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Why is the main sheet 75' long?

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awetmore
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Response Posted - 03/29/2012 : 13:29:15

David: That is similar to what I have planned for my outhaul as well. I was just asking questions about how to attach the hardware to the boom. How is your cleat attached for instance? The screws going into my boom are corroded in place, so I haven't had a chance to see if they are machine screws with backing nuts, self tapping screws, or just machine screws threaded into tapped holes on the boom. I'm going to try and pull off the back of the boom so that I can look at what is going on. I'm a bit of a machinist and generally don't like self tapping screws or fine pitch threads going into thin aluminum extrusion, but if those have been working on thousands of sailboats around the world then I'll do it.

I've setup my mainsheet with the the boom block down low (as suggested by David), but have kept my sheet long in case the block is getting in my way on tacks and jybes. If it all works out well on a few test sails then I'll do a more permanent solution.

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dmpilc
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Response Posted - 03/29/2012 : 15:22:41

The stainless steel screws I use are typically those with threads spaced wider apart than machine screws that have a very fine thread, and they are pointed rather than blunt, sort of like wood screws but the threads are a little bit closer together.
I used a cleat West Marine calls a fairlead V-cleat on the C-25, like the bottom one in the pic below. It takes an oval head screw that will lie flush with the cleat surface. It is important to fit the screw head to the cleat you plan to use, because a screw head that is too big to lie flush will interfere with the line movement:

On my C-22 the outhaul cleat is a regular horn cleat, mainly because it was there when I bought the boat.

Edited by - dmpilc on 03/29/2012 15:30:05

Lee Panza
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Response Posted - 03/29/2012 : 22:14:37

I'll second what David said in his previous post: "Better to drill and tap the holes." The aluminum of our spars is rather tough, and it machines well, so it's easy to get good threads with hand-tapping (especially with a guide). Most hardware scaled for our needs can take #10-24 or 1/4-20 machine screws, which provide two or more full circumferences of thread engagement biting into the aluminum (both the caps are on my boom at the moment, so I can't check it, but if I remember correctly our mast is just over .1 inch thick). Self-tapping sheetmetal screws of approximately that size get a single thread or less. Also, tapping allows you to get greater radial depth of engagement; I've been getting good results with a #22 drill for #10-24's and a #10 for the 1/4-20's, which translates to engagement of over 75% of the depth of the threads. You'll snap-off any self-tappers you try to drive into this hard aluminum with even a much shallower depth of engagement. They really don't get anywhere near as much holding power as tapped machine screws. Of course, most of the loading is just in shear, so the argument isn't as important as when resisting straight-out withdrawl.

Whatever you use, however, it's really important to use a galvanic corrosion inhibiter like Tef-Gel. It's unpleasant to work with, because it's sticky and it's impossible to keep off my fingers when I'm working with short screws, but the little brush that parks in the plunger works well, and you really use very little per screw.

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awetmore
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Response Posted - 03/30/2012 : 07:11:03

The screws that David describes sound like self tapping sheet metal screws, while you are describing normal machine screws.

Typically you want 3 full threads of engagement, especially in soft materials like aluminum, to ensure that a machine threaded screw won't pull out. The wall thickness on the boom won't allow for 3 full threads, which is why I was asking. The cleat and padeyes that I have for this project use #8 screws, my bolt-on block uses #10, both are 32tpi.

If this rain lets up this weekend I'm going to pull the end cap off of my boom and see what Catalina used when the boat was built. I have self tapping and machine screw options on hand. If I follow CD's mounting system for the outhaul then all of my hardware will be mounted near the end of the boom, and I can easily use a backing nut there. I'll bring my tube of anti-sieze down to the boat too.

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JimGo
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Response Posted - 03/30/2012 : 07:26:35

Alex, why not put a backing plate on there to further distribute the forces?

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Lee Panza
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Response Posted - 03/30/2012 : 08:28:34

At the risk of further annoying those who have no interest in working on boats (an oxymoron?), but keeping in mind those future DIY'ers who will follow our lead in restoring the many Cat-25's still deserving of extended lives, and who will be looking to these archives for help, I'll just add one last word to this thread.

