Favorie stupid

[gonzo]

What is your favorite stupid claim about boats or marine systems? :?:

[hoytedow]

Ossifer I had to drive the boat. I'm too drunk to swim.

[Ad Hoc]

That is what my computer program says...

[PAR]

The hours any designer suggests he's designs can be home built in (except mine of course) . . .

[hoytedow]

This stuff is on two threads.

[hoytedow]

"SOME IDEAS ARE SO STUPID ONLY INTELLECTUALS BELIEVE THEM."
George Orwell

[Manie B]

Absolutely me as well

The hours any designer suggests he's designs can be home built in

never ever - and please guys, if we are wrong, be ever so kind as to point us in the right / correct direction :D

Yours truly
Tra la la

:D 3 flippen years and not finished :D

[Leo Lazauskas]

What is your favorite stupid claim about boats or marine systems? :?:

A few years ago, I read a claim that using a transom stern on an Olympic
rowing shell can reduce drag by 10%.

[gonzo]

Don't worry about going offshore fishing, you are covered by the warranty

[philSweet]

First line of very used boat ad, big print, bold, all caps-

THIS IS NOT A PROJECT BOAT

If that one wasn't, I'd hate to know what he though a project boat was.

[philSweet]

1 electric HP = 2 diesel HP. Check any hybrid thread, it's reached the status of legend.

[philSweet]

"waterproof"

[Yobarnacle]

Actually, 1 electric hp rating is closer to 5hp rating in a piston engine.
It's bordering on "stupid" to say it ain't. I'm not attacking you, philsweet. Just setting record straight

[philSweet]

correction- 1 electric HP = 5 piston HP

[Yobarnacle]

yep. Use lots of pumps on ships. A 30hp 220 3 phase will out pump a 167hp 471 detroit, both hooked to identical pumps. The electric will provide higher pressure at a higher head

[daiquiri]

"No-compromise design"

[hoytedow]

I am glad I cpr'ed this thread.

[Outboard Dave]

What do you mean you want me to take a "field sobriety test" on the water?

[troy2000]

Sleeps six comfortably...

[Frosty]

I read somewhere that a man was seen walking his son round a marina one day. His son spotted the wind vane generator and asked what is that?

His Father said when the wind gets low and the boat wont move they turn on the fan.

[philSweet]

wipe on, rinse off, removes rust stains, oxidation, oil, marine growth .........

[PAR]

Some assembly required, using common hand tools . . .

[Mr Efficiency]

yep. Use lots of pumps on ships. A 30hp 220 3 phase will out pump a 167hp 471 detroit, both hooked to identical pumps. The electric will provide higher pressure at a higher head

Er......then it is a little misleading if 30 hp can outdo 167 hp on the same job, no ? Doesn't make sense to class each unit by hp if that is the case.

[daiquiri]

The electric will provide higher pressure at a higher headWhat do you intend by "head" here? Is it not a pressure?

[Mr Efficiency]

I read somewhere that a man was seen walking his son round a marina one day. His son spotted the wind vane generator and asked what is that?

His Father said when the wind gets low and the boat wont move they turn on the fan.

I thought when the wind wouldn't blow and the boat couldn't go, they got Carter, the farter, to start 'er ? :p

[Yobarnacle]

Ten lb oil base drilling mud is a solution of diesel mixed with iron bearing clay so one gal weighs 10 lbs. There isn't always oil under gas but there is ALWAYS gas above oil. The gas has 2000psi pressure or more, because weight of earths crust pressing on it. In order to drill 1000s of feet deep and not have the gas blow out of the well at mach 2 velocity, exploding into fireball the minute it hits the air, you need a liquid cork in the well pipe. Thats what drilling mud is.

A supply boat pumps mud and other products up to the rig. The rig usually stands on legs above the water. The mud tanks and engine room of OSV (Oilfield Supply Vessel), are below waterline/sea level.

Verticle distance from the pump outlet to the hose connection on rig (all downhill after that) is the head. Usually 60 ft or more.
GPM is rate and head psi is pressure at delivery at verticle lift height.

[TeddyDiver]

yep. Use lots of pumps on ships. A 30hp 220 3 phase will out pump a 167hp 471 detroit, both hooked to identical pumps. The electric will provide higher pressure at a higher head

You are right.. thats really stupid :P

[daiquiri]

Yobarnacle, an HP is an HP. Be it provided by electric or diesel motor, or by mine and your hands. It's always the same HP, 550 pounds of force at 1 ft/s. Always. So a diesel HP is the same as electric HP, by definition.

The difference in the pressure value (for the same mass/volume flow?) you have witnessed can be simply explained by the fact that a diesel and an electric motor have their max torque placed at different RPMs (at 50% of the maximum RPM for the diesel, around 70-80% for the electric motor). So your particular pump was better matched by the electric motor, not the diesel one.

To sum it up - an HP is always the same HP, whether it is produced by an electric or a diesel engine. The difference, for a particular application is made by the torque curve, and where is the peak torque located in the RPM range of the engine.

