1976 Evinrude 55HP 55673E: Prop vs jet drive / Long vs short shaft lower unit

[TLewis]

My outboard has a 'long' lower unit and originally had a prop drive. It appears that sometime in the recent past the prop drive was replaced with a jet drive and a jack plate (just the plate, it's fixed) was installed to raise the motor a couple inches.

I've heard that prop drives develop 30% more power (?thrust?) than jet drives. It also seems like the long shaft is less popular and less available than the short shaft.

The boat is a 1998 16.5' Alumacraft center-console, modified V, and tunnel. The primary use of the boat is the shallows of the middle Texas coast. Does someone please provide me with their opinion on this setup?

Sorry in advance if this is not the right forum for this discussion.

 

[Texasmark]

Re: 1976 Evinrude 55HP 55673E: Prop vs jet drive / Long vs short shaft lower unit

Today's OB engines are prop (thrust) rated, not power head rated or "Brake" hp like auto's were labeled before the real hp which was at the rear wheels.

My Merc manual lists engines in the 3-4 cylinder configuration for late '90's and on. If propped, they are listed in HP as: 75, 90, 100, 115, and 125. For their jet drives, they only list two: 65 hp (which is also the 90 propped) and 80 hp (which is the 115 propped). So, yes you loose a lot with a jet.

On mounting the jet mechanism and getting it into a 20 or 25" transom's height, you need a short mid section.

On a bay boat where you run shoals, have to plane out in 6" of water and all, have to battle 2-3 footers back to the docks, who knows what kind of setup your tunnel will have. Additionally, where the prop is in the tunnel, vs your speed is obviously important also. You have a lot of turbulence in the tunnel, which calls for a high performance prop...cupped, high rake, ports, SS and all to keep the lower unit high in the water and still get bite. Otherwise you lower it to keep the prop from ventilating and you produce extra drag which bites into your performance.....and I used to fish down "theah". Grin

HTH,

Mark