Compare OB Power

[billybandman]

I have a 69 Merc 650 that moves my old dory at 26 mph, wide open. Time to modernize and would like to get s Honda. I have heard that the 1969 horespower ratings were measured differently then. I would really like to get the Honda 50 rather than the 75. Any calculated guesses how the new Honda 50 would compare to the tired 65HP Merc

 

[ZmOz]

Re: Compare OB Power

The old motor is measured at the crankshaft, new ones are measured at the prop. The 50 will be closer to 60 in "old HP".

 

[Paul Moir]

Re: Compare OB Power

I don't mean to nit-pick, but that's a 20% reduction in power you're quoting there. A reasonable loss for a pair of hypoid cut gears is 2-5%. Put it another way, do you really think that lower unit is disappating 7.5KW of energy? Don't you think it would need cooling fins if it did?<br />Sorry, but I see those 10-15% figures quoted all the time here on engines running hundreds of horsepower. It gets on my nerves I suppose. <br />As for hi c's question, it's rather difficult to answer without knowing how far out of tune his merc is. And weren't those 650s underrated anyway? Does you're hull have a HP rating, hi c?

 

[billybandman]

Re: Compare OB Power

No HP rating on the old girl. It is a 22' Pacific City Dory made of plywood and a fiberglass flatbottom for launching off the beach. The flatbottom makes it very easy to plane. Think it weighs about 1800 lbs as it is<br />rigged. I would be happy if I could get 25mph with a 50 and not have to jump up to the 75, more weight, more $, etc.

 

[Paul Moir]

Re: Compare OB Power

I think you could get 25mph out of that easily with a 50hp.

 

[BillP]

Re: Compare OB Power

I think 50hp is pushing the envelope for 25mph but it may be close. Regardless, you may be better off running 75hp at 70% power for fuel burn than running a 50hp wide open. They seem to get real inefficient at full throttle so you pay now or later moneywise. A 75 would give plenty of reserve for heavy loads,etc.<br /><br />If your dory is double ended you may have weight problems with a 4 stroke back there...even in a well. That would make a 50hp better.

 

[ivar]

Re: Compare OB Power

You could consider the 60hp Merc or Yamaha, they weigh ~20# more than the 50 Honda , but considerably less than the 75HP Honda. <br />The 995cc merc/yamaha has a lot more grunt than the 808cc honda.