Norwegian sailing pram by Kenchington – Model Shipways – 1:12

[Kenchington]

Begin Step 7: Assembling bottom of boat

 

With the two bottom planks nicely curved, I could get a better look at how they fit on the transoms, which has led to a change of plan.

 

Last night, I intended that the two of them would meet at the centreline of the bow transom, with a  triangular fillet inserted between and abaft. This morning, being able to hold them curved over the moulds while examining them through a magnifying glass, I discovered that the planks are way too narrow to span the bevelled flat on the transom. I don't fancy trying to adjust the other bevels, then fit the next strakes, adjust again etc. etc. So I have fitted the bottom planks to match the bevels, leaving a gap between. Instead of a fillet hidden between and behind, I will insert a stealer (to borrow a term from plank-on-frame planking) to fill the gap. That wouldn't work in full-size, nail-fastened lapstrake construction but, in the model, all that will be visible will be the butt end of an extra plank, between the bow transom and the keel plank.

 

The space to be filled won't be properly visible until the rubber bands come off, but you can see the size of it:

 

Again with the benefit of curved planks to facilitate checking, the junction between bottom planks and stern transom revealed its own problems. Again, the bottom planks are far too narrow. For anyone following this log before building their own pram: Make the two saw cuts in the transom further from the centreline than the laser bevelling marks suggest!

 

Too late for that in my case and I don't fancy placing little spacers alongside where I made the cuts. But at least the stern transom is large enough to give scope for adjusting the other bevels, so that is what I will do.

 

Also, despite carefully matching the bevel marks where the bottom planks must go, the step up to the bevel for the keel plank was still not high enough -- which would leave the gap between transom (plus knee) and keel plank that others have found. Again: If you are following this log before building your own pram: Make the two saw cuts in the transom deeper than the laser bevelling marks suggest, then bevel down to the greater depth! But be warned, the extra depth needed is probably no more than a tenth of a millimetre.

 

My solution, at this stage, will be to sand the bottom planks, from the toe of the stern transom knee to the transom itself, until their outboard face is flush with the bevel that awaits the keel plank. Not an advisable option in a boat that has to face wind and waves but fully viable in a model.

 

With that much decided, it was time for glue. It is, however, important to let the planks take up their natural curves, as those define the longitudinal shape of the hull (while the moulds and transoms set the transverse shape). I put a rubber band around the forward mould (with clips to stop it jumping off), slid the two bottom planks under, then moved them forward and back until they only had a little overhang beyond the bow transom, checked that they were sat nicely in the angle provided for them on the mould ... and glued them to the transom with outer edges aligned to the edge of the bevel. Three minutes finger pressure, then put bands on.

 

Left the glue to set while I made a coffee, then slipped a band over the after mould. I lifted each side of that, while settling the plank into place, so that the wood could take up its own curve, then clamped everything nice and tight.

 

Gluing to the stern transom only added one complication: I had marked the position of my balsa block when it held the knee in what I thought was the right place but that proved a wasted effort. The trouble is that downward pressure on the transom, while the glue sets, causes a bend, which changes the length between mould and transom. It was necessary to first bring the planks down to the transom with the latter in its proper position, hence with as little down force as possible, then move the balsa block until it pushed the knee up ... and then adjust the block's position until the toe of the knee is exactly flush with the outboard faces of the bottom planks (which can be seen well enough in side view).

 

While dry-fitting, I had found that rubber bands around the stern transom tended to force the bottom planks up over the saw-cut steps. Solution was to put pressure on the glue using a piece of scrap and hence a downward, not wanted, force.

 

The net result, as the glue sets, looks like:

 

Edited March 9 by Kenchington

[Kenchington]

Step 7 completed

 

After giving the glue plenty of time to set, bands came off. The tiny bit of infill went into the bow -- in the end, a linear fillet over the knee, rather than a triangle (easier to shape and less obvious in the finished model:

[There: Managed to get the image-size control to work!)

 

Sanded the bottom planks near the stern:

And then turned back to the keel plank. I slipped it under the rubber bands on the moulds, held down one end to its transom, centred that, then traced along the edges of the plank, marking the bottom boards, so that I had mark for where to apply glue (and a guide to placing the keel plank -- though that is mostly done by aligning centre marks at the transoms). Then the elastic bands had to come off. At that point, the bottom boards wanted to move around on the moulds and needed clamps to make them behave.

