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Thread: boring holes in gaff / boom jaws

  1. #1
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    Default boring holes in gaff / boom jaws

    Looking for a bit of advice for bolting on our gaff and boom jaws. We are debating between clamping the assembly together and boring a long hole or doing each part separate.

    thoughts ? comments ? suggestions ?

    Cheers,
    Mark

    gaff1.jpg

  2. #2
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    Default Re: boring holes in gaff / boom jaws

    If I were to bolt them (I wouldn't, I'd glue them thereby excluding moisture thereby excluding rot) I'd pre-drill one of them on the drill press then clamp it in place and use it as a guide to drill thru the rest of the way.

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    Default Re: boring holes in gaff / boom jaws

    I've broken "many" gaff jaws over the many thousands of salt pounding miles on several boats.
    Either water got in those bolt holes and rotted out crap oak , or the bolt holes weakened the wood ,(wtf's with a half inch bolt in 2 inch wood?).
    But the fractures happen at the bolts.
    Also those cars are patently ridiculous on any gaffer under 20 tons. They do almost nothing except induce sweetwater and weakness.
    So, I have come to use screws, epoxy and nylon seizing .
    Let er RIP during gybes !
    Boom is always heavier and less vulnerable to gybe shock, so go ahead and make it herky and bolt er up. ( lift engine, dingy, careen boat.... cruising boat should have a "massive" boom.
    The seizing on the forward end is diual purpose, in addition to "marrying" the two jaws , it keeps strings ( topping lifts, topsl hlyd and sheet, random crap) outta harms way, jamming in between the jaws and mast. It' gets tightened !

  4. #4
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    Default Re: boring holes in gaff / boom jaws

    Here is the same on my little boat. Un sophisticated as yet in the photo , as in new an not broken in yet, but same idea.


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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by wizbang 13 View Post
    Here is the same on my little boat. Un sophisticated as yet in the photo , as in new an not broken in yet, but same idea.

    Bruce,
    The black line the halyard and the white line the throat corner tie?

    I love the seizing on the ends of the jaws. Clever, and it reminds me of building sof boats.

    Peace,
    Robert

  6. #6
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    Default Re: boring holes in gaff / boom jaws

    yup.
    It gets more elegant in the water

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    Default Re: boring holes in gaff / boom jaws

    I glued and screwed mine. Screws coutersunk and plugged.
    Seems I cannot insert pictures at the moment (shaky forum), but here's a link
    https://3.bp.blogspot.com/-16YxBFrPO...0/IMG_0483.JPG
    The halyard attaches to the ring bolt seen, the bolt goes through the gaff and on the underside another ring for the throat of the sail is screwed onto it.

    /Mats

    Elected Swedish Yourneyman of the Year 2019

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    Default Re: boring holes in gaff / boom jaws

    I like the seizing too. But if I did want to through bolt I would ideally drill each undersized and then true those by a long bit through the whole assembly.

  9. #9
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    Default Re: boring holes in gaff / boom jaws

    As it happens I have recently done just what you ask.

    This is the gaff of my catboat as it looked last month. The gaff is nineteen feet long with a maximum diameter of five inches, tapering to three and a half by the jaws. The jaws are steam bent and laminated Black Locust. The three through fastenings will be three eighths bronze rod headed over clench rings. Wood screws will secure tha aft ends. The whole gaff and the jaws, eventually will be sealed with CPES until no more will soak in. My method of sealing the holes bored for the fastenings, screw holes included, is to tape over the holes and pour in enough CPES to fill, topping as needed, and leave it sit for half an hour. The jaws will be glued to the boom with 5200. The tumbler was made from a chunk of Lignum Vitae, and I feel it's not a bad thing to include considering the proportions of the rest of the rig. There's also a string of Lignum Vitae parrel beads, nine in all, in ascending and descending diameters, not so much beads as stretched out beads, twice the diameter of the thickness and nicely tapered, a real necklace. I'll get a picture.

