Mast Splice Location

[GlenM]

Before hurricane Ike I had a 45' Isomat NG-70 mast. It broke at the spreaders that were welded on. The bottom half of the mast is to damaged to be used from contact with the marinas travel lift. The top half including the mast head and all hardware are in good conditon. I am considering a splice. I have found some NG-70 extrusion and an internal sleeve custom made for it.

Should I put the splice where it is broken? (after cutting out damaged area the joint seam will be about 10 inches above where the spreaders are located). The spreader bases will be fastened into the lower part of the sleeve material.

Or should I go up higher on the mast with the splice? If so how much past the spreaders?

Mast load challenged here.
Thanks
Glen

[Brian Duff]

mast splices go just about anywhere, if you have a look around you will see that.

I think 10" above the spreaders is actually one of the better choices, so put it there.

DO NOT USE RIVETS

[GlenM]

This board has been a great help.
From reading other post on this subject these are the steps I am going to use.


1) Both mast pieces are to be perfectly square with tight fitting seam.
(This sounds like the hardest part)

2) Mast splice material should pull tightly up to each side, even if it means cutting the
one piece sleeve in two.

3) Reverse bevel and round the sharp edges of the sleeves to reduce single load points.

4) Drill and counter-sink four rows of screw holes in each section. Staggering the holes in
every other row.

5) Use 5/16 flathead SS NC thread machine screws. Length sized to just clear the sleeve internally.

6) Seal screw threads going into the aluminum to prevent corrosion.

I hope I didnt leave anything out.
Thanks again
Glen

[Brian Duff]

I, personally, would change the rules there a bit.

1) This is the hardest part; do a good job or none of the rest will work right
2) Do not use a one piece sleeve for that mast, that would be waste of time and money, and it won’t work well, use two pieces to do just the sides, maybe one more for the front panel, but not absolutely needed - the sleeves will be 3X mast fore/aft chord - on your stick this is 24"
3) Also make a taper to the splice, i.e. the back edge of the splice will be longer than the front edge by 4" or more -
4) Your first set of holes will be 4 fastener diameters from the joint, and then you will set up a staggered pattern at 8d apart until you have used up the whole sleeve of fastening area
5) Use 1/4"-20 FHMS undercut heads 1/2" long - if you use normal heads you will just bottom out on the plates before achieving clamping pressure
6) Use Life Seal to seal threads, if you really care use Hysol 9342 (or similar) to bond the plates to the mast wall - this is a waste of time unless you prep the inside of the mast for adhesion! Anyway, not needed and most masts go together 'dry' except for something on the screws.

Oh, and of course - this job should only be completed by an experienced rigger after consulting with a naval architect, a yacht surveyor, and the insurance carrier for the yachts' coverage

[CapnVan]

[quote=GlenM;4406]This board has been a great help.
From reading other post on this subject these are the steps I am going to use.


1) Both mast pieces are to be perfectly square with tight fitting seam.
(This sounds like the hardest part)

One method that I have found to work is as follows:
a) Cut the two mast pieces to be "pretty close"
b) Make a pair of short temporary sleeve-plates ( 6 - 8 inches total - 3" - 4" into the mast sections)
c) Drill and tap these short sleeve-plates and machine screw into one mast section
d) Insert the short sleeve-plates into the other mask section
e) Lash/Serve two lines to the "high" side of the splice - one on port the other on starboard
g) Using the winches on the base of the mast (if present), blocks and tackle, come-alongs, etc. tighten these two lines, thus drawing the splice together.
h) Align the two mast sections by sighting down the sail track, and the cheeks, and adjusting until they're perfectly straight.
i) Drill and tap two more machine screws per side onto the opposite side of the splice from step "c"
i) Take a carbide bladed circular saw, adjust the depth of cut to just over the wall thickness of the mast sections.
j) Over-cut the "pretty close" seam. The two mast sections should now match perfectly.
(NOTE: WEAR EYE PROTECTION, GLOVES, LONG SLEEVES, AND BUTTON YOUR SHIRT UP ALL THE WAY DURING THIS STEP !!!)
k) Remove the short temporary sleeve-plates, and proceed with installation of the permanent sleeve/sleeve-plates/etc, using the existing holes (from the temporary plates) as the first set of holes.

I like to re-use my Lashed/Served lines to snug-up the sections on the permanent plates, too.