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Thread: MDO and HDO for boat building

  1. #36
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    Jun 2008
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    hood river oregon rgods4@msn.com
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    Default Re: MDO and HDO for boat building

    MDO ? Did someone say MDO ? I'm on my first build, the 22 foot Simmons Sea Skiff. I ran across MDO through a "discount-cash-only-craigslist warehouse". I bought some and used it on some projects and discovered it was as good or better than any sheet goods I had been using....and at a very sizable discount. For my build, I had already purchased several sheets of 3/8" marine ply, so I used it up on my bottom. Since I wasn't too keen on a 22 foot boat with only a 3/8" bottom, I doubled it, so it now has a highly respectable 3/4" bottom. So that pretty much used up my marine ply. So, I made another visit to my 'discount' guy and bought a number of sheets (3/8"; lots of 1/2"; some 3/4"; and a couple of thicker sheets). Once turned over, my boat got all of its side strakes out of 1/2" MDO....garboards included. I really laid on the epoxy on the garboards, but for the remaining strakes, only lightly epoxied the "inside" face (interior of boat, with no paper on it). All exterior faces of MDO are paper. All my cabin is MDO; all my hartop walls/roof are MDO. My 'splash rail' I'm adding is MDO... My floorboards are all MDO. I went totally MDO. It's very tough stuff. Paints like you wouldn't believe. Very few voids, if you can believe that, especially considering my source!! I'm sold on it. I was able to pick up a few sheets of two face paper, but most of mine is just one face. Sometimes the wood face has the typical "football" fillers; the other wood faces are just as "A" grade as one could ask for. MDO......perfect for boats! And with the current advent of "highway" HDO, it looks like boatbuilders delight....it's paintable. If I were to build another boat, it will be completely MDO'd. (well, other that maybe the trim....use oak, ash, mahogany, etc, but the body is all MDO).

  2. #37
    Join Date
    Apr 2007
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    Pittsburgh, Pa.
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    3,447

    Default Re: MDO and HDO for boat building

    I'm ordering 5/8 MDO for the bulkheads of the Reuel Parker Seabright 33 I am starting. If the cores look good I will probably do the hull in the same. My conundrum then will be do I sheath the whole thing inn Xynole/epoxy or just the bottom and maybe garboards, or just coat it with epoxy and paint? Opinions?
    If he ever drinks the brew of 10 tanna leaves, he will become a monster the likes of which the world has never seen



  3. #38
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    May 2006
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    Spokane, Wa
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    1,477

    Default Re: MDO and HDO for boat building

    If you're going to fiberglass, skip the MDO coating where the glass goes. Epoxy grabs wood much better than paper, and you're still only getting the adhesion of the paper to the wood as your bonding strength.

    Single sided MDO with the wood out will give you a good glassing surface.

    Otherwise, just do straight MDO, no glass, and a glued strip to protect the ply edge. Works like a champ.

    E

  4. #39
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    Nov 2006
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    Winnipeg, Manitoba, Canada
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    669

    Default Re: MDO and HDO for boat building

    Quote Originally Posted by Spokaloo View Post
    If you're going to fiberglass, skip the MDO coating where the glass goes. Epoxy grabs wood much better than paper, and you're still only getting the adhesion of the paper to the wood as your bonding strength.

    Single sided MDO with the wood out will give you a good glassing surface.

    Otherwise, just do straight MDO, no glass, and a glued strip to protect the ply edge. Works like a champ.

    E

    What sort of glue for the strip on the edge? PL Premium work well enough?

  5. #40
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    May 2006
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    Spokane, Wa
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    1,477

    Default Re: MDO and HDO for boat building

    My LYS is my test bed for using PL exclusively in a boat. PL backed with screws, as it is a good gap filler, but can't be used like epoxy where glass reinforcement is used. The designer calls for Sikaflex, but I wanted to give PL a whirl.

    The results speak for themselves.

    E

  6. #41
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    Aug 2018
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    Coeur D' Alene, ID
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    5

    Default Re: MDO and HDO for boat building

    I was just at the specialty lumbar yard. Okoume 1/2” marine ply $120 per sheet. MDO single face $53 per sheet. There were some small voids on the edge panels. I’m pricing out a Big Ben Garvey for my first build. Maybe will do mdo and epoxy exterior single face with sheathing����

  7. #42
    Join Date
    Oct 2009
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    South Puget Sound/summer Eastern carib./winter
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    15,490

    Default Re: MDO and HDO for boat building

    Quote Originally Posted by Uralite1 View Post
    I was just at the specialty lumbar yard. Okoume 1/2” marine ply $120 per sheet. MDO single face $53 per sheet. There were some small voids on the edge panels. I’m pricing out a Big Ben Garvey for my first build. Maybe will do mdo and epoxy exterior single face with sheathing����
    Try to find "aqua tek" or "hydro tek" ply. It's meranti. Cheaper in cost than okoume , far more rot resistant, just heavier.
    Save the okoume for kayaks and weight sensitive boats.
    But yea, good MDO would be fine prolly for a garvey.
    bruce

  8. #43
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    Jul 2011
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    Lindstrom, MN
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    2,323

    Default Re: MDO and HDO for boat building

    MDO core material varies regionally. In the northwest, it tends to be Douglas fir, which should be good for a boat. I used some in the mid Atlantic and it had a yellow poplar core, which is not as good as the fir. You need to pay attention to the source and have a good look at the edge before you use it.

