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TallRedRider
12-12-2008, 11:17 PM
So I just bought a new to me 2006 X-45.

I thought I gave her a pretty decent shakedown at the dealer who is 300 miles away. I was at a family activity that required me to be in best dress immediately before we went to the dealership, so I was did not actually lay on my back under the boat. I did the usual, inspect the prop and rudder for damage and the shaft...all looked good and I bought the boat.

Then after I got home, I found this:
http://i243.photobucket.com/albums/ff206/talltigeguy/X-45%20pics/IMG_7651.jpg

http://i243.photobucket.com/albums/ff206/talltigeguy/X-45%20pics/IMG_7654.jpg

There is a small section of the hull behind the rudder that is at a slant. You don't see this if you kneel under the swimstep and grab the rudder because it is slanted and faces forward a little. The gelcoat was ragged and looked eaten away. Bare shards of fiberglass are bulging from within.

I shot an email to my salesman and his first impression was the same as mine..'WTH?'

He showed my pics to the head tech at the shop who noted that it is due to prop blast going past the rudder and then wearing away the gelcoat and that it happens often enough that MC has now placed a steel plate over the rudder plate to protect that area from the turbulence from the prop.

Sounds sort of crazy to me, but he then crawled underneath an 09 X-45 and indeed there is a plate there that shields that part of the hull from the prop blast.

Here are the cell phone pics he sent me of an 09 with the plate. They look a little funny because the hull is black, so it takes a few seconds to orient yourself.

So the message is to take a look at your hull right there and make sure it is holding up fine.

The guys at Utah Water sports agreed to put a plate on my boat for free. Definite standup guys who are working at giving awesome customer service.

http://i243.photobucket.com/albums/ff206/talltigeguy/X-45%20pics/rudderplate1.jpg

http://i243.photobucket.com/albums/ff206/talltigeguy/X-45%20pics/rudderplate2.jpg

Gamble
12-12-2008, 11:31 PM
that's interesting.......I believe my ol stars and stripes had those exact same marks yours does. Now I know what caused it!

Witness140
12-12-2008, 11:43 PM
Did they indicate this is an issue with all of the boats - or just the 45? I'm looking at some pics of the bottom of an 09' X2, and it doesn't have that plate.

TallRedRider
12-13-2008, 12:12 AM
They did not indicate if this is specific to the 45. I suspect that any of the boats that have a recessed rudder plate and then have a slanting gelcoat 'box' if you will, would be at risk.

coz
12-13-2008, 06:20 AM
I think this needs further investigation, prop wash eating the fiberglass? If that's the case there will be others. I'll bet hundreds of MC owners will be looking under the boat after seeing this post for holes like I just did, I'm good.

Keep us posted this is interesting. To me it looks like a rock chip that maybe was helped by the force of the wash after there was a hole started.

Good luck!

SaltwaterMC
12-13-2008, 07:28 AM
Do you have the 8.1L in your 45? From what I understand, they only put the plate on the 45s with the big block because apparently that engine in that boat can create cavitation which can cause gel damage.

bigmac
12-13-2008, 10:16 AM
I think this needs further investigation, prop wash eating the fiberglass? If that's the case there will be others. I'll bet hundreds of MC owners will be looking under the boat after seeing this post for holes like I just did, I'm good.

Keep us posted this is interesting. To me it looks like a rock chip that maybe was helped by the force of the wash after there was a hole started.

Good luck!

Agreed. That looks like foreign object damage to me. Not only the gel coat, but the underlying fiberglass too. All looks disrupted, as from impact.

prostar205
12-13-2008, 11:54 AM
So I just bought a new to me 2006 X-45.

I thought I gave her a pretty decent shakedown at the dealer who is 300 miles away. I was at a family activity that required me to be in best dress immediately before we went to the dealership, so I was did not actually lay on my back under the boat. I did the usual, inspect the prop and rudder for damage and the shaft...all looked good and I bought the boat.

