Jib Boom Pedestal

[Carlsboats]

Who knows about pedestals for the fwd. end of a jib boom? I see lots of jib booms swiveled onto the jib stay, but I understand that a better way is to tack the boom to a pedestal that stands on deck a short distance behind the jib stay. They tell me that this gives the jib a better set both on and off the wind -- flattens her out going to windward, loosens her up reaching and running. Also raises the tack off the deck, which is a good idea. Anyone have any experience with such pedestals?
If I go this way, I need to know about the design for such a pedestal, appx. heighth, and appx. distance to set it back. Boat in question is similar to the Herreshoff "Fish" or Joel White's "Flatfish." Jib will be about 6 feet on the foot.
Don't see stock pedestals in any of my catalogues, but if one of you knows of someone offering such a product as stock, please let me know. Otherwise, I could get one fabricated, either by making a pattern for a foundry, or having one welded up out of bronze plate stock.

[ishmael]

I think you are going to have to make this or have it made.

I'm imagining welded bronze eyebolts, and a pad of hardwood. One eye with the stem slightly flattened, fitted in a deep slot in the end of the jib boom, and riveted, the other just set in a pad eye of mahogany, or what have ya. All of it beefy. The pad eye well blocked below, and bolted.

[rbgarr]

I saw one once that was made of a vertical pipe with a cutout on the aft side that allowed for ventilation belowdecks. Pretty clever I thought.

I can't help with dimensions or distances, but I bet a sailmaker or Todd Bradshaw here on the Forum would have better ideas about how to measure for something like that.

[Todd Bradshaw]

In terms of sail efficiency, raising a jib's tack farther above deck is seldom a good thing. It allows air to sneak around under the foot, equalize the pressure between the two sides of the jib and lose lift and power. The exception would be in light air, when you might catch a bit more wind higher off the water. Naturally, there is also a practicality issue as well. Deck-sweeping jibs get more abrasion on pulpits and other fittings and often block the skipper's view of what's ahead, so I wouldn't fault anybody for raising the jib a bit on a cruising boat. The performance you lose is not much in cruising terms. If you get into a speed contest with anybody though, lower that sucker to the deck.

As to pedestal-mounted jib booms, I have a vague knowledge of how they work, but not much experience messing with them or their design. I'm not aware of any specific formulas for their placement and dimensions, though that doesn't mean that none exist.

A bit of drawing leads me to think that they're a double-edged sword. They automatically adjust tension across the jib's foot as noted above - tighter upwind when close-hauled and looser off the wind. The problem that I see is that the farther aft of the headstay the pedestal is, the more the upwind and downwind tensions vary and they soon seem to approach extremes that may not be desirable on either point of sail. When you throw in the fact that they are not self-vanging and that the tail of the jib boom is bound to lift somewhat when sailing off the wind, it becomes a pretty interesting proposition to draw out the many potential jib shapes that various angles of attack might create.

Unless somebody knows a formula (mmd? Dave G.? John W.? anybody?) I really think it might be easier to build some sort of accurate model with a flat paper jib and play with pedestal locations and boom lengths to see what happens, rather than trying to draw or calculate the results on paper.

It may also be the case, as it seems to be on a lot of fractionally-rigged boats, that jib shape on a run isn't all that critical because the jib is so small and unless you're sailing wing-and-wing it's behind the main and not doing much. On the Starboat, we just poled it out to windward, wing-and-wing, tight and flat for maximum projected area and didn't worry about trying to create much of an airfoil with it. When it was on the same side of the main, it was pretty worthless. I'd concentrate on a pedestal location that seems to give the best performance between close-hauled and a broad reach and not worry much about jib shape on a run.

