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Thread: Drilling holes in aluminum mast (on a wooden boat :-)

  1. #1
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    Default Drilling holes in aluminum mast (on a wooden boat :-)

    The executive summary for this questions is: do I dare drilling holes in my stayed aluminum mast to make an attachment point for a sprit-boom snotter? The mast is stayed at three points but it does have some flex (lee shroud has some slack on a beat) and I worry about weakening the Dwyer DM-2 mast with holes drilled at a high stress location (a couple of feet or thereabouts above the partner). Am I worried for nothing? Details below if needed. -- Wade

    The details:

    (photos of the rig at http://www.wtarzia.com/NewSaiilforShortDragon.html)

    I recently got a taller, higher-aspect sail (75 square feet, or 6 foot foot and 14 foot luff, battened) for my outrigger canoe, one that requires a stay and shrouds. The 17 foot aluminum DM-2 Dwyer mast (slight oval with sail track as part of the extrusion) now has these things, attached about 80% of the mast height (Vectran lines, 1/8"). Now, To control sail twist better I find I need to add either a vang or a sprit boom. Not much room for a vang with a good angle as the canoe hull is very narrow and decked over at the parnter.

    But something must be done for the sail twists pretty badly when sheeted to the hull centerline on this 22 inch wide outrigger hull. No real sheeting base available unless I extended the boom about 3 feet beyond the clew and sheeted that to a line on the aft cross-beam -- seems very ungraceful for this relatively narrow mainsail, though it seemed to work well for the old standing lug whose boom end was near the aft cross beam.

    I thought a sprit-boom might do the trick, maybe a double wishbone sprit. Any sprit boom would of course have to be attached to the mast roughly a few feet over the partner. I can think of ways to use lines running down the partner to secure the end of the sprit against the thrust. Doable but this seems ungraceful. So I would like to rivet a solid attachment on the sides of the mast for the snotter -- the mast hounds all come with quarter inch bolts, so I am assuming this is the gold standard -- but I hate to think of a quarter holes going through a spot so close to the main stress of the mast (even though stayed). That's the question.
    Last edited by wtarzia; 10-01-2012 at 02:50 PM.

  2. #2
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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Boats like 505's have had goosenecks rivetted to their masts for years.Theres rather more than 75 square feet involved and the various sail controls are being used to provide maximum drive.On the other hand the masts in question are designed for the purpose.

  3. #3
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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Before you drill holes, try out the snotter using a "U" bolt, or hose clamp as something to snug up the choker with.

  4. #4
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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Wade,

    I don't understand your comment about a vang. Every vang I ever used went from the mast foot (just above the partners on your boat) to the boom. The width of the hull should not matter.
    Do you have water stays on the fwd crossbeam to where the shrouds attach? If you don't its going to break the crossarm unless it is really strong. Sorry I just couldn't see anything there.

    I'm sure you don't want anything else to add to the boat, but if you had a traveler from gunnel to gunnel the main would be sheeted from almost the perfect point for going upwind. The main sheet would also be pulling directly on the side of the boat where it is strongest. Moving the traveler a little fwd and sheeting somewhat mid boom would allow more twist control for a wider point of sail - more reaching. When you really have to slack off the main the vang would do a good job for less twist.

    Good luck

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Quote Originally Posted by upchurchmr View Post
    I don't understand your comment about a vang. Every vang I ever used went from the mast foot (just above the partners on your boat) to the boom. The width of the hull should not matter.
    Do you have water stays on the fwd crossbeam to where the shrouds attach? If you don't its going to break the crossarm unless it is really strong. Sorry I just couldn't see anything there.

    I'm sure you don't want anything else to add to the boat, but if you had a traveler from gunnel to gunnel the main would be sheeted from almost the perfect point for going upwind. The main sheet would also be pulling directly on the side of the boat where it is strongest. Moving the traveler a little fwd and sheeting somewhat mid boom would allow more twist control for a wider point of sail - more reaching. When you really have to slack off the main the vang would do a good job for less twist.
    --- No water stays. The cross beams seem strong enough for the 4 afternoons I've tried the new rig, so far. Sure, there is room for some kind of vang, but I thought the angle would be too oblique, and a lot of the force would be wasted in the wrong direction -- but I confess I know nothing about vang angles.

