Would cold molding over a carvel planked hull be a viable solution?

If cold molding can be structurally sound without any frames or stringers, would cold molding over a carvel planked hull be a viable solution for a boat with compromised structural integrity due to broken frames, and a cracked stem?

 

It can be viable - the Falmouth Quay Punt 'Curlew' is a good example of this being done successfully.
Falmouth Quay punt “Curlew” – BC09 | National Maritime Museum Cornwall https://nmmc.co.uk/object/boats/falmouth-quay-punt-curlew/
She was originally built in 1905, and many years later she had 3 layers of New Zealand kauri cold-moulded over her originally carvel hull planking.

I think though that you might still have to consider replacing your cracked stem?
Can you post some photos of the boat please?

 

Maybe, but what is harder?

A stem repair is generally not that bad with epoxies help [sic].

 

I don't think cold molding means that there is no need for frames or stringers.
So I suspect that cold molding over a "broken hull" would be a case of good money after bad.

My two cents worth, AlanX

 

While both are wood constructions, carvel plank is wet wood, and cold mold is dry wood. If you don't dry the carvel planks they will sheer strain the cold mold as they dry. I you do dry the carvel it loosens up.
I have never done it. This is just my opinion.
It seems easier to fix framing.

 

We would need a little more info: How thick is the planking?
It has, and can be done.
The planking needs to be taken down to bare wood and all the caulking pulled out.
Then the planking and structure needs to dry out, this might take a long time, depending upon weather
and storage conditions.
If you can get the boat indoors, tent it and have fans running, you'll have a chance.

 

I am another who has never carried out the process,but if it is a case of adding a substantial skin to a hull that doesn't have rot issues,I can't see why it shouldn't give an existing boat another lease of life.done carefully it is a new hull being added to the boat but done badly it would result in a flimsy skin that could only ever be a temporary extension of the life of a tired old boat.I suppose the outcome revolves around how dry the boat is and how carefully the new skin is added.

 

The old hull could be regarded as a male form for cold molded construction. That implies that the cold molded parts have a sufficient number of plies to hold their shape when the male form is removed. That method would make a whole new hull that is only slightly larger than the original carvel boat. This presumes that the old hull had no hard corners and that it was essentially a moldable shape as with sufficiently rounded chine areas.

Cold molding merely to add thin sheathing to the old boat, probably not a practical idea.

 

How thick would the layer of sheathing need to be sufficient to provide the strength of a "whole new hull" as you described?

 

Let's first examine a couple of differences that start with the basic original construction.
In looking at an end-on-view cross section, in a conventional plank-on-frame boat the boat exists as basically two hull-halfs that are held together by the floor timbers that span across the keel and connected to frames, of course there are variations, but in principle the planking, (garboard plank,) is fastened into a fairly shallow rabbet and much of the keel is external.
What keeps the boat together are those floor timbers.
In Cold Molding the preponderance of the keel is inside the boat. The keel is externally beveled/faired so that there is a large amount of faying surface for gluing/fastening, and then an external "wooden cap", if you will, is installed that covers up the ends of the veneers, spanning the width across the two sides.
As such the two halves of the boat are much more of a one-piece structure, floor timbers being mainly installed to serve as bearing devices for the interior structure and supporting engine beds and mast steps.
The key to success in cold molding over an existing carvel hull is making sure that the existing floors/frames are still capable of holding the halves together, as even with cutting a new rabbet for the veneers, that new rabbet will seldom have the large faying surface that transfers/supports loading to a full extent.
The same can be said of the stem.
As for the thickness of the new cold molded "covering", there are a lot of variables, thickness of individual veneers, fastening schedule, gluing properties of the wood, and the type/strength of the wood itself.
So far in this discussion we have had nothing to go on except "Can this be done".
How big is the boat?
How much does it weigh?
How thick is the original planking?
What type of wood is it planked with?
How are the planks fastened, nails, screws?
Power boat? Sailboat?
If power boat, is it a planing hull or displacement hull?
What type of design?
When these questions can be answered then some groundwork may be established for more specific replies.

 

How

Gerr suggests for plank-on-frame: thickness (mm) = 18.78xSn^0.4 and cold-molded: thickness (mm) = 13.97xSn^0.38
That is a relative thickness of cold-molding is about about 75% of plank-on-frame.

AlanX

 

rout out all caulking of the carvel hull
thoroughly dry it
glue thin strips into the routed seams
plane smooth
min 3 veneer layers cold molded over the hull
next one biggest problem:
each piece of wood inside the hull touching another must be glued
inside of hull sealed with min three layers of epoxy

fibreglass sheathing of a carvel hull is called "shroud" (in the sense of "shroud for a corpse") in German ("Leichentuch"), & for a reason
nobody said rescuing an old boat is easy

 

Several threads on Cold molding as a means of sheathing or prolonging the life of an old boat.
For more years than i care to think i have been restoring a 28ft fast motor launch built in 1905 by Saunders, she was built using their pattented consuta sewn plywood, (think cold molded but as no waterproof glues at that time they sewed the hulls with lines of copper wire). Mine was 2 diag skins of cedar & i thicker mahogany on outside.
Because of severe ice damage to the outer layer of the hull I ended up stripping the outer layers away & laminating a new cold molded hull to the original inside layer.
One aspect of cold molded sheathing or encapsulation of old wooden boats that is often overlooked is contamination. Epoxy does not like contamination from oil or other things like antifreeze. Any old boat that has had an inboard will have had oil spills from sump oil, diesel or petrol, often the frames & planking in the bilge & under the engine will be saturated right through. There is no real way on this earth to get rid of it.
In my boats case the entire bilge was soaked in old engine oil from the bilge, The inner layer was only 1/8" (3mm) thick even this could not be degreased. So all oil soaked wood was stripped out. The construction of this boat lent itself to a full rebuild in this way.
How you degrease a carvel boats bilge? im not sure you can.