Malahini ply bending question

Bob Maskel · **Posted:** Mon Apr 30, 2012 4:05 pm

How have you Malahini builders made the ply bend around the curve at the transom without breaking??? I broke my 3rd panel today, and with the price of marine ply that is getting expensive...although I can use about 6' of each of 'em elsewhere. Twice I have tried using ratchet straps bending it dry and doing a little more each day to "ease" it in, and both times it broke in the middle of the curve when I was about a half inch from getting the bottom to contact the sheer. Today I did the boiling water thing, pouring boiling water onto rags onto the panel flat on sawhorses, then fitting it in place and pouring more boiling water on...and it broke another panel. Maybe I have to do the boiling water a little each day for a couple days to let it s-l-o-w-l-y ease into that bend. The break is not always just on the end...sometimes it has been 5 or 6 inches in...it cracks and makes a flat spot, like what happens when trying to bend cardboard.

The stuff I am using is 1/4" Keruing marine plywood.

Any suggestions????

Thanks...

Bill Edmundson · **Posted:** Tue May 01, 2012 6:30 am

Bob

I can't answer the question for sure. But, you may have to go to 2 layers of 1/8". That would probally mean you would have to paint the hull.

Bill

jeffh · **Posted:** Tue May 01, 2012 7:32 am

Bob,
My Malahini was already at that point when I bought it. But, I have attached Onplane's picasaweb page. Look at photo 60. I don't know if there is anything there that can help you, but that photo is the section that bends around at the transom. I notice his extends beyond by what looks like a foot and he then trimmed it.
http://picasaweb.google.com/11229065623 ... directlink

Here is the section of his build thread:
viewtopic.php?f=2&t=10314&start=60

rbrandenstein · **Posted:** Tue May 01, 2012 7:51 am

Bob
I also had a crack in one piece of my plywood at the rear. One side went fine, the other cracked after it was all epoxied into place. At least, I didn't notice it until everything was glued in.
Here is my blog post on the issue: http://www.bobsboatbuild.blogspot.com/2011_03_01_archive.html I just attempted to repair the crack by injecting epoxy and also adding some plywood backing on the interior.

I used Meranti marine plywood and I really think the cracking is related to the plywood. I believe there was a flaw or weak spot in the internal structure of the plywood. I was cutting some of the 1/4" stuff and found one piece that was not glued on the interior! I also don't think soaking or steaming helps much since the problem is on the interior. I guess you just have to be lucky and get the right piece or repair the piece if the crack is minor.

jeffh · **Posted:** Tue May 01, 2012 7:55 am

Bob, I was wondering about the type of plywood. I think some is more flexible. Mine is Okoume which I have used before on my kayak. It was pretty easy to bend into place. But, from what I have seen, I think the Meranti is a prettier wood.

Bob Maskel · **Posted:** Tue May 01, 2012 8:15 am

rbrandenstein wrote:

Bob
I also had a crack in one piece of my plywood at the rear. I used Meranti marine plywood and I really think the cracking is related to the plywood.

Yeah, that's pretty much what mine looks like...all 3 of 'em.

This morning I called the place I got the ply from (Midwest Boat Appeal in a western suburb of Mpls. if anyone needs a supplier in this area) and they recommended I try Okume ply if possible. You guys are correct, he said that Okume is the most pliable, with Meranti next and the Keruing that I have being the stiffest. He said the boiling water won't matter much as the panels are all boil-tested to resist stuff like that. I still have 3 Keruing sheets left, so I am going to try it again...slowly, very slowly, and see what happens. The guy said it may take 3-5 or more days to slowly let the panel adapt to the bend so I guess I will have to be more patient. If another one cracks I'll go with the Okume (at $129 a sheet :shock:

), but I like the looks of the Keruing much better and had hoped to finish the sides bright...we will see I guess...

Moeregaard · **Posted:** Tue May 01, 2012 4:01 pm

I suspect that there's something plywood-related that's causing the cracking, perhaps a void in the inner ply. We planked our Zip--which has a tighter bend radius around the transom--with 1/4" Douglas fir plywood and had no problems back there. Where things did get a little scary was when we were bending the bottom planking to meet the stem. We had to keep everything really wet to prevent the outer ply from cracking as we pulled things into place.

