Before applying another coat of Z-Poxy Finishing Resin I will fit some spray rails onto the lower chines as recommended and detailed in an update to the Marlin construction sheet.
The designer observed that, with the prototype boats built there was an excess of spray from the bow coming over the hull and onto the decks, and that this could be countered by the addition of some short spray rails extending from the bow keel to about 45 cm aft.
I chose to make these from some 4 mm square Obeche that I had in stock but this would need to be steam-formed to follow the line of the chine without snapping or splitting. Fortunately, I have a wallpaper stripper, of which the steam generator is ideal for such a process.

First, I wetted the Obeche strip by standing it in hot water for about ten minutes and then applied steam to the strip for another five minutes until the strip felt quite pliable.
This was then formed around some panel pins on the benchtop to hold the curve as the wood cooled down, this process was sufficient to produce the required curvature that mostly held its shape when fully cooled.

Before fixing the strips to the chines I ‘keyed’ the resin surface of the hull along the chines to aid adhesion of the epoxy resin glue, the strips were then chamfered at an angle to meet the bow keel and drilled with a 1.5mm bit in a pin drill along their length.
The strips were fixed in place with the epoxy and some short brass pins and the ends of these ‘spray rails’ trimmed at a pleasing angle at the ends.

When all was set, I lightly sanded the edges of the rails to round them slightly and the additional coats of resin on the hull will further protect and finish the rails.

The fibreglassing of the hull continued in much the same way as the first piece on the bottom skin, in each case the cloth was brushed into a coat of resin and left to set before trimming and moving onto the next ‘face’ of the hull ending with the stern skin.

After all the excess cloth had been trimmed, I could start the process of flatting the first coat of resin and cloth using my trusty DeWalt Multi Tool with its sanding attachment.

I used a 240grit abrasive and this is sufficient to level out the surface in readiness for the second coat of resin, being very careful not to sand through the cloth to expose the ply skin.
I use the dust extraction attachment in conjunction with the sander to take away the resulting epoxy and fibre ‘dust’ so no face mask is really necessary at this stage.

I will go on to apply the second resin coat later.

Fitting the deck skins should really be the next thing to tackle but as I intend to fully plank the deck, I decided that I should get the slightly messy process of fibre glassing the hull out of the way first as I don’t want anything to spoil the decking surface before I get around to finishing that.

This is a process that I’ve done on all of my boats so I’m fairly well practiced at it by now and I usually apply the fibreglass cloth and resin in five stages, one for each ‘face’ of the hull. The reason for this is that I keep the surface as level as possible which largely eliminates runs in the epoxy coating.

The resin that I favour now is the Z-Poxy finishing resin, which unlike the product I first started using, hardens within three hours and cures overnight sufficiently to be able to rub down in readiness of further coats.

The fibreglass cloth is a light to medium cloth of 50 gramme per square metre that, once wetted with the resin, is easily worked onto the ply hull surface without wrinkling.
The Z-Poxy is easy to work with as it is a mix of 50:50 by weight of resin and hardener and I found that a total weight of about 20 grammes of this is just right for a single ‘face’ of a hull of the size of the Marlin.

The fibreglass cloth is first cut to size and I make it ‘hinge’ onto the hull surface with a couple of small clamps on the keel.
The resin is first applied to the hull surface with a half inch disposable brush and the cloth is laid onto that and the cloth gently brushed down into the resin until it is fully wetted. It’s important not to overbrush the cloth onto the surface as that can cause dragging of the cloth as the resin starts to harden.

With the clamps removed I can then apply some resin to the keel and then fold the cloth onto that area too.

The ‘working’ time of the resin is just 30 minutes so I have to work quite quickly to cover the required area, after that time the resin mix starts to stiffen as the catalyst does its work in the mix.

I’ll leave this overnight to fully cure before trimming off the excess cloth with a craft knife and then prepare the other bottom skin for the same process.

In a previous blog update I described how the forward lower deck floor was planked, finished & fitted but I omitted to mention that before glueing and fixing the floor in place that I had to make some holes through the foremost bulkhead to be able to bring the cabling through from the ESC to the battery & main power switch, both of which will be within the forward cabin.

Whilst these cables could be simply routed in full view within the cabin, and as always, I made it slightly more difficult for myself than that.

I bored some 20mm diameter holes through the bulkhead at a level below the forward deck floor using a right-angle adaptor and a step drill in a power drill.
The angle adaptor allowed me to make the holes through the bulkhead close to the cabin deck floor. I will build a battery box and power switch bracket onto the cabin side of the bulkhead.

On my Thames River Police launch I disguised the power switch as a steering wheel, as in the pictures I’ve added, and I’ll most likely do the same with the Marlin.

BTW.
You may notice my preference for DeWalt power tools and accessories. I believe that the brand is owned by Black & Decker now?

I’ve lost count of the number of ‘lesser’ brands of tools I’ve got through over the years and its usually the gearbox of a drill or the batteries that give out first!

