Ideas for a Fast Efficient Electric Hull

David
The hull could be easily made from ply. Delftship has the ability to enter the density of materials and panel thickness. I suggest not less than 6mm thick ply for that hull. Approximate density for ply is 0.5t/Cu.m. So you can get a weight estimate of the hull very quickly using Delftship. It will not be very heavy. Allow another 20% for joining, bulkheads and surface finishing.

If you make the enclosed basic hull as suggested it has inherent strength with no severe stress raisers other than where you place attachment points. For bulkheads you can use blue polystyrene foam. Since the hull is enclosed there is little risk of hydrocarbons dissolving the foam. You place bulkheads at attachment points.

The value of the flat panel is the ease of build with stiff panels. You can use glass/epoxy on the seams to join the panels. You would find you could make the whole hull out of 3 sheets of 1.2m by 2.4m ply. Join these into a single large sheet with taped joints and then cut out the 4 pieces required for the hull.

The fairing could be done with 3mm or 4mm ply or the fabric over a frame. You can use Delftship to do the weight estimate if you use ply.

If you have a draft constraint then having two props can result in a more efficient outcome than using a single prop. I have worked on props and supports for large diameter props being compliant so they do not get damaged in groundings. You find that a single prop design will cover a wide operating range. They tend to improve efficiency as you go faster.

A simple model can help your understanding of the boat structure. The flat panel method of construction is fast and is not difficult to get good results using ply.

 

Appreciate the advise.

I'm well versed in plywood and epoxy construction -- have built several boats that way. And I've made too many models to recount. This weekend I'll cobble up a crude scale model of this design to better ascertain some of the final particulars.

Perhaps I'll have some pics to post early next week. Sounds like a fun weekend project! Maybe I'll have the time and materials to do a rendition in both ply and skin on frame for comparison. I'm sure the weight difference will be significant, but I'm curious to how stiff the Dacron version might be over 24 feet. Scale models will certainly help in that regard.

Overall, I don't feel draft will be a concern. I've even tested numbers in JavaProp up to 1 meter in diameter. Although, for the percentage or two improvement, such a large prop seems not to have such significant advantages. I also don't see much difference in big changes in RPMs.

Enjoy the weekend everyone! Hope to have some decent photos to post for you all soon,

David

 

Farewell, Good Luck, We Will Miss You, Rick

Wow....

I'm devastated by the news that Rick has decided to leave the forum....

His insights and knowledge and experience were the primary reasons I found these efficient boat threads so very interesting and worthwhile. His words of advice and encouragement were most deeply respected by me, in this thread, as well as all the others I've followed on this forum.

Let me say that this is a forum -- open to all -- a place to discuss and exchange ideas and dreams and goals and lessons learned. Though debate might occur in the process, it should always be centered around the promotion and advancement of boating -- as a source of passion, and joy, and achievement by (and for) us all. Rick always conveyed and conducted himself in an honorable and dignified manner. His patience and focus and generosity were readily apparent. He has helped numerous aspiring boatbuilders over the years -- and did so without conceit, without self-promotion or with no obnoxious grand-standing.

I feel he was a friend... and I regret I've never met him.

I have nothing but respect and appreciation for all he has contributed so freely to us all...

I know that he will be missed tremendously, and I feel we have lost a truly invaluable source of wisdom and inspiration and leadership.

I am holding onto my hopes that he shall return soon.

Naturally, I wish him nothing but success in all his endeavors.

David

 

Just too many time consuming side distractions for Rick on this list, I think.

You can reach Rick at the email listed on his page:

http://www.rickwill.bigpondhosting.com/

He answers questions by email and is presently helping several people with projects.

He may be posting soon on his new V15 boat at the human powered bikelist boat forum:

http://bikelist.org/mailman/listinfo/hpv-boats

Hope this helps.

Porta

 

Do we have an update?

I just stumbled on this thread. I was wondering if a planing hull could be designed to meet the same objectives. Rick mentioned a while ago that a lift to drag of 8 was achievable which would make your drag around 50-60 lbs.

The hull design might be more conventional and allow for a multipurpose craft. That 35 mile requirement would require a siginificant battery but you have already commited to LiFePo4.

I have been working on a spreadsheet for several years with a planing design but don't fully understand all the hydrodynamics. Everytime I learn something new, I try to incorporate the information into the calculations. I always thought 20mph for 1+ hours was a credible goal. You would need almost double this.

The B&S etek motor seems to have the best power/weight, efficiancy and resonable cost. This motor is rated for 6-8 hp continuous and only weighs 22 lbs. It can produce much more power for short bursts. The benefit is no supplemental cooling is required. I'm sure a prop could be selected to direct drive the motor but reduction might be required for peak system efficiancy. Frequent brush replacement(cheap and easy) seems to be the only downfall.

I am sure someone here could come up with a resonable hull (if not commercially availble) to meet the requirements. If the 'race' was a little shorter, I don't think you could beat a light planing hull.

Anyone ever consider using the motor to drive a fan (air) rather than push water? I recall seeing this approach used on a human powered foil setting the world record. Somewhere on the internet there is a video of an electric boat race with the winner using this method to destroy the competition.

For about $500 you can buy a used jon boat and outboard motor around here. Add around $2500 in an electric powerhead, battery, controller and other parts and you could go fast. But for how long? The key must lie in that lift to drag ratio.

Joe

 

Eteks have been out of production for a few years now, although they do occasionally come up for sale secondhand. A reasonably priced equivalent to the B&S Etek is the Mars ME0708, although I'd tend to lean towards the bigger ME0709, as it has a lower Kv and so needs a lower ratio reduction drive.

The major snag with an electric planing hull is the law of diminishing returns when trying to get decent range. As you add weight (from bigger batteries) the power needed increases, so reducing range. All told, it only really makes sense to use a displacement design for electric power, at least if you need an endurance of more than an hour or two.

Jeremy

 

This is false.

A unirig is faster than a sloop with the same sail area, hence all A class and C class catamarans are unirigs, not sloops. There are no sailplanes with double wings in any orientation. There are no biplane jetliners.

 

Clearly, there are many, many possibilities. In most technology driven endeavors, such as this electric boat race, its execution that beats highly individualistic (idiosyncratic) design.

Therefore, I suggest you take an approach that takes advantage of a design-and-built cycle, where you start with something simple and pretty good, and then evolve from there. Use science, rather than trying to invent in your head and spreadsheets some ultimate radical concept from the beginning.

For example:
Buy a used, beat up rowing shell off of craigslist.
Buy an electric motor, and some batteries, and make some simple prop shaft, and then just use a large model airplane propellor.

This gets you having fun quickly, low cost, low risk, and nothing is really constrained.

Then measure what you've got. Really get good data experimentally: e.g., use science to advance your knowledge.

Then, come up with a hypothesis, such as "adding aero wings will reduce drag" and try it, fitting some simple wings -- they don't need to be optimal -- and see if you get an advantage or not.

Repeat with each idea.

The above approach is science. Nearly all advances are due to science.

The approach being taken in this topic is Socratic -- lots of arguing, postings of opinions, but nothing measurable. As we know, the Socratic principle is far less powerful than science.

 

I agree 100%.

In a Solar Race for boats held in Canberra Australia a few years ago, a retired navy commander won one of the classes in an old dinghy. All he did was to fill it with the maximum allowable weight of lead batteries (low down to maximise stability), and convert the transom stern to a canoe stern.
Simple and effective!

All the best,
Leo.