Could use a little advice. Aluminum or Fiberglass for this?

[Chotu]

I have to make these decisions pretty quickly right now. So, I am reaching out for some advice. I could be here a week trying to go back-and-forth between these two things.

I had a different thread about extending the mast. It turned out that was not so easy.

Instead, I’m just going to extend the boat.

I’m going to create a sort of pedestal for the mast to sit on. It will move the mast step location vertically upward by the distance needed.

You can picture it something like a pyramid, but with a flattened top instead of a point. And the mast will just sit on that flatten the top, with a normal locking mast step up there. It won’t be quite as wide as a pyramid, and it will be a little taller.

Now, I’m facing a few options on how to make this thing. Specifically on what to make it out of. Here they are.

1) 1/4” aluminum sheet. Welded at a machine shop hopefully before the sun ceases to shine and the solar system goes dark

2) 1/4” aluminum sheet bolted together with extra doublers at the edges

3) 3/8” or 1/2” polyester “G10” sheet. Glassed together at the sides using biax and polyester or vinylester.

4) 3/8” or 1/2” polyester “g10” sheet bolted together with doublers


Which approach do you think I should take?

It’s got to be strong. It’s going to hold the equivalent of three Ford F150 pick up trucks. Stacked on top of each other. That’s the compression force on my mast.

Another pesky detail is I have a mast base plate in the mast that is 1/2” aluminum. It has 4 holes in it that are approximately 1.5” in diameter. These holes hold the mast in place. I have to make nubs to go into these holes to receive the mast.

I feel like doing this myself might be significantly faster than waiting for a machine shop given that it has taken six months now to get my crossbeam brackets almost done.

Which approach do you guys think I should take?




Bonus question:

It is also time to fabricate the sail control table. This is basically just a flat surface where the winches and line stoppers will be mounted. It will be at a normal table height. Pretty close by to the base of the mast. What the heck should I make this out of?

By design, I can put verticals in and bolt the winch on either side of the vertical piece that will run from table top to floor, straddling the vertical piece. . That can carry the load pretty well.

This is indoors. But it will get wet a lot from wet lines in the rain coming through and being adjusted.

So what type of material should I make that out of? It really needs to be lightweight. With the vertical piece I’m talking about, do you think I can get away with foam core here? Or do I need to make it out of plywood? Or do I need to make it out of the polyester G 10? It’s very heavy stuff actually. Just not too heavy in comparison to metal.

[Jolly Roger]

Firstly, you don’t tell us why you need to extend the mast. Second, how much are you wanting to extend it by? Third, your pyramid idea will look bloody awful, and cause any future buyer to think twice about anything else you have done to the boat.
Why can’t you extend the mast by just splicing a new section in place, either from the top or bottom?
I did this with my schooner foremast, in order to increase the headsail size and the slot for the jib to pass through between the staysail. You may not even need to remove the mast, if you can find a similar section and splicing pieces, you might just be able to lift the mast with a crane, and drop it down on the new section.
Of course, you’ll then need to extend the standing rigging and the forestay.
Any way you look at it, it’s a big expensive job, and it took me a year to assemble all the parts.

[danstanford]

Though there may be some on here qualified to offer an informed opinion, they will likely be experienced enough to not answer. You should involve/pay and expert designer and engineer to assess the loads to insure this thing doesn't come down and kill you and/or someone else.

[Chotu]

Honestly, do you guys not know me well enough by now? Ha ha ha.

Jolly Roger, you are more than 6 months behind on the project. Most everything in your post is wrong for the project, out of date for the project or doesn’t apply to the situation. I’m asking a simple question. Not looking for all of the stuff you wrote. But I will answer a couple of your questions. For clarity for you.

-there is no other mast like the one I have. No extra sections to be found. Out of production.
-I agree it does not look as good as it should. The criticism does hurt a bit, but it’s the best I can do in the situation.
-The Mast has never been on the boat yet. Do you forget I am building a boat?
-I’m not asking what to do. I’m asking what material choice out of the four I should pick so it’s easy, straightforward and fast.

Dstanford: I guess you probably don’t know me too well. I don’t know you too well either. I haven’t seen you in my threads much. So understandable mistake. Don’t post stuff like that please. I’m asking a simple question regarding choice of materials, not looking for nervous nellies to put their warnings all over the thread.



I’d like to think people know me well enough now on here that they know I don’t want to hear answers like the ones above. Because you know what? They are not answers. Neither of those answered my question.

Allow me to state the question again in case it was missed:

Which of these four approaches should I use for convenience and speed?


1) 1/4” aluminum sheet. Welded at a machine shop hopefully before the sun ceases to shine and the solar system goes dark

2) 1/4” aluminum sheet bolted together with extra doublers at the edges

3) 3/8” or 1/2” polyester “G10” sheet. Glassed together at the sides using biax and polyester or vinylester.

4) 3/8” or 1/2” polyester “g10” sheet bolted together with doublers



Bonus question:

It is also time to fabricate the sail control table. This is basically just a flat surface where the winches and line stoppers will be mounted. It will be at a normal table height. Pretty close by to the base of the mast. What the heck should I make this out of?

By design, I can put verticals in and bolt the winch on either side of the vertical piece that will run from table top to floor, straddling the vertical piece. . That can carry the load pretty well.

This is indoors. But it will get wet a lot from wet lines in the rain coming through and being adjusted.

