@RossM
Hi Ross.
I’ve reviewed the photos and the text, so I have a few questions.
_Everything is perfectly clear; there are no ambiguous points—you explained yourself very well.
I hope to do the same, though I’m worried the translation might let me down._
1. You used a block-and-tackle system with two blocks: one triple block and one double block (the triple block is the moving one, and the double block is fixed).
This is a typical setup—the classic mainsail tackle.
This configuration allows you to reduce the required effort by a 6:1 ratio. In other words, as you know, there are six rope segments supporting the load.
The force is therefore reduced sixfold (Mechanical Advantage = 6).
So, for example, if you need to lift 60 kg, you would need a force of 10 kg (ideally disregarding friction; in real-world, non-ideal situations, friction reduces this ratio).
Put another way—looking at it in reverse—if your winch can lift 1 kg, a tackle set up this way allows you to lift 6 kg.
Bear in mind, however, that to haul in one segment of rope, you need to pull in six times that amount. For instance, if the boom needs to move (move away or come closer) by 1 meter, you have to haul in or let out a full 6 meters of sheet.
So, be aware that if you want to move the sheet by five centimeters, you have to haul in 30 centimeters.
My questions and points of uncertainty are as follows:
Was this choice necessary—even mandatory—based on a calculation of the forces involved? In other words, did you know that your sail area could subject the winch to a load far exceeding the winch's maximum limit? For example: did you estimate that the sail might generate a load of 5 kg—while your winch can only pull 1 kg without overheating—so you adopted this block-and-tackle configuration to move the boom smoothly by applying 6 kg of force (or actually less, due to friction)?
Or did you choose a two-block system—one with three sheaves and one with two—simply because that is how it is done in reality, how it appears on the actual Bluenose, and you wanted to remain faithful to the scale reproduction?
1a. Whatever reason led you to use a tackle system with a three-sheave block and a two-sheave block, I have some reservations.
First of all, in my opinion, the line only runs smoothly as long as tension is maintained on both blocks.
Unfortunately, as all of us ship modelers have observed, scale rigging behaves very differently from real rigging. Let me use the ropes on my model's cannons as an example:
A real rope with a diameter of 3 or 5 cm—or better yet, 10 cm—will settle onto the deck or hang down under its own weight in the way we all consider natural.
That same rope in scale, however, will remain raised, suspended unnaturally in mid-air, or take on a completely unrealistic shape unless it is treated with paint or tamed with glue.
My concern is that the
Bluenose's line—when not under tension (i.e., when the two blocks aren't being pulled taut in opposite directions)—will tend to assume odd positions and risk becoming tangled.
I hope that doesn't happen; I am counting on the fact that your larger scale allows you to use much thicker ropes, which should behave more like the real thing.
1b. What keeps the boom—and consequently the three-way block—under tension? The answer (as seen in the photos you posted) is the suspended weight: the jar with the red lid.
Okay, but what will replace this force when sailing? You’ll probably say the wind.
Well, I’m concerned that since the wind isn't always present, the tension might slacken at times, potentially leading to tangles.
I don't mean to be a pessimist; I’m just warning you about potential issues.
2. However, the issues mentioned so far aren't major, and—most importantly—they won't necessarily occur.
I repeat: I hope the scale of your model allows the sheet to have the right thickness and weight so that its behavior mimics the real thing.
The problem I see as quite difficult to solve, however, is the actual control of the mainsail via the boom's movement.
Judging by your photos, I see the sheet connecting the boom to the winch via the block-and-tackle system.
In this case—aside from the presence of the block-and-tackle—the setup looks identical to mine (along with the associated limitations).
Let me explain: With the boom fully out (for example, on a broad reach or a run), you might decide to sheet in the mainsail (to switch to a beam reach and then a close-hauled course), thereby retracting the sheet to its minimum length. In this scenario, you simply command the RC winch to wind in.
With the sheet fully hauled in—at its minimum length—if you want to let the boom out, you have to send the reverse command to the winch to allow the sheet to extend.
But—and this is important—that action won't provide the force needed to actually push the boom open. What will act as the counterweight (the jar with the red lid) to open the boom and let the sheet unspool? As we said, it’s the wind.
Okay, so you’re building an open system, just like the one I made.
The problem is that you don't have two opposing forces—like in the closed system used to move the yard of a square-rigged sail—capable of pulling the boom to either side; you can only haul in or ease out the sheet. Essentially, you cannot mechanically force the boom to move left or right.
Therefore, during a change of tack—whether tacking or gybing—the boom won't be mechanically controlled; instead, it will swing to the other side naturally, following the hull's position and the wind direction, and adjusting itself to the new situation.
And this brings us to the problem I mentioned earlier: when tacking—and perhaps gybing—at low speeds (with little momentum), changing tacks using only the rudder is difficult and might not succeed.
As you well know, on full-sized sailing ships, the rudder's limited effectiveness is aided by the sails, which are manipulated to assist the maneuver.
However, with a scale sailing model, we don't have full control over the sails—or rather, we do for square sails, but not for gaff sails (i.e., those controlled by a boom).
I’m working on a way to solve this problem.
