Cavitation

[Armin]

Bill Cullen working with Gerry Douglas has been testing a number of props to measure the effect a change in props has on the cavitation/vibration problem some of us have been having. Bill reported that the changing to a 14 x 10 three bladed prop versus the 15 x 9 installed as an option on many of our C350 solved the problem and that Gerry and he would be conducting additional tests.

In view of the number of owners who have expressed concern and the ongoing investigation, it might be good to set this up as one of the technical topics.

Armin
Make Way #207

[Richard Collins]

I agree. However, hopefully the Cavitation forum once formed could soon be moved to the historical archives!

[jnnielsen]

Armin,

I've added a TEMPORARY FORUM for the Catalina Cavitation issue.

Jerry

[Triumph]

Armin is correct. I have now sent my original prop to Catalina, where they are going to have it altered. They will then ask me to test this and compare it to the new 14x10 prop.
I'm going cruising from Tampa to Sanibel this week, and will further test the performance of the 14x10 new prop.

Bill
s/v Triumph

[Bill]

If any one is talking to Catalina could you ask them about just pressing the 15x9 to a 15x10 with out having to cut it to a 14" prop? My knee jerk reaction would be that I would think the 14x10 would cavitate more than the 15x9, but what do I know.

[Triumph]

Took a week long cruise with the 14" prop that I was testing for Gerry Douglas at Catalina. No noise from prop in a variety of conditions. Vibration noise is gone. As i reported earlier, no loss of power or speed either.

Upon returning home, I have received back the original prop that was altered (smaller) and I will test this verses the new prop I've been testing.

Measureed distance from tip of original prop to hull at 2 1/8", measured new prop at 2 7/8". Used a ruler whle scuba diving it, so not very scientific in nature, but that's what I got.

This trip down, I will try to also take a picuture of both props side by side for ya'll to observe.

[LONGHAWK]

Thanks for the info. I too believe that the prop tip to hull clearance is inadequate with the three blade 15x9. Keep the info flowing!
Thanks,
Sam LONGHAWK # 173

[c350makeway]

As I have reported in prior postings, my prop shaft was extended with the hope of solving the cavitation problem. A few weeks ago, after the boat was on the hard for the winter, I measured the clearence from the prop to the hull as well as the distance from the end of the cutlass to the back of the prop hub. The results were as follows:

Cutlass to back of the prop hub ( engine side) distance; 2.275 inches. This permits the use of a standard egg shaped zinc with 1 inch bore. The distance between the end of the cutlass and the back of the prop hub with a standard prop shaft is 7/8 inch.

Blade tip to hull when measured perpendicular to the prop, i.e. at an angle of 85 degrees, is 2.9"; 2.75" when measures as closest distance to hull.

Since the prop shaft has a downward angle of about 15 degrees and since the bottom of the hull has an upward angle of about 20 degrees, the longer shaft provides an additional clearance of about 1/2 inch between the prop tip and the hull. this would mean that the standard clearance is about 2.25 inches.

While I was taking my measurements, I checked the prop clearance of a Catalina 387 which is next to me. It has a 3.2 inch clearance between the prop tip and the hull. The distance between the hub end (engine side) and cutlass was about 1 inch.

Hope this helps with your investigations.

Best Regards,

Armin

[Hans Grasman]

Armin
Is your noise (cavitation) problem gone?
What type of prop do you have?
How long is the replacement shaft and what was the cost?
Thanks for the posting!
Hans
Belcourt #165

[c350makeway]

Hans,

Sorry, I do not know the length of my replacement prop shaft. It was sent to my mechanic and installed while I was on a business trip to Europe last April. From the measurements I took, the shaft is about 1 1/2 inches longer than the original shaft.

My boat, "Make Way" is fitted with a three bladed fixed prop designated as 15R9. This prop is the OEM optional upgrade.

The installation of the longer shaft, which required the removal of the rudder, greatly reduced, but did not eliminate, the cavitation problem. On the open seas (Atlantic) with head winds and three to five foot waves, cavitation will take place. As I have reported before, this can be reduced but flying the jib which unloads the prop and improves the flow under the hull.

Fair Winds,

Armin

s/v "Make Way"

[Hans Grasman]

Thank you Armin for your reply. Now I remember also that you told me before to use the jib.
I will wait for the final results from Bill and Gerry's tests and then take corrective action.
I did mention to Gerry while we were testing Bill's boat on Tampa bay that some folks went to a longer shaft but his reaction was kind of "what will that do?". I thought, well you can use donut zincs
It must be tough to be the designer and have folks with limited boat knowledge critize your design but then I think that Catalina should have stepped up to the plate as soon as we started chatting about this issue.
I told Frank Butler that we had a good meeting and that we are his supporters. We want it fixed.
Anyway let us wait a few more weeks for the final results.
I am going back to my boat in Florida on Nov. 26.
Hans
Belcourt #165

[Triumph]

Tested the original prop that Catalina had cut down to 14". Results: still have a vibration noise, and the boat is slower than with the original 15". This is not the solution.

