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Mast Tuning Question

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GaryB
Master Marine Consultant

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USA
4303 Posts

Initially Posted - 06/09/2008 : 21:03:55

As I'm sure you are all aware I just finished replacing the wiring harness and light fixtures on my mast. Once I got all the bugs worked out of my wiring I started to tune the rigging.

I got the mast vertical athwartships and bow to stern but then I noticed the head of the mast was bowed towards the stern (in other words there's a bow in the mast just above halfway up) as though the backstay was on but I have several inches of slack in the backstay and the lowers are barely handtight. The uppers seems to be tensioned where I get about an inch of movement at shoulder height when pushing with moderate pressure.

I didn't drop the mast so it shouldn't be bent.

Do I have the uppers tensioned too tight?

If I were to get a Loos gauge which model would be best for use on the C25?

Any help would be greatly appreciated!

Association Member

GaryB
Andiamo
'89 SR/WK #5862
Kemah,TX

Edited by - on

frog0911
Master Marine Consultant

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USA
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Response Posted - 06/09/2008 : 21:32:14

Gray you just about got it. Just tighten you aft lowers 1/2 to one turn each then check the bend. Keep doing it until the mast is straight. This assumes you have the forestay tight. If not tighten your forestay first and check for column. I use to tighten mine until I had about 2 inches of pull and the uppers at one inch as you have it. Once the uppers and forestay are adjusted so as the mast is straight you can adjust the lowers for your sailing conditions. Be advised I ran a loose rig(lowers fairly loose) and hardened up with the backstay as the winds came up.

Edited by - frog0911 on 06/09/2008 21:33:40

Steve Milby
Past Commodore

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USA
5902 Posts

Response Posted - 06/10/2008 : 09:06:44

If the midsection of the mast is bowed forward, that means the forward lowers are too taut, and the headstay and backstay are also too taut.

To understand what's happening, take the flexible plastic stir stick out of your cocktail and set it on end. Then put the palm of your hand on top of it and press downward. The stick will bow in the middle. When you tighten the headstay and backstay, that's what happens to the mast. But, in addition, you also have the forward lowers attached more or less to the midsection of the mast. When you add tension to them, they're pulling the midsection of the mast forward. The first thing you need to do is to eliminate that bend by easing the headstay and backstay, and by easing the forward lowers. When the tension is released, the mast should be straight. But, even if it has been sprung a little, and has a bow in it, it can probably be tuned correctly, with no harm to it.

I would not adjust it, however, by tightening the aft lowers, because, if the cause of the problem is that the headstay and backstay and forward lowers are too taut, then you're aggravating that problem by further tightening the aft lowers. Doing it that way might straighten the mast, but it also might overstress the chain plates and damage the boat.

The last time we discussed mast tuning is at the following hyperlink. http://catalina-capri-25s.org/forum/topic.asp?TOPIC_ID=17353& SearchTerms=tune

Edited by - on

GaryB
Master Marine Consultant

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USA
4303 Posts

Response Posted - 06/10/2008 : 11:21:23

Thank you Steve! I knew we had discussed this recently and I looked for the thread above but must have input something wrong because I couldn't locate it.

Can the headstay have tension on it while the backstay is slack? My backstay has several inches of slack in it at this time (I tightened the backstay adjuster when I left the boat so the mast doesn't move while I'm away).

Also, I left all of the lowers very loose. As I mentioned in my first post, the uppers are tight enough that I get about an inch of movement at shoulder height.

When speaking of raking the mast the entire mast is leaning back slightly but is basically straight, correct?

Sounds like I just need loosen up everything and start over? Would you agree?

Edited by - on

Bruce Baker
Captain

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USA
402 Posts

Response Posted - 06/10/2008 : 13:12:40

Theoretically, you need two Loos gauges on a C-25. The Model 90 does your forestay, backstay, and top shrouds (3/16). You need a model 91 for your 5/32 forward and rear bottoms.