Before I can continue with the fitting the deck skins and planking, I do have to fit the rudder servo.
The plans suggest that this is concealed within a false box or perhaps a seating bench within the rear lower deck area, and while this would be very easy to achieve, I thought I’d like to make things a little more difficult for myself by fitting the servo in the cavity at the stern so that it is totally concealed.

I almost never do thing the easy way 😂.

This will obviously involve incorporating a hatch in the deck to be able to access the servo too. This cavity will be quite cramped as it will enclose the servo, servo linkage and rudder arm as well as the ESC water cooling pickup and exhaust plumbing.

I had previously installed plastic ducting within the hull construction for all of the associated wiring and plumbing so all that remained was to fit a suitable servo mount and servo.

I would like to be able to remove the servo if required, so I used a commercially available aluminium servo mounting and adapted it to be mounted on two ‘stand-off’ pillars secured through the bulkhead with two long bolts. The mount was used in an inverted position to be able to access the mounting bolt heads. This arrangement will allow me to extract the servo, still in its mount, through the access hatch rather than attempt to remove the servo alone.

Before fitting the servo mount I had to fit the rudder assembly and determine the correct height of the mount so that the servo linkage would be at the correct height for smooth operation.
This was more than a bit fiddly but I managed to find the right place and then drilled the two mounting bolt holes through the bulkhead.
The real test of the servo operation was to connect up a servo tester and battery to check that it all worked freely, had sufficient arc for the required rudder movement and without the possibility of fouling with any of the ‘plumbing’ that I’ll be fitting later.
I will have to make the access hatch through the rear deck of sufficient size to be able to get the servo in and out and enough room to fit the rudder and linkage.

At this stage it seems likely that I will remove the central plywood ‘brace’ to make the access hatch practical as this ply piece seems to have no critical structural purpose.

Well…here we are in Feb 2025, the new workshop is all finished with a bench, shelving and racking, a ‘personnel’ door in the side; so no more going in and out through the ‘up-n-over door’, new power & lighting circuits, network, ‘phone extension, music system, pool table, mini-bar and beer fridge.

Only joking about the last three🤣

The next stage of construction should be putting the deck skins on but, as always, I’m thinking a few steps ahead have decided to do some planking on the inner decks because, as nice as the laser etched decks are, I want to have some nicer planking on them and that would be extremely difficult at any later stage.

The first area to tackle is the forward lower deck and for this I needed to first make a removable hatch to be able to access wiring etc.

I cut a square hole through the 6mm ply floor large enough for this and then set about applying the planking which is Lime, otherwise known as Basswood, for the planks, Mahogany for the borders and details and black Plasticard to simulate caulking.
I had previously planked small deck areas on my RAF Crash Rescue Tender, and all of the decking on my Thames River Police Boat, so I was reasonably confident of getting a good result.

At this stage the forward floor is easily removable and when planked and finished it will be fixed in place. All of the Lime planking is 1.6 mm thick and the planks 6.5mm width and all is fixed with a medium superglue.

A Mahogany border around the hatch was applied first and then strips of .5mm plasticard fixed around it. These strips were all cut in a 2mm width from an A4 sheet of black Plasticard.
Working out from the centre line for symmetry the Lime strips and ‘caulking’ was glued down until the whole area was covered.

The Plasticard ‘caulking’ was then pared back with a very sharp chisel before the whole panel was sanded smooth with a detail sander and then finished with some very fine grit abrasive paper. The excess planking was then trimmed from around the panel.

As I want a good depth of clear finish on all planked areas I used a two part epoxy ‘finishing resin’ from Z-Poxy, three coats with a rub down after each coat and a final polish with some cutting compound was sufficient to give the desired finish.

This piece was then covered with masking tape to protect it and was then glued in place in the forward lower deck.

Now that the prop-shaft, propeller, flexible coupling and motor mounting bracket have arrived it’s time to think about the motor position and fabricating a support block for the motor mount.

First, I ensured that the shaft and propeller protrusion from the keel was correct in relation to the rudder water pickup tube positions and temporarily fixed the tube in place. Note that the pickup tube has yet to be bent and formed!

I find that the easiest way to ensure perfect alignment of the motor and shaft is to use a rigid coupling to hold the motor and attached mount while measurement and angles can be taken for the mounting block.

With that angle established I was able to shape a piece of hardwood, in this case beech, to the correct size, shape and angle for the motor mount to fix to.
A test fit of the block and motor proved that all was well with the shaft alignment.

The beech mounting block was then drilled and fixed to the deck with some brass screws that go down through the deck floor into the keel and the motor mount was then fixed with four screws to the mounting block. With everything fixed in place and the rigid motor coupling replaced with the flexible coupling the motor turns the shaft very freely with no binding or movement.

When finally assembled the shaft will be greased in the usual manner but for now, I will remove all of these drive components so that I can finish the decks internally and the hull externally.

