Tony - Thanks much! It is helping me narrow down choices, and so - what I need to learn in order to make my own jr. There is SO much info here, it's overwhelming, really, tho' in a good way. :)

I had thought that the jr spar may be a bit shorter than as a sloop, even if not by a lot, but with that I can narrow down prospects and possibles...

...and can rule out completely the largest boat as financially unfeasible at the current time. That is GREAT to know - a full 1/3 less brain work. ;)

That calculator is awesome. Plugging in the numbers I get that the RM for my smallest boat is 1227kpm, and that a 28'/8.5m spar, 7"/177mm base tapered to 4.5"/114mm with a wall thickness of .188 results in a breaking strength of 2935kpm.

As an aside, the .155" thickness with the other dimensions above puts the breaking strength kpm right at a factor of 2, or just over 2400kpm, which is what I think is regarded as a bare minimum. (I much prefer "overbuilt" when dealing with the indifferent ocean.)
Further, going up to an 8" diameter with that thickness jumps the BS to 3200kpm, *and* shaves off about 8 lbs.
It would, of course, add up to an inch in diameter to the mast aerodynamics, but that being only ~12.5% at max and down low, I'm not sure if it would be real-world measurable or detectable, compared to a 7".
At the least, it appears I have options, and with help here, have narrowed them down. :D

As you suggest, I will double check the numbers against the calcs in PJR.
Thanks again, Tony!

Thanks for the input, Len :)


1) Re: SA - the numbers I used look to be Main and 100% Jib. Likely better IMO to make the sail plan using the 130 or so numbers, in order to outrun the spinnaker class. ;)

2) Yes, by 'split rig' I was referring to using 2 spars in order to have 2 easier-handling sails/rigs. I am hoping someone knows of a similarly sized vessel configured that way, which I could use as a reference point.

3) Thx for the link, I will look into that. Might be hard information to determine, if not purchasing directly from a manufacturer. Darn.
(Edit: A quick check it looks like American manufacturers are using 6036-T6, tho' per ASTM 6061 could be used and is stronger, if a bit less corrosion resistant.)

Again, maybe a similar boat is out there, enough for me to get an idea from someone with personal experience...

I'm leaning most towards using the smallest boat, FWIW. :)

Appreciate your feedback, and good luck with your build!

Background info: I have 3 possible hulls upon which to build a junk rig, using an AL light pole for the spar. I like Arne's general sail shape, and plan to put some draft in the sail, perhaps even jiblets.
LOA of my hulls in descending order are approx 36' (11m), 30' (9m), and 25.5' (7.8m).
Displacement (in pounds) for these boats are: 14K (6350 kilos), 9K (4080 kilos), and 5500K (2500 kilos).

The big one has a long fin, shoal draft, split underbody, w/rudder on skeg, and 576 sq/ft (53.5 sq/m) sail area as a sloop.
The smaller two are Alberg designs, cutaway full keel w/aft hung rudder (think Folkboat), SA's of 410 sq/ft (38 sq/m), and 310 sq/ft (29 sq/m).


I've read the short book on building a junk rig, and am in the process of reading "The Bible" (H&M book).

>>---- The Q's ----<<

Note: I understand - and understand why - there will and can be no exact answer for these Q's, but all I am looking for right now is "ballpark", a rough estimate, your opinion based on what you know of junk rigs. :)

1) Generally, given that I plan to design a rig sized to handle light air well and so will shoot for similar SA as listed above, will a junk rig mast be shorter, about the same, or longer (i.e. taller) than the sloop mast on the same boat?


2) On the large boat, from what I have read going to a split rig would be best, w/two same-sized spars - any guess at height needed above deck, if the sail area is split evenly?

3) Re: wall thickness: I've seen .15" (3.8mm), .18" (4.5mm), and .25" (6.35mm) in post lengths from 25-35 feet, w/7-8" bases (tapering to 4-5" or so).
Is .15 simply not to be considered, just too weak, or might it work on the smaller lengths? I'd rather have thicker, but if .15 is sufficient and not a hazard in a blow/under stress, then...

>--- End Q's ---<


The reason for asking the above is that there are several possible used poles for sale in my area at prices well below "new" cost, and I wouldn't mind the savings of 75% or more.
Of course prior to purchase I would inspect them _thoroughly_, including using a 'scope' to see inside, and if I find them at all questionable, will simply buy new.

Thanks in advance for your consideration and input! :)