John H wrote:
On Mar 3, 7:58 pm, wrote:

A fishing buddy of mine is re-powering his early 1976 Boston Whaler
Sport 15 with a new 60hp 4 stoke Mercury. He is replacing a 2 stroke
Mariner that is an 80's model.

He has no gauges and the layout of the console is like a skiff - the
steering wheel is horizontal. He's not concerned about a speedometer,
and shouldn't be, but I think he should have a tach. The 4 stroke will
be heavier and act differently than the 2 stroke. The props are
interchangeable in size and hub configuration so he plans on putting his
SS prop on the new boat. I'm trying to convince him to find, or make, a
spot for a tach so he can make sure the boat is propped properly (say
that 5 times fast!). He's not convinced. The boat is rated for a 75 so
the 60 will still weigh about the same as a 75 2 stroke so the transom
weight will be fine.

Has anyone attempted a similar replacement? Should he need a different
prop? Can you attach a tachometer temporarily for testing purposes?

Thanks in advance,
Larry

This might provide some useful information regarding prop size. The
tested boat was a Boston Whaler 150 Montauk, which is probably pretty
close to the boat he's got. I had a 15' Whaler center console I bought
new in 1985. It came with a 70hp, Johnson 2-stroke. Screaming little
boat. He should get good performance with the 60hp, unless the boat is
water-logged.

http://tinyurl.com/yd8r5zl

The propellor specs are in the lower right of the page.

Thanks, John. That's a Bigfoot in the chart. They have a different
gearcase. The numbers are still quite good for a boat like that!

Larry