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Oheka II Dinghy by TheDane - Scale 1:20 - Finished

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Hi all,


This is a repost of the old Build log:

(from 30 Aug 2011 to 16 Nov 2011)


This is my build log for the dinghy for the RC model of the Oheka II that I am currently building in scale 1:20. The dinghy itself is NOT RC but will live on top of the aft cabin of the Oheka II which is why I put the build log here.


This is the first time i have attempted to build a lap-strake (clinker in my part of the world) boat.

Some of the parts of the build log may seem to move in baby steps but sometimes it is the simple things that get overlooked. One example is the thing or method that is so obvious that everyone is expected to know it therefore it does not get mentioned.
(I had that happen at work recently)

Apart from the Oheka II, I have not built any model boats since I was a kid.

I need to do some testing to find the easiest way to post pictures.

BTW the dinghy itself is not RC but will live on top of the aft cabin of the Oheka II.




This is all the information I have on the dinghy. A top view and a side view cut from the drawing I received from the shipyard.



The two views were copied to a working drawing so I had somewhere to put notes and sketches if needed. The squares on the paper are 5x5mm so it is not a big boat :)



I copied one side (starboard) to a new sheet of paper and folded it on the centerline so I could get it symmetrical.



This is the way I copied the other side. Every time the pencil crosses the line on the inside (starboard side) it transfers some of the pencil lead to the other side (port) of the paper.



After unfolding the port side is drawn up. I now have a symmetrical top view.

Edited by TheDane
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The transom can now be created by marking the width from the finished top view and the the height from the side view.
Draw a smooth curve from one side at the top to the bottom centerline. Copy this by folding the paper as above. This is the finished transom. Repeat at the maximum width and halfvay to the stem, using the width and height at the two positions to mark the ends of the curves. Make sure the curves are smooth.
This shows the three formers drawn onto the top view. The formers of the jig have been cut out and need sanding to the final shape
The finished jig. Made from 3mm balsa and glued to a piece of 10x20mm hardwood so it doesn't twist or move later. Using a narrow base would give me access to the inside while planking, making marking of the overlap easier. The centerline profile was copied from the side view.

Laminating the two layers of the keel. Here I should have extended the keel down to the jig and glued it there. It would have saved me from having to add a bit more when the planking ended up being a little higher than anticipated. Make sure the the keel is not glued to the jig, except behind the transom where it will be cut off anyway.

Another change that would have made it easier would be to make the outer layer of the keel a little wider than the inner layer because that would remove the need to cut a rabbet because the step in width would have served the same purpose.
Anyway the keel may have been too wide at 5mm ie 10cm at full scale.


Edited 2015-02-19 re-uploaded missing photos

Edited by TheDane
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Starting work on cutting the starboard garplank. The piece of plywood in front was big enough for both sides.



Checking for fit of the starboard garplank.



I did not cut notches in the balsa jig so in order to help make sure that the planks were positioned symmetrically I made an oversize template for each of the formers. The idea was to fit the template to the plank on the first side and then use it to place the plank on the other side.



Using the template to check that the shape of the jig is correct on the other side.



I copied the finished plank for use on the other side before gluing it to the keel.
As a precaution all the planks were also copied to paper.

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Post from Mario:

Hi Peter,
Nice idea on getting the garboard planks exactly the same.
Regards Mario


Thanks, glad you like it Mario. I have spent quite a lot of time reading several build logs and there are good ideas in most.

Back to the build:


It is now time to glue the garboard on.



And the other side.



I cut some thin strips and placed one for each plank I was going to use.



Spread the temporary strips out evenly to get an idea of where the planks should run. Mark all the positions where the strips cross the jig. It is the bottom edge of the strips that counts because that will be where the inner plank will end and the outer plank will overlap this edge.



At this point i cut and dry-fitted the second planks. As part of the preparation for the second plank I had to cut the rest of the rabbet in the stem on both sides.

Edited by TheDane
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Cutting the gain so planks will end smoothly without a sawtooth profile on the transom. The bottom plank is shown inside out and will be turned over when it is glued on. This needs to be done at both ends of the planks.



This is a drawing of the method I choose to use for the gain.



