Mast Base Rivet Holes Sheared
- Thread starter GGordonWoody
- Start date
Thanks CC.
Your suggestion matches that of a revered member of our club. I guess my primary concern was for the load straight down on the base of the mast. The thought of that 30' pole pressing straight down on the base, and then crushed down by the shrouds, forestay, boom, mainsheet, vang, and sails, along with the impulse forces of waves trying to pound it through the bottom of the boat, well, left me a bit wary. More holes seemed to imply less meat to resist all that force, maybe leading to the thing deforming and splaying out at the base. I just don't know, so I put my case before my fellow SBOs, whose opinions I value far more than my own.
Cutting the mast down would mean losing about 1 3/8" [Edit: more like only 3/4", sorry], and losing headroom in the cockpit (not that I need it - har har, being of average height for a blow-up blow hard). The shrouds and forestay are likely ok, but the angle of the vang would change, leading to another unknown.
As for removing the shrouds seasonally, ugh, I'm just anal about getting everything off and out for winter. She's 23 now and I try desperately to preserve every piece. No problem, as long as you follow the checklist (manual) in the spring.
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Thanks Peter. My greatest concern was for adding more holes to the base of the mast, which seems to me to be under significant load. There's a bit less material along the bottom edge right now. I didn't want to risk deforming the shape or having the mast "shorten itself" (crumple) under load from the shrouds and forestay. I have already noticed a slight deformation on the forward edge, likely due to falling forward a bit before the baby stays caught it.
I would not think it would splay out unless it has a lot of material removed. How many holes can you reuse? I suppose you could put something like a long stainless hose clamp around the extrusion right above the foot to help keep it in shape, maybe right over the rivets. Or, if you can transport the mast (maybe on the boat), there is a good metal shop in Hawley that might be able to wrap an aluminum band around the mast and weld it shut, if they can do so without softening the extrusion.
That is a solid idea. Can you go up one size on the rivets and reuse some of the holes... then drill a few new ones if you need to.
I'd be concerned about it splitting at the top of the hole were the rivet tore out. There is not enough material on the base cap to get a fastener on both sides of that hole to keep it from splaying out but adding a strap of some sort might be a solution.
A photo of the mast base would help make a better judgement as to there being enough material left on the base to support the stress. Im assuming all four holes were ripped out when the mast kept going forward. You mention that there is a slight deformation in the forward edge of the mast. That is why I said earlier that the mast needs to fit square, flat, against the foot. That way the stress of compression is evenly transmitted from the mast to the foot. If the mast base is curved, only a small portion of the mast material is actually supporting compression force and it could deform under stress. The good news is the mast material is very soft aluminum, and can be shaped and corrected flat easily with a hand file. GSBNY posted in this thread a great idea used in his repair of using a large hose clamp to mark the mast for cutting. You could do the same by using a hose clamp as a guide for filing the mast square. Just test fit it to the mast foot before calling it done. Also, when drilling new holes, make sure the foot is pressed firmly into the mast when the holes are drilled so when its riveted the stress really is conveyed by the bottom edge of the mast and not the rivets. In other words the rivets should be doing nothing once the mast is up.
If the original rivets tore out little triangles, then yeah maybe cutting off the bottom would be the best answer. I really dont think your concern of losing headroom by shortening by 1"-1.5" is an issue. I doubt you would ever notice it because you can raise the boom with the topping lift. And when sailing, the height changes all the time anyway.
Dont over think this. It needs to be done right, but its not that hard. Just take your time. And of course, do it right.
Thank you sir. I have an alternative "doubler" idea which doesn't render the mast foot into swiss cheese. I'll share it as soon as I can model it on paper. Thank you again.
Thanks man. The break tore out two large triangles below the holes and I was just worried that mast wt + shroud force + forestay force + vang force + main sheet force + lunar gravitation might splay the bottom out after drilling more holes. I know I worry too much.
