diagonal planking

Black Locust......Why?

There is no precedent.....I know of no cold-molded boats planked with Black Locust...why would you re-invent the wheel. Because it's rot resistant? Where is the epidemic of rotting bottoms in cold-molded boats? It's hard, heavy, difficult to work, and long term bonding with epoxy is questionable.

If you are building a cold-molded hull, by definition each piece of that hull is entirely coated (all surfaces) with epoxy. This coating limits moisture entering or leaving the wood to a tiny amount. Thus it remains roughly at the moisture level you started with......forever.....as far as we know. This means properly built cold-molded hulls will not rot. Only when the epoxy barrier is broken will deterioration start.

Douglas Fir is strong, easy to obtain, light (weight is only useful in steam rollers), easy to work with, and bonds with epoxy beautifully. Why use anything else? Don't say, "because it's free". That's not a sufficient reason.....you'll be investing thousands of hours in building this boat...to use questionable materials makes no sense...then the whole endeavor becomes worthless.

The only experience I have with Black Locust in boatbuilding is the laminated ring frames and backbone in the 90' cold-molded WhiteFin, built in Rockland Maine in 1983. The guys building her hated it and seriously questioned the bonding (West epoxy). Her hull skin is 2.25" thick, in six layers, four diagonal and two fore and aft. Her deck is 1.625" thick in four layers. After 10 years it was found that her Black Locust ring frames were tearing the structure apart, I guess with the tiny movement associated with wetting and drying of the various woods. The Black Locust is so strong it was ripping up the softwoods bonded to it. There was also some delamination of the ring frames. Her first 10 years were not the best as far as maintenance goes, it's been better since. That was found 15 years ago and further rebuilding has been done since. See WoodenBoat #57 for more info.

Buy the Gougeon Brothers book on boatbuilding and follow it...it works.

 

hmmmm
well one thing I can say is you folks sure are tops when it comes to saving people from themselves
Is epoxy impregnation really all that good that wood species is almost irrelevant. Thats wild, I never would have imagined it.

I was just doing a weight budget for planking stringers and bulk heads in black locust and you are right on about that weight adding up
stuff is dam heavy at 48lb/cu/ft

poplar is only 28 and cherry 36 and white oak is 42. I keep getting blasted every time I mention poplar because of its poor rot resistance. If Im cold molding whats the difference, so I went with a highly rot resistive wood. I can beat any wood into submission so how difficult it is to work with is irrelevant but weight is a concern. Also you mentioned that this wood has proven itself unstable or prone to motion. Yikes. Ill definitely go read that article.
Thanks again Tad you are most helpful
B

ps
just looked up that book
good call
Ill have to give it a try

 

I have read this whole thread through with great interest---when I should have been doing more constructive work.
BOSTON (Who has my greatest admiration I should add) Said:-
"hmmmm. Is epoxy impregnation really all that good that wood species is almost irrelevant."
The answer is a vehement YES.
I have built sailed and sold twenty nine boats in my time. nine of those were foam/fibreglass hulls. The rest were wood. Only one of those was a 38' double diagonal plywood construction. I hated it. So messy and time consuming, not to mention expensive.
The biggest sheet ply boat was a 51 ft Catamaran of simple sheet plywood on integral frames mounted on a strongback. It was made of douglas fir plywood which is not the best for rot prevention. It was built using epoxy glue. All the parts of the boat were saturated with a thin, penetrating epoxy. The hulls and decks were coated with two coats of epoxy on the inside and three coats on the outside. All exterior joints were sealed with fibreglas tape set in epoxy. Two coats of polyurethane marine paint finished the job. That boat was built 37 yrs ago and is still sailing today.
We also built several other boats --mono and multi , in 1/4" marine ply, non of which were covered externally in glasscloth, only glass tape on the seams and epoxy/ polyurethane coated. Multi-chined bottoms are easy to build and approximate the ideal round bottom section for minimum wetted surface and good performance.
The method is simple and could be easily understood by non skilled workers, who produced light, strong, and durable boat hulls.
Worked for me.
Paddy

 

You might have misunderstood the question.

The encapsulation in epoxy makes no difference if applied on a weak timber, say birch, or on a stronger as mahogany. It just makes it "waterproof" and glues it together.
But the strength of the bare timber is of course still the main provider of the structural strength of the boat! Therefore it makes a immense difference, which timber one uses.

Regards
Richard

 

thanks Paddy
I was thinking that the epoxy negates the issue of the differences in rot characteristics in various woods so that say Poplar could be used in hull construction, regardless of its inferior durability ( it does have tremendous bending strength ) . The structural considerations would still apply as Richard is suggesting

my two cents

cheers
B

 

exactly so consider this

a lot of wood species have been passed by because of there poor rot resistance yet have in some cases at least excellent strength characteristics, so what if you impregnated them with that light thin penetrating epoxy you mentioned, seems like now you have a perfectly viable wood for marine construction, readily available and dirt cheap.

