Help me design the "Poorqeedo", another efficient electric boat

[portacruise]

You should also be able to find a third SEALED lead based type the "gel" cell locally. Sealed types are preferred as they can operate in any position or even while immersed which is not possible for the first type you listed. No corrosion cleaning or adding of water is required of sealed type. As Jeremy indicated in a previous post these may be available at no or low cost from UPS maintenance companies in large cities. Their cost when new from retailers is between the flooded type and AGM type. All 3 deep discharge lead type will last longer if used with the specific type of charger designed for them, although they can be charged with a low cost generic "auto" charger.

Hope this helps.

Porta

Originally Posted by mental_boy

Some random battery info.

I've found that the deep cycle 115ah Group 27 Walmart batteries are made by Johnson Controls and are the exact same battery sold by many different retailers in the US:

Costco/Kirkland ($69)
Walmart ($70)
Interstate ($75, wholesale)
Sears Die Hard Gold ($99)
Kragen auto parts ($99)
Autozone Duralast ($?)

The only different lead acid batteries I've found locally:

Optima 55ah bluetop ( $150, also made by johnson controls)
Sears Die Hard Platinum 85ah AGM (~$200, made by enersys)

[mental_boy]

I extended the sides and fiddled with them to create something like the cockpit you drew by hand.

Rick

Ok, I'm still alive.

The deck looks nice. I like the back the best since it reminds me of the combing on many classic boats. I think I might just make both ends look like that.

Something that has really been bothering me about the monohull configuration is the prop shaft. If it's a curved shaft with plastic bushings (and goes above the waterline), I can't see how it will not interfere with the cockpit wells, since a fair amount of shaft will need to be in the boat.

It makes me think the shaft should be straight with bearings and seals, and the motor should be in the very bottom of the boat. That way the shaft could exit after a short distance and the motor could be grouped with the batteries. I could weld a tube perpendicular to the prop tube and fill it with oil, so there is a positive head of oil (similar to setups you have used in the past).

I've also decided the outriggers should not be large enough to support my weight. It will be easier to use aluminum poles than to fabricate a crossbeam that I can walk on. I can just board from the front or rear.

Some things on the agenda I need to do:

1. Shorten the hull to 6.33m so I have more options for storing the boat. Hopefully this won't cause too much trouble.

2. Get a better weight estimate, starting now:

Three batteries: 64kg total (dimensions of each battery are 7"x12.75"x8.75")
likely crew weight, 2 guys: 180kg
likely crew weight 2 guys, 2 girls, 300kg

3. Draw the prop shaft into the profile with an appropriate radius, so I can see if it will interfere with the footwells.

4. Size the outriggers so they have 80kg of buoyancy, like Rick suggested.

5. Finish messing with the model......

I've been busy but I should be able to get to it tomorrow.

[mental_boy]

Originally Posted by portacruise

You should also be able to find a third SEALED lead based type the "gel" cell locally. Sealed types are preferred as they can operate in any position or even while immersed which is not possible for the first type you listed. No corrosion cleaning or adding of water is required of sealed type. As Jeremy indicated in a previous post these may be available at no or low cost from UPS maintenance companies in large cities. Their cost when new from retailers is between the flooded type and AGM type. All 3 deep discharge lead type will last longer if used with the specific type of charger designed for them, although they can be charged with a low cost generic "auto" charger.

Hope this helps.

Porta

The only place I know if that has gel type batteries around here is West Marine, and they're pretty pricey. The AGM optima batteries are still cheaper.

I'm still weary of used batteries. It's my understanding that they can behave very well and maintain 80% capacity until right before they go bad. That's just my understanding.....

The way I see it, the group 27 batteries have the same capacity as the optimas, they're just a little bigger and require a bit of maintenance. They're also half the price. I don't plan on capsizing or getting the batteries wet.

[Submarine Tom]

Double check that West Marine price as some batteries are on sale there right now.

-Tom

[Guest625101138]

Originally Posted by mental_boy

......
Something that has really been bothering me about the monohull configuration is the prop shaft. If it's a curved shaft with plastic bushings (and goes above the waterline), I can't see how it will not interfere with the cockpit wells, since a fair amount of shaft will need to be in the boat.

It makes me think the shaft should be straight with bearings and seals, and the motor should be in the very bottom of the boat. That way the shaft could exit after a short distance and the motor could be grouped with the batteries. I could weld a tube perpendicular to the prop tube and fill it with oil, so there is a positive head of oil (similar to setups you have used in the past).

....

Best to see what shaft material you can get and then what it can be curved to. You can use a thicker solid section through the hull and connect this to the curved bit aft of the tube.

