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Building Clinker Ply boats

The first kit built Oughtred Puffin was delivered to the customer back in June.

The planking went together far better than we had imagined it could, and we now have a high degree of confidence in what we can do with this method of designing kits.

The plank, mould, and transom shapes were developed on a boat design program on a PC, and then CNC routed from the resulting files.

Since we built this hull, we have also built a SFD Coble 15 in Clinker ply, and also part built a Coble 9.  These hulls went together with little problem.

We've also produced kits for the Oughtred Guillemot, Humble Bee, Tammie Norrie, and Tirrik designs of which photos can be seen on the designers pages. 

NO re-shaping of ANY plank was required to build this, or any of the other hulls built so far.

We can do the same with almost any other clinker ply hull.

If you are thinking of building a clinker ply boat, but were afraid of the classic method of building clinker ply from plans, here is how it is done.

Photo courtesy of Tony Burrows Photography Christchurch

Having worked out the plank shapes with the software, we sent the files off to the factory for cutting, and my assistant Billy and I started working on the Stem and the Transom. At this point, everything is done in the same way as you would if building the clinker ply boat as described in Iain Oughtred’s excellent Clinker Ply Boatbuilding Manual. With the Inner and Outer Stems laminated, and the Transom glued up, we got to work on the strongback. In the photos you will see that the strongback extends considerably beyond that required for the Puffin. As this will not be the last boat we build, the strongback was built to use the maximum length that we could from the lengths of timber so we’ll be able to use it for anything up to 16ft.

Laminating the Stems.
The Outer stem has been formed around the inner stem.

The transom is glued up, and the shape is taken from the full size plans supplied as part of the kit.

It is essential that the transom shape comes from the full size drawings supplied by Jordan Boats - there are small differences between the designer's lofting and our own.

On receiving the plywood sheets, the first job is to label the planks up against the sheet layout diagram which goes out with each kit. If you don’t do this, you can have some real fun trying to work out which plank is which (speaks the voice of experience!). Thinking ahead, it is also best to make sure that the labels are removed before the planks are glued.

Marking up the planks – best done before the jigsaw starts work!

Once the planks are marked up, they are cut from the sheets. If you have two sheets the same, save yourself some time by cutting them together.

The tabs are then planed down to give a fair edge. Use a block plane on convex edges, but you will need a spokeshave on some concave edges. Pair the planks to save some more time.

 

CNC Routers are not good at cutting internal angles, so the slot for the hog/keelson needs to be squared off to accept it.

The planks were put aside for the while it took to fillet out the moulds and mount them on the strongback.

 

You’ll see in the photos that the moulds have large indentations at the plank lands. These are not for stringers, but to allow the CNC cutter to cut into the MDF to leave a lip for the planks to lie against. As we discovered on the Feather Pram, they are also useful in other ways, as will be revealed later.

The strongback and the moulds have to be as square and perfectly aligned as it is possible to get them. This is because the computer package that we use to create the kits marries the moulds and the planks in a way that is not evident with ordinary CP building. When building CP boats in the conventional manner, any errors in the moulds are compensated for when spiling the planks. If the moulds are slightly out, the spiling process allows for this.

With the kits, the planks are already cut, and we want them to fit the moulds precisely, hence, the moulds MUST be as perfectly aligned as possible. On this Puffin, Billy had done a superbly accurate job. When we cut the planks from the ply sheets and laid the first one over the moulds, there was an almost perfect line-up of the top edge of the plank on the lands.

Cutting Scarph joints.

Much is made of how difficult making scarph joints is. It is NOT! Plain scarph joints are not at all hard to make, and a bit of practice on scrap ply and a good sharp plane will give you passable if not excellent scarphs.

There are several different methods for cutting them – I have used a belt sander – very easy, and a plane – not quite so easy. These are well documented in many books and some web-sites.

We use a simple Router jig that cuts the scarphs quickly and accurately. The router jig takes a little bit of setting up, making sure that it is cutting the scarphs accurately on pieces of scrap before starting on the real stuff, but that time is well worth it, as can be seen from the resulting scarphs.

The hole you see in the middle of the scarph is meant to be there – it is the vital element in lining up the planks to get the correct shape when the scarphs are glued.

The planks are lined up using three pins and a piece of fine string. I prefer to use sailmakers thread, as it is strong and elastic.

Each kit with scarph joints comes with a scarph line-up diagram, of which we show a single plank from the puffin kit.

On the kit planks, we drill a small hole at the location of each mould, which is used for aligning the planks when gluing up. In the diagram, these are shown by the red crosshairs. We then use an additional hole at the bow (or stern) to give the longest distance that we can, and mark a hole at the centre point of the scarph joint. By aligning the three holes using the thread wrapped around the pins, we can get an almost perfect alignment. There are full instructions on this process in the kit documentation.

A builder of one of our kits reported back to us that this method was accurate to 3mm over a 17ft long sheer strake.

Fairing the Keelson, Stem and Transom is covered in detail in Iain Oughtred’s book, but here are a few photos of how we faired this boat.

The main stock removal on the keel and stem was done with a handheld electric planer. After the hard work was done, the rest was finished off with block plane and chisel.

