Mast bend

[boblarkin]

I just noticed this thread. Fun stuff---I really like measuring things!

So, it was convenient today to measure the deflection of my SCAMP mast. It is birdsmouth with the dimensions per the plans (5/8-in wall) including the taper, but constructed of CVG (clear vertical grain) Douglas fir (DF). Saw horse supporting of the mast as per Simeon, and with my 151-lb at the middle, the deflection was 46-mm (1.81-inches). As I think I learned once, non-destructive beam deflection is proportional to the force applied, so at 120-lb it should be about 37-mm or 1.44-in (1-7/16).

The DF is stronger and heavier than Sitka (or other) spruce. So the lesser deflection is not surprising. At one point, I considered reducing the wall thickness to make the mast equally strong, but then decided to not worry about the extra weight. The weight of this mast, with the halyard and lazy jacks on it is about 22-lb.

An aside is that, if you keep the strength of masts, made with the two materials, the same by decreasing the DF wall thickness, it will weigh less than the one with Sitka Spruce. In that sense, there is not a weight penalty for using DF.

For information, I bought two 17-ft 1x6 (inch) finished CVG boards for about $140. This just made the mast. I just went to my local lumber yard, and did not shop around for price---maybe you can do better, or not. It was special order for them.

I wanted to toss in the DF data in case any one is contemplating its use.

Bob
Scamp #343, Wave Guide

[Roux]

No official measure the yet. I've been busy. But had a chance to put the first coat of urethane on today.

-Johann