Installing a new inner forestay.

[dexneverathome]

I’m installing an inner forestay. I need to install a new tang on the mast. Any recommendations on fixings. I want to install a Seldon Inner Forestay fitting.
Option 1: Rivets… what type?
Option 2: Tapping a machine thread 6 mm in to the mast and using 6mm 316 bolts.
Option 3: open to suggestions…

 

[Hoolie]

Rivnuts? A whole range of sizes and seemingly easy to install. I haven't used them myself but they have come up from time to time on here.

 

[dexneverathome]

Rivnuts? A whole range of sizes and seemingly easy to install. I haven't used them myself but they have come up from time to time on here.

Rivnuts…. Not heard of these…. Thank you. Checking them out now.

 

[dexneverathome]

Rivnuts…. Not heard of these…. Thank you. Checking them out now.

Just looked at these…. A great suggestion… Thank you

 

[vyv_cox]

Rivnuts are excellent for connections that need to be disassembled occasionally. I have them on my boom end fittings for example. But they are probably less strong than rivets and hardly needed for this application. I would just use rivets.

 

[davidej]

I would just use rivets.

Presumably Monel not aluminum?

 

[vyv_cox]

Presumably Monel not aluminum?

Personally no. I would use aluminium alloy rivets (5xxx material) not pure aluminium (1xxx). You have to search for them, RS and others do them. Use Duralac.

 

[dexneverathome]

Rivnuts are excellent for connections that need to be disassembled occasionally. I have them on my boom end fittings for example. But they are probably less strong than rivets and hardly needed for this application. I would just use rivets.

If I go for rivets, what is the best option?

 

[dexneverathome]

Personally no. I would use aluminium alloy rivets (5xxx material) not pure aluminium (1xxx). You have to search for them, RS and others do them. Use Duralac.

Why 5xxx Ali instead of Monel?

 

[BabaYaga]

I think you will find that the Selden fittings for inner forestay come supplied with fasteners. Machine screws in the case of nose tangs, monel rivets in the case of the o-ring type.
https://support.seldenmast.com/files/1456490409/excerpts/595-808v7-E-20-27.pdf

 

[dexneverathome]

I think you will find that the Selden fittings for inner forestay come supplied with fasteners. Machine screws in the case of nose tangs, monel rivets in the case of the o-ring type.
https://support.seldenmast.com/files/1456490409/excerpts/595-808v7-E-20-27.pdf

Ah.. okay.. Thank you BabaYaga, I wasn’t aware. I shall wait now to see what comes in the post.

 

[vyv_cox]

Why 5xxx Ali instead of Monel?

Monel is a lot tougher and difficult to set. 6 mm ones need a very powerful gun. 5xxx aluminium alloy has almost the same strength, is very similar in composition to the mast, so no galvanic corrosion. And is far easier to use.

 

[dexneverathome]

Monel is a lot tougher and difficult to set. 6 mm ones need a very powerful gun. 5xxx aluminium alloy has almost the same strength, is very similar in composition to the mast, so no galvanic corrosion. And is far easier to use.

I’ve just found out that Selden supply fixings with the fitting, so I shall hold fire until I see what they recommend. Thank you for the input. I’m quite a bit wiser re rivets after this post.

 

[William_H]

That forestay fitting to me looks terrible. The entire (inner) forestay load is trying top pull the fitting off the mast relying on grip of rivets or bolts. A far better design for forestay attachment has 2 straps which run from either side of the mast. (meeting in front)So fixings are in shear or better still fit a bolt right through mast one side to the other. So load is on the bolt in shear. You can then fit a sheave block or box for internal or external halyard. But beware again most load will be on the halyard so trying to pull box from mast.

 

[BabaYaga]

That forestay fitting to me looks terrible. The entire (inner) forestay load is trying top pull the fitting off the mast relying on grip of rivets or bolts.

If you are referring to the o-fitting linked above, then you may have misunderstood the design. The base of the eye strap rest on the inside of the mast wall, so no load is taken by the rivets.

 

[dexneverathome]

That forestay fitting to me looks terrible. The entire (inner) forestay load is trying top pull the fitting off the mast relying on grip of rivets or bolts. A far better design for forestay attachment has 2 straps which run from either side of the mast. (meeting in front)So fixings are in shear or better still fit a bolt right through mast one side to the other. So load is on the bolt in shear. You can then fit a sheave block or box for internal or external halyard. But beware again most load will be on the halyard so trying to pull box from mast.