So what type of material should I make that out of? It really needs to be lightweight. With the vertical piece I’m talking about, do you think I can get away with foam core here? Or do I need to make it out of plywood? Or do I need to make it out of the polyester G 10? It’s very heavy stuff actually. Just not too heavy in comparison to metal.

[Jolly Roger]

The answer is none of the above. If you can't get a mast section, do it properly and buy a new mast.

[rslifkin]

If you had well fitting aluminum angle inside and out and sheets of aluminum with bolts through the angle, etc. I would expect that to be plenty strong. Given enough bolts and possibly an adhesive bond as well, I don't see it being weaker than a welded assembly (possibly stronger with the extra corner reinforcement). Corrosion in the bolted joints and around fasteners would be a slight concern, but should be manageable.

I think fiberglass (glassed together not bolted) may be easier to make it look good. Faired and painted, it'll blend right into the boat. And it'll probably be easier to mount hardware to it for line routing, etc.

[Sailer_Med]

oooh, I love building stuff! $65k for a rig: Jeezus!

I don’t know your technology threshold. Personally, I’d go with with bolted up Al. If you’ve already got experience with your weld shop, they ain’t gonna change now…

You can readily machine that Al DIY with conventional tools. Everything, cutting, drilling, tapping, etc. You can also get lots of prefab Al shapes to affix this thing to the boat. The doublers, I’m not so sure about that. What will they do for you?

[RaymondR]

Getting two C sections bent up from 1/8" or 3/16" aluminium and welding the two seams will provide a better looking pedestal. If you are uncertain of the buckling strength you can tack weld flat bars into the four inside corners thereby forming four closed sections at the corners.

[Chotu]

Originally Posted by RaymondR

Getting two C sections bent up from 1/8" or 3/16" aluminium and welding the two seams will provide a better looking pedestal. If you are uncertain of the buckling strength you can tack weld flat bars into the four inside corners thereby forming four closed sections at the corners.

I wish.

Got a 58” long brake and can you get it done in less than 30 days?

That’s where it falls short doing that. No brake around and welders don’t complete projects in 6 months. Assuming they even take the work.

[ItDepends]

You should have a good idea of the maximum compressive load from the mast. From that it is pretty easy to design something to hold it up. With a sharp pencil you'll hopefully do better than Lagoon did on the 450. Building something that "looks" strong enough is likely to be very much heavier than your boat deserves.

A rectangular Al box section is the easiest. You should have the bending moment of your mast section both fore/aft and laterally. From that it would be pretty easy to match those numbers with an Al box. That would be the minimum strength you'd want.

I will give you one more suggestion, and you can feel free to ignore it, but it is offered in the interest of sharing knowledge. Please do not be offended if you already know it.

Changing from a keel stepped mast to what is essentially deck stepped affects many more of the rig properties than the length. Key thing here is the mast is now more flexible.

I am NOT saying you can't go from keel stepped to deck stepped with the same mast section, but you need to be SURE that the wires are in the proper attachment points and that you have enough of them to support what is now a significantly bendier stick.

If you know all that, and have allowed for it... good on you. But this is a discussion forum and others might not be as smart as you are.

[LakeSuperior]

Wow! Amateur boat building at it's finest.

Chotu, you really need to find someone that knows what they're doing to work with...like a naval architect. Else you are going to have a pile of scrap when you're done.

[Chotu]

Originally Posted by LakeSuperior

Wow! Amateur boat building at it's finest.

Chotu, you really need to find someone that knows what they're doing to work with...like a naval architect. Else you are going to have a pile of scrap when you're done.

Wow! Useless posts at their finest.

You need to read my old threads. Must suck living in so much fear. I pity you.

[Chotu]

Originally Posted by ItDepends

You should have a good idea of the maximum compressive load from the mast. From that it is pretty easy to design something to hold it up. With a sharp pencil you'll hopefully do better than Lagoon did on the 450. Building something that "looks" strong enough is likely to be very much heavier than your boat deserves.

A rectangular Al box section is the easiest. You should have the bending moment of your mast section both fore/aft and laterally. From that it would be pretty easy to match those numbers with an Al box. That would be the minimum strength you'd want.

I will give you one more suggestion, and you can feel free to ignore it, but it is offered in the interest of sharing knowledge. Please do not be offended if you already know it.

Changing from a keel stepped mast to what is essentially deck stepped affects many more of the rig properties than the length. Key thing here is the mast is now more flexible.

I am NOT saying you can't go from keel stepped to deck stepped with the same mast section, but you need to be SURE that the wires are in the proper attachment points and that you have enough of them to support what is now a significantly bendier stick.

If you know all that, and have allowed for it... good on you. But this is a discussion forum and others might not be as smart as you are.

Yes. Exactly. All of the numbers are known.

Every last one.

Only issue with your post applying to my situation as this is a Catamaran. There are no keels to step masts on. Just raising the deck step to match the height the mast was stepped at on the boat the mast came off of. It’s a bit lower location on my boat.

[LakeSuperior]

Originally Posted by Chotu

You need to read my old threads. Must suck living in so much fear. I pity you.

I have, which cumulatively have warranted both the caution and editorial comment.

[AKA-None]

Not sure about 1/4 maybe 5/16?
I don’t like the bolt approach as you’ll likely need quite a few bolts to make it act as a single component but would make fab easier
I think you’ll need internal stringers at any rate so the plate has minimal flex areas
Just a quick reply while taking a lunch break