Broad Ambition - The Model

[JennyMorgan]

In the real world I would also clamp the plank to each rib as I go. Nails & roves are also good !

[JanetAnne]

Deffo start at the front. Once the front is in place you have the whole length of the plank to lever on. Start aft and you only have a couple of inches to try and get into place.

Heres another shot or two of planking following hull shape if it helps

 

 

 

[BroadAmbition]

Grendel - when we did it full size, that was 1" thick teak.  We only had to fit one full set of planks - the top one full length on both sides, and then one plank down on the stbd side fwd from the bow going back around 15 ft or so. We also discovered they had to be bent through two dimensions and twisted through another.  Added to this that the plank width progressively changes from fwd to aft as you have noted by your measurements.  This entailed shaping the plank first to the correct width then temporarily fastening it at the bow, then bending it as far as we dared making chalk marks on it as we went.  Removing plank, pairing it to size, drilling clearance holes for the screws and holes for the hardwood plugs  Then it went into the steaming pipe.  Not all of it only as much as we needed to get round the sharpest part of the curve and a bit more for good measure. We always started at the bow, this gave us plenty of leverage to bend the plank into place round the curve, once past the curve proper it was left overnight, we then on the next visit continued with the more gentle curve / twist / bend up / down and completed the fitting.  You really do need to fasten at the bow first, even if that means leaving it overnight to continue fitting the rest of the plank once the bow area has fully cured.   Hope this helps

Griff

 

 

 

or real, on the hull, we only had to replace

[ZimbiIV]

You score the planks on the inside of them ie. the side next to the ribs.

If you do this before steaming then clamp into position to cool they should hold shape.

This is what I am doing on Riva Aquarama I am attempting to build, which double planked with mahogany planking on the outside and the bow is being a pain in the posterior.

paul

 

[grendel]

I have decided to add an additional section of framing in front of the cutoff for the prow, this will be fashioned to give me a surface at the correct angle to clamp the planks in place at the bow. up until now I have had no problems steaming pieces to shape, even with quite tight bends without cutting the backs, you do have to remember you are not stretching the outside face of the curve, but compressing the back face when steaming, ideally you have a steel band at the same length as the outside of the curve to stop any stretching- this should stop any splitting, but truth be told thats a bit impractical at this size.

to be honest this curve isnt too bad, but its almost at the limits of what unsteamed wood will manage, so I will be steaming the next ones to get the curve a bit better. As it is if you dampen the planks at the end they bend easier. I think my big issue has been with the clamping at such an acute angle, its difficult to get the planks to hold without the clamps slipping.

Paul, I would love to see any pictures of your current build that you wish to post

[ZimbiIV]

I will take a photo, WHEN I've tidied my work bench up. I don't want Wildfuzz to see the sanding mess at the moment!.

paul

[MauriceMynah]

Oooh, the list of things I wouldn't want Wildfuzz to see.  

[Vaughan]

Perhaps this may help?

This is the cruiser "Heartbeat" being built in the summer of 1961. This is a "hard chine" construction, the same as Janet Anne has posted, and we can see how much easier it is to build, than the round bilge of BA.

Mainframes are fitted, to which the cabin bulkheads will be added later. The deck edges and all the deck beams are already fitted, to hold the shape.

The first job is to lay down the keel, the stem and the transom post, or knee. everything else gets built around that. Note how the boat is suspended by stringers off the roof beams of the shed, so that she keeps shape while planking is taking place. The horizontal formers on the hull have been fitted just to give the shape for the timbers to be steamed into place, and these are removed as the hull is planked up. We can't see the transom, but that will already be in place.

We can see that the garboard strake and the next two bottom planks are fitted, with no steaming except right up at the bow. Planks would not have been all one length : they would be scarf jointed at irregular intervals along the hull, with two or maybe three lengths per plank (or "strake").

My advice, for what it's worth, is to make the stem, with a suitable rebate for the plank ends, fit it to the keel, and then work back from there. You are going to see some interesting curves in those planks!

 

[grendel]

Vaughan, many thanks for that, it always helps to see the boats in bare bones form, this helps me visualise how things go together, particularly how the prow / stem is shaped, Broad Ambition has more ribs closer spaced than the Hearts cruiser above, which gives more for the planks to be formed to and fixed to, I am lucky in as much as I can fit planks that are the full length of the boat, so dont have to scarf them, but I do need to work out the tapers on the planks to help things fit properly.

