Questions for the junk rig enthusiast

[nuvaslacker]

The JRA has loads of documentation. In addition I would suggest looking at the Derek Van Loan Junk Rig book; it's very practical and deals with the size of boat you're looking at. You may find it a bit of struggle to obtain a copy, as I think it's just gone out of print.

The Chinese Sailing Rig: Design and Build Your Own Junk Rig by Derek Van Loan
ISBN-10: 0939837706
ISBN-13: 978-0939837700

[fryewe]

Roger Taylor's website

Introduction to the junk-rigged Corribee Mingming

and videos on the modifications that he made while constructing Ming Ming II might be instructive for you. He has written several books that you might find useful.

He's a good story teller and the videos are well done with considerable detail on mast step and deck strengthening, mast and rigging and sail construction, and the sea trials of his modified boat.

Good luck.

[dannc]

The JRA has a large archive of magazines they have published over the years. Become a member for about $10 a year and you get access.

Also, read https://www.amazon.com/Practical-Jun...words=junk+rig. It is the Bible for Junk Rigs and will answer your questions about mast size, structure, etc.

The link to Ming Ming is a good suggestion as well. Taylor has a couple of books about sailing Junk Rig boats and converting boats to Junk Rig.

I have not yet read,

The Chinese Sailing Rig: Design and Build Your Own Junk Rig by Derek Van Loan

but it is on the reading list.

Tom Colvin designed and built many a Junk Rig boat and he lived in one for years. I think his books are out of print but I was able to get them used.

Later,
Dan

[Capn Jimbo]

Originally Posted by Force 50

In reference to making my mast solid, I was considering splitting it in half and slowly laying layers of wood until each half was filled, then the two halves epoxied together, I don't see much of a difference in the end between this and a laminated solid mast...

My engineering school days are so far behind, lol, at least I can still boil water. However, it's my distinct recollection that a hollow mast is both a lot lighter AND stronger than a solid. Perhaps minds clearer than mind can address this. The much higher weight of a solid mast adds unwanted intertia, and may require stronger rigging as hollow masts are more rigid. Don't forget the wiring issue.

With this in mind (and your skills) you could split the mast (to be sure all the wood is still good), then put a single layer of cloth on the inside surfaces; reglue the mast back together, then wrap a layer of cloth around the outside.

Frankly, I personally would just split the mast, insure that it is sound, repair only as necessary, then reassemble and be done with it. Maybe a coat of epoxy on the interior/exterior (no cloth).

For your reference on the strength issue:

Making a Square, Hollow Mast

Hollow vs. Solid Mast [Archive] - The WoodenBoat Forum

[Cruisingscotts]

No comment on the rig change plans other than doing lots of reasearch. On your mast proposals all I can say is AHHHHHHH.

Figure the rig out 1st then find a appropriate stick that never had leaves on it. The box section spruce mast is completely dependant on the standing rigging for strength.

[Fore and Aft]

Just have a go, what have you got to lose? I built a solid timber mast for a junk rig on a 25 yacht from Oregon demo timber. It took three guys to lift it when I was finished. My good mate Erik built a mast for his Benford Badger using the correct scantlings and it still weighed a lot. As for shortening the bowsprit why not make it pivoting? My current bowsprit is a 1.5 meter carbon fibre A frame that pivots up when in dock.
Cheers

[Stumble]

Originally Posted by Capn Jimbo

My engineering school days are so far behind, lol, at least I can still boil water. However, it's my distinct recollection that a hollow mast is both a lot lighter AND stronger than a solid. Perhaps minds clearer than mind can address this. The much higher weight of a solid mast adds unwanted intertia, and may require stronger rigging as hollow masts are more rigid. Don't forget the wiring issue.

With this in mind (and your skills) you could split the mast (to be sure all the wood is still good), then put a single layer of cloth on the inside surfaces; reglue the mast back together, then wrap a layer of cloth around the outside.

