Dinghy boom-related struts

[dancrane]

Watching footage of Osprey and Javelin dinghies, I’ve noticed many examples wearing a short diagonally-angled strut between the forward side of the mast (opposite the point where the boom is attached) and the foredeck.

Given its position directly ahead of the boom-end, I guess this is some sort of reinforcement, but I’m wondering whether it’s indicative of the mast being less than strong enough for the forces at work. Is this the case? And, can this support spar be retro-fitted to tired old boats, or does it require some infrastructural work under the foredeck?

Or, does it have some entirely different purpose?

On a similar subject, I haven't seen any 'Gnav' kicking-strap equivalents, on dinghies. I'd have thought the space saved, by not having the vang sweeping the front of the cockpit on every tack and gybe, would make the Gnav ideal for dinghies.

Or are they too scarily expensive?!

 

[Seajet]

Sounds like a mast ram ?

Used to be trendy on some classes, multi-part purchase to give mast bend; no doubt added a little strength if securely mounted & locked off, but that wasn't the purpose.

 

[Kelpie]

A Vibe has a gnav, I believe.

 

[trapezeartist]

Sounds like a mast ram - it is a mast ram! Not so much trendy. More a better solution to the problem than mast gate chocks. Fitted to many dinghy classes.

Quite a few skiff classes use gnavs. I used to have a Laser 4000 with one. In fact I can't definitively think of any skiff that uses an conventional kicker, though I'm sure there are some. It definitely gives much more room for the crew as he runs across. However the mast bend characteristics are completely different as the kicker no longer pushes the mast forward at gooseneck level (meaning that it doesn't need a mast ram ).

 

[William_H]

Mast strut

I conventional boom vang pulls the boom down bit depending on the angle of the vang also pulls the boom into the mast. A vang at 45 degrees will provide as much pull down on the mast at the attachment point as it does push the boom into the mast. Some sailors like huge boom vang tension which relates then to strain on the mast at the gooseneck as related to the vang attachment point. ie usually the bottom of the mast.
This kind of strain needs to be opposed by a strut from ahead of gooseneck to avoid breaking the mast with the vang.
A vang that attaches further out the boom from the gooseneck provides even more strain on the mast while a vang attachment closer to the gooseneck provides less strain on the mast but more on the boom vang attachment point. Best geometry comes from a keel stepped mast with vang attached to the mast base so a good height to the gooseneck.
I mentioned in a post working on 280 lazers set up for World sailing championships. The supplier has already bought 100 spare top mast sections with 100 more to come. There is a warning on the mast near the gooseneck warning against too much vang tension until the mast work hardens. i don't know about that but obviously on a lazer a boom vang can break a mast. In this case the load on the mast top via the leach of the sail can snap the weaker top section.
Young bloods must be restrained a bit with often too much energy and can break things with simple adrenalin.
olewill

 

[Ruffles]

Young bloods must be restrained a bit with often too much energy and can break things with simple adrenalin.

In a blow you tighten the vang before you launch. You sit on the boom until the end touches the deck. Then pull in the kicker. It's the only way to de-power.
Wierdly my top mast snapped on a totally calm day. There was a loud ping and the thing landed on me. But on close examination you could see that there had been a crack for some time. And when this happens you have to replace the sail.
It has to be said that Laser I dinghies are pretty primitive! And very expensive for what they are.

 

[dancrane]

Thanks for those contributions. I admit I've only occasionally and briefly sailed serious performance dinghies, so the huge strain on certain components, isn't an area I'm well schooled in.

Aside from the restrictions that stem from entrenched class racing rules, would a simple solution to the weakness that results from exceptionally taught vang settings, be a stronger or reinforced lower mast? (I recognise that Lasers are a separate area.)

If the sail shape in heavy weather, requires a vang setting that endangers the mast's integrity at the gooseneck, in turn requiring a strut to brace the mast (I'm only inferring and guessing here), wouldn't/couldn't a heavier section of mast for the lower four foot, help?

I also wondered a while back, when I thought of decking over the forward end of a dinghy's cockpit to enlarge the space under the foredeck, whether the vang couldn't have its lower end attached to a curving track on the deck, in the style of the mainsheet's, rather than to the mast. It might be unprecedentedly complicated, and wouldn't alleviate strain on the mast at the gooseneck, but it would reduce the vang's thrust forward. Actually, maybe that would reduce strain on the gooseneck? Just another wild idea...

 

[jwilson]

A Vibe has a gnav, I believe.

Also 49er

 

[Kelpie]

I also wondered a while back, when I thought of decking over the forward end of a dinghy's cockpit to enlarge the space under the foredeck, whether the vang couldn't have its lower end attached to a curving track on the deck, in the style of the mainsheet's, rather than to the mast. It might be unprecedentedly complicated, and wouldn't alleviate strain on the mast at the gooseneck, but it would reduce the vang's thrust forward. Actually, maybe that would reduce strain on the gooseneck? Just another wild idea...

My concern would be that with tension on the kicker, there would be too much friction in the track which directly affects the ability of the boom to move. In a high performance dinghy, when you dump the sheet, you *really* want the boom to be free to move.

 

[Iain C]

In short, the strut controls lower mast bend, and ensures that pulling on the kicker does not push the lower mast forward, dumping power. It does also give you the abilty to tweak whilst on the water...for example if the wind drops and you need more power, pull the strut back a bit to power up the bottom of the main. If it gets silly windy, allow it to go forward (but not back) and you can dump power more easily by really flattening the sail off. What others have missed, is that it also stops the mast inverting on a run with the kite up. There was a move back to chocks in some classes recently (saving weight, money, string, complexity and jib tacks getting worn by brushing against it when tacking) however they would still need some kind of system to stop the mast inverting....either chocks behind the mast, or a piece of dyneema following the path of the strut. Normally this is held out the way by a piece of bungee, running from the mast gate to a ring on the dyneema, but the dyneema is pulled tight on the run.

One of the reasons boats like Fireballs etc have a strut, is because they can't have lowers, either because of class rules, or because they would just get in the way bagging the kite. However they do a very similar job.

The 49er does have a very agricultural gnav, but it has lowers to keep the mast in check. They do a great job too...as I managed to snap a boom recently thanks to a bit too much vang!

WRT to skiffs with proper kickers, the 18s and 12s I sailed have normal kickers. So does an RS800, but that's not a proper skiff, but that's a discussion for Y&Y rather than here!

If you want to see something really odd, look up "Temple Vang". Proper forces at work there!