You really ought to get the steps right. We have personally witnessed three incidents of would-be boaters falling down the stairs of various creampuffs, not underway but at the boat show docks. Maybe their attention was diverted by the prevailing glitz.
It isn’t that difficult to figure out what should be done. Staircase design standards are well documented and if you are not sure, you can go out and measure a few.
But designing good step ergonomics often results in a major conflict with a vessel’s rocketship visuals, step lines being generally transverse and not suggestive of speed.
The catamaran with its multiple accommodation deck heights is a challenge. The relationship between riser height and the tread width, in combination with the step overhang needs to fall within a set of parameters that are derived from human anatomy. The variations in that anatomy are quite significant; the step up ability of a woman of small stature varying significantly from that of her ex-football player husband of 6’4”. These people however represent the potential boat owners the designer should serve. The alternative…
The diagram above illustrates some of the issues pertinent to designing domestic staircases to avoid homeowner tumbling syndrome. Your household staircase doesn’t tilt and heave and get slippery as you may expect your boat’s to do but there are no published standards for pleasure boats.
Obviously some compromises need to be made to avoid having your catamaran yacht resemble a tour boat but where should you draw the line.
Marine companions and stairways often have to be closer to ladders but this application is not without recognized correct design parameters. We all owe a debt to Neils Diffrient , an ergonomic researcher who systematically researched all aspects of human interaction with the physical surroundings. His work, (unfortunately currently out of print) has been used for the responsible design of everything we sit on or at, climb on or through, push buttons on, view, etc. When something isn’t comfortable, convenient, within visual range or easy to reach you may be sure that N.D.’s works are not in the hands of the designer, or perhaps he just doesn’t care to know.
To the left is a lift from part of Neils Diffrient’s Humanscale study of the ways in which we may transit changes in elevation. The reproduction is unfortunately poor but the little chart in the lower right relates the parameters appropriate for different people and establishes workable averages. This is thorough work, if you follow it, your catamaran steps will work.
Making a stairway ergonomically correct does not preclude a tasteful and romantic vision.
When you go on board a catamaran, have a look at the deck height transitions and traffic patterns first. Don’t consider the transom steps in isolation, they are the way on and off the vessel whether it is at the dock or on a mooring.
You will often see vessels with giant height transom steps all the way up to sheer height. The designer has been faced with limitations as to the stair run envelope, (eg. saildrives below, aesthetics, quarter mounted helms, etc.) and has decided to sacrifice good ergonomics.
If the traffic pattern has been thought out and the relative deck heights configured appropriately, the stair requirements will be naturally minimized.
The parameters for landings, tread dimensions, foot stops etc. that apply to safe shoreside stair design shouldn’t be ignored for the sake of cleverness or imagined ‘design statements’. We make necessary concessions for small vessel design but the standards for ship passageways and stairs are more stringent than those for commercial buildings, for obviously sound reasons.
But are you willing to set aside good ergonomics and thereby risk injury on board your own vessel, just to satisfy a designer’s notion of ‘style’?
As a catamaran builder you need to be stair conscious, it goes with the territory, well usually…
Varying the step heights within a set is recognized as a certain way to confuse the motor reflexes, (yours, not the engine’s). Ideally, neither the riser height nor the tread width should vary more than 3/8” from step to step. Maybe this case is an optical illusion? Having a glazed hatch in the landing area and a port in the kick zone is unfortunate.
You don’t need a tape measure at the boat show; your brain is already well aware of your anatomical comfort zones. If you walk all over a potential dreamboat, from water level to the highest deck surface, inside and out, and remain unconscious of having traversed the multiple transitions in altitude, the designer had you in mind. But if you stopped to ponder a possible safe descent, search out a missing handhold, lift a knee up to your chin, tripped, stumbled, climbed, clambered or ducked your head too late, you are being had.
Keep in mind you may have to get to every corner of the vessel, even the masthead, in the dark, cold and wet with the decks and stairs moving around, just like those in the funhouse you remember.
Do you want your boat to represent your adventure or the designer’s?
Questionable deck and stair arrangements are not confined to the fanciful magazine ad computer renderings or one-off boat projects. They are frequently incorporated into many big name production vessels.
Just watch your step.