Prop Repair

skipperdude · May 14, 2012

I was getting a slight vibration at the upper end of the RPM. Started at about 1500 to 1800 and then slacked off. to hardley noticible.

I put the boat up on the tide grid and found two small nicks about 1/4 in by 1/8" divits on two blades of the prop 24" R.H.

One had a tiny chunk missing the other I was able to bend and file.

The water was just to nasty to go out and see if I did any good.

Has anyone ever done repairs of this nature?

Sd

Pineapple Girl · May 14, 2012

Al/ Flywright just had his props worked on and said it got rid of a vibration he'd had for awhile and increased his speed a bit. Hopefully he will pop in and elaborate!

Larry M · May 14, 2012

skipperdude said:
I was getting a slight vibration at the upper end of the RPM. Started at about 1500 to 1800 and then slacked off. to hardley noticible.

I put the boat up on the tide grid and found two small nicks about 1/4 in by 1/8" divits on two blades of the prop 24" R.H.

One had a tiny chunk missing the other I was able to bend and file.

The water was just to nasty to go out and see if I did any good.

Has anyone ever done repairs of this nature?

Sd

A while back we hit a partially floating log. We shut the engine down, I went over the side and found a 2"x1/2" bend on one blade tip. I was able to pretty much bend it back but I can still see and feel the damaged area. We notice no difference in performance. The prop will be sent to a shop this summer to get it properly fixed.

SD: If the only damage is the 2 small nicks, I think you'll be OK.

skipperdude · May 14, 2012

Larry, Did you notice any vibration at any paticular RPM?

The reason for asking is the vibration is bothersom.

I can't stand it when everything is not running properly.

I am afraid the vibration could have another cause.

Sd

Larry M · May 14, 2012

skipperdude said:
Larry, Did you notice any vibration at any paticular RPM?

The reason for asking is the vibration is bothersom.

I can't stand it when everything is not running properly.

I am afraid the vibration could have another cause.

Sd

SD: No more vibration that normal and I think my prop is more distorted.

Did the vibration all of a sudden show up?

You can always check your engine alignment at the slip. The vibration might be that simple and you will have eliminated that as the cause.

psneeld · May 14, 2012

skipperdude said:
Larry, Did you notice any vibration at any paticular RPM?

The reason for asking is the vibration is bothersom.

I can't stand it when everything is not running properly.

I am afraid the vibration could have another cause.

Sd

Whatever caused the nicks may have bent your blade tips just enough to give a slight vibe...the nicks themselves may not, but there might be more to the story that you can't really tell without taking the prop to a shop.

I have hammered back, bent, and filled with marine tex dozens of props...sometimes solved...sometimes.... NOT!

chc · May 14, 2012

Being curious, we always find ourselves poking into places we probably should not go with the big boat. Hence we occasionally find the bottom. easiset thing for us is to pull the props at winter haul out & have them tweaked & tuned. Always seems to help & improve performance

markpierce · May 14, 2012

Better yet, have a hull designed to protect propeller and rudder.

FlyWright · May 15, 2012

Mark's got the right idea, but it's too late for me. I've already got twins. I just wish they had designed the boat with twin keels to protect the twin props! I have seriously considered adding prop-protecting keels forward of the props. Maybe someday when my bank account exceeds my needs.

As PG mentioned, we had a couple of encounters with submerged logs this winter that created a pronounced vibration on the port prop at cruise RPMs. Three years ago I had a 'significant encounter with a submerged object" that caused $8000 damage to my running gear. Ever since then, I have had a subtle vibration in the port running gear that the mechanics could not trace. This latest impact only made that vibration more pronounced.

We were having the bottom scrubbed by a diver on a Friday and decided to have the 20x18 props pulled at that time. Once they were on deck, I knew we made the right decision. The stbd prop had noticeable damage to its tips and leading edges.

I delivered them that day to the only Prop Scan Prop Shop in CA, which just happened to be in my own backyard. Steve Thomas of Thomas Marine Propeller promised to have them scanned, tuned and delivered to my cockpit on the following Tuesday so my diver could reinstall them before leaving town. By Tuesday morning, I had a computer analysis of the as-found and as-tuned results in my email. The pitch of these 1976 date-stamped props remained at the 17.7 degrees found on the stbd prop to retain the WOT 2800 RPM.

Once they were installed, I took the boat out for a trial run to see if there was a difference. I immediately found that ALL vibrations were gone. I proceeded to the San Joaquin River to record the speeds at all signficant RPMs to see if there was a cruise speed improvement.

After running with the 0.4 kt flood tide for 10 minutes recording power and speed combinations, I reversed course to record the same power setting speeds against the current. I averaged the speeds from the two runs to calculate the improvement. Since it was a flood tide, the results are slightly conservative.

The net result was that my cruise speeds increased by 0.3 to 0.4 Kts in the range of 6 Kts to 9 Kts on my 85 HP Perkins twins. My WOT RPM remained at the requisite 2800 RPM, delivering the same 10 Kts. That averages to about a 5% increase in performance at cruise RPM.

What did I gain by having the props Prop Scanned instead of having them traditionally tuned? I got two props that are within one one hundredth of a degree in pitch and near-perfect settings. I gained 5% in cruise speed. I also have a computer recording of each prop's profile. If I encounter the bottom or another log in the future, I can just pull the one prop impacted and have it perfectly tuned to its previous setting. This saves me the cost of pulling, measuring, and replacing an undamaged prop.

What did the Prop Scan cost me over the cost of a 'traditional prop repair"? My prior old-school prop tune cost was approximately $300 for both props combined. This Prop Scan repair cost me about an additional $300 for a near-perfect tune. Future repair costs are projected to be less expensive by the Prop Scan shop due to the presence of the prop profile in the computers for future reference.