Then after I got home, I found this:
http://i243.photobucket.com/albums/ff206/talltigeguy/X-45%20pics/IMG_7651.jpg

http://i243.photobucket.com/albums/ff206/talltigeguy/X-45%20pics/IMG_7654.jpg

There is a small section of the hull behind the rudder that is at a slant. You don't see this if you kneel under the swimstep and grab the rudder because it is slanted and faces forward a little. The gelcoat was ragged and looked eaten away. Bare shards of fiberglass are bulging from within.

I shot an email to my salesman and his first impression was the same as mine..'WTH?'

He showed my pics to the head tech at the shop who noted that it is due to prop blast going past the rudder and then wearing away the gelcoat and that it happens often enough that MC has now placed a steel plate over the rudder plate to protect that area from the turbulence from the prop.

Sounds sort of crazy to me, but he then crawled underneath an 09 X-45 and indeed there is a plate there that shields that part of the hull from the prop blast.

Here are the cell phone pics he sent me of an 09 with the plate. They look a little funny because the hull is black, so it takes a few seconds to orient yourself.

So the message is to take a look at your hull right there and make sure it is holding up fine.

The guys at Utah Water sports agreed to put a plate on my boat for free. Definite standup guys who are working at giving awesome customer service.

http://i243.photobucket.com/albums/ff206/talltigeguy/X-45%20pics/rudderplate1.jpg

http://i243.photobucket.com/albums/ff206/talltigeguy/X-45%20pics/rudderplate2.jpg

Go Red (Tall) -

I had almost the same issue with my '02 X30 a few years ago. My dealer started picking at the gel coat around the rudder area because I noticed some cracking in the gel coat. It turned out to be voids (air pockets) in the fiberglass. They drilled it all out and filled back in with fiberglass and new gel coat. You can't even tell them worked in that area. I would definately have UWS repair the gel coat becuase you don't just want to put a plate over exposed raw fiberglass. Water will still get in there and weaken the structure of the rudder area. After the gel coat has been repaired correctly, then put the plate on it.

By the way, my boat has the L-18 motor in it so there may be some truth to it only happening with the big block boats. I will post pictures (I have a ton) of this repair when I to work on Monday.

bturner2
12-14-2008, 10:30 AM
I'm going to lean towards cavitation on this one. I've seen SS props eaten up by cavitation so some soft fiberglass would be a quick victim if in the path of some boiling water off a spinning prop. Combine that with some hard take offs in shallow water and you get a hole in the unprotected area of the hull.

TallRedRider
12-14-2008, 12:25 PM
Do you have the 8.1L in your 45? From what I understand, they only put the plate on the 45s with the big block because apparently that engine in that boat can create cavitation which can cause gel damage.

Yes, it has the 8.1L engine.

Go Red (Tall) -

I had almost the same issue with my '02 X30 a few years ago. My dealer started picking at the gel coat around the rudder area because I noticed some cracking in the gel coat. It turned out to be voids (air pockets) in the fiberglass. They drilled it all out and filled back in with fiberglass and new gel coat. You can't even tell them worked in that area. I would definately have UWS repair the gel coat becuase you don't just want to put a plate over exposed raw fiberglass. Water will still get in there and weaken the structure of the rudder area. After the gel coat has been repaired correctly, then put the plate on it.

By the way, my boat has the L-18 motor in it so there may be some truth to it only happening with the big block boats. I will post pictures (I have a ton) of this repair when I to work on Monday.

The interesting thing about the rock chip theory is that the damage is exactly behind the rudder and it is going to be a challenge to figure how a rock gets from the prop then swirls around the rudder and hits the glass with enough force to cause the damage. I guess that could happen.

UWS said that they would fix the fiberglass for me, if I wanted, but that it was not necessary because the plate they put on is sealed with sealant, and would stay dry. Frankly, I don't have much faith in that, so I slapped some gelcoat on there yesterday. We'll see if that holds until I can get her up there. It does not need to look factory once it is covered with the plate, but I agree it should be water proof, even if the plate is sealed.

Wouldn't surprise me if the previous owner did hard starts in very shallow water, as that it appears that he beached the boat on the rocks as well. I have some gnarly scratches on the keel. Gel coat is surprisingly cheap to fix by those who know what they are doing. And it is undetectable when done right.

bturner2
12-15-2008, 08:10 AM
I doubt the rock chip theory. If you look around the damaged area you can see the whole area is being etched. Looks like someone hit it with a sand blaster. Typical cavitation damage.

