6ft Fast Electric Mono

[Amp User]

I want to build a 6ft shallow V mono out of door skins and square stock. I plan on using a outrunner electric 3phase motor, its output is around 2800w or 3.7hp max amps 90. I would like to buy a small surface prop around 5in in dia. I hope to run the prop at 3000rpm/2100w/65amps/34v at cruise speeds of 16mph whats that in knots?

What props are out there?????
I have had bad luck finding anything suitable.

Ther are some brass and steel hobby props up to 130mm or 5in roughly. They are submerged props that would require cutting rakeing cupping. I dont mind low thrust and long legs to get the boat up to plane and max speed. I do want a high lift surface running boat like a Cracker Box. Its going tobe a one seater with tight room for two when needed. I would have to keep the loads down with two but hope there is enough mid range thrust to low plane the hual at 70% throttle with two people aboard.
What do you guys think is this possible with a 3.7hp electric motor.:P I plan to keep the hual very light no glass just fill and paint and epoxy clear coat. My guess the boat will be 50pounds bare. And a mere 30pounds extra giver or take a few using a 782g brushless motor and li Ion cells. So 80 pound plus me a 190pound person + another 10 pounds in rudder/prop/stuffing box/axle/controls. So all up weight goal is 275 to 290pounds. The hual will be 6'X3.5''

Any thoughts on this please feel free.

[Amp User]

I have a Hunter ceiling fan motor that is going tobe coverted into a 3phase brushless motor, this one has enough iron to produce an easy 4000w at 70A 60V system. Im shooting for a 100k/V and will terminate in wye with 4 strands of 19g mag wire. I need a custom bell with 40X15x5 N50 neo's. Im going to use lipoly cells in a aluminum protection box with a vent and blower. The vent tube will be off to the side and pointing down towards the water.
The packs I plan to use can put out 100A for approx 45mins. The packs will look like these.:P

[Amp User]

Each cell is rated at 150 amps, so the 14S8P pack could in theory put out 1200 amps at about 46 volts - 55,200 watts or 74hp:cool: I would imagine its now possible to achieve safe and fast running on the water with long duration possible. If I had a choice a all carbon mono perhaps 5.5X 3.8 with 25hp 1.5hr full throttle duration.

I found some 7.4v 5000mah (30C 150amp) lipo's for 126.oo per pack, I take 18cells to produce 22v 15000mah bursts to 1350A 29700w 40hp . I should run it at 150A for 1.3hrs / 4.5hp should get me around 18 mph. I will run for short sprints for fun at times drawing 300A for 9hp. and near 30mph.

[marshmat]

16 mph = 13.90362 kts
You seem to know your electrics pretty well. I would advise caution with the LiPos, though; they're amazingly powerful batteries but also amazingly easy to blow up or permanently destroy. Are you designing your own BPS or buying a stock unit? Each cell may be rated at 150 A, but trust me, you don't want to let them do that ;)
Make sure the intake side of the batt cooling is well protected from water and debris. Inside the boat's forepeak would strike me as a good place for the inlet filter.
I'm not sure about the feasibility of the propeller you describe. Surface props work best when they're big, trimmable, and going 50-plus mph. A small fixed one would be tricky to get going. The huge torque of a BLDC motor would, imho, be better used to turn a submerged prop designed for your speed range.
What are you using as a motor controller? This is often an afterthought in such projects and should be considered from the get-go.

[Amp User]

Hi Marshmat, ty for your input. Im going to use a 150amp esc built for record setting SAWs class racing riggers they are water cooled. Option 2 would be any number of the high amp controlers made for electric go carts.
Yes your right on care with lipo's. The aluminum box to hold them will have cool air drawn through where you sugested and a vent off the left side of the hual and pointing down into the water incase of flame/heat/smoke. I will have the batteries off the floor of the safty box. When in storage I will keep them in ammo boxes. Each cell can put out 3.4v at 110amp continuous this is a safe 110 of about 20C the pack can handle peaks of 150 but short 30 second bursts for fun to play it safe. I have found a few props able to handle up to 10k most are much less sub 5k. I can mod props by adding cupping rake and cutting the lower pitch out. I have built many RC riggers and monos with fixed surface drive set ups. The 1man mono wont plane as high out of the water so im going to have to raise the stuffing box out the transom higher to allow enough hual in the water to suport me at lower speeds and still allow the prop to breath and break the surface. I may suffer performance but the rooster tail will be worth it. I want everything small and light with high output. 30pounds of batteries that act like 100pounds worth of sealed batteries. A light hual and only strong enough to handle its purpose. I will insure floatation incase of a breach.

