Race boat hull design wanted

[gzs]

Hi everybody, glad to be a new member of this great community.

I have a pet project in my mind which is creating a "race" style boat with electric propulsion. (I am totally aware of the cost of electric motor and battery systems.) I'm trying to find a hull design for the following:

I was thinking of a 2 seater, open cockpit model, LOA max 6m, B around 2m, fiberglass or carbon fiber, passenger weight capacity for 2 persons around 180kg (flexible), max speed requirement around 70 km/h, rough preliminary estimate for the electric motor 40kW, maybe less, and around 25kWh effective capacity for the battery pack.

So far all the hulls I found were used for racing (no surprise there). Usually 150-200HP+ outboards are being mounted on them (weight around 150kg+ fuel tank+fuel). The carbon-fiber one seater boats are capable of reaching 100+km/h with a 60HP outboard.

Let me show some examples, they might help to get a bit clearer picture of what I imagined.
I've found this design here in an old forum:

This would be awesome, with an open cockpit, and 2 seats (passenger seat should be optimally next to the driver's seat and not behind it, if possible).

Another example:

And one more:

I don't know if any of you have plans of similar boats. Especially in any CAD format.

I figure I have 3 choices, how to proceed.

a) buying a 2 seater hull, and experimenting with the electric transformation. Since the outboards that are typically mounted weight around 150kg (+30kg fuel tank+fuel), I guess around 180-190kg weight would be available for the electric propulsion system. This limits the battery type to one special and expensive type (260Wh/kg). And who knows what would happen to bouyancy, center of gravity, stability...

b) trying to find an existing design (CAD) and hire an architect to do the modification / simulation (Maxsurf or similar) and see if it's feasible.

c) trying to find an architect who would design the boat from scratch, according to my vision and around the electric propulsion. I'm not quite sure about the cost of this, so any information, quote is much appreciated.

 

[PAR]

Most existing high speed power designs will be designed, knowing there's plenty of power available. With this being the case, the boats tend to be proportionately pretty fat. For your high speed electric boat, you're going to want to look at skinny designs, which aren't all that common, but require less power to ac heave similar speeds.

 

[gzs]

Yes, after doing some research I've found out that the desing (or manufacturers) I'm looking for are quite uncommon. For me, it makes the whole idea a lot more interesting. Well, "relatively high speed" needed only.. in a 6m boat 50-70km/h is enough for me, I'm not focusing on race speed, rather on a joyride, I want to be able to do some thrilling maneuvers but safety has priority to fun... hence no need for greater speed.

Is there anybody who could give an estimate on the approx. cost of creating such a boat design?

 

[DSR]

Hi GZS,

I'm intrigued by what you've looking to accomplish, pretty cool! What kind of propulsion system were you thinking of using?

One thing I was wondering about was your choice of using a tunnel hull design? With your projected top speed in the 70 kmh range, a tunnel hull may not be the best (most efficient) choice(?)
From what I've gathered (and please correct me if I'm wrong), most air-entrapment tunnel hull designs don't start "trapping air" and become efficient until about 90-100 kmh. Below these speeds, a shallow-V warped bottom or a monoherdron hull with lift strakes would be a more efficient design for the speeds you're going for I would think. One of these types of hulls would also give you more bouyancy and load capacity for the size of the hull to boot.

Thanks,
Dave

 

[Yellowjacket]

The problem you're going to have is that the weight of the batteries is going to make the load that you're trying to plane high and this makes the boat really inefficient at relatively low planing speeds. Putting a tunnel or some type of air trapping hull would help, but as noted you're not going fast enough to make that very well.

Most tunnel hulls are actually wing in ground effect type of designs, they don't really "trap" air but they let it out the back and the mid section of the hull is a wing. As noted, in order to get these to generate a good bit of lift you need to be going faster than 70kph

You might look into the Hickman sea sled designs since they were very efficient in this speed range as they trapped air rather well.

 

[BlueBell]

Lifepo4 batteries would be a must, cutting your battery weight by 1/3 over lead acid or AGM.
But if you're asking about price, you may be in trouble.
They are 3 - 5 times the price and you're going to need a few depending what kind of run times you're looking for.
20 minutes okay?

 

[gzs]

Thanks for the comments, I really appreciate it.

As for the weight for the electric propulsion system: the lightest 40kW marine DC brushless permanent magnet motor I could find weighs 40 kgs. The battery pack needed for 30-40 minutes range, at 2C discharge rate which is about max speed, calculating with 94% efficiency and never going below 20% SOC is 27 kWh. The most advanced marine lithium batteries have a density of 260Wh/kg (I know, price is extraorbitant). But I'm just thinking, for the moment.. Battery pack weight would be around 110kg. I know a BMS is needed + wires, but let's say motor+battery total weight is around 150kg.

