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Author Topic:   old 15 hp mercury to new 15hp merc

clmayeux posted 01-11-2006 11:46 AM ET (US)
I previously had an older 15 hp merc on my 11' whaler and it wasn't quite powerful enough-even with various props. an older 18hp merc is powerful enough but i have a long shaft and need a short one.
Question: Should I get a new 15 hp merc or another brand with 18 hp? In other words, is the newer merc going to be more powerful than an older comparable one that was in good shape because of new technology, etc?

bsmotril posted 01-11-2006 12:57 PM ET (US)
Depends on how old the original motor was. Prior to the early 80's, motor HP was rated at the crankshaft, versus the propshaft. When manufacturers standardized on prop shaft ratings, the old ratings dropped by about 12-15%. So, if you have an old pre 80's merc 15HP, it would only be a 12 HP under the new (and current) ratings. Bills
Teak Oil posted 01-11-2006 03:35 PM ET (US)
The Merc 18 is a detuned 25, so thats why it has more power. A 15 will be too weak for anything more than 1 person.
Get a 20 or 25
clmayeux posted 01-11-2006 04:45 PM ET (US)
thanks. what about the tohatsu 18hp two stroke?
Sonic posted 01-11-2006 11:15 PM ET (US)
The Tohatsu 18 is critically acclaimed, and knowing Tohatsus, will run forever.
I'm also fairly certain that it is about as light as a motor in that class is going to get.
What about an old fashioned carbed 2 stroke Yamaha 25...they only weigh about 100 lbs, and weight is significant on an 11'
rbruce posted 01-15-2006 10:18 AM ET (US)
Some members have 35's on their 11's. It makes some sense to me, the hull is very heavy!
To be on the safe legal side, I would have a 25 mounted, I would prefer a Mercury 25 Classic where the weight gain wouldn't be so much.
Be safe.

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Author	Topic: old 15 hp mercury to new 15hp merc
clmayeux	posted 01-11-2006 11:46 AM ET (US) I previously had an older 15 hp merc on my 11' whaler and it wasn't quite powerful enough-even with various props. an older 18hp merc is powerful enough but i have a long shaft and need a short one. Question: Should I get a new 15 hp merc or another brand with 18 hp? In other words, is the newer merc going to be more powerful than an older comparable one that was in good shape because of new technology, etc?
bsmotril	posted 01-11-2006 12:57 PM ET (US) Depends on how old the original motor was. Prior to the early 80's, motor HP was rated at the crankshaft, versus the propshaft. When manufacturers standardized on prop shaft ratings, the old ratings dropped by about 12-15%. So, if you have an old pre 80's merc 15HP, it would only be a 12 HP under the new (and current) ratings. Bills
Teak Oil	posted 01-11-2006 03:35 PM ET (US) The Merc 18 is a detuned 25, so thats why it has more power. A 15 will be too weak for anything more than 1 person. Get a 20 or 25
clmayeux	posted 01-11-2006 04:45 PM ET (US) thanks. what about the tohatsu 18hp two stroke?
Sonic	posted 01-11-2006 11:15 PM ET (US) The Tohatsu 18 is critically acclaimed, and knowing Tohatsus, will run forever. I'm also fairly certain that it is about as light as a motor in that class is going to get. What about an old fashioned carbed 2 stroke Yamaha 25...they only weigh about 100 lbs, and weight is significant on an 11'
rbruce	posted 01-15-2006 10:18 AM ET (US) Some members have 35's on their 11's. It makes some sense to me, the hull is very heavy! To be on the safe legal side, I would have a 25 mounted, I would prefer a Mercury 25 Classic where the weight gain wouldn't be so much. Be safe.