[Amp User]

Here is a fast drawing of the size shape of the boat I drew out full scall on a large sheet of brown paper. I measured myself out and drew myself in the boat and this kinda shows the proportions of the full size plan.:p The low center of gravity should be a plus. CG should be around 35% from the transom. Batteries behind me and motor infront between my legs.

[Amp User]

:cool: Ok found my prop 5.25in 3Blade will spin this up to 3500rpm. Prop sales for $56.25, not a bad price really. I would rather have this in steel that can handle 5k.

[Amp User]

42 tooth 4Kg (8lb) 250mm (10") stator, 14 ferrite magnets in the 2kg (4lb) rotor. Taken off the bottom of a direct drive washing machine at the tip recycler for just $10. Sure enough it has 3 wires in and is wired in star (Y).:P :P :P :P :P :P :P :P :P :P :P Im thinking two of these ganged up direct drive should be very powerful with neo magnets.

[gonzo]

You drew something like a PWC, which is a planing hull that requires at least 30HP to plane. For a power of 3.5 HP you need a longer, lean hull.

[Amp User]

Gonzo what if the hual bottom was wider then you guessed.. as I plan on taking on a passager from time to time for tooling about near the shore line a 3.5ft wide bench seat is tobe used little tight but just doable. The bottom is almost 4ft wide at the rear, the extra surface area was to help a single person plane on 3.5hp. Will this work?

[gonzo]

Wide hulls need a lot of power to get up on plane even if the speed potential is high. Four feet of beam on that length is exagerated. You need a long lean hull to move it with so little power. I have a 9'6" dinghy with a 3.5 HP outboard that has a much better power to weight ratio and it planes.

[Amp User]

Ok will have to redesign the hual type completly. I can push to 7'x3.5' and have a near flat bottom and just keep it away from rough water.

[Tim B]

I did a feasability study for Electric Trimarans some time ago. The two biggest problems were Hull resistance and weight (weight mainly). I suggest that you use a Savitsky power prediction (There's an Excel version on the forums), then talk to a few propellor manufacturers, remember, the best prop efficiency you can expect to see is about 60% to 65%. Usually required power is estimated as ( Resistance*Speed )/0.5. This works in a bit of a margin. I think you'll be surprised how much power you'll need.

Tim B.

[messabout]

Gonzo is right about making the boat longer. Build it 12 feet LOA at least. The 6 or 7 footer, if you ever succeed in getting it to plane, will behave like a motocrosser. Not only will it pound you silly but it will need more power than you are anticipating. Longer boats are a more practical solution. Doorskins are cheap but that is the only thing that recommends them. They have core voids, are not stiff, and they soak up a scandalous amount of paint or epoxy. The boat will be lighter and stronger if you buy some BS1088 okoume. When you consider all the work you'll do in building the boat, trash material does not make good sense.

[Quicksilver]

please bring this topic here, we can help tremendously

http://www.rcuniverse.com/forum/forumid_229/tt.htm

edit: opps you want to ride in it. has to be much bigger like previously said. I dont know very heavy

[Guest625101138]

Some rough numbers might help you.

The best lift to drag ratio for a planing surface is around 8. Your 290lb boat will require a thrust of at least 36lbf to plane if it is a good planing surface. Your target speed of 16mph or 23ft/sec will require 828ftlbf/sec or 1.5HP.

Surface props have very low efficiency at low power levels and low speed. You could maybe get 50%. (My experience indicates their efficiency is lower than this at low power) So the required shaft power is at least 3HP.

