Gaff sail trim

[Dan McCosh]

I was wondering how much a gaff rig twists when sailing downwind, with the boom run well out. Does the gaff end up well forward?

[Jim Budde]

I do not know what the little book of instructions says ( I must have thrown it out with packaging), but I let gaff go too forward twice .. both times I lost control and experienced (a) snapped boom jaw and (b) ripped mainsail where broken jaw snagged lower portion of mainsail. Granted winds were above 20 and my boat is 12'6" LOA .. but I have not run so wild again

In other words, I watch the gaff more than the boom now

[Dan McCosh]

Being often too lazy to rig a vang, I often let the top of the sail lay against the spreaders--usually overtrimming the main just to keep this getting out of hand. It was while pondering this problem that I started to wonder if a gaff also ended up being a problem while running. I also was looking at junk rigs, and noticed they usually use seperate lines to the battens to prevent this excessive twist.

[Buddy]

What kind of boat rig determines the fix. A catboat's boom is much to close to the deck to permit a boomvang, so often the boom is deliberately heavy, and a preventer rigged forward to the rail does it in heavy going. A sloop's main can generally have a boom vang rigged. Sometimes you see a line run to the outboard end of the gaff as a kind of running back, but this is usually for long hauls on the same tack.

[Dan McCosh]

Interesting. The "running back" would be similar to the setup on a junk rig.

[Todd Bradshaw]

The "running backstay-like thing" is called a Gaff Vang. I've never used one but have heard that they can be kind of an annoyance during the times when they aren't in use and are flopping around (which is most of the time). It's also not a particularly direct sheeting-angle (peak to rail) for the job it's doing, so I don't know how effective they are. Before going very far on a downwind run in a gaffer, I'd want to make sure that it wasn't more efficient to head-up a bit, to more of a broad reach, reducing chafe on the sails and rig and getting a little more aerodynamic stuff going on with the wind and mainsail.

[Ronin NW]

As far as sheet leads are concerned, all that I've heard about gaff vangs were in reference to a ketch. Once could lead a main gaff vang to a block on the mizzen masthead then to the deck. This makes a pretty clean line directly aft of the gaff to the mizzen.

It's been suggested to me on Ronin, but I really haven't found the need to try it out and mess with the extra flopping lines.

-Scott

[Andrew Craig-Bennett]

Never had the gaff anything like forward of the mast, in 30 years of gaff cutters with fixed spreaders.

Obviously, allowing any part of the mainsail forward of the mast creates a roll, and seriously promotes chafe, so why would anyone do it?

Let's just lay a myth to rest, here. Gaff sails twist no more and no less than the lower half of a bermudian sail. Besides a kicking strap, which is seldom or never used with gaff rig, factors affecting twist are the position of the mast and gaff blocks for, and the setting of, the peak halyard, the weight of the boom and the shape and cut of the sail.

[John B]

but you'd still look at the swinging spreaders if you were remaking them eh Andrew... just for those little "moments". :D
I know I would.
Fact is , as Jim does and I'm sure you do,I set my main on a run by watching where the gaff goes out to.

incidentally,a couple of hours ago I watched Waitangi( 57 ft gaff boat from 1892 or so) take off triple reefed and with one jib on a passage race up to Kawau island. I swear it was high 30s and 40 knots. A bit feral for sure.

[Andrew Craig-Bennett]

You are absolutely right, John. :D

Tilman used a very short mainsheet, incidentally. Not that he spent much of his time with a fair wind, anyway.

There is some more to this subject, I think.

I do believe that a "properly cut" gaff mainsail on a working boat, an offshore racer or a cruiser (flat water racers are different, in this respect)has the boom quite high at the aft, outboard, end.

Tom Cunliffe makes this point in his book and he is dead right, but besides Tom's point about the boom not dragging in the water when rolling on a run, I believe that it also helps to keep the sail flat, due to a better sheeting angle, when close hauled.

We can be misled by photos of Victorian and Edwardian racers with low booms - these yachts made their passages under trysail, and only set the mainsail when racing inshore.

I am also quite sure that getting the peak halyard blocks higher on the mast reduces twist.

[brian.cunningham]

There's a forum member with this gaff vang setup
http://www.boatus.com/goodoldboat/images/Scan2.jpg

There's a line that goes another line attached to the main mast, and rides up and down with the gaff.

[ 10-16-2004, 09:03 AM: Message edited by: brian.cunningham ]

[Ian McColgin]

All those cool sheet/vangs from the leach ends of a junks battens are gathered at a sort of multi-jam cleat fitting called a euphroe which is attached to the sheet used for major trim. You can fine tune the sail's twist without having to handle a bunch of lines for every tack or gybe.

Flexable spreaders are quite wonderful in their place on a gaff rig. Goblin had them on the foremast, a reminent of her pre-staysail rig days.

I like a rig porportioned such that the normal location of the throat is just below the spreaders. That way you can sag the sail well out, letting the sail push the slack shrouds ahead a bit and, if necessary, sail fairly safely by the lee.

