J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Folding Props

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

Just 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

Ditto on what David said.

You'll find with any cross wind the boat is not easy to steer in reverse. The prop isn't the problem so don't mess with it. Just a function on where the rudder is relative to all the surface area on the boat subjected to wind.

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

That is all very interesting. I actually have no problems in reverse, a little slow getting started, but once she goes it is no problem. I do get alot of vibration in forward though. I am having the prop done by Martec this year, but perhaps I should have the transmission checked. I get decent speed in forward, about 6 knots at 2200 rpms in flat water. Once I push it past 2500 though the vibration gets a litte much. Any suggestions?

HHSA
Velocity Girl#278

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.

Thanks for the info. Much of that was on my short list. Especially now as Velocity Girl is on the hard for the winter. Upstate NY has a short season. I was curious about speed. Is 6 knots at 2200 a normal range in flat water or am I slow? Just want to make sure I am running with herd. Thanks again for the quick responses. I am actually going to take a Desiel repair course over the winter to sharpen my do it yourself skills. None of my previous boats had and engine so the put put put is all new to me.

Velocity Girl
HHSA

6 kts at 2200 RPM is ok. I run my 2GM at about 2600 RPM and get around 7 kts +/- based on the sea state and winds. Rated rpm is higher but you just waste fuel and don't go that much faster.

Jason's suggestions are good ones. I made the mistake of not replacing the original engine mounts when I had the engine out for rebuild 2 years back. The stbd aft mount failed and I replaced all 4 mounts water borne with the shaft disconnected from the coupling flange and blocked in place. I wasn't able to get decent alignment until I pulled the boat the next season. It rattled your teeth out and caused leakage on the shaft seal until I got the alignment right that off season.

I never said that she didn't work in reverse,..as mentionned in the responses, I have to rev it up 2200-2500 to get the blades open and to engage but once I have momentum there is no problem
It is just difficult to make "finesse" adjustments in reverse as I see three fixed blade boats preform,...or stop on a dime
Thus my original question,....would changing the prop to this three blade kiwi model (at 1200$) disqualify the OD rating?
It performs like a thre blade fixed prop and has the folding aspect to reduce drag when sailing

to recondition the martec prop,...we take it off and send it to them?....