New (??) Hull Construction Technique

[imported_Glenn]

Thinking about a way to achieve a maintenance free hull on small boats I came up with an idea.

What if we combined a cold molded hull with the plank on frame technique. If we take a round bottomed hull using say 1/2" cedar over steam bent 1/2" thick white oak frames we could start our planking with 1/4" planks running fore and aft followed by two 1/8" diagonal strips that could be epoxied and stapled with monel staples and possibly vacuum bagged. We could put string tape beneath our final layer of staples which could be pulled out once the epoxy kicks.

When complete we could drill from the inside through the frame and hull and later use the same bit from outside but with a countersink after which we could rivet and rove the hull to the frames after removing the hull from the molds using two people. Or... (and this is where things get creative) we could simply forget the rivet and roves and turn the boat over and drill a tiny (and a shallow 1/8") pilot starter hole in the oak frame. Next we could take a 1" long bronze ring nail and drive it into the frame and hull through a rove with the hat facing up at you the same as with a standard rivet and rove. Finally, we could peen the head of the ring nail and have what would appears to be a traditional plank on frame boat hull but yet with the mainenance freedom of a cold molded hull.

My only reservation would be that the ring nails might loosen over time as the boat is stressed while under sail.

Just a consideration at this point but I'm looking for feedback. If you have hot air, please don't respond but if you have constructive critisism, or heaven forbid praise, please do respond. Thanks...

[Bruce Hooke]

A few thoughts:

1. It seems like a lot of work to get a "look" -- fitting wide planks is a lot more work than, say, strip planking, which is a more common "base" for diagonal cold-molded planking.

2. It seems like the exterior would be so smooth and perfect that it would tend to raise questions about the true "nature" of the boat.

3. Maybe it's my artistic training but I'm a big believer in "integrity" in design. Put simply, if you want the real thing, make the real thing, otherwise make something else and be honest about what you are making. But, if that mode of thinking does not resonate with you then feel free to go your own direction!

4. The inside layer of planks would, I think, need an epoxy coating on the inside face to keep them from moving around too much and overstressing the bond with the diagonal layers.

5. In my limited experience, the major maintenance hassle of small, open wooden boats is keeping the INTERIOR painted. The outside can be sanded and painted in a few hours. Sanding and painting the inside is another matter. So, as a way to reduce maintenance I'm not convinced that this method would gain you that much. What it could gain you is the ability to keep the boat on a trailer.

6. Plenty of small carvel planked wooden boats are put together with screws, not rivets. Screws, of course, would not be visible from the inside. So, I would dispense with the fake rivets. This also adds some integrity to the design because then you are not completely faking something just for the look.

All of that said, I can't think of any technical reason why it would not work, but that opinion is worth exactly what you paid for it!

[Jack Heinlen]

I think this is a bad idea.

Trying to build an essentially carvel boat with a cold molded skin? What about all the holes you propose? What about sealing the inside well?

Nope, doesn't work for me.

Build a cold molded boat, all sealed up, through fastenings few and well sealed, that works.

Build a traditional carvel boat, all kinds of fastenings not hermetically sealed, the wood not sealed terribly well, that works.

Put them together, with fastenings through the layers, EHHH, the buzzer just rang.

Keep thinking though. New techniques do come along from time to time, but they are few and far between. First and foremost must come function.

[Big Red]

Quoted from Glenn "What if we combined a cold molded hull with the plank on frame technique"

One advantage might be that you need to make less molds for the cold molding process. I guess on a small boat the fastenings used to hold the first layer on would be small. Tho, I kinda like the idea of cold molding cause you have less frames inside.

[Bruce Hooke]

Originally posted by Big Red:
One advantage might be that you need to make less molds for the cold molding process.

Just as an aside, the same end is achieved more quickly (and more commonly, I believe) by using strip-planking for the first layer.

[gaffman]

Why bother with steaming oak. A builder I know rebuilt a Trumpy with plastic frames. Easy to work with, won't rot, strong. Time has stood the test and the boat is doing well.

[Garrett Lowell]

Were the plastic frames made on-site? Or did he have to have them special-ordered through a specific manufacturer?

[Tom Lathrop]

I agree with Bruce and Jack. In 1993, I saw Jon Wilson and his boat at the WB show in Neuport. I thought his mast looked a little funny and asked him about the construction. Sure enough, it was carbon fiber with wood veneer overlay.

Same deal, one of the "new classics" I guess.

[Keith Wilson]

It's fairly common to build boats with an inner layer of strip planking, then a couple of layers of diagonal veneer, then sometimes an outer skin of veneer with the grain running fore-and-aft for appearance, and fabric/epoxy sheathing to taste. It's a reasonable way to get a thicker hull for larger boats with less labor than full cold-molding, which involves spiling the planks for each veneer layer.

I think what you describe would work just fine functionally , and it would probably look good too, but I'm somewhat uncomfortable with that much extra stuff added just for cosmetics. The frames are unnecessary; with the diagonal layers you don't need additional cross-grain strength to keep the planks from splitting, and one or two thicker laminated frames (or bulkheads) would keep the hull from flexing. The rivets aren't structural either. It's basically a cold-molded hull with frames and rivets added for appearance, and it reminds a little me of plank lines molded into a fiberglass hull.