    Yes, I could add a traveler around mid-boom though the hull is only about 20 inches wide where I would sheet from mid-boom. But that would be an easy enough experiment, as I've got nothing to lose by trying -- drill a couple of holes and go. The sail twist seems to rob a lot of power; I could hardly squeeze 6 knots out of the boat in a 10-12 knot breeze the other day. This was not as much as gotten in years past from the same sail area (around 90 total) distributed in a set (main and mizzen) of 54' and 37' standing lugs. I thought that shifting more area in to the taller main and less into a mizzen (current rig in photo link above) would have done better.

    But I am fighting a couple of different problems. On another thread I was trying to gain insight into the too-flat head of the sail (the square-top has a diagonal batten/rod (functioning a little like gaff) that seems too stiff to allow draft near the head. That problem needs an experiment in a thinner or re-shaped top batten. Arrr, these nagging problems! But too much money invested to just go back to the old rig :-) The shifted sheeting on the boom is at least a cheap experiment. -- Wade

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Wade,

    From the picture you have a better angle for a vang than many boats, I.E., the boom seems high enough over the partners. It does take a lots of mechanical advantage to get much of a vang force. Of course the vang is only really effective more off wind.

    You might not want to go completely mid boom for the sheeting, but I don't really know exactly where to suggest.

    To me the only problem with your mast setup is that with the buried mast setup - keel stepped and mast partners - is that with any flexibility in staying the mast results in it being heavily loaded at the partners. Aluminum masts typically have no way to be reinforced at the partners and a large sail load will cause the mast wall to dent and the whole thing to fail, rather quickly. Water stays would be cheap insurance for heavy weather with the ama to lee. With the ama to weather the load on the sails/mast are naturally limited.

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Quote Originally Posted by upchurchmr View Post
    From the picture you have a better angle for a vang than many boats, I.E., the boom seems high enough over the partners. It does take a lots of mechanical advantage to get much of a vang force. Of course the vang is only really effective more off wind. ...To me the only problem with your mast setup is that with the buried mast setup - keel stepped and mast partners - is that with any flexibility in staying the mast results in it being heavily loaded at the partners. ...Water stays would be cheap insurance for heavy weather with the ama to lee. With the ama to weather the load on the sails/mast are naturally limited.
    --- Enough angle for a vang? I wouldn't have thought so but I stand corrected. I considered putting a step on the deck for reason you explain (and after tearing out the mast tube and sealing the deck, some weight would be saved), but I hated the thought of a more complicated boat set up. Not pictured in the photos is the addition of an inflatable safety ama, which makes the boat into a quasi trimaran, so now stress is not really bled off any more when the (wooden) ama is to windward (though the safety ama lets the boat heel more on that tack because of the up-curve of the rigged crossbeams). (Video here: http://www.youtube.com/watch?v=tvBu9XmL1oo ) -- Wade

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    That type of sail really needs a traveler for twist control. Even a rope stretched across the hull with the sheet deadened on a block that is free to roll side to side along the rope would be a major improvement. A vang wouldn't hurt and a small one wouldn't be too hard to throw together. Home Depot has some rectangular plastic molding thats white and 3/4" x 1/4" which makes good, tough, cheap and flexible battens.

    Vang (red line) made with Harken Micro blocks.

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Thanks everybody for your help. I will try those things. I do not have the vertical room to achieve that decent vang angle in the last photo posted by Todd, but I will try something, anyway. I will also install a rope traveler further along the boom. Separately I will play witht he topmost (diagonal) batten, whether it be trying a section of fiberglas tent pole, grinding down the fore half of the current batten-rod, or borrowing something from Home Depot for a batten (even a small diameter PVC tube?). -- Wade

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    I have never had good luck with round battens, whether solid, tubular or PVC pipe, even using fancy screw-plunger batten adjusters. Unfortunately, sail chord shapes and the possible shapes with round stock (which is very difficult to taper) just aren't the same (or even close). On a boat like that, we would generally want a fairly soft entry section and our maximum camber depth about 35%-40% aft of the luff. That is very hard to do with rods or tubes, but fairly easy with many types of flat batten stock. Ideally, we would also want the lower batten to be fairly stiff, the second one a bit softer and both the horizontal one and that rooster batten up top just as soft as we could get away with while still holding the roach up and out. Round batten stock just isn't going to do that properly.