Frankly, I personally would just split the mast, insure that it is sound, repair only as necessary, then reassemble and be done with it. Maybe a coat of epoxy on the interior/exterior (no cloth).

For your reference on the strength issue:

Making a Square, Hollow Mast

Hollow vs. Solid Mast [Archive] - The WoodenBoat Forum

A hollow mast will not be stronger than a solid mast, but it can be stiffer.

The formula is

I(rod) = Pi x D^4 /64
I(tube) = Pi x (Do^4-Di^4)/64
Where Do and Di are the external and internal diameters of the tube.

So for a 1" solid aluminium tube... With a weight of .93lbs/ft
I= 3.14 X 1^4/63 = .049

For a 2" sch 10 aluminium pipe, with a weight of .91lbs/ft
I= 3.14(2.375^4-2.157^4)/64 = 3.14(31.81 - 21.65)/64 = .49

So for pretty much the same amount of material the tube is roughly 10 times stiffer even though it is actually a touch lighter.


For a given weight tubes are stiffer, for a given size solid is stiffer. In boats we are almost always (I actually can't think of counter example) more concerned with weight than size, so we always use hollow masts. Except in very small wooden masts where the gains are minimal for the amount of work they require.

[knockabout]

hollow timber mast is stronger than same size solid/bow spit is to increase forward sail area/you may need to consider the position of the ballast if you bring the main mast forward to compensate for no spit and room for giant low aspect lug sail to equal the sail area of your existing rig the upwind-sea handling may be reduced

[peter57]

After owning three Bermudan rigs H28, 43ft ss splined houn pine, 33ft racing Crowther Tri over 35 years have now purchased a Colvin Gazelle Junk rigged and would never buy a bermudan rigged boat ever again for cruising.

Like Greg (Stumble) says, you will have a lot of nutting out to convert and "humans are made of food"

A lot of people have converted their boats to Junk rig, to me the optimal ocean crossing rig.

Peter.

[Force 50]

Wow thanks guys for the info,
It's inspired me to keep digging,
Any thoughts on splitting the wood mast and dropped In a piece
Of square stock aluminum or steel?
Being that I want to lose all the Standing rigging except for forestry
The weight would be the same or lighter, if I bedded the
Stock in epoxy and filler I could keep
The "look" on the outside
Probably could fit 5" by 5" square in there
With just a smidge of room around it?

[Panope]

The idea of converting a normal 'stayed' mast to 'free standing' by adding material (ANY material) to it's internal cavity, is impractical (maybe impossible) because the mast is not wide enough. If you look at boats (big boats, not dinghies) with freestanding rigs, you will find masts that are very large diameter where they penetrate the deck. For the 50,000+ lb. boat in question, I'm guessing a diameter of 18 inches at deck level might be enough. Diameter may taper toward the head.

Also, virtually all junk (and gaff) riggers will have a mast with a round cross section as the Boom, battons, yards (and jaws) must be free to rub against and pivot along the mast.

I cannot imagine (and I am one hell of an imaginative person!) how you will successfully convert your current mast to a free standing junk rig.

You will need a different mast.

Steve

[Bluebeard]

Originally Posted by Stumble

A hollow mast will not be stronger than a solid mast, but it can be stiffer.

The formula is

I(rod) = Pi x D^4 /64
I(tube) = Pi x (Do^4-Di^4)/64
Where Do and Di are the external and internal diameters of the tube.

So for a 1" solid aluminium tube... With a weight of .93lbs/ft
I= 3.14 X 1^4/63 = .049

For a 2" sch 10 aluminium pipe, with a weight of .91lbs/ft
I= 3.14(2.375^4-2.157^4)/64 = 3.14(31.81 - 21.65)/64 = .49

So for pretty much the same amount of material the tube is roughly 10 times stiffer even though it is actually a touch lighter.


For a given weight tubes are stiffer, for a given size solid is stiffer. In boats we are almost always (I actually can't think of counter example) more concerned with weight than size, so we always use hollow masts. Except in very small wooden masts where the gains are minimal for the amount of work they require.

