Mast loads for freestanding masts

[tropostudio]

Can we discontinue the debate whether a stayed or freestanding rig is better? The two boats in post #104 were my attempt at a joke to end that discussion. Two Tom Wylie boats. One older, one very recent. He still designs boats for both rig types, and he can design a fast and seaworthy boat using either.

The thread is ostensibly about mast loads on freestanding masts. Eric Sponberg's papers are about the only online resources for this, and he states right off he doesn't design them for multihulls (and why). It has been done, and there are people here who understand how to do it. I'd like to know more about the design, engineering, and material selection methods used to make them work for lightweight multihulls with RM max at much lower heel angles than monohulls.

 

[gonzo]

Better for what? Unless a set of conditions is defined in which a rig will have to operate, the discussion makes no sense. I would hate to sail a topsail schooner that was unstayed. Climbing the rig would be a challenge.

 

[tropostudio]

@gonzo - we can have a discussion on how loads are calculated and materials are selected for different rigs without having to stipulate which is 'better.' That might illuminate why certain designers prefer one type of rig over another. We can discuss whether the solution is 'good or bad' for a a specific situation after we understand the design and engineering method and have seen it implemented.

 

[gonzo]

Certainly. They both have good and bad points. I think that availablity of materials often dictates what design is best. For example, there are small sailing trading boats along the southern Caribbean. They have self standing masts built from a tree. They barely do much more than cut off the top and branches. It would be rare to find a mast that is bent and crooked in developed countries. However, they run those boats every day and make a living. Steel wire for standing rigging would be too costly for them.

 

[tropostudio]

Cost and availability of material are certainly big criteria. Current knowledge around the materials and liability concerns would both be big factors.

The illo below is by Pierre Gutelle, and appears in an Eric Sponberg's articles. I can't find a date for the article, but his SNAME paper on engineering free-standing masts and wing masts is from 1983. Colored text and arrows and leaders are mine.

Sponberg doesn't consider freestanding rigs for multihulls. Reasons are in his article, or open the attached PDF excerpt. I figure the knowledge around composite material properties and fabrication methods has come far enough since 1983 that one can design and build a freestanding rig for either a monohull or multihull sailboat will perform decently without being unreasonably heavy or costing a bazillion dollars.

Check out the diagram and RM max and 1/3 RM max for both the Hellcat and the Dragon. First off, the boats are pretty much polar opposites (hah hah). But c'mon, a cruising multihulls, even a small one, won't get 50% of its RM max from having 1/3 total displacement as movable ballast that can hang out further windward than the windward hull. The CG just won't move around that much if you aren't a trapeze dinghy.

Secondly, we could approach 'what if?' for a multihull rig using Sponberg's design method and come up with a working sail area at 1/3 RM max. If the hull and rig are light, and the CE of the rig is low, we might have something. No harm running some numbers, doing a bit of performance prediction, and see what we get. Now, suppose we are willing to decrease our safety factor from 3X to 2X because we are more certain about laminate properties: We can produce laminates with consistent fiber/resin ratios, better fiber alignment, and uniform compaction. We can add sail area and push our working stress closer to our yield stress. Risky? Maybe, but not really if we can proof out our materials and processes to justify the decision.

You won't bother consider the option if you have a tight budget, little time, and must meet industry certifications. Heck, the certification and liability insurance should make you wonder why even bother with designing a sailboat! In a personal project, we may care little about ratings and industry standards. The concern is personal risk in light of available time, money, and knowledge.

 

[rxcomposite]

The OP has gone to sleep. His thread has been hijacked.

 

[dustman]

The OP has gone to sleep. His thread has been hijacked.

I'm still lurking... The thread has certainly taken on a life of it's own.

 

[gonzo]

Sponberg doesn't consider freestanding rigs for multihulls. Reasons are in his article, or open the attached PDF excerpt. I figure the knowledge around composite material properties and fabrication methods has come far enough since 1983 that one can design and build a freestanding rig for either a monohull or multihull sailboat will perform decently without being unreasonably heavy or costing a bazillion dollars.

The issue with a self standing rig is that the mast needs to go through the deck and a significant distance down. In a monohull, they normally go to the keel. In a multihull the cross beam is too shallow. It is possible to carry the mast down and add struts or cables, but then it would be a stayed rig on the lower section.

 

[TANSL]

The issue with a self standing rig is that the mast needs to go through the deck and a significant distance down

That is not a "needing", it is simply an option.

 

[gonzo]

So, according to you a self-standing mast can be deck mounted with no bury?

 

[TANSL]

So, according to you a self-standing mast can be deck mounted with no bury?

That would be a stupid thing that I didn't say. End of conversation.

 

[Ad Hoc]

The OP has gone to sleep. His thread has been hijacked.

Most likely, since there is a misunderstanding of simple comprehension of words being used between posters.

In reference to whether a mast is deck mounted or not....we get this:

That is not a "needing", it is simply an option.

This means one option is to be through the deck and another "option" would be not through the deck i.e deck mounted.
Since - it is simply an option....as stated.

So Gonzo's retort is very valid, and begs such a question:

So, according to you a self-standing mast can be deck mounted with no bury?

He is taking the "option" of...ok, not through the deck then....as per stated, it is simply an option.

But with a reply such as:

That would be a stupid thing that I didn't say........

When clearly you did that.....why...because it is an"option".
One can only conclude there is a lack of comprehension in the word - Option - or that Google/ChatGPT is failing in translating.

I'm still lurking... The thread has certainly taken on a life of it's own.

Indeed...and not a very technical one too.

 

[rxcomposite]

And all the OP wants for Christmas is his two front teeth (mast?)

 

[CarlosK2]

Even if the wind knocks down the sailboat, it is very rare to break the mast.

Normally the Force of the Earth through the Hull and Sea/Waves breaks the mast (and the wind is, let's say, a point of support)

In this case, after breaking the mast, the Waves overturned the Hull.

Sharpii2 Heft Factor: ca. 0.50

3 Tons, LwL 8.5 m, Beam 3.6 (!)

 

[CarlosK2]

I can think of the following Cruising Rig

Balance Lug Main Sail Area = 2 x Balance Lug ForeSail Area in the Mainsail Upwash

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For ocean sailing without an experienced crew and if the sailboat is large ... the mast without cables standing free ... is very seductive

At the other end a small coastal cruising dinghy with 3/4 fractional rig and with the mast at the end of the cockpit ...

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Thanks for the Thread and food for thought.