I had planned on building up to / past a front bulkhead where the stem would be, then cutting carefully before fitting the rough stem, then shaping that to the planking, as I know that Griff and Co did replace the stem.

As I am making 2 models I am using the first to test different methods and processes so that the second hull proceeds more smoothly, until I had fashioned the first I wasnt able to envisage the shape of the rebates needed in the stem, (at least until I saw your picture above) and was afraid to manufacture this part before I knew the shape it had to take.

as for interesting curves, I have already seen some of those, the twist on the first plank is nearly 90 degrees at the front. and thats without having them bend around the curve of the hull as well as a bend through the width of the plank. I now appreciate the skills of those old craftsmen who built a lot of these boats by eye, and the planning necessary before laying the planks, just to get the shapes right. this weekend will be spent marking out the widths and positions of each plank for both sides before a single plank is shaped, then planks will be laid along their route and only then can I decide which side of the plank the excess will be trimmed from for a proper fit. Once I have this hull done I may be able to take measurements to be able to create the stem for the next one with the proper rebates before I lay up the keel. (though I am still not sure how I will clamp the front in that case).

Just one question is that a double rebate on the stem, one for the stringers, then a deeper one for the ribs?, though I see your stringers run outside the ribs, or are those the horizontal formers that are removed as the planking gets to that height, she certainly does seem simpler to build that Broad Ambition.

[JanetAnne]

Yes, hard chine is a lot easier and it also allows for the below chine planking to run at an angle which means less twists along each board. To illustrate "here's one we did earlier"

Of course, not relevant to Grendel's build but just as a point of interest.

On the full size BA they may well have needed to hollow out the rear of the boards that run along the curve to get them to fit flat onto the ribs and then taken the corners off the face to give her that lovely smooth shape.

 

 

 

[Vaughan]

The stem of a hire boat was always massive, as it had to withstand frontal collisions. I imagine BA was built with this in mind! The keel and the stem of this Hearts boat were dressed out by hand, on the boatshed floor, with an adze. It was was the only way to do it then, and perhaps it still is now. I watched this being done, and it is a skill above all others! The stem was "grown oak", in other words a specially chosen and seasoned piece from the branch of a tree, where the grain of the wood followed the shape that you wanted to create. Wherries are built like this. Their timbers are not steamed : they are grown, from selected pieces of a tree, called "crooks".

Sorry, I am getting off the subject!

BA has closed spaced timbers, but not many mainframes, as she is round bilged. A hard chine boat gets more of its strength from the chine, and also the chine board, which is the first plank up from it, and usually the widest one in the hull.

I think we need to remember that traditional boatbuilding made big use of templates. A boatbuilder when replacing a curved plank, would nail a narrow strip of hardboard to the timbers where the old plank had been. He would then mark the distance from the adjacent planks onto this strip, using a "constant" spacer which was usually a box of Swan Vestas matches. He could then lay this strip of hardboard onto a board of mahogany, put the matchbox against the marks he had made, and could thus draw out the shape of the plank.

You will need to do something similar, as you will find that it is not just the twist or the bend in them : they are nowhere near straight when you cut them out!

I was thinking about "vac forming" :  In the shoe trade, when they design a shoe, they put the "last" into a machine which drapes a sheet of heated plastic over it and then pumps the air out from underneath. The plastic forms exactly over the last of the shoe and then holds that form as it cools. The designer can then draw on the plastic, and later flatten it out, to form the pattern for the parts of the shoe.

Could you do something similar with your model? Find a company that does Vac-forming, take a mould of the model, draw out the planks on it, and then cut them out to shape.

Just a thought!

[wombat nee blownup]

My idea of a great night out?................ Stephen Fry, Brian Cox, Matt Greoning ,Ronnie O'sullivan and Vaughan quite a few cases of something more than water round Grendel's gaff whilst he beavers away at said model

[BroadAmbition]

On the full size BA they may well have needed to hollow out the rear of the boards that run along the curve to get them to fit flat onto the ribs and then taken the corners off the face to give her that lovely smooth shape.

