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kentjw
02-02-2007, 07:29 PM
Does anyone know a "rule-of-thumb" for the placement of the bridle on a gaff. What is the proper angle of a gaff or is it different from boat to boat?

George Ray
02-02-2007, 10:13 PM
If not in John Leather, or Tom Cunlief then there are some good books on model boat building that are all about measure/proportions.

Might try pictures and pick off the /angles.
e.g. http://www.oldgaffersassociation.org/_sgg/f10000.htm

notes:

image/text from this url:

Here, a two part halyard provides enough mechanical advantage (or purchase) for a small craft sail of, say 80 to 90 square feet. The bridle shown is not always used on the smallest sails, but helps spread out the stresses put on the gaff by the peak halyard. If you are attaching the halyard directly to the gaff, you position the attachment point 3/4 of the way from its forward end (where the gaff jaws are.) The bridle, which can be rope or wire, is positioned to span this point so that when you raise the gaff and belay it to a cleat, the block is positioned at about 1/2 of the gaff, as the illustration shows. I've seen descriptions of using 1/2 to 1/3 the length of the gaff for the length of the bridle, and that appears to be what these illustrations from Knowing the Ropes show. Here, a becket block is used on the mast to a single block with an eye or fairlead that rides along the rope bridle (for wire, I suppose you would use a single block with a fairlead meant to use with wire.) The throat halyard is also a two part purchase, using a becket block attached to the mast, with the throat sheet rove from forward to aft through a single block attached to the gaff near the jaws, back up to the block on the mast and rove aft to forward, and down the mast.

SAIL:
The sail itself is best proportioned with the following ratios: luff 1.0, head 0.833, leech 1.73 and foot 1.02, according to John Leather's The Gaff Rig Handbook. This "best proportion" is not always followed, of course, but in Leather's ideal gaff main sail, the angle of the gaff to the mast should be at 30 degrees, and the boom should rake upwards about 6 degrees (allowances must be made here for the height of the gooseneck, deckhouses, etc.) It seems to me that the luff is a good starting point, as you know how high your throat halyard will raise the sail. Multiplying the factors he gives by the luff length to find the dimensions of the head and the foot seem reasonable, and the length of the leech then sets the angle of the top of the sail.

02-03-2007, 02:30 AM
The "proper angle" of the gaff is the angle that was designed and built into the sail - and it varies a lot from boat to boat. Are we talking about an existing boat and sail or are you designing one?

kentjw
02-03-2007, 08:06 AM
I'm reworking the gaff on my Beetle Cat and the builder says it depends on the sailmaker's cut. I wanted to finish the gaff before getting a sail but I guess that's putting the cart before the horse.

02-03-2007, 08:54 AM
If you have the old gaff why would you be changing the bridle's configuration? Besides dividing the load on the gaff the bridle allows for the changing lead angle of reefing. So with full sail the lead should be more toward the lower end of the bridle while fully reefed the lead should be toward the upper end.

kentjw
02-03-2007, 09:11 AM
Thad, It appears the gaff bridle attachement points have been change at least four times - don't know why.

02-03-2007, 09:24 AM
I have a Beetle gaff that does not seem to have been changed in that way, I can measure and tell you how it is. (For a fifth option?)

TomHaven12
02-03-2007, 11:28 AM
This is a timely subject for those of us building Haven 12 1/2's over on the www.havenbuilders.com site. Neither the plans nor the "How to Build a Haven" book give much detailed information about setting up for a gaff rig. For example, what should the length of the "wire span" (Leathers book, pg. 17) be; and what are the measurements for the points at which each end of the span should be attached to the gaff boom?

kentjw
02-03-2007, 12:02 PM
Thad, I would appreciate those measurements-from gaff aft end to first attachment point, distance to second attachment and length of bridle.
Appreciate very much.
Thanks

TomHaven12
02-03-2007, 02:14 PM
This is a timely subject for those of us building Haven 12 1/2's over on the www.havenbuilders.com site. Neither the plans nor the "How to Build a Haven" book give much detailed information about setting up for a gaff rig. For example, what should the length of the "wire span" (Leathers book, pg. 17) be; and what are the measurements for the points at which each end of the span should be attached to the gaff boom?

What we need to know is, what is the distance from A to B, and from A to C, and how long should the wire that runs from B to C be?
Pretty much the same info as kentjw needs for his Beetle Cat.
http://www.testrong.com/havenbuilders/gaff_drawing2.jpg

kentjw
02-03-2007, 05:02 PM
TomHaven12, Exactly what I need know.
Thanks

02-03-2007, 05:44 PM
In case it helps, the data base says that the angle between the gaff on a Beetle and the mast (which the sail should be cut to fit) is 23.5 degrees.

merlinron
02-03-2007, 06:55 PM
you have the gaff length dimension right there. with a divider it should be easy enough to extrapolate the distances needed. i don't think it needs to be exact, so scaling should get you close enough to work good.
or...

the scale the plans are drawn in should be stated. with an architects scale you should get pretty close.

kentjw
02-03-2007, 07:09 PM
Todd, Great info! Where did you find that?

02-03-2007, 08:22 PM
Sailrite's compuer data base has measurements for thousands of common sailboat rigs and sails.

TomHaven12
02-03-2007, 08:23 PM
merlinron - duh! Why didn't I think of that! Thanks, Tom

John B
02-05-2007, 01:43 AM
Its called a span. gaff span.
The parts of the gaff that need support are the peak so that the leech tension of the sail is opposed , and an average of about 40 to 45 % back down the gaff from there. So I think the top attachment of the span should be just below the peak of the sail and the lower , as I said , 40 to 45% further down the head. You make it so it can shift a little and you fine tune it on the boat to accomodate a full sail set and reefed.

And because rules are made to be broken , I can tell you that we have sucessfully used a 2 part peak halyard ( ie 1 span)on our 600 ft main for the last ... 7 years? approx, saving us something like 25 metres of extra halyard.( bust a block once but Ok apart from that.)

peak angle. The old rule used to be that the head of the sail makes a right angle to a line from the throat to the clew ,but that doesn't accomodate the newer , shorter footed sails or a high peaked sail,so I just disregard that now. Makes a pretty looking sailplan though.

02-05-2007, 09:04 AM
I don't disagree with you John, but the Beetle is the Beetle. The gaff I have has the bridle ends spaced 36 1/2 inches and 63 inches from gaff outhaul. This agrees well with the sail plan drawing in the Catboat Book. I don't have the bridle, but measuring from the drawing in the book I would suggest 35" end to end.

John B
02-05-2007, 04:47 PM