Mast step truss, inevitably:(

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prjacobs
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Re: Mast step truss, inevitably:(

Post by prjacobs » Tue Sep 16, 2014 4:04 pm

Interesting thread ... keep up with the pictures Bob. I'd like to see the full build.
When I drilled a drain hole from the low corner of the closet through to underneath the starboard bunk I discovered that steel plate too!

Bob McGovern
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Re: Mast step truss, inevitably:(

Post by Bob McGovern » Tue Sep 16, 2014 4:37 pm

Mark: Nah, the poured-in resin around the truss was not particularly well-glued to the hull at all -- secondary bonds not being polyester's forte. And that much resin will shrink as it cools, pulling away from the hull slightly and developing hairline internal cracks. That's a source of our headaches here -- it's how water got down alongside the truss -- but it also makes removal much simpler! The resin is old, brittle, detached, and it comes free in satisfying lumps. You'll know immediately when your chisel reaches the hull laminates. Chip-chip-chip-THUNK. :D

I did a bit of light grinding along the sides afterwards, just to ready the area for some fresh biaxial cloth & epoxy. Mostly what you see there was accomplished with blunt chisels scraping along the sides. The filler resin pops right off. Almost no work was required at the bottom of the well. Upon removing the truss, it looked like the photo. Ready for the new one!

Re: cutting the sole. If you don't already own one, an oscillating multitool is simply the greatest invention for boat work ever.

Image

For decades, Fein of Germany held the patents; but they have expired and now lots of cheaper units are on the markets.

https://www.youtube.com/watch?v=IQ9dy8NIHgw

We have various sellers of Chinese knockoff tools here in North America, including a bottom-end purveyor called Harbor Freight. Sometimes you get lucky.;) $30-40USD gets you an incredibly versatile tool you won't mind abusing, and if it dies you buy another. Surgical precision, controllable dust, won't cut your fingers off. Don't know if Europe has similar stores? Anyhow, that's how you make really precise plunge cuts like that in tight quarters.

Peter: It was a surprise to see metal shavings coming out of the hole, eh? Any clue what sort of steel it is? The shavings were either magnetic or magnetized by the act of drilling, but that may not tell us much.

MarkRyan1981
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Re: Mast step truss, inevitably:(

Post by MarkRyan1981 » Wed Sep 17, 2014 8:21 am

Ah, thanks for the information, and I do own one of those actually. My late father was the worlds most awesome shipwright (he didn't pass on too many of those skills, I just parachuted him in when something like this needed doing :D , so some skilling up on my part required), and has left me a treasure trove of tools, including one of these, so I'll get it out and have a frown at it.

How will you replace the sole? Use the chopped out piece as a mould and then fabricate one up?

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prjacobs
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Re: Mast step truss, inevitably:(

Post by prjacobs » Wed Sep 17, 2014 4:03 pm

Bob McGovern wrote: Peter: It was a surprise to see metal shavings coming out of the hole, eh? Any clue what sort of steel it is? The shavings were either magnetic or magnetized by the act of drilling, but that may not tell us much.
Sorry, didn't check for magnetism, but it was hard drilling so I suspect it's of a good quality.

Bob McGovern
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Re: Mast step truss, inevitably:(

Post by Bob McGovern » Wed Sep 17, 2014 4:18 pm

Haven't decided. Leaning toward gluing some ledgers on the bottom of the opening, setting the original patch back in place, and then scarfing/taping the seam flush. The sole has some hull-stiffening function, but not much. The beefed up bilge dividers & floors will take over that duty. Then we plan to lay LonWood or similar product over the whole cabin.

http://www.ameriteakmarine.com/lonseal

A nice thing about FRP is the freedom you have to butcher it. You can always piece it back together later, good as new. After a few trial repairs, you'll think nothing of cutting out whole sections of the boat. :D Your Dad was probably like that -- just dive into the job & sort out the details once you have it all laid bare. Possibly doesn't work so well with computers. :lol: But in the world of macro-stuff, I've found courage carries you at least 2/3rds the way thru any job. Then stubborness, looming deadlines, and remorse drag you across the finish line.

