ePropulsion Pod Drive

Bull City

Bull City
6,850
2,501
North Carolina
Aquamot also makes an electric pod drive, which I'm looking into. Their website says this about placement of the pod:

Where and how should fixed pod motors be mounted?
Generally fixed pod motors are mounted between keel and rudder. Moreover, it is better that the motor is place closer to the keel than at the ruder. After the propeller there are hydrodynamics turbulences and therefore vibrations at the ruder can be the consequences. Furthermore, the motor is also positioned at the lee side from the keel and the motor has a lesser resistance. The fixed pod motors should be mounted parallel to the waterline for having the max. thrust. This is why Aquamot supply custom-made compensation wedges which are also vibration-dumping.

I think they're saying that because of turbulence aft of the keel, there's not as much drag.

WIE SIND FLANSCHMOTOREN ZU PLATZIEREN?
Grundsätzlich werden Flanschmotoren zwischen Kiel und Ruder positioniert. Dabei soll der Motor näher beim Kiel als beim Ruder sein. Der Grund hierfür ist, dass nach dem Propeller Verwirbelungen entstehen und somit Vibrationen am Ruder hervorgerufen werden können. Desweiteren ist der Motor auch im Lee-Wasser vom Kiel und hat somit einen geringeren Schleppwiderstand. Außerdem sollen Flanschmotoren parallel zur Wasserlinie angeordnet sein. Dafür werden von Aquamot maßgefertigte Ausgleichskeile angeboten, welche zugleich schwingungs- und vibrationsdämpfend sind.

 

Crash

Super Anarchist
4,938
919
SoCal
I was wondering if letting it freewheel might cause harm -- stresses diodes, burns bearings, wears seals, makes a horrible racket,  to force a folding prop to fold, whatever. If so, then locking it might be a useful thing. Drag may not be the only consideration.

The drag argument can take over a conversation. My guess, similar to yours, I think, is locked would be more drag. Still, locking the blades, particularly if you could keep them in the wake of the keel, might be desirable all things considered.
It’s a bit of a complicated argument.  With a bunch of “it depends”

on airplanes, a windmilling prop, whether 2 or 3 blades, almost always has more drag than a stopped prop.  But airplanes don’t all have transmissions with a “neutral” to disengage the engine.  Also airplane prop blades are long and thin.  Sailboat props, esp 3 bladers, are short and fat.  Plus sailboats have transmissions to decouple the engine.  
 

My gut says if you have a fixed 2 blade prop, locked, inline with keel is less drag than rotating.  But a locked 3 blade probably has more drag vs a rotating prop.  
 

Note: transmission wear and cutlass bearing wear not considered....

Electric motors complicate the equation as there may not be a transmission neutral position, and regen is possible...

 

DDW

Super Anarchist
6,239
972
Yachting World did drag testing on locked and freewheeling props. The result was mixed, depended somewhat on the drag on the shaft, size and number of blades, etc., but overall conclusion was freewheeling was less drag most of the time. 

 

Bull City

Bull City
6,850
2,501
North Carolina
I noticed a few things about the ePropulsion 3.0 pod compared to the Torqeedo 1003 OB. 

I understand that the Torqeedo has a reduction gear and that the eProp does not. The Torqeedo technical info says the maximum propeller speed is 1200 rpm, the eProp says 2300 rpm.

The two drives are similar in size, but the propellers are different looking. The eProp propeller has a smaller diameter (10.24" v 11.5") but the pitch  looks more aggressive. Combined with a higher rpm, I guess it means more power.

eProp 3.0 v Torq 1003 profile.png

eProp 3.0 v Torq 1003 end.png

 

Bull City

Bull City
6,850
2,501
North Carolina
I've been thinking about installing the pod system. This is a photo of the space shown in Post #72. Usually there is a storage bin here that slides in and out. The space is about 29" deep, and the thru-hulls (for the cockpit drains) take up the last 6" from the aft bulkhead. There is plenty of room for the battery. The space directly astern is not accessible. 

The pod drive would be installed on the centerline. As you can see, there is a drainage hole at the bottom of the bulkhead, and there is drainage that runs forward to the bilge, so that will have to be allowed for. I'm not sure how to do that.

UNADJUSTEDNONRAW_thumb_57ae.jpg

My preference would be to mount the battery (in blue) close to the forward end of the space, so that the various controls and indicators are accessible. In that case, the pod (in red) would be mounted toward the rear of the space. On the other hand, it might be better to mount the pod closer to the keel, and battery behind it, which would be OK. Either way, I would need to fabricate some "floors" with a space for drainage to support the battery. 

I'd be interested in comments and suggestions.

Installation.png

 
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longy

Overlord of Anarchy
6,056
807
San Diego
Whatever you do, replace those two gate valves while you can still access them!! Can you post drawings of drive inside the hull? You have two choices on drainage: totally ignore it, accept that you might have to sponge out behind motor as needed, or create a ditch around motor head, & fill in v-groove to eliminate standing water. Either way, you want to have powerhead on an "island" so that it keeps motor dry at (almost) all times.

 

Zonker

Super Anarchist
8,890
4,803
Canada
Re prop diameter and RPM.  Big diameter slow turning prop is always more efficient than fast smaller prop. At displacement speeds I should add.

 

fufkin

Super Anarchist
What’s behind the bulkhead pictured w the gate valves? Is it lazerette storage? 

Id look real hard at a good reason why you can’t move the prop aft and closer to the rudder. 