A short hull will nose up before it gets on the plane so the lift to drag ratio will be less than 8 meaning you will have more drag to get it on the plane and possibly more power depending on the size of the planing surface. You may be able to use trim tabs to improve the situation.

With such low power level you could make a high aspect submerged prop that would have an efficiency around 88%. This would give you a better chance of getting it up but without all the wasted energy in producing the rooster tail.

Some years ago I built a 6ft long by 3 foot wide boat that had total weight around 250lb. It had a "V" hull with small planing strakes and would plane with a 6HP outboard providing I moved my weight forward to get it on the plane. It would do about 20mph once up on the plane. I have seen 3.5HP outboards get children on the plane.

Rick W.

[Amp User]

Hey guys well time has passed and so has many new changes in what one can buy or make to produce a fast electric small mono. With the gas prices they way they are this trend to electric and going green for local lakes n small water ways is also a plus... Rick and others ty for your adivce Rick your spot on and really in tune with what I want to do. Thank you very good info!!!!
Since my postings I have been working on some motor designs.. My latest uses large 2in dia N42 magnets with a pancake type motor. Since then there are very large outrunner motors on the market now too ..brushless is the only way to go to get the most power and run time out of your system. Outrunners have the most torque so very important with the aplications in this forum. Im going to post a few pics the motor is a new china motor puts out 10hp amazing for its size but thats brushless for ya. I have a smaller version of this one rated for 2hp I was going to buy two more for a 6hp motor since then started on the larger pancake 20hp motor. I found a prop maker who will CNC me a surface prop from steel im shooting for 4k unloaded in the water with a 6pitch 6.5 dia 3 bladed prop. The hual will be 4x7 im shooting for 25 to 30mph. I want the rooster tail for effect and surface drive if set up right will get me going faster. I have alot of time on the water with surface drive setups already and know proper placement and prop type. Should be a blast to have a smaller electric 1 man electric the novelty alone will draw a few ohhs n awes providing I can get 25mph or better. There will be no gearing direct drive max torque out of the hole electrics can produce tremendous ft pounds of torque I will be at speed in a blink of an eye seemingly fooling myself of greater speed and visualy for onlookers too.:p check out this motor for 200.00 bucks vah vahh voom two of these would keep things light and very fast 60KV per volt I want to run 72V 200amps 14.4KW 19.5Hp The shaft on this motor is 15mm Last pic is of one of the rare earth mags im using in a pancake motor 240pouds of pull force per mag..one must be very careful when handleing these.. about $6.91 per mag when bought in bulks of 25 units my son is making a motor too 9arm 10 mag motor wound in Wye with 14gauge wire. about 2hp per mag rule of thumb. Will post more info as the project proceeds. For the rest of you electric users good luck and way to go change the future of boating. :cool:

[Amp User]

Here is a pic of three props made with the CNC machine. Im going with the one on the left scaled up to 6x6.5 with a 3/4 ID hub.

[klick]

Where can you buy that motor you have listed? The other motors in the picture look like AXI's, so does the big one a little bit, except for it's huge compared to the other ones. I need a motor like that :) Are you building the motors yourself? You mention buying it from china then building motors so I wasn't clear.

Machining props has got to be a bit pricey. I used these "mixing propellers" from mcmaster.com (search for 8004K161 or just search for mixing propellers) Although I don't claim to be a propeller design master, they seem alright to me though.

Look forward to hearing more.

Ross

[Amp User]

Its a monster!
The largest motor we have ever had!

Model: HXT80-100-B
Wire Turns: 8
Resistance: 32ohm
Idle Current: 2A
ESC Required: 130A
Input Voltage : max. 48V
Kv : 130 rpm/V
Weight: 1570g
Shaft: 12mm
Voltage Range: 20-48v
Non Load Current: 2.0A
Maximum Power: 6500W
Equivalent: 60-80cc Gas Engine
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5142&Product_Name=HXT_80-100-B_130Kv_Brushless_Outrunner_(eq:_70-55)

[Landlubber]

A 6 foot boat will not get out of the water......you have less than 3 hp available!

