Mainsheet bridle on balanced lug.

Builder's Forum
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I'm closing in on finishing the hull on my Lake Union Swift and looking forward to starting work on the spars and rig.  I'm building the balanced lug version. 

The plans show a rope bridle that attaches to the quarter knees and has a small loop in the middle where the mainsheet attaches.  On other boats I"ve seen these bridles be just a line with no loop, allowing a block or ring that connects to the mainsheet to slide transversely along the bridle.

I'm wondering about the pros/cons of these two different approaches, and how they compare to using a traveler or a horse.  Also wondering how to determine the right length for the bridle. Seems to me that the sail twist will be a little different depending on which is used, and that you might want a tighter/lower bridle when winds are stronger to depower?

My understanding is that with a single sail you can't sheet in as tightly as you would on a sloop, where the jib promotes better close-hauled airflow over the main.  So there's presumably no need on my rig for a mainsheet that brings the boom all the way in toward the centerline.  But still wondering how a bridle can help optimize sail shape for different sailing angles and wind strengths.

Thanks for any insights!

 

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   I use a bridle with a sliding main sheet block on my NE Dory.  It is very conveniently set up with just a line tied through my after set of oarlocks, and thus quickly and easily rigged and derigged with the rest of the sail rig. (I put on 3 sets of oarlocks, allowing for tandem rowing.) Your bridle, as you said, will probably attach to the quarter knees. I use a simple D-shackle to slide back and forth on the bridle, with the pin of the shackle going through the sheave-attachment point on a small block for the main sheet. I don't think it necessary on these small boats to have a pulley running back and forth on the bridle. I do not use a pivot block, so the main sheet can't get twisted up, but this does require just a bit of care when rigging to thread the mainsheet through in the proper direction. Of course you have to choose a shackle/block set up that puts the shackle and block pulley in the correct (in line) oreintation if not using a swivel block. 

I have had no prolems with either the amount of friction involved in sliding side to side, or bridle line wear.  In fact I like the bit of friction, as I sometimes push the boom out a bit and then haul on the mainsheet to get more downforce (flatter sail) without over trimming, friction helps keep the shackle in place further outboard.

Over trimming too much twist into the sail (especially with a centerline mainsheet attachmnet point) is easily possible on a balanced lug rig.  The boom might end up 20 degrees off centerline with the upper spar 40 degrees off centerline.  The bridle also provides a better sheeting angle when off the wind, too.

Back to the bridle, on my NE Dory, with the ends of the bridle being attached at gunwale height, I set it up with enough slack so that the block will be between about 6 to 12 inches above gunwale height when the mainsheet is sheeted in.  (The block is slightly higher when centered than when run out towards either side, based on triangle geometry.)

So, I'd try both using a bridle with a sliding main sheet block and not using one, but I'm betting the sliding attachment will be best for your boat, too.

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For those who can't quite visualize the setup (click on picture to enlarge):

Bridle in the back of the boat (dark line), main sheet (red line) running from loop in center of bridle to the boom, down to the block and up to Andrew's hand.

Laszlo

 

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Thanks Bubblehead!  You articulated just the sort of thing I was trying to imagine when you said you sometimes push the boom out to leeward to get the bridle to flatten the sail without oversheeting.  And I can see how some friction could help with that, so I won't start off with a running along the bridle.  I might try a soft shackle.

And thanks, Laszlo, for the picture!  Though I'm building the lug version, it's the same bridle arrangement shown there on the sloop rig.   

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 In a balanced lug, excessive twist is controlable by means of the downhaul.  I set our Passagemaker up to make this a two-part downhaul to get adequate tension.  In our setup, the sheet comes down from the middle of the boom to just aft of the daggerboard, with the lower block (it is also two-part) attached to a very short bridle worked into two holes in the after edge of the midship thward.  (This is so there isn't anything hard under the oarsman's behind when the rig is dropped for rowing.)

Here's a link to a photo showing the general arrangement:

https://www.dropbox.com/scl/fi/a3t7qvkv864avg1pifzir/462_K30b2214a.jpg?rlkey=jzmpnso0n0xnnuz9245le2nmz&dl=0

...which is worth more than the couple of thousand words I'd write trying to explain it.

Anyway, my point is that the way the balanced lug contols twist with the downhaul makes sheeting the sail to the centerline like this possible.  If this was a standing lug (one with the tack of the sail at the mast), on a boom without an effective boom vang, this wouldn't work at all.  Easing the sheet would allow the boom to rise and the top of the sail to twist off unacceptably.

If sheeting over the stern, it's much the same except the bridle can be longer, and there is some point to having the little block or whatever the sheet runs through at the lower end have a bit of room to slide from side to side. As long as it's all done with rope and knots, you can try different arrangements to see what works best for you.

I used to have a Sea Pear 21 cat ketch with a freestanding jib-headed rig with the booms rigged with very effective, multiple part boom vangs.  Both sails were sheeted quite effectively to hard points on the centerline with no bridles or travellers involved, sail twist being controlled by the boom vangs.

Hope that helps....

.....Michael

P.S.  The problem with sheeting the little balanced lug to the centerline as I've done is that one must let go of the sheet briefly to change hands on the tiller.  Rigging the sheet with the fall coming down at the stern would allow the sheet to be gripped with the tiller hand to free the other hand for...whatever: changing hands in tacking, getting a drink of water, eating a sandwich, etc.  I've been thinking about rerigging things this way, but I love the way the central sheet controls the sail with fewer parts, less line to get foul of something, and nothing overhead along the boom waiting to snatch my hat off or cast a half hitch around my neck if I don't tend the sheet smartly in a gybe.  <;-)