My 384 mast is generally in very good condition, considering her age, but after pulling due to unrelated lightning damage, I see that the lower shroud mount has a couple of small cracks at the entrance of the tube that accepts the through bolt for the tangs. You can see that the crack is in the weld at each end of the tube, and is not large, but I don't like to see cracks in major load carrying parts! My rigger says that this can be reinforced by making two SS plates and mounting these on each side of the mast, so that the ends of the thru-bolt are supported, and reduce the bearing load caused by the lowers. The thru-bolt will have to be lengthened by the two thicknesses of the reinforcing plats, of course. He recommended the plates be made in the shape of a triangle (maybe a bit more like home plate on the ball field) and drilling multiple holes and tapping the mast for machine screws. Has anyone done a similar repair?
Lower shroud mast tube cracks
- Thread starter cadiman49
- Start date
Lee,
Actually, there are no plates currently installed. The crack is located on the mast at the welded mouth of the lower shroud mount, where the through bolt that holds the lower shroud tang goes through the mast. The new 3/16" thick SS plates would have one big hole for the tang through-bolt, and several evenly spaced and closely fitted screw holes above the tang through-bolt. The screws would be for attaching the plates to the mast, and the mast would be correspondingly drilled and tapped for them. After the plates are installed, they would serve to support the tang thru-bolt, and take the load off of the cracked weld. I was just wondering if anyone else with cracked tang mounts has repaired them in this manner. I am wary of drilling more holes into the mast, but, my rigger says that this is a much better fix than trying to weld up the crack. He says that the anodizing causes inclusions and voids in the weld bead. Also, welding anneals the aluminum, destroying the temper in the metal, and greatly effects the mast wall strength in the area. My question is, How many screws are needed through the new plates, and how are they spaced. It looks like the new reinforcing plates will be right at the location of the mast splice, so I hope this does not complicate things.
Actually, there are no plates currently installed. The crack is located on the mast at the welded mouth of the lower shroud mount, where the through bolt that holds the lower shroud tang goes through the mast. The new 3/16" thick SS plates would have one big hole for the tang through-bolt, and several evenly spaced and closely fitted screw holes above the tang through-bolt. The screws would be for attaching the plates to the mast, and the mast would be correspondingly drilled and tapped for them. After the plates are installed, they would serve to support the tang thru-bolt, and take the load off of the cracked weld. I was just wondering if anyone else with cracked tang mounts has repaired them in this manner. I am wary of drilling more holes into the mast, but, my rigger says that this is a much better fix than trying to weld up the crack. He says that the anodizing causes inclusions and voids in the weld bead. Also, welding anneals the aluminum, destroying the temper in the metal, and greatly effects the mast wall strength in the area. My question is, How many screws are needed through the new plates, and how are they spaced. It looks like the new reinforcing plates will be right at the location of the mast splice, so I hope this does not complicate things.
stnick
lee nicholas
Rick, thank you .
I'll get out my chair and take a ride up the spar , to see for myself.
Thank you for bringing this to light.. we all should have this inspected ASAP..
I would consult Ted Brewer , I have talked to him.. He is very easy to talk to and grasps concepts fast..
Second choice would be a metal man , Now if you could find a metal man and sailor that would be perfect.. I just happen to know such a person and I'll ask him..
I'll get out my chair and take a ride up the spar , to see for myself.
Thank you for bringing this to light.. we all should have this inspected ASAP..
I would consult Ted Brewer , I have talked to him.. He is very easy to talk to and grasps concepts fast..
Second choice would be a metal man , Now if you could find a metal man and sailor that would be perfect.. I just happen to know such a person and I'll ask him..
stnick
lee nicholas
Rick , I just got off the phone with my friend the metal guy and sailor..
ADVICE : Grind off the anodizing Never use s stainless steel on aluminum Use 6061 Aluminum and west epoxy it in place. do not use any screws !
The plates should be at least 5 inches wide and curved.
Or could be Tig welded.
Hes said if your welder does not agree fire the guy and get a better guy..
Hope this helps.. LEE all the best
ADVICE : Grind off the anodizing Never use s stainless steel on aluminum Use 6061 Aluminum and west epoxy it in place. do not use any screws !
The plates should be at least 5 inches wide and curved.
Or could be Tig welded.
Hes said if your welder does not agree fire the guy and get a better guy..
Hope this helps.. LEE all the best
david_buckley
David Buckley
Rick,
I had the same problem. I had a welder repair by grinding the crack to a bevel and welding. Just inspected it this spring and it still looks good after 6 years and aprox. 8k ocean miles. The method your rigger suggests would not be my first choice because it makes more holes, point loads at small fasteners and the fasteners tapped in tend to corrode making hard to inspect later.
Best,
David
I had the same problem. I had a welder repair by grinding the crack to a bevel and welding. Just inspected it this spring and it still looks good after 6 years and aprox. 8k ocean miles. The method your rigger suggests would not be my first choice because it makes more holes, point loads at small fasteners and the fasteners tapped in tend to corrode making hard to inspect later.