Now, a 60HP outboard weighs around 110kg + fuel tank + fuel... total weight around 150kg aswell.

Range goal for the electric system around 40 minutes. It could work as intended with 2 sets of interchangeable, waterproof battery packs.

 

[gzs]

Regarding the hull design.. it seems that the tunnel hull is out.

Remaining possible choices: hickman, shallow V, monohedron hull with lift strakes, and catamaran. I guess I have to find out which of these hull designs would be optimal regarding weight, stability, and "look".

I've contacted some naval architects, I've sent out rather long emails to describe what I was looking for. I'm really excited to find out the response ratio... since it's a kinda "wild" idea.. Let's just wait and see, in the meantime, any constructive comments are much appreciated!

 

[BlueBell]

Don't forget those lifepo4's do not like shock, or water, and are subject to fire... uncontrollable fire.
So, you're going to need a CO2 system. More cost and weight.
Don't get me wrong, I love the idea but I just went through this process with a small, motorless
race boat that ended up with a 63 pound (25kg) AGM.
The boat only weighs 300 pounds... now!

 

[gzs]

I'm not that concerned about shock. The batteries I have in mind are DNV-GL rated for commercial marine use.
I think that all the manufacturers selling marine lithium batteries did rigorous tests. Torqeedo gives you 4,5 years warranty when you're using their batteries for commercial operations. 9 for private use. With a state of the are battery management and monitoring system you can take good care of the battery pack.

As for water.. all the marine grade batteries come in a waterproof case. They can be submerged in salt water for 30 minutes (1m depth is their test standard) without a problem. Still safety is first, so thank you for pointing out the CO2 system. I'll have a look at the DNV-GL standards for electric boats.

As for fire... this is only a danger if you are using cheap batteries not meant and developed for marine use, or if you underestimate the kWh needed. Batteries tend to overheat according to the discharge rate (C). I know an electric boat equipped with the same manufacturer's batteries that I want to use. At 0,5 C rate there is 0,5 Celsius temperature rise. They don't even need any kind of battery cooling system. A lot depends on the cell. Cylindrical cells (used in most EV car systems) tend to overheat more, pouch cells however are really "cool". Even at 2C rate, especially in the case of really professional marine batteries, overheating is not an issue at 2C. Some marine batteries like Torqeedo (BMW cells) do come with a cooling system and a heat exchanger, that's because of the BMW cells. They are really good cells but the system is too heavy, (cylindrical cells need cooling) but they have a much more effective cooling system than anybody else (coolant is being circulated around each cell, they are connected to cooling aluminium plates aswell). If you are willing to pay 1,5x their price, you can get real pro marine batteries, the best on the market. Lightweight, max energy density, no overheating, very long life span, high efficiency.

It is however a real danger in case of other products... I know a couple of electric jetboard manufacturers.. they are riding the hype wave that is all around their new products. They are making promises and can't deliver. Huge product launch events announced, then cancelled at the last moment because of a fire in the lab... They are so ignorant. For a jetboard that can deliver speed, you need a minimum of 5-8 kW motor. For that you need at least 7-11kWh battery. If you are calculating with only 150Wh/kg, that's a 33kg battery pack, at approx 10500 USD. Then they would have a reliable, good battery, around 5-6000 cycles life span, and no overheating. Instead of this, they are using cylindrical batteries from electric cars and they are using much smaller kWh packs, that means higher discharge rate, overheating like hell, those EV batteries like the 18650 tesla cell or others are not engineered for high discharge rates, especially not without a battery cooling system. Not to speak about the fact that they are not able to manufacture a waterproof case... Long term thinking is really not their strong point... They are using cheap batteries, that are simply not meant for that use, there is overheating, and their life span... 4-500 cycles max. Wouldn't it make sense to use a 2x more expensive battery with 5-6000 cycles life span?

AGM batteries are a different story. They must be in a waterproof compartment with venting because of the possible hydrogen generation in case of a faulty cell or overcharging. With a pretty solid BMS system however they can deliver, obviously AGM's are not my choice because of their weight.

Thanks again reminding me of that CO2 system, I'll make sure to include an automatic fire detecting and extinguishing system if I ever reach the actual planning phase

 

[BlueBell]

Lithiums are very cell dependent.
Quality is paramount.

My AGM is already in it's own water proof container, it came that way.
All 63 pounds of it is being embedded in the foam hull, monocoque style.
Heat and venting won't be an issue as there is only limited solar panel charging and low discharge rates.
I may upgrade to lithium on the first refit.