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Old 16-12-2018, 03:30   #1696
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
Cats do have a hull speed. Some really fast ones, are so far outside the normal range that it seems as if they don't...but if it really bothers you pick a performance speed that the boat needs to determine motor size requirements.
Ok, what's the formula?

What's hull speed for my 44' cat?

The point being made was that when a cat is sailing at hull speed you can extract power from it with no reduction in speed. This may be true for heavy monos, but I don't think it's true for cat's.
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Old 16-12-2018, 03:42   #1697
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
While it's true you can't come up with a specific power needed down to the nearest watt...that's like saying you can't know the maximum load on a bridge.. so just design for the typical loading...

How it works is you make some reasonable assumptions about the conditions you expect to be able to handle and how much power you need to handle them.

But ABSOLUTELY YOU NEED TO KEEP THE ASSUMPTIONS THE SAME FOR BOTH POWER PLANTS.
Yes exactly.

But my point is that unlike a public works project, from scratch and safety the main priority, where to draw the line is up to each owner.

Like asking "how much should I build my net worth up to before I retire"?

Variations in acceptable risk alone, so many variables, no one answer fits all.
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Old 16-12-2018, 07:55   #1698
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
Ok, what's the formula?

What's hull speed for my 44' cat?

The point being made was that when a cat is sailing at hull speed you can extract power from it with no reduction in speed. This may be true for heavy monos, but I don't think it's true for cat's.
No, that wasnít the point. The point was that that climbing and surfing is inefficient. And if those are the waves youíre encountering, you may be better off keeping the sails up if you can maintain a comfortable cruising speed, and taking in some extra power if you can use it (now or later).

I didnít suggest avoiding bashing over waves wouldnít be slower. Just that with EP the choice isnít between speed and comfort only but also the opportunity to trade excess speed for power and comfort.
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Old 16-12-2018, 08:35   #1699
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Re: Oceanvolt Hybrid Motor

Still the EP evangelists donít look at the energy balance equation. Excess power has to be transferred from sails to hull. So you reef later than normal. Thus rig must be much stouter (50%?). Regen favors big slow turning props. In heavy seas they transfer much larger loads to the hull attachment point (skeg or sail drive). It means beefier hull around the prop (100% stronger?) and elsewhere. Read in this or another thread about EP sail drive getting bashed off a boat.

There is no free lunch. And EP is a really expensive lunch for what benefit? So we can feel good or enjoy less noise is about all I can gather. Seriously, where is the pot of gold at the end of the EP rainbow? And donít tell me we just need a technical breakthrough. Technical has done about all it can with weight and efficiency. Even if the generator, inverter and electric motor are all 100% efficient you have gained very little efficiency (20%?) over mechanical. And added tons of complexity to a life critical system.

Unless solar panels get 10 times more efficient (unlikely) EP will never make economic or environmental sense for comfortable cruising to me.
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Old 16-12-2018, 08:43   #1700
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Re: Oceanvolt Hybrid Motor

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Originally Posted by transmitterdan View Post
Still the EP evangelists donít look at the energy balance equation. Excess power has to be transferred from sails to hull. So you reef later than normal. Thus rig must be much stouter (50%?). Regen favors big slow turning props. In heavy seas they transfer much larger loads to the hull attachment point (skeg or sail drive). It means beefier hull around the prop (100% stronger?) and elsewhere. Read in this or another thread about EP sail drive getting bashed off a boat.

There is no free lunch. And EP is a really expensive lunch for what benefit? So we can feel good or enjoy less noise is about all I can gather. Seriously, where is the pot of gold at the end of the EP rainbow? And donít tell me we just need a technical breakthrough. Technical has done about all it can with weight and efficiency. Even if the generator, inverter and electric motor are all 100% efficient you have gained very little efficiency (20%?) over mechanical. And added tons of complexity to a life critical system.

Unless solar panels get 10 times more efficient (unlikely) EP will never make economic or environmental sense for comfortable cruising to me.
Something is seriously wrong with your boat if the thought of pulling a few hundred watts off your saildrives makes you question wether your sails can handle the load or wether the freaking sail drive is going to get ripped off entirely.

What a ridiculous argument.
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Old 16-12-2018, 09:25   #1701
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Re: Oceanvolt Hybrid Motor

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Originally Posted by ssmoot View Post



What a ridiculous argument.