Best,
David
maluhia
Jim Ball
I would guess that every boat is different and gauges are imperfect. But, as I said, over-tensioning can cause issues above and below deck. Rule of thumb, Windward shrouds on a beat should be tight, and leeward should be loose. Mast should be straight at the dock. A good starting point.
terry_thatcher
Terence Thatcher
there are books and parts of books on rigging set up for masthead rigs such as ours. Will provide rough estimates of tension and suggestions on how to judge rigging set up.
I use a Loos gauge to make sure things are "equal" on both sides and to get close to where I want, but as you would read in the books, the set up depends on how the mast and shrouds/stays behave in wind. Some boats, such as racing rigs, are set up to sail with very high loads. I try to run mine at the point where I do not get excessive side to side mast bend in 12-15 knots and work up gradually to where I want to be so I do not over tighten. The fore and aft tension also considers mast bend ( Morgan masts are too beefy to accept "pre bend,") and head stay sag. Finally, a rig that is too loose will also stress the mast itself, with bending and whipping.
I use a Loos gauge to make sure things are "equal" on both sides and to get close to where I want, but as you would read in the books, the set up depends on how the mast and shrouds/stays behave in wind. Some boats, such as racing rigs, are set up to sail with very high loads. I try to run mine at the point where I do not get excessive side to side mast bend in 12-15 knots and work up gradually to where I want to be so I do not over tighten. The fore and aft tension also considers mast bend ( Morgan masts are too beefy to accept "pre bend,") and head stay sag. Finally, a rig that is too loose will also stress the mast itself, with bending and whipping.
Sorry Jim:
I am going to have to take exception to your comments.
1) I find it unhelpful to make a general comment about it being important not to over tension the rig. Nice truism. Terry is also correct in saying that a loose rig can be detrimental. I'm sure most folks on the group understand why both could be problems but it is not actionable without specifics. I asked if you based your comment on specific numbers from the designer or manufacturer
2) In response, you said every boat is different. Perhaps but most of the boats I race have similar rigging and the designer, sailmaker, builder, and/or sailors have developed basic tuning guidelines and numbers for that class. Of course a lightweight racing boat with very bendy, tunable rig is different from the Morgan. I adjust shroud and stay settings on my race boat in anticipation of the conditions in 5 knot increments. I also have lots of adjustment potential on the water. That's not needed on the Morgan but she does benefit from careful tuning.
3) You say that gauges are imperfect. Yes gauges are not perfect but they are generally repeatable. I use a Loos gauge to good effect. Without a gauge, careful measure of elongation can suffice.
4) Your rule of thumb could also be improved upon. What would be tight on a beat in 5 knots and flat water might be unacceptable in 15 and chop.
I know that everyone contributes to the owners group to help others and share the benefit of their years of experience. It is a tremendous resource. Opinions can be useful too. I am suggesting that it would be more useful if we would all be more specific and provide detail when possible
I am going to have to take exception to your comments.
1) I find it unhelpful to make a general comment about it being important not to over tension the rig. Nice truism. Terry is also correct in saying that a loose rig can be detrimental. I'm sure most folks on the group understand why both could be problems but it is not actionable without specifics. I asked if you based your comment on specific numbers from the designer or manufacturer
2) In response, you said every boat is different. Perhaps but most of the boats I race have similar rigging and the designer, sailmaker, builder, and/or sailors have developed basic tuning guidelines and numbers for that class. Of course a lightweight racing boat with very bendy, tunable rig is different from the Morgan. I adjust shroud and stay settings on my race boat in anticipation of the conditions in 5 knot increments. I also have lots of adjustment potential on the water. That's not needed on the Morgan but she does benefit from careful tuning.
3) You say that gauges are imperfect. Yes gauges are not perfect but they are generally repeatable. I use a Loos gauge to good effect. Without a gauge, careful measure of elongation can suffice.
4) Your rule of thumb could also be improved upon. What would be tight on a beat in 5 knots and flat water might be unacceptable in 15 and chop.
I know that everyone contributes to the owners group to help others and share the benefit of their years of experience. It is a tremendous resource. Opinions can be useful too. I am suggesting that it would be more useful if we would all be more specific and provide detail when possible
Being an ex-engineer, the terms "tight and loose", or "a good tug", or 1-1/2" are all about as inaccurate as, well you name it. Quantified forces and deflections are about all we have to go by, as a starting point at least. The Selden manual on rig tuning gives a pretty good description of how to indirectly measure stay tension by using a 2 meter rod clamped to a stay at one end of the rod. Then with the cable tension slackened, by loosening its turnbuckle, the free end of the rod, which is lying along the stay, is marked on the stay with a Sharpie. Upon tightening the turnbuckle, if the recommended stay tension is, say 15% of ultimate tension, then (correspondingly) elongation of the stay under 15% elongation from slack will show up as 3mm from the end of the measuring rod to the "slack" mark that you put on the cable. Different cable diameters are charted by Selden with corresponding elongations at 15%. Doing all of the stays in the same manner will give you at least a measured starting point, and you can thereafter count turnbuckle rotations during balancing adjustments. If you know what your turnbuckle thread lead is, you can calculate the ratio of turns to percent elongation, and get a feel for the forces that you have applied at the pier. The issue remaining is that we don't seem to have any recommendations of elongation in the stays to go on. Selden's recommendation of 15% is based on their masts. If queried, they may be able to provide some numbers from past knowledge of the Morgan 38's, or their own experimentation.
