ePropulsion Pod Drive

[TwoLegged]

Bull, if I am reading the drawings correctly, then the battery would fit in the mystery compartment marked by the arrow.

So why not put a hatch in the cockpit sole,and install the battery there?  That way you keep your storage drawer in the next compartment

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.

View attachment 417313

 

[Ishmael]

Bull, if I am reading the drawings correctly, then the battery would fit in the mystery compartment marked by the arrow.

So why not put a hatch in the cockpit sole,and install the battery there?  That way you keep your storage drawer in the next compartment

Also an ideal place for a storage of wine, spirits, and other intoxicants. Put at least 12 screws in it and the totally inebriated/stoned will never figure it out, unless they meet and get a synapse together.

 

[fufkin]

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.

View attachment 417313

That adds a bit of unforeseen complexity to the mod. My main reason for suggesting moving the prop back is that, where you  propose placing it, you're losing a gear for close quarter handling and manoeuvring with prop/rudder burst to kick the stern around and pull a 360 on the spot and or when docking. It's not the end of the world but worth considering. I guess you also have to consider the size of the rudder when deciding whether this approach is worth looking at.  The other thing is, the boat will squat a bit under power and that's where I'd try to pinpoint the ideal prop position(in an ideal world independent of bulkhead restrictions), and work from there. Even where you propose it will work fine...just pointing out some possibilities.

Measure twice cut once.

 

[Zonker]

It's not going to squat with such low power.

 

[fufkin]

It's not going to squat with such low power.

Zonker I'll defer to you on that...I'm just checking this thread late. How close to hull speed can proposed E power get to?

 

[Zonker]

The 3 kW is the larger model. That's 4 HP.  Pretty close to hull speed because the boat is a slippery 3200 lb H boat. But squatting really happens when you drive the boat PAST hull speed and the bow wavelength exceeds waterline length

 

[fufkin]

If the boat could be powered to hull speed, and depending on prop placement, would there be a little bit of squat? Or am I misinterpreting it?

Isn't it basically a combo of power and placement on the hull?

_edit-I guess shape of underbody is also a variable

 

[jdege]

The 3 kW is the larger model. That's 4 HP.  Pretty close to hull speed because the boat is a slippery 3200 lb H boat. But squatting really happens when you drive the boat PAST hull speed and the bow wavelength exceeds waterline length

How do you calculate that?

I've not found a good source for even simple rules of thumb as to how much power is required to push a displacement boat to a certain speed.

 

[Zonker]

More experience than anything else for this example. I owned a San Juan 24 which had an 8 HP outboard. Roughly similar waterline and displacement. Could never use more than 2/3 the power of the engine or about 5 HP because it would squat and flood the cockpit. So 4 HP on a similar hull (roughly) gets you close to hull speed.

it does depends a lot on hull shape & displacement/L ratio. Not so much on location of prop unless you are using a very steep shaft angle.

If your sailboat is similar to the Delft Systematic Yacht Series (or even if it isn't) you can use their resistance coefficients to predict full scale resistance. It's just a regression analysis of lots of hull parameters. They create a polynomial curve to fit the tested resistance data on a huge series of scale models in a towing tank.

Note this is for Bare Hull resistance i.e. no rudder and keel. But you can use NACA L/D curves to give you Cd values for typical foils so that part is easy.

Lots of papers on it, but you could start with this one.

http://www.remmlinger.com/Regression DSYHS.pdf

Then once you have resistance you can estimate required thrust at a given speed. Estimating thrust of a particular prop at a particular RPM is beyond the scope of this course

 

[TwoLegged]

My main reason for suggesting moving the prop back is that, where you  propose placing it, you're losing a gear for close quarter handling and manoeuvring with prop/rudder burst to kick the stern around and pull a 360 on the spot and or when docking

Compared with the outboard hanging off the stern, surely any inboard ahead of the rudder will be a step up several gears in handling

 

[solosailor]

RE: comparing the electric vs. gas motors and the "comparable" HP claim.   You simply cannot compare the normal HP equals x in kWh.   There is simply a huge loss of efficiency in gas outboards.

In the real world I've run the T1003 and the Cruise 2.0 as well as a 3.5HP and 6HP (4-strokes).   Boat is a 30', 4500+ slippery sportboat.    

The T1003 could barely make 4.5k  

The 3.5HP gas (I use this motor the most) can make 5.6-5.8k

Cruise 2.0 could make 6k

6HP gas does 6.5+

 

[Bull City]

RE: comparing the electric vs. gas motors and the "comparable" HP claim.   You simply cannot compare the normal HP equals x in kWh.   There is simply a huge loss of efficiency in gas outboards.

In the real world I've run the T1003 and the Cruise 2.0 as well as a 3.5HP and 6HP (4-strokes).   Boat is a 30', 4500+ slippery sportboat.    

The T1003 could barely make 4.5k  

The 3.5HP gas (I use this motor the most) can make 5.6-5.8k

Cruise 2.0 could make 6k

6HP gas does 6.5+

My experience (27' 3200 lbs.) is/was T1003 will reach 4.5 knots in glassy water, a Honda 2 HP about 5.

 

[Bull City]

Bull, if I am reading the drawings correctly, then the battery would fit in the mystery compartment marked by the arrow.

So why not put a hatch in the cockpit sole,and install the battery there?  That way you keep your storage drawer in the next compartment

I thought about that. I decided against it because:

• The battery is 106 lbs. The storage bin space seems better in that it's lower and further from the ends.
  
• I want to have easy access to the indicators and controls on the battery.
  
• I hate cutting holes in my boat.
  
• While the storage bin is handy, I really don't use it much.
  

