Twin mainsheet - deckeyes loading

[zoidberg]

I'm looking to install a suitable pair of deckeyes on the coamings to facilitate a 'twin mainsheet' setup. While there's a choice of deck/padeyes available, I'm puzzling over what max. loadings might be involved, for reinforcement considerations.

The boom's 11 feet long and the mainsail is about 150 sq.ft.

Any guidelines or Rules of Thumb?

 

[William_H]

Can't give you a Kg load but it will be significant depending on the number of purchase of the tackle and the strength of the sheet hand especially if it is an upward pull.
On my little 21fter it had originally a track across the bridge deck for a single main sheet on traveller and track. No one son loved sailing and is a big lad. Pull was upward and as he grew and figured we would go better to windward by adding more main sheet tension I noticed the bridgedeck bowing upward. Fix was support stays under the bridge deck down to the bunk side.
I would suggest lots of backing plates for pad eye or even stay support down to hull or similar. How ever loading on twin main sheets will not be so great as for a single centre sheet. ol'will

 

[Chiara’s slave]

That’s just a tad bigger than our XOD main. But that weighs 1300kg, with a shallow keel. The way the boat stands up to her rig will make a difference. Personally, I’d guess the load, double the guess, and epoxy in some 18mm ply under the coaming, and make up a large stainless washer/backing plate and bolt through the lot. The snatch load with a gybe is the big one, I should think.

 

[fredrussell]

Can't give you a Kg load but it will be significant depending on the number of purchase of the tackle and the strength of the sheet hand especially if it is an upward pull.

Would number of purchase make a difference to load on deck fitting? I would have thought that just determines how easy it is to move the boom when it’s loaded.

 

[Chiara’s slave]

Would number of purchase make a difference to load on deck fitting? I would have thought that just determines how easy it is to move the boom when it’s loaded.

Absolutely. Of course the padeye load is unaffected. You just add purchases to make sheeting easier, not to relieve load on your fittings. More puchase gives you the power to increase loading by sheeting harder, in fact

 

[ean_p]

I'm looking to install a suitable pair of deckeyes on the coamings to facilitate a 'twin mainsheet' setup. While there's a choice of deck/padeyes available, I'm puzzling over what max. loadings might be involved, for reinforcement considerations.

The boom's 11 feet long and the mainsail is about 150 sq.ft.

Any guidelines or Rules of Thumb?

As a place to start to get your head around the loads in the rope, then adjust for the loads at the fixed points.......

Mainsheet Loading Calculator | Harken Marine

 

[RunAgroundHard]

I'm looking to install a suitable pair of deckeyes on the coamings to facilitate a 'twin mainsheet' setup. While there's a choice of deck/padeyes available, I'm puzzling over what max. loadings might be involved, for reinforcement considerations.

The boom's 11 feet long and the mainsail is about 150 sq.ft.

Any guidelines or Rules of Thumb?

From "The Boat Data Book" by Ian Nicolson

Backing pad thickness 4x diameter of the rod that the U bolt is made from.
Assuming a square backing pad, each side should be at least 10 times the distance from the top of the deck to the bottom of the bolt where the nut fits. He does not sate what material, but I assume he is talking about a grade of ply wood.

I have read that if using stainless as backing pad, it should be 5mm thick as any less will cup, deform under load.

 

[Refueler]

Would number of purchase make a difference to load on deck fitting? I would have thought that just determines how easy it is to move the boom when it’s loaded.

The load is same regardless of number of block sheaves ....

What needs to be considered is that the lee side will be taking less load than the windward. The load will not be split evenly between the two.

What to use ? U bolts with good backing plates bedded under deck with epoxy or even Sikaflex. I would strongly suggest small top plate to protect the deck surface as well as the larger under deck plate. Nuts pressing on large penny washers of course. The U bolts don't have to crane lifting jobs !! Have a look at a small to medium sized boats stays and the U bolts used on some ... basically to match the shackles used to attach sheets.

My Kormoran had split main sheet where it was fixed point each 1/4 on transom. Its excellent for bringing boom to centre to gain a few degrees pointing .... but the windward load was significantly more than lee.
I eventually had a sheet horse made for the boat and use a traveller ...

 

[bignick]

I was going to hunt down the Harken loading calculator, until I noticed that Ean_P had already done it in post #6.

 

[Chiara’s slave]

I was going to hunt down the Harken loading calculator, until I noticed that Ean_P had already done it in post #6.

You may know the load from that, the hard part is knowing the strength of the structure.

 

[bignick]

Quite right, but that isn’t what the OP asked.

following on from Chiara’s comment, however, mainstream manufacturers reinforce the deck with alu plates etc where padeyes are going to be attached. it doesn’t sound like it’s a large boat, so a decent backing plate below deck will probably be sufficient.

If you’re going from a traveller system to a twin mainsheet system, then you may also need to consider upgrading your kicker.

 

[Chiara’s slave]

Quite right, but that isn’t what the OP asked.

following on from Chiara’s comment, however, mainstream manufacturers reinforce the deck with alu plates etc where padeyes are going to be attached. it doesn’t sound like it’s a large boat, so a decent backing plate below deck will probably be sufficient.

If you’re going from a traveller system to a twin mainsheet system, then you may also need to consider upgrading your kicker.

