Four Candles 2012

[Alan]

Last year, Four Candles was my entry in the cordless canoe challenge and I used three drills driving three propellers in an old racing kayak hull. It was so unstable that I had ballast in the form of three lead ducks (the weights used to hold down splines when lofting a curve) glued in the bottom of the hull. This year I am leaving out the weights and fitting outrigger stabilisers instead. Each stabiliser looks like the hull of a Hobie cat and is made from 4mm interior ply plus odds and ends of wood which I had available.



The stringers are western red cedar greenhouse glazing strips. The frames, transom and hard points are obeche which was once office shelving. The keels were going to be softwood but I cut the only good bit too short so they are now teak.



I made a real hash of fitting sides to the rest of the structure and had to spend hours filling and planing to hide the worst of my handywork. Partly, this was due to the design. Each deck is 6" wide and 8 ft. long and cut from the middle of a 2 ft. X 8 ft. sheet with the sides cut from each remainder. The deck cut was also the sheer cut of the sides which left no extra wood for errors, hence extra work involved in making good.



The above picture shows as far as I have got today.

This year I'll be using two drills and two propellers. The drills will have to stay in one piece this year due to a new rule; my two 'wing' motors last year were separated from their battery/speed controller and placed outside the hull. They were already separated due to use in a previous project - a motorized twin buggy pushchair.

[Paul H (admin)]

I find fork handles really useful, they have a lovely curve just right for a tiller (not the Hun)

-Paul

[Jeremy]

It's amazing how much stability oars or paddles provide, isn't it?  The trimaran solution sounds good to me, especially as pretty much all the fast pedal powered boats seem to have settled on this form as being the most efficient.  

I don't know if you've been following Rick Willoughby and the development of his pedal boats over the last few years, but his current boat design, with two amas that barely touch the water, is remarkably fast.  It bodes well for your boat this year.

[Alan]

Paul, funny but true!

Jeremy, yep; I have noticed that a rowing boat calms down considerably in roll if you leave the oars sticking out. I have seen a lot of Rick's posts and I can imagine an electric powered thin stabilised monohull making a great river cruiser for two or three people.

Nothing done today except another coat of paint.

[Alan]

Help!
I'm using DIY type materials and have applied a coat of Wickes gloss over Dulux undercoat and it looks terrible! I know it's only the CCC but it just looks too bad to be out in public. The paint is patchy and runny even though it is non-drip and there are brush end marks even though I used an expensive (Wickes) brush.
What should i do - rub it down and apply a proper paint? Half the problem is that Wickes is 5 minutes down the road and I would probably have to order real paint online.

[Jeremy]

Put another coat on with a roller, so it looks truly lumpy, and then claim that it reduces viscous drag by creating micro vortices at the surface, like shark skin........................

[BrianP]

then it will go as fast as this http://vimeo.com/11699194

[Port-Na-Storm]

That's instantly recognisable as the Itchin Bridge in the middle of Southampton.

This video endurance test was filmed at Woodmill, just up the river from the Vulnerable and Ancient St Deny's Sailing and Rowing Club, and right next to Southampton University's Boat Club.
Although we often admire the ladies eights zooming up and down i've never seen this boat out on the water.
 The blue and white launch in the background belongs to our Vice President Dick Bampton, its moored at the foot of his garden, lucky sod.

[Timmo]

I've used Wickes gloss around the house and it wasn't as bad as that. Has it been frozen or damaged in some other way? Maybe you can take it back and get it replaced (and demand free emery paper for the rubbing down!) If the 'make a virtue of the rough surface,' options don't appeal then it certainly sounds like a rub down job but I see no reason why Wickes paint shouldn't do a good enough job provided the paint is OK to start with. Perhaps worth trying a liquid gloss, at least you can give that a good mix before you apply it.

Tim.

On 3 Apr 2012, at 16:50, Alan [via UK HBBR Forum] wrote:

> Help!
> I'm using DIY type materials and have applied a coat of Wickes gloss over Dulux undercoat and it looks terrible! I know it's only the CCC but it just looks too bad to be out in public. The paint is patchy and runny even though it is non-drip.

