View Full Version : how to drill prop shaft on the keel?
09-02-2001, 09:01 PM
Whenever you do a mistake on the early stage of building a boat you most likly going to regret it for a long time!!.
This is our case :
we are building a 45' wooden fishing/pleasure boat using greenheart (for keel & bottom planking) white ceder (for ribs& ) and silver balli (topside planking & deck).
we do not plan for the prop shaft hole while we was layng the keel made of several plank of greenheart (very hard wood) 7" thick and 7" wide and now we facing the trouble of bore an hole 2,5" in dia. long about 14' passing with an angle trough the keel!
We think about few different solution but none are very convincing and we are in serious need of professional advice.
Tanks to anyone that cud help.
09-02-2001, 10:55 PM
Boy, that was a big oversight! http://media5.hypernet.com/~dick/ubb/smile.gif I think I can offer a coupla possible solutions.
The first is the method of running the shaft outside the deadwood, beside it. The shaft comes out of teh hull, possibly at a slight angle. This has been done in the past, especially in sailboats being retrofitted with engines, or some working craft. It keeps the shaft exposed. You would use some sort of standoffs and bearings, as it runs beside the deadwood.
The other method involves cutting a rabbet (groove) in the side of the deadwood for the shaft, and fitting a piece in (a deadman?) to seal the rabbet afterwards, leaving a shaft alley inside the deadwood.
Is that clear enough? Maybe somebody else can explain it better.
Maybe others can offer hope, but I personally don't see how you can drill a hole that size and length, and expect it to come out where you want it, even drilling from both ends. Good luck in any case.
09-02-2001, 11:16 PM
I think Bud McIntosh discusses this in his book. If you don't have it, you might try thru a library? I'll take a look for it later, but I think Mike has the basics covered.
09-03-2001, 12:41 AM
Bud's book might be where I saw this treated (either that or Wooden Boat Magazine.) The concept used was that you take a length of straight iron pipe in the right diameter and make cutting teeth in one end of it, and a shaft on the other end to fit your 1/2" heavy duty drill motor. Then you fix a "ramp" made out of lumber with a "V" design in the top that is fixed so that it extends the desired angle out of the keel. Laying the pipe in the "V", you attach it to the drill motor guide it into the keel. The "V" ramp support thingy keeps the pipe drilling at the right angle. The author who was writing about this said it worked like magic, and he was surprised that teeth cut into the end of iron pipe could "core drill" so well.
You might try making a mock up using that type of technique on some scrap. It would require that you have enough room "down and out" behind the boat to do it, of course, but the concept of stabilizing the drill is the idea you need to find.
09-03-2001, 08:28 AM
Bud's suggestion (too late for this, I think) is to have the shaft log cut in half (top to bottom so the shaft log is now a right half and the left half).
Score a line, end to end, on both halves, on what will be their mating surface. This line represents the center of the shaft alley. A tablesaw/skillsaw could do this, the blade raised a wee bit. Then using an auger with a lead screw (which will follow the cut already made), bore the actual hole.
At this point seems you'll have to employ something along the line of Mike's or Frank's thoughts. Perhaps some other ideas will percolate up. Tough spot. Twin screw?
09-03-2001, 08:59 AM
I've done this operation (on a smaller scale) using a boring bar. The idea is not unlike a boring lathe that is custom fit to your boat.
The boring bar is a piece of 3/4", or larger, shafting about 6-8 feet long - or as long as required for the setup - with a square hole cut through the side of the bar about middle of the length to accept a cutter made from a short piece of key stock (or perhaps the cutter from a metal lathe) that is held in place by a set screw. One end is turned down so it can be chucked in a 3/4" drill.
You start by boring a hole at as close to the correct angle as possible. The hole needs to be large enough to get the boring bar and the cutter through - will probably need a few cutters of different lengths for the shaft hole you need.