You can use a spreadsheet or place objects in Delftship to determine the location of the CofG. You need to do this for at least the light and heavy consitions. The aim is to determine where the waterline will be so you can set the height and angle of the stabilisers. If possible it is worthwhile having adjustment of these relative to the hull for fine tuning. If you load them up too much they will sap power.

With batteries in the bottom of the main hull it will probably be stable so the outer hulls become roll limitters.

[Submarine Tom]

Mental_Boy

Starting July 8th, deep cycle batteries will be $50 off at West Marine.

The only ones on sale right now are starting batteries, not what you want.

-Tom

[mental_boy]

Ok, here's what I came up with in Delftship.

The main modification to Rick's hull is the simplification to dory form. I know it's a less social layout and is not as interesting, but it is simple to make, allows weight shifting and is easier to paddle should something fail. There is about 100% more freeboard, the sheer was stretched in the transverse direction by 1.8, and the chine was stretched by .833. The hull was also shrunk 10% lengthwise from 7m to 6.33m

At the waterline the hull is ~16% wider at every point, and at the chine it's 17% narrower. This changed the displacement at the design depth by less than 2%. Reducing the length changed the displacement by about 10%, so for the same 400kg the hull now needs to sit 18mm lower.

I sized the outriggers to Rick's original specification and the displacement is now 88kg for each.

I'm thinking the two center seats could have compartments below them, with two batteries below the forward seat and one battery and the motor below the rear. I made the middle seats a little bigger to allow larger compartments. Not sure how to draw the in compartments below the seats.

I'm also thinking watertight compartments for the front and the rear, say 1m in length. I couldn't figure out how to draw them without subdividing the control net, seems like there should be a less tedious way to do it. Had I started with Rick's hull with the deck I would have been set.

The seat height and freeboard were pulled from a 6 man hawaiian style outrigger canoe at the rowing club here.

[mental_boy]

I attached the modified main hull to this post. Pq_7A is the 7m hull with more freeboard and the sides flared. Pq_7B is the same as Pq_7A but is 6.33m in length. Pq_7B will draw 0.218m at the same displacement as the original hull.

Pq7_orig is just the original file you posted earlier. I couldn't figure out how to export the models in iges format, and the Michlet format seemed like it would be easy to mess up.

I'm very curious to know how the power requirements change with my modifications.

You can use a thicker solid section through the hull and connect this to the curved bit aft of the tube.

This is a great idea, problem solved.

You can use a spreadsheet or place objects in Delftship to determine the location of the CofG. You need to do this for at least the light and heavy consitions.

I guess this is next on the agenda, assuming you think my setup is good.

[Guest625101138]

Originally Posted by mental_boy

Rick,

I attached the modified main hull to this post. Pq_7A is the 7m hull with more freeboard and the sides flared. Pq_7B is the same as Pq_7A but is 6.33m in length. Pq_7B will draw 0.218m at the same displacement as the original hull.

Pq7_orig is just the original file you posted earlier. I couldn't figure out how to export the models in iges format, and the Michlet format seemed like it would be easy to mess up.

I'm very curious to know how the power requirements change with my modifications.

I have attached the power to speed relationship for the hull.

I do not know what you intend to do with the hull detail so you may already be thinking about these things:
1. The hull will not have much torsional rigidity - suggest it will need robust guwale rails or boxes.
2. It will be easy to swamp if the bow dips into a wave - suggest a short deck at bow and stern with some combing around the cockpit that deflects water away from cockpit. The decks could have slight curve so the water drains quickly. The gunwale rails could tie into a bilkhead at the start of the deck.
3. Bulkheads that seal off the space under the decks would ensure it is unsinkable. Need enough to float the batteries.
4. The flared sides coming into a vertical stem will look tortured. The stern will be OK.
5. The aft stabiliser beam could be tied into the aft bulkhead,


Even a simple cardboard model will help in understanding the structural aspects and the need for the tortionsl rigidity.

[mental_boy]

Cool, Thank you.

So it looks like I'm about halfway between your catamaran hull and your monohull in terms of efficiency. Also looks like the hull loses half a knot on the 7m monohull for a given power level, at least at the higher speeds. Seems OK since I'm not trying to win any races. Windage will still be way down from the cat.

Now I can make a more accurate estimate of the overall weight of the boat, so that's next on the agenda.

I'm still curious to know how the two 7m hulls compare (your original and the pq7A). I understand you're pretty busy at the moment, and I'm in no hurry...

