mast splicing

[DasHaus]

I'm considering a similar project, but was planning on using pan head screws so I could leave as much metal as possible under the screw. I may be confused on the terminology but wouldn't both a flat and oval head require countersinking? Is there a reason not to use pan head screws? Mike, I'm curious, where are you planning on splicing the mast. Are you putting the splice at the deck or further up the mast? Would there be an advantage to moving the splice to a less stressed area of the mast, maybe slightly above the gooseneck or would that mess with the mast bend?

[Douglas]

In my opinion, pan head, or round head screws come to bear flat on the metal underneath the head,,,,, where as flat head and oval head need to come to bear in counter sunk holes.

There are round head machine screws in various places on my boom, and a few times I have had to use vice grips on the screw head to break it loose.

What ever the fastener, ( I think Brion, mentioned on this forum), corrosion will eventually effect it ! SS, Monel, Aluminum and Steel fasteners, included .

A nightmare of mine would be while on hardstand, the mast is lifted out with a crane, and the sleeved joint parts under shear loading on the fasteners, and someone on the ground gets hurt, or worse, you damage your boat with the falling lower mast section.

Mike, this is a dam good question of yours,,,,,,,
" 3. Is the purpose of the taper to gradate the stiffness as to allow the bending loads to dissapate? " ,,,,,, hope we get an equally good answer !

As you suspect, an untapered sleeve end , being a hard edge inside the mast, might just be where the mast could buckle and bend again .

On sectioned sleeved dinghy masts, I usually don't see a taper on the sleeve end, just a rounded edge .

Douglas

[osteoderm]

I haven't had occasion to splice many masts, but I've certainly had to deal with many many fasteners on masts, broken, mangles, frozen, or otherwise!
Based on nothing other than personal observation/experience, panheads are weaker than tapered (ie., needing to be countersunk) screw heads, on account of the more abrupt transition between the shank diameter and head diameter. Additionally, countersunk screws show more metal-to-metal surface area, equating to a better distribution of force and less chance of loosening. Panhead screws seat best on a flat surface, whereas a countersunk hole can be applied to most any profile.
Agreeing with Douglas, ovalhead screws have more "meat", which can certainly make them easier to remove when needed! Here in the islands, ovalheads are harder to source, but I can't see how the barely-protruding head has any other drawbacks, unless the splice is at some area where halyards.sails are likely to chafe.
While a self-tapping screw will "draw" pieces together, I can't help but wonder if greater strength and serviceability might be had from tapped-in machine-screws, provided the internal sleeve fits closely enough that "drawing in" is not required.

[Russ L]

Hello all,
Good thread eh!
For a corroded & stuck fastener, try vinegar, not caustic, it can dissolve the white powdery stuff. If the mast is not anodized then a bit o' heat can work wonders.
On the subject of screws, oval & flat head can be considered equals mechanically, however oval are much more pleasing asthecially. Oval head screws can tolerate slightly different countersink depths and still look good.
On the practical side, you can assemble the splice and drill, countersink & tap without further disassembly. Pan head screws would normally require two step drilling (unless you are very brave and willing to try without making the tap hole too big) and bunch o' pan heads just doesn't look as nice.
The splice material taper AND rounded "taper bottom" are to prevent stress risers. It's a stress riser that caused the damage in the first place (the deck opening).

Cheers, Russ

[Brian Duff]

more important (IMO) than the fastener type, splice plate taper, or splice location, be sure that the mating ends of the two extrusions being spliced are a perfect fit. The ends must be square and true. The rig will not tune straight or bear compression properly if they joints are not perfect. take the time here to get it right. I spent 5 hours once until I was happy. Oh to have a large chop saw for masts !

Most mast splices are not glued, I am the only rigger I know that does this. My thought is that there are no disadvantages to the glue, but the possible advantage of a more even transition of stress is worth the effort of the gluing process. It is not necessary to use adhesives.

Flathead or Oval head screws are stronger because of the less dramatic angle at the bottom of the head to the shank of the screw, (they also offer less resistance to wind, and look better).

