Skeg Alignment - are we on the right track?

[formerlyknownasprince]

We currently have the intermediate skegs shown in this picture off the boat whilst we replace the electrolysis-affected planks that they were bolted to.

http://www.imagestation.com/picture/sraid99/p091edc021904f8a6a97ef6f917507452/f9e99fff.jpg

We blew the starboard gearbox up on the way to the slip and had an almighty difficult time removing that shaft - resulting among other things in my spine rotating on my hips and a visit to the Chiropractor. The Port-side shaft is shown partially out - it took only 4 more turns to slip it right out. We are taking the shafts in to check for any bends on Tuesday. I think the problem may also involve a misalignment between the shaft log and the two skegs.

Given that these 2" shafts are quite flexible, I am proposing to re-install the intermediate skegs using a piece of 2" tube, which will be much more rigid and to use epoxy as a means of getting the right thickness bedding block. That is, fit the skeg in the right spot, held on the temporary pipe and squeegee in some epoxy, let it set then bolt it up and remove the pipe. Is this the best way to do this?

The shaft log is shown below, along with the Stainless Steel bolts that someone has put in at some stage. We are replacing these with bolts made from copper rod to avoid further electrolysis problems.

http://www.imagestation.com/picture/sraid99/p3c2d3d6731b7f293f4b599f342c3d0fd/f9e99ffb.jpg

Whatcha think folks?

Ian

[Ian McColgin]

I've seen folk use a lasar, even a flashlight, from the inside to set up a target. Have a bit of black paper with a white target like chross hairs and concentric rings to locate one strut at a time.

I think that might be more secure and less likely to induce small errors than a pipe, which could be deflected a bit just by screwing down the struts.

Interesting that you have two. Even with a fairly long exposure, I've not seen that before. Is it that the shaft is relativly light for the HP or perhaps someone likes really torturing whoever does the allignment.

G'luck

[Allen Foote]

Sure, that would work....just remember.....

ALIGN THE ENGINE TO THE SHAFT.

Not, the shaft to the engine. So, get the stutts in so the shaft is "ball park" and go from there.
That gear box may have blown because it was bolted to a shaft that was not aligned and the forces at play to "twist" the gear innards blew the seals ect.... :confused:

[ 01-18-2004, 10:17 AM: Message edited by: Allen Foote ]

[Phil Young]

Copper's not all that strong, should the bolts be bronze?

[formerlyknownasprince]

Others have wondered where to get bronze rod in the past.

We are looking for bronze bolts tomorrow for the six floors (three replacement, three to replace the timber cap over the shaft logs) that we are fitting this week. The keel bolts are copper, by the way.

Ian

[cbob]

Ian, Like to comment and ask ask several questions and perhaps comment more later. We call those skegs intermediate (forward in pix) and main (aft in pix) struts. We call the skeg the extension below the keel upon which the boat rests, only one. It appears what we call a shaft log casting, usually inside the boat attached to a flexible stuffing box, upside down on the out side? or is this possibly a housing for a cutless or other type bearing at the aft end of the shaft tube, inside this is the shaft tube, usually bronze or lead pipe/tubing, sometimes nothing, but a hole in the wood.
First, proper alignment requires all the bearings be in reasonably close axial alignment, concentric from end to end, including the gearbox output bearing, 90 degrees to the coupling face.
Then the strut mounting mounting pads must be substantial, afterwhich struts can be mounted, so that the bearings are concentric at each end and on a line from the center of the aft end of the aft strut bearing bore and the center of the gearbox output flange. You most likely know all this, but included here just in case.
I have used the try and fit method using sheet lead as a sort of shim which can be hammered thinner as required, between the wood and strut flange (palm), with cutless bearings so that when the shaft is in place it can rotate smoothly, keeping in mind that you want this to happen also after the boat is afloat, rotating by hand at the disconnected coupling, with the boat in it's normally loaded condition also that the weight of the shaft is more or less equal at each bearing, except for the main strut, as it's also supporting the weight of the propeller.
The engine may need to be repositioned to centerlize the shaft in the shaft (stern) tube, which would need to be done/checked prior to positioning/aligning the intermediate strut. As stated, the shafting is somewhat flexible, which is why there is a rule for the maximum distance between bearings verses shaft diameter, to prevent vibration and whipping.
And as was also stated if this isn't pretty close, misalignment will lunch some more gear box bearings, or boxes for that matter. This can be done right, but might take a while. BTDT, go for it. cbob

[formerlyknownasprince]

Oops - bad terminology on my part - shows why I got into strategy and marketing rather than engineering.

