Gooseneck designs allowing boom rotation

[Marvin Hamon]

Hello,

I have a 39' ketch with wood spars and booms. The goosenecks are fabricated from stainless and originally the boom could rotate along it's long axis by the use of a pin that connected the end of the boom to the gooseneck. The previous owner thought this weakened the boom to gooseneck connection so he welded the thing up so no rotation was possible. A surveyor told me that this could result in the boom failing due to the torque being exerted on it by the sail and the sheet. Watching how everything works while under sail I can see how the forces on the boom are trying to rotate it so it lines up with the sail and sheet forces.

I have looked at a number of gooseneck designs on boats around the same size as mine and find that they seem about evenly split between ones that allow the boom to rotate and ones that don't. What are the pros and cons of one design over the other? Does anyone think it would be worthwhile to return my gooseneck to the original configuration?

Thanks for your input,

Marvin Hamon

[Ian McColgin]

Either your rig is very unusual or the advice you are getting is confused.

Roller reefing is mostly a thing of the past - good thing too - but there was probably no reason to weld the pin.

Nor is there much reason to worry now that it's welded unless you have a most unusual rig.

Most roller reefing booms have a rotating fitting at the clew end to allow the boom to roll up without winding up the sheet as well. This will always allow the sheet to pull fair with no twist on the boom.

Even if this has been replaced - perhaps there are blocks attached to pad eyes under the boom or even mid-boom sheeting - the forces are not very severe.

The best installation is the traditional bale that you'll see on the wooden booms of older boats. Basicly a sort of C of bronze or ss rod that's bent to follow the boom's curve but on about an inch greater diameter. The ends are flattened and drilled so the bale can be either screwed or through bolted to the boom.

The stress of the sail twisting the boom is, at least in my experience, trivial.

G'luck

[John E Hardiman]

How is the spar cap at the tack end of the boom attached? Is it just pop riveted or screwed on? How big are the rivets/screws? How is the sheet block attached?

Many things make up the path leading to a failure.

[cbob]

Marv, I have a cast bronze roller reefing gooseneck, with a worm/worm wheel and hand crank, the boom could rotate with sheet at the outboard end. No longer used for good reason. The components at the gooseneck were the weak elements, mine replaced three times. When locked up as you seem to indicate, by welding, as the sail flogs, as in a lumpy calm sea while hoisted. with the sheet fitting allowing the boom to rotate freely, the jerking of the boom to frequent opposite rotational directions results in shock loading at the gooseneck fittings with too much force to be resisted over time. I would need a better description of your fitting. A proper, non-roller furling gooseneck is designed to overcome these shock loadings, A robust lockup between boom fitting and roller/rotating pin described, is possible. Mine is locked with a couple of flat head machine screws between cap and worm gear, which I watch. Having addional pinning some distance from the "axle" should lower the torque loading on the weld. This is also my second "U joint" to sliding car fitting, replaced for the reasons above. Again, need more info. on your setup? Have a Happy, cbob

[Andrew Craig-Bennett]

Well, I'm in a minority; I have a roller reefing gaff mainsail with a bronze worm gear at the gooseneck and I am very attached to it - I find it far more convenient than reef pennants, bee blocks, reefing tackles, reef points and all that palaver!

I honestly reckon that I can get a reef in in less than three minutes, from picking up reefing handle in the cockpit to replacing it, so I very often slip a reef in and take it out again over short distances where I certainly would not have bothered with a "points" reef.

The worm gear necessarily prevents the boom from rotating unless the handle is inserted and the worm turned. So the boom is, in fact, rigidly fitted. As Ian says, the mainsheet load is taken at the outboard end by a cap that is free to rotate, so the twisting load from the mainsheet is not transferred to the boom.

The more "interesting" force with roller reefing gaff mainsails is the way the boom is pulled out of column by the sail when sailing hard - by as much as the spar's diameter at times.

[cbob]

Andrew, This boom out of column you mention, is a result of having the sheet attached at the boom's very end, which is not possible elsewhere, with the roller setup. When I locked mine up I had a new slab reefing sail, on a low aspect 17 ft. boom. This sail has a "shelf" so there are minimum forces trying to pull the boom out of column, and when reefed the same. Usually gaff rigs have sheets attached somewhat in from the end, so the side forces are somewhat different, maybe producing an "s" shape when its blowing up good, What I previously described wasn't clear, or quite accurate, sorry. I put the machine screws through the cap into the forward side of the worm wheel, not the worm, and the parts that failed were the cap lugs/ears with the holes for the worm axle, and not the "U joint" connection to the car, but the car itself. That's how the boom bends. Luck, cbob

[Ed Burnett]

I may be reading the original post incorrectly, but it does not sound like this has anything to do with roller reefing.

