jet outboards

[ted655]

What are the downsides of the OB jet?
I have a shallow draft boat & wonder if a jet is a good choise? Are they less powerful for the same HP. rating? Is there more maintaince? How are they at slow speed operation? I'll assume they suck more gas, how much more?
I've a chance for a 135 hp. Merc jet.:%

 

[imported_Curmudgeon]

Re: jet outboards

Outboard jets are historically inefficient due to design. They require high rpms to develope much thrust, resulting in increased fuel usage, are very intolerant of high loads, reverse is anemic at best, neutral almost non-existent, slow speed ops are extremely mushy and greatly subject to vagaries of wind and current.

That being said, they're absolutely outstanding (if not required) for shallow, rocky waters. Depending on size of the boat, they will run in spit. Don't know about ops on mud flats, but I can't believe it'd be good. Jet maintenance is pretty much confined to a squirt of grease before use, and adjusting the impeller every so often. Powerhead maintenance is about the same as a prop ...d

 

[ted655]

Re: jet outboards

Thanks. The boat is big & we operate at slow speeds wuth heavy loads. Oh well, it seemed to good to be true.:'(

 

[tashasdaddy]

Re: jet outboards

a jets efficencey is 60% of the hp rating. 100hp engine puts out 60 hp at the jet. so a 135 is putting out 81 hp.

 

[ricksterpr]

Re: jet outboards

tashasdaddy:

Is that true only for jet outboards or does it also apply to true jet drives. I would think that a true jet drive (in which the water is directed through a channel in the hull onto the the impeller) would be more efficient, as the impeller gets water from the channel, and the impeller is also enclosed in the channel, so that water may be more compressed that in an outboard propeller, thereby creating more thrust?

Your thoughts would be appreciated...

 

[tashasdaddy]

Re: jet outboards

true jet drives are more efficient than the outboards, but less than an i/o. too much slip. they certainly have there place in the boating world where the propeller driven boats have extreme trouble operating. rock areas, flats and shallows.

 

[ricksterpr]

Re: jet outboards

they certainly have there place in the boating world where the propeller driven boats have extreme trouble operating. rock areas, flats and shallows.

I use mine to go surfing to the outer reefs. I can be 1 foot above the reef and have no problem. I also surf with the boat if the waves are not too big!!!