Mast base location?

Sail trim, rig tuning, and related topics.

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jng7000
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Joined: Fri Aug 14, 2015 1:04 am

Mast base location?

Post by jng7000 »

Does anyone know if the distance called for in the tuning guides for mast base location is measured from the baseboard trim of the bulkhead or the actual bulkhead plywood? Interestingly, the 2004 North Sail guide recommends the mast base be placed 480mm from the bulkhead but all other tuning guides, including the more current North Sails guide, recommend 460mm. In the 2004 North Sails tuning guide it shows the measurement taken from the baseboard trim along the bottom of the bulkhead but since that measurement is not correct I'm second guessing that information as well. The other tuning guides seem a bit vague when it comes to the exact location where the measurement is taken from the bulkhead, whether it's from the trim/baseboard or the plywood bulkhead material itself?

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Jim
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Vento Solare
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Re: Mast base location?

Post by Vento Solare »

I asked Jack Orr, North Sails J/109 Class one design rep about the mast base position. It is definitely supposed to be measured without the trim piece on the bulkhead. He indicated that the old 2004 North Sails setting of 480 mm was updated in the newer tuning guides to 460mm. He said don't worry about the J dimension since that is pretty much fixed by the Spartite. You should check the swing arc of the jib halyard and set the headstay length.

FYI - the various tuning guides are on the class website if you mouse over "Info" then click on "Tips and Tuning"
jng7000
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Re: Mast base location?

Post by jng7000 »

Thanks Bill! I'm hoping that's where my mast is set from otherwise I have some work to do.
Jim
"Junkyard Dog" #168
California Offshore Race week video: https://youtu.be/R3nHBRV1HbE
San Francisco "Duxship" regatta video: https://youtu.be/BViC3bnHqL0
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Vento Solare
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Re: Mast base location?

Post by Vento Solare »

I made a "template" that is nothing but a dowel 460mm long. This allows setting the mast position from the bulkhead just above the trim piece to the forward face of the mast. No need to remove the trim!
30101
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Location: Long Island Sound

Re: Mast base location?

Post by 30101 »

When placed between the mast and the bulkhead, a 460mm template is at least 20mm short even with the mast base in its most forward position.
Is the bulkhead a consistent reference point across the US and French built boats? Does anyone have a recommendation for a secondary reference point for locating the mast base that is either consistent across both runs of boats or accurate for just the French boats?
For reference, the headstay measures within about 150 mm of the recommended length.
Any thoughts are much appreciated.
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Vento Solare
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Re: Mast base location?

Post by Vento Solare »

Did you leave the trim piece in place on the bulkhead? That width must be subtracted from the 460mm if you measure with the trim piece in place.
30101
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Re: Mast base location?

Post by 30101 »

Mine does not have a trim piece to remove. Maybe none of the French boats have a trim piece at the bottom of the bulkhead?
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Vento Solare
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Re: Mast base location?

Post by Vento Solare »

Not sure - FYI I posted this document with pictures on the Tips & Tuning section of the website back in 2015.

https://j109.org/docs/procedure_to_set_ ... sition.pdf
Bengt J
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Re: Mast base location?

Post by Bengt J »

The 460mm is from mast to bulkhead, most boats had to drill new holes for the mast base to get to 460mm.
The headstay length of 150mm from base length seem too much, the adjustment of the Harken furler is max 3 inches. Some boats adjust the length of the headstay +/- 0.5 inches depending on wind conditions, still the key is to match the prebend of the mast to the cut of the mainsail.
30101
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Re: Mast base location?

Post by 30101 »

Looks like I will have to drill new holes to really get the mast in the right position. The existing base bolts required quite a bit of effort to remove them from the factory bores. Just so I have a sense of what to expect, what material is under the gelcoat beneath the mast base? Hopefully, that strong material extends for another inch or so toward the bulkhead.
Bengt J
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Re: Mast base location?

Post by Bengt J »

On Zig Zag the base is at least 1" thick (hull #37 built by TPI) at factory holes and new holes ~1" forward.
I suggest to move the base to get to 460 mm and then drill new holes in the middle of the slots this will give some flexibility to fine tune the location.
BTW did you get a longer head stay?
30101
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Re: Mast base location?

Post by 30101 »

Thanks for asking. As I measured it last summer, it was maybe 20 mm too long.
Chuck at Sound Rigging has offered to help me get the rig totally sorted this spring. That starts with moving the mast base, then removing the old Spartite, etc.
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Kapama
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Re: Mast base location?

Post by Kapama »

Hello everyone! My name is Jörn from Hamburg, Germany. I´m the new owner of Kapama; J/109 hull no 230, french built.
I´ve been enthusiatic for the boat since 2012, when I crewed one for about 3 seasons. In the end I succeded.

I followed the procedure recommended for correct position of mast base; I elongated the drilled holes in the aluminium bracket to 25 mm.
Unfortunately the metric thread in grp-structure below the bracket 3 of 4 are worn out.

I´m thinking of drilling an inspection port to the grp-structure inside the mast base to use nuts on the bottom side
and by the way have a close inspection to whats in below.

Did somebody here do like that?
What do you think about it?

Thank you for swarm intelligence and support

Tschüß, Jörn
Sailing is like bobsleighing; the brakesman always sits in the aft
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