17' with a 70hp?

[brushfly]

I have a three year old Yammi 70hp two stroke on my 1981
17' Sea Ox. Built in gas tank is leaking and I'm considering the 17' Aquasport. Wondering if I can take the Yammi off the Ox and power an Aquasport of the same length. I know the Aquasport beam is a foot wider then my Sea Ox which weighs 1200 lbs.

I've seen 90's on the 17' Aquasport but any thoughts. My Sea Ox can hit 29 mph with the 70hp on a flat day. Fine. Not looking to break the sound barrier.

Thoughts? Thanks in advance.

[Redfish Ron]

My 1974 170 had a 70 Johnson VRO powering it when I bought it. The motor is toast but I am repowering it with a 75 hp Yamaha 2 stroke...which has the exact same cubic inches as the 90 hp...so in essence you have a 90 hp torque on a 75 hp top end...I doubt if anyone can tell the difference in the performance of the two motors on the same hull...

[RickK]

Welcome aboard BF  
What year 170 are you considering?  The very old ones, like mine, were designed for a 50 or a 70.  I have a 90/115 (can't be sure) on mine (well not right now during the rebuild) and it is about maxed out. Gives the boat plenty of power to spare but we still cruise about 28mph at 4k rpm. I would think 25 should be about max for the 70.

[Capt. Bob]

My 86 170 came rigged with a 70 from Bob Hewes.

I "upgraded" to a 85 115 non TNT.

[wingtime]

I think the 70 will push it just fine.

[gran398]

I think the 70 will push it just fine.

^^^^^^^^^

[brushfly]

Thanks all for the feedback. I'm in between the ideas of a restore to the Sea Ox or buying used and repowering with my fairly new Yammi.

[Coverhill]

Brushfly

I have a 17 ft Aquasport, powered by a recent 90hp 2 stroke and it tops out at 38mph.
That speed was gathered by GPS so it's accurate info, not a guess.

I suspect that a 17 ft Aquasport would get very close to the same 29mph with your
2 stroke Yami as you have been getting on your present boat. The 17 Aquasport is
a great boat, especially those made NLT the early 90s. It will plane off at 20mph.

I almost put 70hp on my boat, and would be competely happy with that motor size.
Went to the 90hp only because the 70 and 90 were built on the same block and
had the same weight, so that going to the 90 did not add any additional weight for
me.

[Coverhill]

FOR ANYONE WHO IS CONSIDERING A 17ft AQUASPORT'S NEEDED POWER

HERE IS AQUASPORT'S OWN "DATA SHEET", compiled in 1970 on its 17 foot model:

The horsepower used then was a 2stroke carbureted 85hp Johnson outboard,
driving a 13 1/4" diameter by 17" pitch 3 bladed propeller.

In Summary:
1. the boat begins to "plane" at 19.9mph at 3000rpm
2. most efficient "cruise" occurs at 25.9mph at 3500rpm
3. max speed is 37.4mph at 5000rpm

SEE "COBURN & SARGENT'S" OWN TEST DATA SHEET BELOW

[gran398]

5 mpg with 2 stroke V-4

[Coverhill]

Gran

They waxed the bottom the day of the tests

[gran398]

Gran

They waxed the bottom the day of the tests

     

[CLM65]

Gran

They waxed the bottom the day of the tests

And it was downhill with the wind at their backs.

[RickK]

You guys have heard of "Marketing math" right?