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Mast base location?

Posted: Sat Dec 05, 2015 10:43 pm
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?

Junkyard Dog, #168

Re: Mast base location?

Posted: Mon Dec 14, 2015 12:56 pm
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"

Re: Mast base location?

Posted: Tue Dec 15, 2015 7:56 pm
by jng7000
Thanks Bill! I'm hoping that's where my mast is set from otherwise I have some work to do.

Re: Mast base location?

Posted: Tue Dec 15, 2015 8:07 pm
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!

Re: Mast base location?

Posted: Thu Sep 24, 2020 9:50 am
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.

Re: Mast base location?

Posted: Thu Sep 24, 2020 9:54 am
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.

Re: Mast base location?

Posted: Thu Sep 24, 2020 1:55 pm
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?

Re: Mast base location?

Posted: Thu Sep 24, 2020 2:04 pm
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

Re: Mast base location?

Posted: Tue Sep 29, 2020 12:50 pm
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.