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Catalina/Capri 25/250 Sailor's Forums

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Rig Tuning Questions

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bbriner
Captain

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349 Posts

Initially Posted - 02/27/2005 : 13:13:40

Finally got the new rigging on and the mast up (yesterday). I used the rigging kit from Catalina Direct. Followed the instructions to tune the rigging at the dock and have a couple questions..
(1) Mast Bend - How much mast bend do you use? Books I've consulted say that mast bend should be no more then 0.5 the fore-aft diameter of the mast, but refer to keel-stepped masts and don't mention deck-stepped masts. I tightened the forward lowers to induce a fair amount of mast bend, but I'm wondering if the max. should be less for deck-stepped masts.
(2) Mast rake - Books say rake should not be more than 3% of mast height. I have mine ** slightly** raked but I can't tighten the backstay any more. Forestay and Backstay tension seems to be where I want it but I don't think I will be able to accomodate any stretch in the back stay without foreward rake, which I don't want.

Cap shrouds are tight and mast is centered (yea!).
Any suggestions/responses are greatly appreciated as always!

Bill B
1984 Wind Dancer 4036 FK/SR

(PS - FWIW, I also installed a spinnaker block and halyard - even though I don't have a spinnaker yet but I wanted to be ready - and a block for the topping lift, per J. Williams of 'Hey Jude' 's advice. I realized last year that this is very necessary for a good reef.)

Bill B
Wind Dancer
#4036 84 SR/FK
San Francisco Bay

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 02/27/2005 : 18:27:50

IMHO disclaimer.

You want to be able to dynamically adjust your rig when sailing to match the conditions.

This means (primarily by using your adjustable backstay) you can go from a 'neutral' mast tune in light airs/downwind to a state where you have rake/mast bend when you're in heavier air or beating.

This is the state I go for...

With the backstay very lightly tensioned, the mast is in column with no rake. The forestay has some tension, but is loose enough to deflect under load and power up the headsail. (I use purely subjective settings as I have no gauges)

As backstay tension increases, the forestay tightens, the mast rakes aft slightly, and by setting the aft lowers a little looser than the forwards, you also introduce a couple inches of mast bend (to flatten the main).

I think the point I'm trying to make here is that the mast tune is a dynamic thing, rather than a static setting... at the dock set up your mast to have the 'upper and lower ranges' you want... backstay 'off'... and backstay 'on'.

Hope this makes sense...

P.S. If you don't have an adjustable backstay... Get one!

Edited by - on

bbriner
Captain

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349 Posts

Response Posted - 02/27/2005 : 18:40:15

Oh right.. I should have mentioned that I do not have an adjustable backstay.

If I had one I suppose that these questions would be less relevant.

BB

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 02/27/2005 : 20:12:12

Although I knew it was an option, I'd never seen a C25 without an adjustable backstay.

I guess you'll have to pick a point in the adjustment range to match your expected conditions. Sounds like right now you're set up at the 'heavy air' end of things.

You know your sailing venue better than I... maybe pick a setting in the middle range and experiment as time permits.

Addendum: If you already have a split backstay attachment with no adjustment... add 2 small wire blocks, 1 small line block, a stainless ring, a snap cleat and you've got your adjustable backstay.

Edited by - ClamBeach on 02/27/2005 23:03:40

Steve Milby
Past Commodore

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USA
5902 Posts

Response Posted - 02/28/2005 : 11:49:06

Whether or not you use an adjustable backstay, I agree with Bruce (Clambeach) that mast tuning is a dynamic adjustment. Ideally (if you are tuning for the big race, and want perfection), you should tune the rig for the weather in which you'll be sailing.

Theoretically, if you want the optimal tuning for any given day, you should adjust the stays for the conditions that you'll be sailing in that day. The advantage that an adjustable backstay has over a fixed backstay is that, with the fixed backstay you have to use one setting for the whole day. It's impractical to re-tune a rig with a fixed backstay while you're underway. With an adjustable backstay, you can induce mast bend, and increase or decrease tension on the headstay on the fly, with every puff and lull. Those adjustments drastically change the shape of both the mainsail and the jib.

Mast Bend - I haven't seen any evidence that any particular amount of mast bend has a significant effect on the performance of the boat. The condition that you definitely don't want is a reverse bend in the mast. You should induce just enough mast bend so that you can see that it doesn't have a reverse bend. IMHO, anything more than that is unnecessary.

Mast Rake - When the books say that mast rake should be about 3% of mast height, that is just an approximation. It helps you get close to the correct amount of mast rake. After the mast is up and the rig is approximately tuned, then you should sail the boat and fine tune it so that you feel about the correct amount of weather helm in the tiller. If you have too much weather helm, you'll have too much tiller pressure, which reduces your boatspeed and is physically tiring.

Ordinarily, you should tune your rig for the wind strength that you usually encounter in your area. If you want to optimize your tuning when the wind becomes especially strong, you should re-adjust the rig by tilting it forward a little bit. The reason is because weather helm increases with wind strength, and tilting the rig forward slightly will reduce weather helm when you're sailing in strong winds.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">I can't tighten the backstay any more. Forestay and Backstay tension seems to be where I want it but I don't think I will be able to accomodate any stretch in the back stay without foreward rake, which I don't want.<hr height="1" noshade id="quote"></blockquote id="quote"> The forestay and backstay are manufactured so that they are just the right length to extend from the transom to the mast top, and from the stem to the mast top, and still have enough room to adjust the rig either way. I always begin with the assumption that mechanical devices have been manufactured correctly. That isn't always true, but it's true more often than not. Therefore, if there's no room for adjustment one way or the other, it is probably an indication that I've done something wrong.

It's possible that your backstay is adjusted all the way down because your mast is raked too far aft. One possible cause might be that your boat was sitting bow down when you tuned the rig, and that might have affected your perceptions.

The more likely reason why your backstay is adjusted all the way down is that you didn't thread your turnbuckles onto the forestay and backstay correctly. Try this. Attach a line to your main halyard, and then affix it securely to either the stern pulpit or the stern cleat. Next, attach a line to your jib halyard, and then affix it securely to either the bow pulpit or the bow cleat. They will hold the mast up while you completely unscrew the forestay and backstay turnbuckle barrels at both ends. Then, start the screws in both ends of the backstay turnbuckle at the same time. Tighten the turnbuckle down exactly ten full turns. Then do the same thing with the forestay turnbuckle. Then alternately tighten each turnbuckle exactly ten turns at a time, until you have the correct amount of tension on each. If your forestay and backstay have been manufactured to the correct length, that will maximize the adjustability of both turnbuckles. When that is done, you’ll have to completely re-tune the rig. If you correctly re-tune the rig, both turnbuckles should still have plenty of adjustability either way.

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