With the pilothouse the same width as the deck, there needs to be some way of getting back and forth down the side of the boat without passing through the pilothouse. You can imagine how inconvenient that would be for moving an anchor line. The Chinese faced a similar problem with they needed to pole their boats up river with the decks filled with cargo. The solution was to place temporary walkways or catwalks over the water and along boats deck.
But we also need a gangway, and possibly a gang way they can lower and also be pitched out to the side and even raised about the deck, in case the dock is higher than the deck of the boat. A gangway can also be used to access the water or ground beneath the boat when Seeker is sitting on her keels in a tidal zone.
There will be no permanent deck on the structure as that would become a hazard in heavy seas. Instead the deck more likely be open. A round rung ladder may be best. However the structure needs to be strong enough that it can resist impact with a dock without damage. This will not only protect a light wight ladder but also the roof of the pilothouse which also overhangs the sides of the hull.
A commercial ladder is an option, but only if it is fiberglass. Neither wood or 6061 aluminum would hold up well to seawater. A 20′ All-Fiberglass Straight Ladder is about $800 each from Werner. We can also build one from 5086 aluminum pipe. We have redesigned the battens for the sails so it just happens that we have aluminum pipe available. This approach would also give us the ability to more easily modify the ladder for the task, such as adding holders for stays and a hand rail. If we built the ladder the goal would to have a stronger ladder that what it typically available commercially, which is to say it can support 400 pounds in the center when placed horizontally and supported only at each end. Raising and lowering the ladder could be done with a manual hoist however is a hydraulic winch or block and tackle were used then the ladder could be raised with along with a diver and equipment. As the structure will not frequently be raised and lowered then it could most likely be best powered by a capstan on the rear deck that is also tasked with handling anchors and the tender.
As for the steel frame outside of the ladder it seems most obvious to construct it from the same 3 1/2″ steel pipe used on the bulwarks. It maybe prudent to stiffen this with a light wight truss framing between the steel bumper and the ladder in order to reinforce the steel pipe from lateral impacts.
In order to minimize the slope of the gangway we can maximize the length to 25 feet. But that length will require a more robust frame than a typical ladder in order to minimize bounce when loaded with two crew and gear.
For most of the stuff I build, we bouncy up and down on the material and then decide how much we need to use, but Dan Germata and Megan Vinci stop in on their way home to Chicago and Dan did some math for us. If we build a 25 foot long gangway from 4 – 2 1/2″ Sch 40 aluminum pipes built into truss then we will be able to support over 3000 pounds without failing and it will deflect less than 3/8″ when you stand in the middle. It will only weighs about 250 pounds and floats! It makes for a rather large structure so we are going to only build one for the port side. The starboard side will only be a steel barrier to protect the pilothouse as well as support a walkway that can be removed and stowed away on deck for bad weather.
We worked up a design for the hing that we think will let us not just lower the gangway but also rotate it out to the side and in a complete 180 degree arc. And pin it into any position we like by dropping a pin through holes in the round plates. We will also make the hinge pin attached to the first step to be removable so we can quickly unpin the ladder from the mount and us it for some other purpose.
Ben Paske – “Not a huge fan of that one bolt. One bolt, one failure.” Offers what I think is a good design as well. My only reservation is it has more parts that need more machining.
I actually like the one bolt, one hinge pin design because we can easily release it from the boat and use it for other purposes. It is after all a sturdy 25 foot span.