The 14R10 new prop that was previously tested is a Michigan Dyna prop. It has wide blades on it. The original prop from Catalina has much skinnier blades. I'd say that the Dyna prop has a lot more "bite" than the original prop. I noticed a lot more power with the Dyna prop too, more muscle. The trade off, is perhaps sailing pereformance. The original prop I would think has less drag than the Dyna prop.

I have pictures, and if I can email them to one of you, you could post it for me.

Gerry Douglas said they will let me know what's next.

[Triumph]

Could someone send me their email address so that i could send pics to of the props, then you could post them here for me, or, send me a place and instructions so that I can learn to do this, I don't have a host sight or whatever it's called. My email is wjcullen@armstrong.com

I think the pictures would help everyone see this better.

[Guest]

Bill Cullen working with Gerry Douglas has been testing a number of props to measure the effect a change in props has on the cavitation/vibration problem some of us have been having.

So whats the next step, remember, take baby steps before you try to walk .

[Triumph]

Got a call from Gerry Douglas yesterday. He has been doing some additional testing out in California. He mentioned that with the 14R10 Dyna style prop, there would not only be more drag, but perhaps more turbulance crossing the rudder. The Dyna prop is a power boat prop with wide blades. Gerry is testing a "Sailor" prop with more pitch, and less wide blades like the original three blade that came on the boat. He will send me one of these, and I'll test it verses the Dyna prop for vibration/cavitation, and power and speed while motoring.

Bill
s/v Triumph
Tampa

[Armin]

Bill,

Thanks for the update from Gerry indicating that the good folks at Catalina are still working to resolve the problem. I received a note from Mr. Frank Butler, dated Dec. 12 2005, which advised me of their ongoing investigation and indicated that he would be in touch as soon as he had final test results.

I am sure that the cavitation problem will be resolved. I commend Catalina for its proactive customer service. It is great to know that the company stands by its products! Not many other companies provided this level of communications and service.

Have a great New Year,

Armin

[Triumph]

Received another prop to test. I think it is a 15R10 Sailor, meaning that it has the thinner blades for less drag while under sail. The original prop on the boat was a 15R9 sailor. Meaning this new prop has more pitch I think. The prop that works well and has eliminated the vibration noise is a 14R10 Dyna prop with wide blades.
Results, the 15R10 new prop is as bad as the orignial.
Next thing I'll do is a test of boat speed while dragging the two types of props. This would tell us the benefit of a folding prop, and the difference between the wide blade and the thinner blade props.

[Triumph]

I'm new at the photo thing so here goes:

Notice the wider blades on the "Dyna" prop verses the Sailor Prop. I painted the props with that spray underwater running gear pint from West Marine. As you can see it din't stick well. what is also interesting is that when I tested the prop the right, the sailor, the paint developed freckles. This is a sign of cavitation I believe. [/img]

[Tim April IV]

Wow! There is a huge difference between the configuration of the current / standard three blade and the original standard two blade (shown in the second post in the thread referenced here:
http://www.catalina350.net/phpBB2/viewtopic.php?t=27

Wonder what they were thinking?

[yodagwb]

It is my understanding that cavitation is the vaporization (boiling) of the water on the low pressure side (forward) of the prop. It in turn makes sense that the lowest pressure is occuring just behind the hull/shaft exit point, as the hull moves thur the water, when the prop reaches the top of its rotation, while the water is trying to move back in front of the prop. The prop blade moving thru the underpressurized water would cause it to vaporize/cavitate. When moving at a slower speed the water is having time the flow properly around the hull and represurize prior to the prop blade's pressure reduction, but the higher speeds is when the excessive lower water pressure and cavitation point is occuring. It would seem that a shaft extention would give the water time to repressurize prior to the prop's depressurizing it and I wouldn't think that the extention would have to be all that long. Maybe the lenght is what they should be testing.

Water flow around the intergrated strut is the start of the problem. The only way a prop change will fix the problem is if the pitch is reduced enough the stop the vaporization between the inergrated strut andprop blade. Reduced pitch typically reduces top end speed which is what is causing the problem in the first place.

Personally I would like to see Catalina come out with an extention for the shaft. Until that happens I don't think this is a fixable problem. At least not while maintaining its current hull speed.