You then need to set up some bearing supports for the boring bar that are fixed to the boat on the inside and the outside - these will keep the bar in the correct plane and are positioned to allow the bar to slide through the deadwood enough that the cutter can pass all the way through (the position of the supports and the length through the deadwood will determine the length of the boring bar). I have used pieces of 2x4, with a hole to accept the boring bar, attached to the hull - on the inside, screwed down to the engine beds; on the outside, screwed down to the cradle (in your case perhaps braced off the deadwood.)
You attach the drill to the end outside the boat and with someone watching on the inside start with the short cutter and using slow speed and slow feed start boring the hole larger. Before you turn the drill on, pass the cutter through the hole turning the bar by hand, if it binds retract the cutter. Adjust the cutter until it doesn't bind and make the first cut at that setting. Advance the cutter no more than 1/32" and make the next cut.
It will make a gawd awful, horrible noise while cutting, and progress will be slow, but it will get the job done. The key is to make small cuts and use slow speed on the drill and slow feed passing the cutter through the deadwood. If the cutter is trying to take too much wood, the bar will start jumping all over the place. If the initial hole is not in the correct plane, open the hole up a bit using the boring bar and then adjust the position of the bearing supports to get the bar to the correct shaft angle.
[This message has been edited by Greg Bauer (edited 09-03-2001).]
09-03-2001, 11:36 PM
is the first time i use this forum and i am amazed by the response!
To Mike and Ed:
the idea of running the shaft outside or to install twin screw shure are practical solution but it will give me the idea of building a different boat.....
I like the idea of cutting a groove on the deadwood(we had it too!!!) but you think that considering this groove will run trough more than one keel plank is still good (or it might be even better?):i try to attach a draw (not in scale and not to accurate).
If we going for the hole i agree with frank that the basic concept is to stabilize the drill.
Greg and Dave advice looks precious too but i need to read them more carefully.(which i going to do now.)
Thanks again and i katch you all later.
P.S. more infos are still welcome!
09-04-2001, 09:07 AM
Teeth on pipe is by far the best system. I have had good success with old TV antenna mast, With a collar of heavyier stuff welded on the end to cut teeth into. Scaffold pipe, or chrome molly tube, would be the best. You could weld on an old hole saw, but standard hole saw teeth will be too fine for end grain boreing. Half of the teeth should have a slight set outward, and the other half should have a strong set inward, to clear the core. Make large holes in the drive end of the pipe to let shaveings out. You can weld on sections as you go if clearance is a problem, but the core will likely have to be removed periodicly to reduce friction. BE CAREFULL OF FRICTION HEAT BUILDUP!!, you do not want to start a fire in the middle of your keel. Shaft alleys are supposed to be bored oversize and fitted with a seamless liner. Lead or copper pipe would be traditional, pvc pipe in a pinch. Hope you left enough clearance on the keel bolt pattern to allow for your bore.
I've been thinking about this one for a little while. I think it boils down to a few issues. My big concern, and Dale touched on also, was what is your fastening pattern for the "deadwood/shaft log to be"? How many of these fasteners are in the way? How many times are you going to have to back out your drill rig, re-sharpen it and start over? How many times will you get bound up hard or bend/break your drill rig with these fasteners that may be in the way? This job can get real nasty, real expensive, real hard and a little dangerous real fast. I've done this sort of thing before more than once. If there was ever an opportunity for Murphy's Law to come into play, this is the kind of situation. What material are these fasteners made of? Are they drifts, spikes, lag bolts or round stock threaded at both ends to take nuts and washers? What's the chance that you can cut/pull the fasteners remove all or part of this mess and re-construct and drill the shaft log as described generally by most of the other guys? What's the configuration of the stern post, deadwood. and horn timber? Can you post some pictures? Personally, even if you use the sound suggestions that have been offered up by the other guys, you are very skilled and lucky I believe it's a low percentage shot. You've got to drill 14 feet thru no-man's-land at persumably an angle that passes thru very hard pieces of timber that may be fastened in such a way as to make drilling difficult if not basically impossible. Is your boat high enough off of the ground or do you have to dig a pit or raise the boat in order the handle the drilling apparatus? Will you develop a drill rig that is sectional? How do you intend to mount the stuffing box and stern tube? Since it is not a sailboat, the best solution may be to cut/drive out the fasteners, drop the deadwood out of there, re-configure as necessary. Cut slots for the shaft bore in each of two shaft log halves (conventional wisdom), re-assemble/refasten (fasteners properly spaced) the shaft log (with cedar stopwaters and splines where required). Then bore the slot out full size as described by Greg and/or the other guys. The boring bar might work best in your situation. Without further details, pictures or information this is a tough call. I'm not trying to sound discouraging, but I think that you need to step back and take another hard look at this problem.
