30 FOOT MOTOR CRUISER, what would it need?

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30 FOOT MOTOR CRUISER, what would it need?

Post by NeilP » May 28, 2015 10:33 am

A mate has a hull from a motor cruiser
Totally stripped bare, so it is just an open topped hul..al the superstructure/ cabins were removed and fuel tanks fitted in the floor as a conversion to a fishing boat. Never got finished .


It is I guess, 30 foot, maybe 35, probably not any bigger,

Not sure what the original motor fit was , but probably something like a pair of V8's
Just wondering what sort of figures we would be looking at in relation to motor size, controller(s) etc.

No idea where you would even start at . not even sure what sort of performance would be required, probably nice to get 20 knots out of it, maybe a bit more.

I guess the motors originally fitted were in the range of 300HP / 230kw possibley less, not really sure.

How does all this power stuff work out when comparing ICE to electric ? I mean if all else stayed the same would a 200kW electric motor give the same boat "on water" performance as a 200kw ICE motor? it depends I guess on where the power output is measured and how it is quoted?


I know I am not giving very much info or what requirements are ..because we don't really know, it was just an idea to discuss initially

Who supplies motors/ controllers in this sort of power rating ? rpm for this sort of stuff. I guess you would run direct drive and bypass the original gearbox? Maybe surface piercing prop?

Ideas and thoughts appreciated for this, very probably , only theoretical proposition ?

If I get chance I'll try and get some pics and more info on the hull
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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by technopeasant » May 28, 2015 12:42 pm

Movement through water is bound to the relationship between displacement (of water) and waterline length which is 1.3 x square root of waterline length, in knots (6000 feet/hour). With recreational boats, one can use the root of overall length to make a good guess. So a 36 foot boat will have a top displacement speed of six knots. To go any faster the boat must be lengthened (catamarans count as double length boats), or be driven up (and possibly over) the bow wave. Powering a boat "uphill" requires a high level of power, i.e., two V-8 engines straining at full throttle. To move your buddy's boat at slow speeds, three or four knots, an electric trolling motor would work. Anything faster will require a lot of $$$, a great deal of time, and a general lack of common sense. :D

My heartfelt advice, from years of boat repair work, would be to saw that hull up and throw it in a dumpster and then buy a better hull for your conversion. An electric motor on a canoe is a helluvalot of fun!

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by NeilP » May 28, 2015 1:34 pm

As I said int eh last line it is very much a theoritticla proposition. It would ahve been good for 25-28 knots in its previoosu incarnation.

The chap concerned is very boat wise, being a local Channel tug boat skipper, in a previous 'life'. His last little ship was the Former US Army Transportation Corps tug ST 1982 (GROTON). It sat for many years in Jersey harbour unti being sold on to a local Arts trust for a 'project'

http://jerseyeveningpost.com/news/2015/ ... paint-job/


This 30 ish foot hull in the title of this post is mroe to see what it would take, rather than a project that is likely to be started on.

Fully realise it woudl cost a lot, if it were contemplated, that is not the isssue, we are jsut trying to quantitify it from 'a lot ' to £20,00, £30,000 ? 50,000 UK Pound.


Local currents would mean that at an absoloute minimum it woudl need a speed of 12-14 knots to be usable against our tides here in the Channel Islands. Closest mainland of continental Europe is France,
https://www.google.com/maps/d/viewer?mi ... UTF8&msa=0


But where woudl you start to look to source a big motor, of the sort of size we are talking.200kw or so ?


So a pair of
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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by technopeasant » May 28, 2015 5:22 pm

There is a post here (from 2013 with recent update) about an electric car ferry in Norway: https://endless-sphere.com/forums/viewto ... 39&t=47249
The designers stayed within the displacement rule by making it a long catamaran and not very fast. With a 500 foot waterline (262 x 2) speeds of 15kts are reasonable, at least in favorable conditions. I don't remember what the article said about electrical use, but at least conceptually, it's a good example of how to economically move cargo (cars are not heavy compared to the space they occupy) through water.

