Electric Launch Design optimized for semi-displacement speeds

That is just a journalistic narrative review of events. Nowt else.

 

OK. What've you got?

 

Since a broad defense would just be more words, how about you specify where you think the problem is and make a suggestion how to remedy it? Without specific input from others, my inclination is to stand by what I wrote at post #126 and in Professional BoatBuilder (attached to that post as a PDF). But suggest something meaningful and I will listen, AdHoc.

The graph at post #125 was a response to your post that focused on my top speed value of lFn=O.9. I don't care about that. Instead, please focus on the intended cruise speed of lFn = 0.7, and please note that the range target, 70 nautical miles in 8 hours, allows for a lower speed.

One thing I'm inclined to revise is that a Chevy Volt battery would be able to achieve that range. I think a Nissan Leaf battery or equal weighing roughly 300 kg could get the job done if the boat is built reasonably light and is otherwise well optimized. In a later post I allowed for the possibility of swappable batteries supplying 35 nautical miles each, but at an increased speed because the time making the swap should be figured into the 8 hours.

Scroll down at Oldport 26 Launches if you wish to read about the advantages of a launch capable of semi-displacement speed over a full displacement launch.

 

The "state of the art" has been talked about repeatedly and, although it has not been defined what is meant by this phrase, to narrow down the terms a little I would like to ask if we are talking about the "state of the art" in naval architecture or in relation to electric propulsion. Both subjects are so different, so disconnected in their theoretical aspects, that different competitions could be proposed for each subject.
The mechanical engineer, electrician, should propose an electric propulsion system, with a limited total weight, with a minimum autonomy and with the shortest possible battery charging time.
With the weight of this system, the naval architect would be responsible for designing the floating device that best adapts to the SOR of the ship (which, I repeat, must be clearly defined).
On the other hand, I would just like to point out that the proposed Fn range, 0.4 to 0.8, for an 8 m boat, would imply a variation in installed power of (for example, since I have not made an exact calculation) between 20 hp and 160 hp. I do not know how the optimum value of Fn can be selected, if only what has been said so far is taken into account.

 

Exactly...and that's the whole point!!

 

Yes, that is the question. Take, for example, a Somes Sound 26. Is dropping in an electric motor and battery enough to make it a modern electric launch? If no, should the issue be addressed with retrofits or materials upgrades, or do our modern tools like CFD and whatever experience we've accumulated in the last few decades indicate there's a better path forward in terms of hull shape?

The SOR, click here, calls for an 8m waterline boat to cruise at lFn=0.7 and have a 3/4 load top speed of lFn=o.8. In order to travel 7o nautical miles in 8 hours on a single charge most efficiently its speed would be lFn=0.52.

I see naval architecture as it relates to semi-displacement resistance as primary (and as generalizable to vessels of other sizes operating at similar Froude numbers).

I see choices as they relate to an appropriate electric power package as secondary (but not unimportant).

On the naval architecture side I see this as an amateur, civilian, small craft oriented effort to compliment the military ship effort described at
Technical Director’s Innovation Challenge Stern flap integration hull form selection > Naval Sea Systems Command > News
I'm very grateful to Ignacio López Almenar and Perry Van Oossanen for their willingness to guide us on this journey.

On the electric power package side I have someone in mind who I will ask to join Ignacio's panel of judges.

There are a number of electric motor companies currently putting together boat / motor packages for production and marketing. It's my hope these companies might take enough interest in what we're doing to build and market at least one submitted design.

 

That is just the point - again.
There is no "problem" and nothing to "remedy"....

It appears to be a figment of your own imagination that there is "something" that needs fixing.

 

Their will be boats of the future, despite your protestations, AdHoc. Dominic Cusanelli calls for the lessons of his stern flap research to be incorporated into new build hull design at
Technical Director’s Innovation Challenge Stern flap integration hull form selection > Naval Sea Systems Command > News
Why not comment on that instead of picking me apart? All I'm advocating are processes of continual improvement (and that one measure of improvement be reduced environmental impact).

 

I'm excited to have finally heard from Nigel Irens, designer of the CLARA. He has shared this important piece of data:

As far as CLARA is concerned I use a local surveyor – who has conducted our inclining tests (loads of them !). He has pronounced that with regard our 12217 Crew Limit (CL) ISO we are permitted to carry 8 passengers for inland waterways, estuaries, harbours etc. For coastal passages we are allowed to carry up to 5 passengers.​

The 5 passenger rating is presumably the Category C limit, while the other is Category D. Since the CL includes the operator as defined by ISO, I'm not clear if 5 passengers = 6 persons, or 5 persons total.

