Ways to Add 6ft to the BOTTOM of a mast?

[Sos]

I am sure the mast providers do not extrude their own sections. They will be done by an extruder. They will only extrude very large amounts to order so you need to find an offcut from someone that uses/supply's that particular extrusion. Not easy I guess!
Bending aluminium is a job for a specialist in aluminium as is welding aluminium. Generally a weld in ali is about half the strength of the parent material which is why is is best practice to connect to aluminium with mechanical fixings, if possible.

[Chotu]

No one in Europe or the USA can find this mast section. Several places don’t even have any mast sections, including sailorman.

So!!!

What about the pedestal idea?

What about taking a larger, beefier mast section and installing vertical bulkheads in it, then creating a receptacle in it to accept the base of the current mast?

I’m looking at a 4-5ft pedestal.

[zstine]

As long as the pedestal is constrained from tipping over, then I see no reason it wouldn't work. You don't need to use a mast section either, but that would be fine. I assume(?) you are deck stepped just in front of the cabin top? I would suggest 2 tubes rigidly attached to the pedestal, angled back to the cabin top at 45 degrees off center, so they make 90 deg between them. maybe even make into an 'A' frame weldment. They will support loads in the transverse and longitudinal directions and will not be too unsightly as they are horizontal and at cabin top level. I would also rigidly attache the base of the pedestal to the original step location to help prevent twisting the A frame, or short stays would be better. But unsightly and perhaps not needed... make sense?? Is the cabin top well supported? eg. do any of the bulkheads extend up to support the cabin top and therefore provide good lateral support of the cabin top? there can be significant lateral loads on the mast. I'd expect many thousands of pounds in the lateral direction.. Don't believe anyone who says a mast is only in compression! A Free body diagram and some analysis is warranted for sure!

[zstine]

Rough Sketch of my idea attached. I believe you want to minimize the height above the top of the cabin to avoid overturning moments. Otherwise you may need to stay the pedestal down.. ugly

[AKA-None]

So tell me again why it can’t be made of 3 parts welded and internally braced? Two curved sides welded in front and the third flat side in back all with internal welded bracing. Heat stress relieved and anodized?

[geoleo]

Originally Posted by Chotu

Huh??? How can it be more expensive to add 6ft to the bottom of the used mast I bought than to go out and buy more masts? This seems way off.

You need a masts exact section to sleave it properly. It will take 3 ft long for the inner sleave + whatever height you want to add. Use Flat Head type 316 1/4/20X 3/8 long screws-- tap the inner sleave and drill slightly larger holes in the outer mast sections so the inner sleave will be drawn tightly to the outer mast sections, make a pattern of screw fasteners where they are within 3-4 inches of each other. Fasten fhe lower sleave entirrely to the sleaves before you marry them together ,then fasten the upper mast pat to the protruding sleaves. Think ahead and be neat! Oh yes-- the cuts on the mast need to be exactly 90degrees to the mast length. Fill these slits with your old friend epoxy glue!!!

[Chotu]

Originally Posted by AKA-None

So tell me again why it can’t be made of 3 parts welded and internally braced? Two curved sides welded in front and the third flat side in back all with internal welded bracing. Heat stress relieved and anodized?

I would also be interested in hearing the argument against this, only because I don’t know the answer to this question.

[Chotu]

Originally Posted by zstine

Rough Sketch of my idea attached. I believe you want to minimize the height above the top of the cabin to avoid overturning moments. Otherwise you may need to stay the pedestal down.. ugly

That’s looking to be pretty good. Only issue is I have steps there so it wouldn’t work.

Question.

If it’s stronger than the mast, why would it need supports there any more than the mast would if it was stepped in the same place?

[Chotu]

Originally Posted by zstine

As long as the pedestal is constrained from tipping over, then I see no reason it wouldn't work. You don't need to use a mast section either, but that would be fine. I assume(?) you are deck stepped just in front of the cabin top? I would suggest 2 tubes rigidly attached to the pedestal, angled back to the cabin top at 45 degrees off center, so they make 90 deg between them. maybe even make into an 'A' frame weldment. They will support loads in the transverse and longitudinal directions and will not be too unsightly as they are horizontal and at cabin top level. I would also rigidly attache the base of the pedestal to the original step location to help prevent twisting the A frame, or short stays would be better. But unsightly and perhaps not needed... make sense?? Is the cabin top well supported? eg. do any of the bulkheads extend up to support the cabin top and therefore provide good lateral support of the cabin top? there can be significant lateral loads on the mast. I'd expect many thousands of pounds in the lateral direction.. Don't believe anyone who says a mast is only in compression! A Free body diagram and some analysis is warranted for sure!