[This message has been edited by RGM (edited 09-04-2001).]
09-04-2001, 11:33 AM
RGM, very good points!
I, silly me, assumed that the deadwood fastenings had been done with a shaft log in mind!
But if the poster of the question assembled the timbers absent that intention then, all bets are off and it's back to square one.
Be'jaysus what a nightmare thinking of drilling through all that stuff!!!!
09-04-2001, 07:17 PM
RGM has made some very good points. I too was not thinking at all about deadwood fastenings - my mind was stuck in 'cold-molded glue boats' mode. I also misread the original posting: I saw 14" of hole length, not 14'. That would give a new challange to using the boring bar as it would have to be something in the neighbourhood of 30+ feet long. Under it's own weight would sag quite a bit, so my original advice of 3/4 dia would not even be close to keeping itself straight while trying to take even the lightest of cuts. Maybe dropping the deadwood out of the boat makes more sense.
Please pass the humble pie...
09-04-2001, 10:38 PM
I have sent you a e-mail with a drawing attached on how I think I would do this...
09-05-2001, 02:49 AM
The fastner are threaded bar with nuts & washer and in theory they have a clarence of 3.5" between one and another; in theory becouse i can't guaranty that each pair is simmetrical with the other and i think that we have to pass trough 4 pair....
One correction :the lenght of the shaft is about 14' but the actual lenght of the hole nedeed is 10'.
Better , but probably not enough to avoid a nightmare job as RGM Dave and Greg explain.
I reconsedering the idea of twin engines and
we contact the designer of the boat for a comment witch i will get soon.
On the same time we contact an old friend wich was on the business of drilling rocks for some advices on a drilling bar...
If we going for the hole the idea that start to shape is to get a bar with the same dia of the hole and about 2' longer, after get 3 boll bearing of the same size build(in steel) a sliding ramp 5' on the keel end 10' outside with the bearing positioned at regular interval to hold the bar steady and the rotation impress by a belt or chain convey from the end of the bar to a slow turning engine device and the pression on the bar give with man power by just pushing the ramp in; anytime we are close to a pair of bolts remouve one or both and once the hole is done riposition the necessary.The keel of the boat is about 3' off the ground and we are in sand so dig a pit should be not a big problem.
I would love to send a drowing but my system give me some trouble (or may be is me that give trouble to it) but tomorrow i will try with a picture.
Thanks again and c u later
09-05-2001, 10:28 AM
Drilling a hole from one end only has about a zero percent chance of success. The best way I know of, if you're going to bore the log, is to drill pilot holes from both ends. That way you're error is halved. It's still not likely that the holes will match perfectly, but you stand a good chance of eliminating the offset when you bore to full size. If you can run an undersized shaft through end to end before reboring, then so much the better. Following up with an apparatus like Greg B describes might do the trick.
And keep looking into the twin prop option http://media5.hypernet.com/~dick/ubb/frown.gif
09-05-2001, 10:51 PM
A suggestion from an amateur- you might try drilling small holes in from the sides as your drilling progresses to determine the position of your drill. If it stays on target, keep drilling. If it veers off go to the other end.
