Ship Deflection in Waves
2014-Apr-02
Structural Detail Design – Component from First Principles
2015-Nov-13
Ship structural scantlings are a contract design level task. They form the general plan for the material thicknesses and section profiles on a vessel. This is starting to form the major details. After the ship scantlings get calculated, you have a good idea of the structural arrangement, the ship structural weight, and any major challenges.
What is not included in the ship structural scantlings:
- Any details of connections between members
- Any adjustments for openings
- Any reinforcements for concentrated loads
- Any reinforcements for machinery foundations
- Checks for global hull strength
The scantlings calculations form the background vessel structure.
The scantlings are based on rules based calculations. This is not a hard requirement. But the vessel will need to meet the scantling rules anyways. You will want to submit your vessel to a classification society to get approval for vessel insurance. That classification society has a published set of rules. The naval architect will use those rules to design the vessel structure.
Ask if the engineer has scantling calculations already developed for your vessel, or if they will need to be developed from scratch. Rules already developed are a lot faster to reapply than to create from scratch. Also ask to see an example of the scantling rules. See what level of quality and what type of presentation you are getting.
Deliverables
The deliverables should be a set of scantling calculations. This will be a large report full of boring math. That is the part that gets submitted to the classification society. Still review the report. It should contain clean formatting. Each rule section should be clearly identified and referenced. You should see comparison tables that list what the rules requirement is, what the actual offered value is, and a clear indication if the actual value is sufficient.
The second major deliverable is a scantling drawing. This is the really important one. It lists the scantlings for each major piece of the vessel. And it shows the general structural arrangement.
There is a lot of room for variation on level of effort. Be very clear with the engineer what level of effort you want. Initially, for the concept design, the engineer may perform scantling calculations that just describe the structure in the midship section. That is a quick solution, but leaves out many of the details.
On the other end, engineers may develop a set of scantling calculations and drawings that show every single deck, every single bulkhead, all of it. That is the level of effort required to submit a vessel for construction contract bids.
Budget
Budget can vary wildely for scantling calculations. Here are some rough rules of thumb.
Midship section calcs: 1 – 2 weeks
Detailed calculations: 2 – 4 weeks
Midship section scantling drawing: 1 – 2 weeks
Detailed section scantling drawing: 1 week per deck
The good news is that the budget is largely dictated by the level of effort. So talk extensively about that up front.
Schedule
The scantling caculations and scantling drawing depend on each other. There may be some overlap between the tasks. You could expect the schedule to take between 70% and 150% of the budget time.
Example: 2 weeks of time for scantling calcs. 1 week of time for scantling drawing. The actual schedule time may take from 10.5 to 22.5 days.
Required Inputs
You must specify who you want to classify with. This determines whose rule sets to use. And specify if there are any special requirements. If you want any ice classification, that is a large increase in design costs. Discuss your concerns with the engineer ahead of time.
