws).

Ply Nailers installed and trimmed to bow curves...
Planks are a better choice, if available

Planking up the bow...
Note kerfs visible across upper bow

Nailers after bow is closed

As you can see, you have to get creative with clamping. There are a zillion ways to go. Most of them work, eventually. Try to find what works best for you!

NOTE: The black schmooey is DAP Polyurethane. Very strong bond, highly elastomeric, workable and about 1/4 the price of some of the name brands.

Complexifications

These assumptions are the simplest among flared side designs. But each builder and vessel is individual... you get to decide what pays off in your long-run. Your design and/or construction abilities will loom large at the beginning. A long-term benefit may well reward extending those abilities at the outset. Simplest is always fastest, but that's not the only question. Weigh it up!

Parallel sides are indeed simple, but both chine and sheer curvature can be enhanced or diminished by curving one, the other or both (not necessarily parallel). Lofting will take up more of your time.

We cut our sides down from a single run of full width plywood, so strictly parallel sides are arbitrary. We chose to add a little extra sheer for vanity's sake (okay... it also gives a little more freeboard, forward, but that's pretty minimal). 

Note the riser above parallel over the forward end... that's a simple way to get extra freeboard, storage and foremast bury. In MUSTELID, we built it up from parallel; in LUTRA, we're simply cutting above the (nearly) parallel cockpit line.

As mentioned twist complicates matters, but may pay in the long run. Generally, it helps increase sheer and rocker, and narrows the forefoot (for an easier entry). There's a bit of extra twist available for 'free' along the bow curve... consider making sure that it fairs in along sheer and chine with no hard spots in their longitudinal curves.

Bulkheads don't have to go anywhere in particular, but it's sure handy to have one at the point of maximum beam (not necessarily mid-ships) and one at the forward end of the straight, parallel chine, both definitive points. Intermediate bulkheads need to be adjusted for their position on the curvy sheer and chine. Many vessels can be designed and built around their bulkheads, with no temporary stations at all.

Simple's a great place to start, but you're not obliged to limit yourself!

*****

Box Barges are as simple and easy as a boat gets. I'd put parallel sided, flared vessels at the next rung of difficulty; still in easy reach. Giving up parallel takes another rung, but we're not dizzy, yet.

A Sampan Bow complements all three, but comes down right handsome in flared hulls!