Signal M.O.D. for the hull

[bateaux]

I am building a 24' bateaux, and weighing my options. How about using signal board for the hull? I got a mix reaction to the idea of A/A DF in my last post. It seems like there is an awful lot of surface work involved in using douglas fir ply - (epoxy, fiberglass). I am working with kids and I can't use epoxy. (And I like 5200 better anyway). This is a working boat - kids / dogs / beaching etc., and I am trying to keep it simple. I have always used okume and I am wondering if using Signal MDO board (3/8" for the sides and 1/2" for the bottom) is a good plan. The last boat we lofted and built, a Smith Island Crab Scrape, (16' LOA, 5' beam, about 300 pounds) had 12mm okume all around. But she is starting to rot after 6 hard years- although she is a sweet boat - solid and stiff and still alot of fun to row and sail. The new boat will be 24' LOA and about 4'5" at the beam. So, is MDO the way to go?

[David G]

Perfectly good plan, but I'd be very leery of trying to do it without epoxy. 3M 5200 is not a substitute. Other viable adhesives will require a quality of joinery that is significantly better that what's required with epoxy. Not unattainable, but very difficult to maintain when working with kids (unless you're gonna do the vast majority of the work while they watch & get bored).

I've built only 5 boats, but all with kids and/or other inexperienced helpers. I'd seriously rethink the "no epoxy" scheme.

"However beautiful the strategy, you should occasionally look at the results" -- Winston Churchill

[Bob Cleek]

For a 24 foot boat? No, but I have the feeling you're going to do it anyway. Aside from the fact that you can just paint the paper covering on it and make believe you actually finished a smooth surface, the price is right. With a pick up truck and a crowbar, a good ole boy ought to have no problem picking up enough to build a 24 foot bateau from alongside the highway in a good night's work.

Your last boat started to rot after less than six years? I guess it depends on how much you want to work building a new boat every so often, as opposed to how much you want to use the one you built.

But, don't mind me. I'm feeling cranky at the moment.

[P.L.Lenihan]

Sounds like an excellent approach,using MDO Signal.Try to get all your stock good two sides. Do not fear epoxy.Learn to work clean and neat,especially with kids about, and they too will hopefully pick up your good work habits. Glass the outside surfaces where you expect abrassion issues,ie; the bottom for beaching, the sole(floor) of your boat for sand and other bits dragged on board by happy campers.
Have built three boats,over the past 20 odd years, with MDO and have never,ever, experienced any problems.Was offered some Okume last year, at nearly twice the cost of the MDO and while the Okume had beautiful surface veneers, the inner veneers looked like soda biscuit.

Good luck with your new build!

Peter

[Martin Pflanz]

You might want to visit the Bateau site. They recently have had a long discussion about the use of MDO. The consensus seemed to be that it would be better to stay with Marine Ply. But I know that other builders including Jim Betts advocated the use of MDO. So, you takes your pick. Let us know how it comes out.

Martin

[Chan]

I wouldn't use mdo without encapsulating it in epoxy.
Take a test piece and put it in water with no finish on it and see how long it lasts.

[David G]

I wouldn't use mdo without encapsulating it in epoxy.
Take a test piece and put it in water with no finish on it and see how long it lasts.


I don't think that's necessary - except as Mr. Lenihan notes. You can go to Olympic Plywoods website & check for yourself, but IIRC the face paper is in a phenolic resin. Every bit as durable as the epoxy you'd apply over it is my impression (if not more so). So, if you get the Good 2 Sides, it eliminates the checking issues of the typical rotary cut fir faces found on normal marine fir ply, and serves as a very good paint substrate (with a little scuffing).

"Every man is guilty of all the good he didn't do" -- Voltaire

[kulas44]

I have peices of cheap mdo 1/2 in thick laying outside on the dirt for the last two years, they are darker but still look fine. And no, this stuff aint made with cottonwood. My experience with it has been that it is better quality than comparably priced marine plywood. AND, it really takes paint good. I would not be a bit concerned about building a 24 foot boat with it, using nothing but 5200 (I would use PL Door and Window) and some screws. If you need it to last a few days short of forever, seal the edges with CPES. Have fun, cheaply !!!.