A mast is only in 100% compression at rest. I agree. I’ve been at sea enough to know what a mast looks like pounding through the waves or with gusty winds. It wobbles quite a bit in unsupported areas.

Question:

What if the pedestal is simply another, bigger mast section (for looks) with internal framing to support the compression?

Then what if it also has a receptacle for the current mast to slide into? A lip around the circumference that is the also bolted to the mast? I’ll do a drawing in a few hours.

[rslifkin]

I wonder... Could you come up with a pedestal that would look decent, be strong enough, and also serve as a storage cabinet for stuff like lines and fenders? I'm not sure how it would look (would need to see side and front views of the boat I think), but it seems like it might be useful.

[Chotu]

Here is the fancy drawing I did using rendering software. Ha ha ha.

But to summarize, wouldn’t this be able to lift the mast step up 5ft? With the bulkheads inside the pedestal, nothing could move at all at the upper pedestal.

The question would be the attachment and backing plate of the pedestal given the lateral forces on the pedestal would be basically cantilevered. I could put some monstrous backing plates in and even increase the lateral footprint of the base of the pedestal to give it more structural integrity from a lateral standpoint.

Criticisms and comments on this drawing?

[carlosproa]

Have you tried passing this idea to a multihull designer like Richard Woods or Berndt Khoeler? Their designs are practical and do not relay on fancy materials. Maybe they can give you a pointer.
I still think you can fit a sleeve on it from a different mast with cut outs to form inside and out

[Knotical]

The way I see this is you are bringing the boats internal structural bulkhead up 5’ and then attaching the mast - the extension does seem pretty strong, what I’d be concerned about is the mast connection point which may create a weak “hinge” joint, is it going to be strong enough to take fore-aft and lateral forces?

Take for example a 50’ foot mast spliced in the middle - same concept however the long lower segment does give it some flexibility in movements and the whole mast moves as one. In your case I see the bottom support as extremely rigid which will enable to mast to flex at the joint - leading to increased stresses.

[Chotu]

Originally Posted by Knotical

The way I see this is you are bringing the boats internal structural bulkhead up 5’ and then attaching the mast - the extension does seem pretty strong, what I’d be concerned about is the mast connection point which may create a weak “hinge” joint, is it going to be strong enough to take fore-aft and lateral forces?

Take for example a 50’ foot mast spliced in the middle - same concept however the long lower segment does give it some flexibility in movements and the whole mast moves as one. In your case I see the bottom support as extremely rigid which will enable to mast to flex at the joint - leading to increased stresses.

Yes. I see the same possible drawback too. A very rigid upper mast step at the top of the pedestal, then a free floating mast above that.

It sounds like it could be a problem.

But when I continue thinking about it, I have to ask myself, how would that be any different from taking the same mast and setting it on a lower mast step?

If both mast steps don’t move, wouldn’t a mast that is already designed and proven work just as well on a higher mast step as it would on a lower?

I mean as an extreme example, imagine your own mast (or any deck stepped mast) complete with stays and the entire setup that’s currently working on any boat.

Now take this entire rig and install it at the top of the Empire State Building. Will it behave any differently? I don’t think so.

All that would matter is the upper mast step doesn’t move.

And that brings me to another interesting thought.

If a standard mast step works on this rig (this rig is from a catamaran like mine) why would I need to do any splicing and burying of the mast at all? If I just provide the mast step to the rig at a higher point, assuming the mast step is stationary, there is no need for any of the extra work you’d do with a splice or to bury the mast into the pedestal.. It’s just a higher mast step.

Anyone see anything off about that thought?

[Chotu]

Originally Posted by carlosproa

Have you tried passing this idea to a multihull designer like Richard Woods or Berndt Khoeler? Their designs are practical and do not relay on fancy materials. Maybe they can give you a pointer.
I still think you can fit a sleeve on it from a different mast with cut outs to form inside and out

Richard woods is a great guy. I’m a huge fan. He helped me a lot with my build actually in the beginning. I had a lot of help from some very well known people.

Richard is retired these days and deserves all the peace and quiet he can get.

He’s on this forum and if he happens to see that’s and comment, all the better. I definitely don’t want to bother him though.

But this is less about boat design and more about straight mechanical engineering. I have a proposed pedestal that should provide a completely stationary higher mast step to the mast. If it does and if it can withstand the lateral forces of slamming into waves, accidental gybes (for shame!) and gusty winds, then I’m just providing a higher position of the mast step, like one stepped on the coach roof.