The working boats around here are often at a near-standstill during the fastest tidal flow (6kts) but one can pick one's tides, or wait for slack water, etc. To see how much power your boat would need in your waters, I'd look at commercial fishermen, who tend to be frugal. Some will need a fast boat to get out and back, 15-20kts, others will use a slow boat 5-10kts. Your tugboat friend probably knows this well: slow and steady wins the race.

I don't know where electric marine motors are sourced, but I expect you could find a wide assortment, new and used. Diesel electric power is a common thing on the water at least for auxiliary work. More important (IMHO), is the hull design and what you want to do with it. If the boat originally had two motors in it then it is likely to be a go-fast boat, and might be an awkward conversion to a single screw, if that's what you envision. But I suspect the motor would not be the expensive part, nor even two of them. Ah, I just remembered! There are charter companies who use twin electric motor catamarans for their charters. They're popular, I think... Here's one link I found: http://oceanvolt.com/sig45-electric-catamaran/ That's a 90 foot waterline, more or less, so likely less than 10kts cruising speed, but for a sailboat that's quite fast. Catamarans also have less parasitic drag from water (and less carrying capacity as a result), so difficult to transform that data into useful information for a 30 foot motorboat hull.

If I were in your shoes, I'd try to find the absolute minimum power my dreamboat would need in local waters (which in my case was a canoe and a 35 foot-pound 12volt motor) and then do a careful conversion to electric power (and stretch the boat longer if possible). One thing in your favor is the weight of batteries. Within the displacement rule, more weight means more waterline (as the boat is pushed down) and faster speeds. Outside the displacement rule, the bow needs to rise and at least attempt to climb the bow wave, so all weight needs to go aft (or overboard).

Good project, I think! There are electric outboards on the market, but generally most of the recreational marine industry is tied to twelve volt lead-acid batteries and either gasoline or diesel propulsion. You knew that, I'm sure, so am only mentioning it to point out that it's a fairly clear horizon for any entrepreneur or wiseguy inventor Brainiac-type.

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by NeilP » May 28, 2015 10:01 pm

Went past on the way home, grabbed thes iphone shots. Now uploading from bed at 4 in the morning
Shorter than i thought, only 22 foot.

Yes, had read up on the Car Ferry , nice piece of kit.
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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by JackB » May 29, 2015 12:47 am

Boats take a huge amount of energy to move at speed.
If you go really slow, they need much less.
So a fast electric boat is just not a viable option, unless you are just going a few miles and back.
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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by Punx0r » May 29, 2015 4:30 am

I'm struggling to think of motors with a great enough continuous power rating... Adavanced DC brushed motors? Otherwise you're possibly looking at salvaged drive motors from commercial electric cars. Neither would be rated for a marine environment.

You could run industrial 3 phase motors, there are even marine-rated ones. However they're ridiculously heavy: ~700kg for a 100kW motor...

For batteries a salvaged commercial li-ion EV pack might be your best bet.

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by technopeasant » May 29, 2015 8:28 am

Hmmm...five or six knots, might be fun. Try to go faster and you'll be fighting physics. Agreed, two or three hundred horsepower would help, as you originally said. To spend that sort of money, start with the right hull, not this one.

Fast boats (as this once was) are a product of the petrol age, where the limitations of water travel, I.e., the displacement rules, were overcome by simply mashing the throttle down. To do that with electric motors and batteries will require an equal level of wasted resources

Sorry to be a downer, but I'm on the sidelines with your wallet in this one.

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by Punx0r » May 29, 2015 9:06 am

A quick websearch and this is the most powerful EV motor that jumped out:

http://www.electriccarpartscompany.com/ ... p_424.html

Still only a little over 50kW continuous in vented configuration (who knows what the salt atmosphere will do to it). Two of those *might* do the job for you.

If the original boat engines were the popular 3.5 litre Rover V8's I doubt they would have been making more than 150 HP each.