I cheat and use the Model 90 for everything. I kind of extrapolate down to a 5/32 cable based the readings for 3/16, 1/4, and 9/32.

Edited by - on

Derek Crawford
Master Marine Consultant

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USA
3321 Posts

Response Posted - 06/10/2008 : 19:31:25

I just use the smaller guage. My forestay and backstay are so loose that the guage won't register, the uppers only need to be balanced, and the forward and aft lowers will register perfectly on the small guage.

Edited by - on

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 06/10/2008 : 21:37:09

I ran a relatively tight rig, and I could grab my backstay and make it wave about 8-10" at its midpoint. The leeward upper shroud was always tight, and the leeward aft lower just a little slack. I never used a Loos gauge. I raked the mast back about 5" as I recall (measured at the boom), which gave me a light weather helm, and very close to neutral helm under 130 genny alone. Hang a wrench from the main halyard to measure the rake.

Edited by - Dave Bristle on 06/10/2008 21:38:18

GaryB
Master Marine Consultant

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USA
4303 Posts

Response Posted - 06/10/2008 : 22:16:09

Well I went and tuned it up using the input and knowledge gained on this forum. I appreciate everyone's advice!

If you don't mind I have some more questions. It was almost dead calm today for literally the first time in about 4 or 5 months but the boat was still moving a fair amount due to wave action. How do you ever figure out when the mast is plumb with the boat when the boat is in the water and moving around? I just kind of averaged out the swings of my make shift plumb bob. How do you know when it's in column when the boat may possibly be leaning slightly due to the way it's loaded or the wind is blowing on the mast and causing the boat to lean slightly?

Derek - What numbers do you use on the Loos gauge for your lowers? How much deflection do you get on your uppers when you push on them?

Dave - I have quite a bit of slack in my back stay but nowhere near 8"-10". I could probably get that much if I loosened it up but I was afraid that was too loose so I tightened it some. I plan on taking up the rest of the slack with the backstay adjuster.

There is no way that I can get 5" of rake on my mast. I might be able to get 3 or 4 if I loosen up the fore-stay the rest of the way but I only have about 3/8" - 1/2" of threads left now. I hate to get too close to the end of the threads.

Edited by - GaryB on 06/10/2008 22:18:16

Dave Bristle
Master Marine Consultant

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Djibouti
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Response Posted - 06/10/2008 : 22:34:28

Don't worry about the rake now--see how your helm behaves--you want a little weather helm ("two finger helm" in a 10 knot breeze)--lee helm is not a good thing. "In column" is not a measure of verticality--it's straightness. One way to measure it is to lie on the cabintop and look up. Another is to tension a halyard and see if the mast curves away from it. Verticality can be measured by extending the halyard to just touch a stanchion top, cleat it, and then see if it just touches the stanchion on the other side.

The good news is, if the mast leans to one side, you'll have more speed on that tack and less on the opposite tack. The average will be the same.

Edited by - Dave Bristle on 06/10/2008 22:37:23

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 06/11/2008 : 06:04:52

I sail a tight rig, to each his own. 28 on the uppers and 23 on the lowers. Where I sail we are seldom concerned with powering up, it is all about powering down.

Edited by - on

DaveR
Master Marine Consultant

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USA
2015 Posts

Response Posted - 06/11/2008 : 08:06:55

Great topic, Awesome advice! My rigging is all new 2 years ago so haven't had to mess with it but I'll be saving this thread to my pc, thanks!

Edited by - on

Derek Crawford
Master Marine Consultant

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USA
3321 Posts

Response Posted - 06/11/2008 : 10:33:54

GaryB - I can't remember what numbers I use, but I'll be tuning the rig for racing on Saturday so I'll write 'em down and let you know.
I should wran you that all my leewards wave in the breeze...but as Steve Milby once said "loose is fast" (unless you're sailing on Lake Cheney!)