    But I digress, let me address the question directly. The holes through the three parts were bored in from each side. First, after determining the locations, which was no trivial matter and required a full, sized lofting due to the moving parts and the high peak angle required, a line was drawn on top of the knees in the clamped-up assembly. To do this a two foot long one-by-three was roughly notched to clear the boom so it could be laid across and the line drawn. This line was squared down the outer edge of the jaws, the thickness bisected and the hole location marked with an awl. The hole was carefully started so to get the hole right in the center, but only about a quarter inch deep. Sometimes it's good to use a little Fuller bit with a tapered point and the plug diameter the same as your bolt, it gets the hole on the spot better than the twist drill that gets used for the actual bolt hole.

    So clamp the one-by-three with the edge right on one of the lines. You're gonna use this stick as a visual guide to line up an electricians bit, from the top and from the front. If you have a helper its good, but it can be done alone without much trouble. Thke small bites with the drill, making sure to correct any misalignment. Have a piece of tape on the bit just past half the depth, drill up to it. Repeat on the opposite side.

    If it was me I wouldn't graduate the drill sizes up because I don't think that the drills center on each other that well and anyway the resulting hole is ragged.

    Forgive me the rambling, it's just that Ive been thinking this through lately and it good to put some of it down. There's probably better ways but I kinda like this.

    jim



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    Default Re: boring holes in gaff / boom jaws

    More elegant work, and a picture to illustrate ..., Thanks for posting this, Jim - it helps me to 'visualize' what you describe.



    .Rick

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    Default Re: boring holes in gaff / boom jaws

    Interesting shape to your jaws, Jim.

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    Default Re: boring holes in gaff / boom jaws

    Bruce- The seizing across is a great idea. Reminds me of old windsurfing days in the later 80's before stiff carbon booms you could cut a small hole in the sail and seize the two sides together - made an amazing difference. I've seen photos of larger boats with a metal rod across the front with parrels - it would be similar.


    I'm 100 % certain we are going to through bolt (silicon bronze rod), with a 735 ft^2 sail I'm not about to try things out.

    I'm assuming we want to use a ships auger bit for this ? Any recommendations ?

    We are thinking about drilling the spar first, using it as a guide for one side clamped on, then clamping on the other and coming back again through that first jaw and the spar. That should keep things lined up.

    Thanks for all the posts !
    Mark

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    Default Re: boring holes in gaff / boom jaws

    While the face that lands on the boom is still flat and square, I lay out the holes on both sides of both pieces (before I shape them) and drill them in the drill press. Fit and them to the spar and using the drilled piece as a pilot or fixture, drill the spar. Then shape them afterwards.
    I have always fastened them with copper rod and thickish home made roves, or "clench rings" peened up like a rivet.

  14. #14
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Mark0 View Post

    I'm assuming we want to use a ships auger bit for this ? Any recommendations ?

    We are thinking about drilling the spar first, using it as a guide for one side clamped on, then clamping on the other and coming back again through that first jaw and the spar. That should keep things lined up.

    Thanks for all the posts !
    Mark

    A ship auger is one possibility. I used a long twist drill.

    The important thing to keep in mind is that you want the holes centered in the width of the jaws, both for appearance and for strength. It would be difficult to drill accuratly though the spar alone as there's no reference plane available to guide the bit, and then you're faced with the problem of lining up the jaws with the bored holes.

    The problem that I see with boring the holes through the jaws on a drill press is that the inside jaw faces might not be parallel with each other. There should be some tapering of the spar under the jaws in addition to the taper of the spar. This looks best and , in my opinion, strengthens the assembly against loads pushing the jaws aft, such as getting slammed against the mast. Without any taper the force gets directly transerred to the bolts as a sheer load. With taper the bolts get put in tension as well as sheer.

    I like the idea of keeping the inside jaw faces, where they contact the spar, flat, and making flats on the spar with a small shoulder at the aft end.

    Here's a thread with some further discussion...

    http://forum.woodenboat.com/showthre...aws&highlight=

    Jim

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    Default Re: boring holes in gaff / boom jaws

    Hi Jim,

    I too think the taper is important - it really does transfer the load to more tension than shear. Our jaws / spar interface is also flat, but I didn't make a shoulder at the end.

    Cheers,
    Mark

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    Default Re: boring holes in gaff / boom jaws

    If you know the taper, and you do, you can either tilt or shim the drill press table. If you have doubts try the angle on some scraps to see how they line up.

    I never try to compete with the accuracy of a machine, it's not worth the trouble.

