Electric 15 - great raid/day boat?

[Paul H (admin)]

There are various Electric 15 boat designs, all with a fine entry and minimal drag for electric drive; in turn that makes them good for rowing and the mythical river sailing.

Selway Fisher:
http://www.selway-fisher.com/Mcup16.htm#SKIFF

Hird Island:
http://www.dhylanboats.com/hird_island_plans.html

Chesapeake:
http://cmdboats.com/electricboats_15skiff.htm?cart_id=62328d62ff97a1179d6b7e5fc7a1709b

Most have a 4' beam to be slippery, the 4'10" beam version would be more stable with sail around Chichester Harbour. But if the weather is rough at Cobnor we just jump into Wayne's Ever Hopeful don't we?

What do you think of the designs? Perfect inland and in harbours?

-Paul

[Jeremy]

My take on this would be that you must have the transom clear of the water at all times (to reduce drag) and that the beam need not be great if the boat has a flat bottom.  There is a very tiny trade off because the flat bottom increases the wetted area (and so drag) slightly, but at speeds below about 5kts this isn't really an issue.  Besides, a flat bottom makes for more practical space inside and a slightly easier build.  

The really big problem is draft and the pesky big diameter prop needed on an electric boat (for efficiency).  This is something that has seriously vexed me, to the point of having made at least three major alterations to my Winsome hull in order to overcome the problem neatly.

My (hopefully) final solution is a very narrow retractable sail drive type leg that can swing up inside something little wider than a centreboard case (in fact it could easily be integrated into a centreboard if you wanted a motor sailer and could cope with the extra drag from a rudder).  The key to making this work was to find a way to always stop the (2 bladed) prop in the vertical position, so it would fit up the slot.  I have a working prototype that uses an optical sensor to determine when the prop is vertical, together with a bit of circuitry that slows the motor down to a very low speed when the throttle is closed, until the prop vertical sensor is detected when it then stops dead.  This reliably stops the prop vertically every time, and a relay then closes to short the motor windings, acting as a pretty effective prop lock (the relay is a normally closed one).

This means that whenever you shut the throttle the motor is in a position to be tilted up into the case, to reduce the draft to something that's less of an embarrassment in most of the sort of places I'd want to launch or moor up.

I do quite like the idea of just adding a centreboard drive to a small sailing skiff.  All this would need is a slightly thicker centreboard to allow for a double universal type right angle (or near-right angle) drive, with the motor being fitted in a box on top of the centreboard.

[Chris Waite]

Paulie

Isn't this just a continuation of the 'Perfect River Raid Boat' discussion?

http://uk-hbbr-forum.967333.n3.nabble.com/The-Perfect-River-Raid-Boat-PRRB-td3087587.html

These all seem to be narrow flat bottom boats, one of which has a slight 'V' to the after sections of the floor.  (Sorry, just noticed one of them bothers to have a 'V' bottom.  So?)   Again, I insist there are ways to improve the hydrodynamic flow over the forward sections of flat bottom boats by curling the floor up to meet the stem; just like that, no more bumping into waves.  

Otherwise choose a length and beam that meets your requirements and jump in.  They're all the same boat, just pushed, pulled and squeezed here and there.  Then choose if you want a deck or not, a rig or not, or whatever other propulsive device your little heart desires.

Electricity is fine.  However it also occurs to me having seen Joe's pedal powered unit -

http://uk-hbbr-forum.967333.n3.nabble.com/Pedal-powered-canoes-td4026756i20.html

 ....along with Jeremy's ideas for centring props would be a useful consideration.  I even wondered if it would be possible to do away with the expensive looking gear-box in favour of a cheap con-rod, which is what I thought the first submarine had, though looking through the images, it seems it was hand cranked.

The question then is, could you buy a propeller for rotating at the same speed as is suitable for stubby little sailor's legs to pedal?  Oh, and why can't you use a set of suitably proportioned pulleys at right-angles and a drive belt?

Friction, I s'pose

CW

[Paul H (admin)]

Thanks chaps for the feedback. I was searching around for a light weight day boat, and the Electric 15 caught my passion for electric drive to obsolete combustion engines. 

Slight detour, a motor boater at the HBBR start said his narrow boat used to use one litre of diesel per mile!...that's shocking and 10x worse than a modern diesel car which is starting to look out of date with this year's hybrid diesel / electric cars giving potentially another 2x efficiency. 

