Author |
Message |
Ross
Member Username: roscoe
Post Number: 4 Registered: 06-2011
| Posted on Tuesday, January 31, 2012 - 03:37 am: |
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balxland twins are said to be 5/7 hp, twice the singles 3.5 hp. what does the '5' mean? how does 7 hp from a blaxand twin compare to the hp of a seven hp outboard? there is a big difference in bore and stroke and also operating speed. are the twin and the outboard out putting the same hp? |
David Myers
Senior Member Username: dave_myers
Post Number: 114 Registered: 11-2006
| Posted on Tuesday, January 31, 2012 - 04:32 am: |
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Ross, The Blaxlands are rated under the old S.A.E. formula. The twins are 700cc so are rated at 7 HP. The Outboards are rated with "Developed" HP. They are high revving and only about half the size of the Blaxlands but develop more HP at a certain rev range. Thats the simplest way I can describe it. Hope this helps. Cheers Dave... |
Greg Y
Senior Member Username: gregoryan
Post Number: 94 Registered: 09-2004
| Posted on Tuesday, January 31, 2012 - 07:12 pm: |
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Interesting question; "what does the '5' mean? " Surely with the smallest sustainable throttle- opening when in gear,[Blaxland 5 \ 7 ] one would be producing less than 5HP?? Perhaps the factory's quality and machining tolerances would be so varied that any one engine could end-up between 5 and 7 HP ! ? [joke] Other examples; 6 \8 HP Greyhound Simplex 10-12 HP. To add another question to the Horsepower Ratings; I would like to know the difference in bollard- pull of equivalent powered outboard versus these direct-drive inboards, as there are a lot of other factors involved; prop size and dia, is the outboard HP taken at the crank before the reduction gear?, etc. |
Ross
Member Username: roscoe
Post Number: 5 Registered: 06-2011
| Posted on Wednesday, February 01, 2012 - 12:23 am: |
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I wonder why then is there no 2.5/3.5 singles? so which HP rating does maritime go off to determine your horsepower rating? |
Eric Schulz
Senior Member Username: eric_schulz
Post Number: 70 Registered: 01-2007
| Posted on Wednesday, February 01, 2012 - 12:33 am: |
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The only horsepower type that I know of for stationary and marine engines was brake hp. I never could see any sense in the 5-7 or similar style hp ratings rather than just 7hp. Anyone knows that an engine must have a tested maximum hp, which is the one quoted in the specifications. It should also be obvious to most that if you slow the engine down you will get less hp. Anyway, some thought it was a usefull selling point. To me it is like advertising a 1 to 2 gallon bucket! David, I am not sure about “the old SAE formula”. In England and Australia car engines were rated in RAC hp size for registration purposes. This had little to do with the developed hp. It was only the area of the cylinder (ie. top of the piston) multiplied by cylinder numbers. This resulted in small bore, long stroke engines to keep the rating down. Greg, I am no marine engineer, but theoretically an inboard with no gear box should be a fraction more efficient than an outboard that always has to use a gearbox. There may be advantages in placing the prop in a better location than available to an inbourd drive with shaft position limitations. Again, out of my depth. Pun intended! I would be fairly certain that the hp of an outboard motor is the bare engine. Eric |
Greg Y
Senior Member Username: gregoryan
Post Number: 115 Registered: 09-2004
| Posted on Saturday, March 08, 2014 - 08:38 pm: |
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Maybe the 5 \ 7 HP rating means; that it's 5 HP when the throttle is open only 5/7ths! lol |
neil r jones
Senior Member Username: senojn
Post Number: 114 Registered: 08-2006
| Posted on Saturday, March 08, 2014 - 11:18 pm: |
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At 7/5ths we're really putting ! |
jack innes
New member Username: jacky_boy
Post Number: 1 Registered: 11-2014
| Posted on Sunday, November 09, 2014 - 11:25 pm: |
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I've been told that being hand made and the power of two engines are never the same so the hp ranges between 5/7. |
Ross Cook
Visitor
| Posted on Sunday, November 09, 2014 - 11:41 pm: |
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my 1942 750cc Harley Davidson was also known as a 5/7 while the 1200cc version was known as a 10/12. all very confusing |
Eric Schulz
Senior Member Username: eric_schulz
Post Number: 87 Registered: 01-2007
| Posted on Sunday, November 09, 2014 - 11:59 pm: |
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Jack, if you are still referring to Blaxland Rae, their engines were certainly not "hand built". That firm was known for their engine component manufacturing, so they were precision engineers. Although I have not compared different Blaxlands, I would imagine they were all identical. Eric |
jack innes
New member Username: jacky_boy
Post Number: 2 Registered: 11-2014
| Posted on Monday, November 10, 2014 - 12:06 am: |
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cheers Eric, I'll have to pass that on. |
J.B. Castagnos
Senior Member Username: jb_castagnos
Post Number: 971 Registered: 07-2002
| Posted on Monday, November 10, 2014 - 05:49 am: |
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The engines I've seen with dual ratings also had the rpm listed, 6-8 was 6 at 800, 8 at 1000. |
Barry Millar
Senior Member Username: bcm
Post Number: 58 Registered: 11-2009
| Posted on Monday, November 10, 2014 - 09:41 am: |
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Here is an except from the original goslowboat.com
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