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Old 29-04-2008, 17:58   #1
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are there any engineers?

O.K. I am trying to build a bowsprit for my boat, I want to use stainless tube of about 1 1/2 dia. My question is how thick material should I use, I was thinking 3/16ths would be enough? I have a fisher ketch with a 40ish foot main and I want to extend approx 3 ft. from the end of bow. I have original pics of the factory unit. Any input would be apprec. Thanks in advance Randy
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Old 29-04-2008, 18:02   #2
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is this going to be for anchors or are you moving the headstay forward?
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Old 29-04-2008, 18:13   #3
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This is going to be for both, dual anchor rollers and single furler
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Old 29-04-2008, 21:16   #4
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Adding bowsprits is not for the timid. By and large the addition of one after the fact isn't worth the actual cost but it is no way impossible. I think you need a real engineer to to really examine and compute this all out and not some Internet opinions.

Adding a 3 ft extension for some frivolous thing is no big deal but for what you are thinking about it needs to be computed properly. These are big numbers you are dealing with and the thickness of the sprit is maybe the least of the problems. All the attachments and how this is connected matter a whole lot too. The details here are quite important.

All the real success stories I have heard all lead me to think it's one of those more money than brains adventures - and that is when it works. It generally adds little to the basic performance of the boat.
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Old 29-04-2008, 21:29   #5
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It is probably best to hire a naval architect who knows sailing vessels.
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Old 29-04-2008, 21:37   #6
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Adding a bowsprit will also significantly change the balance of the sailplan. Which is OK if that is your intent, but as has already been suggested this task involves a lot more than just engineering the materials strength, it effects the entire rig in ways that can be very important and very subtle.
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Old 29-04-2008, 23:48   #7
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In regards to actually making it. What are your choices of welding? MIG, TIG or Stick? And have you any experiance welding and in particular, welding SST??
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Old 30-04-2008, 16:20   #8
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Well my intention is have a pro weld the unit together someone qualified with stainless, I do have a blue print with exact specs of meas,where the reinforce plates are etc. for this specific boat the only meas I do not have is the thickness of material. Im not taking this lightly. With the addition of the sprit the Fisher 37s sail and tacking proformance is suppose to be greatly improved not to mention the anchor will not be banging off the bow when we raise them in choppy cond. About ten years ago I had heard of someone with the same boat order one direct from the manufact. in England and I belive the $ then was around 6k. This is a addition dream down the road but I like to have all my opps. in front of me.

Tahnks all Randy
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Old 30-04-2008, 16:33   #9
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3/16" = .1875 wall tube. I think that would be plenty strong.
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Old 30-04-2008, 17:44   #10
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bow sprit

1 1/4" sched 40 pipe is 1.66" OD and .140" wall... more than adequate for the staple, or u-shaped piece. Schedule 80 1 1/4" pipe is same OD, and .191" wall, good for the center piece. At least 1/2" plate for the fore stay attachment, going thru a slot in the center pipe with a fitting on the underside for the bob stay. This, with various cross pieces and anchor troughs, is plenty strong enough for a 37' boat, provided the attachments are engineered and built well, especially the bob stay fitting at the waterline, which does most of the work triangulating the structure. Most that you'll see in this size range are built with lighter tubing than that.
Best, Bob S/V Restless
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