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by NeilP » May 29, 2015 9:15 am

Not a wallet issue really as, as I said, it is really jsut to see what sort of figure it would cost, but if you are sayign that motors powerful enough within a reasonable weight range are jsut not possible, and not available then that is the end of it.

Yes the power requirements are great, but once up on the step, they do reduce a bit I had thoguht? or is that wrong?


So it seems from what you are all sayign is that althuogh smaller motors have a much better power to weigh compared to a IC engine, as the HP goes up , it swings in favour of ICE again.
a 240kW v8 mercruiser weighs in at about 880lbs, so 400kilos
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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by technopeasant » May 29, 2015 10:26 am

yes, yes, and yes...
a client of mine had (he ripped off a ride on a log and sank it) a fifty foot boat (made in England, btw), fifty knots, consumed a hundred gallons per hour at top speed (he's rich). Excellent boat, three diesel engines, two-speed gear boxes, but wow, that's a lot of BTUs down the drain. My boat, at the other end of the spectrum, is efficient, top speed of 6-7 knots (maybe), but each engine (diesel) still costs two gallons per hour to run at 1500 rpm. My last boat, petrol, 130 hp outboard, a light eighteen foot version of "your" hull, needed at least 100 hp to get up on a plane and then had to maintain 18kts to stay up there, at maybe 1/2 to 3/4 power. I could go two or three miles on a gallon in perfect conditions.

The key to understanding watercraft propulsion is a careful examination of the operator's wallet. Opinions vary wildly, but boats fall into three broad categories: slow and cheap (those within the displacement rules, like commercial boats, sailboats, or slow stink pots like mine), slow and expensive (power cruisers, forever trying to climb over their bow wave, I.e., a 1.5x speed increase and 4x cost increase), and planing boats (inefficient, but at least you get somewhere in a hurry).

The displacement rule (professionals use a different nomenclature but I don't remember what it is) also hides an interesting water trap: the speeds between displacement and planing are not possible for many hull designs because of the difficulty in climbing the bow wave. My eighteen foot Boston Whaler was a good example.The zone between 5kts and 18kts meant almost no helm control with a big stern wave and gaping hole behind the open transom as we climbed up the small bow wave. To slow down was to risk being swamped so careful adjusting of motor trim required at the same time. This is something every powerboat operator gets used to (and in bad weather many drown from it), but in your proposal (just a fun mind experiment at this point) that particular hull, with its short length, could be unsafe if underpowered, except in calm weather. That closed transom would help keep a wave out though. This is also why there are no round boats. They just sink into the trough between bow wave and stern wave.

Heh, I've had some coffee, can you tell? But the limitations of water craft are worth examining, I think, when one considers repurposing a hull designed for a particular type of propulsion, with a different type of propulsion.

And as always, just my two cents. Others might have better suggestions than mine.

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by dnmun » May 29, 2015 11:38 am

if you turn it upside down and raise it up on some posts then you could park underneath to keep dry. attach it to the top of some posts at the gunnels and it should make a long lasting roof. hang tarps from the gunnels down the sides to expand the coverage area. recycle, reuse.

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by Hillhater » May 31, 2015 10:59 pm

You are all over complicating it !
It's all been done before, so all you need is to purchase a few components off the shelf (AMG' shelf that is )
Shopping list..
12 x 185 hp AC motors
2 x 6 input gearboxes
12 x 200kW inverters
2 x high performance surface drives
240 kWhrs of lithium cells arranged into a 400v, water cooled pack.
..a few bits of wire !
https://www.cigaretteracing.com/eng/SP_amgelec.php


....you might get away with a few less motors ?
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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by technopeasant » May 31, 2015 11:27 pm

a really long extension cord works wonders...

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by NeilP » Jun 01, 2015 2:23 am

Yea, that cigarette racing is more where the hull owner wants to go. shame there is not much technical detail.