Regen is not efficient. It requires about 10 times more power from the rig than the energy it produces to the batts. So to get 1kW regen the sails have to produce about 10kW. That loads up the rig and increases stress. Rigs and hulls are designed for certain loads. Ignoring that detail is a mistake no matter how overbuilt your boat is. And EP is most attractive to lighter boats. It is not a ridiculous point.
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Old 16-12-2018, 09:42   #1702
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
Bigger prop on the OV spinning at same rpm?

It commonly uses a 17.5" Gori or Flexofold for the SD15, and their own variable pitch Servoprop is 18.7" (475mm).

My data inputs are admittedly limited, until we get more data from OV users that are out there, with the specifics of the use in calm water; kW used, boatspeed, prop used etc.

I compared owner reports from a Freeflow 46 with Yanmar 54HP 4JH5E's and 8 years experience cruising with them > 7 knots on one engine at 2250 rpm , and a Slyder 47 with SD15, 7 knots using 15kW. They are very comparable boats wrt hull shape, Lwl/Bh, Displacement. The Freeflow has daggerboards and they were up. The Slyder has mini keels. So hull resistance I'm taking as being very similar, apples to apples.

I looked at the propeller power curve for the Yanmar, as being about 17kW, is that correct?


#1
Freeflow 46
Yanmar 54HP 4JH5E
> 7 knots on one engine at 2250rpm using ~17kW output at prop (yes, you look correct).
Prop?

#2
Slyder 47
SD15
7 knots using 15kW (not output at prop)
Prop?

The problem with the above data is the ">". How much greater? And not knowing the props. Any more details you could provide will help, but I understand it may not be easy to get. Whatever you got.
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Old 16-12-2018, 09:49   #1703
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Re: Oceanvolt Hybrid Motor

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Originally Posted by transmitterdan View Post
Regen is not efficient. It requires about 10 times more power from the rig than the energy it produces to the batts. So to get 1kW regen the sails have to produce about 10kW. That loads up the rig and increases stress. Rigs and hulls are designed for certain loads. Ignoring that detail is a mistake no matter how overbuilt your boat is. And EP is most attractive to lighter boats. It is not a ridiculous point.
While it's not ridiculous to consider the effects of regen on build, for certain:
  • If the drive can push the boat at 15kW (or whatever), it certainly can take a tiny fraction of that load in negative. It's certainly within design constraints by a healthy factor.
  • If the sails can take the load at speed, then they certain can take the load during regen. The load is the same, just in one case you are going faster.

So "never" and 100% more rigging and 50% beefy mounts is unlikely.

I never trust a sentence that has "never" in it, nor do I always trust "always".
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Old 16-12-2018, 10:31   #1704
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Re: Oceanvolt Hybrid Motor

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Originally Posted by bridaus View Post
While it's not ridiculous to consider the effects of regen on build, for certain:
  • If the drive can push the boat at 15kW (or whatever), it certainly can take a tiny fraction of that load in negative. It's certainly within design constraints by a healthy factor.
  • If the sails can take the load at speed, then they certain can take the load during regen. The load is the same, just in one case you are going faster.

So "never" and 100% more rigging and 50% beefy mounts is unlikely.

I never trust a sentence that has "never" in it, nor do I always trust "always".

Easy to test!


20kt wind, full sails, boat at speed, put engines in reverse with couple thousand rpm! See if the rig fails!!
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Old 16-12-2018, 10:50   #1705
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Re: Oceanvolt Hybrid Motor

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Originally Posted by bridaus View Post

[*]If the sails can take the load at speed, then they certain can take the load during regen. The load is the same, just in one case you are going faster.
Going downwind, slower = more apparent wind. If you have the same sails up, loads will be higher.

Anyway, this should be obvious - if you're extracting power when sailing, that power has to come from the sails.
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Old 16-12-2018, 11:35   #1706
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by ssmoot View Post
Something is seriously wrong with your boat if the thought of pulling a few hundred watts off your saildrives makes you question wether your sails can handle the load or wether the freaking sail drive is going to get ripped off entirely.

What a ridiculous argument.

Well, I think the point is a "few hundred watts" is a meaningless quantity of power for propulsion purposes.



If you intend to produce enough power by regen to use later for propulsion, then you need to be producing kilowatts, probably many of them. This would indeed require attention to the things TD mentioned.
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Old 16-12-2018, 11:39   #1707
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by bridaus View Post
While it's not ridiculous to consider the effects of regen on build, for certain:
  • If the drive can push the boat at 15kW (or whatever), it certainly can take a tiny fraction of that load in negative. It's certainly within design constraints by a healthy factor.
  • If the sails can take the load at speed, then they certain can take the load during regen. The load is the same, just in one case you are going faster.

