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Author Topic:   losing speed

bocadrew posted 08-27-2002 05:29 PM ET (US)
With my 100 hp gt Johnson on my Montauk I was able to easily go high forty's (mph)at 5200 rpms, now suddenly I can only get to go 40 tops (wot.) The RPMS seem to want to go higher quicker, no I can get them at 5500 where 5100 used to be a struggle, but this does not seem like enough of a slip to decrease my speed by almost 10mph. Also if boat got heavier for some reason wouldn't rpms go down?
Tom W Clark posted 08-27-2002 05:38 PM ET (US)
The prop is spun. Take it to a prob shop and have it re-hubbed and/or straightened out. Is there any visible damage to the blades?
SpeedyWhaler posted 08-27-2002 05:39 PM ET (US)
I can't belive a 100hp will push a montauk 50mph....
bocadrew posted 08-27-2002 05:52 PM ET (US)
I see no visible damage to prop, and if the prop was spunn wouldn't there be sudden high acceleration in the rpms? Could 5 or 6 rpms higher still mean the prop is spun?
JBCornwell posted 08-27-2002 07:01 PM ET (US)
I agree with Tom, Bocadrew.
Spun props can exhibit a wide range of slip.
Red sky at night. . .
JB :)
Bigshot posted 08-28-2002 09:53 AM ET (US)
Mark the hub and then the prop with a marker or paint and see if they move(kinda like the tape trick on a door to see if it was opened). How clean is the bottom? Just a little slime will trap air causing your engine to cavitate and slow down.
bocadrew posted 08-28-2002 12:44 PM ET (US)
Am curious to mark hub and prop and test, now I need to know where and what is hub and where do I mark it and mark the prop. Please forgive my ignorance...thanks...drew
MilwaukeeWhaler posted 08-28-2002 12:58 PM ET (US)
If you take the prop off it will be obvious that it is spun. There will be plastic or metal shavings around the edges. Check your intake. I thought mine was spun and it turned out to be a clogged intake.~mw
David Ratusnik posted 08-28-2002 01:23 PM ET (US)
boca- Lucky you, no blade damage. I know a guy who spun 2 Merc props just hitting a wave. Have prop shop inspect. .03 David
jimh posted 08-28-2002 03:19 PM ET (US)
I spun my prop with a 50-HP tired old Mercury just getting it tangled in weeds.
This is almost at the FAQ level of popularity:
Almost all propellers have thrust washers. If the propeller has been "spun" then the thrust washer will still have been rotating while the propeller hub did not. This will score the propeller hub or the thrust washer with circular scratches.
I learned this when I set my propeller on the counter at K&M Marine, my favorite Mercury dealer, and asked them if they could check the prop to see if it had spun the hub. Gary, my favorite Mercury Service Manager, picked it up, looked at the forward surface of the hub, and said, "Yes, your prop is spun."
I had him explain it to me. It is really quite obvious once you see it.
simonmeridew posted 08-28-2002 08:34 PM ET (US)
OK
this brings up a question I've had all summer. How tight should the prop nut be? Mine is loose enough to turn by hand--a little bit of course because the cotter pin keeps it from turning more than a few degrees. If I tighten the nut up enough to engage the next set of slots for the cotter pin, it seems really tight. Problem??
simonmeridew
JoeH posted 08-29-2002 01:30 AM ET (US)
The book for my 93 150 Johnson gives a torque spec of 70-80 ft. lbs. Latter it says that if the holes do not line up continue to tighten prop nut until they do. Joe
Bigshot posted 08-29-2002 11:08 AM ET (US)
No need for 80lbs of torque. I tighten by hand and then use a wrench to get the next hole, maybe 2.
SWarren posted 09-03-2002 08:46 AM ET (US)
Talk about a spun prop, I had one heck of a weekend. I was running about 4M rpm on my twins when all of a sudden my port motor went up to 6500. I put in neutral went over to a dock and trimmed the motor up to see the shavings or whatever it is between the propwasher and the hub. I went back to the boat landing on one motor about 40 miles the port motor would run to aboout 2500 before it would spin or cavitate. At the landing I used the port motor to help steer me to my trailer ( had it in reverse). When the boat came out of the water my ballistic ss cupped prop was gone. The only thing left was the nut and cotter pin and the inside part of the hub shaft. I have two extra stainless steel props the original ones for the motor but not the ballistic ones. Talk about a bad friday.