That is the sort of answer the owner was looking for, but does not seem to be experience with that sort of build on here, which is a shame.
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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by Punx0r » Jun 01, 2015 3:56 am

I guess there aren't many here who have the resources to drop a cool million on a DIY boat project ;)

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by blisspacket » Jun 22, 2015 7:48 pm

Here's a brief look at some electric boats
http://www.elcomotoryachts.com/electric ... ines.shtml

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by John in CR » Jun 22, 2015 10:41 pm

Take a pass on it unless you can trade it for a sailing hull, or even better a sailing cat.

Seriously, you'd be better off starting from scratch and building a lightweight form that's efficient through the water. The energy needed to get that big pig up on plane would be a total waste, and as a displacement hull it falls woefully short.

A 30ft hull puts you at a hull speed of about 7 knots. The sailing cat designer I was working with came up with only a 1500W power requirement at the prop to maintain 7 knots with the 9.5m 1,800kg displacement catamaran I was looking at building. That of course ignored windage and seaway, so it would be running on a nice smooth lake to get that kind of speed on so little power.

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by John in CR » Jun 22, 2015 10:41 pm

Take a pass on it unless you can trade it for a sailing hull, or even better a sailing cat.

Seriously, you'd be better off starting from scratch and building a lightweight form that's efficient through the water. The energy needed to get that big pig up on plane would be a total waste, and as a displacement hull it falls woefully short.

A 30ft hull puts you at a hull speed of about 7 knots. The sailing cat designer I was working with came up with only a 1500W power requirement at the prop to maintain 7 knots with the 9.5m 1,800kg displacement catamaran I was looking at building. That of course ignored windage and seaway, so it would be running on a nice smooth lake to get that kind of speed on so little power.

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by NeilP » Jun 23, 2015 1:27 am

Oh yes, if it was that sort of project. but then you are going down the lines of:

"i want an electric boat, .. what shall I use" rather than what the owner was wondering...can we electrify THIS hull, what would it take.
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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by hagerty1 » Feb 01, 2016 10:58 am

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by hagerty1 » Feb 02, 2016 11:58 am

Also remember H.P. isn't H.P. The word Rated @ R.P.M. always gets left out My 3 phase DC motor is running full torque at 450 r.p.m. A 10 H.P. internal combustion is not generating Jack at that rpm.
Generally with the torque you can get on 3 phase D.C. ()()()()()()a power a factor of 2.7 can be used.
Basically if you convert the internal combustion H.P. to KVA you will get a good idea. But
IN GENERAL a rated 10 H.P. gas internal would need a 2.7 H.P. D.C. 3 phase to replace it. Marine propulsion
does not like to run at high rpm. (This is all assuming we are not making hydroplanes) Props become very inefficient as rpm goes up, hence marine reduction gears on Internal combustion power/////not to mention the need to have gears for reverse.
The other HUGE NO NO is doing the 90 degree bend in the drive .........................AIN"T NO GOOD WAY to do it without sucking a lot of power. Just run a straight drive shaft through an off the shelf stuffing box.
The most efficient drive you will ever get is....Biggest diameter prop you can fit and spin and get to full rated r.p.m.
with the least number of blades, but at least 2. My hub motors run nice at 450 rpm. That's fine for almost any prop.
Prop slip will also go way up with r.p.m......................Look up Youtubes of Asian straight drive river boats Big ass stick with a freaking engine and a prop at the end that's the way to go.................... Oh yea catamarans do not use double their hull length to determine hull speed...it is a very complex formula, as the hulls are particularly narrow for the length and flotation to gross tonnage is a huge factor. For anything but displacement speeds it's a loosing battle. I say this as I am fitting out an electric 32 foot Cat for a 5000 mile trip around the Great Loop......
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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by ecycler » Feb 04, 2016 3:50 pm

