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Forums28
Topics3,984
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Most Online238 Feb 9th, 2024
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Folding Props
#1482
09/25/08 05:12 PM
09/25/08 05:12 PM
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Joined: Jun 2008
Posts: 137 Montreal, Quebec, Canada
Taras
OP
Senior Member
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OP
Senior Member
Joined: Jun 2008
Posts: 137
Montreal, Quebec, Canada
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As a new J30 owner I was warned that the two blade Martec folding prop was not the greatest in reverse.... I was considering to replace it with a three blade folding prop www.kiwiprops.co.nz/ Has any one on the list replaced the martec with something that offered better thrust is reverse? Would changing the prop disqualify the boat from OD racing? Taras
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Re: Folding Props
#1483
09/25/08 05:43 PM
09/25/08 05:43 PM
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Joined: Apr 2003
Posts: 649 Marblehead, MA
dbows
Senior Member
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Senior Member
Joined: Apr 2003
Posts: 649
Marblehead, MA
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Originally posted by Taras: As a new J30 owner I was warned that the two blade Martec folding prop was not the greatest in reverse.... I was considering to replace it with a three blade folding prop www.kiwiprops.co.nz/ Has any one on the list replaced the martec with something that offered better thrust is reverse? Would changing the prop disqualify the boat from OD racing?
TarasJust floor it. That is what I do and the thrust is fine. You will get use to it. Props are not cheap and you will see a marked difference in sailing speed. The hardest part is to just get flow over the rudder - once you do this you have very good control over the boat. Also have your prop reconditioned - this made a noticeable difference. David #397 - Mallorca
David Bows Mallorca - Hull# 397 ~~~~~_/)~_/)~~~~_/)~~~~~~~~~~~~~~~~~~~~~~~~~|~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|~~~~~
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Re: Folding Props
#1485
09/26/08 09:03 AM
09/26/08 09:03 AM
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Joined: Feb 2003
Posts: 127 Chicago, IL, US
rdpierce
Senior Member
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Senior Member
Joined: Feb 2003
Posts: 127
Chicago, IL, US
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There are two issues here. If there are mechanical problems, boat handling in reverse can be substantially worse. The question in my mind is whether the prop is opening and in gear. These are old boats. If you feel a horrible vibration in reverse, that's a problem.
I'd suggest checking the prop for any slop in the blades. You shouldn't be able to squeeze the tips together and make them touch, and they shouldn't have much play. Martec does a great and fairly economical (at least, relative to a new prop!) job reconditioning props. Now they can only do it a limited number of times because each recondition requires drilling and sizing up to a larger pin.
Also, the transmissions can go south, too, which can prevent the prop from opening in reverse.
And if there's a lot of vibration, the cutlass bearing could be worn, and/or the prop strut loose.
Personally, I had all four of these happen. They're all fixed now, and my boat actually operates in reverse. (Fancy that.... ;-) Now I just have to get rid of all that anxiety that came from years of not knowing whether putting the boat in reverse will result in a horrific kathunka-thunka-thunka-thunka and virtually no thrust!
Ryan Tesara, #337
Ryan Pierce, #337
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Re: Folding Props
#1487
09/26/08 10:39 AM
09/26/08 10:39 AM
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Joined: Jan 2009
Posts: 140 New Orleans, LA
Rambunctious
Senior Member
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Senior Member
Joined: Jan 2009
Posts: 140
New Orleans, LA
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Vibration can be caused by a number of things. One point is that normal cruising RPM should be about 2200 RPM, with occasional runs at higher revs. Above 2500 the engine is working hard.
Some potential causes of excessive vibration can be the motor mounts, cutless bearing, strut, the prop or prop shaft, the coupling, and I'm sure other culprits that aren't occurring to me right now.
My point is that I would not look first at the transmission if vibration is an issue, particularly if it only occurs at high revs.
To check the motor mounts, take the cover off the motor when you're out motoring around. Have the person driving goose the throttle, in your case, go from 2200 to above 2500 if that's the range that's causing a problem. Does the motor lurch (a lot)? If so, suspect the mounts.
The prop, cutless bearing and strut can be checked in the water. There should be zero play in the strut. To check the cutless bearing, grab the shaft forward of the strut and shake it. It's easier to see on land, but if there is play in the bearing, you should be able to notice it. Obviously, the boat will need to be hauled to fix either of these issues.
Anything relating to the prop can be handled with the boat in the water by a decent professional diver. A lot of growth on the blades of the prop can cause a great deal of vibration. I saw this in action after having my boat in Florida for a few weeks this summer. I hopped in and scraped off the barnacles with a paint scraper and was good to go. Also, check to see if the blades are loose. Another issue is that the prop itself can be loose on the shaft. Grasp the prop's hub and give it a shake. There should be no play.
You can also check the prop shaft. Use calipers and turn it by hand to see if it's out of round. Also check the coupling that attaches the prop to the transmission.
Also make sure your motor is tuned up. If it's running roughly, something that often gets worse as you add revs, then that may be mistaken for a vibration.
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