[Landlubber]

I tuned up my 3.5 hp Tohatsu on a 10 feet allow boat, it could plane quite easily, but 6 foot....nup.

[Amp User]

That one is the smaller version the other pulls 200amps plus I cant find my link on the other one at the moment arggg. 6500W thats good for 8.7hp for this smaller one. Yes the magnet I showed is for my own motor build im going to use 10 of them with 9poles terminated in wye I hope to get 20hp. The CNC machined props your seeing are $38.00US each.. my custom order will be lil over $100. I want a pure surface diven prop for maximum top end on 20hp. Unloaded at full speed my amps will drop down under what it takes to run at 75% throttle given there will always be a blade out of the water. I saw the props your talking about. I would completely rework those props the steel ones could be sharpend cupped. I would detongue the leading edge and rake the back and put a texas cut on the tips with a nice flat edge on the rake. This would decrease load increase rpm and give you more speed if you modified a larger prop then you are currently using in essence the over all blade area would be closer to the same but with higer pitch and a much more agressive design that puts out more at the same amps. I have reworked alot of props in my day. I would also put a bar cut in to reduce amps and allow more pitch. :D

[Amp User]

Hi Landlubber I agree . I have changed to a 8ft hual on 20hp now this post is over 500days old times have changed on my options and whats out there for parts.

[Amp User]

I have been doing some doodles and liked this design here is a redering of the basic look 4.5 x 8ft mono two seater side by side. 3.5ft wide bench 42in or
21in per person. Im looking for some Cobalt Iron plate for the pancake motor now. It will be the back iron for the magnet aray.:P

[MTC-Merlin]

Hi AMP,

I was led to your web blogs thru several links and read with great interest all of your fantastic contributions to the electric boat discussions.

I'm planning to make a 10 ft electric boat and don't need high speed, just 6 mph. You mentioned the $200 motor and I also saw that you make your own propellers. I was wondering whether your motor and prop are available for me to purchase please?

Best regards, Merlin

AMP WROTE: Since my postings I have been working on some motor designs.. My latest uses large 2in dia N42 magnets with a pancake type motor. Since then there are very large outrunner motors on the market now too ..brushless is the only way to go to get the most power and run time out of your system. Outrunners have the most torque so very important with the aplications in this forum. Im going to post a few pics the motor is a new china motor puts out 10hp amazing for its size but thats brushless for ya. I have a smaller version of this one rated for 2hp I was going to buy two more for a 6hp motor since then started on the larger pancake 20hp motor. I found a prop maker who will CNC me a surface prop from steel im shooting for 4k unloaded in the water with a 6pitch 6.5 dia 3 bladed prop. The hual will be 4x7 im shooting for 25 to 30mph. I want the rooster tail for effect and surface drive if set up right will get me going faster. I have alot of time on the water with surface drive setups already and know proper placement and prop type. Should be a blast to have a smaller electric 1 man electric the novelty alone will draw a few ohhs n awes providing I can get 25mph or better. There will be no gearing direct drive max torque out of the hole electrics can produce tremendous ft pounds of torque I will be at speed in a blink of an eye seemingly fooling myself of greater speed and visualy for onlookers too.:p check out this motor for 200.00 bucks vah vahh voom two of these would keep things light and very fast 60KV per volt I want to run 72V 200amps 14.4KW 19.5Hp The shaft on this motor is 15mm Last pic is of one of the rare earth mags im using in a pancake motor 240pouds of pull force per mag..one must be very careful when handleing these.. about $6.91 per mag when bought in bulks of 25 units my son is making a motor too 9arm 10 mag motor wound in Wye with 14gauge wire. about 2hp per mag rule of thumb. Will post more info as the project proceeds. For the rest of you electric users good luck and way to go change the future of boating. :cool:[/QUOTE]

[XPC Bearings]

For your shaft bearings take a look at our XPC Bearings at http://www.xpcbearings.com/ Our Hilube Vesconite bearing has very low cofficient of friction (.09) These bearings run very smooth and do not swell in water. We also produce dripless shaft seals (stuffing box) that are very light weight and non conductive. If i can be of assistance please let me know.

