Clinker boat design

[gusblake]

Hi,
does anyone know how I would determine the exact shapes that the planks need to be for a clinker/glued lapstrake dinghy?

cheers,
Gus

[gusblake]

Just to clarify, I'm referring to the process of creating flat templates for the planks from the full scale line drawings. Does anyone know how to do this?

[TeddyDiver]

Don't excactly know how detailed drawings you have, but I'm familiar with doing planks just shaping them in in their place.. so no templates. Plank width also varies depending of their quality etc..

[gusblake]

Oh.. how do you get them all accurate and symmetrical then?
Sorry if these are stupid questions but I'm new to boatbuilding and no-one seems to be able to tell me exactly how the actual build process works.

[TeddyDiver]

Originally Posted by gusblake

Oh.. how do you get them all accurate and symmetrical then?

You pair them up for starters. Try to choose best fitting pair to their place. Build up both sides advancing same pace, each plank first shaped individually to previous one, then shaping upper sides so that their advance suits the hull form and as identically as possible. Makes that sense? It's kind of "in the eye" of the builder to determine how to shape boards.

[TeddyDiver]

Peaked up Richard Birmingham book Boat Building Techniques Illustrated.
A quote:" Prior to commencing planking the run of all the planks is marked by "lining out". The girth of at each mould is measured and divided..." then "light battens are tacked to the moulds..." then "Once the projected position and size of all the planks are considered satisfactory, the batten positions are marked on each mould and then the battens removed"
Hope this helps. It's somewhat labour insentive but secure way to start

[tom28571]

Gus,

This is too complicated to learn here. I suggest that you get a good book or two. These three helped me in this process.

Tom Hill....Ultralight Boatbuilding

Ian Oughtred....Clinker Plywood Boatbuilding Manual

John Brooks & Ruth Hill....How to Build Glued-Lapstrake Wooden Boats

There are several methods to do what you want from "rack of eye" to detailed measured process. It's not too difficult but fairly easy to mess up.

Most people build a mold with ribbands (stringers) defining the edges of each plank. These are placed to fit either the designers predetermined points on the molds or to fit the builder's eye. In either case, a plank or plywood is placed over a pair of adjacent stringers and marked for cutting in pairs for each side. Almost always, some scarfing is involved, either because full length planks are not available or because it is too wasteful of material not to scarf.

This is pretty much how I do it.

[tom28571]

Gus, Here is a thread on another forum of a recent lapstrake build of mine. It may help to visualize the process a bit.

http://www.messing-about.com/forums/...p?topic=5716.0

[gusblake]

Thanks for clearing that up,
Will have a look at some books today.

Cheers
Gus

[kengrome]

I'm referring to the process of creating flat templates for the planks from the full scale line drawings. Does anyone know how to do this?

Hi Gus,

I just did it for Weston Farmer's Pop Gun. It takes a couple hours for me to do it in FreeShip, more if you're new to the software. Actually I only started with Pop Gun, then I modified the design so it will be a better boat for my particular purposes.

Once I have finished designing a hull in the software, I use the feature that creates a cutting pattern for each panel. Then it's a simple (but somewhat time consuming) task to transfer these patterns onto the plywood so I can cut them out.

Every time I've designed a boat in my software and used its patterns like this, the results have been practically perfect. I'm very satisfied with the software's ability to produce precise patterns for each panel.

The software can produce patterns for frames and bulkheads too. This makes most boats easier to build because they can be used to position the hull panels correctly without guessing at it ...

[tom28571]

Ken,

Does you program allow for the thickness of the strakes and/or whether they are beveled at the lap or not?

[kengrome]

Hi Tom,

No, it's a relatively simple program.

To lap the strakes I would simply cut them an inch or two wider than the patterns illustrate, depending upon how much I want them to overlap. If I build 'stitch and glue style' without any overlaps they fit together perfectly on the inside joints, but there's a gap outside which gets filled with epoxy filler.

If I were going to build 'stitch and glue style' with a bright finish I would probably cut the strakes maybe 1/2 to 3/4 inch wider so I would have enough wood on each edge to bevel and get a nice tight fit without any gaps inside or out.

[tom28571]

Ken,

I did not know if you had actually done this to completion of a clinker boat from a computer program before. Width allowances for actual shape beyond computer predictions may (emphasis on may) work but is not a sure thing. Further, you still don't have the actual shape needed to make the designed shape of the boat. You said that the computer solution is perfect for edge fitting which is the same as carvel planks. Be careful before committing a lot of lumber to clinker by this method because there be dragons awaiting. Lapping the edges , beveling the lower plank as well as thickness of the strakes changes the shape of the strakes considerably, especially when they are narrow or create a compound surface. It can be done by computer which I know because I have a friend who can do it but it is not particularly simple.

Lining off a lapstrake hull is as much art as science anyway. It can be technically correct but still look ugly.

[kengrome]

Thanks for the info Tom!

