Electric Launch Design optimized for semi-displacement speeds

You still have not defines what YOU mean by limited scale!

 

You're asking me to engage in a double negation. I created another thread so skeptics of the concept of a large scale use of batteries can take the discussion there. Some of the skepticism I've run into was in a different forum inhabited by fans of Atkin's designs.

In this thread it's been suggested that my initial range goal was too ambitious. I've reduced it to 70 nautical miles and am prepared to extend the time required to make a 70 nm run to 8 hours.

 

Nope.

If you cannot define words/terms that you use...DO NOT use them.
Simple!

 

The thing I'm struggling to calculate mathematically (despite having relevant background) is passenger capacity. I'm lacking access to the full text of the Recreational Craft Directive and am requesting help in this area as explained in post #90.

 

The number of seats onboard is the clue to how many passengers it can take!

 

It is usually mandatory that all passengers have a seat. But it is also necessary to check, within the stability studies, whether the ship is capable of carrying the desired number of passengers on board. For example, one of the conditions (there are others) says that the list of the ship when all the passengers crowd on one side is no more than 10º.
These studies can condition, reduce, the number of passengers, regardless of the number of seats there are.

 

Courtesy of ABYC I've obtained a copy of ISO 12217-1 Fourth edition 2022-12, being circulated for comment prior to its adoption. Of course, there may be some of you with far more experience using ISO 12217 than I, and perhaps someone has access to a database of Category C capacities and crew limits correlated with vessel parameters? As it stands, it doesn't appear easy to derive Crew Limit (CL) or Maximum Load (mML) for the purpose of preliminary design - but if one focuses on the offset load test section it might be possible.

Here's my initial comment back to ABYC, which is preparing a response to the draft for the US:

Please consider that ISO 12217-1 2022 ed.4 could be improved by a simple method for determining CL ("crew limit") for initial calculations as part of the preliminary design process. The need for this to occur is stipulated at section 5.1, yet no method is supplied.

My suggestion is to come up with a formula for a preliminary CL estimate based on:

• Section 6.2 with Annex B

and possibly

• Section 6.8 with Annex F

I think it's reasonable for a DWL length, DWL beam, overall beam, preliminary lightship displacement & VCG, and preliminary crew VCG to be input (independent) variables, but because the intent is a preliminary design value one should assume that other values, such as freeboard and down-flooding angle, are TBD at the time the calculation is first performed.

Reiterating: the dependent value to be solved for would be preliminary CL, a value to be carried into the design spiral. The word "test" should not be part of this definition (unless it specifically applies to a computer model). If this derived CL does not meet design objectives one would presumably change something about the design, iteratively, until one could reasonably believe the boat's parameters adequate to support the intended CL. The objective would be to do this early in the design process with respect to the boat's basic parameters.

I'll attempt to further develop this idea, and would like to invite others to work this problem as well.​

 

A procedure, for the first stages of a project, could be the following :

1. Calculate the maximum angle of heel allowed by the corresponding standard.
2. Calculate the hydrostatic values of the ship with that heel angle.
3. Interpolate the hydrotastic values to obtain, for the displacement under study, the draft and position of the CoB.
4. Once the draft is known, we can know if the freeboard is sufficient or if it needs to be increased.
5. Knowing the lateral position of the CoB and knowing the position of the CoG with the passage on the side, we will check if the CoG is in the same vertical as the CoB. This will allow us to know how much we should vary the total weight so that both CoG and CoB are in the same vertical. (This will be approximate because when the total weight changes, the position of the CoB will also change slightly).

Of course, if you do not have adequate software, it will be very laborious to carry out any simulation.

 

I like it in some ways, but can the logic be applied to writing a formula to approximate CL? Because metacentric height is a product of waterplane moment of inertia it varies with LB^3, but the lever of the crew weight shifting also varies with beam, so would one expect CL to scale with LB^2 ?

Above, L and B are to be understood as waterline length and beam. In the next paragraph I'm asking about the regulatory implication of overall length.

I see where it's implied a vessel over 8m would require a second operating crew. Is that part of the regulations as implemented by national authorities?

 

I do not know of any formula that, in the early stages of a project, allows the CL to be deduced. In any case,
It would be a very approximate thing and, if at the end of the project, you discover, as would be normal, that the boat does not meet the maximum CL. You would have to go back many steps. My procedure, a little (not much) more laborious at the beginning, will surely save you some unpleasantness. With it you will only have to go back a few steps.
On the other hand, in my opinion, a formula that depends on LB^3, LB^2 or anything else, and does not take into account the height of the CoG, cannot be correct.
Regarding the minimum number of crew members, I don't know of any rule (although it may exist, I don't know) that limits, above or below, that number.

 

What is your objective of this?

Define 'crew', as you understand it or from a source.

 

From ISO 12217-1 2022 ed.4:

"Crew limit = maximum number of persons on board."
​

This differs from the nomenclature used in the U.S. CFR, where a distinction is made between "crew" and "passengers".

 

And that's the point...to which are you referring to?

And still, what is the objective of this?

 

One goal is to get you to offer something constructive. Should the lowest resistance boat be declared the winning design, or should capacity play a role? If you'd like to edify me about something technical, how about the quantifying of transport efficiency?

 

I never use Transport Efficiency as any metric. It is a non-starter.
It is a term used by many academics and non-technical-designers, who wish to place "designs" into a certain category to help them to create a narrative based upon their research of focus of attention.

One never starts an SOR with a client asking - what Transport Efficiency do you wish to have!
What ever metric one uses, as Transport Efficiency, to define - whatever you wish/want - it is the end result of a design that works, not the other way around.

A design that full-fills the SOR is all that is required.