Gluing on plank number two after copying it as above. Note the high-tech clamps :)  (copied from full-size practice)



Gluing the other side. The templates in front have now been filed down to fit both planks.



Third plank. I added the needles so I had 3 fixed spots where the edge of the plank should end, making it easier to fit. Later needles were added in the same positions on the other side to help ensure symmetry.
UPS, just noticed the third needle in the transom former is missing in the photo.



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Hi Peter,
Nice idea. Looks like a nice little boat you going to build there. Maybe you can attach a photo of the RC boat your going to place her on. I am going to enjoy watching the progress of your build. have fun...........

Regards Mario


Mario, you asked to see the model I am building this dinghy for so here it is:



I marked the waterline from the drawing on the stem and both sides of the transom.
Then it was wrapped in plastic wrap to make it watertight and weight was added until it floated at the correct depth. Luckily I could gain access to a large enough body of water for these tests. :)

So now I know how heavy I have to make it: 2.7kg or 6lbs.

It is 111cm long and about 16cm or 43inches by 6inches.
Will be powered by 3 Speed 400 motors.

So I am watching the weight :)


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Planking continues.



Planking continues.



The last plank is added.



The transom was built from 4 strips of mahogany and shaped to fit the planking.
Next time I will make the transom first and glue the planks to it while planking, that will avoid the job of having to fit it afterwards.



This is what she looked like off the jig. The top planking it too high at the stem and will be filed down until there is a nice curve from end to end. Now it is clear that my decision not to extend the keel to the building board has come back and bit me in the posterior :(  I will need to extend the keel.
The transom has been left to high on purpose. I will shape the top as a nice curve as one of the last steps.
If I am not using the correct maritime terms from time to time it is because I am unclear on what the name should be.


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Hi Peter,
I am not into RC. But that is very interresting how you figure how much weight you need to I guess go with the running you plan on using.
Your plank job on your little dinghy looks great. Nice little scratch build.

Regards Mario



Hi Mario

Well, the dinghy could be considered a static build on a movable RC boat stand :D

Thanks, I am pretty satisfied with the planking, especially since it is the first time.

Regarding the target weight it can be calculated as

Full-size weight divided by scale factor cubed
or with Oheka II numbers

Full-size weight for Oheka II was 22tons, the scale is 1:20
22000Kg / (20x20x20) = 2.75kg



This is the weight i found after ballasting the hull down to the waterline.

It corresponds to a full-size weight of 22tons 224Kg so it was drawn correctly on the drawing.



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This is the outside view after the top plank has been sanded to shape. Two formers have been temporarily fitted to help hold the shape until the internal pieces have been added.



View inside.



Adding the missing bit of the stem.



Adding internal support structure.
BTW. What are they called in english?



Adding the knee that supports the transom.


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Post from Russ:

Nice work on your dinghy. I especially like your formers to keep the hull in shape while you add the frames. That is a handy little jig. I will have to use that one on my next small boat.
Once you get the frames in the hull, I think the entire structure will stiffen up quite well.


Thanks Russ.
The dinghy had very little twist in it so the loose formers work well. If it had needed de-twisting the formers could have been connected with some diagonal pieces to stiffen it up.
Are the strips across the planks called frames?


Yes. Those are just bent frames as opposed to sawn frames. Small boats use bent frames quite a bit, especially those built upside down.


Thanks Russ. I now know another term.

The build continues:


This is how she looks with the framing almost done. 1 set of frames is still missing in front of the current ones. This will be in two pieces, one on each side of the keel.
The hull is quite stiff at this point and has very little twist I need to adjust.



Adding more to the aft keel. This will be sanded into the final shape later.



Gluing the starboard twart support in. The port one was clamped in place in order to balance the stress while the starboard support dries.



In order to mirror the placement of the port support I created these small spacers (clamps). They will be placed on the other side so the height can be determined easily.








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Placing the spacer-clamps on the port side.



Gluing the port support in place against the spacers.



Test fitting the twarts. The shape and placement come from the plan shown in the first post.


It is not possible to tell if all three cross members shown are twarts or only the aft two, so I have decided to consider all three of them twarts because it is still be possible to enter and leave the dinghy from the front is it is a twart and not a deck.
Adding the floorboards will be the next step before finishing the twarts.