Hi William, thank you for taking a look at the fitting. Do you have a suggestion for something that you feel will distribute the loads better? I’m open to other options.
My intention is to use the forestay for a storm sail, the the loads will not be minimal.

 

[William_H]

Hi William, thank you for taking a look at the fitting. Do you have a suggestion for something that you feel will distribute the loads better? I’m open to other options.
My intention is to use the forestay for a storm sail, the the loads will not be minimal.

f you are referring to the o-fitting linked above, then you may have misunderstood the design. The base of the eye strap rest on the inside of the mast wall, so no load is taken by the rivets.
Hello babagaga yes I can see that the fitting which uses what I call a "saddle" does drop the bottom part inside the mast which would help take the load. Stilol doesn't strike me as being very strong as top could pull rivet/bolt and bottom could cut out the ali of mast over small area. No I have never seen one in flesh.
dexneverhome I don't know what sort of inner forestay fitting you have bought or if you can exchange it. (or even want to) However as I said 2 straps of ss plate about 20cms long 2cms wide with holes in each end 2or3mm thick would do. bend the plates so with one end of each on side of mast witha bolt right through one side to the other, the other end of the plates can come together to carry a clevis pin or bolt on take forestay. Thus bolts and pin are all in shear. (You could use rivets on side of mast as they would also be in shear. (in shear means loads are trying to cut the bolt or rivet in half through the shank. As opposed to "in tension" when load is trying to pull the head off the bolt or rivet)
If you use a bolt do make sure the plate load on each side is rubbing on the unthreaded shank of bolt not the threaded part. (tricky to get length right). PM with photo of what you have if you want more "cheap" advice. ol'will

 

[john_morris_uk]

f you are referring to the o-fitting linked above, then you may have misunderstood the design. The base of the eye strap rest on the inside of the mast wall, so no load is taken by the rivets.
Hello babagaga yes I can see that the fitting which uses what I call a "saddle" does drop the bottom part inside the mast which would help take the load. Stilol doesn't strike me as being very strong as top could pull rivet/bolt and bottom could cut out the ali of mast over small area. No I have never seen one in flesh.
dexneverhome I don't know what sort of inner forestay fitting you have bought or if you can exchange it. (or even want to) However as I said 2 straps of ss plate about 20cms long 2cms wide with holes in each end 2or3mm thick would do. bend the plates so with one end of each on side of mast witha bolt right through one side to the other, the other end of the plates can come together to carry a clevis pin or bolt on take forestay. Thus bolts and pin are all in shear. (You could use rivets on side of mast as they would also be in shear. (in shear means loads are trying to cut the bolt or rivet in half through the shank. As opposed to "in tension" when load is trying to pull the head off the bolt or rivet)
If you use a bolt do make sure the plate load on each side is rubbing on the unthreaded shank of bolt not the threaded part. (tricky to get length right). PM with photo of what you have if you want more "cheap" advice. ol'will

Or put a sleeve through the mast so that either the sleeve protrudes just enough to take the shear load of the plate or just to take the compression loading of the bolt through the mast. The only way I can think of getting exactly the right length of bolt to ensure that the stainless plates do not rest on the threads, would be to get a length of plain round stock and cut it the right length and then cut threads on either end to allow a nut and washer either side. Either way it’s much better to sleeve the bolt through the mast to prevent the mast being put under undue compression and perhaps distorting the mast extrusion. Duralac is your friend in the final assembly along with nylocs or lock nuts (or punch the end of the stud to lock the nut…)

 

[BabaYaga]

f you are referring to the o-fitting linked above, then you may have misunderstood the design. The base of the eye strap rest on the inside of the mast wall, so no load is taken by the rivets.
Hello babagaga yes I can see that the fitting which uses what I call a "saddle" does drop the bottom part inside the mast which would help take the load. Stilol doesn't strike me as being very strong as top could pull rivet/bolt and bottom could cut out the ali of mast over small area.

Not just the bottom part, but also the top part of the eye strap or saddle rests on the inside of the mast wall.

 

[andsarkit]

I liked the Wichard version which does not rely on the strength of the rivets. It fits inside a slot in the mast and the rivets just hold it in place. It has one hole for the inner stay and one for an external halyard block. Each half is inserted separately and then the two halves bolt together. Babystay tang

It seemed a bit oversize for my little boat so I made one up out of 2mm stainless at zero cost.