A sail well out in 'push mode' develops develops inconclusive venturies on the luff and leech (and along the head on a gaff sail. This phenomenon - also why spinnakers can wobble so psychoticly - is called self-excitation and can really make your darling roll. Combined with a little broaching in a following sea, and maybe getting the boom caught in the water, and you can get to the glorious death roll, which is why mammas tell their kiddies to always have your bottom clean - never know when it will be seen.

Many gaff sailors have a clew about half way from the regular clew and the first reef clew exactly to pick the sail's outboard end up a bit for safety. Similarly, quite a few have a noticable slope to the line of reef points.

I recollect one race where it looked like we'd either death roll or gybe disasterously as the boom caught in the water. Even my 250# on the topping lift was a slow cure as the water had to drain out of the bunt as I hauled the sail clear. Taught me to pick up the clew before trouble!

Gaff rigs that are too flat at the head or have too little height from throat to truck are very hard to make set nicely and often really need a vang. While lots of schooners and some ketches vang the foresail or main, it's not nearly as needed as some think, as you want the two sails to sag off in harmoney anyway.

Gaff sail trim is an incredible gas as there are so many controls available and the size and location of the draft can be moved all over.

I always wanted to sail with Tilman but I realized from reading his books that, brilliant adventurer and genuine tough guy that he was, he was an indifferent sailor. I'd no sooner ignore how the boat wants to sail than I'd slouch in a cowboy saddle on a good 18-hand hunter.

[Andrew Craig-Bennett]

Worth says that the gaff should lie at angle of 90 degrees to (normal to) a line drawn from throat to clew.

[McB]

I learn more from some of these Forum posts than anything else, but I want to learn evenmore. Could some of you post a list of good reading material about Gaff rig sailing. I have only found a couple of books, and they were more about history.

[John B]

As you might recall from previous posts, I have a copy of Worths Yacht Cruising and hunted down both Maud and Tern II ( before Tern left here last year). It was fantastic looking at the very boat and fittings he made ,from the book.
The problem I had with Worth's general guideline with that 90 degree rule was that as you shorten the boom, the gaff angle lowers.
Now if there is anything that has been learnt about gaff sail plans, it is that the higher the gaff is peaked ( within reason) the better the sail will perform to windward. The other thing that is well learnt is that long boom length gives a relatively small performance gain when measured against the issues that go with handling the bigger sail.IE ( general example % only to make my point)you can chop 10 % off your boom length and get a 3 or 5 % decrease in performance off the wind and perhaps none on the wind.
A modern gaff rig will be shorter in the foot than ( in my case) an Edwardian design. But hang on... apply Worths rule and the gaff is now peaked lower than the original early design and thats not what we want.
So I used Worths rule as a guideline to get a sail that was within tolerance aesthetically but I wasn't going to let it impinge on what I thought were the best performance features.
I peaked mine a fraction higher than 30 degrees off the mast( 28 or so from memory) as the highest I could go and still set a decent topsail. If I was doing it again I think I'd go around the 30 to 35 degree mark ( slightly bigger topsail) but like weight aloft,something you defend against, I'd fight every degree I was giving away.
BTW,I still have the Tern Pics on Imagestation if anyone wants to see them again.

[ 10-17-2004, 04:11 PM: Message edited by: John B ]

[PeterSibley]

McB...."Hand ,Reef and Steer",Tom Cuncliffe.Perhaps ACB and John would comment?

[John B]

eureka.

http://www.messing-about.com/gaffrig/

[Andrew Craig-Bennett]

Yes, good site. Incidentally, none of John Leather's eight peak halyard arrangements shows mine, which I think is also by far the commonest, on boats of moderate size - two spans on the gaff carry two single blocks and there are three single blocks on the masthead.

I have already commended Roger's ("Smacksman's") site:

http://www.alberta-ck318.freeserve.co.uk/index.htm

but will do so again!

The drawing of a "tyical peak halyard arrangement" on this site is precisely the arrangement that I have and which I reckon is the best for moderate sized boats. Note that the hardener purchase should be long enough to permit reefing - it commonly will be, as, with most arrangements, you can pull down the first reef without touching the peak halyard ar all.

Unlike John, I do agree with Worth about gaff angles; it is correct to flatten the angle of the gaff where the boom is short. The example Worth gives - a schooner's foresail - illustrates this perfectly. I see many "modern interpretations" with a short boom and high peaked gaff where the head of the sail falls off remarkably, though, in fairness to John, "Waione"'s gaff certainly is not doing so in the photo taken from above!

Whilst we now know that the sail area at the end of a long boom is not doing anything very much, a mainsail of the old shape with a long boom sets very much better to windward, as can be seen in any of the photos of the old racers.

On the whole I advise tracking down a copy of Worth. He assumes you already know the stuff in Leather and Cunliffe, because he is writing for readers who know only gaff rig.

I disagree with Tom Cunliffe on one point - Tom says that you do not need to mouse the hooks on the peak halyard blocks where they hook onto the gaff span shackles.