I corresponded with a fellow H-Boat owner in Switzerland, who had a little diesel inboard, because he hates OBs. Fossil fuel engines were banned from his lake, so he removed the diesel and installed an Aquamot electric pod. He loves it. (The US Aquamot dealer has not responded to my inquiry.) I mention it because he had to make a hatch in the cockpit sole to accommodate the diesel.

That reminds me... I need to ask him about fouling.

 

[Bull City]

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). I don't know which way the prop goes. Which way is best - same or opposite?

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. I agree.

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.

 

[TwoLegged]

I thought about that. I decided against it because:

• The battery is 106 lbs. The storage bin space seems better in that it's lower and further from the ends.
  
• I want to have easy access to the indicators and controls on the battery.
  
• I hate cutting holes in my boat.
  
• While the storage bin is handy, I really don't use it much.
  

Fair enough.  My thinking was that a) the after compartment was still a long way from the stern, and b) there is probably some remote panel available for the battery.

But if you can live without the storage space, then the fwd location is simpler and cheaper and a better place for the weight.

BTW, I am really enjoying this thread.    I think it's kinda wonderful that this sort of auxiliary propulsion is now available more-or-less off-the-shelf, for probably less money than a new diesel.  For those of who go sailing for the sheer pleasure of the sailing and want an engine only for docking rather than passage-making, electric propulsion feels like an answer to a prayer. Have you established whether the E-Propoulsion pod does regen? 

 

[Bull City]

Have you established whether the E-Propoulsion pod does regen? 

I haven't. I asked the dealer a bunch of questions just before Christmas, but haven't heard back

I think it's kinda wonderful that this sort of auxiliary propulsion is now available more-or-less off-the-shelf, for probably less money than a new diesel.  For those of who go sailing for the sheer pleasure of the sailing and want an engine only for docking rather than passage-making, electric propulsion feels like an answer to a prayer.

I agree. The Torqeedo has been great, despite its limitations. I think the pod addresses a lot of them. Plus I'll have about 1200 more Watt hours.

 

[DDW]

A little hard to get the scale from the drawings, is it possible to cut a hole in the bulkhead and install the pod drive in the mystery compartment? You only need to reach in there once, to do the install. 

If it was my boat, I'd remove those cockpit drain hoses, gate valves, and thru hulls and hard plumb it with G10 tubes. No valves. No rubber hose. No hose clamps. Unless there was some compelling reason to close them routinely. 

 

[DDW]

RE: comparing the electric vs. gas motors and the "comparable" HP claim.   You simply cannot compare the normal HP equals x in kWh.   There is simply a huge loss of efficiency in gas outboards.

In the real world I've run the T1003 and the Cruise 2.0 as well as a 3.5HP and 6HP (4-strokes).   Boat is a 30', 4500+ slippery sportboat.    

The T1003 could barely make 4.5k  

The 3.5HP gas (I use this motor the most) can make 5.6-5.8k

Cruise 2.0 could make 6k

6HP gas does 6.5+

The frequent claim of "a huge loss of efficiency in gas outboards" makes as much engineering sense as the electric industries "equivalent horsepower". Alternative facts may play well in politics but are useless in engineering. Your results pretty much confirm that horsepower is horsepower, however produced.

T1003 (1000 watts or 1.3 hp) made 4.5 knots

3.5 hp gas made 5.7 knots

Cruise 2.0 (2000 watts or 2.6 hp) made 6 knots

6 hp gas made 6.5 knots.

That's pretty much the expected curve for a displacement hull. The slight deviation of the 3.5 gas can easily be explained by having the prop and gearing poorly matched to the speed. Horsepower is a physical quantity and is supposed to be measured at the output shaft. Doesn't matter if it is electrons or gas explosions or rubber bands or squirrels spinning it.  Prop efficiency is another matter, it may be more convenient to make an electric with a slower, more efficient prop, but there are gas outboard that do that too. 

 

[fufkin]

Compared with the outboard hanging off the stern, surely any inboard ahead of the rudder will be a step up several gears in handling

Sure but why give up on extra stern handling by not putting the prop closer to the rudder? Its a small boat so the difference between 'kicking the stern' and throwing a line or what not might be somewhat academic. Nevertheless, looks like the fellow owner who Bull consulted with opted to put the prop further aft and below the 'mystery compartment'. Also, as far as drilling holes, a small hole in the bulkhead and you can easily put the battery closer to centre in the 'storage area', if desired.

BTW, you can turn an outboard but you can't turn a fixed prop. Luckily for me I swore off auxiliary outboards on a sailboat 40 years ago so its a distant never to be revisited memory.

 

[weightless]

RE: comparing the electric vs. gas motors and the "comparable" HP claim.   You simply cannot compare the normal HP equals x in kWh.   There is simply a huge loss of efficiency in gas outboards.

I don't want to jack the thread but AFIK <-- not much on this -- most of the potential comparative efficiency losses of gas outboards are accounted for in the rating. In the US, at least, I believe gas outboards are rated at the prop shaft.

International Council of Marine Industry Associations Standard No. 28-83 3.3.1--Power shall be declared as Propeller Shaft Power at the propeller shaft of engines sold with complete propulsion units

IME, a Honda 2.3 (1.7kW at the prop shaft) is noticeably more powerful on a small keel yacht than a 1003 (1kW at the battery). I haven't taken data and haven't made any effort to optimize the props -- using stock on both. So, there are confounding issues. Still, the difference is obvious and doesn't support the theory that electric outperforms its rating. My feeling is that shp is a reasonable way to get a quick comparison of the propulsive work a gas or electric or steam or whatever auxiliary can do. YMMV, and I'm happy to let it go at that.