Horsepower Question

Ok, here we go.....Purchased a boat a few weeks ago, it has a 1968 65hp evinrude on it. Upon tearing it down there are a ton of things broken and the parts and my own labor are going to end up costing me more then a used Outboard from a dealer.....so......here is my question. I searched thru old posts, but only found max's for hp, not minimum's.....Since the original motor is a 1968 65, what would be comparable? I found a 1991 40hp Johnson that is at my local dealer with a one year warranty. The boat is missing the plate so I can't see what the "real" max is and the boat company is no longer in business. It is an 18' West Wind Tri-hull. I am not looking to go skiiing, flying across the bay etc, just something to get me out to my fishing hole and back. Any help would be greatly appreciated!

Re: Horsepower Question

Parrot,<br /><br />Your 65 was rated at the powerhead. You can figure it's about 55-60 at the prop.<br /><br />That is a bit light, in my opinion, for the boat you described. A 40 will probably not plane the boat.<br /><br />I would be looking at 70 minimum.

Re: Horsepower Question

Hi, Parrot.<br /><br />I agree with DJohns. An 18 triHull should be rated for 90-130hp max. at least. <br /><br />On the other hand, whoever put the "65" on it must have gotten satisfactory (to him) performance, so a modern 70 to 90HP engine should do well.<br /><br />Good luck.

Re: Horsepower Question

Look for a 3-6% reduction in prop hp compared to flywheel hp. 65 hp at the flywheel would be equivalent to about 61-63 hp at the prop, as the others have said.<br /><br />There are some calculations (which I won't get into here) that use established marine constants to figure hp differentials. It is common to use up to a 3% reduction for the gearing and up to a 1.5% reduction for each bearing along the turning shafts.<br /><br />Of course each outboard is designed differently and the original ratings on the new outboards allow some variance to begin with.<br /><br />The 40 hp won't be enough. Anything 60 hp and above will give you equal performance and above from what you currently have.

Re: Horsepower Question

Here is one that iBoats is selling. Probably more than you wanted to spend, but if you are like most of us, you are going to want to upgrade the boat sooner or later, and you would already have a good engine. <br /><br />2001 Mercury 20" ERN 2-stroke New/Demo (MSRP 4216.00) 1 Yr Mfr. Warranty (3 Year Additional Protection 520.00) $3,399.00 <br /> http://www.boatmotors.com/rebuilt_outboard_motors/

Re: Horsepower Question

My boat is an 18 fiberglass tri of about the same vintage. It goes 40mph at 5000rpm wot with a 73 135hp Johnson ,loaded. <br /><br />Thats my motor's twin in the bottom photo. <br /><br /> http://www.classicglastron.com/74gl-v187-186swingers.html