The fairing for the transom lands is found from a batten, then a fine saw is used to make many cuts in the waste to ease the chisel work.
A chisel is used to remove the waste.
Leaving a smooth and fair plank land.
Finally, the sheer plank is offered up to obtain the correct angle on the lip of the transom.
Billy uses a batten from scrap ply to check the fairing on the stem. This can vary from plank to plank.
A perfectly faired stem.

Each plank needs to be dry fitted before any glue is applied. Though the kits are pretty accurate, any misalignment of the moulds needs to be compensated for BEFORE the plank is glued. The planks are actually glued up in the same manner as shown in Iain’s book. The preparation for the gluing is just a little simpler as the planks are already cut to shape!

A few things to bear in mind before the planking is started…

The planks are deliberately cut 15-20mm long at either end – this will help compensate if the stem or the transom are slightly out from where they should be.

Use the holes drilled on the top edge of the plank to align the plank with the moulds.

 

The plank should lie flat against the land and on the lip on each mould. You will find that on some planks on some moulds, the plank’s natural lie will take it over the lip by a small distance. On this first kit, we found the biggest error was about 3mm. This will stop the plank lying fair on the mould, so the lip needs to be chiselled away to allow it to lie fair.

Fairness on the moulds is more important than anything else.

  

We recommend you try each scarphed up plank against its land before you do any gluing or bevelling. You’ll be able to see if any of the planks seem to be wildly out – if they are out by more than a couple of millimetres, it will almost certainly be a symptom of misaligned moulds. Your two key references on this are the lie of the plank at the transom and the lie at the mould nearest to the stem, or the bow transom if you are building a pram dinghy.

Once you are happy with the planks’ lie on the moulds, you can start gluing the planking.

 
The processes here are:  
1. Remove the overlap from the previous plank at the stem and transom.

2. Use a lap gauge to mark the lap on the previously glued plank. The lap is given on the plans or in the kit documentation. This is a useful guide for positioning the plank, but fairness on the mould lands is more important.

3. Bevel the lands. With the plank lying fair on the mould, the lip of the mould will indicate how deep the bevel should be. Check the bevel against the mould land for the plank you’re about to glue.
4. Check the lie of the plank by dry clamping it. If it doesn’t lie quite fairly on the bevel, take it off and get it right now – errors will tend to accumulate.  
5. Once you are happy with the lie of the dry clamped plank, some marks need to be applied.  

a. On the plank mark the positions of two or three moulds in the midships area so that it can be presented to the moulds accurately when glued up.

b. Mark the top of the plank on the stem – you will know where to stop applying the glue.

 
c. Mark the gain line on the previous plank from the bottom edge of the new plank with it lying as naturally as you can get it over the mould lands. Some assistance can be very valuable to push the plank tight onto the moulds further astern.

d. Make sure that the bottom of each pair of planks are horizontally aligned across the stem.

This may not be exactly on the lap line you marked earlier, but trying to force the plank into a gain cut to the lap line may well distort the plank, leading to more problems later (this was the one bad experience with the first Puffin).
e. Mark the locations of the nail holes on the plank where it lies over the transom land, but don’t drill the holes for them until it has been glued.
6. Cut the gains.

7. Except for the garboard, tape over the lip lying under under the bevel where the glue is going to be applied (circled in blue). Don’t do this for all the planks in one shot as you may then need to chisel out the lip if a plank does not fit quite right.

8. Check that any labels you stuck on the new plank are removed. It is not so easy to do this when you realise that they are covered in glue.

9. Apply the glue to the bevelled plank, the transom land and the stem. Find the balance between plenty of glue and too much that it is dripping onto moulds, strongback, floor and shoes.  
10. Offer the plank up to the moulds in the midships area by lining up the marks you made earlier with the moulds and resting the top edge on the mould lip. Gently position the plank against the bevel and apply a couple of clamps to hold it in position.

11. Smooth the plank back to the transom, and get the position over the transom correct, then clamp it up tightly, moving forward and clamping at each mould. Make sure that the previous plank is lying fair on its mould land as you clamp the new plank. It will have a natural tendency to spring up a little, and this can affect the shape of the boat.

12. Smooth the plank over the moulds towards the bow, and you should find that it will run into the gain. Tightly clamp up the rest of the plank before you secure the plank to the stem. You may need to bend the plank up or down a little at this point to get it fair. Remember that running the plank fairly over the moulds between the transom and the gain is the most important consideration. If it doesn’t quite match up to your dry fitting, do not panic, and don’t be scared to take a bit more off a mould lip if needed.

 
13. Secure the plank to the stem, and apply as many clamps as you can find to the plank. If the plank is lying off the moulds at any point (it almost certainly will be), pull the clamps in to the moulds using bungee cords, clamps, or anything else that comes to hand.

14. Have a final look at you work, and then remove as much excess glue as you can now, both from the outside and the inside. Small (but sensible and gloved) children are especially useful for cleaning glue from the inside.

15. Relax, make a cuppa, have a beer, whatever, and leave the clamps on until the glue is set…then leave them a while longer – I have learnt from bitter experience that glue that is apparently set is usually not!

When you have glued the Sheer strake, Jordan Boats’ job is done, and we pass you back to Iain’s book.

 
In building the Puffin hull, we found that it took two of us approximately 2½ to 3 hours for each pair of planks.

We were genuinely surprised at how well it went together, and the same kit design principles are applied to other designs.

We'll look forward to hearing from you.