No evidence of this practise when we got right into her ribs.  There is plenty of twist / curve / bend evidence though.  We had to replace a few of the exterior dressing planks on the transom,  The shaped planks looked anything but straight before we fastened them into place, this meant a fair amount of waste timber left over

Griff

[grendel]

I think the vac forming is a good idea, but not quite practical for this particular build, I will approach this with a draughtsmans approach to things and carefully measure and work from there, by marking the plank lines onto the ribs, I can then lay a plank on in best fit and mark the edges straight to the plank (more akin to the old timers matchbox method) then I will at least know the plank will be lying straight, once I have the planks shaped I can restart fitting them, tonight I will prepare the extra bits to allow clamping at the front of the planks. more and pictures later.

[BroadAmbition]

Stem / Apron - some confusion here with terminology which I will admit to being somewhat confused too.  That huge piece of varnished oak you see today on 'B.A's bow, is it the stem or apron? Whatever it's correct name, it was well past it's sell by date.  When we got hold of her it was painted.  Only once the paint down to the bare wood was removed could we see what we had to deal with, it had been repaired / graving pieces / filled so many times we had no option but to change it.  Now then the front of the hull planks are not fastened to it all other than a bead of sikoflex where it meets the planks, then primed / painted over.  That lump of oak has two jobs, it forms the bow proper and the other reason is just cosmetic.  Behind the varnished oak is where the strength lies.  There is another huge lump of hardwood, teak to be precise, it is flat front and back, it runs from under deck level at the top where it is about 30" across right down to the front of the hog / keel at the bottom where it is about 6"across.  The  stringers are attached to it, the ribs in turn to the stringers, then the planks thereafter.  The front end of the planks are shaped in a gentle curve from top to bottom, the varnished lump of oak is then shaped in turn to fit neatly with the front end of the planks. It is then through bolted with long recessed s/steel coach bolts with the washers / nuts on the inside of the teak lump from inside the fwd cabin.  Hope this helps

Griff

[grendel]

Strangely enough Griff, that is how I have made the model, except my teak is plywood. I have now inserted a couple of slips of wood behind the protruding ends of the stringers / ribs, which will hopefully give me something to clamp to for the front of the planks. The measurements have been taken, and now need to be divided by 12 to divine the width of the planks, the plank lines will then be marked onto the ribs.

 

[grendel]

this is where things get technical, working out the plank widths at each rib for every rib down one side, so they have been measured, and a spreadsheet created to calculate the plank widths - there will be 11 15mm wide planks and 2 10mm planks in total, this means at each frame each of the wide planks is 15/185 of the total, and the 10 mm planks are 10/185 of the total - now I have to mark them onto the ribs. see below for a sample of the spreadsheet.

Now to mark up the ribs and make sure the lines are smooth.

[JennyMorgan]

Now how on earth did those old Broads boatbuilders plank up before the advent of computers? Must ha had em fairly scratchin their ol noddles!

[grendel]

no, there is an easy drawing way, you take a measuring stick, put it at an angle, and the parallel lines sub divide the measurement into 12 equal parts, its the way I would have marked it up full size.

[grendel]

right that's 2 hours with a pencil and ruler and the lines are all on, though as my eyes were tiring towards the end there are a few spurious lines. these will be removed and redone later, I also calculated a running total for the lines, then marked them on a scrap piece that I could roll around the ribs marking as I went. I am now ready to carry on with planking.

[grendel]

whilst thinking (as you do) in the middle of the night, I was wondering how I would represent the screw hears on things like the deck fittings. I quickly dismissed any available miniature screws as too big, so the decision is how best to represent a slot in the head of a pin, for the meagre sum of £4 I have 500 stainless steel pointless pins on order as all I need is about 1/4" (6mm) of the pin from the head, a tiny hole will be drilled and the pin pushed in, with a representation of a slot scratched or ground onto the head. I guess this is how they get rid of the rejects in the factory, but then they are perfect for what I want.

[grendel]

I have been working hard so far this morning, now I know the plank widths, I can get on with them, this one had been started already, so its getting steamed and dry fitted before it is shaped to width. As you can see with the new clamping system at the front, plus the steam, the plank is taking the bend a lot better, now I am wondering how to steam that plank above, maybe steam fed into a plastic bag? - I have seen that done on the real thing.

[grendel]

Also shown is how I know my plank lines are straight, a laser line does the job.

[MauriceMynah]

Are you sure your laser is straight? I know mine isn't by looking at all my DIY work.

[grendel]

a second plank has been steamed and clamped, once again that curve  was easier I have even had a go at pulling one of those other planks into line. This plank was trimmed to shape before I steamed it.