To answer your concerns:

I was thinking of having a deck and with a sealed compartment below on the front and rear of the boat. So decking from 0-1m and 5.33-6.33m, and bulkheads at 1m and 5.33m. The two center seats would be boxes for motors and batteries. I'll have to figure out how to draw that.

I was also thinking thick rails on the gunwale rails. I hadn't considered torsional rigidity, but it seems this is a common configuration for a boat.

Good point on being swamped, I'll definitely put combings on the decks right before the cockpit.

I'm hoping the foredeck, the thick rails, and the seats will keep the hull from looking tortured. No experience with this.

The aft beam will be tied to the aft bulkhead.

Originally Posted by 376135

I have attached the power to speed relationship for the hull.

I do not know what you intend to do with the hull detail so you may already be thinking about these things:
1. The hull will not have much torsional rigidity - suggest it will need robust guwale rails or boxes.
2. It will be easy to swamp if the bow dips into a wave - suggest a short deck at bow and stern with some combing around the cockpit that deflects water away from cockpit. The decks could have slight curve so the water drains quickly. The gunwale rails could tie into a bilkhead at the start of the deck.
3. Bulkheads that seal off the space under the decks would ensure it is unsinkable. Need enough to float the batteries.
4. The flared sides coming into a vertical stem will look tortured. The stern will be OK.
5. The aft stabiliser beam could be tied into the aft bulkhead,


Even a simple cardboard model will help in understanding the structural aspects and the need for the tortionsl rigidity.

Rick

[mental_boy]

While I'm thinking of it, comments on the overall beam of the boat? I'm thinking slightly narrower wouldn't hurt.

I'm also wondering about the shape of the outriggers for the bay here. Seems like it could be beneficial in rougher waters if the bottom panel curved up more toward the bow of the outrigger.

I've been looking at outrigger racing canoes and they have a pretty dramatic rise on the front of the outriggers:



But they also encounter some pretty wild conditions:

[Guest625101138]

The attached shows how the two hulls compare. I expanded the scales so it opens out a bit more in your range of interest. The 7A is about 10% less power at 6kts but at slower speed there is not much difference.

I have an OC1 with pedal power and I do not like its high ama.

The stabilisers on a monohull work differently to a single ama on an outrigger canoe. I find you want then to slice through waves. They can be completely submerged for part of their length at any time. They just need enough buoyancy so they never entirey submerged. You roll if this happens.

I flipped my OC1 twice and an early version with a single outrigger once. Others have also has unintended swim from it. With a single outrigger you rely on the load it carries for stability. If you turn into the outrigger at speed you can easily flip. With twin stabilisers you just load up the outside stabiliser in a turn.

The high bow on the single amas really plough when you dig them in. They do give more progressive roll but this does not matter when you have rudder steering with twin stabilisers because you can set the roll dynamically with steering input

[mental_boy]

Rick, thanks again for all your help.

I think I'll meditate some more on the design.

Still need to do a better weight estimate...

[mental_boy]

Ok, got the gearmotor in the mail and I made some measurements.

At 37v and no load, the amperage was 5.25A, so that was good for a laugh. I measured the winding resistance directly and it's less than 0.1 ohms.

So that motor will burn up ~200w just idling. ugh. I'm guessing it's mostly drag from the gearbox and a fair amount of core losses. I can see into the motor and the fill of the windings in the slots is low. It's also possible there is something wrong with it....



So then I measured the the sanyo reel motors I have. At 37v the no load amperage is 0.24A and Rm is 1.0 ohms.

I then dug around and found this page:

http://adamone.rchomepage.com/guide5.htm

Making calcs from that page, at 36v and 5.6A (the rated amperage) the motor should be ~80% efficient. 36v and 2.8 amps the efficiency goes up a bit, 84%.

So if my motor is 80% efficient and my props are 80% efficient, then the overall efficiency is 64%.

The two sanyo motors put out 403w combined, so at 64% eff that's 257W on the hull. Looking at Rick's graph for the pq7B hull that's almost exactly 6kts.

I could also choose to go 5 kts at 36v and draw half the amperage, which would improve motor efficiency and give me some headroom for wind and wave resistance.

With the sanyo motors the pitch would need to be about 8.4" for 6kts and 7" for 5kts.

[Motivator-1]

Hi Mental,
I thought that I'd check up on your progress and bring your Thread back up to the top. My Electric Cat Thread seems to be fading away, so I might have to go it alone from here. (Thanks to all of you that have helped)

Have you finalized your Hull? Also, what did you end up with in regards to Motor/Transmission/Battery/Controller choices?

Anyway, Thanks for your input regarding my Cat design.

Regards,
John