1997 Mercury 200HP OffShore Thrust Problem

[Randy22]

Have twin Mercury 200HP OffShores in great condition. Was running about 30 knots and felt a hard jar as if I had possible hit something (and I may have) but never saw it. Powered down and shut both engines off. Checked for physical damage and found nothing. Cranked back up, throttled back up and the boat (26 ft. open fisherman) wouldn't get back up on a plane although both engines were at good rpm but starboard prop was not equally responding. Prop was spinning but barely and delivering little to no thrust. Shifts into forward and reverse but shift seems not to be same as before and feels different from port engine shifter. Again, engine power seems fine. Something going on between power and thrust that doesn't match. Hoping for a beginning point to start looking for the cause. Thanks.

 

[GA_Boater]

I think you broke something inside the lower unit or spun the prop hub. Simple way to start is to drain the starboard lower unit oil and look for metal debris.

 

[Randy22]

Thanks. On the lift now but will put on trailer and check suggestion. I assume if nothing unusual in lower unit oil (metal shavings, etc.) then possible spun the prop. If prop, what would I look for to determine cause? Thanks for the assist.

 

[444]

Check for oil like suggested. If nothing, swap props from side to side and retry to see if problem moves to other engine.

 

[Randy22]

Will do. Never had prop issues in the past so help me understand something if you don't mind. So if you spin a prop, then the prop is the problem and not the shaft? That is my take-a-way from the comment of moving prop from one engine to the other. Your tracking to see if the possible problem moves from one engine to the other. Guess I always thought a spun prop was shaft related and not prop related. Anxious to see if it follows to port engine. Thanks!

 

[Chris1956]

Props have a rubber or plastic "hub" connecting the brass splined part of the prop to the outer blades part of the prop. This rubber or plastic can fail when you hit something or sometimes without hitting anything. In your case rough seas could have put extra strain on the prop hub causing the failure. Try to avoid having the prop come out of the water and then "slam" back into the water, as this can hasten prop hub failure.

 

[Randy22]

Well, probably going to be a tough answer back, but got boat off lift and on trailer. Thought I would pull the prop off to see if it did indeed spin it. Put the socket wrench on shaft nut and it just turns the entire shaft (both ways) without any resistance while holding the prop. Tried it on good engine and I got resistance. Next steps? Sounds like shaft may be broken?? Thanks.

 

[Chris1956]

Well, the prop hub sounds like it is well-spun. Can you put her in gear and loosen the nut? Make sure the spider washer is out of the way. You may need to put her in gear and find a way to hold the flywheel, to loosen the prop nut.

 

[Randy22]

Cool. Maybe not as bad as I thought then. I'll see what I can do tomorrow about getting the nut off. I wondered what would have to be done to get it off with no resistence. I'll put in gear and try that first and then try and find a way to secure fly wheel should putting in gear not work. I have the spider washer ready as well. Thanks for the help!

 

[Randy22]

Placed motor in gear and nut and spider ring came right off. Hub seal was eaten up. Called Mercury dealer to see if they could repair. They referred me to prop shop. Called this guy and he recommended pulling the port prop. I did and inside fell apart with cracks throughout so would have been matter of time before port prop went out. So lesson learned, if you have twin engines, may as well do both props. Cost to repair will run at most $190.00 for both and could be only $175.00 and ready in 2 days. Will offer final post when back in water. Thanks much to all who helped. Good stuff!

 

[Chris1956]

Randy, when you say "hub seal" you mean "prop hub", right? So you are getting both props rehubbed, right? If so, I would recommend you take it a bit easier in rough water, and try to eliminate anytime the props come out of the water while under high power. I would also recommend you carry two spare props, prop nuts, spider washers and the tools to replace the props.

 

[Randy22]

Sorry, Yes...prop hub and they are rebuilding both. I actually do carry a non stainless prop in my storage but not a spider washer or spare nut. I sometimes run 50-60 miles off shore from Dauphin Island, Al., so before making that run again, I'll be better equipped. I do try to allow boat to stay in water when running at high speed but have had some rough rides running from storms. Thanks for suggestions.

 

[Randy22]

Something just occurred to me. I didn't mark which prop came off which engine. Is one prop made to fit starboard motor and the other the port? If so, is there a way to tell one prop from the other so to match back up to the right motor. What would occur if they were incorrectly put on wrong? Thanks.

 

[Chris1956]

If one motor is counter-rotating, you will have 1 left hand prop and 1 right hand prop. Install the right handed prop on the starboard engine.

If the props are the same, neither motor is counter-rotating and it doesn't matter which prop is where.