Total cost:
Pull and reinstall prop - $150
Prop Scan two 20x18 props - $580
Total: $730

Efficiency improvement of 5% equates to:

100 hrs / year at 3.5 gal/hr at $4.00/gal = $1400/year in fuel. 5% of $1400 = $70

$280 cost increase over manual prop tune/ $70/year saved = 4 years to break even.

The value of vibration-free cruising - priceless!!

Edelweiss · May 15, 2012

FlyWright said:
Mark's got the right idea, but it's too late for me. I've already got twins. I just wish they had designed the boat with twin keels to protect the twin props! I have seriously considered adding prop-protecting keels forward of the props. Maybe someday when my bank account exceeds my needs.

As PG mentioned, we had a couple of encounters with submerged logs this winter that created a pronounced vibration on the port prop at cruise RPMs. Three years ago I had a 'significant encounter with a submerged object" that caused $8000 damage to my running gear. Ever since then, I have had a subtle vibration in the port running gear that the mechanics could not trace. This latest impact only made that vibration more pronounced.

We were having the bottom scrubbed by a diver on a Friday and decided to have the 20x18 props pulled at that time. Once they were on deck, I knew we made the right decision. The stbd prop had noticeable damage to its tips and leading edges.

I delivered them that day to the only Prop Scan Prop Shop in CA, which just happened to be in my own backyard. Steve Thomas of Thomas Marine Propeller promised to have them scanned, tuned and delivered to my cockpit on the following Tuesday so my diver could reinstall them before leaving town. By Tuesday morning, I had a computer analysis of the as-found and as-tuned results in my email. The pitch of these 1976 date-stamped props remained at the 17.7 degrees found on the stbd prop to retain the WOT 2800 RPM.

Once they were installed, I took the boat out for a trial run to see if there was a difference. I immediately found that ALL vibrations were gone. I proceeded to the San Joaquin River to record the speeds at all signficant RPMs to see if there was a cruise speed improvement.

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Interesting, never heard of the prop scan before, but it makes sense!! I have to admit, I got to the part in your post where you took it out on the river for a test run and I thought you were going to say you hit another log. I Love a happy ending.

I get some odd vibrations that seem to come and go, I haven't had my props checked in years, so maybe I had better check around Seattle for a shop that does that kind of prop balancing.
Thanks Al

Larry B

JD · May 15, 2012

FlyWright said:
Mark's got the right idea, but it's too late for me. I've already got twins. I just wish they had designed the boat with twin keels to protect the twin props! I have seriously considered adding prop-protecting keels forward of the props. Maybe someday when my bank account exceeds my needs./QUOTE]

There is a Trawler that has twins with skegs on both props and rudders on the whole Great Harbor line from the GH 37 to the GH74.

They also afford more room inside than any other trawler of it's size with stand up head room in the engine room and a Boson's Locker that will hold several large roller bags or what ever you want.

FlyWright · May 15, 2012

Edit: "The PORT prop had noticeable damage to its tips and leading edges."

JD, those look like very seaworthy trawlers. Out of my league, but fun to look at. I really like the fact that you get the twin redundancy with the dual keel protection. That's exactly what I have pictured in my own feeble mind as the best of both worlds. Thanks for the info.

FlyWright · May 15, 2012

Edelweiss said:
I get some odd vibrations that seem to come and go, I haven't had my props checked in years, so maybe I had better check around Seattle for a shop that does that kind of prop balancing.
Thanks Al

Larry B

Larry, here's a link to the Prop Scan locations webpage.

Contact Page - Prop Scan USA State Locations

Looks like the closest to you is near Portland, OR.

Marin · May 15, 2012

Edelweiss; said:
Interesting, never heard of the prop scan before, but it makes sense!!

Larry--- FlyWright is right on the money in that PropScan is a the best way to tune up a prop. A number of years ago I read an article about PropScan in one of the local (PNW) boating mags. At that time PropScan had just been introduced by a prop shop in, I believe, Bremerton. If the PropScan directory does not list a company in this area that uses it perhaps the company featured in the magazine article has since gone out of business or is no longer associated with PropScan.

If there is, in fact, no PropScan shop in this area you might check in the greater Vancouver, BC area.

If there is still no joy and you don't want to drive to Portland, I can recommend Kruger & Sons in Seattle as one of the best if not the best prop shop in the area. They don't use the PropScan system (to my knowledge) but they do computer-based analysis and tuning. Much more sophisticated than the "beat the prop on a form" method that had been done with our props in California before we bought the boat.

Kruger did our four-bladed Michigan props several years ago. We had been told by another shop the props were worn out and needed to be replaced but after getting recommendations for Kruger from numerous people in the local marine industry, we took them there. Kruger checked them and said no, the props were fine but they were horribly out of alignment and dimension. They said that one blade on one of the props wasn't even pushing water at cruise speed. They said they'd be happy to sell us new props for some $2000 or so apiece, but suggested that we might rather pay $350 or so per prop to have them totally reworked. Which is what we did.

A good PropScan shop would absolutely be my first choice, but if you can't find one close enough for you to be willing to take the props to, I would talk with Kruger & Sons.

psneeld · May 16, 2012

My experience with prop scan versus old timer shops...

Yes prop scan is wiz bang for checking the prop...but there's still the guy with the pitch block, the hammer and the brazing torch.

I've had the old timers that just throw the props on the block and get to work put out a product equal to the "prop scan" crowd without the "fancy computer charge"...

Now all the said...I'm sure there's a mix and match out there. Good shops in both camps. But untill the computer does the actual rework of the prop...just having the propscan technology is like having a butcher with a medical MRI mechine and calling himself a surgeon.

Prop Repair

skipperdude

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skipperdude

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Larry M

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