HP Formula

[jsfinn]

Hello,<br /><br />I asked this question in the Boat Restoration forum but didn't get a reply so maybe I posted it in the wrong spot. Sorry for double posting.<br /><br />I'm working on a 1956 Chris Craft 16 foot plywood kit boat. I have a 1950something 30 HP Johnson motor that goes with it that will need restored when I'm done with the boat if I decide to use it, but more power sure would be nice.<br /><br />The information guide for the boat say that it's rated for up to 40 HP but when I do the coast guard formula, ( (2 X 6 X W) -90 = RATED HORSEPOWER ), I come up with 70. I wonder if the boat is rated for 40 HP because that's as big as outboards came in 1956. The transom is strong. Would I be safe hanging a 70 HP on it?<br /><br />I want to keep the boat as orriginal as I can but I'm not sure I can live with only 30HP on this boat.

 

[Paul Moir]

Re: HP Formula

Since the coast guard formula relates only to stability, it'll be up to you to be sure that the transom is strong enough to support the extra load. A 1956 30hp Johnson weighs in at 130lbs. A '93 70hp Johnson weighs in at 240lbs. So there's a lot more weight bouncing around on the back of the boat.

 

[jsfinn]

Re: HP Formula

Hey Paul - I didn't realize there would be that much weight difference so thanks for your pointer. The boat only weights 550 lbs so 240 lbs would be way too much back there.<br /><br />What's the largest outboard they made in the 50s and 60s?

 

[Paul Moir]

Re: HP Formula

I belive the largest commonly available outboard would be the Mercury Mark 55 (40hp). I'm not certain how much it weighs.<br />The largest retail Johnny/Rude was the 30hp you've got.

 

[jsfinn]

Re: HP Formula

30HP?! That's it!? Man! That's a bummer! Oh well, I guess I won't have any problems with no wake zones.

 

[ED21]

Re: HP Formula

I have a 16' alum. boat that weighs a little less w/ a 40 hp Johnson & it has plenty of power.<br />I think the outboard weighs about 180.<br />You might find the 30 hp does OK if you decide to rebuild it.<br />I think the original motor would be a nice combo.