    If you google 'mdo fir core' and then 'mdo poplar core' you will find a number of manufacturers using the core you searched for. The one China plywood agency site said "Core: poplar, hardwood, birch". It is hard to say which poplar would be used in China.
    Last edited by MN Dave; 12-26-2018 at 10:32 PM.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  9. #44
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    Aug 2018
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    Coeur D' Alene, ID
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    5

    Default Re: MDO and HDO for boat building

    All good points. I am just getting started, bought the plans and doing checks for materials. I did look at the marine fir they had being in the NW. It was not looking very good. I have so far to go before doing the planking that Ill just hold off and wait, check as I get closer. Thanks for info though.

  10. #45
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    Mar 2009
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    Texas
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    2,599

    Default Re: MDO and HDO for boat building

    Interesting stuff. Thanks.

  11. #46
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    Mar 2003
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    NJ
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    16

    Default Re: MDO and HDO for boat building

    I am in the process of building a doghouse out of MDO for an older 1988 Intrepid. The house is 51 wide by 6 foot long with 20 degree forward windows. I'm using MDO. it is remarkably good stuff from harbor Sales in Md at 52.05 a sheet. I am glassing it with 6 oz - too late I already did it. Assembly starts this weekend of the actual house

  12. #47
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    Apr 2007
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    Charlottesville, Virginia - USA
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    Default Re: MDO and HDO for boat building

    Quote Originally Posted by DavidTanya2 View Post
    . . . I'm using MDO. it is remarkably good stuff from harbor Sales in Md at 52.05 a sheet. I am glassing it with 6 oz - too late I already did it. Assembly starts this weekend of the actual house
    I bought some MDO from Harbor a few months ago. Lots of voids, and lots of knot holes on the back face. I'm glad you got some good stuff, but I'm not sure I'll risk it from them again.

  13. #48
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    Dec 2003
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    Portland, Oregon
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    52,156

    Default Re: MDO and HDO for boat building

    Quote Originally Posted by DGentry View Post
    I bought some MDO from Harbor a few months ago. Lots of voids, and lots of knot holes on the back face. I'm glad you got some good stuff, but I'm not sure I'll risk it from them again.
    MDO comes in 'good one side' (G1S)... or 'good two sides' (G2S) for a bit more $$. For boatbuilding, it's rare to use G1S, for the reasons you mention.
    David G
    Harbor Woodworks
    https://www.facebook.com/HarborWoodworks/

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  14. #49
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    Nov 2008
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    Northern Neck VA
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    205

    Default Re: MDO and HDO for boat building

    We are building a new push boat for a Chesapeake Skipjack out of MDO. We ended up getting pre-primed MDO. I am grinding the primer and paper layer away where there are glue joints. Would it be fine to at least leave the paper in place at the glue joints.
    Also there are more voids in the inner layers than I care for.

    Egbert

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  15. #50
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    Apr 2007
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    Charlottesville, Virginia - USA
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    Default Re: MDO and HDO for boat building

    Quote Originally Posted by ejds View Post
    We are building a new push boat for a Chesapeake Skipjack out of MDO. We ended up getting pre-primed MDO. I am grinding the primer and paper layer away where there are glue joints. Would it be fine to at least leave the paper in place at the glue joints.
    Also there are more voids in the inner layers than I care for.

    Egbert

    What?? No cross-planked skiff? In Reedville? Shame.

    Glad to see you are still in the mix there, though. Where did you get your MDO?
    FYI, Harbor Sales delivers free to the NN - at least to Kilmarnock - and they do also sell marine fir, Okoume and Sapelle plywood. But MDO does have its advantages.

    David G: MDO comes in 'good one side' (G1S)... or 'good two sides' (G2S) for a bit more $$. For boatbuilding, it's rare to use G1S, for the reasons you mention.
    Not that I use MDO for very much, but always in the past either one has been a quality product - I was just surprised to see how poor this latest sheet was. I'm hoping it's an anomaly, as I do mention MDO as an alternative for those folks who just can't get proper marine plywood.

    In any case, it has made a fine door for my daughter's playhouse.
    Last edited by DGentry; 01-10-2019 at 11:04 AM.

  16. #51
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    Nov 2008
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    Northern Neck VA
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    205

    Default Re: MDO and HDO for boat building

    Quote Originally Posted by DGentry View Post
    What?? No cross-planked skiff? In Reedville? Shame.
    It is a shame not to use the traditional planked method. In this case we needed to be more practical and reliable. The old one needs to stay in the water to stay sealed up and also gets rain water from the top in it. We do use Harbor Sales and I also used them personally.
    At least for finishing the MDO is nice and smooth.
    At the museum we made almost every year a deadrise or flat bottom cross-planked skiff. Nobody wants them anymore because most people want to keep it on a trailer or lift. Doesn't work out very well.

    I'm still slowly plugging away at the Piankatank River Pram. Still some painting left to do.

    Egbert

  17. #52
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    Jun 2018
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    Geeveston, Tasmania, Australia
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    16

    Default Re: MDO and HDO for boat building

    MDO seems to be what's sold here as form-ply i.e. for concrete work.Sometimes called film faced ply.
    It's great for workbench tops. nice and flat, tough and glue doesn't stick to it.
    17mm seems to be the only readily available thickness so as someone previously said, not for small boats.

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