I did not know if you had actually done this to completion of a clinker boat from a computer program before.

Well, it works great on the kayaks and other small boats I've built, but they only had 6 hull panels at most (not the 10 panels in the design I posted earlier) ... and the panels are not lapped or beveled in this type of construction either. Instead the edges are butted and the edge gaps filled with epoxy then glassed over.

Lapping the edges , beveling the lower plank as well as thickness of the strakes changes the shape of the strakes considerably ...

I'm sure it does.

If I try lapping the panels I will probably still use pre-cut plywood strakes and epoxy filler instead of bevels at the joints. This preserves the exact computer-generated shapes of the strakes, but it does not account for the different angle at which they are installed, which will require some adjustments during construction.

Or I can put more time and effort into computer modeling and come up with precise patterns specifically for lapped strake construction. It takes more time and effort to go for this much detail in the software because each lap must be modeled individually, but it can be done. This extra time is probably worth it in the long run too, since construction should have almost no problems if I produce this much detail in the software to begin with.

------------------------

One of my concepts for the construction of a light weight lapped strake boat is to use thin plywood strakes, perhaps only 4mm or 5mm. This means the joints themselves will not have much lap thickness nor will such thin joints look very good. But I have a way to deal with these issues:

I'm thinking of installing 1/2" x 3/4" (or maybe 3/4" x 1") stringers in the middle of the lap joints -- between the strakes. This will make the joints look much thicker and therefore give the impression that the strakes themselves are thick. It will also stiffen and strengthen the boat a lot while adding minimal weight.

John Welsford designs boats with stringers installed first on bulkheads and frames, then his strakes are 'cut to fit' on top of the stringers, each one beveled to the next, with the stringers visible inside the hull. My concept would be similar but different ...

I would set up the bulkheads and frames on a strongback or on the keel if the boat has one, then alternate the installation of strakes and stringers -- install a strake first, then a stringer, then another strake, then another stringer, etc. The stringers would be sandwiched in between the strakes, and the strakes themselves will lie directly on the computer engineered bulkheads and frames.

In this type of construction the hull should be as self-fairing as in a strip planked boat. Not only that, but when the boat is finished and painted it should look like it is built of thick, heavy strakes -- when in reality the strakes will be thin, light weight plywood. This means the boat will be very light weight yet still have the classic look of a much heavier lapstrake hull inside and out.



Granted this is only a concept at the moment, but I can see no reason why it won't work, although I'm sure I will discover some issues the first time I try it.

[tom28571]

Originally Posted by kengrome

Well, it works great on the kayaks and other small boats I've built, but they only had 6 hull panels at most (not the 10 panels in the design I posted earlier) ... and the panels are not lapped or beveled in this type of construction either. Instead the edges are butted and the edge gaps filled with epoxy then glassed over.

Sure Ken, but this is not a lapstrake boat.

I'm thinking of installing 1/2" x 3/4" (or maybe 3/4" x 1") stringers in the middle of the lap joints -- between the strakes. This will make the joints look much thicker and therefore give the impression that the strakes themselves are thick. It will also stiffen and strengthen the boat a lot while adding minimal weight.

One of the reasons for beveling the strakes is to make them look thinner. thicker can make a small boat look clunky.

John Welsford designs boats with stringers installed first on bulkheads and frames, then his strakes are 'cut to fit' on top of the stringers, each one beveled to the next, with the stringers visible inside the hull. My concept would be similar but different .

This is the way most build them, including Oughtred and Hill
..

I would set up the bulkheads and frames on a strongback or on the keel if the boat has one, then alternate the installation of strakes and stringers -- install a strake first, then a stringer, then another strake, then another stringer, etc. The stringers would be sandwiched in between the strakes, and the strakes themselves will lie directly on the computer engineered bulkheads and frames.

If a boat has no need for frames for strength, I see no reason to ever include them in its construction. I almost never use frames. I prefer monocoque construction for lightness and include seats, air tanks, gunwhales, etc for stiffness.

In this type of construction the hull should be as self-fairing as in a strip planked boat. Not only that, but when the boat is finished and painted it should look like it is built of thick, heavy strakes -- when in reality the strakes will be thin, light weight plywood. This means the boat will be very light weight yet still have the classic look of a much heavier lapstrake hull inside and out.

Granted this is only a concept at the moment, but I can see no reason why it won't work, although I'm sure I will discover some issues the first time I try it.

Boats like Welsford's use few strakes and tend to show a thick lap at the turn of the bilge caused by the small radius there and thinner laps elsewhere. Oughtred's boats use more strakes and show thinner laps everywhere. On boats in the mid teens LOA, I like about 8 strakes which is more like Oughtred. I don't mean to second guess either designer here but that is what it looks like to me. The thickness of the laps should have some relation to the size of the boat since the eye expects to see thicker planking on larger boats.

Like much in boat design, it's mostly personal opinion and that is mine.