Please visit our home site at www.TRILOBOATS.com.

Anke and I are building our next boat, and writing about it at ABargeInTheMaking.blogspot.com. Access to the net comes and goes, so I'll be writing in fits and spurts.

Please feel free to browse the archives, leave comments where you will and write, and I'll respond as I can.

Fair winds!

Dave and Anke
triloboats swirl gmail daughter com

Saturday, March 14, 2015

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.

8 comments:

  1. When I ordered plans for SuperBrick (Bolger), dimensioned drawings for a cutwater below the bow transom were included. I wonder how much this will affect actual performance. It certainly makes an excellent space for a chainlocker or tanks.

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    Replies
    1. Hi Charles,

      How great that you got SB plans! Are you planning to build? So far as I know the SuperBrick Challenge ($1K to the first builder) is still unclaimed. Details here:

      http://www.duckworksmagazine.com/03/r/articles/superbrick/

      I hadn't heard about a cutwater... like a step sharpie? Is there a matching one aft (skeg or step)? Sometimes they track better with as much or more aft as forward, especially with a round 'belly' like SB's. But second guessing Phil is perilous business! 8)

      If it's a step sharpie type, it will certainly add forward buoyancy and help dampen pitching (to which abrupt rocker boats are prone). It will also provide lateral resistance, especially if fitted with chine runners (a la Matt Layden). And, as you say, the extra storage is welcome on a small boat.

      Only downside is increased drag from extra wetted surface area. But SB won't be a 'performance' vessel in that sense, anyway. Off wind, I doubt you'd notice. On the wind - if you can manage - my guess is that the benefit of increased LR will more than offset increased drag.

      Long time ago I ran across a drawing of SB from behind, sailing for the horizon. The artist had sketched a beautiful, Japan-style rising sun across the stern.

      The stuff of dreams!

      Dave Z

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    2. Will I build? The answer is a very strong Maybe. The design is competing with a triloboat of similar dimensions or one of Tad Roberts' 20-foot houseboats, which are more visually appealing (and Tad says he'll happily draw a sail plan for a few extra $.)

      The cutwater basically extends of extreme-bottom of the rocker in a more-or-less flat triangular shape until it's stem can be joined with the bow transom. There is not a corresponding shape at the stern, although I'm sure Suzanne would draw one if I asked; whether she would try to talk me out of it, I do not know.

      If I build the SB, once I have the lower hull completed, I'll write and ask her personal opinion on cutwater and how it might effect the performance. It's not mentioned in the book.

      Delete
    3. Hi Charles,

      Okay, got it. I'm sure Suzanne would, but nuthin' to it on your own, either. I used these on the T10 B'TUGLY... you can see the 3D tour here: http://triloboats.com/downloads/T10x4BTuglyTour.avi

      It seems odd NOT to have it balanced, both for distribution of displacement and lateral resistance.

      Good luck with your decision and on whatever you build! If you need Triloboat assistance, drop me a line at triloboats swirly gmail period com. I don't have a 20 footer, but it's easy enough to whip them up.

      Dave Z

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  2. Hello Dave. I tried to post a post this morning but it seems to have disappeared! Anyway. Would you by any chance be thinking of (gulp!) A next boat!? What with all those lovely junks and other boats you're posting about! Anyway I am still at it, slowly building mine. And sort of idly thinking of the next one! Reading the like of Dmitry Orlov makes me want to run away to sea!

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    Replies
    1. Hi Joel,

      Are you posting on your barge build? Let me know and I'll add it to the bloglist.

      No... these Asian boats are beauteous and well within building reach, but we went with the Triloboat.

      But I'm always looking at their clever solutions to many of the problems various low road sailors face. They were Masters of the Low Road!

      It's always inspiring to be reminded that there is not a single item onboard a fully functional boat that cannot be handmade, DIY. Most of these boats never saw so much as a nail!

      And, reading the likes of Dmitry Orlov, it seems as if the sea will be coming to us. 8/

      Dave Z

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    2. I have written a new entry with a few pictures on my blog: a wood man's wandering and ramblings. joeldelorme dot blogspot dot co dot uk

      Yes those old junks were marvels of simplicity and invention. It maybe that in a not too distant future man will have to remember how to do things simply.

      Delete
    3. Hi Joel,

      Looking GOOD! That's going to be a roomy, beautiful home! And your joinery puts us to shame, not that that of itself is high praise. But yours shine with competence.

      The present seems pretty good to me for going simple and DIY. I glance through the catalogs of gear, these days, only for ideas to copy. And durn few of those! Can't afford the rest.

      Dave Z

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