 

In this pram, as with most lapstrake boats, the strength and stiffness of the hull is almost entirely in the plank-to-plank connection -- glue, in the case of the model. Makes me a bit nervous but this one went straightforwardly. The instructions say to glue from the bow transom half way to the forward mould, then do the rest as a second operation. I did it in three bites instead, with 5 minutes setting time between them, each time working the tip of the glue brush into the narrow gaps where the joint was already glued. Cleaned up the limited amount of excess glue while it was still wet, took care to avoid gluing planks to moulds ... and that was about it. I used clothes-pegs for most of the clamping, with something more aggressive where the keel plank had to be held to the transom knees (or spaced was limiting), while the ends were tight to the transoms:

After giving the glue ample time to set, clamping and bands came off. Then it was time to trim the excess length of the planks, with saw, snips and sanding sticks. 

 

At last, after all the preparation time, I have the beginnings of a boat!

All of the effort to keep the two ends tight has paid off too:

 

Next up: Garboards

[druxey]

That looks good, K!

[Kenchington]

Thank you, sir!

[Kenchington]

Gains and Things:

 

A digression here, while I figure out next steps and maybe ask for some advice.

 

With the garboards and all higher strakes, the pram kit's instructions call for a "gain" to be shaped in the inboard side of the lower edge of each end of each plank. Admittedly, explaining a lapstrake "gain" in a few words and one picture is challenging but I was lost -- and I know others have been before me. Part of my trouble was that I learnt lapstrake (or I should say "clinker") construction in the UK, where the terminology seems to be different, so I had never heard of a "gain". (Oddly, Chapelle didn't mention them in his "Boatbuilding", only noting that the bevel of the lower strake has to transform into a rabbet as it approaches stem or stern.)

 

I learnt the theory in the UK, I should say, as I have never built a clinker boat at full size and never want to try. (I have rowed and sailed various of them, for a time even owned and maintained one, but that's not the same as building.) And that long-ago learning drives me to digress from my digression ...

 

I've seen lots of accounts of clinker/clencher/lapstrake boat construction but the only one that could teach me how it is done was Eric McKee's wonderful little "Clenched Lap or Clinker", published by the National Maritime Museum (the UK one), more years ago than I care to count. Druxey drew MSW's attention to that booklet near ten years ago but nobody seems to have followed up. Long out of print, it can still be picked up on eBay or through AbeBooks.

 

The centrefold of McKee's booklet was printed on card stock and showed everything needed to build a 1:15 (or maybe 3/4"-to-the-foot) half-model of a 10ft workboat (with a very clever arrangement for setting the moulds in position). I could have sworn that I built that model as a teenager but, from the publication date, I see that I must have been on vacation from my undergrad university at the time. The little thing has been kicked around on bookshelves ever since, battered, bruised and ignored, but it is still with me:

Filthy inside, breaking up, with oars that are an utter embarrassment -- but I see that I fitted it with a grating for whoever sat in the stern sheets, along with a scoop bailer and a painter on its own eyebolt. (I had quite forgotten those touches.) And, before anyone disparages the state that I allow models to fall into, that little half-boat has circumnavigated our watery world. Went around in shipping containers, along with much household furniture, but it went by sea, which is more than I have done.

 

Aside from drawing attention to McKee's booklet, my reason for posting (other than as an excuse for showing off!) is to suggest that a 1:12 full-hull wooden version of that same boat would be an excellent next-step after the Model Shipway's dory and pram. With 9 strakes each side and rabbets at keel and stem, it would add another level of skills. Maybe that's a hint to one of the kit manufacturers?

 

Or do I have to scratch-build from McKee's strake drawings?

 

 

Edited March 10 by Kenchington

[SaltyScot]

I must say, Trevor, I have the bug now. The CEO was in here just now and, having asked me a few days ago to think about building what in essence would be a good old fashioned lifeboat, she saw your blog here and said, "See, there are some out there who are building them too." I would like to build the James Caird form Shackleton's expedition in 1912, but not the one with all the rocks etc. in it, just the plain old lifeboat. We will see. I guess what I am trying to say is you have inspired me, sir.

