"Twilight" an electric boat

It has been suggested I start a new thread.

Here's the idea:

Design and build a "stitch and glue" boat to be powered by an electric motor.

The boat is to be used for quiet, probably evening, cruises on fresh water lakes, hence its name; "Twilight."

The boat will usually carry two adults, each in a comfortable seated position. Passengers will face each other.

The boat will fold in half, or possibly come apart in two pieces, for storage and transport.

Launching will usually be done from a pier.

To exploit "hull speed" advantages, the LWL will be about 20 ft.

Maximum width will be about 30 inches, less if practical.

Cockpit will be 20 inches wide at seat back -- same as my office chair.

Batteries to power the boat will be low in the boat, keeping CG low.

Consider flooding fore and aft sections of box keel.

Current (7/27/08) model shows 10 inch high sides on hull, plus 10 inch deep box keel. Can sides be lower? Maybe 8 inches?

Decks will be crowned, if possible. This might inhibit folding, and might suggest the boat come apart in two pieces instead of folding.

Boat will have a "box keel," wide enough for comfortable placement of passenger's feet -- and to house batteries low in the boat. Current (7/27/08) model shows depth of box about 10 inches.

Boat to be powered with a 40-pound thrust Minn Kota trolling motor.

Not sure yet if motor will steer boat, or if a rudder will be added. Experience shows a rudder system might provide for sturdier motor mount.

Boat will have white hull and "natural" decks, and of course, provisions to fly ensign at stern and owner's burgee at bow.

Storage for a wine bottle and a rack for two wine glasses will be provided.

Photos of a "concept model" have been posted on this website.

Updates will be posted both here and at

www.grantmaclaren.com/twilight

I've built a few small boats, but this one will be of my own design and concept (I think!) I'm looking forward to comments and advice.
Thanks!

 

The trolling motor will steer just fine. I had a big canoe I made a centre hole in it with a little transom where the trolling motor mounted on. It worked very well, the trolling motor was comfortable to steer (better than side-mount) and easy to lift in the shallows.

There was only drawback on the canoe I had. The bottom was smooth, so when you turn it side slipped a bit. Having a couple of small strips on the bottom would solve that. Mini-keels.

I would suggest maybe two batteries (and oars). The 24V trolling motors draws less current than the 12V ones, so the batteries last somewhat longer.

Oh yes, it is not always much fun when these things roll over. I would be carefull not to make it too narrow.

You can shape the hull so that it is a bit wider outside the water for less drag, but when it rolls it would resist that. I would say that 700mm is ok for a minimum for the in the water part. I like the length... 6m is going to be ok.

Could I suggest a little 'table' between you... hold the bottle and the glasses for a hands-free.

A foot control steering could also be very comfy. Paddle left paddle right.

 

Hi Fanie,

Here's a video of our first electric boat's steering:

http://www.youtube.com/watch?v=qu4xPA-z42o

Intend to use two 6-volt deep cycle batteries as used in golf carts.

Don't want to think about roll-overs, but plan to use "dry" batteries just in case.

Love your table idea!

We like our steering. Push/pull rod with friction hold.
It's very simple and works great.

Worked on displacemnt calculations tonight. There MUST be
some changes made:

www.grantmaclaren.com/twilight/displacement.html

 

if its only an occasional user u might think of throwing a few solar panels on it to help keep it charged when your out earning your keep

I was kicking round the idea of using twin electrics instead of diesel
In a live aboard sailer Ive been planning forever
( I hate the smell of diesel )
and power them with an alcohol fueled generator and a battery back up with solar assist
( I love the smell of alcohol )
now granted the solar assist wont be much
but in a pinch it might keep the lights on

I like the idea though
it could be that a small generator would still afford you that piece and quiet you are after and still augment the battery pack
when needed

B

 

Solars make a big difference in how your trolling motor holds out. Used to have a 2A jobby on my previous boat and it does help. Unfortunately solars are very unefficient and expensive. But then they do work every sunny day

You can't go and waste alcohol on motors, good gried B, what kind of a person are you ?

 

Grant
What is the capacity of the batteries you plan to use?

How long would you want to cruise at design speed on any one charge?

If you give me these conditions I will provide an optimised hard chine hull for the box keel. It will be based on your displacement figure, 90% battery discharge at 60% overall propulsion efficiency. Would be possible to do better than this but not with a trolling motor. Going slower than design will increase the range.

I am thinking the faux-tri concept that ASM has proposed is the best option here. There are a few variants around now. The last one was this 20ft canoe:
http://boatdesign.net/forums/attachment.php?attachmentid=22533&d=1213778526
It is low drag because the main hull is so narrow. This was a 5-minute exercise so is rough around the edges but gives you an idea.

The advantage of the fauux-tri is that you can go beamier for stability without suffering increased drag. It also is an inherently strong hull for carrying concentrated loads like batteries.

For the folding requirement I think you would be better off having a solid middle section of say 10ft with two smaller sealed fore and aft sections. The stabilisers for the box keel would be part of the central portion.

Rick W.

