WWII era submarines - ragged bow projections

I am curious as to why some WWII era submarines had jagged/toothed structures above the front bow, raked backwards. Almost like a jigsaw blade. Was this to break the impact of waves on the flat 'deck' when surfaced? I saw one on a wave piercing boat bow recently, and was curious as to what purpose it serves?

 

Apologies - I see it is a 'net cutter' on a Dutch website. Still does not explain why I have seen it on the odd boat with wave piercing hulls. But these were home designs, perhaps the builders felt it lent a certain 'look'. If not this, I would be interested as to their use.

 

Harbor entrances and naval vessels were once protected from submarine attack by stringing underwater nets. The net cutters fitted on the bow of the submarine could be used to defeat this netting or to keep the submarine from getting entangled.

Nets were also used as a defense against torpedo attack, whether by submarine or torpedo boat. British battleships from the late 19th century up to WWI had a series of booms fitted to their sides which carried the netting, which was deployed by the ship when at anchor. These nets and their supporting booms appear very prominently in photographs of these vessels.

 

Thanks!

 

it's also interesting to watch film footage of subs at sea in rough weather. Athough they are extreme examples of VSV (very slim vessels), and even though when they're on the surface and 3/4 of the hull still remains submerged, they seem to pitch very badly in a head sea..... defeating the concept of wave piercing hulls!

Anyone like to explain ?

 

Perhaps read up on Pitch RAO's.

One vessels sweet spot is another vessels worst condition, depends on hullform and weight distribution and the sea state. Surface running subs are already a compromise.
Subs are also heavy for their size and there's a lot of entrained water between the pressure hull and the casing that adds to the apparent displacement for dynamics.

Low buoyancy bows (aka 'wave piercing')need to be matched to the expected conditions, that's part of the design SOR.

 

..and they have torpedoes and other heavy stuff in the bow, and massive engines in the stern.

 

I have read a number of documents , most from the crews and skippers' point of view, about submarines and their seakeeping ability, but one stuck in my mind.
The skipper had received notice of a convoy that he was required to attack as part of a "wolf pack", but there was a winter Atlantic storm in the way and if he went around it, he wouldn't make the attack (and probably face court martial) so he pointed the nose straight through the storm. What I remember reading was that he went through with most of the conning tower out of the water, but the bulk of the sub underwater under diesel power. The crew ate, drank as per normal and that the sea didn't seem too bad so he popped his head up out of the conning tower to find a wave breaking level with the tower and the bow of the sub in the trough where he could see the planes.

I don't profess to know the truth or lies of it all, I just remember reading about this.

 

that's a fantastic idea for a new sort of displ. hull: the sub-surface-Displ. or SSD Type........

 

Rusty, here is one of my faves.

I'd guess much of the idea was to reduce target size to avoid gunfire from surface ships, while still making good speed through choppy water that would beat up a planing hull.

http://strangevehicles.greyfalcon.us/VS 5.htm

By Rob Arndt

​

​

VS 5 was an experimental semi-submersible torpedo boat (Versuchs Schnellboot) completed in 1941 and based on a 1938 patent by a Berlin dentist. The intended armament included two 21in torpedo tubes and two 2cm cannon. Its fate after 1941 is unknown.

​

PS- I can't recall any stories of a sub actually using 'net cutters'. Maybe it was to keep random stray nets from collecting around the conning tower and scopes, since subs had lower bows and often operated 'decks awash' to reduce their target size.

 

Normal state for a Fleet submarine on the surface was "over 2 and under 1". Similar for the DDs of the same era.

 

There aint really nothing very new around just variations on a theme so to speak, most of its all been done before or at least thought off before.