[Amp User]

Thank you for your support, and the bearing tip. I have been educating myself on the task at hand. And have enjoyed my findings, I would like to share some..:D

The bottom hual is mono hual in the front and a hydro ish.. tail. Supported lift for the prop and has enough sideboard.. so to speak to aid in turns as the front end will want to bank in the turns. To control some of the bank, I would have to have a wider foot print in the turns.

The prop is a simple design, one I would like to try as I will need to mod the pitch and dia as I go into testing. This form of prop could be made out of large steel spoons.. and some hub material. If you notice the right blade shows a simple half spoon design. This gives a long fade back on the leading edge, alot of grip which transfers to thrust with a sharp edge. Notice we have a cupping effect already built in. I dont think this prop would work well for lifting the back end of a hydro at first glace you see alot of slip off the trailing edge. Which doesnt help lift the rear up.. but the broad scooping effect of the blade as the hydro effects form from the spinning blades would suggest this long area of control on the front face of the right prop show promise. I like the two point hual it has the legs for a stable ride of a boat its length minus the extra weight. The blue shows the wet areas on each hual, the prop needs to focus on providing thrust rather then lift in my case. Another thing about this prop if you wanted to add rake there should be all you need built in already by nature of the spoon shape. Rake of course helps focus that thrust cone back. I will add one more pic a of the prop with a mod.
This looks more familar...and a fast way to unload the prop and show why this prop makes lift... just doesnt have a abrupt ramping trailing edge rather a longer hand in the water to ride up, adding some lift.

[Amp User]

Here is a great example of the use of pan cake type motor frames that allow these sort of ironless stator cores you can produce with minimum effort. The value is aparent in the large aray of pure torquelicousness. :P The neat and well used trick here is the magnet fields overlap and max out copper fill. 0 eddie current effects with ironless cores; and weight / cost savings. To be fair back iron for the coils would increase the motors performance. Soon as I can im going to do coils of this nature for my 2in dia magnets, shown further back in the thread.

[kistinie]

I will add one more pic a of the prop with a mod.
This looks more familar...and a fast way to unload the prop and show why this prop makes lift... just doesnt have a abrupt ramping trailing edge rather a longer hand in the water to ride up, adding some lift.

Can this propeller regenerate as well when sailing ?

[Amp User]

Good question .. Im not sure at this point I can only speculate what a prop of this shape could do. When I get the chance to try one out I will be posting my observations.

[kistinie]

Good question .. Im not sure at this point I can only speculate what a prop of this shape could do. When I get the chance to try one out I will be posting my observations.

When regenerating a propeller need to have a wider Rpm capability as you can sail much faster than you will motor. Most multihulls reach 8 to 10 Knts, average.

Maximum speed is 15 to 25 Knts.
15 is reached by most light 33_40 feet multihulls.
25 is for 2500Kg F40 tri or cat or 6 tons 60" commercial sail boats, mainly cat are they are less expensive

Courage !


About windmill boats are there any operational ones can be seen sailing ?

Or do we need to do a 1/10 to 1/5 scale RC prototype or beach cat, for this summer or solid works and other Catia in winter to calculate effect of gyroscope and behaviour in high sea and wind.?

Can be full mechanical because you will get an efficiency close to 90% with a clean mechanical work , or partially by example torque transmission is mechanical but a generator added and propeller or windmill pitch is assited by a controller. Ride should be very smooth most directions and need low marine skills to drive. A, air and sea propeller pitch computer controlled boat, could be incredibly fast in all sectors. Its my favourite choice.


A challenge could be done this year with 16 feet size limit on boat, 4 to 6 is better to limit the danger and power of these beast. Because pitchpoling a meat cutter is a bad idea.
The effect will be close to an helicopter blade meeting an object. Will cut less as speed lower. Full Lateral frame and minimum intake framing of the air blades should be compulsory to avoid tears.
unframed models reserved for, away from public, use and big commercial applications.

