Mast reinforcement/doubler plate

[alaskanviking]

Hi,

I am in the middle of refitting my mast. I was looking up stuff and found my way to this site https://theriggingco.com/gallery/

There are quite a decent number of Picts/projects where they added doubler or reinforcement plates. Either riveted or welded on.

I was curious as to the why, I don't see any cracks or damage issues in the before Picts.

Is this a good idea to have added during a refit? Is there value added or is it only worth while as a repair? I Was thinking maybe at the tangs

Thanks

[GordMay]

A doubler plate is often used to reinforce a structure around cut-out openings, or any other feature that could weaken the structure ie: [load concentrations].
The doubler below, accomplishes both.

[Benz]

If your boat hasn't needed them since 1984, why start now? If you're radically changing something, then you may need doublers, but it's best to consult an engineer at that point. There are several ways to locally reinforce spars, but it's not always a doubler plate.
Also consider that welding will affect the temper of the spar in that area, and that rivets have a danger of eventual corrosion.
In short: don't bother unless you really need to.

[Chotu]

Originally Posted by Benz

If your boat hasn't needed them since 1984, why start now? If you're radically changing something, then you may need doublers, but it's best to consult an engineer at that point. There are several ways to locally reinforce spars, but it's not always a doubler plate.
Also consider that welding will affect the temper of the spar in that area, and that rivets have a danger of eventual corrosion.
In short: don't bother unless you really need to.

Exactly.

Adding to this a little bit, your current aluminum spar is designed to bend to some extent. The entire thing is one extruded isotropic piece of material.

The minute you add a doubler on there, you have changed that. Now there is a section that is more stiff than the other sections. That opens the mast up to localized stressors on the edges of the doubler. A localized stress riser there with the right bend could cause a buckle or a kink in the mast and you might lose the whole mast. This is really tricky stuff actually.

As an example, take a plastic straw and hold both ends. Then push it a little in the middle to bend it. Now, wrap your plastic straw with a bunch of masking tape in some area. Do the same thing. Grab the ends of the straw and push the middle. What happens? It kinks for the masking tape is. That’s what can happen to your mast.

They are used, as Gord mentioned, to spread out localized loads. But they must be applied carefully.

[Joh.Ghurt]

I had this summer a quite unhappy moment, when it turned out there's heavy corrosion under the spreaders. The rigger proposed to have a few doubler plates welded onto the mast after cutting out the corrosion. The alternative was a new mast. Now my mast looks like Frankenstein's creature

In general, doubler plates aren't ideal, because they make the mast stiffer at those spots. This will prevent the mast to bend in an elegant curve and might create small kinks where the stiffer part with the plate ends, which in turn might lead to cracks in the mast. So it's important to check for this at regular intervals. But if the mast is sufficiently over-built for the use, it shouldn't be a problem for a cruiser. For racing this isn't an option.

[alaskanviking]

Originally Posted by Chotu

The minute you add a doubler on there, you have changed that. Now there is a section that is more stiff than the other sections. That opens the mast up to localized stressors on the edges of the doubler. A localized stress riser there with the right bend could cause a buckle or a kink in the mast and you might lose the whole mast.

This was my thoughts also. They had a lot of pictures of refit masts with doublers added throughout. I was wondering if I was missing something

My mast is a strong Kenyon cruising section. I don't have any issues that I can see. I am changing to cheeky tangs. I pulled the beating plates for the old tang to prep for paint and realized they are too small for checky tangs. I was wondering if a larger doubler in this area may be needed to replace the bearing plate, or if I can go without?

[Bowdrie]

For the mast on a cruising boat "elegant" bends/curves are neither wanted nor desirable.
The mast wants to stay in column.
Doubler plates can be quite useful for reducing point-loading at various places, such as where the spreader mounting devices are used.
This is where the dreaded "5200" shines.
The plates are well covered with 5200, placed in location, and strap-clamps, or large hose-clamps are used to obtain a good compression until the 5200 sets-up.
Then, the holes for the machine screws can be drilled/tapped, and the hardware installed, the machine screws passing thru both thicknesses of metal.
Welding is generally undesirable, it changes the temper in localized areas, and as doubler plates in that application are in compression, the use of rivets is of little value, except for perhaps a few to hold the plates in position until the 5200 sets-up.

[Manateeman]

You don’t want to weld anything to the mast because it will set up a unequal flow of electrons to every weld in your all welded aluminum boat.
The manatee crew all enjoy Acadian cuisine but cannot find a recipe for ribbits.
They don’t eat frogs no matter how many ribbits they hear at night.
I told them riggers routinely stick ribbits into aluminum spars and they got all confused wondering why frogs would go to a spa rather than a pond.
I told them to coat the ribbits with Tef-Gel but they can’t believe frogs...especially GREEN frogs...(one of them writes great posts here ) ever wear coats but live life in the nude.
The less rags and strings you attach to your mast, the longer it will last in strong winds.
Which is why people began to put engines in sail boats. So don’t fret about your mast.
Happy trails.
The ever confused captain of the manatee boat.

[Benz]

Originally Posted by alaskanviking

This was my thoughts also. They had a lot of pictures of refit masts with doublers added throughout. I was wondering if I was missing something

My mast is a strong Kenyon cruising section. I don't have any issues that I can see. I am changing to cheeky tangs. I pulled the beating plates for the old tang to prep for paint and realized they are too small for checky tangs. I was wondering if a larger doubler in this area may be needed to replace the bearing plate, or if I can go without?

I would consult with the purveyor of the cheeky tangs. Surely they have done plenty of engineering of the loads involved, and it's in their interest to see their products installed correctly.