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150hp Mercury OB - 1994- Too big for boat?

PostPosted: Mon Dec 05, 2011 3:34 pm
by cmassucci
I have a 1967 Thompson Offshore camper that is 21 ft long. It originally had a 1968 100 Hp johnson on it. I have a chance to pick up a nice 1994 150hp Mercury OB. - Is it Too big for my boat? My manual for the boat said it could handle up to a 180hp OB.

PostPosted: Tue Dec 06, 2011 7:10 am
by Phill Blank

Check for a OBC plate on the transom this should give you the max HP for the boat.
Also, in looking at the 1966 Thompson literature the 21 footers were rated for a max of 215 HP for outboards and 225 HP for I/Os.

Hope this is of some help.



PostPosted: Tue Dec 06, 2011 9:14 am
by cmassucci
Thanks Phil! The OBC plate has 215 as well, but the catalog I have for 1967 Thompson boats shows 180 for OB and 225 for I/O. Just wanted to make sure I didn't put too heavy or powerful a motor on this boat.


PostPosted: Tue Dec 06, 2011 9:39 am
by LancerBoy
There was a HP rating difference betwween the traditionally shaped hull and the full V hull for the same length boat. Make sure you are looking at the proper model, traditional or full V.


PostPosted: Tue Dec 06, 2011 5:42 pm
by cmassucci
How would I know which one I have? What are the differences between the two? Would the 150 Hp fall into both types? I will try to post a picture of my boat so you can see my type. It has a big flare in the front, but is pretty flat at the transom. I didn't see that there were two types in my catalog for that year? Thanks everyone for the guidance. Going to test out the OB on Friday. Hoping it is as nice as it looks.

PostPosted: Tue Dec 06, 2011 6:31 pm
by cmassucci
Here is the link to my photo album: ... directlink

Maybe we can tell from the photos? Thanks!

PostPosted: Wed Dec 07, 2011 3:45 pm
by john
I owned both a 1968 100 hp Evinrude and a 1970 135 Merc in line 6 same cubic inch as the 150. There was about a 4 or 5 mph gain on a heavy 16' running 36mph with the 100. Actually sold it to a guy with twin 1962 Johnson 75's on a 20? or so Cruiser inc. did fine.
He loved it.

My best question for your boat is how structually sound is it. When new the 150 would be fine. It is not a question of weight but the increase in thrust that could harm your hull!

I would go for it.

PostPosted: Thu Dec 08, 2011 4:45 am
by LancerBoy
Your photos tell me she is a traditional hull, not the V hull. The V hull will be just that, in the shape of a V as you look at the boat from the transom. The V shaped bottom will go all the way back to the transom.


PostPosted: Fri Dec 16, 2011 12:22 pm
by Tim the Toolman
Hey Chris, obviously lurking to see what kind of comments you get. Guess my '68 is not a V-hull either, good to know. As I've mentioned I have a 125 hp Force on my Offshore now and although I only ran it the one time before i realized what a sieve she is, it ran great, got right up on plane and had lots of power. Should be even better with a 150. Let us know if you pick it up. Tim Allen

PostPosted: Fri Dec 16, 2011 1:33 pm
by john
Sorry Chris, just reread about your 150 merc, its a 1994 not 1974, huge difference. The new 150 is probably about another 5 mph faster than the old in line 150. Prop shaft Hp on the old engine was 127, the newer 150 are at least 150 to 160! Very powerful engine. The old ratings were crantshaft hp, the new since 1980 are prop shaft about a 10% difference.

The newer 150 should push your boat almost 40 mph! Your old 100 should be 25 to 30.

The big question again is how structualy sound is your boat?

PostPosted: Mon Dec 19, 2011 2:33 pm
by thegammas
Is this 1994 a four stroke? If so they are significantly heavier than the two strokes. Though the weight is not as big an issue in the water, in my opinion it is a very real concern for the boat out of the water. I'd get the weight of that 94. My '63 inline 100 weighs in a ~300 pounds.

PostPosted: Sat Jan 07, 2012 4:50 am
by cmassucci
Sorry everyone I have been traveling like a mad man. Actually just picked up a 1982 Mercury 115hp. Very nice motor and it runs!! Anyone know when Mercucry started rating the HP at the prop? The guy I bought the OB from said it was 1982. She is real clean with new power head, rebuilt carbs and rebuilt lower end. Started her on an 8 degree night and she stated right up!! Nice! She should push my 67 Thompson Offshore real nice. After two years, I am ready to see her run! As always, thanks for all your help!