Carbon Skeleton in Wooden Boat

Good Afternoon,

Starting with a 55'x10.5' wooden New York Commuter, she's framed roughly every 14" and double planked. Having not yet gotten into her, I had some ideas and was looking for opinions. She's old, like 1928 old, and therefore definitely not as strong as she used to be. She's also been dried out for nearly 12 years in a warehouse.

1. Strengthening- what do you guys think about routing out all of the seams (would need to be re-caulked either way) and packing them with carbon fiber rope. At the same time, route out a 1/8"-1/4" groove around the hull (following frames) and inlay carbon rope as well. The point of this would be to effectively build an exoskeleton for added strength. Then sand entire hullside/bottom, fair, and wrap in a few thin layers of glass for moisture/waterproofing. I haven't decided yet if she should be sprayed inside and out with something like Devoe 167 or similar, very thin epoxy to saturate and preserve wood as it's as dry as it will ever be.

2. How would they glue the two layers of planking at that time? When refastening, would the planks be pulling off then?

Thanks!
ALP

 

If you are going to fiberglass the outside, there is no need for carbon. It will not help much, since most of the tension and compression on a laminate is close to the surface. However, a surveyor with knowledge of wooden boats will be your best initial investment, before making any plans.

 

I agree with what you've said, however, I figured I'd keep the glass to a minimal mainly because I don't want to lose the lines of the vessel. Further, by inlaying the carbon into the un-caulked seams, the epoxy and carbon compound would then mold three boards (the two side boards and the inner layer board) into a single unit, thus greatly increasing the strength of the vessel.

 

If you pack gaps in a planked vessel with anything hard, you are going to "spring" the planks badly when you get back in the water, and the planks absorb moisture.

The only sure way, would be to totally encapsulate the wooden hull with epoxy, which is not easy with all the double planking and ribs.

There is a method of strengthening that involves routing vertical continuous 1/4" grooves and running carbon fibre along those grooves, and glassing the outside.

There is a lot of discussion on this site about the topic. eg.

Fiberglass skin on old plank wood boats https://www.boatdesign.net/threads/fiberglass-skin-on-old-plank-wood-boats.42736/

 

Yes yes. I read through that. That thread was OK though- it was old and the guys just argued a lot and weren't really all that productive in their conversation.

However, to address your piece. I would clad the entire hull in glass so that popping a plank when she went back in the water wasn't an issue. Further, my thought process was to spray the entire hull, inside and out, in something like Devoe 167, an epoxy the consistency of alcohol, to seal it before beginning the carbon and then glass job.

 

THAT will take a hell of a lot of fibreglass.

My gut instinct would be to diagonal plank the whole outside hull with plywood, and Epoxy just the outside, but I don't know the hull very well.

 

You know, I was thinking about that. I also thought about just taking the two layers of playing off and starting with 1/8" ply and building a cold-moulded hull from the frames out but again, my fear would be losing the gorgeous turns, curves, and such already there....the hullsides are in great shape but the boat was never built heavily and I'd like to stiffen her (she's 90 years old for goodness sake!) as well as strengthen for a new, increased speed- looking to go from a top end of 22 (cruise 16-18) to new top around 40, cruise 35. She's VERY sharp, like the stem is cast bronze and literally filed (except where she's been braised over the years to touchup hitting objects in the water) to a sharp bow. Very narrow at only 10.5' over the course of a LOA of 55'

 

I have several questions about the logic behind some of your conclusions. You've indicated she's "weak", but what is this based on just age, or a careful look at her scantlings in combination with her surveyed condition? I also question the need to change her build type, thinking it too may also be weak. Double planking isn't the lightest method but not the worst either and it has good longitudinal stiffness, which is good on a long skinny design. Lastly, you don't really think you can double her speed reasonably do you? This is fraught with major issues and frankly should be reconsidered. That old lass may do well in the low 20's, but also just as easily may not be shaped appropatly for the 40's. It's not just the shapes, but bottom loading, slamming loads, etc., would also come to play. Typically this type of effort requires a whole new design, that has a look of the previous one, just built lighter, stiffer and stronger, utilizing shapes more appropriate for the target speeds identified in her SOR.

 

So a quick background piece- as I think you noted, she is double planked but being so long and narrow, yes, she is longitudinally, but what's an issue that long and narrow boats suffer from? Twisting.

So with that being said, she's in great shape for her age, but similar to metal, she is obviously not as strong as she was when new simply from age of the material. Further, I presume some sort of glue was used (but I'm not yet sure) by Consolidated in between the two layers of planking it would presumably be weaker than when new. Finally, as said above, she'd be prone to twisting and therefore shear forces. The initial goal here is to strengthen an old hull while preserving her lines.

Regarding speed- she's a round bottom. Simply adding horsepower will add speed....to a point. I would figure that she'd suffer from a stability issue as speed increased over a point as well as eventually having a nose-diving issue somewhere. I'm not sure, without running a model or software, where these critical points should be. Ideally, modifications to the bottom, similar to maybe bilge keels or stabilizers, may solve some of this, but those are ideas for later. And agreed, bottom loading and the dynamic forces associated are certainly an issue that would need to be addressed but with a reinforced skeleton in the hull and then sheathing over the entire hull, I would think this could mitigate a lot of issues.

Your thoughts?