-Mark Shipley

sawford11 · **Posted:** Tue May 01, 2012 6:07 pm

I had a similar issue late last year when trying to bend the panels on my zip. I cracked two sheets of ply and then changed my procedure. The bend went perfectly after I did the following. Here is what I posted late last year regarding my build:

"I made a shallow trough from plastic sheeting and some 2x laying flat. I filled it with water and placed two 2'x8'x1/4" panels in the water. Soaked them overnight. I then aligned them with the boat frame and "lightly" clamped them in place. I placed some soaked rags over the panels where the max stress/bend is required. I then used my wife's iron (she wasn't home, so I borrowed it) to steam the heck out of one panel at a time. Probably 20 to 30 minutes, continually adding more water to the rags. The iron's steam feature doesn't work when the iron is held vertical, but by manually pouring water on the rags, it really created a lot of steam. In fact, all the windows in my shop were fogged up! The hot iron not only steamed the wood, but I think it also heated up the water that soaked in over night as the heat could be felt soaking though both sides of the panel. As I steamed, I also increased pressure on the clamps a little at a time. All said and done, two bent panels!"

ttownshaw · **Posted:** Wed May 02, 2012 1:52 pm

hmmm...Bob, I didn't have that problem. After screwing into the chine I just clamped progressively from the center (fore and aft) along the sheer. I used a whole bunch of 1' bar clamps and clamped against frames where possible. I screwed a temporary block into the transom to use as a clamping surface to pull the side flush to the sheer at the transom. I'll admit there was a lot of pressure but it didn't break. I used meranti. Have you trimmed the panels to rough size? I was concerned about going the strap route because if not spaced propperly it consentrates pressure (tension) in one particular area. Do you have enough clamps to try the clamp route?

Bob Maskel · **Posted:** Wed May 02, 2012 6:33 pm

Thanks to all for the suggestions...I will try soaking it and then clamping from the middle out, and try that block too. I started clamping at the forward end each time, top and bottom, so by the time I got to the transom there was no relief for the panel, all the bend was concentrated in the lower corner where, coincidentally :idea:

, the stress was the greatest ... and each time it broke. Sounds like if I take my time, let the panel adapt as it goes, and not try and make ALL the final bend in that corner I might be ok...

I'll say one thing though, I'm sure glad I built the Sea Knight first, or there wouldn't be a second, or maybe even a first, boat. For some reason this Malahini is giving me MUCH more problem than the big cruiser...maybe because the cruiser had large pieces and not a lot of bend and I had no idea what I was doing...maybe ignorance was bliss!!

ttownshaw · **Posted:** Thu May 10, 2012 1:12 pm

Any update Bob? Would like to know if you've crossed this hurdle.

Bob Maskel · **Posted:** Thu May 10, 2012 3:12 pm

ttownshaw wrote:

Any update Bob? Would like to know if you've crossed this hurdle.

Hi, yes, I have gotten past it!! Thanks to all that offered suggestions. I looked at a lot of the customer photos in the archives, and I have always liked the paint scheme of Doug Hodder's boat...he wrote in one of his narratives that he only wanted one joint per side to show, so he put one in the rear and painted over it.

Attachment:

File comment: Doug's paint

Hodder paint.jpg [ 25.67 KiB | Viewed 499 times ]

Sooo, since I still had over 6' of good ply on the bad sheet, I went to my local lumberyard that stocks Douglas Fir marine ply...bought a sheet ($55) and it made the bend without so much as a creak. So I have the one joint about 2 feet from the stern and the other a little ahead of frame 3 in a much straighter area. I will do the same on the other side...the DF marine ply is much easier to bend than the Keruing I have forward on the side...the Keruing is MUCH stiffer...the photo makes the joint look bowed in, but in actuality it is a very good flow from one piece to the other...the butt block didn't flatten it out at all.

Attachment:

File comment: Good bend

Bob's Malahini2.JPG [ 38.45 KiB | Viewed 499 times ]

So, all in all, I am back in business.

red · **Posted:** Thu May 10, 2012 3:16 pm

great news and nice work

ttownshaw · **Posted:** Fri May 11, 2012 2:01 pm

Lookin' good Bob! And yes I envy Doug's builds too...I wish he were still active here.

Glen-L.com

Malahini ply bending question

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