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I drew up the basic idea on paper first to see what it would look like. The center floorboard is shorter aft so that there is room for a lifting eye mounted in the keel.
Support strips are being glued to the center floorboard.



After that was dry I clamped it to a former with the edge of the floorboard just a little higher than the former.



The spacers were positioned and the next floorboard was glued to the supports. This was repeated until the full width was reached.



I tried two different ways to shape the assembled floorboards and the top shape was by far the best. The stick is not a mast and is only used to hold the floorboards in place for the photo.



Here I have added an outline to make it easier to see. The other side will be a mirror copy.


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The floorboards look good. Very nice work shaping them to fit.


Thanks Russ, glad you like them. They are only the template for the final ones. I have not decided what to make them of yet.

Much of the construction is based on a full size dinghy I found photos of on the internet, adjusted to the size of this one. Finding those photos really helped with ideas.

The materials used for the model are 0.4mm (1/64") ply and 1mm thick mahogany.

The full size dinghy was almost certainly built completely from mahogany so it would match the superstructure on the Oheka II, this means I will have to "paint" it mahogany. Are there ways to stain or other wise do this?

If not, them I will have to build a copy in mahogany and retire this one to a display stand of its own. :)


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I would look for some mahogony stain. That should look very good and I think much better than paint. Keep in mind that if the wood is very soft, it might not soak up the stain evenly. This could lead to a blotchy finish.
I use Minwax stains. They make a pre stain conditioner that goes on clear before you stain. The conditioner will make sure that the stain goes on evenly without a blotchy effect.
I am not sure what brands are available over there, but you should check for some sort of pre stain conditioner if you are using very soft or porous wood.


Russ: I agree about staining versus painting. Thanks for the name of the stain. A guick search indicated that Minwax might be available here. So now I know exactly what to ask for. I will contact my local "color dealer" to see what they suggest then do some tests on the ply I used before trying on the dinghy.



Just a little progress.


I have now cleaned up the ends of the planking and the keel.
The oar is just a test for size and shape. Perhaps the blade part is a little long but overall I think it looks acceptable for 1927.

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Mahogony will be a little more reddish in color. They have a nice cherry stain that I have used with some success. It is not quite as reddish in color as the mahogony.
Also, see what their natural stain might do for the wood. It will not really change the color as much as it will darken the wood. Like other stains, it will bring out the grain of the wood.
Also keep in mind that stain will not adhere to any glue marks. Make sure everything is sanded down and there is no glue left on any exposed surfaces.


Great, now I have some alternatives to compare that I know might work.
The full size yacht was varnished with a shiny finish, if my comprehension of the German article I found from 1927 is correct, so the dinghy was probably done in the same way. On photos it has the same dark color as the cabin. (if you can call it color on a B/W photo) 

If possible I think I should go with half shiny / half matte finish after staining it, so it does not look to shiny and toy like.


See what you can find in semi gloss clear finish to go on top of whatever stain you use. A little shine will be fine for a yacht like finish.


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Russ: I agree on the semi gloss finish. I will ask for a compatible finish when I get the stain.


meanwhile the build continues:


The floorboards after rough shaping. At this point supports have been added only to the rear so the front is free to move. They have been placed so they do not interfere with the frames already in the dinghy.



In order to get the floorboard slots parallel when they are pushed down on the curved bottom planking and keel it is necessary to open the slots at the front. Pushing the floorboards down will make the front plank ends move towards the center closing the gap.



After sanding the starboard side of the floorboards to the finished size it was flipped over and the outline was drawn on the paper.



Needles were added to create stops so the floorboards could be placed precisely when checking the shaping of the port side.



This shows that the lowermost plank is shaped correctly and that the front of the two inner planks still need more sanding. The short vertical pencilmarks show where the planks should end so they match the other side. Getting the starting and ending points lined up is more important that the outside shape because any misalignment here will be noticed.