[Kenchington]

I had this posting all ready to go some hours back, then my internet link went down. Fortunately, MSW has remembered my draft, so I can finish up my original digression, then catch up on other messages:

 

The pram kit instructions call for a gain at each end of each plank. I now understand that a "gain" (in at least American nautical English) means a rabbet in the end of a lapstrake plank. I have modified a drawing found for me by Google into something clearer than the kit instruction's photo:

1 is the inboard face of a starboard strake where it nears the stem. 2 is the end of the plank, to be embedded in the stem rabbet. 3 is the end of the bevel on the outer, upper corner of the strake, shaped to receive the next strake -- though, as Chapelle made clear in his "Boatbuilding", that bevel would have had to transition into a rabbet this close to the stem. 4 is the lower edge of the strake. The gain is the sloping rabbet cut into the nearest corner of the plank. (A scribed line corresponding to the upper edge of the next strake below is just visible, extending from the end of the cut.

 

Except for the shape of the bevel at 3, so far so good. I understand the shape of a lapstrake gain. With Chapelle's aid, I can even get my head around its normal purpose:

This is my crude drafting of the junction between two lapstrake strakes, seen in section, as they should be (maybe could be?) on a typical round-bilged boat with a straight stem -- lower strake in brown, upper in tan. The left-hand diagram shows the junction somewhere amidships. In transverse section, the boat is curved there and that curve appears as an angle between the strakes. The upper, outer corner of the lower strake is bevelled, so that the strake above can sit flat and firm. So far, so good. That's the way that the pram model is built, amidships. 

 

With a straight stem, however, the boat's transverse section must transition into something near to a vertical line, as the planking approaches the stem. Continuing to bevel further and further (not shown) would reduce the planks to paper-thickness. Going the other way and mounting the upper strake on the outboard face of the lower one (middle diagram) works if you are putting clapboard onto the side of a barn but, used at the bow of a boat, it leaves a wide hole (blue) for the water to pour in.

 

So the solution is to trim the last 6 inches or a foot of the lower, inner edge of each strake into the form of a gain, while transitioning the bevel on the upper, outer edge of the strake below into a mirror image. Then the two fit together, where they reach the stem, as a form of lap joint, while presenting smooth outer and inner faces (which fit neatly into the stem rabbet). The hood ends of the planks are nailed to the stem, so the removal of wood does not involve an unacceptable loss of strength. Nice, if not always well explained in print.

 

Our pram, however, does not have a stem but rather a bow transom, which changes things because the angles between the strakes are carried to the transoms -- to the stern transom in most lapstrake boats, to both transoms in the case of a pram. In the case of our pram, the angles are almost constant from bow to stern.

But if the structural arrangement was maintained throughout (top left) we would get a water gap again. There seem to be three ways around that.

 

#1: With a lot of work, we could joggle the edge of the transom, so that one corner of each strake sits down in its own recess. On our pram, the junction between bottom plank and keel plank is handled that way, but I have not tried to illustrate it here.

 

#2: We could develop the bevel until it fines away, at the transom, into a knife-edge (top right). Then the next strake could sit on both the transom and the strake below without trouble.

 

#3: We could cut off the edge of the lower strake, perpendicular to the bevel, cut a gain in the upper strake and match them up. That's the version that the kit instructions call for. (And they call for the gain to be cut in 3/64 stock!)

 

What the instructions do not say is that it is necessary to match each gain to the shape of the strake below. They do say to cut away no more than 1/3 the thickness of the wood but that gives no account to how much of the thickness of the other strake remains after its bevelling. I would welcome any advice or comment but I suspect that each gain needs to be individually shaped to fit with the strake below. And that's doubly interesting because the kit planks are so narrow that some transom bevels will need to be adjusted. So we have the shape of the bevelled lower strake, the shape of the upper strake's gain and the shape of the transom, all of them rather fluid, yet needing to be matched into one unit with no gaps. Interesting challenge!

 

 

Separate from all of that, previous build logs have suggested practicing cutting gains on scrap. I'm going to start with scrap a lot thicker than 3/64 and see how I progress. But I just might end up sanding the transoms down until the lower-strake bevels form knife-edges.

 

Your thoughts and comments would be much appreciated!

 

 

Trevor

 

 

[Kenchington]

2 hours ago, SaltyScot said:

I must say, Trevor, I have the bug now. The CEO was in here just now and, having asked me a few days ago to think about building what in essence would be a good old fashioned lifeboat, she saw your blog here and said, "See, there are some out there who are building them too." I would like to build the James Caird form Shackleton's expedition in 1912, but not the one with all the rocks etc. in it, just the plain old lifeboat. We will see. I guess what I am trying to say is you have inspired me, sir.

It seems that I have inspired someone. Not sure whether you or your better half!

 

I do enjoy large-scale models of small, open boats. Every piece of wood in the prototype's structure can be (maybe: has to be) represented in the model, so the builder gets to experience the structure of the boat and not just its shape. That can be done with small-scale models of large ships but it is very, very demanding -- way outside my skill level.