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    Default Re: boring holes in gaff / boom jaws

    Try to figure out if those bolt heads will be rubbin on the shrouds off the wind.
    That's when and where the wear happen.
    (Breaks happen during gybes).
    Sevenfifty main ! How big IS your boat Mark?

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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by wizbang 13 View Post
    Try to figure out if those bolt heads will be rubbin on the shrouds off the wind.
    That's when and where the wear happen.
    (Breaks happen during gybes).
    Sevenfifty main ! How big IS your boat Mark?
    I was thinking about putting those bolt heads under a plug, or at least counterbore them.

    To the answer of of how big i the boat, the official answer is about 62 cm too long... it's going to be 550000 lbs or so. Some photos here: http://mimijane.ca/a-few-updated-views-of-mimi-jane

    Cheers,
    Mark

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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Mark0 View Post
    I was thinking about putting those bolt heads under a plug, or at least counterbore them.



    Cheers,
    Mark

    The trouble with counterbores and plugs is that too much wood gets removed from a critical area. My recomendation is to rivet bronze rod over clench rings. This is a neat solution that removes minimal wood from the jaws and presents a smooth, non-snagging surface. The rings can be made on a lathe from a piece of old propeller shaft, or with a drill press if no lathe is available.



  20. #20
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    Default Re: boring holes in gaff / boom jaws

    the riveted heads still want to avoid contact with the shrouds ideally. one could lam a piece over the lot, but the jaws are getting wider and wider.get to a certain size, might wanna go with a saddle. ih ad no idea your project was so big
    the wider those gaff jaws get, the more they push on the lee shroud. they actually lever the hell outta them, something that does not happen on a shroudless boat. no wear at all on the pic above. she is either a catboat, a showboat or a museum piece .

  21. #21
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by wizbang 13 View Post
    the riveted heads still want to avoid contact with the shrouds ideally. one could lam a piece over the lot, but the jaws are getting wider and wider.get to a certain size, might wanna go with a saddle. ih ad no idea your project was so big
    the wider those gaff jaws get, the more they push on the lee shroud. they actually lever the hell outta them, something that does not happen on a shroudless boat. no wear at all on the pic above. she is either a catboat, a showboat or a museum piece .
    Stop reinventing the wheel.
    Because of the distance between the gaff jaws and hounds to accommodate the throat halyard blocks combined with the spread of the shrouds as they lead out to the deck edge the possibility of chafe is vanishingly small. I suppose that some incompetent designer could create an arrangement where contact could occur, but basically that problem was resolved centuries ago.
    That arrangement of riveted jaws is standard practice. If it ain't broke don't fix it.
    It really is quite difficult to build an ugly wooden boat.

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  22. #22
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by wizbang 13 View Post
    . no wear at all on the pic above. she is either a catboat, a showboat or a museum piece .

    Guilty on all three counts, yer Honer, and the gaff jaws were new when the picture was taken.


    Here's a few jibes later getting a fresh coat of varnish.



  23. #23
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Jim Ledger View Post
    Guilty on all three counts, yer Honer, and the gaff jaws were new when the picture was taken.


    Here's a few jibes later getting a fresh coat of varnish.


    Rover jaws?
    The clench rings on the boom in #19? Yes, please. Much nicer than the refuse I normally make and work with.

    Peace,
    Robert

  24. #24
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    Default Re: boring holes in gaff / boom jaws

    That arrangement of riveted jaws is standard practice. If it ain't broke don't fix it.
    Nick, Yer sayin you never broke a gaff jaw?
    Yes, my gaff jaws tuck up close to the shrouds, but even reefed, gaffs come in contact with shrouds . I suppose perfectly sailed boats can avoid it ,,,someone to baby the mainsheet ,( I don't ).
    Jim, A spar that gets that kind of attention probably is not getting rain goin up in the holes year round either, No night time wild gybes on big seas, (I do).


  25. #25
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    Default Re: boring holes in gaff / boom jaws

    Hey,

    Quick question.... what sort of clearance hole should we drill ? We have 1/2" Silicon bronze rod for the bolts (nuts on either end) , do we use a 9/16" ships auger ?

    Cheers,
    Mark

  26. #26
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    Default Re: boring holes in gaff / boom jaws

    I would drill 1/2" holes.