As described, it sounds as if the gooseneck fitting allows the boom to rotate as it wants to. This is not unusual, and can be nice in certain circumstances as has been pointed out. Then again, it can be a bit of a pain when stowing the sail and at other times.

In principle, I see nothing wrong with welding up the swivel so the boom is no longer able to rotate. However, if the other componants of the gooseneck are not inteded to take the twisting load that is now imposed on them they might not be up to the job.

If the spar is of normal proportions it should be quite happy dealing with the torsional loads, with the assumption that there is nothing unusual about the way the sheet is attached that would put more twist into the spar than would normally be expected.

Assuming this was done some time ago, the fact that it all seems to be hanging together is a reasonable indicator that it will continue to be o.k. However, it would be worth a very careful look to check that none of the compnonants of the gooseneck assembly are showing signs of deformation or excess wear.

[Lucky Luke]

I don't see in your post that "rotating" boom was for roller furling as some of our friends here understood it.

Boom left free to rotate, in order to avoid any torsion on the boom/gooseneck by the pulling of the sheet and of the sail is - or should be - neccessary if the original boom/ sheeting/ gooseneck design was intended with this feature.

I would think that the previous owner felt uncomfortable by the play induced by such mechanisms, but I- a priori - think that the yard and designer were more capable than this person to determine what arrangement was necessary.

Anyway, you have to watch carefully the wear of the gooseneck components, and any other signs of prejudiciable efforts. In doubt: have it back in original configuration.

[Marvin Hamon]

Thanks for all the information. The boom was not designed for roller reefing. The rotation was to allow the force from the sail to line up with the force from the sheet without putting torque on the boom. Since I see plenty of goosenecks that don't allow the boom to rotate it must work but as several people pointed out if mine was not designed to resist the torque something else could fail. The boom bails for instance are not nice rounded curves that would allow the sheet block to slide from side to side as the boom tacks. They are triangles with the point down so that the sheet amplifies the torque. If the boom rotated then this design would keep the sheet centered as it should be.

I will have to ponder what changes to make or to fix the boom so it rotates again.

Thanks again

[cbob]

Luke, Don't know if you meant roller reefing vice roller furling, but, anyway different animals. cbob

[Lucky Luke]

Originally posted by cbob:
Luke, Don't know if you meant roller reefing vice roller furling, but, anyway different animals. cbobMy mistake: meant roller reefing. Marvin's boom quite probably did not allow for roller furling (not reefing)either, as it was not left totally free to rotate: cf his sheet arrangement.
Thanks for correcting me.

[ 01-05-2004, 11:53 PM: Message edited by: Lucky Luke ]

[Lucky Luke]

Marvin: a few pictures would be welcome.
Anyway, your main sheet's arrangement suggests that, if you keep it as it is, you should allow your boom to rotate.
Still, the correct question remains: do you see any sign of wearing that could warn that, in some strong wind one day.....?

[Marvin Hamon]

I don't see any signs of wear. I was told the danger would be during a jibe if the boom went over hard the torque might cause a failure.

I'm leaning toward returning the gooseneck to its original condition but it's not a priority project.

[Lucky Luke]

Originally posted by Marvin Hamon:
the danger would be during a jibe if the boom went over hard the torque might cause a failure.
You were told right

[Ian McColgin]

All the gooseneck damage I've seen due to sloppy gybes has been the result of the very rapid compression strain applied through the boom and usually at an angle 45 degrees or greater. This causes the attachement to the mast to be twisted towards the new weather side. It may look like it has something to do with torque but it's just the linear force on the boom. Occasionally a boat might suffer this damage without a gybe if sailing off the wind in very heavy weather, but mostly it takes impact loading to tear up the ordinary gooseneck.

If you've any doubts about how seriously loaded a gooseneck can get, disconnect it on some moderate day and try sailing around holding the boom in the palm of your hand. Have the slides nearest the tack along both luff and foot off and have a safety line looped around the mast to restrain the boom if you let go. Next only to crushed hands, torn sails are a drag.

G'luck