[palmerit]

I was also completely lost by the “gain” too. 
 

@Bryan Woods pointed me to the@modeller_masa build of the Pram that had some drawings. 
 

I didn’t understand what I was doing and why until I had it done (kind of) and it made sense. 

 

[Kenchington]

Thanks for that, Palmerit! I'll likely put steel to basswood planks this evening and I'll need that bit of reassurance.

 

Trevor

[SaltyScot]

13 hours ago, Kenchington said:

but I suspect that each gain needs to be individually shaped to fit with the strake below.

 

That is what it looks like to these inexperienced eyes as well, Trevor. 

[Kenchington]

Thank you for the approval, Mark! 

 

My progress has slowed but not stopped. It's not only the gains that need attention but also the bottom-plank bevels, transom bevels and even the moulds -- all to be shaped so that the garboards fit nicely. I found that I could not so much as check what needs work while the garboards were straight, so last night I bevelled them, soaked them and set them to dry:

They were looking nice by this morning, but I had a day in the city and have not yet proceeded further with them. 

 

I have been practicing at cutting gains too. It has gone much better than I expected, mostly because the grain of basswood is so agreeable. (Quite unlike the bloody-minded bit of sapele that I am trying to turn into a small table for my wife!) One example:

As ever, it does pay to have the right tools:

Yes, that's a standard cutting board with a one-inch grid marked. The chisel is great for making a first, careful cut, creating an edge for the blocking plane to run down. Then the plane develops the slope of the gain, while making it a straight slope.

 

Those are Lee Valley miniatures. I suspect that they sell more as collectable novelties than for practical use, but they are ideal for this task. Now I have hope that I can justify the extravagance by using them on other models.

 

 

My trip into the city yielded the dye needed for a leatherwork project that was always supposed to precede construction of the pram, so that must now take priority. My updates to this log will slow down but (hopefully) not stop.

 

 

Trevor

 

[druxey]

That plane is certainly not a toy! I've been using mine for the past few days tapering planking. It works a charm.

[SaltyScot]

11 hours ago, Kenchington said:

My updates to this log will slow down but (hopefully) not stop.

 

At least that will give me some time to catch up on it all then, Trevor. Have fun  

[Kenchington]

Leatherwork project completed yesterday, so I could turn back to the pram today. Before tackling the gains, I tidied up the moulds, the bevels of the bottom planks and those on the transoms which, together, must take the garboards. At first, I thought that I would have to sand a lot off one of the moulds but then realized another detail of the geometry of this build:

 

There is no problem with the mould (shown below in tan) projecting beyond the edge of the bottom plank (orange), provided that the garboard (brown) sits on the bottom plank's bevel. The remaining gap (blue) will be an air space. The same will be true between the garboard and second strake or between the second strake and the sheerstrake.

However, that is not true at the transoms, where the blue would a route for water to enter. So the moulds can (and do) project beyond the edges of the planks, before angling away to take the next plank, but the transom bevels must be sanded until they meet the edge of the previous plank. (Then the upward step shown above in orange is accommodated by the gain cut in the brown plank.) Maybe everyone else saw that long ago but it came as new understanding to me!

 

With the existing structure of the model as good as I could get it, the time had come to nerve myself to cut gains in the planks. In the end, I hardly used the miniature chisels but (almost) only the little blocking plane. I did not attempt to follow the kit instructions, except in making each gain an inch in length, but rather custom shaped each one to suit the place where it had to fit. Each of the four was quite different in width and/or depth. At the bow, I could have carved away the garboards to nothing, so deepened the bottom-plank bevels instead. Only afterwards did I think of developing those bevels into rabbets (as Chapelle explained for full-size boat building). If I had to do it again, that is what I would do. With the bow-end gains cut, the point along the garboard where it would cross the stern transom could be found and marked, then the gain shaped, starting one inch back from there.

 

As the gains can barely be seen, even with a magnifier, I did not attempt to photograph them.

 

With the gains cut, it was time to glue a garboard into place, let that set, then glue the other one. I did not attempt to do both together. The instructions suggest gluing only from the bow back to the forward mould, letting that set, then doing the next length and so on. The trouble with that is that you may need to adjust the forward part of the plank a little in getting it to fit further aft. I glued and clamped, then glued further and clamped further etc., but did not wait for one length of glue to set before continuing. I did use a lot of pegs to ensure that the joint was tight, without placing too much pressure on any one point.