09-06-2001, 09:55 PM
The pipe/drill will not veer much of any, but rounded over bolts run into Syd's holes. kept near the drillhead, would allow one to "tweak" the hole to perfection.
09-06-2001, 11:05 PM
They bore holes, the hard way, in gun barrels, donít they ?
I once did a four-foot hole in the solid butt of a hollow mast for electric wires.
My approach was to practice on scrap pieces until I felt that I understood what I was getting into. I did many, many pieces. The first discovery was that the hole pretty much followed the grain of the wood of the practice pieces. My method, which I would not recommend for your case, was an extension on the shaft of a regular auger bit. Not very rigid, and there was nothing to keep the alignment after the front did the cutting. I suspect that the spiral was also taking some wood out. If I did it again I would use a much more rigid set up, with some means for supporting the shaft, centered in the hole and not wearing away wood. I would also give a lot of thought to chip removal. I had a few tense moments, when I though that I had jammed the bit.
The one thing I did when I bored the actual mast was to rig a small light bulb (proctoscope) that I could feed into the bore to check the progress every time I removed chips. I had a measured spot on the shop wall that I could sight from. Simple arithmetic yielded the deviation. The plan was to stop short of drilling through the side of the mast.
The actual bore was not perfect, but it didnít break out, and I was able to feed the electrics through it.
09-06-2001, 11:39 PM
A core drill made from a heavy pipe will cut straight. Your problem is the aiming. A small mistake can be a big one at 14'.
09-07-2001, 11:28 AM
I am surprised Glenn Ashmore hasn't jumped into this one. I seem to remember him drilling a similar shaft hole in Rutu. He found the center of the back of his drill and marked it with an X. Then he set up a laser beam at the correct angle. He then centered his drill bit on the mark and kept the X centered on the laser beam. If I remember right he came out pretty darn good!
Someone should see why Glennn hasn't answered as it seems like a great answer to this problem.
09-07-2001, 12:18 PM
Originally posted by Sailing-Randy:
Then he set up a laser beam at the correct angle.
Sounds like a great idea, only rather than having the laser set to "mark" crank it up to "drill".
Anybody consider a combination answer to this? You could drill a hole for the first and last few feet, and cut a rabbit (slot) for the center long distance portion that would be covered by a dutchman(as mentioned early in the thread). The slot concept certainly is a proven method that was used years ago. You could use a further combination (hole-slot-hole-slot-hole) which would eliminate much of the drilling, yet leave much of the deadwood integrity.
09-07-2001, 07:15 PM
Boring of shaft logs is not rocket science.
It was done quite frequently. Yards had a dedicated jig setup for this.
As I briefly described in a previous post to this thread.
The jig was a fabrication of angle iron and sliding brackets with bearing seats that were adjustable lengthwise. After, and I cannot stress this enough, the pilot hole was drilled and then followed with the first extension usually no more than twice as long as the original bit and then a third so much longer and then the barefoot auger would be brought into play.
Yards had racks of these bits already welded up and ready to go. You didn't try to bore a 2 or 3 inch diameter shaft hole. You did a 1 inch hole all through and then started with the boring bar. I cannot recall being more than 1/2 inch off center in 22 feet
doing some flat bottom tugs for use on the Sacramento River. First time I saw laser used was at Dakota Creek in Anacortes, WA..
Our shop and house was across the street and just at dusk this van showed up and a couple of fellows got out and set up this stuff and in a little while I heard the screetch of metal. I wondered over and got my first introduction to laser sighting. That was in steel and the shaft log was already fabricated into the hull but the final alignment was done with that laser sighted boring bar. Took them 2 nights to get it done but I doubt if they were more than a 1/16th or so off when done. The shaft log was a big honking piece of extra heavy walled tubing to begin with. Lots of swarf on the ground when they were done.
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