hagerty1 wrote:Also remember H.P. isn't H.P. The word Rated @ R.P.M. always gets left out My 3 phase DC motor is running full torque at 450 r.p.m. A 10 H.P. internal combustion is not generating Jack at that rpm.
Generally with the torque you can get on 3 phase D.C. ()()()()()()a power a factor of 2.7 can be used.
Basically if you convert the internal combustion H.P. to KVA you will get a good idea. But
IN GENERAL a rated 10 H.P. gas internal would need a 2.7 H.P. D.C. 3 phase to replace it. Marine propulsion
does not like to run at high rpm. (This is all assuming we are not making hydroplanes) Props become very inefficient as rpm goes up, hence marine reduction gears on Internal combustion power/////not to mention the need to have gears for reverse.
The other HUGE NO NO is doing the 90 degree bend in the drive .........................AIN"T NO GOOD WAY to do it without sucking a lot of power. Just run a straight drive shaft through an off the shelf stuffing box.
The most efficient drive you will ever get is....Biggest diameter prop you can fit and spin and get to full rated r.p.m.
with the least number of blades, but at least 2. My hub motors run nice at 450 rpm. That's fine for almost any prop.
Prop slip will also go way up with r.p.m......................Look up Youtubes of Asian straight drive river boats Big ass stick with a freaking engine and a prop at the end that's the way to go.................... Oh yea catamarans do not use double their hull length to determine hull speed...it is a very complex formula, as the hulls are particularly narrow for the length and flotation to gross tonnage is a huge factor. For anything but displacement speeds it's a loosing battle. I say this as I am fitting out an electric 32 foot Cat for a 5000 mile trip around the Great Loop......
Peace.

Wow, that project sounds awesome. Where are you documenting the build and great loop voyage?
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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by cncdesigns » Mar 29, 2016 1:12 pm

This is a well known issue, not too hard, and hundreds of electric boats are in use.

1.
A HP from an electric motor == 3 Hp from an ICE engine.
So, if it had 2x 280 hp, about 2 x 90 Hp would give similar performance.

This is a general rule of thumb, holds up well.
Reason: Elctric has much more torque at all speeds.

2.
Electric motor and gearboxes (=VFD or ac brushless servo drive, very similar tech) are really cheap vs mechanical gearboxes.

An industrial 3-phase electric motor, or servo, is readily and cheaply available anywhere upto 1000 hp.
Its really cheap.
E.g. Surplus center, usa, 3 phase 100-200-400 hp electric motors are 500-1500$, new.
They all cost about the same, so cost =/= power.

A VFD for running one is 500-1500$, new.

A used 3-phase motor, 60-90 kW, might be as little as 200-400$.
Motor rebuild places can find one for you, and a suitable VFD, used maybe 200-600.

3.
Range.
This is the killer.

Look at tesla.
A 100 kWhr battery == 40-50 l tank of diesel in range.

So, as a car might have a 50 l tank, and the boat 100 l, you would ideallly want a 200 kWh battery, for the same 3-6 hour planing/running performance.
This is unaffordable, at approx 200-300$/kWh, at the moment, low end, new.
The tesla industrial 100 kW powerpack is the cheapest new tech solution, around 30k$ / 100 kWh iirc.

Typically, running at 2x25 kW load, you might be planing at 15-23 knots, 50 kW load, so 2 hours running for 40 knots range.
If you ran at 12-14 knots, this might be approx 160 knots range, or 4x more.

The problem is the hull, thats wasteful in power.
If you run at displacement speeds, with an efficient sailboat-type hull, ie canoe type, at 1.0 x max displacement speed, the 100 kWh battery, for a 9 m boat, might have a 165 mile range.
33 hours at 5 knots at 3 kw.

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Re: 30 FOOT MOTOR CRUISER, what would it need?

Post by d8veh » May 24, 2016 2:52 pm

If you kept the weigh down, it should be able to plane with something like 60 to 80 kw.

The easiest way to do it would be to find a crashed BMW i3 or similar, and transplant all the electrical stuff. It has a motor that can produce about 140kw and the battery should last a couple of hours while you're planing.

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