This looks excellent, and is another example of how powerful this forum is. I can't even conceive of a problem. It looks factory, and you can remove it if you ever need to replace the rig. Yes, I will definitely consider this... Thank you for posting!
If the doubler idea works, great. If not and if you feel you don't have enough material at the base to support the mast, I'd use the hose clamp idea as a cutting guide and cut off say 1 or 1.25 inches - I'd use a rotary tool and cutting wheel carefully then maybe a grinding disc to square it off. If you know your shrouds are already on the short side, you could use it that way. But to avoid having to redo the shrouds, I'd follow the advice above to install a spacer of starboard or similar, equal thickness to the loss of the tube length. If it is at least an inch think, I'd screw it to the deck using holes with countersunk recesses big enough to fit the screw heads, and deep enough countersunk to get the heads below the top surface. Then screw the mast base to that spacer. Seems to me it would help get the hinge a bit higher, which is an advantage IMHO. And as long as you are even a little careful, the height of the shroud attachments won't be more than about 1/8 " off, which ought to be well within your turnbuckle range.
Yup - yup - yup! Thank you for detailing the problems with the welding solution. Consider the "down" forces applied to the rig: standing wt + shroud forces + forestay + boom + main sheet + vang + sails, plus the wave impulse forces that want to drive the thing through the bottom of the ship. I was warned about the annealing effect too by a professional welder. As soon as I said "extruded" and "anodized", he went all nervous and jerky. Just getting the TIG to arc through the oxidize layer was a speed bump. "Wait, you gotta grind off the surface? And then you're gonna make it weaker?" Ha! No. Thanks man.
Yeah, I finally read down to that post and I am pretty much sold on the idea. I can't think of any problems, yet, but I have to keep reading. Thanks Pete.
Aaaah, yes. That was my take as well. Rivets would be required on both sides, right? Keep it from deforming. But now we're looking at interior casting meat, and more swiss cheese at the base of the rig. I have a repair "doubler" in mind that addresses the "meat and cheese" issue (haar), but does nothing to reinforce the base. I like your "strap" or "band" solution, similar to wide pallet straps, but would have to be Al or SS, or maybe Ti (that whole galvanic corrosion thing). Thanks man.
Please post pics when you are done. Sounds like an interesting problem to solve.
It looks like the spacer idea would work well. The deck is flat on our H23.5's where the mast base attaches to the deck. I dont know about using a cut-off wheel to cut the mast tho. It will work, but the mast is so soft I feel like its overkill. I'd just mark it in what ever way you like and use a hack saw with a fine tooth blade. Much more control. I would not just cut straight through like cutting a board. I would cut around the mast. That way you will stay on the mark. Clean it up with a file.
Since you just need a very small piece of thick plastic, you may be able to acquire some scrap from a shop that uses a lot of it. It would be interesting to hear from GSBNY on what his material is and where he got it.
EDIT: Actually a quick search yielded this: https://www.tapplastics.com/product/plastics/cut_to_size_plastic/king_starboard/526
12" x 12" x1" $30.70. They will cut it any size you want.
Since you just need a very small piece of thick plastic, you may be able to acquire some scrap from a shop that uses a lot of it. It would be interesting to hear from GSBNY on what his material is and where he got it.
EDIT: Actually a quick search yielded this: https://www.tapplastics.com/product/plastics/cut_to_size_plastic/king_starboard/526
12" x 12" x1" $30.70. They will cut it any size you want.
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Yeah, that's a fancy HDPE they can colorize. Perfect choice - thanks a bunch! I'll just need some longer screws to secure the step. And I totally agree about the saw. Scribe it and hack away! But how do you locate all the existing holes in the foot casting for new rivets? Does Harbor Freight sell X-Ray glasses?
Maybe you could use the piece you just cut off as a guide for the new holes.
Or you take a piece of paper and wrap it around the mast base, punch holes through the paper where the holes currently are located with a pencil and then take the paper to the mast and transcribe the hole location to the new mast foot.
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