 

well ya know Im just thinkin luck favors the prepared
if its sunny
Im drinkin
if its shady
Im paddling and drinkin
if Im dead drunk
I can breath into the gas tank

what kinda guy do you think I am

B

 

Grant
The most important part of the attached is the underwater portion of the central hull. I looked at the Minn Kota 40lb and saw that it was rated at 42A. So taking the 12V battery and allowing a bit I am working on it requiring 480W. Allowing for all the inefficiencies I am working on 280W for the hull.

So the constraints I tested were square chine, 260kg displacement and design speed of 3.5m/s. As it turned out it will take a bit more than 280W to do 3.5m/s. The target is hence 6.7 knots. The Minn Kota may not be suitably propped to do this but it should go close.

You can see the main hull is very simple. Almost flat rocker. I have left a little V in the bottom but you will not lose anything to make it flat. Forcing a slight curve prevents it from pumping.

For the boat, I have thrown together a concept with central hull and two 100mm wide outer hulls set up to just kiss the water at design draft. The overall beam is 1m. This will be a very stable platform. You could make like a 3-sided seat so you can face either side as well. I have not done the stability anaysis but I expect two people could sit on one side without tipping it.

The bow and stern sections could be produced as sealed spaces. Possibly hinged at the deck to fold into the main cockpit or be easily detached. I expect they could be stowed inside the cockpit for storing and transport.

Anyhow this is a concept that does not compromise much in performance for stability and load carrying capacity. I think it requires 11 surfaces so is not all that complex to build. It is about 30 minutes work for me to draw so not too much thought.

If you like the idea then you should build a small model just to see how it looks. Cardboard would do.

ASM, of this list, is in the process of building a large model of a solar powered version of a larger boat using the same concept. He has not updated for a while but you could find out how he is going.

The FT in the file name is for faux-tri to distinguish it from what you may eventually arrive at.

At 5kts it should draw about 16A. So I expect it will have an impressive range on 120lb of batteries.

Rick W.

 

Hope I'm using this "Quick Reply" feature in the correct way. (I'm a newbie to boatdesign.net.) Anyway, my experience with my first little electric boat tell me battery life will not be a problem with this new boat. I've managed nice little cruises with a 12 v. Wal-Mart car battery with a less efficient motor than the new Minn-Kota. A solar panel would be a nice talking point, but doubt if I'd notice any difference in real performance. Thanks to all, esp. Rick for the tri-hull concept dwg.

Have you seen my displacemnt "study?" It show me two things.
1) The boat as I've designed it would bob like a cork and maybe turn over if at anchor.
and
2) I'm no marine architect!

I'm now thinking about building the boat in three sections rather than two.

I'l be posting more later today or tomorrow. Later today I'm taking the little gren boat to a nearby lake, meeting the local kayak club for a "show and tell."

Thanks all!

 

Grant
I looked at a hard chine monohull having reasonable stability to compare with the FT above.

For the same power it is 0.5 knot slower. So not a huge compromise. It would be easier to build. Just 5 main panels.

The KMT is 490mm and beam is 760mm. It would be very similar to what you have drawn in the original post. Loaded draft is 90mm.

I still think you would be better off making 3 bits, leaving the central portion intact. This needs to be a strong structure to support 120lb of batteries and two people.

Rick

 

Rick,

Thanks.

I'll try to find more RE: KMT. Are there photos on
this site?

I've also been thinking of cutting my little gree boat in
half (after installing "transoms") and using those two
pieces for the two end bits.

See "little green boat" at

www.grantmaclaren.com/zac

I've also made the "concept model" waterproof
and having two fellows look at it floating.
Doubt if we learn much. i have a bit of
confidence in my calculations.

-=Grant=-

 

Rick,
I've added a retouched photo to original post.
It is me in my 14' "little green boat" (below) and the same
photo retouched to show a 20' version.
(i.e., add the ends of the original boat to a new center section
with box keel for batteries and feet.)
-=Grant=-

 

the box keel sounds great

one additional thought
a simple pond pump under the batteries could end up handy in a pinch
might save unloading those batteries any more than absolutely necessary
B

 

Grant
I am getting the impression you do not like the FT idea. You want a more conventional looking boat just a bit bigger than you have,

How do you plan to transport?

Also what is the size constraint on a single hull component for the hull.

If you are going to do a nice job I think you would find problems matching to the old hull.

KMT means transverse metacentric height above the keel. You need to have your CoG lower than this for initial stability. I would think your current boat has KMT around 400mm so possibly on the twitchy side to stand in.

I am not 100% certain of the box keel idea you have but if it is just under the feet, therefore quite short, I think it will impact badly on performance. If you are keen on the box keel idea then the FT idea is the best variation of that as it maximises the waterline length. A shorter box keel will create a nasty protrusion making for problems with draft and transport compared with a nice straight keel line.

Rick W

 

Hi Grant, I like the idea of a quiet canoe ride facing my girlfriend, chatting and eating crackers and stuff....very romantic and fun.
I would be more concerned about stability though. If you are not using paddles, and there are two people making separate movements, and you are momentarily distracted, then the chance of capsize is quite high compared to normal canoeing.
Just a thought