 

I found that the clamped plank wanted to flare outwards, away from the moulds. Bands around those cured that tendency.

 

Otherwise, all went well, except that the first garboard fitted drifted off position at the stern. I delayed fixing that in case I had a similar problem with the second one, when they could have been cured together. In practice, a clamp on the transom tamed the trouble:

Tomorrow, I will let isopropanol work its magic and re-set half the length of the one plank. meanwhile, it is just nice to see a model begin to look like a boat!

 

 

Meanwhile, I checked the two second-strake planks, which were nicely symmetrical, without the problem with the bevel line seen in other planks. So char could be cleared off, bevels shaped ... and the last task tonight was to wet those planks and mount them to dry overnight.

 

More tomorrow.

[SaltyScot]

18 hours ago, Kenchington said:

meanwhile, it is just nice to see a model begin to look like a boat!

 

Absolutely. Thank goodness for wooden clothes pins  

[Kenchington]

Continued progress today but not much to say about it. I released the after end of the garboard that had got misplaced, then glued it where it should be. The kit instructions do hint at the difficulty of getting the planks into place and I know that other builders have had similar problems. Mostly, it is a matter of care and especially careful placement of clamps.

 

I continued custom cutting of the gains. The two second-strake planks (one each starboard and port) barely needed anything at all at the bow but both needed deep gains at the stern. Then it was on to gluing of first one, then the other. The first of the two slipped low at both ends -- by much less than 1mm but still enough to produce gaps at the transoms. I will fix those in the morning.

 

Final step was to put on the sheerstrakes, to dry overnight:

 

All being well, I will finish planking tomorrow and maybe complete the external work, then release the boat from the building board at last!

 

Trevor

[SaltyScot]

I may wait it out a little before I tackle something like this Trevor, it looks incredibly involved. Watch and learn is the mantra of the day for me as far as this goes sir. I look forward to seeing her off the board!

[Kenchington]

Thanks, Mark!

 

But I can't see how a little pram is as challenging as recreating Mosquidobit from the Lynx kit. Your skills are well beyond mine.

[SaltyScot]

4 hours ago, Kenchington said:

Your skills are well beyond mine.

 

Ha, you do me too much justice, sir. I am finding the way you shaped those planks with the gain etc. to be a lot more intricate that modifying some plans  

[Kenchington]

Completed all planking, hence instruction steps through to #11 (aside from a bit of trimming and tidying).

 

Today's effort began with releasing the two ends of one plank that had drifted out of position yesterday. Those went back on with no real trouble, except that the bow end got the reverse error and ended slightly too high off the building board. I doubted I could do any better with a third attempt, so left it as it was.

 

Then it was on to the sheerstrakes. The moulds and stern transom needed little attention before providing properly aligned surfaces for those last planks to lie against. The bow transom did need some serious sanding to bring the bevel for the sheerstrake into line with the bevel on the mis-positioned 2nd strake. That gave the pram a slightly asymmetric transom -- hopefully not noticeable, but time will tell. As that change moved the location of one sheerstrake away from the building board, the other had to be narrowed by a millimetre or so, to keep their upper edges at the same height in the finished hull.

 

Aft, I found (as have others before me) that both planks rose too high up (i.e. towards the building board) the sides of the stern transom. Holding the two planks together (for symmetry), I narrowed them by nearly 1/10 inch (call it 2mm), by sanding, running that width-reduction out to nothing over 5 inches (125mm) along a straight line. After assembling everything, I see that I have produced a very slight hump in the sheerline. That will be easy to correct later.

 

Close inspection showed that the starboard sheerstrake did not need any gains cut. The bevel on the 2nd strake on that side made a smooth surface with the bevel for the sheerstrake on each transom. In contrast, the port side did need deep gains, both fore and aft. I matched them with short rabbets in the ends of the 2nd strake, worked out of its bevels. The gain+rabbet at the bow seem to have fit very well, the stern pair maybe less so, though I doubt that any gap will be visible. 

 

What I should have done at that point was to soak the sheerstrakes in boiling water again, get them exactly into their final positions and live them to dry overnight -- probably meaning two nights, as it would be hard to get both into position at the same time, without using glue. After rebounding, they might have fit comfortably and easily. What I actually did, however, was force each one into position, with an elaborate complex of clamping tools. One wrinkle that would have been needed either way built on a suggestion gleaned from a previous MSW build log: I inserted Lego blocks between build board and strake to hold it up against the pressure of the rubber bands. As the strake curved towards the board at each end, the blocks could be slid a little, fore or aft, until they held the strake at just the right height:

 

It's not yet quite time to remove the boat from its board: I still have to trim the sheerstrakes where they project beyond the transoms, then fit a skeg and two bilge runners to the outside of the hull. But that's for the morning. At least I have the hull shape complete!