Cheers

[Yobarnacle]

static head pressure is weight of column of liquid on discharge side of pump when pump is stopped. A 5in ID hose holds a gallon+/- every linear foot. 60 feet head @ 10 lbs per gal, means these pumps have to restart fighting 600psi static head.
Eletric motors are torque motors. So are steam engines. They can produce torque, working against a static load when stalled. Piston engines (with exception reciprocating steam) produce no torque when stalled.
A diesel engine is rated at its max rpm. At start up rpm, its hp and torque are hugely reduced. Electric motors are rated at continuos power and provide same torque at startup as at 3500 rpm.
The 471 is rated at 2800 rpm, but no engineer would stand near it at that speed. It's about to fly apart. 2200 rpm is usually "maxed".
Can you see how a lowly 30hp hi-torque electric motor can do more usefull work than a diesel of much higher rating?
Of course these are direct drive centrifugal pumps. The diesel does have a PTO or it could never start.

[Yobarnacle]

On paper and in mathematics hp is hp. I agree.
The purpose of inventing hp, was as a measure of work.
When 2 different machines can do same or similar amounts of work, then their true work capacity is similar.
If the varios mfgs assign hp ratings that make these machines appear un-equal, who is to blame?
Are we to blindly accept their assessment as gospel? Or are we inteligent enough to observe, this works and ignore mfgs marketing tactics.

[daiquiri]

If the varios mfgs assign hp ratings that make these machines appear un equal, who is to blame?
Nobody is to blame. The pump has to be matched to a correct motor, or to a correct gear box.
This drawing will hopefully explain my point better, both engines are rated the same max power output, but have a max torque at different RPMs:

65311

Cheers

[Yobarnacle]

Maybe someone can explain this to me. My knowlege of electrical theory is marginal. The 30 hp motor electric is rated as hi-torque motor. 208v-211v 3 phase. We run at 220 volt. Is the 208volt design, being run at 220volts, what gives it its "hi-torque" as opposed to a normal 220 volt 3 ph motor?

[daiquiri]

No, it is about it's constructive characteristics. See the document attached below, pages 3 to 6, where main constructive differences of AC motors are explained. I have downloaded it time ago from somewhere, so don't have a direct link anymore.
Cheers

[Yobarnacle]

Thanks for the great graph. I'm saving it. My only point is, we can't compare apples to oranges. For boat propulsion, a propeller working in water and an impeller in a pump, are doing similar kinds of work.
The direct drive electric motor is more suited, because of high torque start up, to this task than piston engines with their clutches and reduction gears.
How much electric motor do you need? A lot less than a piston engine doing same job.
Different job, like a truck or car? Maybe piston engine more appropriate.

Trains and ships use diesel electric for a reason. Efficiency.

Some ships use piston engines hooked to shafts thru gears. Lower initial costs.

It depends on your application and needs.

[Yobarnacle]

Im saving pdf too. thanks. how did you post a pdf? I've tried and won't let me

[Yobarnacle]

seems I hi-jacked this thread. Sorry

I guess its on topic if I make a stupid A__ of myself?

[daiquiri]

Thanks for the great graph. I'm saving it.
I have updated the graph, to show the engines of the same max power (plus a correct pump torque curve), as is the point I wanted to explain. Cheers!

[Yobarnacle]

Thanks.
Since I already hi-jacked the thread, let me ask one more question.
If a vessel design called for a 16 inch diam 14 pitch prop driven by 35 hp diesel with 2.5:1 reduction. but you wanted to drive same prop with direct drive electric. How big an electric motor is needed to swing the same prop? 35hp?

[daiquiri]

How about starting a thread dedicated to that question? ;)

Then perhaps Jeff (BD.net admin) could move there this side-drift discussion about pumps and electric motors...

[Yobarnacle]

ok, ok is too few letters, so ok again

[hoytedow]

ok, ok is too few letters, so ok againMaybe use the alternative spelling "okay" or "au quai".

[Yobarnacle]

now at this link

http://www.boatdesign.net/forums/open-discussion/how-do-you-compare-electric-motor-power-diesel-power-41038.html#post511437

[Yobarnacle]

hmmm? What's MY "favorite stupid" around boat stuff? hmmmm.
MOI

[hoytedow]

My wife's favorite stupid around boat stuff is me. :P

[rwatson]

"You can learn to sail in an afternoon."

http://www.macgregor26.com/easy-to-sail/easy_to_sail.htm

[Yobarnacle]

"Clean her up a little, she'll be good as new!"

[gonzo]

It must be true, Gonzo said it on the forum.

[Yobarnacle]

Ahhh! :( But you BELIEVE the things you say are true. Same as the rest of us. :D

[Doug Lord]

"My boat does 20 knots per hour!"

[philSweet]

from Cariboni's brocher on magic trim systems. Forget learning to sail a 26' footer, just start with the real thing:D:D:D

Wally 148’ “Saudade”. MagicDouble cylinders manage the jib sheet and the
mainsheet in this fast maxi. So, even a boy can sail fast and safety just
pushing a button.

maybe something lost in translation? Any comments from the Italians, this isn't something I would have advertised, even if it were true.

References to Clint Eastwood would make more sense than to Alfred E Neuman.

[Yobarnacle]

"What! Me worry?"