by Admhawk » Fri Aug 22, 2025 9:07 am
TZoli wrote:Admhawk wrote:Definition of Perpendiculars
The forward perpendicular, abbreviated as FP, is a vertical line in the sheer plan that is drawn at the intersection of the DWL, which is often the estimated summer load line and the forward side of the stem.
A corresponding vertical line is drawn at the stern, designated the after perpendicular or AP.
- When there is a rudder post the AP is located where the after side of the rudder post intersects the DWL.
- When there is no rudder post, the AP is drawn at the centerline of the rudder stock, which is the customary location for merchant ships without a well defined sternpost or rudder post.
- In the case of naval ships, it is customary to define the AP at the after end of the vessel on the DWL. Such a location is also sometimes chosen for merchant vessels- especially vessels with a submerged stern profile extending well abaft the rudder.
Erm... then why ww1 and ww2 warships had 3 lengthts not just 2? Your definition mixes waterline and perpendicular length!
What I learned that the pp is fixed except if the hull is changed like the modernizations of the IJN Capital ships.
WL is the length at waterline in standard condition and could change as equipment added for example Iowa had different wl lengths at ww2 and at modern times.
OA is mostly fixed and changes if equipment or modifications were done at the ship ends or to the the entire hull. For example the Clipper or Atlantic bow added to the Bismarcks.
I don't make this stuff up. I refer to published documents.
The USN, and many other Navies, use this approach.
There is a difference between Warships and Merchant ships.
There is a difference between Rounded sterns and Transoms.
Load calculations are different between Merchants and and Warships.
You also have to pay careful attention to wording. FP and AP are used for calculations during initial design. If the waterline changes, the AP and FP may or may not change, I don't know. They are used to define the Stations of a ship when designed. This is different than the frames. I haven't tracked if stations change when load increases. It typically doesn't matter to me.
Anyway, here is an excerpt from a USN training course. I've highlighted the relevant line. If you want to learn more, you'll need to talk to Naval Architects.
http://www.resinshipyard.com/files/HULL ... tation.pdf[quote="TZoli"][quote="Admhawk"]Definition of Perpendiculars
The forward perpendicular, abbreviated as FP, is a vertical line in the sheer plan that is drawn at the intersection of the DWL, which is often the estimated summer load line and the forward side of the stem.
A corresponding vertical line is drawn at the stern, designated the after perpendicular or AP.
- When there is a rudder post the AP is located where the after side of the rudder post intersects the DWL.
- When there is no rudder post, the AP is drawn at the centerline of the rudder stock, which is the customary location for merchant ships without a well defined sternpost or rudder post.
- In the case of naval ships, it is customary to define the AP at the after end of the vessel on the DWL. Such a location is also sometimes chosen for merchant vessels- especially vessels with a submerged stern profile extending well abaft the rudder.[/quote]
Erm... then why ww1 and ww2 warships had 3 lengthts not just 2? Your definition mixes waterline and perpendicular length!
What I learned that the pp is fixed except if the hull is changed like the modernizations of the IJN Capital ships.
WL is the length at waterline in standard condition and could change as equipment added for example Iowa had different wl lengths at ww2 and at modern times.
OA is mostly fixed and changes if equipment or modifications were done at the ship ends or to the the entire hull. For example the Clipper or Atlantic bow added to the Bismarcks.[/quote]
I don't make this stuff up. I refer to published documents.
The USN, and many other Navies, use this approach.
There is a difference between Warships and Merchant ships.
There is a difference between Rounded sterns and Transoms.
Load calculations are different between Merchants and and Warships.
You also have to pay careful attention to wording. FP and AP are used for calculations during initial design. If the waterline changes, the AP and FP may or may not change, I don't know. They are used to define the Stations of a ship when designed. This is different than the frames. I haven't tracked if stations change when load increases. It typically doesn't matter to me.
Anyway, here is an excerpt from a USN training course. I've highlighted the relevant line. If you want to learn more, you'll need to talk to Naval Architects.
[url]http://www.resinshipyard.com/files/HULL%20FORM%20AND%20GEOMETRY%202.3%20-%20representation.pdf[/url]