 

Trevor

[SaltyScot]

9 hours ago, Kenchington said:

As the strake curved towards the board at each end, the blocks could be slid a little, fore or aft, until they held the strake at just the right height:

 

Right tool for the right job I always say, Trevor or, improvise, adapt and overcome  

[Kenchington]

3 hours ago, SaltyScot said:

Right tool for the right job I always say, Trevor or, improvise, adapt and overcome  

Exactly so!

[Kenchington]

Steps 12 (fitting the skeg) and 13 (bilge runners) completed

 

The pram has a large centreline skeg aft. The instructions say that it is to protect the rudder and supplement the daggerboard in resisting leeway, when sailing on the wind. It would doubtless help with both of those, but its primary role will be in providing some directional stability when rowing. Any good rowing boat tends to track straight, so that minor differences in the forces exerted by the oars do not make the boat yaw. (When there is a need to change course, the wide reach of the oars provides plenty of leverage for the turn.) Without its skeg, our pram would be a mere cockleshell, spinning around whenever one oar catches a wave and the other misses or if one oar is pulled a little harder than the other, while it would weathercock even in a light breeze -- much to the aggravation of the oarsman!

 

The instructions explain how to sand the upper surface of the skeg, so that it matches the curvature of the keel plank. That was not necessary in my case and probably won't be in any build that had the moulds and transoms carefully set on the building board. Hence, it was mostly a matter of cleaning char, softening edges etc. until the skeg was ready to glue in place. The only elaboration I added was to round the forward and aft lower (with the boat upright) corners, as those are the points which would most strongly encounter obstacles on beach or trailer.

 

Gluing the skeg in place (with its aft end aligned with the aft face of the transom, both ends on the centreline of the keel plank) posed only one issue: How to keep it perpendicular to the keel plank. I turned once again to Lego blocks.

 

The pram also has two bilge runners (which the instructions curiously call "bilge keels"!), to protect the planks when the boat is ashore but also to give it stability when sat on a flat surface. Those also fit easily, after cleaning up and having corners softened, with only some extra rounding of the ends for the same reason as with the skeg. I did break one, through overly enthusiastic sanding of char, but it went together again as both parts were glued to the hull (though needing one extra rubber band). I glued runners and skeg in one operation:

When the glue was set and the bands off, it was finally time to slice through the holder for the bow transom and release the boat from its building board!

Internally, there is some excess glue and marks from the moulds to clear up, but not much:

Those pesky plank ends don't look bad either:

At the bow, one sheerstrake will need more glue, while I am adding other pieces there. The asymmetry in the 2nd and sheer strakes is visible but probably not to the casual viewer. 

 

The kit instructions include a rather cryptic direction to "Sand the outer surfaces [of the runners] vertical". One MSW build log states that the plans for the full-size version of this pram call for the runners to have a 5-sided section: Square to the garboard plank where the two are attached, but parallel to the waterline at the bottom and perpendicular to that on the outer faces.

 

I was just going to leave the ones on my pram rectangular (as the runners on my full-size boat are). However, that would leave the model perched on the angles along the inner edges of the runners. So I lightly penciled the lower faces and got busy with a stiff sanding-stick, laid transversely across the two runners, continuing until the pencil marks were gone. There is no need to extend that sanding to the forward or aft ends of the runners, as  the curve of the hull and the presence of the skeg prevent the model from sitting on those ends anyway.

 

The result is a nice thwartships flat, which lets the pram sit level and stable on my cutting mat:

It has, however, created an acute angle between the new flat and the outer side of the runner. That's where the vertical sanding is needed -- on a full-size boat if not also a model. Maybe I will address that further when finishing the outside of the hull. But the next tasks will concern the interior of the boat, until the rubbing strips go on (under step 26 of the instructions).

 

Trevor

 

 

[SaltyScot]

10 minutes ago, Kenchington said:

it was finally time to slice through the holder for the bow transom and release the boat from its building board!

 

Free at last! 

10 minutes ago, Kenchington said:

The asymmetry in the 2nd and sheer strakes is visible but probably not to the casual viewer. 