    We want a pretty soft, round entry because it will make the trimming/steering more forgiving as the boat goes through directional or wind speed changes, especially on what should be a reasonably quick hull. A flatter entry might have somewhat higher top-end speed potential, but only if perfectly trimmed and steered. We can usually go with about 35% aft for maximum chord depth on multihulls. Since this one isn't as heavily-powered as some, we might go aft just a bit more, but I wouldn't go farther aft than about 40%. Flat battens can be tapered in thickness with a sander or plane and then you can stand next to a wall, press the front end against the wall, push inward a bit on the aft end and check out your tapered camber curve. Go a bit at a time and check them until you get a nice curve. If you want a final check, prop up the mast and boom on sawhorses (or lay the hull on its side) hoist the sail horizontally to full hoist and then set a marble at every batten. They'll roll down along the battens until they reach the maximum camber position. If you then sight up or down the sail from its top or bottom, your marbles should line up in a nice fair curve. On this sail where you only have four battens it's not a big deal, but on something like a beach cat sail that may have ten battens, it can be.

  11. #11
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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Thanks. Heading off to West Marine now for double blocks, low-stetch line, and stuff to make vangs (I figure one for the mizzen is not critical because so often sheeted down hard to the stern, but I might as well try one because the mizzen is big enough to be some assistance in reaching) and maybe even some batten materials to fiddle around with the troublesome diagonal. The little traveler line across the narrow hull is the work of 15 minutes. The new cognitive categories made by a different rig are of course timeless :-) --Wade

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Brion Toss
    Use of Drill Taps:

    Rigging modern boats with metal spars entails a whole lot of drilling and tapping, usually into aluminum. Riveting is an option, and is very attractive from a profitability standpoint, but machine screws are stronger in both tension and shear, and are removable for inspection or for replacing hardware. But drilling and tapping for machine screws can take a whole lot more time and skill. I can’t do anything about the need for skill, but I can recommend a way to save time by using a combination drill bit and tap, so you do both operations in a single shot. No more finding the right sized bit, then drilling, then switching to a tap.
    Drill taps come in all the common sizes. The ones we use most are 10/24 and 1/4”/20, but we keep larger and smaller ones on hand as well. These combination units are still far from common, but one good source is Fastenal. Here is a page from their catalog: http://www.fastenal.com/web/Search.e...rm=drill+n+tap
    It is important to lubricate these drill taps before making each hole. I’ve found that McLube’s One-Drop makes an excellent cutting oil, and comes in a convenient little tube. Also important to know is that, while these things work great on most spars as long as they are not too thick, you’ll still likely be using conventional means (drilling, then tapping) for thick pieces or ones made of stainless steel.

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    I drove to West Marine to buy stuff for a vang but found it out of business; I did install a traveler rope across the canoe hull (about 23 inches wide there). I went sailing and filmed a brief shot of the sail twist post-traveler (short video at http://www.youtube.com/watch?v=k2hvR...ature=youtu.be with the view of the twist starting at 1:50).

    I thought the twist was *slightly* improved when tightly close-hauled as Todd suggested (but the mizzen starts getting back-winded; the happy point when the mizzen works and the mainsail telltales are all starting to get proper is a bit looser than close-hauled). As a quickie fix, it was better than nothing (I think the downhaul needed another tug in that film).

    When I brute-force the boom down by hand, the twist becomes nearly right, so I just have got to get there. I will have to mailorder the vang stuff as West Marines get fewer between. (I suppose I could buy a few cheapy Home Depot "blocks" to finagle a basic vang, and it worked to satisfaction, invest in a good set, a set also for my mizzen, sheeted now at the stern centerline).

    Next cheap experiment as I await vang blocks could be moving the boom attachment point of the sheet a *little* further forward. -- Wade
    Last edited by wtarzia; 10-22-2012 at 08:55 AM.

