Mast alignment in mast partner

[CAM]

The two important points when initially setting up a mast are the top and the bottom. You can't move the bottom side-to-side (generally), and you want the top centered. You want the rake where the designer intended, or somewhere different if you are curing a balance problem. Very few partners will be centered on the mast in either direction on a production glass boat, just don't worry about that. Most glass boats will have some taper at the partners (called "release" in mold making). Spartite is used all the time by folks that frequently step and unstep their masts.

[Jim Fulton]

The original question had to do with whether it is a problem if the mast is not centered in the partners. It may be that the mast is in the right position but the boat is not perfectly symmetrical--few boats are, particularly older boats. If the mast is positioned and tuned as well as you can get it, I wouldn't worry much about its position in the partners.

Jim Fulton

[Patrick_Seattle]

Thank everyone... I tend to be a bit of a perfectionist especially when I'm writing checks. I'm more foregiving of my own work.

I'm hopeful that in a couple years I'll be able to answer a few questions instead of just asking. ;-)

Thanks again!
-p

[Brion Toss]

Hello,
Great discussion. I would just like to back up a bit, maybe fill things in.
First, the whole reason that you have a keel-stepped main is so that you can have a lighter mast than if it were deck-stepped. With the mast firmly secured (wedged) at the partners your mast can be at least 40% stiffer than a deck-stepped mast of the same dimensions and material. This also means that if you put a real tune on the rig before the wedges (or Spartite) are in, the mast, if it is of proper size, will want to buckle from the compression loads, and you won't be able to keep it steady at the partners. As always, I recommend that you run the numbers on mast scantlings, but the very fact that the mast wants to bump up against the partners is a good sign.
That adjustable step is a great thing, since it means, as someone else pointed out, that you can get a fair curve right from the bottom of the mast. Ideally, you should be able to set your rake, get the mast centered laterally, move the butt aft an inch or so, wedge the partners, and then put a real tune on.
The partners might indeed not be centered in the hull, something you can discover with measurements. Or the mast step itself might be off-center. What matters is that the mast comes up vertically, whether or not it and/or the partners are centered.
It might seem that the partners aren't big enough to give much adjustment room, but remember that a little move at the partners can translate to a big move at the masthead. It can also make a big difference in the amount of bend you can get. We typically put the mast well forward in the partners, for the sake of easy bending. Whether using wedges or Spartite, you'll need enough space forward of the mast that the wedge or rubber isn't too thin.
As you can see, this stage of things is quite fussy, at least if you want to get the most out of your rig. Be in touch if you'd like a visit.
Fair leads,
Brion Toss

[jhambly]

Brian.

The spartite I removed from the single inline spreader, keel stepped, mast head, cutter rigged aluminum 52' spar was a mere 1/8" thick at the leading edge and 1" at the aft end. I moved the maststep aft 1/4" with the idea that would help to provide slightly more thickness and now in the process of replacing spartite. Having read your post about keeping the "butt" as far fwd as possible, perhaps that wasn't such a good idea but 1/8" just seemed so thin. Of course, now the teak and holly boards in the cabin sole don't fit (1/4" gap - no surprise there). Clearly I didn't think that one through!

Is it really possible, or recommended, to drive (or to quote Hall Spars, "finesse") the butt forward without a crane if the rig is slackened off?

Q. When preparing to spartite, here are the steps I understood from your post?

1. Lateral tune to center mast in boat with an effort not to bend the rig. So commence with a loose (hand tight?) rig. Adjust using uppers (caps) to center mast head with respect to top of chainplate or gunwale on each side?
2. Adjust rake using forestay and backstay without adding bend( are lower shrouds used at this point?)
3. Don't stress about being centered in the partners. Hard one for me to adhere to but I'll try.
4. Spartite or wedge and allow to cure.
5. As you stated above, now put "a real tune on the rig".

So if i understand correctly, the compressive loading and pre bending is not added until after the spartite is set in the partners?

Thanks for the help.

James

[Brion Toss]

Originally Posted by jhambly

Brian.

The spartite I removed from the single inline spreader, keel stepped, mast head, cutter rigged aluminum 52' spar was a mere 1/8" thick at the leading edge and 1" at the aft end. I moved the maststep aft 1/4" with the idea that would help to provide slightly more thickness and now in the process of replacing spartite. Having read your post about keeping the "butt" as far fwd as possible, perhaps that wasn't such a good idea but 1/8" just seemed so thin. Of course, now the teak and holly boards in the cabin sole don't fit (1/4" gap - no surprise there). Clearly I didn't think that one through!

Either I misspoke at the time, or you misunderstood -- or both -- but here's some clarification:
Moving the butt of the mast aft at the step is done either to change rake,or, as in this case, to help induce bend by starting it at the keel. For bend, the butt at the mast is moved aft, and the mast at the partners is kept forward. By moving the butt aft, if that is what you did, and also moving the mast aft the same distance at the partners, you have preserved the previous shape, while providing more bearing thickness in front of the mast at the partners. Nothing wrong with that.

Is it really possible, or recommended, to drive (or to quote Hall Spars, "finesse") the butt forward without a crane if the rig is slackened off?

Yes. Asterisk. Some masts are more reluctant to move than others, because of step stickiness and/or a shortage of places to brace against or pull on for the finessing. But again, if better bend is your aim, you want to finesse the butt aft.

Q. When preparing to spartite, here are the steps I understood from your post?

1. Lateral tune to center mast in boat with an effort not to bend the rig. So commence with a loose (hand tight?) rig. Adjust using uppers (caps) to center mast head with respect to top of chainplate or gunwale on each side?

Yes, lateral tune, but start by using the lowers, not the uppers. Once the mast is centered down low, you can sight your way up to the top, using the uppers (and intermediates if any) as you go.

2. Adjust rake using forestay and backstay without adding bend( are lower shrouds used at this point?)

Yes, to set rake. Later, you will use the stays and shrouds to set bend.

3. Don't stress about being centered in the partners. Hard one for me to adhere to but I'll try.

Rather, don't stress about the partners if your measurements show that the partners are off-center. Get the mast on-center, and if the partners are, too, it's gravy.

4. Spartite or wedge and allow to cure.

Not quite yet. This is where you induce some desirable basic bend; the Spartite or wedges will confirm and keep that bend. Whether or not the bend will be adjusted under way, go for a median shape.
5. As you stated above, now put "a real tune on the rig".

So if i understand correctly, the compressive loading and pre bending is not added until after the spartite is set in the partners?

If you add too much compression before securing the mast at the partners, it will get squirelly; just tune sufficient to get the shape you want, then wedge. Later, you can add tension without changing the shape.

Thanks for the help.

James[/quote]

I have far exceeded my "too short to charge for" rule here, so if you need more details, let's set up a consultation. Meanwhile I hope this all helps.
Fair leads,
Brion Toss

[jhambly]

Brian
Excellent clarification and I really appreciate your detailed response.
If I need more on the topic, as you suggested, I'll come to you for a consult.
Thank you.
Regards,
James