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Horsepower rating

Old Marine Engine » Blaxland » Horsepower rating « Previous Next »

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Ross
Member
Username: roscoe

Post Number: 4
Registered: 06-2011
Posted on Tuesday, January 31, 2012 - 03:37 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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?
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David Myers
Senior Member
Username: dave_myers

Post Number: 114
Registered: 11-2006


Posted on Tuesday, January 31, 2012 - 04:32 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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...
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Greg Y
Senior Member
Username: gregoryan

Post Number: 94
Registered: 09-2004


Posted on Tuesday, January 31, 2012 - 07:12 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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.
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Ross
Member
Username: roscoe

Post Number: 5
Registered: 06-2011
Posted on Wednesday, February 01, 2012 - 12:23 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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?
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Eric Schulz
Senior Member
Username: eric_schulz

Post Number: 70
Registered: 01-2007


Posted on Wednesday, February 01, 2012 - 12:33 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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
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Greg Y
Senior Member
Username: gregoryan

Post Number: 115
Registered: 09-2004


Posted on Saturday, March 08, 2014 - 08:38 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

Maybe the 5 \ 7 HP rating means; that it's 5 HP when the throttle is open only 5/7ths! lol
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neil r jones
Senior Member
Username: senojn

Post Number: 114
Registered: 08-2006
Posted on Saturday, March 08, 2014 - 11:18 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

At 7/5ths we're really putting !
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jack innes
New member
Username: jacky_boy

Post Number: 1
Registered: 11-2014
Posted on Sunday, November 09, 2014 - 11:25 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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.
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Ross Cook
Visitor
Posted on Sunday, November 09, 2014 - 11:41 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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
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Eric Schulz
Senior Member
Username: eric_schulz

Post Number: 87
Registered: 01-2007


Posted on Sunday, November 09, 2014 - 11:59 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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
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jack innes
New member
Username: jacky_boy

Post Number: 2
Registered: 11-2014
Posted on Monday, November 10, 2014 - 12:06 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

cheers Eric, I'll have to pass that on.
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J.B. Castagnos
Senior Member
Username: jb_castagnos

Post Number: 971
Registered: 07-2002


Posted on Monday, November 10, 2014 - 05:49 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

The engines I've seen with dual ratings also had the rpm listed, 6-8 was 6 at 800, 8 at 1000.
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Barry Millar
Senior Member
Username: bcm

Post Number: 58
Registered: 11-2009
Posted on Monday, November 10, 2014 - 09:41 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

Here is an except from the original goslowboat.com

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