Planking a ply on frame design with solid wood?

[Heimfried]

A friend has trouble to source marine plywood to plank his 18' boat (the frame is ready built). Now he thinks to use solid wood and glue and screw the planks in place and cover these planks with epoxy and glass. In my opinion this mixed construction will fail and I try to convince him. My argument was that he will not be able to prevent pin holes or micro cracks in the epoxy coat and it will cause swelling the solid planks and eventually break the hull open.

Are there other points or am I wrong?

Edit: " corrected to '

 

[gonzo]

It can be done successfully. Many boats are built that way. The hardest thing to do, in a small boat is to keep the edges of the planks aligned, because they are rather thin. Double planked could be a good option. However, lumber of good quality will be more expensive than plywood. Is your friend in Europe?

 

[Heimfried]

The building site is located in Germany, sure marine plywood is available here. The point is, he is building slowly in a tent (not roomy at all) and is able to store only a very few sheets of plywood. But ordering the plywood step by step means the costs of transport are more expensive than the ply itself. His idea is using solid wood planks means to buy locally small portions of it at the lumber yard without punishing prices. He was using exterior grade plywood (it was fir, I think) in another boat build which was successful, but he didn't like working with this plywood very much.

 

[bajansailor]

Heimfried, I presume you mean that the boat is 18 feet long, not 18 inches!
Even so, how many sheets of plywood will it need to build this boat? It cannot be a huge amount.
If he ordered say 10 sheets, they would not take up much space if stored on edge (rather than flat) - perhaps behind the sofa in the living room if there is nowhere else? Or maybe your friend's wife refuses to allow this?
As Gonzo says, yes, you can build with planks of timber - but your friend's boat was designed for plywood, and it would be a lot of extra work to build this boat by the strip planking method instead. Not to mention more expensive, because he will surely use a lot more epoxy, as well as the wood being more expensive than the plywood.
And you cannot use 'ordinary' planks like in traditional carvel boatbuilding - the planks need to be fairly uniform narrow strips, hence a lot of extra work.
There is a good explanation of 'strip planking' in this article -
Strip Planking http://www.selway-fisher.com/Stripplank.htm

Can you provide us with a link to the boat design / plans that your friend wants to build?

 

[gonzo]

One solution would be for him to make patterns and cut all the pieces in one day. It may take some shifting to work around them, but they will be smaller. It shouldn't take too long to plank and 18' with plywood.

 

[Mio]

Hi,

first of all I would like to introduce myself here. I am a hobby boat builder since 2016, live in the Ruhr area in Germany and am the friend mentioned above by Günter (and proud to be called so). Pardon my English right at the beginning, but I am more used to reading English than writing. Additionally, I ask for your consideration if I get mixed up in places when converting the units of meters.
Since 2018 I have been building the 18 foot boat mentioned above, but I don't want to name the designer, because the plans are a bit meagre compared to the price, but I don't want to make my debut here with a designer bashing.
But I think the designer didn't put much brain power into the plans.
To give you some marginal data: the frames have a thickness of 2'' x 3'' and a distance of 10", the beam is 6' 8''m LOA is 18' and LWL 16'8''. It will be powered by a 6 HP outborder, the plans demand for a 7 HP 1 cylinder inbord diesel engin.
The "planed" planking is 1/2'' for the topside and 1'' plywood for the bottom (the boat is a single chine construction). The chine and sheer were build with laminated fir 1 1/4'' x 2 1/4'' (6 layers) and the inner keel is 1 1/4'' x 4'' (also laminated instead of solid wood of the same dimensions and type of wood)
The boat will be trailered if necessary, at most it will be in the water for 2 weeks at a stretch during the holidays.

As Günter already mentioned my space is limited, the shelter has 13' x 26' and is located in my garden. The storage in the living room mentioned by bajansailor is out of the question, not because of my wife (who I have chased to hell) but because of my cramped living situation with about 650 sq.ft. for me and my son (16 years old).

Gonzo's idea to cut the plywood in one day according to the templates is certainly good, but fails again because I have to store the cut parts temporarily. It would be difficult to store the plywood upright in the tent, because the tent protects the building site against the weather, but is not stable enough to hold the 12 panels 1/4'' that are required when standing upright with a slight inclination. An immediate processing of the cutouts and planking of the boat is not possible due to time reasons, I have to work in between.

Günter's fears were that, as described above, water could penetrate into the wood and by the swelling of the wood could break the bonds with epoxy putty (epoxy with cotton flocks).
According to my information (Georg Buehler), laminates made of solid wood should not be used with wood thicknesses over 2''. I had planned the floor planks in 10/16'' cross planking and the side planks in 1'' simply planked with fir. Afterwards the wood should be completely covered inside and outside with glass fibre laminate.

I didn't know the link to selway-fischer yet, but I had imagined the whole thing as in picture 3 and 7.

I'm not afraid of more work, it's not the question if I need more epoxy, but rather if I can finish the boat at all.

So far a "little" of information, which might describe the situation in more detail.

Cheers

Mio

 

[bajansailor]

Welcome to the Forum Mio!

Some initial thoughts - the scantlings (timber dimensions) appear to be excessive for an 18' boat.
Are the frames (2" x 3") actually spaced only 10" apart?
Heimfried suggests that the frames are all set up already?
If the hull bottom is 1" thick plywood you will need much less in the way of framing - or less thickness plywood if you have all these frames already.
You mention that you would now like to build the hull planking from solid timber, with 10/16" (5/8"?) thick crossplanking on the bottom, and 1" timber sides - this is going to be a heavy boat, especially so if you have lots of frames as well.
If you do this, think of the old time wooden boats like the dories that were planked with timber - they didn't have plywood or epoxy in those days.
If you have scantlings like these, there is no point in sheathing the boat inside and out - you might as well just caulk it and paint it.