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Hi Peter,
A lot of detail in that little dinghy. When you mount it to your RC, will it be right side up so it can be seen? Very nice progress. :)

 Regards Mario


Hi Mario
Thanks for the nice comments.
Yes it will end up in a cradle, right side up, on the roof of the aft cabin under a single david/crane.
If not, I might have been tempted only to do the planking and keel. :D


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Staining test

I bought some stain and tested a piece of the ply the dinghy was built from. On the color chart the stain is a little darker than cherry and between the dark mahogany and regular mahogany so it should be close.



Photographed indoors with a flash with a white sheet of paper sticking out.
The three wood parts on top of the ply are the mahogany twarts placed there for color comparison.



From a different angle the colors changed.



I also tested by doing a quick and not very thorough staining of the floorboard template, which is placed on top of the finished floorboards in this photo. Just to see what it would look like.


From the way the ply looks I can see that I should have stained it first so I could cut the parts from the areas where color of the stain is consistant, even if this wastes some wood.



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I think the color looks very good. The look of the floor boards inside the boat is good.


Thanks Russ. The color came out a little darker that I thought it would. however it is that same color as the partial floorboards in the previous post. I compared them side by side.




I stained the finished floorboards and they took the stain quite evenly. A friend of mine suggested wetting the wood first to raise the surface so the stain could penetrate more. It seems to work.

As a way to postpone the decision between staining this one or making one more from pre-stained wood, I made a set of oars :)



Here the oars are at rest. Along with a size indication.

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The oars came out very well. Nice work. So long as they are the proper length for this boat, they will work well.


Russ, Thanks. I was going for classic oars
I did some research first regarding oar length inside/outside vs boat width, hand grip diameter, hand grip length etc. Most of what I found was for modern oars, not oars made in 1927 when composite meant different types of wood glued together
There are many opinions for the correct length. These are 1.7 x distance between oarlocks. That may be a little short, but then it is easier to maneuver in tight spaces and they fit inside the dinghy.
Hopefully I can find a 1:20 scale person to test them (and crew the Oheka II)
Now for some oarlocks.


Hi peter,
Your little boat came out nice. The oars look great. when I built my oars for my Lobster Boat. Blue Ensign if I remember right told to set up a scrap piece and just look to see how it looked. Thats how I decided on the length. It's on my thread
Regards Mario



Hi Mario
Glad you like it. There are still a few finishing touches to add though.
I went through your build log for the Lobster Smack. That is a very nicely built boat and the method of hiding the mounting screws is ingenious.


Thanks Peter,
I hope you saw how I worked out the length on the oars for the Lobster Smack. Because the kit had me add oarlocks , but no oars. So a little help from my friends here on MSW helped me out with that situation. PETER THANK YOU FOR KIND WORDS.

Regards Mario


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The framing all looks good. Very neatly done.


Thanks Russ. I am glad you like it.


Now for the breasthook. The first cut.



Ready to be trial fitted after cutting the in-wales to the correct length.



Gluing it in. It is too thick on purpose and will need sanding down to the correct level.



Close-up view. Ready for final sanding to shape. The curve at the back still needs more work.

I haven't decided whether to stain the rubbing strips and breasthook or not, yet.

The next step will be making the oarlocks themselves.


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Hi Peter,
Nice progress on your little boat there. You mentioned the inside support. I'm building the Bounty launch and the book refers this support to be the sheer clamp. I hope I am correct on this. I am still learning n have along ways to go. Since you are glueing it across from the sheer plank of the hull.


Hi Mario

I think this piece of wood has several names :)

I did a Google both on both "inwale" and "sheer clamp" and found that they both mean
a horizontal reinforcing strip of wood holding everything together.

1. (in an open boat) a horizontal timber binding together the frames along the top strake.
2. a strip of reinforcing material within a gunwale.

Sheer Clamp
a heavy beam running along the sheer strake inside the frames of a small wooden vessel and connecting the upper ends of the frames. The sockets for rowlocks may be fastened to the sheer clamp of a launch.

So I think we are both right. :)


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A little more progress.


Stained the breasthook, inwales and rubbing strips after sanding/ filing into shape.



Made two knees for the transom by wrapping sandpaper around a round pencil and sanding a curve into a 4mm wide strip of Mahogany. Then cutting the sides. The first one was used as a pattern for the second so they are identical. These were then glued in place.



