My choice of bow thruster eventually became the Raboesch model 108-03 from http://www.raboeschmodels.com. Here’s why and how.
Up front, I made a slight mistake by purchasing model 108-04. This was after reading forum posts that recommended “the bigger, the better”, and I figured its jet nozzles/tubes would suit my model scale-wise and “look good”.
This is where it went wrong though, because the re-seller (I’ll avoid name-dropping here…) mislead me by labelling it “22/25mm”. I interpreted this as the tube being 22mm and the housing 25mm. But these measurements actually refer to the inner/outer diameter of the tube itself. The tube surely has an outer diameter of 25mm, but the housing on this model is 28mm. This is clearly stated in the specifications on Raboesch website, but the “title” of the product at this particular re-seller’s webshop misguided me.
The problem is not critical, but in my opinion this model became less optimal. What makes 108-04 more “difficult” to work with is that the tube is conical in the housing-end, like this:
This means, that in order to mount the tube into the housing from the outside of the hull (i.e. push it left into the housing in the image above), the hole in the hull obviously needs to be 28mm, as this is the biggest diameter of the tube. In fact the hole needs to be even bigger, but more about that later. Then, as the majority of the tube itself is only 25mm, the hole will need to be filled with a lot of filler material.
The difference with my preferred model 108-03 (22/22mm) is that it is “straight” (not conical) in the housing-end. Meaning, if the hole in the hull is 22mm, the tube can be pushed through, and will fit more or less perfectly. Or at least require much less filler material after the tube has been mounted.
On a side-note, the above “problem” may not be a problem, if you have plenty of room on the inside of the hull. If the tubes can be pushed through the holes from the inside, while you still have room for the housing (this becomes 40mm for the housing + some 10mm per tube), the hole can be kept at the outer diameter of the tube. This all depends on the shape of the hull. The more “V-shaped” hull, the less likely you are to be able to use this approach. In the case of Tsekoa II and my preferred placement of the thruster, this was not possible to do.
The bow thruster is a completely optional accessory of course, and as such, there was no indication on the hull, where to place it. I went for some kind of “lowest possible, and as far towards the bow/ahead as possible”-strategy, while still of course being able to fit the entire housing on the inside of the hull.
When marking the location of the holes, a smart move is to cut off the tube at the “blocked” end, at an angle that is reasonably similar to the hull, like this:
Then use the “cut off”-end of the tube to draw the hole onto the hull. At this stage, you will notice that the hole is not a perfect circle, it is actually slightly oval. That’s why I mentioned above that the hole will not be a perfect 22mm hole – it will be slightly bigger, in an oval pattern.
I drilled multiple small holes with a 2mm drill in a slightly smaller diameter than the drawn “circle”, and cut out the remainders with a cutter. Then I filed the hole wider until the tube fit well, and repeated the procedure on the other side of the hull.
After cutting the tube/s at an angle as mentioned above, you will have the housing and the remainders of the tube/s looking somewhat like this
Detach the tubes and place the housing in the hull.
Now push each tube through its corresponding hole, and glue them to the housing. I used normal 60 seconds glue for this.
Then move on to glueing the tubes to the hull. Here I used two-component epoxy glue, to make it waterproof. Pay attention and do the job properly – we don’t want water getting into the hull, okay? 🙂 The result:
And a view from the outside:
Now, file/sand the tubes down so they align nicely with the hull
Back on the inside, I glued a small platform to the bow to host the electronics for the bow-thruster. This actually turned out to be too small in order to mount the electronics esthetically perfect, but I decided to live with it. It will do its job.