How much can a mast flex before breaking?

[caguy]

We were out sailing yesterday and had the gennaker up. The Mac 25 is a fractional rig and I noticed that the side load with the gennaker is considerable when on a beam reach to close hauled. It was only blowing about 10 kts but the top of the mast was flexing a good 4-6'' maybe more it was hard to tell without a reference point. The rest of the mast remains ridged as you would expect. Is it only safe to use a gennaker in a downwind situation. It never concerned me until I looked up yesterday. I'm not just concerned about the breaking point but also the fatigue at the point where the upper stays attach.

 

[Ross]

I doubt that it was moving that much in a flexing mode. That would be a lot of bow in the stick. The halyard will serve as a straight line reference and you can check the flexing against the tight halyard.

 

[Barnacle Bill]

With a fractional rigged boat, it is not uncommon for the top of the mast to fall to leeward while going to weather in heavy air which in fact helps depower the rig, but that effect is really applicable to the mainsail. So, based on what you have said, the gennaker or cruising spinnaker, which is attached to the forestay which does not go to the top of the mast, will not have as much an effect. A gennaker is really designed for downwind use anyway in lieu of a spinnaker with a pole, but, because it is hanked on like a genoa, you can sail to weather more than that of a poled symmetrical kite and it is considered less effective when the wind is from broad reach to a run. I would check out the tension of your stays and make sure they are adequately taught. In 10 knots of wind, I would not think the top would fall off very much for depowering purposes. I would question rig tension. Many MacGregors did not use turnbuckles for stay adjustment, but only holed plates for less than finite adjustment, which makes it hard to properly tension a rig. And one wonders why they are so inexpensive. But, that is the deal.

 

[Timo42]

Hey Frank, if you break your stick, can I have your mainsail?:stirthepot:
Sorry we couldn't hang around yesterday, but Elise was worried about a sick goldfish. :troll:No, really... I am sorry to report that Albert Finny passed last night, so today she bought Albert Finnagain, I told her if that one dies we will have Finnagain's Wakehttp://www.youtube.com/watch?v=geX8IVBv4wk

On a related note, I noticed my forestay turnbuckle retainer had fallen out and the stud had started to back out, time to check the rigging folks.

 

[caguy]

Has anyone ever broken their mast above the outters on a fractional rig

or am I worried about nothing.
It was only bending above the upper stays below that the mast was perfectly straight. My spinnaker block is attached about 6'' above the forestay but my gennnaker is attached at the masthead, which is only supported by the back stay. Would removing the split backstay and going to a single center stay cause that? (doesn't seem so).
We have sailed the gennaker pretty close-hauled, granted it doesn't point nearly as well as the genoa, but close. I'll take a video of it next time. I didn't think to look and see if the mast was straight again after getting back to the docks. Something else to worry about.

 

[Jenni]

If your Gennaker is attached to the masthead its not really fractionaly rigged anymore and you may be putting to much force on the top of the mast. When you are flying your genoa it would be supported from side to side motion by the shrouds. Metal has two types of bending. There is the elastic bend where it will return to its original shape. Then there is the plastic bend where the metal deforms and does not return to its original shape. If you keep your mast bending in the elastic range you should be good.

 

[caguy]

If your Gennaker is attached to the masthead its not really fractionaly rigged anymore and you may be putting to much force on the top of the mast. When you are flying your genoa it would be supported from side to side motion by the shrouds. Metal has two types of bending. There is the elastic bend where it will return to its original shape. Then there is the plastic bend where the metal deforms and does not return to its original shape. If you keep your mast bending in the elastic range you should be good.

I guess that was my question. How much is too much? And what about fatigue? If no one has ever broken their mast in that situation then I have less to be concerned about.

 

[higgs]

Jenni makes an excellent point about you using your fractional as a masthead rig.. I would contact Mac and ask them about this. You rig is pretty light and I would be quite concerned about putting too much strain on it.