In applications like fastening cleats, where most of the load is in shear between the fitting and the surface it's attached to, the more metal-to-metal contact you can get between the connector and the substrate the better. Pop-rivets would be good if they were wider diameter and solid shafts, which they're not. Coarse-threaded fasteners like self-tappers are better, and they're certainly convenient, but they provide bearing only on a very narrow band where the edge of the threads digs into the aluminum. They also leave sharp protrusions inside the spar that present hazards for internal wiring or cordage. Fine-threaded machine screws, with nuts to retain them, would be far better, and - if it's possible to cut good, tight threads into the aluminum substrate (and where galvanic erosion of the aluminum around the stainless steel threads can be prevented) - they might be the best choice where it's not possible to install a nut. However, the most practical compromise for hand-installed hardware would seem to be NC (National Coarse) machine screws, like #8-32, #10-24 and 1/4-20 in hand-cut threads.

Anyway, that's all of my two cents (plus an allowance for compounded annual inflation for as long as the last Cat-25 is still in need of restoration).

Edited by - on

Frank Law
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Response Posted - 04/01/2012 : 19:18:34

Question??--Wherever you mount the cleat / block will you be able to reach far enough inside the boom to put the nuts on the screws ?????
Frank Law
"ABOUT TIME"
1983 # 3519
SWK SR

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awetmore
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Response Posted - 04/02/2012 : 06:37:06

Not the cleat, but I will for the block and padeye. Look at how CD does it:
http://catalinadirect.com/images/products/D1718_715.gif

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dlucier
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Response Posted - 04/02/2012 : 09:01:27

Alex,

Do you ever plan on having a bimini? If so, take that into account when placing the outhaul cleat as you don't want to have it so far forward that it becomes hard to reach/adjust with a bimini up.

I routed my outhaul to the cabintop for both the bimini and if I'm tensioning the outhaul, it probably means I'm sailing close hauled in a breeze heeled way over with the rail in the water and the boat is pounding over whitecappy waves. Not needing to stand up to adjust the outhaul is a plus in these conditions.

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awetmore
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Response Posted - 04/02/2012 : 10:27:48

I don't plan on having a bimini, the sun is a foreign concept up here in the Pacific Northwest.

When the mast is down I am planning on installing a deck plate and running some more lines back to the cockpit. I haven't made a prioritized list yet (currently I only have my halyards back there). I don't really want to go crazy with clutches and winches as I've seen some boats do, especially because I don't yet want to buy a large pile of clutches and winches.

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dlucier
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Response Posted - 04/02/2012 : 10:44:25

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by awetmore
 I don't really want to go crazy with clutches and winches as I've seen some boats do, especially because I don't yet want to buy a large pile of clutches and winches.<hr height="1" noshade id="quote"></blockquote id="quote">

Yep, I know what you mean.

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awetmore
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Response Posted - 04/04/2012 : 22:04:25

I installed the outhaul parts today.

While I had the end cap off of my boom I shot a flashlight down there and confirmed that everything that is already installed was installed with self tapping sheet metal screws. I used machine screws for my new hardware, but I'll use the self tapping screws farther down the boom for the cleat.

Thanks for the discussion, and I should have looked first before bringing up the fasteners.

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JimGo
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Response Posted - 04/05/2012 : 05:58:37

I thought it was a good discussion. Lots of helpful information! I wouldn't be sorry about having asked the question.

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awetmore
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Response Posted - 04/07/2012 : 21:47:31

and now to bring the thread back to talking about main sheets...

I tried the 3-foot-ish fixed line between the boom before the blocks, but went back to the regular setup. I didn't like having the blocks in the middle of the sheet when running downwind and having that block rubbing against the lifelines. In light airs they also seemed to weigh down the sheet unnaturally.

However I can still confirm that 51' of mainsheet is plenty, at least on our boat. I'm glad to have shortened it up.

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awetmore
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Response Posted - 04/17/2012 : 09:30:18

I wanted to close this thread by saying that 75' is the right length if you use the main sheet to lower the mast with the boom rigged as a gin pole.

50' is enough if you just use it as a main sheet.

My solution is to have a 75' jib sheet that I can pull and rig as the main sheet for the occasional chance that I do lower the mast. The rest of the time I can just use the 50' main.

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dmpilc
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Response Posted - 04/17/2012 : 09:50:01

Sounds like a good plan.

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redeye
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Response Posted - 04/17/2012 : 11:07:48

<< I'll just add one last word to this thread. >>

Yepper.. that'll happen...

and then some of us ( around saltwater ) add some resin or glue to the screw just to add some strength and try to reduce some corrosion.

I do this in aluminum cause I'm kinda scared of tapping the hole out so I go a little easy with the tightening down and let the resin do the rest..

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