Electric Launch Design optimized for semi-displacement speeds

[Stephen Ditmore]

Happy New Year 2024!
Let's design an innovative semi-displacement electric launch as a group project. I've said I would propose this at
Semi-displacement boats don't generate lift? https://www.boatdesign.net/threads/semi-displacement-boats-dont-generate-lift.67859
Stern taper on semi-displacement hulls https://www.boatdesign.net/threads/stern-taper-on-semi-displacement-hulls.60336
and
Heritage Class Offshore Patrol Cutter Argus launched https://www.boatdesign.net/threads/heritage-class-offshore-patrol-cutter-argus-launched.68524/
It's time.

If others would like to propose a different project or goal, OK, but to get rolling how about we attempt to improve, specifically, on the Oldport 26 launch with electric power in mind. British designer Nigel Irens has taken a shot at this with the low displacement / length ratio 39' Rangeboat. The problem that I'd like to quantify involves payload and the need to accommodate battery weight - light displacement will no longer be light displacement at full load, after all. Then there's the question of intact stability. In the US, a passenger launch is considered a "Subchapter T" vessel. Its full load intact stability must comply with the formula on page 226 here. If someone wants to propose a minimum GM designers might use as a target based on experience with this rule, it's possible that would simplify matters. My first shot at it was 0.70 meters (2.30 feet). I proposed a method for deriving waterline beam based on it at How wide should it be?...a method proposed https://www.boatdesign.net/threads/how-wide-should-it-be-a-method-proposed.12440/.

It may be that the concept of transport efficiency, used frequently in papers by Donald L. Blount and Associates (DLBA) could be helpful in comparative analysis. See https://dlba-inc.com/library/effective-use-of-transport-efficiency-concept/ + articles and papers by Dean Schleicher, formerly of DLBA, and, of course, Donald Blount. Fully loaded with fuel at the beginning of her record transatlantic run, the 220 foot DLBA designed Destriero operated within the semi-displacement speed / length range, and is therefore much discussed in DLBA's literature on semi-displacement resistance. Note that number of passengers is effectively a variable in both the USCG rule and the definition of transport efficiency; it'd be awesome if someone sees an elegant way to optimize something by solving the equations simultaneously.

There's a notable attempt at predicting semi-displacement performance at:
Development of a reliable performance prediction tool for semi-planing hull forms https://www.boatdesign.net/threads/development-of-a-reliable-performance-prediction-tool-for-semi-planing-hull-forms.46630/

It's notable that Friendship Systems of Germany just opened a New York office
FRIENDSHIP SYSTEMS Establishes Direct Operations in North America › FRIENDSHIP SYSTEMS AG https://www.friendship-systems.com/news/2023/friendship-systems-establishes-direct-operations-in-north-america/

Bruno Bouckaert's Hull Vanes seem to be particularly effective in reducing semi-displacement vessel resistance.

Doubtless I'll have more to say; I've been wanting to pursue this for some time.
I'll end this discussion by showing a sketch of where my thoughts are going.

 

[HJS]

Semi-planing boats.
Why make it simple when you can make it complicated?
Follow the KISS rule, keep it simple stupid, according to Dick Newick.
JS

 

[Stephen Ditmore]

Because I don't believe a monodendron is the way to go here. I also believe advances have been made (in military craft, as we've discussed in the other thread, and the recent America's Cup hulls have some things in common with Phil Bolger's box-keel boats - hard to call those complex). The question becomes how to evaluate the design options. By putting our heads together I think this can be a learning / teaching moment.

Regarding the America's Cup boats, yes, they're foilers, but that's part of my point. Maybe the way to go is to design the hull for semi-displacement speeds and to fly at what would be planing speeds - if those higher speeds are sought.

The Oldport is not terribly complicated, nor is the Rangeboat, nor is my sketch. (The fact that the spray chines are dead flat surfaces that become the stern makes it pretty simple, in fact. For the displacement hull forward, I'm wondering if it could be sliced from the underbody of an Etchells 22, Dragon or similar.) My idea is monodendron at the stern, displacement hull forward.

 

[HJS]

To limit the dialogue, what slenderness ratio is meant here? Maximum and minimum.
JS

 

[Stephen Ditmore]

I'd be comfortable saying the Oldport represents the minimum and the Rangeboat represents the maximum. I'll get around to calculating those sometime in the next 72 hours. For semi-displacement speeds narrower tends to be better, but because the boat must meet full load intact stability criteria, resistance is not the only determining factor.