B

 

I'm not really a denier of the value of epoxy coating, although I think that - having gone to the trouble and expense of epoxy - one might just as well toss in glass for the durability and, in the case of fir, the prevention of checking. I read elsewhere of the impossibility of truly sealing wood with epoxy and these sources note that, once in the wood, the moisture cannot easily get out again. So the seal has to be perfect and I am sceptical of perfection, shall we say.

I question the extra cost of the epoxy when it is used to justify the use of a cheap wood, if inferior. I think that it might be a good idea if it allows the use of a wood like poplar, which has good characteristics other than lack of rot resistance, and is also available in wide planks unlike many other formerly boat-useful woods.

 

well there is a lot of precedence for the use of poplar in the past, there is a neolithic site just discovered with a 6500 year old poplar door perfectly preserved so ya, old growth heart wood poplar does seem to have some sticking power. Thing is that if the impregnation is not complete then yes infiltration does seem like it would be an issue although, thin enough veneers will ensure complete penetration of the epoxy which ensures resistance to decay.

Perfection is not necessary but care and consideration in construction methodology definitely is

a little thought and some careful planing might just go a long way in building a modern yacht and taking advantage of modern materials

 

Yellow Poplar, if you can find good old growth or old second growth it's a great material, but not a common item any more, unless you pull it off a 50 year old mid western barn, which I've done.

The thing I think Terry and Dan are missing is that epoxy can afford modern building techniques, which will dramatically reduce building costs with savings in materials and labor cutting and assembling them. Yes, you run the risk of trapping moisture under a plastic coating, but the alternative is to not use epoxy as a coating and now you're back into massive deadwood assemblies, frames, floors, stringers and other assorted pieces that simply aren't necessary with modern building techniques. Yea, some of us like to look at 2" thick planking with 6" deep sawn frames and 1" thick ceilings nailed over them, but hell man that's a lot of wood to hang.

How substantial a difference between an old style build and a new, encapsulated build? I'm currently working up scantlings on a friendship sloop, built in Lord's method strip plank, which is the lightest of all, without getting into fancy cores. It's very similar in every regard to the Morse built boats at the turn of the 19th to 20th century. At 28' on deck, she's bigger then Dictator, though she looks a lot like her, except I've got a more stylized bow rake in it. 7 to 8 tons would be reasonable for for a traditionally built craft of this scale, I'll likely see this one built with 4 full up and carrying a healthy ballast ratio too.

What does this mean? Money, you get to keep more of it, because you don't have to buy it, labor over it's shaping or install it. This has been the motivating force behind most building trends in recent centuries.

On small craft you have choices and often they don't cost enough to force your hand, but on larger projects, traditional is nice, but you're paying for the look and massiveness of these structures. Dan, as you know a timber frame building is fun to build, but can't compare to platform framing in cost, which is the ultimate bottom line for most signing the check. Hell they'll install some foam beams and paint them brown, who'd know the difference, right.

 

ever have one of those aha moments, well reading that was kinda one of mine. I've been looking at a 32" friendship sloop and thinking of how I would rebuild her ( see OK I dont own it ) my thinking is I would use the old hull as a mold and cold mold over it then loose the ole hull and place the two halves over a few stringers and a false keel. Ends up lighter, stronger, cheaper, better all around. Bolt on the lead and finish to suet.

completely not suitable for the inside passage though but hey
a guy can dream eh

anyway I have been looking into cost comparisons for a while now and I can only concur. Cold molded over stringers is the way to go as far as I can see for not only ease and cost but also for creating the driest hull possible.

chears
B

 

When we were building lightweight boats, we would lay up all the wood we were going to use on scrap wood distance pieces and cover them with polythene plastic sheets. We put a small hot air electric heater at one end with an outlet at the other, and left it running for seversl days. after the first few hours water was literally running out from under the covers. We aimed to lower the water content of the wood to about 12% from the common amount of 24%. This not only made the wood lighter and stronger--but it enabled the Epoxy soak coat to really bite into the surface of the wood. This prevented the wood absorbing water vapor again . Don't let anybody tell you that a proper 100% solids epoxy can't keep out water. It can keep out water vapor which is a much more insidious thing. We used to convince unbelievers by showing them a piece of wood which had been coated with two coats of epoxy, weighed, then left in a capped jar of water permanently. When the jar was opened the epoxy coated wood weighed the same as before it was immersed.

 

G'Morning Boston,
As Tad mentioned, the Gougeon Bros. book is very good and fairly thorough. But you might be surprised at how helpful and genuinely interested all the guys at their tech line are. Give 'em a call, you'll get a lot of information and probably enjoy it too - (866) 937-8797
And thanks for these threads! Very interesting and entertaining.

 

Morning to you as well
Ya I think I might have that book around here somewhere. At present I'm reading "The Sail-makers Apprentice". Really interesting read, covers a lot more than just sailmaking.

 

Poplar posts have, I am told, been pulled out of 100+ year old houses after demolition and were in near-perfect condition. It’s the young stuff that’s not durable.

Huh? I love epoxy; as an adhesive. Because of it I can build lightweight boats - I have never built a boat I couldn’t pick up and carry. Epoxy is the best thing since sliced bread - way better actually as I prefer to bake my own, but I digress. I cannot bring myself to use it as paint though.

Par: the friendship sloop sounds great.