MYMC
12-15-2008, 09:26 AM
http://en.wikipedia.org/wiki/Cavitation

Cavitation damage

Cavitation is, in many cases, an undesirable occurrence. In devices such as propellers and pumps, cavitation causes a great deal of noise, damage to components, vibrations, and a loss of efficiency.

When the cavitation bubbles collapse, they force liquid energy into very small volumes, thereby creating spots of high temperature and emitting shock waves, the latter of which are a source of noise. The noise created by cavitation is a particular problem for military submarines, as it increases the chances of being detected by passive sonar.

Although the collapse of a cavity is a relatively low-energy event, highly localized collapses can erode metals, such as steel, over time. The pitting caused by the collapse of cavities produces great wear on components and can dramatically shorten a propeller's or pump's lifetime.

After a surface is initially affected by cavitation, it tends to erode at an accelerating pace. The cavitation pits increase the turbulence of the fluid flow and create crevasses that act as nucleation sites for additional cavitation bubbles. The pits also increase the component's surface area and leave behind residual stresses. This makes the surface more prone to stress corrosion.

coz
12-15-2008, 09:29 AM
http://en.wikipedia.org/wiki/Cavitation

Cavitation damage

Cavitation is, in many cases, an undesirable occurrence. In devices such as propellers and pumps, cavitation causes a great deal of noise, damage to components, vibrations, and a loss of efficiency.

When the cavitation bubbles collapse, they force liquid energy into very small volumes, thereby creating spots of high temperature and emitting shock waves, the latter of which are a source of noise. The noise created by cavitation is a particular problem for military submarines, as it increases the chances of being detected by passive sonar.

Although the collapse of a cavity is a relatively low-energy event, highly localized collapses can erode metals, such as steel, over time. The pitting caused by the collapse of cavities produces great wear on components and can dramatically shorten a propeller's or pump's lifetime.

After a surface is initially affected by cavitation, it tends to erode at an accelerating pace. The cavitation pits increase the turbulence of the fluid flow and create crevasses that act as nucleation sites for additional cavitation bubbles. The pits also increase the component's surface area and leave behind residual stresses. This makes the surface more prone to stress corrosion.

I love wikipedia :headbang:

SkiDog
12-15-2008, 09:38 AM
I love wikipedia :headbang:

Apparently so do others!:D

coz
12-15-2008, 09:46 AM
Apparently so do others!:D

I didn't know this :confused:

MasterCraft was founded when the owners decided to start making their own. The owners took a Ski Nautique manufactured by Correct Craft and hung it from a tree and cut the back of the hull off in order to modify the hull to their preferences.

http://en.wikipedia.org/wiki/MasterCraft_Boats

TMCNo1
12-15-2008, 01:57 PM
Apparently so do others!:D

I didn't expect this,

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bigmac
12-15-2008, 02:04 PM
OK, the combination of Mike and Wikipedia has persuaded me. Cavitation damage. Change my vote, moderators.

SkiDog
12-15-2008, 02:08 PM
I didn't expect this,

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Damnit man, i ain't as popular as somebody thought I wuz!:uglyhamme:uglyhamme:uglyhamme

prostar205
12-15-2008, 02:43 PM
Here are the pictures of my repair around the rudder box area.

prostar205
12-15-2008, 02:44 PM
Here's more...

prostar205
12-15-2008, 02:45 PM
The last two shots...

Hrkdrivr
12-15-2008, 06:02 PM
Same year/model boat w/L18 engine. Initial damage was done while getting onto the trailer and the prop hit something (low water at the end of the '07 season). We had it repaired and a year later the gel-coat had come off again in exactly the same spots as the original damage. The shop that did the original repair fixed it again.

After the original repair job, it looked like the gel-coat had been vacuumed out of the original damage holes. We have a 14.5 x 22 prop, and with the big engine, I'm sure it can create quite a low-pressure area along the hull, which might have sucked it out, as it were.

