Stairways and ladders? Now he has gone completely nuts you might think, what’s the big deal about them? They are just there when we need them and since they are normally just something we walk we don’t give those many thoughts.
But try to think about it!
Haven’t we all tried walking on stairways and ladders finding that they didn’t felt natural walking?
How about walking stairways where the stairs were so low it felt like you were tipping and walking like a fool. And then when you try taking two stairs at the time you feel you are in ‘The Ministry of Silly Walks’ by Monty Python.
And contrary to this there are the stairways where the stairs are too short. Sometimes so short that you feel you have to walk on your tiptoe risking sliding down and getting hurt.
Also the high stairs where you feel that the folks manufacturing the stairway has actually forgotten half the stairs. Then when you try walking with just a small bucket of water you feel like you have been exercising leg press for hours in the gym.
The important issue here is that when designing and constructing stairways and ladders for boats it’s essential that they fell natural and comfortable to walk. Since the stairways and ladders are on your boat the chances that you will have to climb them when the boat is at sea are obvious so they should be designed and constructed the best possible way to make it safe using them.
So what’s the secret for making perfect stairways? Well luckily for us it’s quite simple and don’t require much beside some simple calculations. Before revealing the formula there are some terms we need to get right first.
First there is the tread depth. This is the horizontal depth of the stair shown as A on the illustration below. Second there is the rise height. It’s the vertical distance, shown as B on the illustration below. V is the pitch of the stairway.
Now if the stairway shall be most comfortable to walk you will have to keep the relation between A and B such that one A added with two B shall be a distance between 600mm [23.6”] and 660mm [26.0”]. Or written as a formula:
600mm ≤ A + 2B ≤ 660mm
23.6” ≤ A + 2B ≤ 26.0”
Let’s take an example. If you have a rise height of 178mm [7”] and a tread depth of 269mm [10.6”] the total will be:
269mm + 2x178mm = 625mm
10.6” + 2×7” = 24.6”
This means that the stairway will meet the requirements and be comfortable walking. Beside the formula above there are also some other guidelines that you should take into consideration when designing and constructing the stairways.
- Minimum tread length: 230mm [9”]
- Maximum riser height: 210mm [8.25”]
- Minimum riser height: 130mm [5”]
- Pitch angle: 30° (often difficult in boats and small ships but remember it’s just a guideline)
If you follow these rules and guidelines you will be sure to get the best possible result for designing and constructing your stairways.
So how about the ladders? Ups sorry, I almost forgot that 🙂
Constructing ladders is much easier than constructing stairways. There is only one guideline you should follow and that is the distance between the steps or rungs (C on the illustration above) should be 300mm [12”].
Happy boat building,
Morten Olesen, Naval Architect