David Boat Inconsistencies

[JohnDLittlefield]

One of the main drivers behind my work on David and the class of sister-boats spurred from her initial success was the inconsistency I found in my first readings about the little boat. Dimensions, impetus for design, even the source of the name have been reported differently in a number of sources. So, I ask your help here.
Outside the ORN and the ORA, please post (and cite) any source you come across offering dimensions of a David-class vessel so I can check it against a database I have put together. Expectedly, there will be duplicates, but better to post a duplicate than miss the obvious, right? I am simply looking at the variation of dimensions recorded and trying to trace the sources of that data.

I am also trying to trace the sources saying that this class of vessels used water-ballast tanks, so any citations you can offer about this topic would also be greatly appreciated.
Thanks in advance.

 

[Mark F. Jenkins]

I'll keep a weather eye out. The torpedo boats haven't been a principal area of focus for me, but I bump into material about them every so often.

 

[AndyHall]

I am also trying to trace the sources saying that this class of vessels used water-ballast tanks, so any citations you can offer about this topic would also be greatly appreciated.

Along those lines (see what I did there?), have there been any calculations of how the reconstructed boat would ride in the water? It seems possible to make some rough calculations as to her displacement for a given set of dimensions.

I don't know about references to water-ballast tanks, but my first question would be, why? Hunley had them but that boat had to be able to change its buoyancy as part of its normal operating cycle to submerge and (one hopes) surface again. The Davids didn't need to do that, so why add the complexities of tanks, valves, pumps, etc.? Just drop some pig iron in the bilge and be done with it.

 

[JohnDLittlefield]

Along those lines (see what I did there?), have there been any calculations of how the reconstructed boat would ride in the water? It seems possible to make some rough calculations as to her displacement for a given set of dimensions.

I don't know about references to water-ballast tanks, but my first question would be, why? Hunley had them but that boat had to be able to change its mass as part of its normal operating cycle to submerge and (one hopes) surface again. The Davids didn't need to do that, so why add the complexities of tanks, valves, pumps, etc.? Just drop some pig iron in the bilge and be done with it.

Good questions Andy. I have calculated the displacement of the boat, based on dimensions and a scantling list. Sources say 9 tons were used to get the boat submerged properly. Various other sources say that 12-24" of the boat was above the water. Not coincidentally, my calculations fall in that range. I published this recently in an article about the boat's construction in Mariner's Mirror.

As for the water ballast tanks, David did not use them. As you mention, they weren't needed, but there are (lots of) sources say she did. I am trying to flesh out the original source of the bad info, if possible. Most likely, these folks conflated David and H. L. Hunley, as often happened in official records and in popular sources.

 

[Mark F. Jenkins]

The only reason I could think of for ballast tanks would be to adjust trim... a small boat like that would be considerably affected by loading/unloading, coal use, etc. But it seems like a waste of resources and an unnecessary complication.

 

[georgew]

Good questions Andy. I have calculated the displacement of the boat, based on dimensions and a scantling list. Sources say 9 tons were used to get the boat submerged properly. Various other sources say that 12-24" of the boat was above the water. Not coincidentally, my calculations fall in that range. I published this recently in an article about the boat's construction in Mariner's Mirror.

As for the water ballast tanks, David did not use them. As you mention, they weren't needed, but there are (lots of) sources say she did. I am trying to flesh out the original source of the bad info, if possible. Most likely, these folks conflated David and H. L. Hunley, as often happened in official records and in popular sources.

Just a thought. Has anyone seen any graphics or text anywhere on the issue as to whether any of these boats had external keels? I ask because the shape of the hull would be very likely to roll considerably in a sea state above calm. If you can keep enough of the machinery weight low enough you will some a certain measure of stability. Response to helm changes is another issue worth considering. The highly tapered bow would be useful in dispersing loads from displaced water from the detonation of the torpedo, but I wonder if the submerged torpedo prior to firing has a disproportionate effect on yaw?

 

[JohnDLittlefield]

Just a thought. Has anyone seen any graphics or text anywhere on the issue as to whether any of these boats had external keels? I ask because the shape of the hull would be very likely to roll considerably in a sea state above calm. If you can keep enough of the machinery weight low enough you will some a certain measure of stability. Response to helm changes is another issue worth considering. The highly tapered bow would be useful in dispersing loads from displaced water from the detonation of the torpedo, but I wonder if the submerged torpedo prior to firing has a disproportionate effect on yaw?

There were no keels... the ballast and weight of the machinery was enough to keep them very stable. Remember, this was a wooden hulled boat that floated, so any weight added to the bottom would have had great effect and acted in a keel-like manner. All accounts say the boat performed well, except in heavy swells when water would threaten to swamp her low freeboard.
As for the effect on the boat of the lowered torpedo I cannot comment. However, I'll point out that in one mission, David couldn't hit the proper spot of the target, but the target was moving. It is impossible to diagnose the single greatest cause, but perhaps the effect of the torpedo- kind of like an artemon sail, made steering in currents more difficult, especially when approaching a moving target.