Not to worry Richard. It was a long time ago and I appreciate your advice.

Ray
The DF 95 bulb weight is less than half what I need for the IOM.  I have just seen on Frank Parsons catalogue that he has some IOM bulbs for £38 which is getting better but he is not listing fins, only rudders.

For the time being I have around 60 planks to fit and being a varnished hull they will need to be precisely fitted.

Tim R

Thank you Chris

Here are the shadows set out on the building board.  In full size we would call them moulds.

They are only 4mm thick so actually quite flimsy.  If they were to move out of position at any moment, the true hull form would be lost and the boat would be out of fair.  If they twisted, the boat would be a different shape from one side to the other.  This is the reason I have fitted plywood spacers which are accurately cut to conform to the spacing.  The shadows are now very stiff and the spacers ensure that all of them are exactly 90 degrees to the base board.

There is no shadow at the bow and the piece in the picture is the actual stem.  It is mahogany and comes from a drawer from an old dressing table mirror that used to belong to my grand parents.  Beautifully aged and seasoned!

This is the first modification I did by making the stem a fraction wider and a fraction deeper.  The stem has been made deeper and with a flat at the bottom instead of coming to a point.  It is impossible to plank on a point that acute!

The reason I want to make the stem deeper was to get it down on the waterline.  The plan shows the waterline a bit back from the stem and so some of the waterline length was lost.  Maximum theoretical speed is related to the waterline length and the more the better.
The other reason is that IOMs tend to submarine when going downwind in a blow so lowering the stem meant adding some material to shadow 9 and you can see that I have wrapped a thin piece of balsa to make up the difference.

The square balsa attached to the base of the stem locate the height of the inwhale where it meets to stem.  The location of the inwhale is therefore jigged and will ensure we arrive at the same height on each side and I don’t have to fiddle around when the inwhale is glued up.

To follow

Tim R

Here is a better photo of the mahogany planks stripped from the 4-poster pelmet rail.  A few years ago and with model yacht building in mind, I purchased a Proxxon FET table saw.  This has carbide teeth on the blade which lasts a long time and makes a very clean cut.  The planks are 3mm thick and I have two widths (8mm and 5mm).  The general idea is that the 8mm wide planks are used where the cross sections are quite straight in the topsides and the narrow planks are used where the curves are much tighter.  There is a particularly tight curve at the transom.  There are over 60 planks in total for the hull.  I have not thought about the deck yet but at the most it may have some mahogany trim.

3mm is far too thick for the finished thickness and would be unnecessarily heavy.  I aim to arrive at a nominal 2mm so there is quite a reasonable finish sanding allowance.

Some while ago Richard marvelled at the compound curves that can be achieved with straight pieces of wood.  Taking the outside surface I will be building a hull that effectively has around 30 chines on each side.  This means that each plank (chine) is making an average change of angle of around 3 degrees so as to be hardly noticeable.  The resulting shallow ridges are easily sanded off (planed on the full sized) to finish the compound curves of the surface.

There are other important factors that I shall come on to.

To follow

Tim R

Hello Ray.  It seems like you may have to convert some of your boats into ice yachts!  Here in Mallorca the temperatures have plummeted to around 13 degrees. There has been some snow in the mountains above 500m.

Planking Nimble is a very slow job but I have been able to make a couple of folding stands as a diversion.

Looking forward to seeing your pictures from Ludham.

Tim R

Nimble’s hull will be varnished mahogany, for the topsides at least.  This means that filler of any kind is out of the question and every plank has to fit against its neighbour without gaps.  This is quite easy for the first few planks of the topsides but gets increasingly difficult when starting to plank curves and especially difficult when getting to tight curves and concave shapes.  Fortunately on all the IOM’s that I know of, there are no concave areas.
The other consideration is that as the beam increases towards midships, the girth increases which means that you don’t need as much material to get from the keel to the deck edge at the bow and the stern.

There are two features necessary when planking a curved surface of a hull;
1.   The edges of the planks need to be bevelled
2    The individual planks need to be tapered.

In the first instance the tighter the curve the bevel angle needs to be larger.  In modelling situations when the curve is gentle you can get away with bevelling one edge of the plank only.  When the curve get tighter you will need to bevel both edges. If the curved is really tight you may have to hollow out the inside of the plank (or use narrower planks which has some disadvantages).
If you imagine two planks with square edges, side by side on a convex surface there will be a gap on the outside.  This will either be an ugly, wide glue joint or it will require filling.  Even worse on a concave surface because the planks will touch on the outside and you will have a gap on the inside.  When you start sanding to fair everything up, the gap will get wider!  The other advantage of having the correct bevel is that you have continuous contact along the glue line that makes a much stronger joint.   In a perfect joint, the seam will be normal ie 90 degrees to the surface which in most cases will be a frame.

In the second instance tapering every plank helps get around the difficulty of the differences in girth.  Often this is not 100% possible in which case plank inserts need to be fitted called stealers.  It is aways good to keep the number of stealer required to a minimum and to take a full sized fishing boat which are quite tubby, there may only be two stealers each side, normally at the stern.  In a model and where using fairly narrow planks you only need to put the taper on one edge.  If you use parallel planks, after a while you cannot bend the edge of the plank sufficiently to meet its neighbour and it will run off leaving a gap that has to be filled later.
I  think Richard and Colin will appreciate this next description.  If you imagine the vessel as a globe, each plank should try to follow the Great Circle Route as closely as possible and you do this by tapering.
Where there is a greater change of section, the steeper the taper needs to be.

The easiest way to visualise all this is to look at how a barrel is made.

The taper creates the barrel shape  because the top and bottom of a barrel are quite straight, the taper in these sections is also straight.  In the middle section where the barrel curves, so too does the taper.

The bevelled edged mean that there are no gaps which is obviously critical or there would be a grave shortage of whisky and wine!  When you look directly from the top to the bottom the seams will appear straight.  This is because they are following the Great Circle Route.

In reality Cooper have an easy job because each stave is the same.  On a boat there are no planks that are the same. not even between port and starboard because they are mirrored.

This is the theory so I will try to show how I deal with these things in practice as I go along with the build.

Tim R

Just to show that I haven’t been completely idle

I was short for folding stands for use down by the harbour so with the remaining mahogany I have made up three simple scissor stands.

For the webbing I used dog leads.  We have six leads but only two small dogs.  They are not too wide which was perfect for the frames.

Tim R

Hello Ray

Very elegant Slipper.  Have I missed anything? Has it been out on the water yet?

Planking coming on slowly with Nimble.

The transom has a very tight bend where it transitions from nearly vertical to horizontal.  It is one thing to tape the planks to get around the curve but there is also a very fierce twist.  In Balsa or Bass this would be a doddle but getting the twist into the mahogany is a real exercise in improvisation!

The end of each plank is left a bit long and a piece of scrap plywood drilled and epoxied just clear of the transom.  This can then work like a spanner to keep the twist in place while the epoxy sets in the seam and the edge of the transom.  The “spanner” was wedged in place with a scrap piece of balsa and and all held in place with some elastic.

The plank on the left is waiting for the treatment and has been glued up to the last frame.  This gives me something to twist against because doing the plank all in one go would be next to impossible.  To get the glue right up close to the last frame, I applied epoxy to both sides of a strip of paper and slid this up as far as it would go.

Some more brute force to keep the joint nice and tight.

Plenty of elastic gives a good clamping force and doesn’t bruise the edges of the planks.

Here you can see the very narrow planks.  All will be revealed when the sanding is started and only then will I know if I have managed to keep the seams tight.  Fingers crossed.

Tim R