I wonder if the original owner of your boat damaged it like we did and then got a not-so-great repair job which later failed like ours.

Link to the thread that has pics of the damage before it was fixed the second time.

http://www.mastercraft.com/teamtalk/showthread.php?t=25849

TallRedRider
12-15-2008, 07:46 PM
HRk,

You have a 22 inch prop? That is a monster. It looks like you got the blades almost touching the gelcoat, or maybe it is just an optical illusion.

How do you like the prop?

WakePowell
12-15-2008, 09:52 PM
14.5 is the diameter of Hrkdrivr's prop. The pitch is 22. That was the standard prop on the 2005 X45's with the 8.1L engine.

TallRedRider
12-16-2008, 12:05 AM
14.5 is the diameter of Hrkdrivr's prop. The pitch is 22. That was the standard prop on the 2005 X45's with the 8.1L engine.

Yes, I am a retard. Thanks for the clarification. Oops:o

Jesus_Freak
12-16-2008, 01:07 PM
http://en.wikipedia.org/wiki/Cavitation

Cavitation damage

Cavitation is, in many cases, an undesirable occurrence. In devices such as propellers and pumps, cavitation causes a great deal of noise, damage to components, vibrations, and a loss of efficiency.

When the cavitation bubbles collapse, they force liquid energy into very small volumes, thereby creating spots of high temperature and emitting shock waves, the latter of which are a source of noise. The noise created by cavitation is a particular problem for military submarines, as it increases the chances of being detected by passive sonar.

Although the collapse of a cavity is a relatively low-energy event, highly localized collapses can erode metals, such as steel, over time. The pitting caused by the collapse of cavities produces great wear on components and can dramatically shorten a propeller's or pump's lifetime.

After a surface is initially affected by cavitation, it tends to erode at an accelerating pace. The cavitation pits increase the turbulence of the fluid flow and create crevasses that act as nucleation sites for additional cavitation bubbles. The pits also increase the component's surface area and leave behind residual stresses. This makes the surface more prone to stress corrosion.


Lets dive a little deeper. I dont question the existence of conditions that can be conducive to cavitation on the prop outer ridge (greatest slip velocity, lowest static pressure), but the question I am wrestling with is....Does the trajectory of the high momentum fluid leaving the prop pass close enough to the hull with enough energy to wear to this extent? I am going to vote no. Rocks being slung from the prop = yes....fluid = probably not. Can the fluid aggravate a condition that was initiated by a rock...maybe.

I picture myself holding a Milwaukee industrial grinder with a cutting compound attempting to get the oxidation out of my gelcoat. It takes me 10 minutes working an area again and again with 80% of my total tricep output to get microns removed. Yes, I am not Rocky, and yes I am spreading out the force over a potentially larger area. But even when I lean the grinder some on its side such that I magnify the pressure (force/area), it still is difficult to remove microns.

Then I picture the trajectory of the swirling flow from the prop. The prop entrains some fluid around it, maybe 15% of its diameter (Eric?), so the effective bounds of the swirling fluid (potentially with cavitation bubbles looking to collapse) is maybe 1.15x the prop diameter. I dont know if this reaches high enough with enough energy to damage the gelcoat. What is the shaft distance/spacing from the hull?

If Eric, Mike, or other can give me 1) dimensions and placement of shaft relative to the hull and 2) some idea of a reasonable 2D or 3D velocity profile leaving a prop, I might be able to run some calcs. If we have any takers, send me a PM.

coz
12-16-2008, 01:12 PM
Lets dive a little deeper. I dont question the existence of conditions that can be conducive to cavitation on the prop outer ridge (greatest slip velocity, lowest static pressure), but the question I am wrestling with is....Does the trajectory of the high momentum fluid leaving the prop pass close enough to the hull with enough energy to wear to this extent? I am going to vote no. Rocks being slung from the prop = yes....fluid = probably not. Can the fluid aggravate a condition that was initiated by a rock...maybe.

.

That was my initial question. I know all about cavitation but my question was if the hole could be created without help i.e. chip, scratch or hole, or just the cav.

