Problems with a medieval bipod mast

[Brinkman]

I'm scratchbuilding a small cog based on a thesis about a wreck of a medieval cog. The ship is just 11 meters (36') and the author hypotheses that it maybe had a bipod mast. This is based on the two mast steps in the wreck and a medieval image that maybe shows this kind of mast.

 

 

Bipod masts are almost unheard of except for egyptian ships and modern catamarans and I find it hard to fasten the yard. It will have a square sail.

 

If it has a parrel on one leg than the yard can't really swing to the other side.

 

 

But is it possible to skip the parrel and just pull the halyard tight? This doesn't feel particularly secure.

 

The bipod mast didn't catch on, if it ever existed in the medieval period at all, and this could be one of the reasons. But imaging a shipwright that thinks that he got the best idea ever - a bipod mast! How would he solve this?

 

I have a thread of the build over at 

 

[Jaager]

If support for a sail does not fit, could it fit another function?  Would it work as part of a crane?  Would there be work for a floating crane during its period.

I tried to imagine how or even why it would function as a single mast with alternate steps.

[Brinkman]

One possible reason for not having a single mast step could be the weak bottom. The keelplank is very thin and perhaps it buckled when they tried using a single step?

 

I like your idea of a crane, but I think it would have been placed much further forward to reach in front of the ship.

 

But a possible reason could be that the bipod mast was holding a lifting boom, something like this (I'm just using the yard here for show).

[Louie da fly]

Yes, sheer legs.

 

But regarding the fixing of the yard - perhaps a vertical "topmast" above the bipod? Then the parrel could swivel without hindrance. Otherwise it might be possible to have some kind of adjustable truss which could be loosened every time you tacked - somewhat like this one marked trozza (used on a lateen sail), but allowing for the bipod? Might be completely impractical, but it's a thought.

 

 

The other thing would be to look at how the yard was held on Egyptian ships, if it's known. Unfortunately Sceatha's magnificent Byblos ship has the mast lowered and no yard fitted, or you might be able to get some ideas from his. However, on page 1 of his log there's a picture of a ship with the yard fitted, and it seems to be perched on the very top of the bipod, where the legs come together. 

 

 

 

 

 

 

[bolin]

On such a small ship, the sail would not be so large. Which means that it would not be totally impractical to raise and lower the sail while tacking. It could probably be done by one or two persons.

 

You may not even need a parrel. A line (the down haul) from the middle of the yard running between the masts and tied to som point in the aft could be enough to keep the sail in place.

 

[Brinkman]

Steven, I think lowering the whole mast egyptian style would be too much work for the crew but the idea of using a trozza sounds like a simple solution that probably would work, thanks!

 

Bolin, I'm sorry but I'm too new to this whole sailing business to follow. What is a down haul in this context? And what do you mean by lowering the sail while tacking?

[bolin]

Sorry for being so brief in my comment.

 

What I know of sailing square rigged single masted ships is mostly form a ship called Helga Hom (helgaholm.se). There is an introduction to the principles here https://helgaholm.files.wordpress.com/2020/04/ledsagaren-segling.pdf (in Swedish).

 

For the rest of you I will summarize my thinking.

 

In position 1 the ship is sailing against the wind with the wind from starboard. The ship then turns into the wind until the wind comes into the sail backwards which helps the ship to turn. In position 4 and 5 the yard is turned about to get the wind in from port, and continue sailing in 6.

 

My thinking is that during the steps 2 and 3 the ship does not necessarily need the sail. If the speed (momentum) is high enough and if you put out one or two rowers, you might be able to come through the wind anyway. The sail could at the same time be lowered and raised again only in position 5 with the parrel and maybe some other lines switched.

 

The down haul is the opposite of the halliard, a line attached to the middle of the yard used to pull the sail down when lowering it. For your bi pod mast it could also be used to pull the yard backwards in between the masts. In that case there would be no need for a parrel.

 

By the way, I'm really enjoying your build.

[Brinkman]

Bolin, thank you so much for the added details! Interesting idea to switch which leg the parrel is on!

 

Now I have some more ideas to play with when planning this, thank you both.

[Roger Pellett]

I’m not sure that a lot of swiveling of the Yard was necessary or intended.  The sail might have been used for sailing only in favorable winds- downwind or a broad reach.  When the wind shifted ahead, the sail would have been dropped and the boat rowed or anchored in a protected cove “waiting on weather.”

 

Flat bottomed boats without a keel will not sail upwind as proven by the replica of the American Revolutionary War Gundalow Philadelphia and trying to tack a boat like this is hard to imagine.

