Surviving A Lee Shore

Our storm trysail, on our McCurdy and Rhodes 56, rigged and ready to head for Bermuda on a passage made some 30 years after the one I describe in the article.

Lee shore. These two words have struck terror into the hearts of sailors for centuries. And justifiably too, since it is generally not the sea that kills sailors but the hard bits around the edges.

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Paul

As I was reading this I was thinking “in-mast furling trysail?” However, I guess the vertical slot could make it difficult to retain rugged mast strength.

Clint

John, the antel track you are referring to; is it the 316ss track?

Charles Starke

I am specifying the slides on a storm Trysail for 1″ T-track. Paul Savage of Hathaway, Raymond and Reiser wanted to make them every 24″ with doubling at the head and tack. Boat is a 40,000 lb Trintella 47. You used slides webbed every 12″. What should I insist upon? Any recommendations?
Thanks.

Marc Dacey

It would seem the most ironic item of the sail inventory on which to take a shortcut.

Charles Starke

No shortcuts are intended by me. I specified 12″ as per John, but the sailmaker, John Savage, insisted strongly on 24″. (And compromised on something in between. I’ll let you know what I get and how it looks and works.)
I insisted on 1″ track. One boat nearby put a fitting up the mast and one at the deck with wire stretched between and he runs his Trysail on the wire with hanks. This is meant to comply with Bermuda race requirements. But the loads on the ends, because of the geometry, are going to be tremendous, and it’s exactly the time not to have these fittings fail.

Marc Dacey

I concur concerning the end loads. I am not going for a trysail but rather a very deep reef on the main and a reefable staysail, a relatively rare choice, but one I feel comfortable with in a steel motorsailer. I look forward to hearing about your results, although I’m not sure how you’re going to test a trysail before you need one…perhaps in 30-40 knots?

The deck to mast wire sounds convenient, rather than correct, like a Highfield lever as a shortcut to make a sloop a cutter with a wire luff. If the point is to spread the enormous loads of a 60 knot wind on a scrap of taut sail, two points isn’t much of one.

Justin Davey

Any experience using rivnuts to fasten hardware (trysail track) to aluminum mast?
Small boat (Contessa 26)

Thanks
Justin

Eric Klem

Hi Justin,

I generally try to avoid rivnuts if I can but acknowledge that they are sometimes the best solution. The beauty of them is that they provide threads in a surface that is too thin to otherwise thread. Of course, it is still effectively a blind rivet so if a similarly sized rivet would pull out of the material, this will pull out also. The real annoyance to me with these is that if the bolt ever corrodes/galls, then you can easily spin the rivnut in the hole and it is a real bear to drill one out, much worse than a rivet usually. Loctite is in order here for a few reasons but if you pick something too strong, you will find that you have to drill everything out just like rivets but that it will be even harder.

If you decide to look at drilling and tapping or also looking at the bolted part of the rivnut installation, there are 4 failure modes that you need to consider:
– The first one to check is always bolt tensile strength. This is simply a matter of the shank strength of the bolt versus the load on it. Bolts in stable joints are typically torqued so that they are at ~75% of shank yield strength. To prevent fatigue, you then need to make sure your maximum load is below this point (tension from torque is a bit inexact so you should leave some room here). There are times where you torque to lower values but it is because of one of the other factors.
– Bolt thread strength. A good rule of thumb is that on a coarse bolt, 5 threads engaged is enough (3 is actually usually full strength) and on a fine one, 7 is enough. This is easy enough to calculate too based on tension, thread stress area, number of threads and material yield strength.
– Mating thread strength. This is usually a much bigger deal as the mating threads are typically made out of a weaker material. If the material is the same or stronger, then the same rules of thumb apply but if it is weaker, you need to calculate it. On a mast, this is going to be your limiting factor, the wall is just too thin and it is a weaker material so you will be limited on the torque and corresponding tension you can apply. In these situations, you ideally have a locally thicker area of material or thread into something behind the material such as a nut with a proper backing plate.
– Head strength which can mean a few things. For something like a socket head cap screw, this is not a worry in a properly designed joint but for something like a low head, button head, or flat head allen drive, this is a big deal. Sometimes the head is too weak for the tension applied and basically snaps off. More commonly, you are limited in how much torque you can apply before stripping the head out.
While the calculations are not hard, I generally recommend to people that they use a bolt torque calculator such as http://www.futek.com/boltcalc.aspx which takes into account the first 3 factors. Once you have done it a few times, you get a feel for it and don’t have to explicitly check each factor each time.

For your application, I would recommend starting by figuring out what the max tensile load on the fasteners is. You can then run the numbers for whether screws could work (I expect number of threads into the mast is going to be your limiting factor). Also, you can look at rivets where you need to look at tensile strength and also the strength of the mast underneath them. Finally, with rivnuts, you need to consider both the rivet and the bolt calculations as you have both things going on at once. This is the work that I would need to do to feel comfortable with the answer on my own boat. As a sanity check, you should also make sure that whatever you come up with is stronger than your mainsail track system.

And putting a trysail on a 26’er means you are braver than I am.

Eric

Garryck Osborne

Thanks for the link to the bolt torque calculator. However, the link is broken, since, as always seems to happen these days, the website has moved things around. The correct links are now:

https://www.futek.com/bolttorque/american
https://www.futek.com/bolttorque/metric

Ernest E Vogelsinger

No experience, just some guesses (sorry John) and considerations.