MYMC
12-16-2008, 01:57 PM
Lets dive a little deeper. I dont question the existence of conditions that can be conducive to cavitation on the prop outer ridge (greatest slip velocity, lowest static pressure), but the question I am wrestling with is....Does the trajectory of the high momentum fluid leaving the prop pass close enough to the hull with enough energy to wear to this extent? I am going to vote no. Rocks being slung from the prop = yes....fluid = probably not. Can the fluid aggravate a condition that was initiated by a rock...maybe.

I picture myself holding a Milwaukee industrial grinder with a cutting compound attempting to get the oxidation out of my gelcoat. It takes me 10 minutes working an area again and again with 80% of my total tricep output to get microns removed. Yes, I am not Rocky, and yes I am spreading out the force over a potentially larger area. But even when I lean the grinder some on its side such that I magnify the pressure (force/area), it still is difficult to remove microns.

Then I picture the trajectory of the swirling flow from the prop. The prop entrains some fluid around it, maybe 15% of its diameter (Eric?), so the effective bounds of the swirling fluid (potentially with cavitation bubbles looking to collapse) is maybe 1.15x the prop diameter. I dont know if this reaches high enough with enough energy to damage the gelcoat. What is the shaft distance/spacing from the hull?

If Eric, Mike, or other can give me 1) dimensions and placement of shaft relative to the hull and 2) some idea of a reasonable 2D or 3D velocity profile leaving a prop, I might be able to run some calcs. If we have any takers, send me a PM.
I will try and get the requested specs to you in a reasonable amount of time; however, having been doing this for a number of years I can assure you this is cavitation...or there are a lot of floating rocks that are seemingly attracted to large displacement/high power boats that swing large props that are in close proximity to hull bottoms.

Further, isn't awfully nice of MasterCraft to build a "rock guard" and install it under warranty? First they screw you being complicit with Cash Rewards and then try to make nice with a rock guard...some things I'll never understand.:confused:

MYMC
12-16-2008, 02:07 PM
2009 X45 with L-18 is .6000 from the hull bottom from the prop tip. I can guestimate distance to damaged are if needed based on pics...if you need it.

Jesus_Freak
12-17-2008, 12:32 PM
I will try and get the requested specs to you in a reasonable amount of time; however, having been doing this for a number of years I can assure you this is cavitation...or there are a lot of floating rocks that are seemingly attracted to large displacement/high power boats that swing large props that are in close proximity to hull bottoms.

Yes, floating rocks attracted to certain boats. I like that theory. :D Arent certain volcanic rock flavors less dense than water? Dont remember.

Jesus_Freak
12-17-2008, 12:36 PM
2009 X45 with L-18 is .6000 from the hull bottom from the prop tip. I can guestimate distance to damaged are if needed based on pics...if you need it.

Are you saying the tip of the prop is only 0.6 inches from the hull bottom?!?!?!?!:eek3:

How fast does the prop turn (dont know which tranny the boat has), and what is its diameter?

What is the ballpark longitudinal distance from the aft-most part of the blade to the point of damage?

TallRedRider
12-17-2008, 01:48 PM
FYI. There was a service bulletin back in October 2007 addressing the gel issue. It was for all 2005-2007 245/X-45 w/ 8.1. The dealer can get that bulletin easy enough.

I wonder if most of the 08's then have the plate as well.

I will be at the boat today, and will try and measure that distance from the prop to the point of damage.

magnum
12-17-2008, 02:37 PM
Was it just the X-45 that was included in the Service Bulletin , I have an X-Star with the 8.1L. Mine looks to be ok

Hollywood
12-17-2008, 04:30 PM
Having trouble reading? ^^^

TallRedRider
12-17-2008, 08:40 PM
Are you saying the tip of the prop is only 0.6 inches from the hull bottom?!?!?!?!:eek3:

How fast does the prop turn (dont know which tranny the boat has), and what is its diameter?

What is the ballpark longitudinal distance from the aft-most part of the blade to the point of damage?

The rearmost part of the propeller is 6 inches from the area where the damage is on my gelcoat. So somebody do some calculations and figure out how much energy is eating my gelcoat there. One interesting part of this is that the worst of it is exactly behind the rudder, where I think there would be more turbulence and hesitation in the water flow.