So "never" and 100% more rigging and 50% beefy mounts is unlikely.

I never trust a sentence that has "never" in it, nor do I always trust "always".

I think that's all correct, but it's a theoretical discussion, because regeneration of a "tiny fraction" of the propulsion power is not going to be useful for propulsion purposes.


Not only is it hard to produce propulsion-grade quantities of power by regeneration, it is hard to store propulsion-grade quantities of power in batteries.


I think it was you who made the important and correct point that we need to look at the entire system.
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Old 16-12-2018, 12:43   #1708
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Re: Oceanvolt Hybrid Motor

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Originally Posted by OldMan View Post
Easy to test!


20kt wind, full sails, boat at speed, put engines in reverse with couple thousand rpm! See if the rig fails!!


Not really a valid test. And we are talking again about safety of life equipment. No one pushes their rig even close to failure. But that safety margin can only exist when all loads are considered and sufficient safety factor applied to the rig.

If you can only get 500W from the regen then the loads are insignificant but so what? So is the power produced.

Power is not free. Just like lunch.
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Old 16-12-2018, 13:14   #1709
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by bridaus View Post
#1
Freeflow 46
Yanmar 54HP 4JH5E
> 7 knots on one engine at 2250rpm using ~17kW output at prop (yes, you look correct).
Prop?

#2
Slyder 47
SD15
7 knots using 15kW (not output at prop)
Prop?

The problem with the above data is the ">". How much greater? And not knowing the props. Any more details you could provide will help, but I understand it may not be easy to get. Whatever you got.
Sorry for delay bridaus, busy time of year and I've been more lurking than participating lately...

Yes that breakdown is correct. The Freeflow 46 uses Brunton Autoprops 16.5" don't know the pitch.
The Slyder 47 I don't know the props but for performance cats they are "usually" 17" Gori feathering.

Apologies, the ">" was a typo, I meant to put in a ":: .
I did not mean that the boatspeed was greater than 7 knots

On the issue of regen, this sounds like some thing that would be right up your alley. The analysis, I mean. Because the understanding of why regen is so attractive will come down to math. I think I understand the principles, but don't have the math skills to tackle it even if I had the time.

What some of our engineer friends could do for us is take the hull resistance values for a given cat, then calculate the force produced by a given sail area (main + jib) that results in a resultant boatspeed from a given wind speed, and then make a prediction on how much of that force the regen would "rob" from the sails and therefore how much the boat would slow down. The nice thing about science is that it looks for falsifiability, and can make predictions if the hypothesis is correct.

So here is my guess. The force produced by the sails to move a cat at a given speed is so large that, the regen produced that acts in the opposite direction ( yes, Mr. Newton was exactly correct about conservation of energy) is a very small percentage of the total resultant sail driving force. We guesstimate it at 1 to 2 %. Thus, the speed does not drop by much. But I would LOVE to see the math done.

Here are some data for starters ( Merry Christmas ) from our hull resistance analysis.

Values are hull resistance in Newtons (N) at boatspeeds calm water in Knots (kts):

3.0 kts 320 N
4.2 kts 710 N
5.4 kts 1,380 N
6.5 kts 2,832 N
7.7 kts 3,482 N
8.9 kts 7,634 N

Mainsail 70 square meters, Jib 42 square meters

All I can tell you from direct observation of the regen from Oceanvolt is that when you "push the button" to turn on the regen, you do not see the boatspeed drop very noticeably. It is tenths of a knot, maybe up to half knot from what I have seen. This also accords with the reports from several OV SD15 owners, because i always ask about their regen experience, as I did with SV Reality. His result seems to be an outlier as far as the kW produced, and I look forward to hearing more from him as he gathers more information.

Strangely, from my point of view, nobody seems to ever record good data, which is frustrating.

Here is the Slyder 47 with the older SD15 motors on a reach producing about 1 kW ( per motor) from 9.5 knots boatspeed. When I spoke to Slyder, they did not notice the boat slow down appreciably as they put it in and out of regen, so what can I say? Let's do the math, shall we? It would be a valuable contribution, and I for one would love to get to the bottom of it.

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Old 16-12-2018, 13:17   #1710
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Re: Oceanvolt Hybrid Motor

Oh Jeez, I made a typo correcting a typo. Hopeless typing skills, sorry

Should read ":" instead of "::
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