Thru-mast Or Mounted On The Coachroof?

[skipmac]

Originally Posted by Rakuflames

I have a question for you -- purely academic as my rigging is in good condition (not my opinion -- it's been checked).

I have a Hunter with swept-back spreaders, so I have a lot of rigging (it does have a split backstay). I get how easily the mast could come down if the forestay or back stay snapped, but there are three shrouds on each side. I do have line on board to replace one if it pops, but ... with three shrouds (assuming I'm not in adverse conditions at the time) ... would the mast be at risk of coming down immediately if one of those six shrouds gave? I hope I never find out from real experience but ... such discusions make us newer sailors curios, to say the least ...

Fortunately don't have personal experience of this but from reading every incident of rig loss I see I can offer an opinion based on that information.

First, will depend on which shroud and the point of sail. I'm assuming your three shrouds per side are fore and aft lowers, one upper?

The most severe result will depend on whether you lose a windward or leeward shroud. More common is the loss of a windward shroud since those will be under the most stress. If you lose a windward upper shroud you will most likely lose at least part of the mast. Loss of a lower is less common and if you do lose a lower you have a much greater chance of saving the mast.

I have read of situations where a boat lost a windward upper shroud, tacked instantly and saved the mast. I think this is rare as usually the mast goes immediately with the shroud.

While not stressed the loss of a windward shroud does happen, usually due to something coming loose from the movement of the shroud rather than breaking. Unless it goes unnoticed and the boat is tacked it would be rare to lose the mast in this case.

These scenarios are based on a reach. Running downwind you can have stress on the shrouds on both sides but otherwise similar situation.

[osirissail]

Originally Posted by rebel heart

. . . My vote would be for spare cable clamps, knowing how to use them, and some amsteel. Tie a quick trucker's hitch and you can fashion a temporary stay pretty quick. . .

I would add to that - that inspecting your standing rigging, especially before and during a circumnavigation will go a long way to preventing any catastrophic failures. Most failures occur where the wire enters the terminal fittings or just inside. Water wicking its way inside combined with lack of oxygen leads to stainless steel intragranular corrosion and failure of the wire. Brown/black/redish stains are the telltale that you might be getting a problem.

But in my "spare parts kit" for rigging I keep a couple Sta-Lok Long Stud Terminals that are great for repairing such a problem. Also if you use Sta-Loks terminals be sure to put some silicon caulk inside the fitting during final assembly to insure that water cannot seep inside.

Sta-Lok Long Stud Terminals

[Sailmonkey]

Originally Posted by osirissail

Also if you use Sta-Loks terminals be sure to put some silicon caulk inside the fitting during final assembly to insure that water cannot seep inside.

Sta-Lok Long Stud Terminals

I thought they specifically said to not use silicone as the ammonia was bad for everything involved. From memory, I thought they wanted a poly sulfide used.

[Jim Cate]

Originally Posted by Sailmonkey

I thought they specifically said to not use silicone as the ammonia was bad for everything involved. From memory, I thought they wanted a poly sulfide used.

No, they specifically DO say to use silicone sealant. There is no ammonia in the silicone, but there is acetic acid, but this is harmless (white vinegar) to the 316 s/s terminal.

Cheers,

Jim

[osirissail]

Boatlife Caulk is specifically recommended by Sta-Lok - see: Sailing Services - Sta-Lok Assembly Instructions

[Sailmonkey]

That's what I thought. Boatlife life-caulk is specifically polysulfide. Not silicone

[barnakiel]

Originally Posted by carstenb

(...) Other opinions? For coastal cruising, I feel rooftop masts are fine. Different story when blue water.

I believe there are IMOCAs, VORs and Minis with deck stepped masts. Also plenty of out-and-out bluewater cruising boats. In my eye, both solutions work fine if they are designed and executed fine. Both give trouble when not.

b.

[Jim Cate]

Originally Posted by Sailmonkey

That's what I thought. Boatlife life-caulk is specifically polysulfide. Not silicone

OK guys, this is very interesting. This morning I googled sta-lok assembly instructions, and the first one that came up looked exactly like the sheet that came with the last batch of sta-loks that I bought some years ago. It really did say to use silicone sealant.

So, after reading your posts, I went back and couldn't find the one I had this morning. Did find the official Sta-Lok site, and they make NO mention of using sealant of any sort.

Hmmm... then I found a Sailnet forum thread that had some references, and one chap had actually queried Sta-Lok on the subject. They said that it was up to the user whether to use sealant or not, but (despite their earlier advice) said not to use acid cure silicones, for the acetic acid would attack the s/s. Interestingly they no longer mention using Lock-tite on the threads, either. Wonder what gives there?

Hmmm again... so I looked up the tables of chemical resistance for metals (see http://www.pexuniverse.com/docs/pdf/...tance-data.pdf) where it says quite clearly that even highly concentrated acetic acid had NO EFFECT on 316 s/s. This is in agreement with my memories from laboratory applications years ago.

So, I'm somewhat confused! However, I have used acid cure silicone in both Sta-Lok and Norseman terminals in teh past with no issues. I certainly think that some sort of sealant should be used, and there is certainly no reason not to use a polysulphide based one if the silicone worries you.