So best would be to do RC boats. All the technology is available, variable pitch included.
Full electric solutions could be tested too.


Ideas invent revolutions but the object does revolution.


Prototyping is vital to valid the ideas.


Have fun ! Try new solutions !

[Amp User]

Well I have obtained two large 7kw brushless outrunners.. there 48v 145A motors. I have two 120A HV controllers made for 48v systems. I have obtained some 150A , 48v Li Poly packs. Good for 30C continuous. I plan to use about 15 to 18hp out of the motors combined this is electrical hp so the torque is going to be insane for there size. I would imagine the torque will be like a 30hp engine. The motors spin at 12,000 rpm at 48v so I will need a 5in dia prop with about 7in pitch. Here's a pic. :p I plan to run the motors in line with a coupler. The axle's on these are 12mm so will use an adapter to a 1/2in drive to the prop. Think I'm going to use lead teflon bushings in the stuffing box and will inject a load of grease and settle for that. I'm trying to stay lite as possible for all out speed rather then handling on flat water. Lastly is a rigger design I like the sponsons could be removed for towing to the water. The belly area of the tub will be where I sit and motor in front of and then batts between the sponson tubes. FYI that prop was Lazar tached at 34.7k and I made the prop myself. So will use the same design for the big motors. I will actually start with a 6in prop with 7in pitch and adjust it down in dia and pitch till the amps are around 110 for each motor. Im shooting for over all 12ft L x 10ft W rigger with 3in dia carbon booms. All up with motors batts.. 65Lbs. If I can get the tail up with me in it I will be happy. Run time is only 30mins at full throttle. So will only run it hard enough to get on the prop and will feather back till its just staying on the prop hub.

[Amp User]

Found these specs on a known electric trolling motor systems. Here are the stats the highlight is 400watts IN and provides 200W OUT- produces (Kt..or torque of of a 1hp engine). Here's data; this one is 1000W IN and states equal to 3hp engine(out) mainly do to the high torque electric motors provide.

Specifications:
Input Power Watts: 1,000
Output Power: 480 Watts (Comparable to 3 HP gas outboard)
Static Thrust: 68lbs.
Battery Output: 400 Watt Hours
Integrated Battery: Lithium-Manganese (13Ah@29.6V)
Steering Type: Twist tiller
Gearing: F-R continuously variable
Prop Size: 12" x 10"
Weight: 28lb.

[Amp User]

And another 400W In.

Range:
EX.: Ultralight 402 with integrated battery (28.8 V / 8 Ah), Fishing kayak 13.5ft, 58lbs Example of use
Speed in mph Range in miles Run-time in hours

Full throttle
5.8mph
3.5
0:36 mins

Half throttle
3.7mph
11.1
3:00 hrs

Slow speed
2.6mph
15.6
6:00 hrs


Specifications: Input power in watts
400

Rated voltage in volts
28.8

Final voltage in volts
33.2

Propulsive power in watts
180

Comparable gas outboards
(propulsive power)
1 hp

Comparable gas outboards (thrust)
2 hp

Maximum overall efficiency in %
45

Static thrust in lbs
33

Total weight in lbs
15.4

Weight of motor without battery in lbs
9.9

Weight of integrated battery in lbs
5.5

Shaft length in inches
17.7

Integrated battery
230 Wh LIMA

Propeller dimensions in inches
8 x 8

Propeller speed at full power in rpm
max. 1,200

Control
Remote throttle control

Steering
Provision for connection to kayak rudder; lockable

Tilting device
manual with grounding protection

Stepless forward/reverse drive
yes

[Amp User]

Using the above info I could speculate using just one of the gold 7KW engines could provide up to the torque of a 35hp engine. I have two of these motors so double the fun. I have done the math and with the batteries currently I have on hand I can run for 30mins with the torque of a 16hp engine. So far it has cost me 120bucks for 200W hr. In my case I can say approx 1hp per hr. I'm using 30C 5000mah lipo cells. I have basically choice a 8P/6S pack at 6k rpm or 4P/12S for 12K rpm What would be nice would be a 24P/12S system if lipo's grew on tree's.:P

This pic would need 12k at the prop if I use a 5.5x6in surface prop to hold the tail up.

