Electric Launch Design optimized for semi-displacement speeds

I don't have time, right at this moment, to make the numbers work out right, but let's say we stick with that we're looking to build some number of electric launches, x, 8m long at the waterline, to work at a club, and that they are to be optimized for semi-displacement speed operation. Assume one launch will at all times be unavailable for maintenance. At crunch times a certain number of people, n, will show up at the club needing to be transported a certain distance, d, within a certain time frame, t.

Each boat will have a capacity, an initial cost and an operating cost. The operating cost will include paying a single qualified launch operator, the cost of sustainably sourced electricity, and upkeep. Since the scenario is hypothetical, allow that x need not be a whole number.

That's the optimization component of the SOP. Once n, t, and d are established we would write a function for optimizing x to minimize cost = x *(initial cost per boat, amortized + operating cost per boat) per some unit span of time. The capacity of each boat will figure into how many boats need to be built and operated. Minimizing cost according to such a function need not be the only criterion of a design contest, but some attempt at optimization like this ought to be considered. That's what I mean by 'transport efficiency'.

[Note: the operating cost per boat should probably be further broken down to those that are time dependent, those that are distance dependent, and those that are essentially overhead such as the employment of launch operators outside of peak hours.]

For those who have access to ISO 12217, what I'm thinking is that a preliminary category 3 CL might be solved for using the equation at Annex B: B.3.2.5, second bullet (with substitutions). That expression, which corresponds to Table 4, only yields heel angle, but that might be enough when combined with first principles and a few basic assumptions. The reference is from ISO 12217-1 2022 ed.4, which is the only version I have access to. At this time I'm not comfortable posting the expression I'm referring to without the appropriate permissions.

 

I think you should set the minimum number of people on board, and some other parameter, and have the designer design the optimal boat.

 

Then I think I'd want to set category C CL just above what it is for the Clara 8m (which I do not know). If Nigel Irens wants to submit a version we'd effectively be asking him to design some modification that would increase that boat's capacity. I'd be OK with that - what do you think?

The Moonday 850 WB (at my post #79) has a capacity of 8. I wonder a little about what feature of that boat limits the capacity to that. Anyway, can you provide other relevant data points?

Looking into the point at which a deckhand would be required in addition to a qualified "master" (a.k.a. captain or operator) here in the United States, there doesn't seem to be a firm answer, but the conversion appears to be that a deckhand is required if the number of passengers exceeds 12. I don't see any reference to length in US regulations on this.

 

The formula in ISO 12217-1, Annex B: B.3.2.5 (formula B.1) only tells you a value that should not be exceeded when all personnel on board are placed on one side. Therefore, you must draw the curve of the righting arms (which depends on the shapes of the boat and its CoG), then draw the curve of the heeling arms due to the people on the side, and calculate at which point they cut, that is, at what angle of heel both curves have the same value, that is the point at which the ship would reach equilibrium. This angle must not be greater than that indicated in formula B.1.
The ISO, then, does not prevent you from having to carry out some naval architecture calculations that are not simple.

There is a magic number, 12 passengers, that indicates when a ship should be considered a passenger ship and when it should not. The security conditions, stability, etc., are more rigorous for a passenger ship. But all that refers to ships that have to comply with SOLAS. Vessels smaller than 24 m do not have to comply with SOLAS. ISO standards set various standards for these "small" boats. One of the advantages it offers us is that any type of boat, be it cargo, passenger, recreational, recreational for commercial use,... always has the same requirements regarding its stability and buoyancy. There are no "passenger" and "non-passenger" ships for the ISO. The only thing that standard 12217 says is that the maximum number of personnel on board, whether crew or tourists, must comply with the tests indicated in ISO 12217.

There are methods, although with limitations, to get a boat that does not comply, to comply: lower its center of gravity (reduce high weights and place lower weights), increase its freeboard (raise the bulwark without changing the displacement), create watertight spaces as a buoyancy reserve, etc. or to get a certain value of the CL. The designer must know how to handle these circumstances. But studying ISO 12217 does not tell us how to solve the problem. For that, once again, naval architecture is needed.