[mikestevens]

Brian,
Thanks for sticking with this thread. I give a lot of credibility to what you have been saying. In your first post you suggested flat head fasterners. I want to confirm that you are then countersinking. And that seems to leave you with enough meat to tap?

Also, Das Haus, I know your boat. Colombia Defender right. I think I saw your boat up in Block on my way down to VA and then I saw you again in Norfolk. Could that be? The current name on my boat is RIP Curl, but that is changing.

[Brian Duff]

Yes, flat head machine screw fasteners. Only the mast wall gets a countersunk and clearance hole, the splice plate receives the tapped hole . IF the head of the #10 is too thick, use # 8's (or a diffenet angle or undercut screw head, or any of so many options...)
I do not know what mast you have, but guessed at its wall based on the dimensions you gave. It is important to obtain the 'drawing in' of the splice plates to the mast wall. This is another reason that the splice pieces shouldn't be one piece. When splicing something like a 'pipe' mast where it is easy to obtain an extrusion that fits well inside, we split it lengthwise so the fasteners can draw the plates tight to the mast wall. I usually use three complete rows of fasteners each side of the splice, then two more rows with half as many fasteners.
Russ L is right in that the idea is to avoid stress risers. We also (sometimes, depending on the budget of the client) thin the plates toward the ends, as as antoher way to taper the material away. Most spar builder splices I have worked with have not done either type of tapering. some of the builders of spars use just three rows of fasteners each side, with a rather closer fastener spacing. Some have way more fastneners...

call your spar builder and have a chat with them about your plans, thats what we do.

heat works to loosen corroded stuck fasteners on all masts- anodized, powdercoated, awlgrip, or bare, you just gotta be careful ! Impact tools also are very effective at removing stuck fasteners. PB Blaster can help too. If a splice with mechanical fasters was corroded enough to "fall" apart, that should be clearly visable to even an untrained eye. Use some 'goop' to help slow the corrosion of fasteners in aluminium.


Self tapping screws are only to be used on wood. Do NOT use self tappers on aluminum or fiberglass, as it is WRONG. Self tappers are weak becasue they have both a smaller root diameter and must have less thread grip as well (in such hard materials) becasue the threads cannot compress the material away like in wood. It seems to me that self tapper screws in fiberglass are alway leaking, and the surely delaminate the fiberglass where they go through. thats for another thread though, if someone wants to start one....

[mikestevens]

Thanks for the reply brian.
If the splice is 12" long, plus the 3" tapers, than that gives me 6" on each side, not counting the tapers. If I make the first row 1" from the edge of the splice, then that leaves me with 5" until I get to the taper. if I follow your spec of 8X the thickness of the screw or about 2" apart It seems I would have room for only for 3 rows on each side of the splice.

Now for a new question. I have stripped the mast and was wondering how to do a dye penetration test to the standing rod rigging. Easy? Hard?
Mike.

Also, for managers of tghe site; is ther a way to post images?

[Russ L]

Hi Mike,
Your source for the dye penetrant kit is likely going to be an auto parts supply that has engine rebuilders as customers.
The kit will have a cleaner, penetrant & developer. Follow the directions on the cans... easy!
Brion recommends a small microscope to check for cracks.

To post images: you include a link in your messages to images that are stored elsewhere on the net. No provisions to send images to the Spartalk server.

Cheers, Russ

Originally Posted by mikestevens

Thanks for the reply brian.
Now for a new question. I have stripped the mast and was wondering how to do a dye penetration test to the standing rod rigging. Easy? Hard?
Mike.

Also, for managers of tghe site; is ther a way to post images?

[Wannafish]

Originally Posted by mikestevens

Now for a new question. I have stripped the mast and was wondering how to do a dye penetration test to the standing rod rigging. Easy? Hard?
Mike.

Mike,

You might also want to do a web search for a dye penetrant called "Zyglow". After it dries you shine a blacklight on it and the die in the crack shows up really well.

Rick