To plank or to cold mold?

[TK1]

Hi,

Seeking the collective wisdom of the experienced builders (or those who've done more research than me!) on the pro's and con's of strip (carvel) planking vs cold molding (in the latter case either ply or veneers, with a final layer of veneer unless I can get nicely faced ply).

Not expecting consensus or a correct answer, but interested in experiences from those who have used one or both methods.

Here's the scenario: boat will be inboard-motored "gentleman's runabout" type around 20' long, living on a trailer and will be used in salt and fresh water. Frames will be ply (as thick as required) and use will be a runabout - won't need the lightness or strength of a proper race or ski boat. Round hull, not hard chine.

So, original boats I have in mind (still finalising choice) were single or double-layer planked mahogany (in double layer, the second layer offset 50% of the plank width longitudinally to strengthen joints), and copper screwed or nailed.

And finally to the question: Given modern techniques, the cost of solid wood, the fact it won't live in the water, etc, should I go straight for cold-molding? Or should I aim for some historical accuracy and go for solid wood?

I can plank the outer layer in a decorative veneer, and it wouldn't need nails/screws, so finish would essentially look similar. I believe molding would be a lot lighter too.

In either case, would I fiberglass the boat as it will not live in the water? Would this work OK on a planked boat? Or would the wood crack it as it shrinks?

Hope this question isn't too long, I could have just said "what are the pro's and con's of each?" but I wanted to put it in context.

Thanks in advance,

Darren

[Auld Bassoon]

Hi Darren,

For the purposes that you have stated, I personally would go for cold moulded construction. It's lighter and a bit easier.

Carvel, whilst very traditional, is quite a bit heavier, but may not endure immersion/drying out cycles quite so well. I believe that it would also cost rather more based on more timber being required. The flip side, though, is that I think it looks much nicer.

My 2c worth :)

[scottyk]

I have just completed a hull 18' long, cold moulded (2 X 4mm layers of King Billy), with one layer of 200gm/m2 over the outside only. Have a look at some of my other threads for pics.
I'll try and give you the pro's and con's of the method.
Pro's:
- Keeps the construction light due to better control of the glue used.
- Hull is strong due multi directional grain achieved through the multiple layers.
- Because thin veneers are used shrinkage isnt a problem after the hull is finished before it is sealed or even after.
- Cold moulding doesnt need a layer of glass on both sides so you get to put a nice clear finish on the inside.

Cons:
- Can be for time consuming due to the time to make the mould and failr it up, plus the time it takes to drive an infinite amount of staples and the pull them out!
- you need to get failry good timber to cut your veneers from.

My final piece of advice for any one building a boat using epoxy is get a copy The Gougeon Brothers on Boat Construction. It is still in print and in my opinion is the Bible for this type of construction.

Lastly, good luck and have fun
Scotty

[Ecca]

Darren,
There is a slight confusion in my mind as to your methods. Do you mean :carvel or strip planked ? They are very different.
If your boat lives on a trailer, then strip planks with f/glass inside and out is fine as is a cold moulded style.
I would not use traditional carvel for a trailer boat as it will dry out and leak when re immersed.
If you are into speed and some pounding of the hull I would go cold moulded, but with a diagonal layer in the middle of 2 layers of planks or a layer of carbon fibre at 90 degrees, and in the middle of the planking.
Also is the boat to be clear finished? If so you MUSTdo a top job on the glass. You only get one shot at it.
My second last sail boat was strip planked , glassed and still looks fine 4 years later. My launch is cold moulded and glassed externally only and painted with epoxy internally. [bullet proof almost] Problem was that I basically built the hull 3 times.
I had intended to have the launch clear finished as I planked it in Huon Pine, but there appears to be a reaction between the oil in the huon and West systems 207 catalyst.It discolours the timber to a light brown and sometimes PINK.
You will obviously have to refer to your plans as to what they recommend and do no less.
Basically if you satisfy the structural requirements all you have to do is creat a situation whereby leaving the boat on a trailer does not compromise its integrity.
Hope that helps
regards Ecca

[TK1]

Thanks guys,

I think I will go the cold moulded. I figured it was the way to go and your comments have reinforced that. I think the extra time taken will pay off in strength and lightness, and as it will live on a trailer this is another reason.

Now I just have to buy the wood, cut the frames, get the veneers, epoxy and glass it all and I'm done! Will post pics once I start - this summer, as I need to rearrange the shed first and finish a couple of small projects then I can get into it.

Regards,
Darren

[Boatmik]

Howdy Darren,

I am not sure that you are comparing apples to apples.

Strip planking is a modern method - not the same as carvel.

It has the same advantages as cold moulding but is perhaps a faster, usually simpler process as far as everything from the building of the jig, through to planking, fairing.

Its main drawback is having to fair and glass the inside of the hull as well.

Most building these days is in strip planking - partially because veneers have started to become hard to get and you can use any species of timber for strip (providing it glues well) - and because of the relative efficiency of the building process.

MIK

[TK1]

Hi Mik,

Thanks for the reply. The boat(s) I have in mind were originally carvel - with seams, caulking and screwed to frames - so I think I had the right term, but in the modern context probably meant strip-built.

With strip planking, I assume glassing both sides of the planks alleviates the shrinkage that would be caused by keeping the boat out of the water? I like the idea of strip-building, and this would seem to work based on the original design (just more planks) but having had another look at the lines I think ply sheet or strip ply would work well too. It will be built on permanent ply frames.

The Chris-Craft replics I have looked at seem to be ply sheet. When I consider 'cold molding' I would use thin ply rather than actual veneers and so a couple of layers of ply would give more strength than the same number of thin veneers.

Will keep thinking, and now it's time to buy a few books on the methods.

Then there's the fact I keep finding other plans I'd love to build too, which doesn't help :D All I need is a coupld of Lotto wins and a couple more lifetimes and I can build all the ones I want...and given the chances of that, I want to make the right choices so in my limited time I get to build at least a couple I want!

Thanks,
Darren

[Boatmik]

The really big advantage of the cold moulding is that you can set up the last veneer fore and aft to look like traditional planking. Which doesn't need glass over the top for a really schmik finish.

Strip planking requires glass over the top on both faces to take the cross grain loads - preventing the timber from splitting. A 6oz glass on the outside won't be visible from a couple of metres away. But if you really want it to look trad - stick with the cold moulding with the last veneer fore and aft and spile the edges to look like planking.

Up to you - swings and roundabouts

MIK

[TK1]

Sounds like a winner Mik, I'll be going the cold molding. Now off to buy some books and visit Marine Timbers.

Once I'm 100% on the plans I'll be using I will let you know and be sure to post progress pics....hope to sort the shed out and then get started in the next few months (finance, time, work, wife's permission, etc permitting :D )

Regards,
Darren

[Boatmik]

Bless your cotton socks - look forward to it!!!