 

I don’t see why the yard could’nt be suspended by a single block secured to the apex of the two masts.

 

Roger

[bolin]

You would swivel the yard quite a lot even if you sail in favorable winds to get the most out of it. The more I think of it I don't think that a parrel would be a practical solution on a bi pod mast.

 

Regarding the ability of this hull and rig to sail against the wind I think its hard to judge unless you try it. What I know from similar ships, they can handle rather well (but may not be fast) when sailing against the wind. The option to row against the wind would only be an option for a ship with a lot of rowers and a long and sleek hull. For this type of shorter and broader hulls with only a few rowers, rowing is only an option of there is now wind at all, or for maneuvering in harbor.

 

[Brinkman]

Thank you Roger and Bolin, it sounds as if I don't have to worry about a parrel and maybe just add a trozza if I see the need. Thank you!

 

I havn't seen any signs of oars in these wrecks and imagine the ships running with a minimal crew and probably waiting for favorable winds, or maybe finding a farmer with oxen to drag them?

[Roger Pellett]

You might want to consider that this Yard was set “flying” a halyard secured to the center of the yard and sheet at each bottom corner of the sail, that’s all.  To swivel the yard the halyard is slacked off and the sheets trimmed.

 

Roger

[amateur]

On 10/4/2020 at 8:52 PM, silverman834 said:

Thank you Roger and Bolin, it sounds as if I don't have to worry about a parrel and maybe just add a trozza if I see the need. Thank you!

 

I havn't seen any signs of oars in these wrecks and imagine the ships running with a minimal crew and probably waiting for favorable winds, or maybe finding a farmer with oxen to drag them?

 

Which is not compatible with the location of the wreck. The zuiderzee was a rather shallow, relatively large open water, with in some locations a bogland between water and coast. No way vessels could be drawn.

 

same holds for 'favorable wind': winds can be from the same direction for weeks. Waiting for favorable winds can take some time. 

 

Interesting to see a mast like this. Never saw one in the context of Dutch shipbuilding.  But then, medieval ships never my main interest

 

 

Jan

[Brinkman]

18 hours ago, Roger Pellett said:

You might want to consider that this Yard was set “flying” a halyard secured to the center of the yard and sheet at each bottom corner of the sail, that’s all.  To swivel the yard the halyard is slacked off and the sheets trimmed.

Thank you Roger for the input and as I'm new to sailing I want to make sure that I understand you correctly; you mean that the only running rigging should be halyard and sheets? I thought I also would add braces and bowlines.

 

18 hours ago, amateur said:

 

Which is not compatible with the location of the wreck. The zuiderzee was a rather shallow, relatively large open water, with in some locations a bogland between water and coast. No way vessels could be drawn.

 

same holds for 'favorable wind': winds can be from the same direction for weeks. Waiting for favorable winds can take some time. 

Thank you Jan, you are of course correct that the ship couldn't be drawn on the Zuiderzee, but not even along the rivers as they also must have had very soft edges.

 

I wonder how they did it as it sounds hard to punt a 20 ton ship.

[Roger Pellett]

Yes, that’s right, just a halyard and a pair of sheets.  I don’t have time to look it up at the moment but a replica of the Bremen Cog has been tested under sail and may provide some answers.  I’ll look it up tonight and report tomorrow.

 

On time deliveries are a feature of mechanized transportation, roughly the past 150 years.  Befote that time people were dependent on the weather.  Sailing ship historian Allen Villers has written that a major factor that doomed the sailing ship was an inability to predict when any given cargo would be delivered.  Since shippers were dependent on weather businesses had to maintain large inventories to assure deliveries to their customers.  Waiting on weather, whether a day or a month was a feature of the age of sail

 

Roger

 

 

[Brinkman]

1 hour ago, Roger Pellett said:

Yes, that’s right, just a halyard and a pair of sheets.  I don’t have time to look it up at the moment but a replica of the Bremen Cog has been tested under sail and may provide some answers.  I’ll look it up tonight and report tomorrow.

 

 Good thougths regarding timing, I'm stuck in the modern concept of just in time delivery and have a hard time imagining a ship waiting for days for favorable winds, but yeah, you are right about it.

 

There have been three replicas built of the bremen cog and they seem to also have lifts and braces, but no bowlines. They are also bigger then my cog and I don't think the lifts will be necessary but I think it could have been good to have braces as most square sailed ships my size seem to have them.

 

I think I'll skip the bowlines. I partly planned to have them as the bowsprit otherwise would just have the forestay, but I guess that's ok.

[bolin]

I agree that braces are likely for the rig. Maneuvering the sail only through the sheets would definitely make it hard to go higher against the wind.