An extra thought - as you are reluctant to name the designer, would it be possible to post a sketch or drawing (or two) showing what your 18' boat looks like, perhaps with the designer's name hidden?

 

[Rumars]

Hi Mio, and welcome.
You can talk metric units here, people understand, no need to convert.
What I would advice is to do as gonzo said, double plank/cold mold the boat. For that I would do as follows: find a carpenter shop with a big resaw and have them saw your wood to thickness and lenght. Then cold mold the boat either with both layers in the same direction or at 90°. This way the longest plank you need to store will fit under your bed or sofa and you can buy and have the wood sawn all at once. Just measure a bottom half and topside at their widest point at about 45°, I doubt it will come out at more then 1,5-1,8m. If you want to keep the bottom at 25mm do three layers of 8mm. Topsides can be two layers of 6mm.
Wood choices would be: fir (Tanne, abies alba), spruce (Fichte, picea abies), pine (Kiefer, pinus sylvestris), douglas fir (Douglasie, Pseudotsuga menziesii), larch (Lärche, larix decidua). I would favour true fir (Tanne) first since it it lightest, and has no resin pockets. Next would be douglas fir, the home grown variety will be lighter and cheaper then the imported stuff. At the prices fir and spruce have right now and the lenghts you will need you can even afford chooseing only the best of the best all clear, quarter sawn wood (beidseitig astrein, stehende Jahresringe).

 

[Mr Efficiency]

I'm confused as to why the ply cant be stored in the house, makes no sense to me.

 

[DCockey]

It would be difficult to store the plywood upright in the tent, because the tent protects the building site against the weather, but is not stable enough to hold the 12 panels 1/4'' that are required when standing upright with a slight inclination.

Have you considered building a simple wood rack to hold the plywood vertical? Another way to hold the plywood vertical would be put two posts in the ground. Or if the area is paved then bolt brackets to the pavement to support two posts.

 

[fallguy]

Günter's fears were that, as described above, water could penetrate into the wood and by the swelling of the wood could break the bonds with epoxy putty (epoxy with cotton flocks).
According to my information (Georg Buehler), laminates made of solid wood should not be used with wood thicknesses over 2''. I had planned the floor planks in 10/16'' cross planking and the side planks in 1'' simply planked with fir. Afterwards the wood should be completely covered inside and outside with glass fibre laminate.

I have the answers you seek.

Cotton flox is hygroscopic and not my favorite to use; it is bulky and uncooperative. I prefer cabosil or aerosol greatly.

The problem with your plan is the moisture in the lumber. You can buy dried lumber, but you can't store the lumber outside long if it gets wet and you don't want to put a few planks on and have them swell up and get wet.... so.. what to do?

Wood requires precoating before laminating or it will dry suck resin from the fiberglass matrix. You can leverage this problem.

Purchase the lumber you desire, making certain it is dry and neat coat the boards on the faces with epoxy at a rate of 2 ounces per square yard. They really require it in a good build anyhow. A poor builder may not neat coat the wood, but risks a real problem with dry patches when glassing.

If you get epoxy on the edges that are to be bonded, that is fine, but you must sand them with 40-60 grit as you must sand all the wood prior to glassing the hull.

Basically, your plan is fine, but you must precoat all your lumber before applying it to the frames, then you have no risk of trouble.

 

[Ike]

I'm confused as to why the ply cant be stored in the house, makes no sense to me.

have you tried to live in 650 square feet? With two people and their belongings there isn't a lot of room to store lumber. I know. My Motorhome is about 450 sq feet. When I bought plywood to build a couple of small rowboats I transported the sheets in the motorhome. With them in here there wasn't any room for anything else.

Mio, Welcome to the forum. Don't worry about your English, it's far better than my German. I don't know if this is possible where you live or not, but you said there is a local lumber yard. Maybe you could pay them to store the plywood for you in a dry place, until you need it. Order it through them and they may allow you to store it for a small fee. And any cutting or planing could be done by them. Doesn't cost anything to ask. As was said by someone else, metric is fine here.

 

[Mr Efficiency]

have you tried to live in 650 square feet? With two people and their belongings there isn't a lot of room to store lumber. I know. My Motorhome is about 450 sq feet. When I bought plywood to build a couple of small rowboats I transported the sheets in the motorhome. With them in here there wasn't any room for anything else.

Mio, Welcome to the forum. Don't worry about your English, it's far better than my German. I don't know if this is possible where you live or not, but you said there is a local lumber yard. Maybe you could pay them to store the plywood for you in a dry place, until you need it. Order it through them and they may allow you to store it for a small fee. And any cutting or planing could be done by them. Doesn't cost anything to ask. As was said by someone else, metric is fine here.

Seriously, there is not much ply in an 18 foot boat, a little inventiveness and it could be easily stored inside. Your motor home is 450 square feet ? Must be one helluva motor home, 8 feet by 56 feet ! This is just silliness.

 

[Ike]

8 by 35 on the road. With the slides out the the width is around 13 feet, maybe a bit more. 13 x 35 = 455 Sq ft. Probably closer to 400 than 450. But with slides in still a lot of room for two, but not five (or was it 6?) sheets of 4 by 8 plywood. Nowhere to store them. Had to cut them to the right size right away. Fortunately it was summer so we weren't getting too much rain (this is the Pacific Northwest and it do rain a bit even in the summer) and I could keep them outside covered with a plastic sheet under one of the slides. The RV park Ok'ed my project as long as I didn't make a mess or too much noise. They are both on my website.

 

[Mr Efficiency]

Maybe the guy has found a source of free off-cuts etc and doesn't want to pay anything for the ply, if so, a false economy. I could easily slide that ply under a bed, virtually.