1982 Seahorse 4.5 vs 2010 Tohatsu 6

[mikehoyt]

Currently running a 1982 Johnson Seahorse 4.5 Long shaft J5RHLCNR on a 27 foot racing sailboat. Weight is a big issue so must keep under 60 lbs.

The motor is fine til wind pipes up to 25-30 knots.

Considering a Tohatsu/Nissan 6hp 20 inch shaft with hi thrust prop. Concern is that it will not be much of an upgrade for the $1500 difference.

Would changing prop on the Johnson Seahorse produce much effect? Anyone know if the 4.5 has any tricks like a carb kit replacement to boost power? Is the Tohatsu a big increase in power as hp is now measured at prop vs at powerhead on the 1982 Johnson?

Note that the Johnson Seahorse runs like a top

Mike

 

[Vic.S]

Re: 1982 Seahorse 4.5 vs 2010 Tohatsu 6

You are right about the change in method of measuring the power. The method for rating at the prop, described in ICOMIA 28/83, was I believe used by OMC from 1984 onwards.
If measured now I expect your 4.5 would be the equivalent of a modern 4 hp. so going to a 6hp would be a 50% increase in power.
A high thrust prop can make a useful difference on a displacement hull too.

A different prop was fitted to the sail (slr) versions of the 4.5 but is is no longer available and the parts list does not state it's pitch and diameter. ( 8⅝" x 5?" possibly)