My prop is apparently a 'high altitude' prop since it is only 13.7 inches in diameter. I forget the pitch, but it is not 22 either. It seems like it is 19 or so.

I am open to prop suggestions too. The highest place I go boating is Lake Powell, 3600 feet or so. Lake Mead is 1100 feet, my home lake is 2700 feet.

TMCNo1
12-17-2008, 08:46 PM
The rearmost part of the propeller is 6 inches from the area where the damage is on my gelcoat. So somebody do some calculations and figure out how much energy is eating my gelcoat there. One interesting part of this is that the worst of it is exactly behind the rudder, where I think there would be more turbulence and hesitation in the water flow.

My prop is apparently a 'high altitude' prop since it is only 13.7 inches in diameter. I forget the pitch, but it is not 22 either. It seems like it is 19 or so.

I am open to prop suggestions too. The highest place I go boating is Lake Powell, 3600 feet or so. Lake Mead is 1100 feet, my home lake is 2700 feet.

Talk to Eric, http://www.ojprops.com/contact_us

WakePowell
12-18-2008, 08:25 AM
Go Red – I predominately used my ’05 X-45 with the L-18 at Lake Powell and used the 14.5x22 prop. At Lake Powell you typically travel a long distance to get to where you want to be and the large pitch gave a much better cruise (lower RPM’s). I could still load the boat with people and ballast and pull a rider with no issues. I also felt that the 14.5x22 prop was much smoother and quieter than the 13.7x19.

Ole Miss Rebels
12-18-2008, 11:28 AM
I have an 08 XStar with L18 and 14.75 X 15.5 oj prop. i checked my hull and saw no signs of wear/damage. Is the XStar immune to this phenomenon or is it likely to show up a little later? i only have around 70 hours on the boat. thanks in advance

MYMC
12-18-2008, 12:01 PM
Are you saying the tip of the prop is only 0.6 inches from the hull bottom?!?!?!?!:eek3:

How fast does the prop turn (dont know which tranny the boat has), and what is its diameter?

What is the ballpark longitudinal distance from the aft-most part of the blade to the point of damage?
Transmission is a 1.52:1...that is the distance on an X45.

NO OTHER BOATS HAVE BEEN EFFECTED...INCLUDING X-STARS...THEY ALL USE DIFFERENT SHAFT, STRUT & PROP COMBOS...THIS IS A 245/X45 ISSUE ONLY.

Jesus_Freak
12-19-2008, 10:19 PM
So I ran some quick easy numbers, no time for rocket science here. The water is leaving the prop at about 100 m/s in the circumferential direction (the direction the prop is turning) and maybe 20 m/s in the axial direction (the direction opposite the boat's travel). Assuming vapor bubbles are generated at the blade tips, they need to find a place to collapse on the hull in order to do damage. At the aforementioned speeds, the only place they are going to hit the hull is in a slow/low-pressure zone. The perfect spot is just behind the vertical rudder shaft (or whatever it is called). Here, the flow is separated from the hull and provides a place to collect low-momentum fluid or bubbles. I can see how they can do damage there like the picture in the first post. I still dont see, however, how they can eat an inch into one spot without showing scattered damage, such as that of prostar205's pictures.

JohnE
12-19-2008, 10:37 PM
So I ran some quick easy numbers, no time for rocket science here. The water is leaving the prop at about 100 m/s in the circumferential direction (the direction the prop is turning) and maybe 20 m/s in the axial direction (the direction opposite the boat's travel). Assuming vapor bubbles are generated at the blade tips, they need to find a place to collapse on the hull in order to do damage. At the aforementioned speeds, the only place they are going to hit the hull is in a slow/low-pressure zone. The perfect spot is just behind the vertical rudder shaft (or whatever it is called). Here, the flow is separated from the hull and provides a place to collect low-momentum fluid or bubbles. I can see how they can do damage there like the picture in the first post. I still dont see, however, how they can eat an inch into one spot without showing scattered damage, such as that of prostar205's pictures.