I was thinking the twin mainsheet system is to get around kicker issues. We don't have a kicker at all, we have a tackle with a snap shackle to attach to the boom end and to a ring bolt on the end of the aft beam. Makes it into a twin main, kind of. Useful when cruising, with low traffic. Too much hassle in the Solent, where tacking and gybing to avoid other craft is once every 10 mins on a busy Summer Sunday. We have a traveller. It's been ditched on the latest incarnations of the Dragonfly. Shame, really.

 

[bignick]

Interesting, I assumed that changing to a twin mainsheet system was to get the mainsheet out of the cockpit to free up some lounging space. Shows how two people can read the same info and come to separate conclusions having made different assumptions to fill in the gaps.

@zoidberg:
What sort of boat is it?
What are trying to achieve by making the change?

 

[fredrussell]

What to use ? U bolts with good backing plates bedded under deck with epoxy or even Sikaflex.

Don’t use U-bolts. Use padeyes. Much better load bearing abilities.

 

[zoidberg]

Thanks to 'ean_p' and 'big nick'.... and to others.
I'm aware the peak load to consider is likely to be a big unintended gybe such as a wild broach. Thanks for the pointer to the Harken calculator. That suggests a peak load of about 1400lbs/force.

Now - the setup. The original mainsheet track was on a bridgedeck very close to the companion hatch - an occasionally dodgy arrangement. That's gone. I'm fitting a 22mm, 30" broad reinforced ply panel transersely across the front of the cockpit, bolted down to the bridgedeck and the seats forward. A new traveller track, with a conventional multipart purchase, will be fitted to that. This may prove satisfactory.

I've been cued to the potential of a twin mainsheet arrangement due to its use by several long-distance voyagers....

.....and its potential in a MOB recovery situation, so would like to fit FOLDING deck/padeyes on the coamings so I'll have the option for 'single' or 'double', depending on what I'm doing. These are probably sufficient, both in working AND break loads....

I do have appropriate material for 'robust' backing pads.

Edit: for 'big nick' et al. The boat is a Cutlass 27, similar to Matmut above but smaller at 27' overall.

Edit2: I do know the Dragonfly(s), both the 8m and the 10m variants, having sailed/raced both with MB and others in MOCRA Series, back in the day.

 

[Refueler]

Don’t use U-bolts. Use padeyes. Much better load bearing abilities.

OP has decided on folding Padeyes .... so our difference of opinion is voided.

But must ask - what load do you think he's going to have ?? Considering that thousands of yachts around the world have U bolts to carry mast stays and various other that will carry significantly more load than OP is going to have.
One of the reasons I shy away from Padeyes - is that the U part is usually welded to the pad ... and I have seen them fail. A U bolt is a continuous rod without weld. Personal preference. Folding Padeyes are IMHO weaker still.

 

[Chiara’s slave]

My vote goes to Refueller’s solution. I wouldn’t dare attach my mainsheet to a folding padeye.

Looks like you were right, Nick. The change is largely ergonomic. Though the extra sail control is good. I think its a great idea, however zoidberg chooses to implement it

 

[bignick]

I just looked up a Cutlass 27 to see what you’re talking about. Pretty boat.

lt seems like you have a similar arrangement to my Elan 295; the traveller runs across the front of the cockpit just aft of the companionway opening. it’s probably the feature I like least about the design of my boat and I can understand why you‘re thinking about changing it.
It’s a menace for anyone coming out of the companionway and it’s also just far enough from the helm to be difficult to get at if you’re short handed.

I can’t quite get my head around where your new traveller position will be. If the new plywood support is bolted to the original bridge deck, and the seats, then you must only be moving it aft by 30“ and making the bridge deck wider. Or have I got the wrong end of the stick?

 

[bignick]

I can understand the rationale behind a twin mainsheet arrangement for long distance cruising (especially if you could disconnect one and run it forward as a preventer), but I would have thought it would be more of a hindrance than a help during normal sailing, as you would always have one crossing the cockpit.

 

[zoidberg]

the new plywood support is bolted to the original bridge deck, and the seats, then you must only be moving it aft by 30“ and making the bridge deck wider.

That's about right, 'bignick'. It reduces the hazard of the traveller slamming over and pinning me/someone else, and the frequent blocking of free movement of me in and out. Further, it provides a shelf wide enough for me to sit/lounge on watch protected by the sprayhood while the windvane takes the strain.

I want to have a multi-part purchase close to hand as part of a 'readily-available' MOB recovery setup. Initial thought was to have that in a bag clipped handily onto the guardrail. Then the idea of using it as part of a twin mainsheet setup occured. Each end of both mainsheet purchases will have/does have a BIG Wichard clip, which is 'man enough' and permit repositioning in seconds.

I don't know which arrangement I'll find the more satisfactory. I'll certainly use the 'new' mainsheet traveller/track, and perhaps the 'twin' when it fits the need..... during longer legs with the windvane in charge. It's a 'suck it and see' situation, with little cost in the fitting of those padeyes.

I do have some spare U-bolts and I do understand that they're likely to be more robust, but there's not a lot of room, there are sheet winches and their handles to consider, and I don't want U-bolts sticking up if they're not in use.