J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Replacing Propeller Shaft 7/8 vs 1 Inch

Hey, while my J/30 is out of the water, I am considering upgrading the shaft. I think the current diamater is 3/4 inch. After reading the posts, I have noted some references to 7/8 inch and some to 1 inch upgrades.

For those with an upgraded to 1 inch, did you change out the strut?

Did you ask a local machine shop to produce the new shaft?

Any tips are appreciated.

Dave@j30.us

David - Rhapsody has a 1" shaft. I met the original owner this summer and he indicated the boat (Hull #348 originally named Tontine in 1981) was built with a 3/4" shaft, but he had heard of other owners complaining of "shaft whip" vibration, so he convinced Everett Pearson to change the shaft. He said that the day before he took delivery that TPI cut out the old strut, and glassed in a new one. This explains why I have a 9" square seam line above the strut inside.

So, it is major work to upgrade to a 1" shaft. I'd try 3/4" for now and see if you have a vibration problem. If not, you're set. If so, consider this the 1st item on the list next time you haul the boat. Just remember you'll need a new shaft seal and coupling flange too. It's only money....

Bill

Would you not also need a new prop? That could also be a bit expensive.

I am almost certain the shaft in my boat is 3/4". It definitely isn't 1". I don't buy that the larger shaft is necessary to reduce vibration. I'm sure it would be a nominal improvement, but I would first look issues like the cutless bearing, shaft alignment and motor mounts before I began to even consider beefing up the shaft. If there is enough abnormal vibration to cause you to wonder, I would bet that the cause is one of those symptoms rather than an undersized shaft.

If it aint broke, don't fix it, right?

(Or, on my boat, if it aint broke, don't use it.)

Oops - the most expensive part I missed. Dennis is correct. I'm sure the strut isn't cheap either.

When changing out the stuffing box this weekend, we discovered that the shaft is not exactly the same size as the coupler. Keep in mind that I have never used the engine as this boat is new to me, so I do not know if there was any existing vibration. The part of the shaft where it connects to the coupler is black indicating that area was heated. I am hoping that the actual problem with vibration was related to a mismatch in size vs. shaft size. Perhaps the problem was misdiagnosed in the past? I am getting the shaft and coupler measured with a micrometer today to see where we go. While the boat is out of the water, this of course is the perfect time to address issues like this. :> ) I sent the Ecliptec prop to Martec today to be rebuilt.

We're painting the mast and boom. Baltoplate will be applied when it stops raining.

We haven't painted the area around the Windows. Can't make up our mind about to paint white like the hull or Zephyr blue.

There is a light at the end of this tunnel.

A new coupler for 3/4" shaft is about $110 (or thereabouts).

Dave - if it is a 2GM not a 2GM20 then you are wasting your money on a bigger shaft. The larger shaft was due to the added horsepower of the 2GM20 on the new boats. The shaft is so short that vibration is coming from other things like shaft mis-alignment, shaft ware at the stuffing box and strut, bad motor mounts, prop needs reconditioning and/or new cutless bearing. My boat has NO vibration underway and it has a new 3/4 shaft that was professionally aligned, new dripless seal, reconditoned prop and new cutless bearing. However this all was a small fortune.

David
#397

Dave - FYI

While you are at it, remove the sound proofing on the engine cover/steps and paint with Silent Running paint. I removed about 30lbs of lead from the sound proofing and made a huge improvment in sound dampening down below.

David
#397

David,

Thanks for the clarification. Can you direct me toward a part number or source of the dripless stuffing box?

Thanks,
David Erwin