Edited by - on

GaryB
Master Marine Consultant

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Response Posted - 06/11/2008 : 11:38:20

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Dave Bristle
 "In column" is not a measure of verticality--it's straightness. One way to measure it is to lie on the cabintop and look up. Another is to tension a halyard and see if the mast curves away from it. Verticality can be measured by extending the halyard to just touch a stanchion top, cleat it, and then see if it just touches the stanchion on the other side.

<hr height="1" noshade id="quote"></blockquote id="quote">

Thanks for clarifying that Dave! Based on your comments my question was referring to verticality and you answered my question. I'm not sure if may mast is vertical but it is in column. I checked that last night using both methods you mentioned. I'll have to verify the vertical piece of the puzzle.

Thanks again for setting me straight on my terminology!

Edited by - on

GaryB
Master Marine Consultant

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Response Posted - 06/11/2008 : 11:45:48

Frank - I may have to tighten my rig up some then. It was much tighter before than it is now. It's been blowing on average 10 - 12 knots with gust to 15 - 20 knots non-stop for the past several months. Last night was the first calm night that I've seen in months. Timing couldn't have been better!

Derek - I'd appreciate it if you could jot down your numbers. With Frank's input and yours I should have a good baseline for high winds and low winds.

My guess is that after months of moderate to high winds we're about to run out of wind in the bay so I'll probably have to use both sets of rig tension numbers.

Edited by - on

stampeder
Master Marine Consultant

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1608 Posts

Response Posted - 06/11/2008 : 23:33:59

What's the difference between mast bend and mast rake?
My mast has had a slight bow or bend - approx 2", about half way up the mast, but I'm not sure if this is rake or bend. For a raked mast, where on the mast should the bend/rake be?
As I was not sure of this, I've kept my mast perfectly straight this season, and because of the high winds, tight.
I don't know what the wind speed was yesterday, but I was sailing at 7 knots under 110 jib alone, to windward.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 06/12/2008 : 07:52:02

To rake is to tip... generally aft. A raked mast can be perfectly straight (no bend). The purpose of raking is to shift the overall Center of Effort (CE) of the rig forward or aft, which affects your helm balance (weather/neutral/lee). Bending flattens the mainsail by stretching it around its midsection, which "depowers" it for better upwind efficiency and less heel in high winds. Unbending "powers it up" for light air and sailing downwind. Some masts and sails are designed more for bending than others. I'd say the C-25 rig is not really one of them. Any bend should be a fairly uniform arc with the forward lowers pulling the midpoint forward--not a bend at one point of the mast. (Tapered masts bend more at the top, but the C-25 doesn't have one.)

Edited by - Dave Bristle on 06/12/2008 08:10:19

stampeder
Master Marine Consultant

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Response Posted - 06/12/2008 : 16:26:16

what do I do to my rig to get RAKE instead of BEND?
I've monkeyed around with my mast and standing rigging and what I see as a result is what I would call 'bend', generally starting mid-mast.
I sail with a tight, straight rig because in part, I don't seem to be able to achieve what I believe to be true rake. When I think of a raked mast, I think of the old Wooden Schooners that had 10Degrees or more of rake on straight masts.

Perhaps my question should have been, in terms of adustments in the standing rigging, what are the differences in rake and bend.

****PS**** ya gotta ask a question the right way. When I was a kid I asked my brother if it would hurt to get shot by a BB gun....he shot me and I had my answer.

Edited by - stampeder on 06/12/2008 16:31:30

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 06/12/2008 : 17:13:53

On a C-25 (with straight spreaders instead of swept spreaders, and double lower shrouds), rake is achieved by easing the forestay and forward lowers, and tightening the backstay and aft lowers, keeping the mast in column but tipping it back. A very few inches can have a noticeable effect on the helm.

Bend is achieved by easing the aft lowers and forestay, tightening the forward lowers, and cranking down the backstay. The middle of the mast shifts forward and the top pulls back.