Chris every boat is a comprise, the electric bows are designed for flatter water and lowest possible drag to length ratio.

Clearly some tweaking is needed for Chichester Harbour. 

Cheers

Paul

Sent from Samsung Mobile

[Jeremy]

Chris W,

The snag with pedal power is that for direct drive (say at around 60 to 80 rpm, which is fast as most wish to pedal) you need a prop that's around 4ft in diameter.

By increasing the rpm up to around 400 or so you can reduce the prop diameter to around 12", which makes things more manageable, in practical terms.  However, even getting a 1 to 7 ratio between pedals and prop can be demanding, as the largest bike chain wheel is around 60t, and the smallest practical rear sprocket is around 17t or 18t.  This inevitably means that two stages of speed increase are required, plus a method to turn the drive through 90 degrees.

This can be done, using something like a 1 to 2 right angle gearbox coupled to a bike chain drive at around 1 to 3.5 or so, but it starts to get a bit complex.

There is an alternative, using smaller chains than bikes use (typically 6mm pitch chain), with a twisted chain drive.  These use a large chain wheel in a centreboard like case, driven by pedals, with the chain twisted through 90 degrees and driving a very small sprocket (10 to 12 t) at the bottom.  The casing is made of hollow alloy, steel or even composite, and filled with oil, so sealed, with just the prop shaft sticking out the back and the pedals out of the sides at the top.  Such a unit can either be made to pivot or slide up and down a centreboard type case.

[BrianP]

I would say of the three you listed Doug Hylan's design is by far the nicest. He designs some lovely boats and she fits the brief. S&T, not too wide and only 9" draft with the electric motor in place which is protected by the rudder, it's self a nice shallow design.

She already has a rig designed and a hull designed to take that sail area.

Looking at where he is sitting in electric mode, she might take a Mirage Drive.

She's a cracker, get on and build her!

Study plans here http://www.dhylanboats.com/plans/hird_island_study_plans.pdf

Brian

[3styler]

I agree, I prefer Doug's one as well......The Selway fisher looses on waterline length, whilst the Chesepeake is too flat at the back and would be draggy and hard to handle....

I am liking the design space, For efficiency and load carrying capacity you can beat waterline length and 15' is of course the limit of two sheets of plywood scarfed together.......I've got something similar on the drawing board (technically ProEngineer CAD) at the moment which I will share when it is finished...It is a lengthened version of a 10' nesting dinghy I was going to make for the Makita CCC but never committed to....

Interestingly the hull shape for Doug's seems like a larger version of this.....

Richard-Woods-10-Row-Sail-Dinghy-Duo

so borrowing from this concept if you guys are worried about taking would slender river craft somewhere a bit choppy why not give her some extra flotation.......:)

Cheersm

Simon.

[Chris Waite]

What, Paulie

What is an 'electric bow'?

I have an inkling, or Premise, that'd go with Jeremy's waterline length and smidginal flat-bottom-drag-difference at low speeds; along with Simon's additional buoyancy for the likes of the lumps in Chichester Harbour.  I also take due note of J's four foot propeller - back to the midnight drawing board on that one.

Apart from that, there's Octavia who's already tried a yuloh -



....and she's not got much on at the moment; she'd be happy to take your electric outboard on a bracket, as long as it leaves no permanent scars....

Forfeit a forefoot?

Christo

[Alan]

I thought my Welsford Joansa was a great shape for an electric boat, but narrow on the waterline so very twitchy for nervous crew. Also it was difficult to install lead batteries due to the arrangement of long (fore and aft) thwart and buoyancy tanks. On the other hand my lead batteries have a RD of 2.3 which makes for pretty good ballast in a very narrow boat.
Here is a pic of the boat at almost full speed from a standing start just out of shot. 600w through a standard outboard prop and not properly trimmed. I think almost anything long and thin will do; if it wobbles add another battery for ballast.

[simplesimon]

A fore-and-aft seat is almost crying out to be turned into a battery box.
S

[Alan]

A fore-and-aft seat is almost crying out to be turned into a battery box.
S

After 3 weeks I finally get it. My description was poor - the thwart is a piece of ply about 24" in it's fore-and-aft direction, spanning the width of the boat and only 6" from the cockpit sole. So I had to tie each battery (with string) in front of and behind this thwart.

[simplesimon]

Yes, a bit low for hiding batteries under.

Simon