The top of transom should be a nice curve so I made a template using a dinner plate to get a large curve.



After finishing the template, the transom was marked and sanded/filed to the final shape.



Gluing in the aft twart.


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Hi Peter,
Very nice progress going on with your little boat. Your showing that everything under your roof is subject to being turned into a jig. Nice idea with the plate. I see no food stains so I'm guessing you served your dinner afterwards. :)


Mario: Yep, I picked a clean plate :)


A little update.


The floorboards were glued in and after the glue dried the support under the center twart was added.



Followed by gluing in the center twart itself.



After adding the front twart the oars were tested for fit. They are placed about 30 scale cm. behind the twart center.



The next step is making the oarlocks. I began with drilling the holes that will become the inside of the oarlocks in a 1mm thick piece of brass.



Then the industrious use of a hack saw gave me this. I decided to finish one oarlock at a time in case I make a mistake. :)


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Testing the hole size with an oar during the process.



More filing to shape.



Making progress. I have left material at the top of the hole deliberately. It adds strength, making it easier to file without breaking it. One of the last steps will be opening the oarlock to an U shape. The pin at the bottom needs more work. Its not round yet.



This is the current state of the boat. I still need to add 6 knees to support the twarts.


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Hi Peter,
Your little boat is coming out really nice. You installation of the floorboards looks great. I like the way you went about making your oar locks. Very clever.


Mario, Thanks. I desided to make the oarlocks like this beacuse I could easily get the inner diamer to fit bu just selecting the right size drill. Afterwards I just removed everything around the hole that did not look like an oarlock  :)


I did go out and bought a set of needle files before making the second oarlock so that went much quicker. My wallet felt it though :(



Some of the steps.



Almost finished and nearly identical. To give an idea of the size the squares on the paper are 5x5mm. (3/16+1/128 inch+0.0099inch)



I decided that the oars needed leather protection so I printed several colors on a sheet of paper so I could choose.
Because I have not done this before I made a test oar first.



I wrapped the paper around the test oar twice and cut through both layers. This left a close fitting strip of paper.
After gluing on the paper I tried the test oar in an oarlock. There are a few white spots on the brown area but with more care they won't happen.



Does this look right?

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Hi Peter,
Hey thanks for showing your step by step progress on making your oar locks. :) You know when I made oars for the first time it was on my Lobster Smack. But on my Dinghy build I made a better effort. Go to page 4 of my build and you can see how they turned out. It's on my signature. I also made a turkshead knot for each oar. I practiced at first with larger scale thread. Then I used the correct scale. The whole process of learning to tie the knot and placing it on the oar about 3hrs. I'm a slow learner. :( Plus I also found a couple of sites on the internet that helped me out on making knots and the leather protection or you can use thread to simulate rope. The site will give you info on what size to make the leathers and where to place them on the oar.
Thats a good idea using paper to simulate the leather. But by white spots do you mean after cutting your paper. I use card stock. That way when I cut it for example if I use black, it's black all the way thru.


This one shows you how to make the knot...

This one shows you where to place the leather and make the leather...

another on the leathers...

info on oars...

i hope this helps you Peter. Good Luck........................Mario



HI Mario,

Thanks for the nice comments and the links to the sites with info. I just took a quick look and there is a lot of information there I have not found myself.

I went to your build log and saw how you made your oars for your dinghy and they came out great.

The paper method I tried still needs some improvement. The white spots I mentioned are where the layer of color is broken so the paper underneath shows through. I agree that using colored paper is better but I did not have any.
I may end up using colored paper though, if I can't control the white edges. Card stock is too thick for my oars though, unless I file down the diameter where the leathers will go so that the diameter of the leather surface is just a bit larger than the original diameter. This would be trickey, I think. The diameter at that location is only about 2.8mm or 7/64inch.

I haven't decided what method I will use to ensure that the oars don't slip out of the oarlocks: turkshead knot or several layers of "leather".
But I will learn how to make turkshead knots anyway :)




HI Peter,
I have been following your build and am enjoying the learning experience. Thanks very much for sharing your techniques.
Bye for now!

Hopeful aka David

Edited by TheDane
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