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prop vs. lower unit jet on '1983 80 HP

N

novice_marine

New member
well now i really need a new prop thanks to the drift wood i hit yesterday:mad:. i never got a wot rpm reading before i messed up the prop, and now that would be way off anyway. it was roughly a 13*21. it came out of the hole good, but with no top end speed. also the lower unit needs re-sealed at the very least. would i be farther ahead to buy a prop and re-seal my lower unit or find a jet lower unit and not worry about any of the prop missery anymore? are there even jet units out there for my engine? if so what would i expect to pay for a good take off? i normally run in rivers so there is the risk of more debris in the water and acidentally going into a channel that shallows faster than you think. so i'm thinking a jet will be more trouble free. i would like some more info if anyone has it. thanks alot.
 
Re: prop vs. lower unit jet on '83 80 HP

13 x 21 sounds like an awful lot of pitch on an 80 horse - unless your rig is wickedly light (like around the 1000 pound mark, dry) I would expect to see you run closer to a 17 pitch (but depends what boat you have the motor mounted on).

You can reseal your current unit for maybe 50 bucks worth of parts and a couple/few hours of your time.

There was never a jet lower specifically designed for your model. I suspect a later model jet would fit (maybe with a little jury rigging), but even used I think you could expect to pay close to a grand for one.

And you need to consider your significant loss of horsepower (at the prop) if you convert.

A Jet Outboard is significantly less efficient at producing power than a prop job.

Bolt a jet on and you turn your 80 horse "prop" motor into a (about) a 55 horse jet. They routinely lose 30% of the rated power.

A 65 Jet (Merc) uses the "regular" 90 horse powerhead and the 80 Jet uses the powerhead from the 115.

That's the cost/trade-off of being able to run in water no deeper than a puddle.

So if you thought you had no top end speed before, even if your prop was somewhat mis-matched, your top end would "totally suck" with a jet drive bolted to that powerhead...
 
Re: prop vs. lower unit jet on '83 80 HP

another option is to get a tunnel drive boat, like an old penn yan, very little prop exposure.
 
Re: prop vs. lower unit jet on '83 80 HP

thanks for the input, i was not aware of the power loss. boy i wish i got an RPM reading before i tried to use the prop as a chipper. i think i will talk nice to the local marina and see if we can try a couple of props in the water before i buy another one miss matched. i hope i don't come off as a complaner wanting record setting speed out of a pleasure boat, but i think 8 gal. per hour on the water justifies exploring a few options.
 
Re: prop vs. lower unit jet on '83 80 HP

Most decent shops should have a few props laying around that you can try out - especially if they feel they will get your business.

8 gallons per hour from an 80 horse sounds bang on.

At full throttle just about every outboard out there will burn 10% of it's horsepower in gallons per hour - so 8 for an 80, 20 for a 200.

That applies to ALL outboards, even the 4 strokes that claim massive fuel savings.

They (4 strokes) are easy on fuel in mid to low rpms (at 3000 rpms a 4 stroke Honda burns about half as much as a 2 stroke Merc of the same horsepower), but at top end it "drinks" just as much.

So if you buy a 4 stroke to save gas, just don't run it above 3500 rpms. If you do, you may as well have kept your pollution spewing 2 stroke hung on the back and used the money you saved, by not buying a new 4 stroke, to pay for the extra gas you burn at mid throttle.

Most recreational outboards are really just two speed motors - idle and full throttle :)
 
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