 

Correct  

[robert952]

I love seeing the use of LEGO blocks (or similar). Their precision seems a big advantage.  I wonder if I can talk my grandson out of a  few of his LEGOs.

[Kenchington]

21 minutes ago, robert952 said:

I wonder if I can talk my grandson out of a  few of his LEGOs.

I may be the only person who bought his first Lego set after passing 70!

[Kenchington]

Step 13: Daggerboard case

 

I started on the interior of the pram last night. The daggerboard case came out well:

That was more by luck than judgement, though. I rushed the job, carelessly, which is always a bad mistake. Fortunately, all is OK.

 

The case is simply four pieces: 2 sides and 2 ends. The ends are long and project through the slot in the keel plank:

A bit out of focus but it makes the point. The projecting ends will need trimming later.

 

The sides of the case are not square. The instructions don't say but the longer dimension runs fore-and-aft. No problem figuring that out as the long sides are as long as the ends (leaving nothing to project into the keel slot). What is more challenging is that the bottom of each side is very gently curved. I missed that with the first side, sanded off the char against a straight sanding stick ... and had to re-create the curve in parallel to the side that I had not messed up. Bad mistake but recovered.

 

By shining a flashlight through the keel slot and holding each case side in place, any deficiency in the curvature would be easily seen. Mine did not need further shaping.

 

The instructions also don't say but the curve isn't symmetrical. It leaves one end shorter than the other. The shorter end goes forward, making the case vertical even though the keel plank curves up towards the bow.

 

To glue the pieces together while keeping all square, I followed an idea in another build log and assembled the four pieces against the weight and perpendicularity of a pair of mechanics squares. I added some weight while the glue set, though I don't know whether that was needed:

The instructions then say: "bevel the top edges and corners, as well as the vertical sides". That would be a mistake and its consequences can be seen in too many build logs on MSW. The reasons why will come into play later in the build, so can best be explained here.

 

When a full-size version of our pram is sailing on the wind, that wind would push her sideways. Almost the only thing stopping her from sliding across the water's surface (making extreme "leeway", to use the technical term) is the deep, narrow daggerboard. The hydrodynamic force is considerable (balancing the aerodynamics of the sail) while the shape of the board gives that force a lot of leverage. It is transmitted from board to hull through the case alone. So, if the case wasn't well braced against side forces, it would break free of the keel plank, resulting in at best a nasty leak, at worst disaster.

 

There are various ways that the bracing might be provided but, in our pram, it depends entirely on the midship thwart -- which is notched to fit around the upper, aft corner of the case. Thus, the joint between thwart and case has to be tight and the case should not be bevelled nor rounded where it meets the notch in the thwart.

 

Moreover, when the pram is being rowed, the oarsman will usually sit on the midship thwart and must have his/her backside on the centreline (to keep the boat, and the pull on the oars, balanced). Lumps and bumps there would not be welcomed.

 

The vertical front of the case could and should be well rounded (not bevelled). There is timber enough to make it semi-circular in section (so long as that isn't carried all the way down to the keel plank, or a leak would open in the corners) but I didn't go that far. The outer edges of the top of the case cannot be curved quite so much but something more than a softening would be good. The case is, after all, the thing that our intrepid sailors are most likely to bang into. Doubly so at the top of the case front, which needs three-dimensional curvature and can be well rounded. The back of the case can be rounded off a bit too, but only below the thwart and above a frame that will later fay against the case. However, the case back will be under the thwart, so out of harm's way.

 

Fortunately, all that shaping was easily done with sanding sticks.

 

Another thing that the instructions do not emphasize applies as much to model as full-size: It is critical that the case is installed upright -- in a thwartships (port/starboard) sense, when the hull is upright. The long daggerboard will be a prominent feature of the finished model. It would look awful if angled off to one side. Since the thwart and its notch where available, I simply used that to hold the case in position while the glue set.

 

Also, and as others have found before me, the laser-cut slot in the keel plank is longer than the case. I opted for the common solution of placing the case at the forward end of the slot, leaving a gap abaft it:

Under the next step, that will be covered by the midship frame. I will insert a fragment of scrap from the same sheet that the case parts came from. I was thinking of doing that after the frame is in place but I think it would be easier to glue in a longer piece, then slice it off both inboard and out, while also trimming off the outboard excess lengths of the two case ends.

 

And then on to Step 14: Bottom frames

 

 

Trevor

[SaltyScot]

14 hours ago, Kenchington said:

Under the next step, that will be covered by the midship frame.

