Short Shaft Rarities

Tigerguy

Cadet
Joined
Nov 3, 2015
Messages
16
I'm running a 1992 30 HP Evinrude short shaft O/B on my 1958 Lone Star Nassau (16' Aluminum). It maxes out at 25 mph. I'm looking for a little more top end, so I'm trying to locate a 35-50 HP short shaft motor. Are HP ratings the same, regardless of vintage? Assuming good compression, would a vintage 40 HP motor (e.g Big Twin) really push more than the 1992 30 HP motor, or does improved technology get more performance? (For now, I'd rather stick with existing motor than go the jack plate route to let me run a longer shaft.) Any other considerations? I'm finding that 40 HP short shaft motors are actually hard to find. Thanks much,
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,033
Yes they are harder to find.-----Your location may be a factor as well.
 

jbcurt00

Moderator
Staff member
Joined
Oct 25, 2011
Messages
24,829
Pre-82 motors were generally rated at the crank, post 82 they were rated at the prop.

your 1992 30 might be lighter then a vintage 40hp, its more fuel efficient and likely to provide nearly the same umph as a vintage 40 would. Theres @10-15% hp lost from crank to prop, so a pre-82 40hp is about equal to a post 82 35hp+/-...

is your 30 reaching peak RPMs at WOT?

your Nassau should be rated for a 50-75hp motor, isnt it?

I think early 90s (late 80s maybe) 50hp Johnson/Evinrudes came in a short shaft....

Pretty sure I know a guy running 1 w T&T on a 15ft vintage aluminum boat. It hauls arse, even w 4guys @200lbs+ each aboard..... although It is only rated for a 40, IIRC......
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
All other things being equal, the newer motors with thru-prop hub exhaust lower units are faster than the older non-thru hub lower units. The shape is the secret.
 

Tigerguy

Cadet
Joined
Nov 3, 2015
Messages
16
Thanks so much for the insight. I learned a lot about how HP ratings changed over time. The capacity and HP ratings for the Lone Star Nassau changed from '57 to '58 (40 HP to 60 HP). My original data plate was missing from my "mulch' transom, but some great fellow owners provided me with images of their data plates.
 

Attachments

  • 1957 Dataplate.jpg
    1957 Dataplate.jpg
    605 KB · Views: 0
  • 1958 Dataplate.jpg
    1958 Dataplate.jpg
    151.7 KB · Views: 0
Top