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Author	Topic: losing speed
bocadrew	posted 08-27-2002 05:29 PM ET (US) With my 100 hp gt Johnson on my Montauk I was able to easily go high forty's (mph)at 5200 rpms, now suddenly I can only get to go 40 tops (wot.) The RPMS seem to want to go higher quicker, no I can get them at 5500 where 5100 used to be a struggle, but this does not seem like enough of a slip to decrease my speed by almost 10mph. Also if boat got heavier for some reason wouldn't rpms go down?
Tom W Clark	posted 08-27-2002 05:38 PM ET (US) The prop is spun. Take it to a prob shop and have it re-hubbed and/or straightened out. Is there any visible damage to the blades?
SpeedyWhaler	posted 08-27-2002 05:39 PM ET (US) I can't belive a 100hp will push a montauk 50mph....
bocadrew	posted 08-27-2002 05:52 PM ET (US) I see no visible damage to prop, and if the prop was spunn wouldn't there be sudden high acceleration in the rpms? Could 5 or 6 rpms higher still mean the prop is spun?
JBCornwell	posted 08-27-2002 07:01 PM ET (US) I agree with Tom, Bocadrew. Spun props can exhibit a wide range of slip. Red sky at night. . . JB :)
Bigshot	posted 08-28-2002 09:53 AM ET (US) Mark the hub and then the prop with a marker or paint and see if they move(kinda like the tape trick on a door to see if it was opened). How clean is the bottom? Just a little slime will trap air causing your engine to cavitate and slow down.
bocadrew	posted 08-28-2002 12:44 PM ET (US) Am curious to mark hub and prop and test, now I need to know where and what is hub and where do I mark it and mark the prop. Please forgive my ignorance...thanks...drew
MilwaukeeWhaler	posted 08-28-2002 12:58 PM ET (US) If you take the prop off it will be obvious that it is spun. There will be plastic or metal shavings around the edges. Check your intake. I thought mine was spun and it turned out to be a clogged intake.~mw
David Ratusnik	posted 08-28-2002 01:23 PM ET (US) boca- Lucky you, no blade damage. I know a guy who spun 2 Merc props just hitting a wave. Have prop shop inspect. .03 David
jimh	posted 08-28-2002 03:19 PM ET (US) I spun my prop with a 50-HP tired old Mercury just getting it tangled in weeds. This is almost at the FAQ level of popularity: Almost all propellers have thrust washers. If the propeller has been "spun" then the thrust washer will still have been rotating while the propeller hub did not. This will score the propeller hub or the thrust washer with circular scratches. I learned this when I set my propeller on the counter at K&M Marine, my favorite Mercury dealer, and asked them if they could check the prop to see if it had spun the hub. Gary, my favorite Mercury Service Manager, picked it up, looked at the forward surface of the hub, and said, "Yes, your prop is spun." I had him explain it to me. It is really quite obvious once you see it.
simonmeridew	posted 08-28-2002 08:34 PM ET (US) OK this brings up a question I've had all summer. How tight should the prop nut be? Mine is loose enough to turn by hand--a little bit of course because the cotter pin keeps it from turning more than a few degrees. If I tighten the nut up enough to engage the next set of slots for the cotter pin, it seems really tight. Problem?? simonmeridew
JoeH	posted 08-29-2002 01:30 AM ET (US) The book for my 93 150 Johnson gives a torque spec of 70-80 ft. lbs. Latter it says that if the holes do not line up continue to tighten prop nut until they do. Joe
Bigshot	posted 08-29-2002 11:08 AM ET (US) No need for 80lbs of torque. I tighten by hand and then use a wrench to get the next hole, maybe 2.
SWarren	posted 09-03-2002 08:46 AM ET (US) Talk about a spun prop, I had one heck of a weekend. I was running about 4M rpm on my twins when all of a sudden my port motor went up to 6500. I put in neutral went over to a dock and trimmed the motor up to see the shavings or whatever it is between the propwasher and the hub. I went back to the boat landing on one motor about 40 miles the port motor would run to aboout 2500 before it would spin or cavitate. At the landing I used the port motor to help steer me to my trailer ( had it in reverse). When the boat came out of the water my ballistic ss cupped prop was gone. The only thing left was the nut and cotter pin and the inside part of the hub shaft. I have two extra stainless steel props the original ones for the motor but not the ballistic ones. Talk about a bad friday.