Greg, you will spoil a good argument if you introduce engineering into the discussion.
I won't comment on junk rigs or the work involved in any conversion, but any logic for strengthening the mast doesn't stand up.
The property I that Greg is calculating is the Moment of Inertia and is the measure of bending stiffness (ie how far your mast will deflect) in a homogenous material. It is proportional to the fourth power of the diameter.
To illustrate why you gain so little from having a solid mast over a hollow mast, lets consider a 2 foot diameter mast, it's I is c x D^4 = c X 16, now if we put a 1 foot diameter hole down the middle we are removing c x 1^4 = cx1, so we are removing 1/16 of the bending stiffness.
There is a second property S or section modulus that is the measure of the bending strength (ie when it will break) that is proportional to the diameter to the third power. So the hollow 2foot - 1 foot mast will have lost 1/8 of the strength of a solid mast.
A far bigger problem in trying the reinforce a wooden mast is the axial stiffness of the reinforcement v the axial stiffness of the wood. This is called the Youngs Modulus or Modulus of Elasticity E. E for steel is approximately 3 times that of aluminium. I don't know the equivalent number for wood but it will be many times smaller. So using any metal, glass or carbon fibre reinforcement, it will be many times stiffer than the wood and will take the lions share of the load. There are too many variables to be able to produce a simple illustration where different materials are used, and in any case I'm too lazy to look up E for wood and run the numbers.
Suffice it to say that the reason why you won't find any real life examples of your mast strengthening ideas is because they don't work.
Sorry

[Force 50]

Thanks guys,



Sent from my iPhone using Cruisers Sailing Forum

[Panope]

Tom Colvin pioneered to concept of inexpensive, do-it-yourself, junk rigs on western boats. His formula (50 years later) is still unmatched for simplicity, economy and low maintenance.

Schedule 40 Aluminum Pipe masts lightly stayed with just one or two shrouds per side and a headstay. No spreaders, no lowers, no sail tracks. Shrouds are led aft far enough to give decent headstay tension without the need for running backstays.

If you can find a suitable tree, this will be cheaper initially than the aluminum pipe. However, the tree mast will eventually cost more due to ongoing maintenance. The pipe (if left unpainted) will be virtually (totally) maintenance free.

Steve

Tom and his wife aboard the original Gazelle

[first wind]

Originally Posted by Stumble

Can you slit open your mast and make it solid? Probably not, the heat from the epoxy curing would likely catch the wood on fire. Worse there is absolutely no reason in the world to do this.

Converting from a sloop to a junk rig is certainly possible, but it's a bad idea. Particularly if the sloop rig is in good shape. But if you insist... Then you need to run the numbers and calculate the new sectional area of the mast you need to make it free standing, en find a mast that size. You cannot reasonably convert a smaller mast into a bigger one.

Cutting off the bowsprit is again possible but not recommended. You would need to rerun the calculations on the mast to figure out the new forstay loads and redesign the rigging to suit. You would also be removing a huge amount of sail area from the boat, and require all new sails.

i agree about the spars. however...

if he intends to do a junk rig, and there are good reasons you might decide to do that, he won't need standing rigging. that means, he won't need a bow sprit...unless he wants to add a jib. then he might.

he should do a junk schooner for the size of his boat.

most importantly, he will need to plan the sails carefully to get it right. he will have to get the right size masts for the job. the masts will have to be keel stepped and mast location and deck re-enforcement will need to be considered. he will also have to decide on flat sails or modern cambered sails... depending on his type of sailing. coastal sailors and day sailors tend to like the cambered panels for better performance. passage makers tend to like flat sails.

lots of info on the web. the JRA is a great resource but, he can find lots of stuff just by googling.

it would be a good idea to find someone who has a junk rig and ask for a chance to go sailing with them to see what he thinks before investing the time and money.