 

I disagree about some less than ideal application of high modulus fabrics, some sheathing and a few athwart (my assumption) stiffeners tossed in for good measure addressing loading concerns, at double her typical speed. I also will likely disagree in that a round bottom (which doesn't describe much of anything about her shape) may be capable of these speeds, even if reinforced.

If you want to go much faster, you'll need a set of shapes that will do so, with a reasonable margin. A round bilge will be getting into her max range, though is inherently stronger and stiffer, given the usual set of shapes employed on pre series '63 hull forms, not a lot of hope. A lot does depend on your boat, but it'll likely need a radically new shaped bottom to see 40 MPH. It probably has concave sections, just where you'd prefer it didn't, more wetted surface than desirable, naturally a warped bottom common of the era, etc., etc., etc. You might be able to lighten her enough, reinforce her enough, but shape limitations alone may just relegate you to high 20's or maybe low 30' MPH ranges, which isn't bad, given the (assumed again) shapes employed.

I don't think carbon isn't the answer and I wouldn't assume she's any weaker than she once was. In her current condition, yeah likely, but if properly repaired, she'll be as good as she was, likely a little better, because of material and technique advances made in the nearly a century of time, since construction. This fact alone would be the route I'd take on this. Make her whole, with an eye on lightening her up where practical put a little more power in her and live with what you have.

Conversely, I did a carvel hard chine cruiser some years ago. The owner just couldn't live with the leaks, the recaulkings, etc., so she was put on the hard and every other plank was pulled, temporary bracing installed and the frames partly repaired as she dried out. The removed planking was labeled and split, from 1.5" thick (bigger boat than yours) to make two, identical planks from each. These where then planed to a common uniform thickness (about a 1/2"), removing their patana. One by one the frames were removed, repaired, holes restored, etc., then the remaining planks where removed, split, planed, hole restored, etc., just like the previous set.

The frames and the planks were epoxy encapsulated. The now two sets of planking had the inner run glued and screwed to the frames, covering the hull, next a double layer of 1/4" plywood was applied on a bias, also encapsulated and bonded to the inner planking and itself. Lastly, the outer planking was glued and screwed through the layers of planking to the frames. This process was laborious and costly, but it was a well noted hull, from a well known designer and in need for a near full up restoration anyway. The now tight, seamless hull needed no caulk, in fact special treatment was made on the previous caulk seams to remove them, for good close seam fits. The boat has been continuously in the water ever since, but her bilge is dusty. In fact, she lost a couple of tons of water gain during the process and hasn't picked any up since. She sees regular haul outs and good care, befitting of this yacht, but her owner is able to live with her now, even if it cost a small fortune to get there. She's moderately faster, because of the weight lose (we added ballast the following year), but being a displacement hull, just not a significant gain to warrant this set of changes alone.

On a boat like yours, you can kiss some of the planking thickness away on a plane and substitute epoxy and plywood or just epoxy alone. This assumes a few things, like the planking comes off clean and given her age, she's likely a 9 pound shellac job, not resorcinol as an inter plank adhesive. She might just have felt and fasteners hold things together, which makes things even easier. In any case with the planking set in goo, there's not going to be movement and edge bonding can permit at least half of her framing to be removed, lightening things up quite a bit.

My point is, you can make significant modifications to this old puppy, but a diet, possible scantlings changes, structural changes, shape changes and better methods and techniques can get you close to where you want to be. The first thing is a real assessment of her condition. Next up a solid SOR so you know how high to shoot. With these two in hand, you can plan an attack, budget, engineering and method approach. Much less is fodder and after 3 beer conversation. How about some images of this old lass?

 

Hahah I like the last paragraph!

Other than being dusty, you can see her currently. Not the best pictures of the bottom, I know and that bow is, as I said before, a file-sharpened piece of cast bronze.

Caulking is out and new keel on (orange primer). She cruised between 18-22 knots before. Would love to get upgrade from the 671N, play with the hull strength, be rid of water, and go double the speed!

 

Now I helped my father (partially as I grew up) rebuild an old buyboat that's been all over the East and Gulf Coast in the past 20 years. She's built like a tank but she's not designed to do more than 9 knots.....

 

Doubling the speed is a pipe dream. However, laminating the whole structure can be done. The deck should be included to make it a monocoque. Further, to epoxy the interior of the hull it will have to be stripped of previous coatings and degreased; particularly around the engineroom area. Also, the outer planking will have to be removed and re-set in epoxy. Most likely it had muslim and shellac in between.

 

Koehler Kraft Co here in San Diego is the local restoration yard that handles all the classics for much of SoCal. The owner/shipwright, C.K., uses a method of re-caulking using fiberglass rope wet out with epoxy, then sealing the planking with epoxy, fairing, then paint. To my knowledge they don't, or at least don't always, use glass cloth to cover the hull - I could be wrong about that, lol. Anyway, there are a few articles of C.K's method floating around. Like gonzo said, carbon rope would be expensive and a waste. Koehler Kraft replaces or sisters ribs, floors, and other structural members as required. They are particularly fond of Purple Heart for these replacements.

 

There's a number of methods to "fix" a carvel, spines, harder caulk, edge bonding, etc., some have good things about them, but others, not so much. Unfortunately, this is a double plank hull, not a carvel, so a different approuch is necessary. How she's built and more specifically, how the layers are bedded are key to working though a reasonable updated planking approuch. It can be assumed she's mechanically fastened, as they all were back then, but the planking interface and edge treatments will tell a lot about the boat and usually govern how to proceed. Pull a plank and see what's between them.