[Port-Na-Storm]

Alan, back to the problem in hand.

I have happily used undercoats and top coats from different manufacturers without any problems.

Polythene Pam is painted with Crown water-based paint, splashed on with a roller over probably Dulux undercoat and she doesn't look too bad after 70 miles down the Thames.

I found the trouble with anything that says non-drip or quick drying, is getting an even spread before it starts to dry. Rolling helps, tip off with a dry brush to lose the stipple effect. However the side door to my garage is testimony of what happens when you try it in near freezing temperatures. Its not a pretty sight!

If you want "proper" paint go for Weather Shield or Sandtex which you should find in the next isle at Wicks, or if not down the road at B&Q.  Katie Beardie is getting a combination of Weather Shield Hull and Santex Deck, due mainly to colour choice.

[Jeremy]

BrianP wrote

then it will go as fast as this http://vimeo.com/11699194

Whilst an admirable endeavour, I'm a bit surprised at this university project by boat design students.  They lavished enormous amounts of money on all that carbon fibre (looking at the time-lapse build video it was massively over-engineered), did an average sort or job on the hull design, but completely and totally failed to get the prop and drive system optimised.  

Using two monster Lynch motors they should have had a lot more performance than they seemed to have from those videos.   The electric speed boat "An Stradag" managed over 50 mph with four older (and far less powerful) Lynch motors back in 1989.  Since then "An Stradag" has been refurbished, equipped with four newer Lynch motors and has done around 70 mph.

Had they used a better prop design they could have probably doubled their performance on that much power, maybe more.  As marine engineering students I'd have liked to have seen a bit more effort put in to the design and less money wasted on a massively over-constructed foam sandwich hull.

[Alan]

Well, I think I'll try non non-drip paint of a reputable make then, after rubbing down. If it doesn't work I can at least get on with another part of the build while the paint is hardening prior to rubbing down again.

I thought that little boat was a CCC contender! If it really has two lynch motors then it's a dog. At least they genuinely built it themselves; in my experience as a university workshop technician the phrase "built by the students" usually means built by the technicians. I think that using motors, ESCs and batteries from the radio control hobby it would be possible for HBBs to built a boat that would take the record from An Stradag.

[Jeremy]

Alan wrote

 I think that using motors, ESCs and batteries from the radio control hobby it would be possible for HBBs to built a boat that would take the record from An Stradag.

Absolutely.  I have a couple of big outrunners (specially built 80-100s good for around 7 kW each continuous) that would almost certainly get a light boat, with a LiPo battery pack, up to 50 mph plus for a short run.  An Stradag was pretty heavy, and although she used a pretty good prop and hull design a lighter boat with less power and hydrofoils would almost certainly be quicker.

Model aircraft technology is great, but their ESCs aren't that robust when presented with high torque loads at low rpm, as they are pretty fragile at part load, in my experience.  I've designed and built a few BLDC controllers now, and have gradually worked through the various failure modes.  The nicest design I've seen so far is a field oriented control design, using a dsPIC, that has the potential to build a pretty bomb-proof controller with full and accurate timing compensation for varying torque and rpm.

[Alan]

Yes, I was thinking of the Turnigy 80-100s. I've built one into an outboard motor for the little grp dinghy that I take on holiday once a year. It draws about 750w on freshly charged 24v leisure batteries which is a perfect match for the boat but all parts are sized to handle a 36v supply. I don't think I would believe the manufacturers claim for power handling though. I think Jeremy and probably many other HBBs would be interested in this o/b motor so I'll start another thread soon, with some pictures.
On youtube there is a man who has claimed an unofficial water speed record of 98mph using a hydroplane powered by a fork lift motor. He caned the living daylights out of the motor, drawing about 400A from his batteries if I remember correctly. PM BLDC might be lighter and more efficient maybe?