While CLARA is inspiring and exactly the direction in which we should all be looking, a higher capacity is in our contest SOR, and belongs there. Mr. Irens will not be submitting a revised version of his design. I continue to encourage him to submit the CLARA design, as is, for TANSL's consideration.

In addition to hearing from Mr. Irens I've come across other notable UK based efforts in the last few weeks and days.

• £5.4million project aims to develop world’s largest network of electric workboats
• https://www.roundbritain-erib.org/
• Hybrid Marine Power - Energy Transition Consultancy

There is someone (not in the UK, but in Europe) who has indicated to me his intent to submit a design to the contest.

 

As we prepare for a judge's conference call Perry has suggested each contestant supply their own resistance curve, and that Perry's calculation at a couple points, perhaps lFn=0.5 and lFn = 0.7, serve as checks for calibration. (For those working with displacement / length^0.5 ratio, lFn=0.6 corresponds with a D/L ratio of 2.0.)

Does anyone know of free or low cost software that would facilitate a standardized approach among those entering with respect to generating a resistance / power curve? Perhaps this could be as simple as a spreadsheet with a formula in it from one of the tank test series.

Besides de-emphasizing the top speed value in favor of the cruising speed and the range calculation, the one thing in the SOR as published in Professional BoatBuilder I'd change is to rescind the recommendation of starting with the Pure Marine Outboard. That 25 kW motor is probably insufficient, and I would like instead to suggest the RAD 40 Outboard or an equivalent 40 kW unit (or twin 20 kW motors).

 

Such software requires validation and verification against a “known” vessel’s resistance data to establish its accuracy. And such software is parametric based. Thus unless the target vessel falls exactly into the parameters of said software (which most do not), you’ll just get GIGO.

 

True, but:

1. 26 foot launches are not an uncommon type.
2. I think this is what Perry Van Oossanen is proposing to do - ask people to submit their own resistance curves, then validate them using his means and methods at two or three points. If the general shape of the curve is right perhaps a few points are enough to shift it a bit and thus improve its accuracy.
3. I think the graph you posted, the old CAT slide rule, and graphs in Robert Beebe's book Voyaging under Power are all pretty consistent and are probably good enough as a first cut. A single program or spreadsheet we could recommend would lend consistency in a format with which younger participants are familiar.

 

My optimism concerning the possibility of an ISO 12215 compliant boat markedly lighter than the Oldport 26 is based in part on Nigel Irens' CLARA 8m in plywood and the RS Electric Boats Pulse 63 in FRP. Note also that Old Town BoatWorks in Nova Scotia has executed an Uffa Fox Ankle Deep based lightweight launch, Wild Rooster, in dual-diagonal wood/epoxy.

If anyone knows how to reach this person: https://www.youtube.com/@flomoflowingmotion, that would be of interest relative to obtaining a 3D model of Ankle Deep and/or inviting said person to participate in the competition as they see fit.

 

Using ISO 12215 to calculate the structure of a ship does not guarantee in itself that the ship will be lighter than using any other regulation. Of course, a well-designed structure of a ship, in FRP, should be lighter than with any other material. But, always, the main factor to obtain a light structure, is the experience of the designer.
In addition to this important factor, it must be taken into account that ISO 12215 does not consider, in general, the global loads on the hull, it only considers the local loads, so, yes, that good designer we are talking about, could achieve a lighter structure with ISO than by applying, for example, the rules of a Classification Society.

 

That's the point - "should be".
Most people, who do not design structures for boats, think any composite will be lighter than say aluminium.
This is not the case though.

When designing to any rule, say, Class rules, there are minimum levels of compliance, viz:-



And so after going through the rules and establishing scantlings, if the amount calculated, is less than the minimum requirement, it must default to the min rule.

And it is no different with ISO rules:


That is the issue - the first round initial calculations - oh yes, lighter than aluminium, perfect. But when applying the Class/ISO min rule requirement to the structural member under consideration, the overall structure of any composite/Glass structure is basically the same weight as if designed using aluminium. But the myth still persists...why, no idea?

One can only take advantage by using higher modulus materials, such as carbon fibre, to "reduce" weight.
But, as always, at the expense of cost.

So, if cost is NOT an input, design the whole vessel in CF.
If cost IS an issue, there is very little to be gained by limiting the hull structure to just composites.

The lightest full load vessel, no matter how it is designed, the hull shape, or the materials of construction, the propulsion etc etc, will always be the best performer.
It is not rocket science.