i think a standard spin pole (no idea what the I/D or O/D is) could work.
why do you need endcaps? unless you plan on backing the boat up very fast.. i don't know how you could do any damage with the aft part and the forward part will be "looking" at your mast...
that being said, if you really want them i think apsltd.com sells them ( APS Part Number: SLD53485301 - Price: $54.00) but i would go to a hardware store and look for pvc or simmilar.
New boom for a Prindle 18-2
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Posted: May 19, 2010 - 12:44 PM
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Posted: May 19, 2010 - 12:57 PM
The end caps would just be to prevent crushing at the end where you attach the goose neck to (same reason they are used on a spin pole). The one at Murrays is similar to the one Yurdle showed above, but they are only $10.
D.
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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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Posted: May 19, 2010 - 02:42 PM
3/16 is 0.1875
You're thinking it's 3/32.
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Rob
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Posted: May 19, 2010 - 02:46 PM
actually, on a spin pole they have a few uses but i have never heard of crushing being a reason why.
1. end caps are often used for internal tack lines, they come out the end and up to the block. Delron works will dyneema and alum for any line. SNU sells an alum one
2. to avoid "cookie-cutting" of any object you run into (another boat, person, etc) a "cover" is required in the F16 rules i believe for this exact reason
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Posted: May 19, 2010 - 03:20 PM
Yeah, I can't do fractions today for some reason (not a good thing for an engineer). 3/32"
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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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Posted: May 28, 2010 - 06:56 PM
I just acquired 2 - 10 foot lengths of 1.5" diameter 6061 Aluminum tube with a 3/32" wall thickness. Do you think this will hold up to the forces put on a 5.2 boom?
Does anyone have a round boom and if so what are the dimensions? Rob what diameter was the tubing you used? Catdan, do you have specs on teh tubine you used
If I attach the main sheet directly to the main clew (like more modern boats) do you think it will rip out the 3:1 outhaul? It would move the main sheet about 8" back and the high angle is concerning..
edited by: Wolfman, May 28, 2010 - 11:59 PM
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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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Posted: May 29, 2010 - 02:20 PM
Even if you rotated the rear beam back some to keep from tearing up the traveler, I think the load from the main blocks would tear up the mast rotator limiter or the outhaul or both. You need a main with a shorter foot to set it up that way.
I just bought another tube in case my first one is too thin, but I could only find 1/8 as the next step up from 1/16. I'd much rather try 3/32, as 1/8 seems like too much metal. I'll have a much better idea once I actually try the one I built, though.
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Rob
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Posted: May 29, 2010 - 03:48 PM
What diameter of pipe did you get? I'm thinking of getting a 1/8" thickness 2" diameter pipe instead of using the 1.5" 3/32" diameter pipe.
Wish I new more about the magnitude of loads that could be experienced, it would make figuring out the required boom strength much easier.
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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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Posted: Jun 01, 2010 - 01:48 AM
I built the first one out of 1.5" OD, 1/16" wall, 6061. I used it today.
It flexes like crazy. I won't take it out 2-up, but 1-up it seems OK. I need to talk to someone that knows aluminum better than I, though, before I count on this one as 'safe'.
When flying a hull and trapped out, if you were to draw a line between the top of the front and back of the boom, I bet the top of the center of it is about 3" below the line. I don't know how much the aluminum can flex before giving out, but I'd imagine that it's nearing its limit. (at r=.5d, (1/24)d thickness, 64d length, and 2d distance of flex in the center...I think that's the relevant info for any of you engineers)
I also have a 1.5", 125 wall thickness tube, and a 2"OD, 065 wall thickness tube, both of which are FAR stiffer. If the blocks will fit on the inside of the 1.5"/125 tube I'll probably switch to that if this one breaks or if I get too concerned about safety.
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Rob
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