MarkRyan1981
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Re: Mast step truss, inevitably:(

Post by MarkRyan1981 » Tue Jan 06, 2015 1:54 pm

Any updates Bob? Happy new year all btw

Bob McGovern
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Re: Mast step truss, inevitably:(

Post by Bob McGovern » Tue Jan 06, 2015 6:42 pm

MarkRyan1981 wrote:Any updates Bob? Happy new year all btw
Hi, Mark. And Happy New Year to you. :) The boat is mostly hibernating for the winter (minus 31F the other day, 65mph winds yesterday, etc.), tho we have been scrounging the internet for bargain gear. New/old Origo stove, lovely 1.5m Lewmar traveler for half retail, and so on. The plywood mast truss prototype is with a local welder, with strict instructions to hurry not a bit. :lol: His MIG wire spool for stainless is 304/308 grade, so we will likely use 304 for the build. He thinks welding such thin material will require some care, as apparently stainless wriggles more than mild steel as it heats (??). I'm willing to use 1/4" material, although that is overkill for pure strength. 3/8" (10mm) 6061 Alu is likely the best choice, if there is a competent welder nearby.

What winter/spring projects have you got lined up?

MarkRyan1981
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Re: Mast step truss, inevitably:(

Post by MarkRyan1981 » Tue Jan 20, 2015 11:33 am

Triola is still in the water, I'll take her out for a couple of months in spring to get some work done. I want to fit our bilge pump I've had floating around in a locker for an age and finally get my new sprayhood on - all my time is being currently taken up by my wife expecting our second child! I may use this year of child induced 'reduced sailing' to get the mast step done and top hat the bulkheads to sure them up.

Thanks for the update Bob, I'd be interested in getting the plans of your mast step when you write them up so I can give them to my local stainless man to get a price.

MarkRyan1981
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Re: Mast step truss, inevitably:(

Post by MarkRyan1981 » Mon Mar 09, 2015 3:54 pm

What ho Bob, are things starting to thaw out a bit there now? Any progress? I had an interesting email from West System re whether encapsulating the mast foot would be beneficial.
Thank you for your interest in our products.

As we are not structural engineers it is not for us to advise whether timber or metal is more appropriate to this load barring structure. However we can advise that should timber be used then it is advisable to ensure the component is completely encapsulated in epoxy to prevent moisture ingress. Also adding glass sheathing will increase the thickness of coating and improve moisture protection.

Whether metal or timber is chosen filling the surrounding cavity with epoxy to aid load transfer will be beneficial. Careful resin and hardener selection will help to prevent excessive exotherm and depending on the volume of the cavity it make also be necessary to fill the void in a number of hits.

We trust this information meets your requirements and if you require any further information please do not hesitate to contact us.

Regards,

Hamish

Techinfo Mailbox
Wessex Resins & Adhesives Ltd.,
I've decided to not dig the mast foot out as yet - no rusty patch on the front of the keel, no rusty water in the bilge, and no reason to worry. If I get any signs of rusting I will excavate it - I will however do the bulkheads when I take her out in the next few weeks. Not doing the foot now gives me the advantage that when I come to do mine, I can lean on your experience as you will have long finished putting yours back together! :)

Hope you are well.

Bob McGovern
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Re: Mast step truss, inevitably:(

Post by Bob McGovern » Wed Mar 11, 2015 3:42 pm

Good luck with the bulkheads, Mark. It will go well, I'm sure. :) If you can get your hands on one of those USB aperture cameras & bring yourself to drill a small hole next to the mast step riser, I bet you'd know for sure what kind of shape your truss is in. I think eBay has them for about $12 USD. They plug into your laptop.

No word yet from our welder; I'll start pestering him once we reach epoxy temps. Rather than fill the entire cavity around the new truss with resin, I think we will just epoxy in some wedges along the sides and bolt it front and back to structural members. At a guess I'd reckon <200kg lateral thrust at the mast foot, much of which is dissipated by the cabin sole. Good luck with the repairs, & keep us posted.

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