I read Tom's book and tried this - once. :(

Within a few hours, beating in a stiff breeze, she shool one block off...lowering the resulting mess, climbing to the upper peak block on the mast and retrieving it in a respectable 5-6 as, with no mainsail set, she did her best to chuck me off, was a "performance" during which I cursed the name of Cunliffe ! :rolleyes:

A point made by Uffa Fox, which I have also put to the test the hard way; use separate stops to secure the head of the sail to the gaff, not a lacing. The lacing will chafe through on the lee shroud, for sure.

[ 10-18-2004, 09:05 AM: Message edited by: Andrew Craig-Bennett ]

[George.]

I have only about a year's serious gaff rig experience, but here is my bit:

Dalia's sails never have had a problem with twist. I think that has to do with the heavyish booms, the rake of the masts, and the aft-swept shrouds, Gloucesterman-style (aah, those Gloucestermen...). The spreaders are square to the masts and forward of the topmasts, so no problem there either.

One thing I found that helps when running before the wind is to ease off the peak halyards quite a lot, and maybe even top up the boom a bit - especially on the foresail. This is not on Cunliffe or any of the other books, just idle trial and error on long runs. Not only do the sails belly out and fill better, but you can go a lot more by the lee that way - helps to avoid unintended jibes, and keeps a schooner going wing-and-wing even if the wind is not dead aft - the foresail fills by-the-lee and behaves quite nicely that way.

Then again, maybe in another year I'll find out why that should never be tried under any circumstances... :D ;) Ian? Anyone?

[tomgallant]

You're right George. Topping lifts, twins on the main so you can use them on both tacks, and peak halyards are just the thing for setting up when you're wing and wing. Offshore, I also run gaff and boom preventers. Set'em up piano wire tight and roll on down the trades. Baggywrinkle at the spreaders is great chafe gear.

[George.]

We have twin topping lifts in the main, mainly out of fear of the boom dropping on out heads...

I set up a tight boom preventer on the main, but just a bunjee cord 'round the boom and shrouds on the foresail - just to keep it still when the boat rolls. Of course it could break if the helmsman screws up bad enough, but I find that even in strong winds the foresail never jibes hard, because it goes into the main's wind shadow.

But I never set up gaff preventers. Am I missing something?

[Carlsboats]

Ian McColgin's comment about swinging spreaders caught my eye. I see the advantage in not having the gaff jam into the lee spreader when running,
but I don't know a practical way to fit spreaders on a round mast, so they will swing out of the way. How would you do that? To complicate matters, the mast I have in mind will be hollow, I want it light, so will be going to a birdsmouth spar. I can beef it up in the way of the gaff, but it will still be hollow. Any ideas Ian? Anybody ?

[Ian McColgin]

Goblin's were quite simple. The inner end of the spreader (wrought iron) was pounded flat and had an eye drilled through. The fitting on the mast looked like a sidways H curved at its base to follow the mast and holes on the upper and lower arms toa accept a pin. The spreader just pinned between them.

By the way, an oft neglected part of correctly mounting a striker (down sticking spreader) under a bowsprit uses this same principle, unless you want the veering of your anchor line to flex and weaken a rigid striker.

With both the spreader and the striker, the base is on the other side of a straight line from the chainplate to the spar. Simple mechanics will show you that when tensioned it can only line up one way. But when loose, as on the lee side, the sail can push against it easing it out a tad.

For both spreaders and strikers, it's not that the give allowes more freedom. The striker is never under relaxed pressure and an anchor line pushing against it won't move it any noticable amount. It's that by not directly resisting the lateral motion at the base, the spreader or striker avoids fatigue failure.

This is less a problem on marconi rigs as the press of the sail introduces less strain than the gaff rig's press of sail and gaff.

[Carlsboats]

Ian, understand everything you say, except --what do you mean by lining up the spreader "on the other side of a straight line from the chainplate ..." ? Carl

[Ian McColgin]

I don't know how to draw on the computer but try this:

Horizontal line low on the page for the deck.

Verticle line for the mast. We're only making an example of one side. For arguement's sake, let's have the horizontal line have maybe 1-1/2" from its left end to the verticle and make the verticle maybe 9" high.

Say 2/3 up put out a 1-1/4" line to represent the spreader. (Let's not worry about cocking this one up a little as you would in life.)

Now draw the stay from the left edge of your deck line up to the spreader and into the mast truck.

Make another straight line from the bottom of the stay directly to the mast truck.

Were the spreader to end at that line, then a pivoting spreader would tend to topple over. Since it goes past and to the mast, the stay will seek the shortest route when under tension and that will hold the spreader normal to the mast.

Or try with ruler, rubber band, and paper clip. Get the rubber band lengthwise over the ruler. Open the paperclip and bend a sort of crutch in one end so it can hold the rubber band.

If you put the point of the paperclip on the ruler (which now approxomates that straight line from chainplate to truck) the rubber band will wobble off. If you push it up with your finger from the other side of the ruler, it will be stabile.