I still think that they are great terminals!

Cheers,

Jim

[stillbuilding]

Originally Posted by osirissail

One thing that is probably driving the use of deck stepped masts versus keel-stepped is the ability to route the running rigging from the mast to the cockpit. It is quite easy and economical to do with deck stepped masts. However. with keel stepped masts, there needs to be serious modifications made to the cabin top/mast interface to allow the running rigging to be routed to the cockpit.

Can you elaborate on this cos I do not understand. Do you mean using a tie to prevent deck distortion?

[osirissail]

Originally Posted by stillbuilding

Can you elaborate on this cos I do not understand. Do you mean using a tie to prevent deck distortion?

Yes, most cabin top are designed to resist downward direction forces but looks what happens when you have running rigging that is led back to the cockpit from the mast.

Take a halyard for instance. The line is attached to the headboard of the sail and the bottom of the sail is attached to the boom which is attached to the mast tube. The halyard is then run up to the mast head where it goes around a sheave (pulley) and back down the mast tube. Then the halyard is attached to another sheave attached to the cabin top usually at a mast ring which is bolted to the cabin top then the halyard is redirected aft to the cockpit.

Since the keel stepped mast is sitting on top of the keel, tightening the halyard "pulls" up on the sheave attached to the mast ring or cabin top. This exerts a force pulling the cabin top upwards distorting it. Anti-pumping rods are commonly used to redirect this force to the keel. This is a thin stainless steel rod that runs inside the cabin from the cabin top down to the keel just behind the mast tube itself.

With deck/cabin top stepped masts the sheave is attached to the mast shoe sitting on top of the cabin top so the forces are contained within the mast tube system and the only possible force is aftwards - the mast base being pulled towards the cockpit. But this is a direction that the cabin top can easily resist.

So with a keel-stepped mast a clamping system needs to be attached to the mast tube at the cabin top level to transfer the vertical forces off the cabin top and back onto the mast tube system or an anti-pumping rod added. Basically this is one or more parts that need to be manufactured and properly installed and maintained which can be avoided with deck-stepped mast systems.

When I converted my running rigging from being situated at/on the mast tube to being run back inside my pilothouse, I designed and had the clamping collar built as part of the deck ring that covers/seals the hole through the cabin top where the mast passes on its way to the keel.

Additionally, these days, shipping mast tubes which are 60+ feet (18m) long from manufacturing plant to boat assembly plant is rather expensive. Deck stepped masts are about 7 ft +/- (2.2m) shorter and subsequently easier to ship. And if you look now at the really new boats you will see a joint about halfway up the mast that allows the boat manufacturer to get masts that are - obviously - only half as long when shipped to them and then assemble the mast system to full length at the boat.

[osirissail]

As to using Sta-Lok versus swaged fittings - during the last rigging job I did a few years ago I found that the number of "shops" has have the huge 50-ton or heavier rolling swagging machine had drastically decreased. So having new stays and shrouds made now cost nearly the same as the cost of the wire and a Sta-Lok type fitting. Adding in the feature of Sta-Lok type fittings of being able to be "re-used", purchasing wire with swagged terminals was not competitive anymore.

But be careful, the different manufacturers of reusable compression terminals like Sta-Lok, Norseman, etc. have to make their system slightly different to avoid Patent infringement. Sta-Lok is unique in that they use a little circular dished "cup" (called a "former") under the "cone" that allows during assembly and tightening the strands of wire passing around the cone to maintain their alignment and not be "dragged" by friction with the base body of the fitting. I prefer this system so use Sta-Lok exclusively.

See: Sta-Lok Formers

[Seaworthy Lass]

Originally Posted by carstenb

So here is a question for the experienced blue water cruisers. What are your opinions on coachroof mounted masts, as they are in most production boats today. Versus a thru-roof mast that is stepped in the keel?

My boat has a thru-mast. I will be circumnavigating so I feel this is a necessity.

Other opinions? For coastal cruising, I feel rooftop masts are fine. Different story when blue water.

Our super strongly built aluminium boat was designed with a deck stepped mast. We were not looking at mast stepping as a big factor in boat selection. Both are fine for blue water cruising if well designed and fitted. It is not the keel but the shrouds that hold the mast up.

A few advantages with deck stepping in my opinion:
Absolutely no water ingress (our bilge is always bone dry and is used for storage)
No damage to the deck in a dismasting
More room down below

[daddle]

Originally Posted by osirissail

... So with a keel-stepped mast a clamping system needs to be attached to the mast tube at the cabin top level to transfer the vertical forces off the cabin top and back onto the mast tube system or an anti-pumping rod added. Basically this is one or more parts that need to be manufactured and properly installed and maintained which can be avoided with deck-stepped mast systems.

Keel stepped masts should have a system that retains the foot in the shoe. Otherwise if the rig fails the remaining portion has been known to flail around inside the cabin until it destroys something important ... like the hull.

In my opinion either keel or deck stepped is fine so long as it has been properly designed for the task.