 
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TwoLegged

Super Anarchist
5,665
2,081
AIUI, Bull, the Pod's intrusion into the interior consists solely of some mounting bolts and one or more cable connections for power and control wires.

Do any of those holes need to be on the centre line?  If not, then the pod itself won't impact on drainage.

Also, why can't the pod go under the battery if that helps?

Another thought: after decades of near-stagnation, battery technology is now developing fast.  It is probable that radically better batteries will be available in five years, and that they will have a different form factor.  After ten years, that's near-certain.

So it seems to be to be wise to keep the battery mounting as adaptable as possible.  How about rails along the bunkfronts, with the battery suspended on a cradle hung from the rails?  That way, anew battery would just need a new cradle.

 

Bull City

Bull City
6,850
2,501
North Carolina
Whatever you do, replace those two gate valves while you can still access them!! Can you post drawings of drive inside the hull? You have two choices on drainage: totally ignore it, accept that you might have to sponge out behind motor as needed, or create a ditch around motor head, & fill in v-groove to eliminate standing water. Either way, you want to have powerhead on an "island" so that it keeps motor dry at (almost) all times.
Here's a photo of the pod drive. The Compensation Wedge has to be modified to fit the hull. The mounting instructions recommend Sikaflex as a sealant. I think some kind of backing would be needed inside the hull so that the nuts and washers meet a flat surface. maybe a glob of Marine Tex. There ain't much inside the hull besides the battery, a control box, the charger, and some cables.

eProp Pod 3.0 photo.png

 

Bull City

Bull City
6,850
2,501
North Carolina
What’s behind the bulkhead pictured w the gate valves? Is it lazerette storage? 

Id look real hard at a good reason why you can’t move the prop aft and closer to the rudder. 
This is the area behind the bulkhead - forward of lazarette, and between P&S cockpit lockers. It's not accessible from anywhere. I would have to put a hatch in the cockpit sole to reach it. God knows what's in it.

H-Boat Aft.png

 

Bull City

Bull City
6,850
2,501
North Carolina
I wonder what mounting it slightly offset would do. That would get it out of the drainage ditch, and be much easier to mount.
That's good question. I'm thinking about all of the Herreshoff-era boats that had their propeller offset. I wonder about drag. As it happens, there is a 12-year-old thread on that, and you made a couple of posts:



Schrödinger's cat?
Judge Crater?

 
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Bull City

Bull City
6,850
2,501
North Carolina
AIUI, Bull, the Pod's intrusion into the interior consists solely of some mounting bolts and one or more cable connections for power and control wires. That's correct.

Do any of those holes need to be on the centre line?  If not, then the pod itself won't impact on drainage. The holes for the wiring tube and aft bolt are on the center line. I guess you could off set it as Ish suggests. After all, it's not a companionway.  :p But you would still want to have the nut & washer meet a flat surface.

Also, why can't the pod go under the battery if that helps? I suppose it could.

Another thought: after decades of near-stagnation, battery technology is now developing fast.  It is probable that radically better batteries will be available in five years, and that they will have a different form factor.  After ten years, that's near-certain.

So it seems to be to be wise to keep the battery mounting as adaptable as possible.  How about rails along the bunkfronts, with the battery suspended on a cradle hung from the rails?  That way, anew battery would just need a new cradle. Very good point. I will definitely keep it in mind. I like the idea of the rails & cradle. The battery weighs 106 pounds, and I'd like to keep it low. The rails would have to be pretty stiff. Maybe if the bottom corner of the rail rested where the bunk front tabbing meets the hull?

 

weightless

Super Anarchist
5,607
581
Not sure if it's helpful but can the battery be installed in any orientation? Perhaps rotated onto its side and mounted against a berth would give enough room to mount the pod next to it on/near center line?

Also, just to toss a random thought, the pod strut doesn't need to be oriented straight down. If you felt it would be useful to put the upper end a bit off center you could still have the prop end on center if you wanted.

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Bull City

Bull City
6,850
2,501
North Carolina
Not sure if it's helpful but can the battery be installed in any orientation? Perhaps rotated onto its side and mounted against a berth would give enough room to mount the pod next to it on/near center line? I thought about this at one point, however, it will fit in the space "right side up" pretty easily. The only other place in the boat where this is possible (other than the cabin sole or a bunk) is the lazarette, which would be awful. Plus, I'd like to have the controls & indicators easily accessible.

Also, just to toss a random thought, the pod strut doesn't need to be oriented straight down. If you felt it would be useful to put the upper end a bit off center you could still have the prop end on center if you wanted. ePropulsion says the pod should be parallel with the waterline. If it's off center line, I think it would be good for the strut to be vertical.

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Zonker

Super Anarchist
8,890
4,803
Canada
Some of the Gunboat catamarans had their saildrives mounted at a significant angle to the hull so the drive didn't protrude below the base of the hulls

Mounting it off center is no worse than a sailboat with an outboard on a bracket that is a bit offset to center to clear the rudder. A few inches either way won't matter (but ask which side because one side is better due to different direction of prop rotation).

Yes to a backing plate. The thrust is > hundred or so pounds at least. And it's continuous, and it reverses when the prop is in reverse.

And likely yes to getting rid of ancient gate valves. Gate valves don't seal well if a tiny bit of growth or debris gets in the gate and often were not bronze. Though given the age of the boat and they are still intact, they might be.

 
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