[ 06-30-2004, 01:03 PM: Message edited by: Keith Wilson ]

[Jack Heinlen]

I think what you describe would work just fine functionally

No, I don't think it would, precisely because he's going to add all the rivets for show. And if you want to talk about show, there's no need for half the frames. Add in that steam bent timber wood is dicey with epoxy, and the way he's going about it is backassward, and it adds up to disaster as far as longevity goes.

I see all kinds of problems as proposed. It could be I'm not seeing it clearly, but what he proposed is to build a carvel boat skinned with a cold mold and then fastened through with a thousand fastenings. Bad idea. IMHO

[Wiley Baggins]

Originally posted by Glenn:
Thinking about a way to achieve a maintenance free hull on small boats I came up with an idea.

What if we combined a cold molded hull with the plank on frame technique. If we take a round bottomed hull using say 1/2" cedar over steam bent 1/2" thick white oak frames we could start our planking with 1/4" planks running fore and aft followed by two 1/8" diagonal strips that could be epoxied and stapled with monel staples and possibly vacuum bagged. We could put string tape beneath our final layer of staples which could be pulled out once the epoxy kicks...

I'm almost with you to this point. Paul Gartside (and others?) sort of split the difference by building double planked hulls with (epoxy) glue between the two layers of fore-and-aft planking rather than other concoctions (muslin and white lead paste being one).

If I were inclined to take your approach, I would forego the fasteners between the frames and the cold-molded veneer layers. That's what the glue is for. Rivets or screws could be used for the initial fore-and-aft layer of planking.

In my view, the positives include a strong (stronger?) hull with traditional appearance while the negatives include likely difficulty in effecting repairs and having to deal with frames during the construction of the interior.

[ 06-30-2004, 07:49 PM: Message edited by: Wiley Baggins ]

[Jack Heinlen]

Okay, building a carvel boat, then overlaying it with diagonal planking, no through fastenings, would work, but what a lot of work. Why, when a cedar planked small boat, with reasonable care, will last for forty years or more?, an encapsulated one, built with conventional methods...?

Add in the complication of repair and it still seems a bad idea.

I still don't get it.

[ 07-01-2004, 09:21 AM: Message edited by: Jack Heinlen ]

[Ian McColgin]

I guess Glenn's trying to get the look of plank and frame on the inside and painted carvel on the outside. Since many plank and frame boats are nailed or screwed into the frames, rather than rivited, I don't think there's any gain to the pseudo inside fastenings. If you really want that look, just embed some little copper discs.

It's a little harder to start a fair hull from longitudinals over which you're going to put an ashcorft pattern than putting the dual diagonals on the inside over a strongback and stringers, but only a little.

In the technique as described, I certainly agree with those who don't see any structural virtue to the frames.

There are a number of designers who have plans for pretty 'low maintenance high epoxy' boats that will stay nice and tight even living on a trailor or car top. Usually glued lapstrake plywood. I'd go that route for the look of interior frames and gobs of interior brightwork.

G'luck

[Jack Heinlen]

Ian,

I get the part about carvel appearance combined with cold molded performance, and your idea of gluing roves onto the frames sounds okay, silly but okay, if that's what he wants.

I think, maybe, it comes down to his original statement, which is delusory.

Thinking about a way to achieve a maintenance free hull on small boats

T'aint no such thing.

I don't know, the entire thing seems affected to me. Glen hasn't peeped since he posted originally, so we have no added information.

My advice: If you want the look of a traditionally planked boat then build a traditionally planked boat. Carvel if it suits you, lapstrake too, particularly if it's going to be out of the water a lot. If you want a cold molded boat, then build that.

[imported_Glenn]

Thanks everyone for your feedback.

Yes, I agree the frames would be not needed and also that the ring nails and roves are cheesy at best and again unnecessary but I am striving for 2 things.

1. To have a boat that LOOKS very traditional from the inside and...
2. A boat that looks great from the outside and provides a hull that can easily be trailered without having to recaulk seams when needed, etc.

Someone mentioned that hull repair could be tricky and I agree to a certain extent. I guess it depends on how bad the damage. Scrapes would be no problem. Holes would be more involved but still not a big deal.

Also, to hang 1/4" plank strips fore and aft would be a snap without the need to get your bevels set and your planks to fit tightly.

I think I might go off and do this thing albeit a conundrum of uncertainty. I'll let you know how she goes. Please check in with any additional feedback or interest of status. Won't start on her until September.

thanks again

[Paul Pless]

1. To have a boat that LOOKS very traditional from the inside and...
2. A boat that looks great from the outside and provides a hull that can easily be trailered without having to recaulk seams when needed, etc.

Doesn't lap-ply fulfill these requirements? Add frames and rivets if you really feel the need.

Or, what about how the old wood and canvas canoes and guideboats were built? Doesn't get much more traditional than that.