[marshmat]

The specs sound impressive; alas, the marketing guys have apparently been running on bad math here.

When trolling motor manufacturers say "comparable to a 3 hp gas engine", they're leaving out some very important factors. For example: the trolling motor has a prop optimized for pushing a 2500 lb boat at 2 knots, while the gas outboard has a prop optimized for pushing a 500 lb boat at 6 knots. Obviously, in a test cycle geared towards pushing a big boat slowly, the trolling motor will fare well. Put a comparably optimized prop on the gas outboard, and it will become painfully clear that the prop simply does not know or care what's on the other end of its shaft.

A 7 kW electric outboard could be legitimately compared to a 9.9 hp gas outboard. Given comparable props and similar shaft RPM, these two will perform quite similarly at full power. Neither will come close to a 35 hp gas outboard.

You'll likely find, when you finish working through your propeller calculations, that a much slower turning, much larger diameter prop will make more efficient use of your electric motor's power at the speeds such a boat is likely to operate at. The losses from a belt or chain reduction gear will be more than offset by the greatly improved efficiency you'd get with a larger diameter prop.

Best of luck with the project :)

[Amp User]

Yes understand and thank you for your advice. I plan on using a small prop for max speed at the loss of some low end out of the hole power. So would rather leg it out a bit to gather as much speed as possible with reasonable run time. In lu of your advice perhaps the new pic would provide better performance as I wont be gearing the motor or using large dia low pitched props. I understood the torque of these motors where equal to 400win puts 200w out makes 1hp of similar torque. It was that torque I'm interested in as I would like to run 12,000 rpm at the prop out of water and hope for 8k unloaded in the water. I'm going to try hand made 5.5inx7 prop first.

[kistinie]

The specs sound impressive; alas, the marketing guys have apparently been running on bad math here.

When trolling motor manufacturers say "comparable to a 3 hp gas engine", they're leaving out some very important factors. For example: the trolling motor has a prop optimized for pushing a 2500 lb boat at 2 knots, while the gas outboard has a prop optimized for pushing a 500 lb boat at 6 knots. Obviously, in a test cycle geared towards pushing a big boat slowly, the trolling motor will fare well. Put a comparably optimized prop on the gas outboard, and it will become painfully clear that the prop simply does not know or care what's on the other end of its shaft.

A 7 kW electric outboard could be legitimately compared to a 9.9 hp gas outboard. Given comparable props and similar shaft RPM, these two will perform quite similarly at full power. Neither will come close to a 35 hp gas outboard.

You'll likely find, when you finish working through your propeller calculations, that a much slower turning, much larger diameter prop will make more efficient use of your electric motor's power at the speeds such a boat is likely to operate at. The losses from a belt or chain reduction gear will be more than offset by the greatly improved efficiency you'd get with a larger diameter prop.

Best of luck with the project :)

100% ok with you on that
Torqueedo is the industrial proof of this statement

Congratulations Amp U.! Very nice project !

[Amp User]

Thank you Kristine, Its going tobe intresting to see what I can make happen. I have a guy milling me out couplers for the 12mm axles.

[papawoodie]

Great Idea,

So what's happening now?
How much further along have you gotten?
When will we be seeing reports for testing
on the water?

Thanks, and keep us posted!

David

[Amp User]

I have a prop from Ron Hill a 6.5x11 cleaver 3 blade (very nice). I will be testing it with the rigger. I have a coupler now and have on order the drive line and stuffing tube need bearings and bushings next = )
So its going.. just slow and cautious. Im going for high rpms so have to be careful my choices and as cash allows.;)

[Amp User]

New design will test at 30% scale as a 4ft rigger on 2.4kw 780kv out runner 22.2v 6S 5000mah cells. 3in prop.