Another RWP question
Printed From: CorrectCraftFan.com
Category: General Correct Craft Discussion
Forum Name: Common Questions
Forum Discription: Visit here first for common questions regarding your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=35390
Printed Date: November-24-2024 at 2:35pm
Topic: Another RWP question
Posted By: GMacLaren
Subject: Another RWP question
Date Posted: February-10-2015 at 12:12pm
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(Maybe not "common.") Given that many/most of these boats spend much of their lives out of the water, has anyone ever used an electric RWP? One advantage being the pump coud be located at the thru-hell pickup; hence below the water line. It would push the water, rather than pull it through a long hose and the transmission cooler. I'm sure others have considered the idea. I just can't think of any big downsides, other than the pump being dependent on the electrical system, and the circuitry needed for the system to be fail-safe.  ------------- -=Grant MacLaren=- Retired Expert http://www.grantmaclaren.com/72skier" rel="nofollow - http://www.grantmaclaren.com/72skier |
Replies:
Posted By: 8122pbrainard
Date Posted: February-10-2015 at 12:17pm
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Grant, I don't understand what's wrong with the RWP set up now and it needing to suck? As long as the suction head isn't exceeded, a flex impeller pump is pretty simple. What design of electric pump are you thinking of? Centrifugal? ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: Gary S
Date Posted: February-10-2015 at 12:27pm
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How would you vary the speed of the motor to push the water needed between idle and wide open? How big would it need to be to be able to push that amount of water? Why hasn't a company like PCM already done this or even Ilmor who seem to build engines with price no object? Why reinvent the wheel? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: Mountain Man
Date Posted: February-10-2015 at 12:34pm
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Yes see the link. It can be done. This applies more to off-shore fishing boat that are equipped with a raw water wash down system. Same theory. In concept an electric raw water pump would free up some engine horsepower. Many modern performance cars have electric water circulation pumps. www.thehulltruth.com/boating-forum/145799-connect-raw-water-wash-down-engine-flush-emergency.html#b |
Posted By: Hollywood
Date Posted: February-10-2015 at 12:39pm
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This 42' Fountain I was on had electric water pumps. Just not needed in our boats. ------------- |
Posted By: GMacLaren
Date Posted: February-10-2015 at 1:07pm
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Not much wrong with the way it is now. But as in high performance cars, the electric pump would provide more hp at the prop (or wheels in the case of cars.) I think it would also "clean up" the belt area, etc. I can't suggest a "kind" of pump. Its speed would not have to be altered, methinks. It would be sized to always provide more than needed at the engine's thermostat, with excess sent to exhaust manifolds. I'm not arguing FOR the idea. Just thinking aloud. One of my cars has gravity fed fuel. Then the car mfgs. used mechanical pumps ABOVE the fuel level. A bad system that was used for many years -- while our car-makers added tail fins(!). My boats have mechanical fuel pumps, below the fuel level. My car current has an electric fuel pump -- below the fuel level. Maybe there were some good reasons for these changes. Just thinkin'. ------------- -=Grant MacLaren=- Retired Expert http://www.grantmaclaren.com/72skier" rel="nofollow - http://www.grantmaclaren.com/72skier |
Posted By: JoeinNY
Date Posted: February-10-2015 at 1:17pm
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You could use electric circ pumps without much issue - many cars and performance boats do- but for a raw water pump I doubt you can source something adequate that's not pulling serious current- it's a lot of water. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: Gary S
Date Posted: February-10-2015 at 1:42pm
Many current cars have a way to call for help too,a coincidence?  ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: 8122pbrainard
Date Posted: February-10-2015 at 1:58pm
You're off on your concept and need to calculate again!! Free up engine HP and then tie it back up generating electric??? Then, factor in electric generation and the pump motor not being 100% efficient and you are at a loss. Think about why alternators or generators and electric motors generate heat. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Mountain Man wrote:Posted By: Mountain Man
Date Posted: February-10-2015 at 2:43pm
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For your reading pleasure and enlightenment. www.motor.com/magazine/pdfs/112009_07.pdf |
Posted By: 8122pbrainard
Date Posted: February-10-2015 at 3:45pm
You're still off on your calculation. The article is for CIRCULATION pumps. The OP is asking about the RWP. Joe's right on top of the issue agreeing.It doesn't take muck to run the circ pump but the RWP is another story.
