I am designing a bimini
40ft wide and 19ft long. The center line will be supported by the boom. I have the following design questions.
Question 3 is the most important one.
1. Currently I have designed it to have 4 panels
of cloth 59 inches wide. I am being quoted WeatherMax 80 by one vendor and Ferrari Stamoid by another. I am leaning away from the Ferrari Stamoid since it seams to be a PVC film and not a fabric
. Any experiences with either?
2. I can design the slope from 10 degrees up to 45 degrees. The problem with the higher the slope, the more material and greater the wind
load. However, a high slope has a faster water
run off and looks cool. I have no problem calculating wind
loads based upon finding the exposed vertical surface area.
Is it valid for me to use the exposed vertical surface area? I recall
when caught in a typhoon in the Philippines
that i could feel a lot of downward force of a high wind. However, the vessel is now in Langkawi Malaysia
. I have never seen any thoughts on calculating downward wind forces and everyone seems to only talk about vertical forces.
Another problem I am finding is where to find record
high wind conditions. Anyone have an idea where to find record
winds for a given area?
3. The flatter the slope the less vertical wind resistance, however, the longer it will take water
to run off. I can't seem to find any rule
of thumb to calculate the weight of the water running off a slanted roof. I found that if I assume 2mm thick film of water during a monsoon downpour, that the weight of the water on the canvas
is actually more force than a 35 knot
wind. However, I just pulled 2mm out of thin air.
4. I am not a mechanical engineer
, however, used beam calculators to try and find the deflection of the support under load. If any kind sole could check my work
I would be very grateful. What I calculated seems too good to be true.
A. I found FRP pipe that is 50mm OD and 5mm wall thickness. The manufacturer never heard of Young's Modulus of Elasticity however, I found a website saying use 17 for FRP.
B. I used another website to calculate the Area Moment of Inertia and found for this pipe a value of 181000
C. I used 15 degree slope case. I calculated wind load at 35 knots, weight of the fabric
, 2mm of water on the canvas
, and weight of the beam to be 130 kg per panel. This 130 kg seems reasonable to me.
D. I calculated the beam deflection as being only 8.5mm using this online calculator
This deflection seems to me too good to be true. Things I can do to improve support is to add a proverbial skycrane support coming down from the mast
to support the canvas midway. This would reduce the unsupported length from 20.7 ft down to 10.35 ft and reduce design weight by half. Deflection of the beam when I enter these numbers is only 0.26mm which again seems too good to be true.
Note: I am intending to support the first and last of the 5 beams midway since these will see an additional load. The canvas will be held down using tiedowns leading fore and aft. I need to counter these two forces with an upforce since the tie downs will add a downward force.
Thoughts are greatly appreciated.