Recalling that metacentric BM = I (waterplane) / Displ (volume), my feeling is that beam / depth is more critical than slenderness ratio, so I would propose to draw an inboard profile and locate weights before committing to a slenderness ratio, as outlined at How wide should it be?...a method proposed https://www.boatdesign.net/threads/how-wide-should-it-be-a-method-proposed.12440/.

But also, what about a shape that is wide just above the waterline, but narrow at the waterline? What I drew has that shape midships, with the wide spray surfaces making contact with the water aft of midship in the static condition.

I like the look of this one from Bill Prince: BPYD - BPYD 26 http://www.billprinceyachtdesign.com/ind_boats/bpyd-26.html

 

[Stephen Ditmore]

Looks like the 8m from the Clara Boat Company is the more comparable boat to other 26 foot launches and the more recent design from Nigel Irens.

• Oldport Launch slenderness ratio = 25.83 ÷ 9.17 = 2.82
• Clara 8m slenderness ratio = 26.25 ÷ 6.5 = 4.04

 

[HJS]

Looks like the 8m from the Clara Boat Company is the more comparable boat to other 26 foot launches and the more recent design from Nigel Irens.

• Oldport Launch slenderness ratio = 25.83 ÷ 9.17 = 2.82
• Clara 8m slenderness ratio = 26.25 ÷ 6.5 = 4.04

Slenderness ratio is not length-width, it is the ratio between length and total weight.

An optimum is achieved between load capacity, interior space and total weight with a slenderness ratio around 7.0 together with a length-width ratio around 4.0. This applies to all boats at all low and moderate speeds.

The length sharpness, slenderness ratio, the wave-forming length in relative to the total weight, L / V1/3, have a very high impact on the boat's efficiency at low and moderate speeds.

Very few of the boats sold today meet these requirements. Usually the slenderness ratio is around 4.5. Old-fashioned boats have a slenderness ratio of around 7.5. Especially on small and light boats, the slenderness ratio can vary greatly depending on the highly varying load.
JS

 

[wet feet]

I suspect that studying the most recent stand out designs from the Dutch solar challenge would be a useful starting point.I understand that the better efficiency of solar panels since the first edition of the race would be very useful to aid performance,without the restriction of the original challenge but weight will still be important.I will be watching with interest.

The Dutch Solar Challenge: World Solar Boat Championship https://blog.upsbatterycenter.com/dutch-solar-boat-competition/

Dutch Solar Challenge Under Way https://www.energymatters.com.au/renewable-news/dutch-solar-challenge-em5552/

 

[Stephen Ditmore]

Slenderness ratio is not length-width, it is the ratio between length and total weight.

An optimum is achieved between load capacity, interior space and total weight with a slenderness ratio around 7.0 together with a length-width ratio around 4.0. This applies to all boats at all low and moderate speeds.

The length sharpness, slenderness ratio, the wave-forming length in relative to the total weight, L / V1/3, have a very high impact on the boat's efficiency at low and moderate speeds.

Very few of the boats sold today meet these requirements. Usually the slenderness ratio is around 4.5. Old-fashioned boats have a slenderness ratio of around 7.5. Especially on small and light boats, the slenderness ratio can vary greatly depending on the highly varying load.
JS

Could you provide a formula for what you're calling slenderness ration, Jurgen, including units? If what you're referring to is displacement / length ratio, the formula I'm familiar with for that is (Long Ton Displacement) / (0.01 * LWL)^3, with the heavier boat having a higher value (so perhaps an inverse relationship to what you're calling slenderness ratio)?

The speed / length^0.5 ratio (or the Length Froude Number) most of us use is also inverse relative to your way of calculating (except I'm not sure your exponent is equivalent. It might be - I'll need to think on that). Are your alternatives to the conventional ratios specifically Swedish?

I could use the published displacement to determine the displacement/length ratio for the Oldport and the Clara 8m, but I think it would be more meaningful to understand how many passengers each is rated for, what the basis of that is, and to have whatever full load displacement is being used in the calculation of that capacity.