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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Mark0 View Post
    Hey,

    Quick question.... what sort of clearance hole should we drill ? We have 1/2" Silicon bronze rod for the bolts (nuts on either end) , do we use a 9/16" ships auger ?

    Cheers,
    Mark
    No 7/16". You need a tight driving fit, with 8/16" through the hard wood jaws if you are concerned about splitting.
    It really is quite difficult to build an ugly wooden boat.

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  28. #28
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by wizbang 13 View Post
    That arrangement of riveted jaws is standard practice. If it ain't broke don't fix it.
    Nick, Yer sayin you never broke a gaff jaw?
    Yes, my gaff jaws tuck up close to the shrouds, but even reefed, gaffs come in contact with shrouds . I suppose perfectly sailed boats can avoid it ,,,someone to baby the mainsheet ,( I don't ).
    Jim, A spar that gets that kind of attention probably is not getting rain goin up in the holes year round either, No night time wild gybes on big seas, (I do).

    "If it ain't broke don't fix it" means do not reinvent the wheel. If it has worked for centuries there is no need to try to improve it.
    It really is quite difficult to build an ugly wooden boat.

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  29. #29
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    Default Re: boring holes in gaff / boom jaws

    I guess I broke more gaff jaws than most here. Yes, I see the irony here of posting a busted jaw that is seized .They still break, but are easier to fix and not all rotten through the holes.
    Last edited by wizbang 13; 08-10-2019 at 09:24 AM.

  30. #30
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    Default Re: boring holes in gaff / boom jaws

    Bruce, I'm not seeing how the gaff jaw gets cracked on the outside face. It seems to me that the forces encountered during a violent gybe would put the outer face into either compression or no load at all. Obviously, I'm wrong. Can you explain?

    Jeff

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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by jpatrick View Post
    Bruce, I'm not seeing how the gaff jaw gets cracked on the outside face. It seems to me that the forces encountered during a violent gybe would put the outer face into either compression or no load at all. Obviously, I'm wrong. Can you explain?

    Jeff
    Compression fracture in crappy wood, something like a thunder shake?

    It really is quite difficult to build an ugly wooden boat.

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    Default Re: boring holes in gaff / boom jaws

    Originally Posted by Peerie Maa
    No 7/16". You need a tight driving fit, with 8/16" through the hard wood jaws if you are concerned about splitting.



    Hi Nick,

    Why such a tight fit for these ? They are going to have washers / nuts. In my mind such a tight fit would be for drifts ?

    Thanks,
    Mark

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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Mark0 View Post
    Originally Posted by Peerie Maa
    No 7/16". You need a tight driving fit, with 8/16" through the hard wood jaws if you are concerned about splitting.



    Hi Nick,

    Why such a tight fit for these ? They are going to have washers / nuts. In my mind such a tight fit would be for drifts ?

    Thanks,
    Mark
    Fastenings in wood work in shear. If there is a sloppy fit the joint surfaces will slide one over the other, fret, wear away, crack the paint/varnish, allow in wet and so on.
    It really is quite difficult to build an ugly wooden boat.

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  34. #34
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    Default Re: boring holes in gaff / boom jaws

    I would think in this case the bolts are mainly in tension ? - there is a wedge formed from the spar taper between the jaws. Most bolts I put in materials don't have interference fits - so this seems odd to me.

    I've looked through my library of boat building books and haven't found a reference for holes sizes for bolts.

    Cheers,
    Mark

  35. #35
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Mark0 View Post
    I would think in this case the bolts are mainly in tension ? - there is a wedge formed from the spar taper between the jaws. Most bolts I put in materials don't have interference fits - so this seems odd to me.

    I've looked through my library of boat building books and haven't found a reference for holes sizes for bolts.

    Cheers,
    Mark
    Nope. The soft wood of the spar will crush and relieve any tension. Bolts through wood work in shear, always.

    Time served shipwrights know what size holes to bore, generally 1/16th under the diam of the bolt. For square boat nails, half of the diagonal for softwood, or the width of the flat for hard woods. Time served shipwrights rarely publish books.
    Last edited by Peerie Maa; 08-12-2019 at 06:32 PM.
    It really is quite difficult to build an ugly wooden boat.

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