So how does all that translate if the metal plate is installed?:D8p

Jesus_Freak
12-20-2008, 05:51 AM
So how does all that translate if the metal plate is installed?:D8p

Thanks for asking. :) I actually meant to continue that, but didnt have time.

The metal plate simply buys you distance for reattachment. The flow behind that rudder assembly will eventually become calm/smooth again and attach itself to the hull. At that point pressure has recovered and the flow is relatively smooth along the bottom of the hull. Having the metal there gives a little cushion on this distance. This is (sorta) like when you draft behind an 18-wheeler, in that drafting is less productive the farther you move back from the truck. I personally think an expanded metal plate is a simple, logical fix.

ProStar Slalom
12-20-2008, 08:48 AM
JF, I knew you'd come through with some good fluid mechanics analysis. So in simple terms, I'm assuming this condition would only occur during high RPM and relatively low forward velocity. I would think that with higher forward velocity you would maintain a laminar boundary layer along the hull of the boat, right?

coz
12-20-2008, 09:12 AM
JF, I knew you'd come through with some good fluid mechanics analysis. So in simple terms, I'm assuming this condition would only occur during high RPM and relatively low forward velocity. I would think that with higher forward velocity you would maintain a laminar boundary layer along the hull of the boat, right?

By may calcs you could be right :rolleyes:

http://www.eschoolnews.com/media/images/math_image.jpg

:D

ProStar Slalom
12-20-2008, 03:38 PM
That's some serious higher math, coz. I'm out.

TMCNo1
12-20-2008, 07:52 PM
By may calcs you could be right :rolleyes:

http://www.eschoolnews.com/media/images/math_image.jpg

:D

I ran those same calculations and determined the plate is a sister of a mudflap in no uncertain terms!43119

Jesus_Freak
12-23-2008, 12:20 PM
JF, I knew you'd come through with some good fluid mechanics analysis. So in simple terms, I'm assuming this condition would only occur during high RPM and relatively low forward velocity. I would think that with higher forward velocity you would maintain a laminar boundary layer along the hull of the boat, right?

High RPM and low forward boat velocity will raise the blade tip slip velocity, so yes. Plus, at lower boat speeds, there is less bulk motion to keep the bubbles (looking for a place to collapse) swept off of the hull. BUT....at higher boat speeds, the pressure deficit behind the rudder mount increases, thus increasing the potential for bubbles to get sucked into that area. It is not clear to me which way this would go.

As far as your BL question, typically higher speeds will move the point of BL transition from lam to turb forward on the hull. In other words, you are more likely to have a turb BL on more of the hull the faster you go. This depends on surface roughness and water conditions to a great extent; I am only speaking in general terms.

Jesus_Freak
12-23-2008, 12:22 PM
That's some serious higher math, coz. I'm out.

This is only higher math if the functions T, f, and L, are nonlinear. Other than that, it just boils down to undergrad calculus then algebra.:)

EDIT: I meant to add that T, f, and L must also be functions of only one variable...If not, higher math just turns to numerical approximations (algebra).

MYMC
12-23-2008, 12:52 PM
This is only higher math if the functions T, f, and L, are nonlinear. Other than that, it just boils down to undergrad calculus then algebra.:)

Jeez...like we all didn't know that!

Sodar
12-29-2008, 12:45 AM
Totally possible, feasible and likely.

In 2004, the ferry company I worked for repowered all the boats with government grant money for cleaner burning engines. They ended up getting 2 of the 100' boats into the 40 knot range, yet they kept losing blades on the props. It turned out that the cavitation bubbles were eating the nibral at the hubs and causing the blade to break off. They ended up solving the issue by installing a stainless steel cone on the prop shaft about the diameter of the hub to help. It turned out to work, but 4 sets of $25k props were lost in the process. Incredible that a few bubbles can eat through solid metal.

TMCNo1
12-29-2008, 06:43 AM
Totally possible, feasible and likely.