  14. #14
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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    FWIW, used vang sets (like those for a Laser) come up on Ebay regularly.

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Wade

    You could use a lever vang which would require fewer parts/ pulleys. The commercial ones were sheet metal folded over once, but something solid would work if it was thick enough. There is not a large range of motion, so you have to set it up carefully.

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Quote Originally Posted by wtarzia View Post
    .....
    Next cheap experiment as I await vang blocks could be moving the boom attachment point of the sheet a *little* further forward. -- Wade
    You should do the sums first - moving the attachment point forward (towards the gooseneck) reduces the mechanical advantage of the system - i.e. makes it less effective.

    It's easy to make a cascade kicker using just a few simple blocks and some suitable line.
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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Wade,

    If that twisted main is backwinding the mizzen, you probably need something better for the Mizzen. How about a small wind surfer rig?

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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    @PI: I thought the sheet would pull more dirtectly downward if I moved it forward 6 inches or so.

    @upchurchmr: (1) interesting lever vang, good to know about. Not sure if the 12 inches of clearance I have between gooseneck and deck is enough for all that. (2) Mizzens generally have a backwinding problem, no? Hauling in the mainsail so that the upper half draws best (with the current twist) means the lower half is hauled in enough to backwind mizzen. (not so much to create a bubble, but enough to notice). A windsurfer sail would be a pain in the butt for storage and set up (I had one in an earler incarnation of my boats) but a nice sail; can it be found in the mizzen size? (my mizzen is 20 s.f.). But I do like my mizzen sail as is; its size balances well with the biggest reef my main can take (which brings it down to around 30 sf); it does deserve its own vang, though. --Wade

  19. #19
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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Quote Originally Posted by wtarzia View Post
    @PI: I thought the sheet would pull more dirtectly downward if I moved it forward 6 inches or so.
    ...
    --Wade
    The downward force at the clew (which is after all the whole purpose of the vang) is the product of three terms:

    (tension in vang line times mechanical advantage of system)
    x
    (sin of the angle at which it meets the boom)
    x
    (Ratio of the vang to gooseneck and the clew to gooseneck distances)

    Moving the attachment point forwards improves the sin of the angle but at the detriment of the ratio of the lengths...

    There are a couple of other tricks.

    1 Move the attachment point off the mast and put it a few inches aft and as low as possible:-
    this improves the angles and makes the operation semi-automatic in that when hard on the wind the tension is taken out of the system courtesy of the geometry.....
    N.B. the mast foot loads change.

    2 An Arc vang traveller - See Star class for details.

    3 A vang rigged only when needed - a tackle hooked to the gunnel or aka as and when you need to - old fashioned but effective



    Don't go crazy with the mechanical advantage (Force multiplier) -it is all too easy to create a thing which can do real damage.


    Cascade HowTo using simple single blocks - http://www.wayfarer-international.or...cade_vang.html
    Last edited by P.I. Stazzer-Newt; 10-26-2012 at 05:55 AM.
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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Can't help any with the sailing tips, but the original question sounded like a structural strength issue. You won't have any problems drilling a couple of 1/4" holes in a 2-1/2" aluminum extrusion. Especially if you then fasten a bracket which will reinforce any stress concentration you create. I don't like tapping into a thin wall extrusion like this, it's probably not deep enough to give you enough threads. You'll most likely strip the threads when you go to tighten the bolts. Unless the wall can give you 4 threads or more, go with the rivets. 4 threads on a 1/4-20 bolt means the wall needs to be at least 0.200 thick, the Dwyer website doesn't give that dimension. I really don't like to use tapped holes if I can possibly avoid it, Mr. Murphy pretty much guarantees problems. I see that Dwyer makes a number of brackets of different sorts that can be riveted onto this mast. If any of those work, that might be best.

  21. #21
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    Default Re: Drilling holes in aluminum mast (on a wooden boat :-)

    Nettie and PI, thanks. I like the arc vang traveler approach but on my skinny hull it would be a cantilevered structure. Geez, I am already nostalgic for the days when my standing lug with its long boom could be set on a traveller rope across the aft cross beams, and twist wasn't a big issue :-) Where are all those 75 square foot lugs when you need them? -- Wade

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