Until a stay tension can be "felt", it will take a fair amount of practice "calibrating" one's tug in comparison to the known tension. I remember doing a similar exercise in the Navy, when one did not have a torque wrench, or enough time to go get one! We got pretty good at applying the correct torques after some practice. Obviously, a seasoned sailor will have "the hand" without knowing what the numbers are, but until one gets there, some starting exercises probably would be good.
Rick, Xanadu
Until a stay tension can be "felt", it will take a fair amount of practice "calibrating" one's tug in comparison to the known tension. I remember doing a similar exercise in the Navy, when one did not have a torque wrench, or enough time to go get one! We got pretty good at applying the correct torques after some practice. Obviously, a seasoned sailor will have "the hand" without knowing what the numbers are, but until one gets there, some starting exercises probably would be good.
Rick, Xanadu
Hi Rick:
In my opinion, once an engineer, always an engineer (and proud of it).
I agree with your comments. I use a Loos pro gauge to set up our 382. Lacking specific numbers I set the shrouds at 10% of breaking strength and forestay at 15%. I've been happy with the results.
The measurement of elongation is a good, simple approach if you don't have a tension gauge. (Described on page 28, 29 of the Selden manual) A digital caliper helps. I recommended it to a friend
setting up a boat with rod rigging since my gauge wouldn't work.
For those who haven't seen it, the Selden manual has good info applicable to all. See http://www.riggingandsails.com/pdf/selden-tuning.pdf
In my opinion, once an engineer, always an engineer (and proud of it).
I agree with your comments. I use a Loos pro gauge to set up our 382. Lacking specific numbers I set the shrouds at 10% of breaking strength and forestay at 15%. I've been happy with the results.
The measurement of elongation is a good, simple approach if you don't have a tension gauge. (Described on page 28, 29 of the Selden manual) A digital caliper helps. I recommended it to a friend
setting up a boat with rod rigging since my gauge wouldn't work.
For those who haven't seen it, the Selden manual has good info applicable to all. See http://www.riggingandsails.com/pdf/selden-tuning.pdf
Hi Steve,
Sorry I haven't seen you at the yard. I was there a couple of days ago, but no Steve!
The crane company is Grace Crane. You can set up everything with Crystal when you get ready. If you can team up with another owner(s), the cost gets better. Expect 1 day to a week lead time.
Are you going to be working on Arrrrrgh! all this Fall? Xanadu will be in storage for a while, so I won't get down there very often, but might get there soon to pull the dink out of the water. Will look you up.
Best,
Rick
Sorry I haven't seen you at the yard. I was there a couple of days ago, but no Steve!
The crane company is Grace Crane. You can set up everything with Crystal when you get ready. If you can team up with another owner(s), the cost gets better. Expect 1 day to a week lead time.
Are you going to be working on Arrrrrgh! all this Fall? Xanadu will be in storage for a while, so I won't get down there very often, but might get there soon to pull the dink out of the water. Will look you up.
Best,
Rick
Alan,
Getting back to rigs, how did your friend make out with the elongation measurements?
I was thinking that it might be tough to get a good measurement from a Sharpie mark, but with the calipers, one could take a slack measurement from the rod end to the upper or lower edge of the mark, then subtract that from the loaded stay distance. I guess that might be more accurate. Maybe a hose clamp could provide a hard edge to butt a caliper jaw against, instead of the mark.
Rick
Getting back to rigs, how did your friend make out with the elongation measurements?
I was thinking that it might be tough to get a good measurement from a Sharpie mark, but with the calipers, one could take a slack measurement from the rod end to the upper or lower edge of the mark, then subtract that from the loaded stay distance. I guess that might be more accurate. Maybe a hose clamp could provide a hard edge to butt a caliper jaw against, instead of the mark.
Rick
I gave him the instructions and tools and left it with him so I don't know how he faired.
I provided him with an old piece of sail track 2 meters long and a hose clamp to attach it at the top to the shroud with the bottom end of the track a set distance above the turnbuckle swage. Then he simply used the digital caliper to measure the change in distance between the end of the track and the top of the swage. The rod rigging would elongate under tension but not the sail track clamped at one end to it.
As shown in the Selden manual 10% = 1.4mm, 15% = 2.1mm elongation. The digital caliper can read 0.1mm with a good degree of accuracy for a resolution of about 75# on 10mm rod rigging.
I provided him with an old piece of sail track 2 meters long and a hose clamp to attach it at the top to the shroud with the bottom end of the track a set distance above the turnbuckle swage. Then he simply used the digital caliper to measure the change in distance between the end of the track and the top of the swage. The rod rigging would elongate under tension but not the sail track clamped at one end to it.
As shown in the Selden manual 10% = 1.4mm, 15% = 2.1mm elongation. The digital caliper can read 0.1mm with a good degree of accuracy for a resolution of about 75# on 10mm rod rigging.