BTW, at 746 watts per HP, the circ pump would draw about .12 HP and that's NOT taking into account the inefficiency of the electric pump. The formula is P=VI, or Power = Voltage x current. This becomes P / V = A, or Power divided by voltage equals current. The article was interesting but certainly not what I would call technical. They finally mentioned amp draws at the very end and mentioned nothing about were these amps come from. Ether they have come up with a perpetual motion device or more logically just want to sell electric pumps. http://www.motor.com/magazine/pdfs/112009_07.pdf" rel="nofollow - For everyones reading pleasure and enlightenment, here's a link ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: Mountain Man
Date Posted: February-10-2015 at 4:38pm
| Your math is sort of right - at least at low rpm's approaching zero. What your calculation lacks is the change in power input required to drive a mechanical water pump at varying RPM's. The power required increases as a cubic function of the engine speed; whereas, the power input required for an electric pump is relatively constant assuming fluid viscosity and resistance remains constant. At higher rpm's the ewp's become more efficient than the mechanical pump. I'm not selling electric water pump's...... but, it also seems like there are a whole lot of people selling and spending time working on the mechanical pumps too. I like to see technology change and improve and I believe this is an area of opportunity. |
Posted By: Gary S
Date Posted: February-10-2015 at 4:59pm
Are you talking about raw water pumps or circulation pumps now? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: Mountain Man
Date Posted: February-10-2015 at 5:42pm
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Both, but the greatest opportunity I think is with raw water pump improvement. There has not been much change in the technology in the last 45-50 years. We are still running the same exact type/models of rwp's that we had in the 70's when I was in high school. If we don't think there is anything wrong with the technology, just consider for a moment how many questions and discussion points arise on this forum (and others) about pump impeller failure, bearing seizure, leaking, and the resultant heat exchanger fouling just prior to engine and/or head damage from overheating. Can't remember the last time I packed a spare part for an automobile trip... but, we sure carry an extra rwp when we go off-shore to chase fish in the Gulf. We are currently a building a new engine for my 86/87 Fish. I went through my spare parts inventory to see if there was anything left from when I sold my Shamrock we could use - Shammy's used a crank mounted Sherwood P105. Was trying to see if there was enough room to mount it on the 351 - there is not. I have both an P-105 impeller and a complete pump in my tool shed. Where we fish we are always one sandbar, mud flat or soft bottom at low tide away from needing one or the other. Pardon me while I get down off my soap box long enough to call Skidim for a belt driven Sherwood............and a spare impeller. |
Posted By: 8122pbrainard
Date Posted: February-10-2015 at 6:59pm
You're saying none of the above on an electric pump?  ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: phatsat67
Date Posted: February-10-2015 at 10:03pm
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My G21 pump is plugging along with somewhere north of 1600 hours. I'd say those are pretty reliable pieces of equipment. ------------- |
Posted By: Gary S
Date Posted: February-11-2015 at 12:38am
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I think as a mechanical device a G21 pump simple and trouble free and with a circulation pump hard to beat. Be thankful they are still made,it makes parts way easy to find. My HM uses a direct drive Jabsco with no circulation pump,temps rarely reach 120. Later HM's added a circulation pump so they must have realized they had a problem. Jabsco parts are very hard to find now,lucky for me I was at one time able to get what I needed,only the housing is original to mine now. With the direct drive pump there is less I believe to go wrong,but when it does like a impeller or alternator belt,it is more work to change compaired to a Sherwood system. Carrying a complete extra Sherwood pump in the saltwater boat seems to be cheap insurance since it can be changed out so quickly. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: 8122pbrainard
Date Posted: February-11-2015 at 8:48am
I have mentioned it before that there really wasn't a problem with running a RWP only on the early V8's 6's or 4's. It was a matter of history more than anything. When the early industrial blocks were marinized, they knew a pump with some suction life was needed due to most engines sitting above the water line so the RWP was added. They didn't want to be redundant plus back in those days T stat's were not even used. Then they found it was actually less expensive to purchase the long block with the circ pump rather than making up the block off plate for where the circ pump would have been in a non marine application. Before the advent of decent rubbers, the early RWP's were gear pumps. They did need to be primed to close off the tight fit (.0005" when new) between the gears and hosing. Screw in grease cups served the purpose. Before starting you would screw the cups in which would pack the pump with grease sealing the clearances. After years of usage, the clearance due to wear became to great for the grease to seal and the pump would need a rebuild or replacement. Along came the flex impeller pump. Yes, I too believe the present day RWP is pretty simple and proven to be reliable. An electric in my opinion just adds complexity and the need to be sized for the max heat removal during max RPM's. This means an electric needs to deliver the same GPM at idle as WOT adding inefficiency. The crank or belt driven RWP delivers the needed water at varying loads since they run at the varying RPM's of the engine. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: GMacLaren
Date Posted: February-11-2015 at 12:42pm
Speaking of gear pumps, this from my junk drawer:    ------------- -=Grant MacLaren=- Retired Expert http://www.grantmaclaren.com/72skier" rel="nofollow - http://www.grantmaclaren.com/72skier |
Posted By: 8122pbrainard
Date Posted: February-11-2015 at 1:17pm
Pull the cap and get a feeler gauge between the gears and between them and the housing. Anything past .0005" and it's bad. Also get the dial indicator out and measure for any axial play in both shafts. It maybe junk! Where did it come from? ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: GMacLaren
Date Posted: February-11-2015 at 2:36pm
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Speaking of gear pumps, this from my junk drawer: ******************** "It maybe junk! Where did it come from?" ******************** I'm not going to mess with it in the near future. I don't know its history. It was given to me by a guy who (with his brother and father) built steel hulls for use on the Mississippi River and Lake of the Ozarks. Been in the junk collection for years. ------------- -=Grant MacLaren=- Retired Expert http://www.grantmaclaren.com/72skier" rel="nofollow - http://www.grantmaclaren.com/72skier |