When thinking on rivet nuts you are basically using rivets – regardless if there’s a second-level thread with bolts or not. The whole unit is a rivet that is blind-riveted to your mast.
As your mast is most probably aluminum the question of rivet material comes into play, you will most certainly avoid steel or SS as this is more noble on the electrical scale, and by time will eat your rivet holes (it doesn’t seem possible to me to place a blind rivet and successfully use an electrical isolator). So you are confined to aluminum and monel rivets.
You may want to compare the material characteristics of aluminum and monel, e.g. here: https://www.makeitfrom.com/compare/5052-H32-Aluminum/Monel-400-NiCu30Fe-2.4360-N04400-NA13 which will show that monel would be the superb alternative.
Then there is the issue mentioned by Eric that rivet nuts tend to spin when the bolt is somehow corroded/galled within the threads, so you might use a rivet nut with a hexagonal body but as far as I found out these are only available in steel…

If it were my mast I’d either go with the backer plate John suggests, or if not possible for what reason ever use the fattest monel rivets available. There really is no advantage to use a rivet nut in this case IMHO, you most certainly would not want to remove your trysail track again?

Justin Davey

Hi.
I did not subscribe to the thread. Oops. First time posting a comment and my apologies for the late reply. Secondly, sorry for asking this same question somewhere else, when I went looking for answers again, now that I am involved in my spring commissioning.

Thanks Eric, Ernest, and John for your insights. It appears the large monel blind rivet approach will win out (, thoroughly coated in Tefgel. I had thought perhaps I could used a chaser line to pull a backer plate into place lining up top and bottom holes, but the curve of the extrusion would mean a possible gap.

Justin

The only other thought I had

Justin Davey

The only other thought I had was relating to fastener spacing. Is there a tool for calculating the number of rivets needed based on expected load?

I have no intention of being out in 45+ knots, but after my 3rd reef, or if my main blows out, I like the idea of a redundant option in strong winds. I have yet to test the theory, but Carol Hasse argues the trysail makes for a more forgiving stabilizer sail too. With its highvis and lack of boom to flog around, I suspect that might be a sane alternative in light winds to, perhaps for motorsailing.

Justin

Eric Klem

Hi Justin,

Spacing is all about how well the fasteners load share. Load sharing is based on relative stiffnesses of the mast and the track. Think about a stiff mast and a floppy track, in this case the load will be shared by somewhere between 1 and 2 fasteners. Then think about the track being super stiff and the mast being super flexible, the load will share very well across a large number of fasteners.

One of the workarounds for the issue of poor load sharing is to temporarily stiffen a section of the track. In practice this is usually done with a car that is stiff and of a significant length. An example of this is what is done with jib cars, the cars are often on the order of 2X the distance between fasteners. meaning that the load is well shared over 3+ fasteners (if your deck is flexible, it can actually be quite a few). On older wooden masts, I have seen the attachment of the track to the mast beefed up just in the area of the head of the sail where each reef will go but I don’t get the impression this is common.

Unfortunately, I don’t know of a quick and easy to use resource for this. I would start with the track supplier and see if they have installation guidelines, hopefully they have done some calculations that are relatively conservative that can be applied. I have not bought track often but it is usually predrilled and if it is marketed for the purpose, I would hope that they would have calculated the spacing with conservative assumptions but I can’t guarantee it.

Eric

Justin Davey

Oddly, this (no holes) track was supplied by my sailmaker so will address the fastener spacing question with them. I’d prefer go with a predrilled track that was then anodized, seems like a sensible alternative so will enquire about this option too. Thanks for describing the forces involved
Justin

Charles Starke MD

Dear John
I was re-referred to this page from your Boreal article today, reread it, and found that I had previously commented and therefore had signed up for notifications. But I see that this article was revised in February 2019, and my notifications were turned off. Would you kindly check to see if a revision in a page turns off further notifications?
It would also be nice to get notified of a page revision.
Thanks and best wishes,
Charles
Charles L Starke MD
s/v Dawnpiper

Charles Starke MD

Dear John
Thanks so much! I also found that a revision turned off future notifications that I had signed up for. Can you keep notifications on a page turned on after a revision?
Thanks!
Best wishes
Charles

Kenneth McCallum

A boat like our Oysters with in-mast furling with the push of a couple buttons offer infinite reefing options. The main and jibs can be safely furled in seconds from the safety of the cockpit. The DYS tri radial sails are constructed to have added strength as they furl in, so the staysail becomes the storm jib and the main can be furled to act as a storm sail. We’ve used them in this way on several occasions. There’s no need to leave the cockpit to go forward.

Kenneth McCallum

John,

The hydraulic and electric furling systems each have a manual back up system which we’ve needed to deploy on three occasions during an electrical failure over the past 9 years. It’s not a big deal to turn a little hand crank or winch handle. Meanwhile, we have the convenience of push button controls from the helm and cockpit to use the other 99.99 percent of the time.

George L

Hi John,

very good points, thanks!

Do you have by any chance some photos of the track and cars for the trysail the way you had it rigged?

Many thanks

George L

Hi John,

sorry, didn’t see your answer before.

I am interested how exactly the sail-track for the trysail is set up.

We were planning on a 4th reef to avoid the trysail, but the cost of the 4th reef is almost exactly the same as getting the trysail. Hence packing the main away when it gets nasty makes much more sense.

Many thanks
G