On a C-250, with its swept spreaders and single lowers, I expect some bend could be induced by loosening the lowers, tightening the uppers (so the spreaders push the middle forward), and cranking down the backstay.

Edited by - Dave Bristle on 06/12/2008 17:15:33

GaryB
Master Marine Consultant

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Response Posted - 06/12/2008 : 20:10:57

Will the aft lowers hold up the mast if I release the backstay? I noticed the other night that I have a bent T-Bolt and would like to change it out before I go out this weekend. I assume I should use the main halyard as a safety before I release the backstay?

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
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Response Posted - 06/12/2008 : 21:43:57

yes

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Even Chance
Captain

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USA
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Response Posted - 06/12/2008 : 21:58:36

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by GaryB
 

If you don't mind I have some more questions. It was almost dead calm today for literally the first time in about 4 or 5 months but the boat was still moving a fair amount due to wave action. How do you ever figure out when the mast is plumb with the boat when the boat is in the water and moving around?
<hr height="1" noshade id="quote"></blockquote id="quote">

Gary, another method is to attach a long tape measure to your main halyard shackle, and run it to the head of the mast. Measure the distance to common points on either side -- I use the top of the upper shroud chainplate (where the toggle from the upper shroud attaches to the metal plate that runs down through the deck). When the distance on both sides is equal, your mast is plumb.

Edited by - Even Chance on 06/12/2008 22:01:05

knightwind
Navigator

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Canada
114 Posts

Response Posted - 06/15/2008 : 10:07:41

Being somewhat of a newbie I just connected the shrouds in the order the manual said and tightened each by hand until it was snug. The side shrouds all have 8-10" of motion at shoulder level and the forstay and backstay are a bit tighter.

When I got to the tuning-the-mast phase I didn't even try and plum-bob methods because of the rocking boat issue. The measuring-tape idea sounds good. By eye everything looks ok.

How big a concern is this? i.e. mast tuning?
Under sail I have a nice weather helm with windward shrouds tight and leewards loose.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 06/15/2008 : 11:14:53

IMHO, your shrouds are way too loose. At rest, there should be no "waving" possible. At heel, there can be a little looseness in the leeward lowers, but the leeward upper should not be waving. That means your mast is leaning away from the wind, which is not good for performance or for the mast step. In a slip or on a mooring with any wave action, that looseness allows the mast to put shock-loads on the swages and chainplates with every rock-n-roll.

Edited by - on

knightwind
Navigator

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Canada
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Response Posted - 06/16/2008 : 11:17:33

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Dave Bristle
 IMHO, your shrouds are way too loose. At rest, there should be no "waving" possible. At heel, there can be a little looseness in the leeward lowers, but the leeward upper should not be waving. That means your mast is leaning away from the wind, which is not good for performance or for the mast step. In a slip or on a mooring with any wave action, that looseness allows the mast to put shock-loads on the swages and chainplates with every rock-n-roll.
<hr height="1" noshade id="quote"></blockquote id="quote">
I checked them yesterday. Each shroud and stay is snug with 2-3" of play at shoulder height. Do I really need to buy a loos-guage? The leeward shrouds obviously slacken up when heeling but I figured this is normal. I think you're saying I should tighten them up even more.

Edited by - on

Stardog
Captain

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USA
319 Posts

Response Posted - 06/16/2008 : 12:00:42

My recommendation to you is to go to your local sailmaker and ask for advice and help. What I mean by that is ask what the optimum tunings are. Your sailmaker should have, or be able to get this information. They will also have gauges which you can probably borrow, or at least rent. It will make a difference to have your rig tuned properly, your mast will stay in-column regardless of conditions and will perform exactly the same on both tacks. Also it's really easy to tune, once you have the specs.

Edited by - on

stampeder
Master Marine Consultant

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Response Posted - 06/16/2008 : 13:52:15

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Do I really need to buy a loos-guage<hr height="1" noshade id="quote"></blockquote id="quote">

many sailing clubs have them.

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