The easy way to solve this, would be that you have decided that the boat you have is 1/36 scale.
So any 1/36 scale parts will be correctly sized. 1/32nd scale parts would be a bit large, or "heavy duty" in
size to your chosen scale.
The reason you are having difficulty getting an answer would be the following.
The parts in question vary with each boat, and each manufacturer.
With out visiting an actual boat most of us do not know the actual dimensions.
Modelers rely on part manufacturers to provide the properly scaled parts.
To make one on your own might incorprate the following.
A decision that the boat being modeled is 1/36 scale.
A referance photo of a similar tug boat showing the winch or bollard.
The reference photo must now be "scaled" the photo must be examined and an
item in the photo must be identified and be of a known dimension.
The most obvious item being a door, or a person standing in the photo.
At this point many assumptions are then made, The door is 6'-8" tall, or the man is 6'-0" tall.
A measurement would then be taken of the door, and what ever that measure is, it must be broken down in scale.
Say the door measures 1.625" tall in the photograph. We assume a 6"-8" door... 80"....
So, 1.625" ÷ 80" = 0.020... Therefore 0.020" = 1" in the photograph, or 0.24" = 1'-0"
This establishes a rough scale for the photograph.
One can now measure objects in the photograph and roughly measure and calculate the size of objects in the photo.
If a bollard can be seen in the background of this image, it could then be possible to compare the bollard to the
near by railing, or bullwarks. Lets say the bollard is half the height of the railing.
Since we can see the photograph that the railing is a consistent height from the door all the way
back to the bollard, we can then make a reasonable correction for perspective and distance in the photo.
The railing can be measured at a point close to the door we measured earlier.
If it measures 7/8" tall we can calculate that .875" ÷ 0.020" = 43.75 therefore we establish that the
railing in the photo is approximately 43.75" in height, the bollard is half that height, so the bollard is 21.875" tall.
If we accept that the bollard is 21.875" tall, then at 1/36 scale, the scale of your model, we can then calculate that
the model bollard should be 21.875" ÷ 36" = 0.607... Therefore the bollard at 1/36 scale is 0.607" tall.
Now, if in this same picture, you can see or measure that the width of this bollard is half it's height, then it can be
calculated that 0.607 ÷ 2 = 0.3035, the diameter of the bollard should be built at 0.3035" in diameter.
I hope this helps you understand the value of referance photos, and gives you some idea of how to use them
to calulate the sizes of objects, and then scale them to your model. I also hope this helps you undersand why
a simple question may not be an easy answer.
Umi