A couple of things about my boat. The shafts weigh 150 pounds each (plus or minus) - 2" shafts about fifteen feet long. Not easy to play with when things are out of alignment. The strut mounting pads were not good. We replaced the main strut deadwood and bolts in August 2002 and may have (but did not appear to have) changed the alignment. The starboard shaft was also stiff both before and after we did this, but we did not get it out at that stage, as we were replacing the transom as well and after 20 days straight, we had had it.

We have milled (thanks Paul & Scott) and shaped (thanks Barry) six new floors to repair and strengthen the shaft log and strut areas and will fit these over the next two days (hopefully). Then we need to get the strut alignment right, at least as far as the stuffing box, so that the boat can go back in the water.

We are now looking to do this with water pipe (much stiffer and lighter than the solid shafts) with bushes machined to fit where the Cutless bearings are (much easier to insert than a continuous shaft). I like the lead idea. Whatever was in there before was brittle.

I'll report back later.

Ian

[Ian McColgin]

Fifteen feet is almost too long to support without an intermediary or pillow bearing. In great lengths, some shafts bend under the torque load and start to whip about. The foreward of your two struts is really a pillow.

But it might not be too long. Were I you, I'd consult with a good prop and drivetrain person. If you can go straight from the shaft log to the after strut and cutless, allignment will be much much easier.

Most pillow bearings I've dealt with had adjustable mounts so that you could get fore and aft set up and then make the pillow fit that.

It's highly probably that the extreem difficulty of alligning three bearings with none of them adjustable in use is a large part of the boat's problems.

Short shafts are divine. When I went to allign Goblin's engine the first time it was huge work to pull the coupeling. Hadn't been done in years. Got it loose and the back of the engine fell an inch. It seems that the rear engin mounts were shot and the engin was essentially self-alligning.

Back to your boat, can you give bigger pix to show the whole unit? What is she and what's she meant for? Dragging the props out so shallow is unusual to my eye.

[cbob]

Ian, I dont understand how the (hollow- 70 percent lighter) pipe could be less bendy than the shafting, but a lot easier to handle. Sounds like what you'r trying for is only ball park, inasmuch as the main strut has already been possibly re-positioned? Anyway, never done this, but it's a thought, lighter PVC pipe, with a laser thing at one end and an target at the other, or at each each end of each bore with the cutless' removed, in a progressive fashion. Way back when this was done with a taught wire,never saw it done, but describes the principal. Did this once with a crosshair telescope mounted 90 degrees to the gear coupling and targets at each end of each bearing, rotating the shaft and progressivly. scribing a circle from which to align boring bar setup.
For preliminary setup, would use a flashlight rather than a laser, to avoid one eye blindness. Windows could be cut in the pvc at each bearing, and if properly accuratly and temporarly bushed at each bearing, would provide axial, but not center alignment, which might be deternined by observation of a target inserted through a small window and observation through another. Excessive bending of the pipe won't occur at the bearings where it's supported, and slight sagging in between bearing bores won't matter.
Another thought along these lines, talk to a gunsmith and get a borescope that can be perfectly bushed central to the aft strut bore and aim the strut, when in place, at the exact center of the drive coupling, then by targeting, the same for the intermediate, also the drive flange must be exactly 90 degrees to this alignment line, so engine (re)alignment is also an element in this exercise.
Rember also, the assumption is that the hull alignment will remain the same after launching.
Are there any more bearings between the intermediate strut and the gearbox output bearing? Whats the distance between bearings?
Later, cbob

[formerlyknownasprince]

The pipe, being so much lighter than a solid shaft will not sag like the 2" shaft and will be easier to put in and move because we are bushing it to 2" only where the Cutless bearings are. We had major problems with sag when we had the main struts off last time.

Here is the boat, Grantala, a 1938 Holmes Bros built to an AM Deering (Chicago) design which was featured in July '37 Rudder magazine. Sorry about the unflattering angle. We have left the cabin back off to make it easier to do the fitout. We had planned to repair the transom damaged by an idiot houseboat renter this time on the slip, but it won't happen yet.

http://www.imagestation.com/picture/sraid101/p3b65f8c91c26419c081e9d9340be3e55/f9dff0d1.jpg

This is the current state of the planking repairs. Still to complete fastening of the new ribs and caulking of the planks. Only one of the six new floors in so far too. We were concerned about the closeness of some of these plank joins but the additional three floors are being used to overcome potential problems here. The intermediate struts will go back on this Friday or Saturday.

http://www.imagestation.com/picture/sraid101/p034ed4020fe256173bac0156744bc575/f9dff0ba.jpg

Time to rest my weary bones.

Ian

[Domesticated_Mr. Know It All]

Keep up the good work Ian. She's a wonderful boat. smile.gif Thanks for posting the photo's. ;)
Peace---> Kevin in Ohio