[Jeremy]

My 80-100s aren't the Turnigy ones from Hobby City, they are the Colossus ones that come from the same Chinese factory, but via a firm in Croatia that has them specially made.  They are properly wound with tighter windings, fitted with NSK bearings and Hall sensors so they can run from a sensored controller and have a lower kV of 75, which means a higher voltage can be used to get more power at a safe rpm with lower stator current.  They are OK for around 7 kW peak, maybe 4 or 5 kW continuous, unlike the Turnigy ones that start to cook at around 2 kW or so continuous.

[Alan]

Jeremy, now I understand about the motors; do you have a project in mind for them?
Regarding ESCs blowing up, isn't this usually on electric cycles when it is the inertia of the whole machine causing a long term over current condition from a standing start, while the motor is turning slowly?

[Jeremy]

The plan is to use two of these motors to replace the big and heavy Mars electric brushed motor I currently have in my Yamaha project bike (see pic below).  The Mars motor weighs around 14 kg, and takes up a lot of space in the frame, so the plan is to fit two of the Colossus motors to a common shaft and then belt drive a jack shaft that will drive the rear wheel via the chain, so that I can get the right sort of overall reduction ratio.


The problem with RC ESCs is that the vast majority of them have no form of current limiting at all, the exceptions being the very expensive high performance ones, like those from Castle Creations, for example.  This is OK in a model aircraft, where there will be no significant torque, and hence current, at part throttle, but pretty much any application where a load could be presented to the motor at anything other than full power tends to cause problems.

[Alan]

I bought some more paint for Four Candles stabilisers and used it to paint up to masking tape around the varnished deck, but the paint crept, or flooded under the tape so I have temporarily given up trying to achieve a respectable finish, but here they are:

Since this I've been working on the motor mounts. I am going to use big aero propellers in air for several reasons:
No weed problems
I got a good power match to my drills
I just like propellers

The last picture shows one of the drills with its prop fitted temporarily. You can see a little red connector on wires coming out of the handle and whizzing back in again. I can separate these and insert a meter which measures current and battery voltage drop and so on and got some surprising numbers. Not sure if I want to share them though as I want to have an edge...

[Jeremy]

Looks good, Alan.  I like the idea of an airboat, but then I would, this Scrapheap creation was my go at building one a few years ago:

 

I did think of making an airboat this year, as I have a spare 70" carbon fibre two blade prop sitting in the workshop, but decided the safety and stability issues of spinning something like that were more than I wanted to deal with.  Your two prop solution looks sound though, have you seen this video of the electric bike with a similar propulsion system?

[Alan]

Jeremy, can you just stop building things and give me a chance to catch up!

I have seen the youtube video of your airboat, it's quite an achievement. As for the CCC, I suppose you could have geared your big carbon prop to a couple of drills but your various monohulls might not be suitable platforms. but it would be very efficient and probably very quiet. Since deciding to make an airboat I have been toying with the idea that a cat or tri airboat (not like the overpowered Florida types) might be a nice small eco boat and dammit, you already have the makings of one with your propeller and Mars motor from the motorcycle conversion.

I hadn't seen that particular propeller bike before, which looks almost sensible, but I have seen a similar insanely fast single prop version. In the garage right now is my own propeller bike: a found bicycle, a B and S 2hp engine mounted on a frame made from 316 stainless scrap tubing and a hand carved prop. It can be started while seated if the engine is warm and I actually rode it on the road one firework night when no one could hear it! Can't lay my hands on a picture right now but here is the prop and my secret numbers-

The props I am using on Four Candles take less power because they are a much better profile but I can't get an accurate rpm reading so far, probably because of interference with the tach light.

The irony of retiring early and having plenty of spare time is that I no longer have access to a wonderful machine shop so have to work out alternative ways of doing things. The big props have so much inertia that there is a chance of destroying the drill brake or gearbox or loosening the prop, so to get round this I had to make a one way drive as we are not allowed to modify the drills. I got that all working today but I'll save details for the next post, which will be in a few days time.