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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.

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Fair winds!

Dave and Anke
triloboats swirl gmail daughter com

Friday, November 8, 2019

Travelling OffCenterBoards (aka LeeBoards)

OCB in forward, sailing position
(Photo from Pete Frost)

OCB in aft, stowed position
Windows clear!
(Photo from John Herschenrider)

Truly, she doth block a staircase!
-- From 
by Wallace Tripp


Travelling OffCenterBoards (aka LeeBoards)

Let's start with a leeboard.

As we sail into the wind with our leeboard down (on the lee side), the leeway we make presses it against the hull. It likes to slip forward but not sideways (LR for Lateral Resistance), so we don't make as much leeway as we would without it.

Ready about!

Helm down, we turn into the wind, sails flogging as the bow and boom cross the wind. We drop the leeboard on the new leeward side and raise the first one clear of the water. Sails fill, we heel over and off we go on the new tack.

If it sounds like allemande left and dosido, it is. A little choreography on what may be a heaving, wet deck and your partner is a big, heavy leeboard.

Lazy sailors that we be, our interest was aroused by Ida Little as she clamped a 2x2 outboard of her Bolger DUGONG's leeboards to form a slot, instantly converting them to OCBs (Off Center Boards).

No need to tend 'em between tacks! Just put 'em down and leave 'em. If you want to reduce drag sailing off the wind (no need for lateral resistance), you can raise 'em if you want to.

Years went by, and we transitioned to big view side windows. Problem is, with the boards raised (always the case at anchor), they block our view.

We wanted to haul and store them out of the way. We wanted a simple installation. We wanted it quickly and easily handled by one person.

So we scratched our heads and came up with travelling OCBs.


*****

Walk-through of set and stow
Please watch first for overview

The video above walks through from stowed aft to set forward and back. Notice that the stowed position is in the 'blind spot' below the pilot house.


Tour of system components:

Upper cable, eve guard and stop

This is one of our early prototype stops for the board. It's two purposes are to act as a stop at one of the board's two positions, and to shorten the span of the cable.

The traveling block (description to follow) travels along the upper cable until it hits the forward stop (set) or aft stop (stow).

Both functions will eventually be met by a shorter upper cable (shorter span) and crimp on swage sleeves (stops).

In the meantime, we currently tie a double sided rolling hitch around the cable, with the ends led up to a handrail post (i.e., the vertical part, and not the grip), rather than the arrangement shown.

That aft tail is just 'cuz I hate cutting line.


Aft lower guard, mounting plate, lower cable and slot
Forward lower guard, sheathed turnbuckle, mounting plate and slot
Note the guard struts

The lower guard and lower cable - offset by mounting plates - form the slot.

The lower guard doubles as bearing for the OCBs and mounting steps fore and aft. Handy for boarding from the ground or a dock.

A rule of thumb for leeboards is to toe them in 2 degrees. This helps the vessel 'climb' to windward. We haven't done this on these lower guards, but plan to at the first opportunity.

On the lee side, the OCB acts like an ordinary leeboard. It bears up against the lower guard and pulls at the upper cable.

On the windward side, the lower cable prevents the board from winging out, and the upper board bears up on the eave guard.

We adjust cable tension to let them angle inboard, also at 2 degrees. Our thinking is that, when heeled, this produces a downward force at their Center of Effort, equivalent to someone hiking out, acting against heel. I mean, since we're leaving it down, why not?

Incidentally, since both boards remain down, we use only a little more than half the area one might in a leeboard (where one board handles all LR). This is cheaper, faster to build, lighter, and induces less stress.

There are big stresses on OCBs. I would like bigger and thicker mounting plates down the road, though these (1/4in aluminum) seem to be doing fine. I'm guessing the cables help to absorb and disperse some of the stress.


Bottom of OCB from aft

Here we see the retrieval line, its block and cleat. It is used to raise, lower and angle the board with 2 to 1 purchase (we're trying it out... may go to 3:1).

For stowing, the board is moved to the aft stop and raised clear of the water, but with its lower edge still in the slot. This prevents waves from clunking the board when stowed.

For sailing into the wind, the board is moved to the forward stop and tied, then the retrieval line is hauled in a bit to angle it back a skosh. This encourages it to kick back if we bounce it on the bottom in a swell, relieving stress all round.

For sailing off the wind, we haul the board to as near horizontal as possible. This reduces drag from the now useless boards (lateral resistance is not required off the wind).

Due to the relatively poor lead for the retrieval line, while deployed, we can't quite clear the water with the OCBs' lower edges. We're considering a snatch hook under the eave directly above the load... this would improve the lead, but requires awkward handling with low payoff. Still mulling that one over.

Note the upper mounting plates which were cut from aluminum angle.



Top of OCB from Inboard

These two pics show the hanging / travelling arrangement for the OCBs.

As seen above, an inverted block runs its sheave above and along the upper cable. A lanyard is fixed to the block, and passed through the board to the outboard face. The board pivots from the block when raising and lowering.

[NOTE: We've found Stanley™ Pulleys to be perfect for the job... cheap, strong enough, and the sheave pin is R-sprung for easy dis/mounting.]

Below, we see the lanyard emerge and tie off to a cleat. We pull the block as snug as possible, inboard to set the board as high as possible. This gives good landing on the eave guard. The eave has the dual function of bearing against the upper board, and keeping deck runoff from the windows.

The tail of the lanyard - stopper knotted at its end - is used to haul the boards fore and aft. In the forward position, we tie off to the handrail with a clove hitch to keep the board from pulling aft when raised in place for off-wind sailing.


Top of OCB from Outboard


A little miscellany... 

There are two main criticisms of OCB/leeboards; clunking and picking up 'scultch' (seaweed Klingons).

We've only had board clunking issues in light winds and riptide conditions. Otherwise, the boards either immediately bear up and go silent or 'shuffle' along in no wind. In LUNA, we added firehose along the lower guard, which eliminated clunking, but it's seems only vaguely worthwhile.

We do pick up weed now an then, but it's easily dislodged by raising the board briefly.

As a frequent criticism of OCB/leeboards, I don't get it. Any LR device picks weed, and in most it's a LOT harder to ditch. I see plenty of fixed keelers dragging a garland.

OCBs are easy to construct and maintain, requiring no hull apertures or complex structures. Ventilation is most excellent!

Maintenance is a relative snap. To dismount, we uncleat the lanyard, which can then lower the board with 2:1 purchase. We temporarily hang the board by its cleat's lower horn hooked over the lower cable. We can leave it like that until ready to remount or take it ashore.

We shoot for a ballast load that floats them vertically, about a foot or so proud of the water when dismounted. We can easily tow them ashore on a 'leash' for whatever. Propped up flat, they make a great work bench, ashore.

We don't always sail with both boards down. Each significantly reduces leeway, but there are days we just don't need to be sailing at our best to windward (e.g., a short leg after a long run). In case we change our mind, the second is easy enough to set up, underway. If not, that much less to put away at the end of a pleasant sail.

Retractable LR is a given for ultra-shoal draft. It opens up a hundred sheltered spots for every reasonably deep anchorage. When the wind come on, it can save hours to the next hidey-hole.


*****

We've been sailing with OCBs, now, for 20 years, and travelling OCBs for about half of that. We sail year round in SE Alaska most years, across a considerable range of wind, weather and water.

I'd say it's working!




[NOTE: In SLACKTIDE we had windows along the entire cabin. To stow, we had to lift the boards clear of the slot and slide them dead aft. This complicated retrieval to brute force. Lighter boards are recommended.

There's a primitive ancestor of this post on SLACKTIDE's system, here.]

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