Perhaps we should agree to utilize ratios and units that comport well with the formula posted by Julien_C at https://www.boatdesign.net/threads/development-of-a-reliable-performance-prediction-tool-for-semi-planing-hull-forms.46630/

Rr=Δ*(a0+(V^(1/3)/LWL)*(a1*(BWL/LWL)+a2*(V^(2/3)/WPA)+a3*(Vtun/V)+a4*(LCB/LWL)+a5*tan(α))

Where Rr is the Residual resistance, Δ displacement, V volume, Vtun volume of the tunnels and α angle of entrance
And the coefficients a0, a1, …. vary with the Froude number following a polynomial equation of the 5th order.​

When graphing I like the convention of making the ratio of resistance/displacement the Y axis so factors that are independent of weight 'pop'.

 

[Stephen Ditmore]

I suspect that studying the most recent stand out designs from the Dutch solar challenge would be a useful starting point.I understand that the better efficiency of solar panels since the first edition of the race would be very useful to aid performance,without the restriction of the original challenge but weight will still be important.I will be watching with interest.

The Dutch Solar Challenge: World Solar Boat Championship https://blog.upsbatterycenter.com/dutch-solar-boat-competition/

Dutch Solar Challenge Under Way https://www.energymatters.com.au/renewable-news/dutch-solar-challenge-em5552/

I see the image of the Stevens hull:

Would you call that a basic "warped bottom"? Do you know if any boats had more notable or interesting hull shapes, and at what displacement / length ratios (or Length Froude Number) these boats typically operate?

We will need to bring propulsion related considerations into the discussion at some point. This is good reading about the challenges the Clara Boat Company is facing: Electric Propulsion - A whole new learning curve. - Clara Boat Company by Nigel Irens https://claraboat.co.uk/electric-propulsion-a-whole-new-learning-curve/

 

[HJS]

Only the US uses imperial units, the rest of the world uses metric units.

Slendernes ratio:
L/V^1/3 L=length in meters, V=volume in cubic meters=total weight in metric tons.

Semiplaning speed= Froude length number= 0.7
Fn = V (speed in m/s) / [g (9.81 m/s^2) x Length (m)]^0.5

Hope I got it right.
JS

 

[Stephen Ditmore]

Velocity is the numerator in Froude Number. If L is the numerator, you've inverted the fraction.
Fn = V (speed in m/s) / [g (9.81 m/s^2) x Length (m)]^0.5

[From froude's number https://www.boatdesign.net/threads/froudes-number.44961/]

While I'm griping, I don't like that Julien C uses the variable V for volume, not velocity. I'm OK with standardizing on metric, but this isn't going to work if we can't adopt some conventions. I haven't been able to find an inverted delta in MSWord, but this V with a tilde: Ṽ, is character code 1E7C. An inverted delta is used at https://apps.dtic.mil/sti/pdfs/ADA401336.pdf page 24.

I'll let Jurgen define what he means by semi-planing speed. What I mean by semi-displacement speed is the entire range of Length Froude Number 0.4-0.9 (for backward Americans, speed-length ratio 1.34-3.0).

[The upper limit should actually be independent of static waterline length in part because some boats have their bows in the air at semi-displacement speeds, affecting their running waterline length. If anyone is interested in a more sophisticated examination of that boundry see Definition of Planing https://www.boatdesign.net/threads/definition-of-planing.45248/page-22, especially my reference to Almeter Number.]

 

[HJS]

You're right, I messed it up.
Fn = V (speed in m/s) / [g (9.81 m/s^2) x Length (m)]^0.5
JS

 

[wet feet]

I see the image of the Stevens hull:
Would you call that a basic "warped bottom"? Do you know if any boats had more notable or interesting hull shapes, and at what displacement / length ratios (or Length Froude Number) these boats typically operate?

We will need to bring propulsion related considerations into the discussion at some point. This is good reading about the challenges the Clara Boat Company is facing: Electric Propulsion - A whole new learning curve. - Clara Boat Company by Nigel Irens https://claraboat.co.uk/electric-propulsion-a-whole-new-learning-curve/

A quick google search for boats from the Dutch Solar Challenge will take you to catamarans and several other hull types.They are limited to very modest power.

 

[BlueBell]

Dutch Solar Challenge will take you to catamarans

Are you sure they're not "stabilized monohulls"?
Terminology.