 

That answers the question I was going to ask then.........

[Kenchington]

Step 14, bottom frames, completed; Step 22, mast step, commenced

 

The design calls for three pieces (not really "frames", closer to "floors"), spanning from garboard to garboard or a bit further. The midships frame (also called "number 3" in the instructions) goes in first and doesn't pose much trouble. Mine only needed removal of char, followed by a little adjustment (to compensate for minor errors in the placing of the planks), softening of the exposed angles and a general clean-up. Then it could be glued in place, tight against the after side of the daggerboard case. It does have to be at right angles to the centreline of the hull. I laid the boat on my cutting mat, aligned with the marked grid, then eyeballed the orientation of the frame in alignment with the other direction of the grid. That seemed to work.

 

I had tried inserting a plug into the hole left by the over-long slot in the keel plank, but basswood proved too breakable for anything so small to be pushed tightly into a hole. So I put the frame in first, then flipped the hull over, filled the remaining hole with glue and dropped a tiny fragment into the mess. Once set, I snipped off most of the excess and sanded down the rest. That seems to have worked too:

If the midships frame went in easily, the next one did not. Challenge #1 was figuring out where to place it along the length of the hull. The instructions offer a paper "measuring strip" but that is clumsy and its distances do not correspond to the design of the full-size pram (maybe because it was been scaled down during the printing process). Fortunately, the kit material also includes a (very small) reproduction of the original design's longitudinal-section drawing, which has enough measurements given to figure out the required spacing. From that, I determined that frames 2 and 3 are supposed to be 37 3/4 inches apart (centre-to-centre)at full-size or 3 1/8 inches at scale (to the nearest 1/32) -- call it 80mm, for those enlightened ones who only work in metric. With that set on a draughting compass, the distance of the forward edge of frame 2, ahead of the forward edge of frame 3, could be readily marked on the planks. The only tricky point is keeping the measurement parallel to the centreline and not following the run of the planks.

 

It is important to mark the position on each plank. It would be all too easy to install frame 2 perpendicular to the keel plank. That was fine for frame 3, as the plank is parallel to the waterline near the daggerboard case.  But the keel plank slopes up towards the bow and a frame installed at right angles to it will have its heads angled aft. As others have found, that plays havoc with positioning later pieces.

 

Marking up the hull was, however, the easy bit. It was then necessary to bevel the frame to match (by trial-and-error) the slopes of each plank that it contacts -- a very fiddly task which I fudged enough that the poor fit will not be noticed. After the usual clean-up and final preparation, frame 2 was glued in too. "Clamping" was by means of two blunt thumbs pressing the piece into place.

 

The bow frame is much smaller and much more steeply bevelled but a simpler shape and perhaps easier to work on. Or maybe I just wasn't so worried about a neat fit. Its distance from the midships frame should be 51 1/4 inches or 4 1/4 (108mm) at scale. Much more important, its distance from frame 2 has to match the length of the mast step. I therefore constructed the step and had it on hand for dry fitting to confirm the spacing.

 

There's a problem here that has caused some grief to other builders of this kit. The mast step is made of two layers of wood, glued together -- one spanning across the two frames, the other filling the space between them. The instructions say that "The top layer has the hole for the mast foot and the lower layer is solid for it to rest on". However, the kit comes with two identical pieces, both of a length to span across the frames and both with mast holes. On top of that, both have the grain of the wood sheet in the same direction, running across their widths, making them vulnerable to splitting where the sides of their holes are narrowest. One solution is to pass the mast through both holes and let its heel rest on the keel plank. That would be a mistake (at full size). The whole point of having a mast step supported upon two frames is to spread the load across the thin planking. It's not just the weight of mast and rig. There is also the downward portion of the tension in the rigging -- which has to be several times the forward force conveyed to the hull through the shrouds.

 

My alternative was to cut a new bottom piece for the step from the same sheet of basswood, making it as wide as the laser-cut top piece but shorter by twice the thickness of a frame. I made sure that the grain ran along the length of that bottom piece, then glued it to one of the kit-supplied mast-step pieces (centred along the length of the latter). After final shaping (the instructions call for a 45° bevel on each of the upper edges), the mast step was ready for dry fitting in checks of the position of the bow frame.

 

The end result looks like:

The mast step (dry-fit for now) is:

And that's enough for tonight. Completing the rest of the internal hull structure occupies steps 15 to 22 and will likely take me a few days.

 

Trevor