Mast Splice below the partners???

[HappySailor]

I found a rig that might work for my boat, but it's set up as a deck stepped rig... Whereas the rig I am replacing was keel stepped...

I would like to know the group's thought on using a deck stepped rig as a keel stepped rig by splicing a section just below the partners???

Or If go the other way... Converting to a deck stepped rig with a compression post and associated hull work???

Big rig, 48 ft boat, 72 ft stick...

Thanks for looking!

HS

[Ian McColgin]

You're going to need a proper rigger-engineering consult here. The dynamics of a deck stepped and a keel stepped mast usually are quite different. Keel stepped can be lighter by a little bit if the partners are correctly engineered and the mast is held well in two places - step and partners - before relying on rigging above that.

So presumably you're getting a stick - wood or aluminum? - that's a bit beefier than strictly needed and whatever its old wire may have been could also be heavier than you'll need if you go keel stepped. Think that whole bit through before you even ponder keel or deck.

I don't have metal working experience with extending an aluminum tube but it's done often enough that it should be simple enough, especially if the join is at the partners where the hard spot of a sleave or insert for the join would be placed. Certainly if the stick is wood, a nice long clothspin scarf that follows the construction of the mast (I presume hollow) down past the partners (compressing plug there) to the solid mast heel that might be a foot or so high is perfectly feasable.

If you want to go deck stepped, that should be very simple as you already have plenty of structure to land both the top and bottom of the compression post.

G'luck

[HappySailor]

Originally Posted by Ian McColgin

You're going to need a proper rigger-engineering consult here. The dynamics of a deck stepped and a keel stepped mast usually are quite different. Keel stepped can be lighter by a little bit if the partners are correctly engineered and the mast is held well in two places - step and partners - before relying on rigging above that.

So presumably you're getting a stick - wood or aluminum? - that's a bit beefier than strictly needed and whatever its old wire may have been could also be heavier than you'll need if you go keel stepped. Think that whole bit through before you even ponder keel or deck.

I don't have metal working experience with extending an aluminum tube but it's done often enough that it should be simple enough, especially if the join is at the partners where the hard spot of a sleave or insert for the join would be placed. Certainly if the stick is wood, a nice long clothspin scarf that follows the construction of the mast (I presume hollow) down past the partners (compressing plug there) to the solid mast heel that might be a foot or so high is perfectly feasable.

If you want to go deck stepped, that should be very simple as you already have plenty of structure to land both the top and bottom of the compression post.

G'luck

Thanks for the reply Ian!

The proposed extrusion is current production aluminum 285x147mm, 6% stiffer than my current rig of about the same size, 2% lighter...

I've got plenty of room below to work, and it's all 100% concealed... So I don't have to worry about aesthetics...

I'd have a professional rigger work up the standing parts, spreader reconfiguring etc... ... I need all new wire anyway...

Changing to a deck stepped rig seems the preferable choice of the two that is winning out...

Thanks!

[Brion Toss]

Hello,
I'd need to see the numbers on the sections' stiffness, but a keel-stepped mast is typically around 40% stiffer than a deck-stepped one of the same moments, so if you are correct that the two are close to the same stiffness, then the new one will be much more buckle-prone than the old. Have you run the numbers on the ideal moments of inertia for this boat? Again, I don't have access to the data here, but if things are the way they sound, deck-stepping the new mast could be disastrous.
Fair leads,
Brion Toss

[HappySailor]

Originally Posted by Brion Toss

Hello,
I'd need to see the numbers on the sections' stiffness, but a keel-stepped mast is typically around 40% stiffer than a deck-stepped one of the same moments, so if you are correct that the two are close to the same stiffness, then the new one will be much more buckle-prone than the old. Have you run the numbers on the ideal moments of inertia for this boat? Again, I don't have access to the data here, but if things are the way they sound, deck-stepping the new mast could be disastrous.
Fair leads,
Brion Toss

Thanks for the great info Brion!

So what I'm taking away here is... that say two identical profiles, one keel and one deck stepped, the keel stepped rig will be 40%ish stiffer just by configuration?

In the latest iteration of possible take-off rigs, I've found the same exact profile except 11 ft shorter, going from a triple aft to double aft... Butt splicing this 7 ft brings the kicker and goose in the right height, and leaves the splice just below the deck...

Impossible idea?

I have not run moment numbers, only going by what was on the boat prior. Dubois and Wauquiez have been completely unresponsive for the better part of 3 years of attempts for all other inquiries as well as this... Any recommended reading???

Thanks Again!

[Brion Toss]

Hi again,
If your sleeve has generous overlap, properly secured, then you will have a mast that is at least as stiff as one of the same dimensions that ran full length. All you need do now is to find or form the sleeve. This still leaves the question of whether or not the section is correct, so it might be nice to run those numbers, see what you have.
Fair leads,
Brion Toss

[HappySailor]

Originally Posted by Brion Toss

Hi again,
If your sleeve has generous overlap, properly secured, then you will have a mast that is at least as stiff as one of the same dimensions that ran full length. All you need do now is to find or form the sleeve. This still leaves the question of whether or not the section is correct, so it might be nice to run those numbers, see what you have.
Fair leads,
Brion Toss

Hi Brion,

Sounds reasonable if done right... I don't have any RM numbers for the boat... But will run with the published table... I'll run the calculations found in the apprentice to what I had before, and the proposed changes... See if the section still holds up...

Any major SF or constant changes for triple 20 degree aft swept, cutter stays, and 4 baby stays in addition to D1/V1's?

Maybe I just need to cut you a check instead... )P

Thanks Again!

[Brion Toss]

Hi again,
Yeah, you were already well over the "questions too short to charge for" standard that I try to use here.
Fair leads,
Brion Toss

[HappySailor]

Originally Posted by Brion Toss

Hi again,
Yeah, you were already well over the "questions too short to charge for" standard that I try to use here.
Fair leads,
Brion Toss

And for that I'm truly grateful !
Spartalk is a fantastic resource to be sure...

Actually the major questions were answered....
1. It is entirely possible to have a splice just below the partners if done correctly
2. it is NOT POSSIBLE for an extrusion to be configured as a decked stepped rig, when the boat was previously designed with the identical extrusion as a keel stepped rig... The profile isn't stiff enough...

I'll send an email to your consultation address, rigging@

Thanks so much for your help!