Roll Yer Own: Roll-Up Bows for Boxy Boats

Traditional Junk and the Latest Thing
(SKROWL 900 by Yann Quenet)

I like the way you roll!

Roll Yer Own: Roll-Up Bows for Boxy Boats

Box barges (scows) very often have a rectangular bow transom. They're easy to build, and help provide a little extra room and buoyancy at the extreme forward end. Mostly, they ride clear of the water.

Mostly.

'Course, when they don't, they're a little like a bulldozer blade. Even if we don't feel the resistance when it hits green water (and can't say I ever have), we know it's there.

By rolling the bottom up to meet the foredeck (or top of gunnel), we can eliminate the bow transom, and smooth interactions with the water.

Triloboats can be built with all flat bottom planes, their end rise joining the deadflat at a 'knuckle'. Or they can be curved. Generally, a long deadflat shortens the end-curves, making them more abrupt than a fully rockered bottom. Thicker sheets of plywood (more efficient for building up the bottom quickly) may not be able to follow the bend unaided.

One solution is kerfing; transverse cuts through several laminates of each layer, leaving a few intact. Kerfs in each are offset from others to avoid their lining up. Once the layers are laminated together, a smooth, strong, curved structure results. See more details here and here.

Once you've given up simple bending, and started kerfing, there's no construction reason not to continue with a roll-up bow. The curve is a little more extreme, so your kerfs must be closer together and possibly deeper. But that's it!

In other words, a roll-up bow costs very little extra effort, if any, over a transom bow.
 

A few possibilities for roll-up bow profiles...
Note that curves drawn outside the original lines
ADD volume, those inside REDUCE volume.

Design-wise, there are any number of ways to arrange a roll-up bow.

Some considerations:

• Weight distribution within the hull - Does forward weight encourage forward buoyancy?
• Storage - Do you wish to prioritize forward volume vs other considerations?
• Typical sailing - Do everyday considerations outweigh rarer ones?
• Extreme conditions - Do you wish to prioritize for rare occasions vs other considerations?
• Speed - Do you want to minimize resistance (easier entries) vs other considerations?
• Lift - Buoyant (more volume) or kinetic (angled entry)?
• Pounding - My theory is that pounding occurs when bow angle matches wave angle... the higher the angle, the less often it will pound, all else being equal.

Virtually any boxy, flat bottomed boat can be redesigned for a full or partially roll-up bow. Most of these considerations can be juggled to produce a bow that fits your situation.

Wanna roll one up?



PS. Anke and I chose to stay with a bow transom on our new boat... it has a short foredeck, and we wanted to maximize the anchor locker volume for a given curve, and maximize our corner post bury. But we waffled... could'a gone either way.