In 2004, the ferry company I worked for repowered all the boats with government grant money for cleaner burning engines. They ended up getting 2 of the 100' boats into the 40 knot range, yet they kept losing blades on the props. It turned out that the cavitation bubbles were eating the nibral at the hubs and causing the blade to break off. They ended up solving the issue by installing a stainless steel cone on the prop shaft about the diameter of the hub to help. It turned out to work, but 4 sets of $25k props were lost in the process. Incredible that a few bubbles can eat through solid metal.

Makes you wonder just how good a bubble bath is for your body, right?http://smileys.smileycentral.com/cat/36/36_19_1.gif (http://www.smileycentral.com/?partner=ZSzeb001_ZSfox000%283%29)

Jesus_Freak
12-29-2008, 12:14 PM
Totally possible, feasible and likely.

In 2004, the ferry company I worked for repowered all the boats with government grant money for cleaner burning engines. They ended up getting 2 of the 100' boats into the 40 knot range, yet they kept losing blades on the props. It turned out that the cavitation bubbles were eating the nibral at the hubs and causing the blade to break off. They ended up solving the issue by installing a stainless steel cone on the prop shaft about the diameter of the hub to help. It turned out to work, but 4 sets of $25k props were lost in the process. Incredible that a few bubbles can eat through solid metal.

Cool. Just for kicks, was the cone installed upstream or downstream of the prop? Any pictures?

TallRedRider
12-29-2008, 01:22 PM
Cool. Just for kicks, was the cone installed upstream or downstream of the prop? Any pictures?

I would guess since he said the cone was on the prop shaft, it would have to be upstream of the prop.

How do cavitation bubbles form immediately on the prop, when I thought the prop caused the cavitation? Or is the cavitation formed in front of the prop when the blade spins and essentially pulls the water molecules apart in front of the prop?

helton333
12-29-2008, 03:32 PM
last time I fart in the tub!

flipper
12-29-2008, 03:38 PM
last time I fart in the tub!

now that was funny

helton333
12-29-2008, 03:48 PM
That explains why my tubs wear out. Where do you get the metal plates again? Will my anti-slip rubber duckies still stick?

Jesus_Freak
12-30-2008, 12:34 PM
I would guess since he said the cone was on the prop shaft, it would have to be upstream of the prop.

In incompressible flow, pressure waves are elliptically moved in all directions. In other words even a cone installed immediately downstream of the prop can have an effect on the prop. That is why I was asking.

How do cavitation bubbles form immediately on the prop, when I thought the prop caused the cavitation? Or is the cavitation formed in front of the prop when the blade spins and essentially pulls the water molecules apart in front of the prop?

They form near the blade surface due to low static pressure around certain parts of the blade surface. It is more complicated than this, but let's say that a bubble is formed when the local static pressure drops below the vapor pressure of the liquid (at a given temperature). The damage occurs when these bubbles collapse on a given surface.

TallRedRider
05-18-2009, 01:46 PM
I got my plate installed last week. Here are a few pics:

http://i243.photobucket.com/albums/ff206/talltigeguy/X-45%20pics/IMG_7970.jpg

http://i243.photobucket.com/albums/ff206/talltigeguy/X-45%20pics/IMG_7971.jpg

TX.X-30 fan
05-18-2009, 07:49 PM
I have a good size nick back there but assumed it was the log that floated up under at night 2 years ago and logged between the prop and rudder. Made a hell of a noise when i cranked the boat. 175 and the prop is as good as new. :D

Hrkdrivr
05-18-2009, 09:38 PM
Go Red,

Did you do the installation or have the dealer do it?

TallRedRider
05-18-2009, 11:22 PM
The dealer did it, and it was covered under warranty since this was a known MC recall.

Apparently it only applies to 8.1L engines.

Hrkdrivr
05-20-2009, 09:52 PM
I gotta get mine in...

Acesn28
07-12-2011, 05:32 PM
I know I am late to the party, but i just bought a 2005 X Star 8.1L, and it has this problem. I thought I hit something the first day out on it. Does anyone know if Mastercraft is still correcting this problem for the customer? Thanks for any feedback.

TallRedRider
07-13-2011, 12:29 AM
Acesn,

Good use of the search button to find my thread! Hard to know what they will do on a 6 year old boat. But it is essentially a recall item, and the dealer that hasn't done it already is slacking.