The application that interests me most and that I've played with a bit is using a pedestal mounted jib boom to make a self-tending jib that can be set up on a roller furler. Pedestal location and boom length are then primarily determined to get the sail to furl properly without having to detach the boom from the clew yet give reasonable foot shape upwind. Off the wind, it starts to get baggy fast and downwind the shape is pretty bad. The boat in question is a design for a mini-schooner with a self-tending, roller-furling, boomed forestaysail that I've been toying with for several years. It would be a real fire-drill to sail it dead downwind anyway and I'd probably never seriously sail below a broad reach, so I didn't worry much about foot shape on a run for the boomed sail. It was more just a way to depower the forestaysail to avoid slamming into the dock, etc. It is an interesting concept though and has been used on bigger boats. This is the only drawing I have that shows how it works. Note that it is a roller-furling sail, not a roller-reefing sail. The pedestal boom system allows "on" and "off", but not "half-way on".
http://www.imagestation.com/picture/sraid46/pa4228b7beea404a83555c412afb3aab6/fcccf9c6.jpg

[Dan McCosh]

I rigged a pedestal on a cutter I once owned that started out with a boom attached to the headstay, with the staysail foot on a track on the boom. The pedestal was a piece of 1/2 in. stainless pipe welded to a base bolted to the deck about 6 ins. behind the stay. The jib boom had a 1/2 in. eyebolt at one end that simply dropped into the open top of the pipe. The sail was attached only at the clew. All and all, the efficiency was considerable. I also put a fitting on the mast which took the same boom. When running well off the wind or downwind, I went forward, picked the boom out of the pestal, and put it on the mast--a bit short for a good jib pole, but awfully easy to do.

[Dan McCosh]

I rigged a pedestal on a cutter I once owned that started out with a boom attached to the headstay, with the staysail foot on a track on the boom. The pedestal was a piece of 1/2 in. stainless pipe welded to a base bolted to the deck about 6 ins. behind the stay. The jib boom had a 1/2 in. eyebolt at one end that simply dropped into the open top of the pipe. The sail was attached only at the clew. All and all, the efficiency was considerable. I also put a fitting on the mast which took the same boom. When running well off the wind or downwind, I went forward, picked the boom out of the pedestal, and put it on the mast--a bit short for a good jib pole, but awfully easy to do.

[shadow99]

Bristol Bronze carries an abundance of the Jib club gooseneck assemblies for the different class Herreshoff designs. See pages 9 & 10 of there catolog. There at www.bristolbronze.com (http://www.bristolbronze.com)

[JimConlin]

Seems to me that i've seen such in the catalogs of:

Spartan Marine (http://www.spartanmarine.com/) Bristol Bronze (http://www.bristolbronze.com/)
or
Port Townsend Foundry (http://www.porttownsendfoundry.com/)

[Ian McColgin]

You only need a pedestal if you can't bring the attachment reasonably close to a plane where the staysail's tack is.

On Goblin the forestaysail was tacked to the stem on the gammon iron and the attachment for the boom was about 4" abaft that point, just a pad eye on the bowsprit.

Goblin's main staysail (really the same problem) had both tack and boom coming to the foremast. Since the boom's gooseneck was a few inches lower than the tack, it managed to develop a nice fullness in the sail off the wind even though the tack and boom pivoted at about the same place fore and aft on the boat.

From that I conclude that a pedistal is not useful unless the verticle seperation is quite large and/or you need to get the gooseneck up to clear other deck obstructions like sampson posts or a forehatch.

To some extent, you need to consider verticle as well as horizontal seperation but the horizontal seperation is more likely to be critical as almost any installation will perforce have the tack and gooseneck within a half foot or less of verticle seperation, with only a coule of inches being common.

Happy installations have the boom's pivot a bit more than 5% of sail's foot abaft the tack. Certainly not too close to 10%.

Pitch for a different rig - The boomed staysail is a seriouis menace. Off the wind it's tendency to gybe, while a nice warning to the helmsman, is terrifying to anyone on the foredeck. Even on the wind, that thing coming across the deck in a tack can cause anyone on deck to dive behind the bitts.

I really like Grana's 'camber spar' staysail. Here the boom (curved) is inside a sleave in the sail. It runs from a pin and roller arrangement normal to the luff back and down to the clew.

Even when it's flogging around, only a bit of the hard part is even close to head height and is easy and obvious to duck under.

And the sail sets super fantastic, self vanging, good shape, and all that. Very quiet when you're way off the wind and the staysail's main function is not so much to drive as to warn of a gybe.

Whatever

G'luck

[Roger Cumming]

We mounted our jib boom to a short length of track (an old Merriman outhaul fitting for the end of a mainsail boom). The track is on the top of the bowsprit. A light line led aft allows the draft of the jib to be adjusted to wind conditions. It works very well. I believe this originated in fishing schooners where the jib boom was mounted to a simple horse on the top of the bowsprit.