It's at this point in July 2022 that I had to put the Marlin build aside to concentrate on moving house and building a new workshop in the garage to be able to continue with the build.

Old workshop seen in the last picture.

See you again in 2025…….(so to speak!)

The last remaining piece of ply to fit to the hull is the stern skin and like the others is 1.5mm ply that is easily bent to the required curvature.

Before it’s fitted though I decided to fit an additional piece of balsa to the area that the water-cooling outlet will pass through just to provide a firm support to the tube. This was just a piece of scrap balsa glued in place and then the whole stern area was sanded back using my sanding plate to ensure that the area was completely flat in the vertical plane and the required curve in the horizontal.

The ply skin was then glued and pinned in place with some additional clamps and packing tape to pull the skin firmly into place, and when dry the skin was trimmed and sanded to meet the side and bottom skins. Before fitting the skin I took the precaution of marking the position of the extra balsa block on skin for when I eventually fit the water cooling outlet.

The external keel can now be fitted. This consists of three parts in 6 mm ply that are glued together as a single piece and glued and pinned, using some long brass pins, along the internal keel as far as the exit of the prop shaft.

The brass pins were punched below the surface and some filler used in the holes and then it just needed some sanding to slightly round off the edges along its length.

As my order for the prop-shaft, coupling and motor has now arrived I can think about the motor position and fabricate a suitable mount which I'll cover in the next part.

With the bottom and side skins fitted and trimmed the bow can be finished with the balsa blocks supplied in the kit.

The bow has to be made this way because ply skins would could never be made to fit, as ply cannot be bent in two planes to form the required compound curve, and balsa is an ideal material for this purpose as it is easily carved and sanded to the required curvatures.

This can be quite tricky to do well so it deserves to be done slowly and with great care as I didn’t want to resort to the use of any filler to correct any mistakes on my part.

The balsa blocks supplied with my prototype kit needed to be arranged and laminating to produce a single block that would fill the area required together.
It’s likely the production kits will have one-piece blocks to simplify this stage.

The largest piece was placed in the bow and marked with a pencil line so that a basic cut could be made with a coping saw, and then the smaller pieces and offcuts arranged to fill the required area, and then all were glued together in the bow.
When the aliphatic glue had set some more basic cuts were made with a fine saw and then further refined with a coarse file to the rough profiles required.

The final shaping was done very gradually and carefully with fines files and sanding blocks to produce the final shape, taking great care to extend the line of the lower chine along the block to meet with the front keel former.

I used a card template (not shown) to make sure that both blocks were symmetrical and checking with ‘mark-1 eyeball’ as well.

I also temporarily attached the false keel to check that it would conform and fit to the blocks as seen in the last picture.

With great relief I decided that it was as good as I could make it and it only remains to fit the ply skin to the stern to finish the hull.

Both of the side skins are in two pieces of 1.5mm ply, a short bow piece and a longer second piece that extends from F2 to the stern.
As with the bottom skins I used my heat gun to bend and shape these skins so that they fit the contours of the hull but I did find a problem with the dimensions of the larger skins after test fitting them.

It was apparent that the skins had been made slightly too short by about 10mm to span from former F2 to the stern allowing for a small overlap for trimming. Not a major problem, and to overcome it I simply made up some ply doublers from some scrap ply and added them to each of the F2B formers that would allow me to set the skins back sufficiently to reach the stern correctly.

The kit of parts that I am assembling is a pre-production prototype and my build is primarily to discover any construction snags such as this. I understand that this has now been ‘designed out’ of the later production kits of the Marlin.

There was another small problem 😮 with the upper chines in that they were not wide enough at the stern to meet the edges of the formers but again a simple solution was to add some scrap balsa to bring them out to the correct position. Once sanded back they were just fine to meet the top edges of the side skins. Again, this will be rectified in the production versions.

Some sanding sealer was applied to the internal faces of the skins, avoiding the glue areas that meet the chines and formers, something that is not strictly necessary but to me it seems like a reasonable precaution to protect the internal faces of the skins from damage by any (unlikely) water ingress.

The skins were held in place by the usual assortment of clamps and pins but in addition I also use brown packing tape pulled tightly across the hull to really pull the skins down tightly along the joint with the bottom skins. The packing tape has extremely high tensile strength and is ideal for this purpose and leaves no residue when removed.

The smaller skins at the bow were then heat formed and sealed internally before glueing, pinning and clamping into place and once all of the glue had set the clamps, pins & tape was removed and I then had the very satisfying job of planning and sanding back all of the skins along the top edges and the meeting edges of the side and bottom skins. There's a small gap in the skins as seen in the last picture that will need a bit of filler after the bow blocks are fitted and shaped, this is because the skins were moved further back to get the overlap at the stern, again a small revision required for the production models.

I feel that I'm now finally making some some good progress with this build 🤗 but there's a long way to go yet 🤔 and hopefully those following this blog aren't totally bored yet 😴. Let me know?

The next part will cover the fitting and shaping of the balsa bow blocks 😎.