[bateaux]

Well, Bob is correct, I am gonna build this 24' boat, like it or not. With MDO. New MDO that is, as I don't care for an interstate green hull on a bay boat, although the whole pickup truck and crowbar concept does have its merits. Thanks for the input guys, we will send pics in a couple of months.

[Dan McCosh]

I've use MDO ply for interior bulkheading, and it generally seems to be high-quality marine ply with the paper overlay that makes for a good finish. Not cheap, however--I paid close to $70 a sheet for 1/2 ins. recently. As for building a boat hull with it--main problem I could see is doing a neat scarfing job for longer sheets. I would at least epoxy exposed edges, as well.

[Thorne]

Do keep us posted on the progress.

As above, you will need to seal the edges of the MDO with epoxy. You could try CPES (wear a good respirator with new organic vapor filters) when the kids aren't around, or heat / thin regular epoxy to get maximum penetration on the edges and into the plies.

Good luck!

[kulas44]

If the inside of the boat will be seen/painted, use double sided mdo. The exposed side of one sided mdo will check, even under paint. The double sided is about the same price, maybe a little more. I bought a stack of 1/2 inch mdo, single sided, about 30 sheets, for 24 bucks a sheet. They'd had it for years and needed it gone.

[kulas44]

Don't be tempted to use HDO. It's made for building concrete forms and while it is good quality, and dense (actually heavy) nothing wants to stick to it. That's why it makes good concrete forms, but it don't hold paint very good.

[Cuyahoga Chuck]

MDO has a paper overlay. Anything you glue to it would be glued to the paper. Doesn't sound like that is a scheme that will keep anything as ponderous as a 24' boat together.
Also, anything that kids will ride in better be put together with a max amount of retention. Your attorney can advise you more about that than I can.

[P.L.Lenihan]

MDO has a paper overlay. Anything you glue to it would be glued to the paper. Doesn't sound like that is a scheme that will keep anything as ponderous as a 24' boat together.
Also, anything that kids will ride in better be put together with a max amount of retention. Your attorney can advise you more about that than I can.

There must be a number of different quality MDO panels out here as there appear to be a fair number of folks who believe MDO is just"a paper overlay".As if it was nothing more then gift wrapping. Quality panels, like those made by Olympic panel ie; Signal MDO are incredibly tough.A cellulos resin empregnated overlay layed down in phenolic resin glue.
Here is a little experiment I did once, by fluke : I had a number of MDO cut-offs stacked on their edge and leaning against my boat jig. Some epoxy resin had dribbled or run down onto these cut-offs from a job being done just over them. A few days later, I went to pull out a single piece of cut-off and discovered several had become glued together.Well, pull,bend and twist as I might, I could not seperate them.Finally, put the mess in a vice and really pulled hard.CRACK! One of the cut-offs broke free and taking with it not only the "paper" overlay but the first wood veneer as well. I was so impressed, I repeated this with the remaining cut-offs and had the same result.
Keep in mind too;none of these cut-offs had been properly sanded or prepped in any way, no clamps had been used and the"glue" line of epoxy was in the vertical axis.Gravity was the only force at work as the epoxy ran down onto the cut-offs.
So.....get a small sample from you local supplier and give it a try.Good quality MDO will not let you and yours down. Poor building practices however................

Peter

[kulas44]

I have never seen the overlay seperated from the wood, under any circumstance. It takes glue just like it takes paint, excellent. BUT, if you don't wanta try it then don't, good marine ply will work just fine for you. What I have seen is that you can build a boat with signal mdo and PL premium and stainless screws, no paint no epoxy saturation no preservation at all, put it in the water and leave it all summer long then put it out back behind the shop till next spring and it will still go to work. AND my "painter" boat has been doing this for 5 years now. It is, however, the ugliest most ungainly little thing you've ever seen. 4x8 across the bottom, slightly curved up at the bow, 18 inches on the sides. Two whole sheets and scraps, plus a few peices of PT yeller pine for screwing the thing together. It fits right in the back of my truck and a 7.5 Johnson pushes it just fine. Good MDO is tough.