SB18 - Where to splice the mast together?

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lncc63
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SB18 - Where to splice the mast together?

Post by lncc63 » Sun Feb 14, 2010 8:03 am

The Hobie 16 mast is 26', the SB18 mast is 30' . I was able to get a 5'+ section from a broken mast. Where would be the best place to splice the two together: on the top or at the bottom? Also advice on how to make the splice would be most helpful too.

I realize this is an odd question. The best thing would of course be to buy what is specified but that's out of the question right now.

Or would it be better to deck mount it like others are doing? I really do like the redundancy of a keel stepped mast so I'm asking.



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chrisobee
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Re: SB18 - Where to splice the mast together?

Post by chrisobee » Sun Feb 14, 2010 8:05 am

what are the masts made of?

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Re: SB18 - Where to splice the mast together?

Post by PJPiercey » Sun Feb 14, 2010 1:20 pm

You could go either way. At the bottom you would keep the extra weight of the splice lower, which is a good thing.
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TimF
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Re: SB18 - Where to splice the mast together?

Post by TimF » Sun Feb 14, 2010 3:16 pm

I would think that adding the extra section to the base of the mast is the better option. The jointed section will be stiffer than the regular section assuming that you are going to use an inner section and sleeve the two parts together. With the keel stepped mast on the SB18, i guess that your joint will be somewhere close to or just above the boom gooseneck fitting and will not greatly affect the bend characteristics of the mast
I know that Holt Allen in the UK used to produce jointed masts for some of their boats sold in kit form, to facilitate shipping, (The Streaker and Enterprise if memory serves) but these masts were jointed in the middle.
You do not want to add weight or stiifness to the upper end of the mast.
Good Luck!

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lncc63
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Re: SB18 - Where to splice the mast together?

Post by lncc63 » Sun Feb 14, 2010 3:55 pm

Thanks guys. The mast is aluminum though I don't now what alloy it is. I've seen Hobies sail and the masts are pretty flexible. Yeah putting the splice on the bottom makes sense, extra weight at the bottom and less bending, mostly compression.

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Evan_Gatehouse
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Re: SB18 - Where to splice the mast together?

Post by Evan_Gatehouse » Mon Feb 15, 2010 11:25 pm

Yes at the bottom - but avoid the gooseneck area if possible. 5' would put it pretty close to that wouldn't it?
designer: FB11/GV10,11,13/ HMD18/
SK17,MM21/MT24

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lncc63
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Re: SB18 - Where to splice the mast together?

Post by lncc63 » Tue Feb 16, 2010 1:45 am

Thanks Evan.

The joint is located 8-1/4" above the mast partner (SB18-mast-length - H16-mast-length - Mast-partner-location = 357-5/8" - 312" - 37-3/8" = 8-1/4").

How about I add the 8-1/4" at the top of the mast so the splice will then be exactly at the mast partner? Being exactly at the mast partner seems the best location.

A bit off-topic, does it make sense to let the mast rotate on the SB18? - Please forget I asked. I forgot the SB18 has spreaders.

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lncc63
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Re: SB18 - Where to splice the mast together?

Post by lncc63 » Wed Feb 17, 2010 5:39 pm

No hurry really Evan but maybe you missed my questions above.

I've another question. How is the mast best spliced? How long should the sleeve be? Would adding epoxy make the joint better?

This is what one builder here did:
ImageImageImage
Image

The above is a splice at the middle of the mast where there is a lot bending stress.

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Evan_Gatehouse
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Re: SB18 - Where to splice the mast together?

Post by Evan_Gatehouse » Wed Feb 17, 2010 11:15 pm

Normally what is done is have the short piece with notches inside the two long mast sections. I think that is what is also shown in your pictures. A few more hints:

- use larger drill at the bottom of the notches for the inside splice section.
- make sure the upper and lower mast sections are a tight fit with as little gap as possible (this makes the compression load transfer best)
- staggered rows of s.s. drilled and tapped machine screws or s.s. pop rivets are both acceptable. For a small mast like yours the pop rivets are totally o.k.
- no need for epoxy too.
designer: FB11/GV10,11,13/ HMD18/
SK17,MM21/MT24

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lncc63
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Re: SB18 - Where to splice the mast together?

Post by lncc63 » Wed Feb 17, 2010 11:48 pm

Thanks Evan. I think I understand.

What about moving the 8-1/4" to the top of the mast? This so the lower joint is exactly at the mast partner.

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