As far as I know, but I may be misinformed, the USCG does not have specific regulations for small boats. In any case, a boat that complies with ISO standards (CE marking) should not have problem meeting USCG requirements.

 

USCG Subchapter T is for small boats, and there is a simplified stability test that I cited early in this thread that is similar to the ISO 12217 offset load test. I think some of the very high USCG values I see, on the Oldport 26 website for instance, must be for fully protected waters, the equivalent of ISO Category D rather than Category C.

I'm settling into feeling that CL=8, seven adult passengers + 1 operator with personal effects at 86 kg (190 lbs) per, total 688 kg (perhaps round to 700 kg), is a reasonable target full load and target category C rating. If each contestant submits an inboard profile showing weights and their centers this will go a long way toward running checkable calculations. Does that seem right to you, TANSL?

 

I'm sorry, I was wrong. What I should have said is "I don't know the specific USCG rules for small boats, but in any case..."

 

Have a look at the Hickman Sea Sled Information thread. @baeckmo built half a dozen where he found that the planing resistance transition was quite low. That seems ideal for your application.

 

I think I was specific that at full load the top speed need only be Fn = 0.8; that the top speed of Fn = 0.9 was with two persons aboard.
I'm considering backing off of that, perhaps it should be Fn = 0.8 at 3/4 load. Note that's a flank speed, not an intended cruising speed.

At post #7 Jurgen suggested an LDR (or "slenderness ratio") of 7.0. On an 8m waterline that puts us at about 1530 kg (3373 lbs). I've recently stipulated full load to be 700 kg (1543 lbs), so to have an LDR of 7.0 at

Full Load: Lightship would have to be 830 kg (that seems unlikely to me).
3/4 Load: Lightship would have to be 1005 kg (a little more likely).
Half Load: Lightship would have to be 1180 kg (not out of reach with careful engineering).​

The Chevy Volt battery is said to be 400 lbs (182 kg).
Batteries from other EVs come in at:

​

I've dialed back the demands of the 70 nautical mile range I'm requesting. That can be at half load and take up to 8 hours, so it can be at 8.75 knots.

 

You need extremely cheap, genuinely green sourced electricity, or this thing will cause great environmental harm for no gain whatsoever. Not mind, greenwashed power like Germany touts.

 

More discussion of this should probably be its own thread, but some quick thoughts:

• An extended club roof over a waterfront deck is often a good opportunity for solar.
• Electricity in Florida is quite cheap - probably too cheap for solar to be properly incentivized. I learned this when a friend flipped a house there and I helped her review her options.
• Yes, there are worst case scenarios. Lebanon is one right now according to the latest episode of NPR's Living On Earth.

Advances in designing simple yet easily driven hulls could also improve the efficiency of conventionally fueled boats like the crew and supply boats that service offshore oil platforms.

 

Saw this Mako model, resembling a sea sled, in a boatyard yesterday.

Let me take this opportunity to say one could submit a multihull if they believe it would be a viable launch meeting the SOP.

My view is that people get hung up on section shape, while it might be the longitudinal distribution of volume that makes the greatest difference at high displacement and semi-displacement speeds.

 

Too much wetted surface on that one I think.

 

You know, DC, this didn't occur to me when you first brought up sea sleds, but my sketch at posts #1 and #86, with its inverse deadrise stern and wide spray chine, could be seen as a sea sled with a displacement hull or box keel appended to the bottom (mostly forward) so that the sea sled part maintains bow up trim continually with only the stern immersed. Since the sea sled bow is already above the water there's no need for it to sweep up (so I've given it an elliptical shape in planform instead).

 

While exhibiting my front-facing rowboat at the WoodenBoat Show in Mystic, CT, got a good look at the East Passage 24 and met the designer, Walter Ansel, Director of Mystic Seaport's Preservation Shipyard. East Passage 24 https://www.epbws.com/services/new-construction.aspx

Also met John Lentz, builder of the Pulsifer Hampton.

 

Too much power for the size and speeds specified in my SOP I think, but I just found out about a company in Bristol, RI building a 100 HP electric outboard: Flux Marine https://www.fluxmarine.com/. If the additional power were used to swing a big prop at reduced RPM for towing that might make sense in my working launch scenario.