55 replies to this topic

[akasideshow]

went sailing today on share kahn in 20+kts and the brand new betts rudder resonated for half of the time
I normally sail on tigger and we haven't had this issue with the new rudder, but this was bad
real bad, were talking as loud as a lawn mower and very persistant

hard to see why, pintles seem tight, just noisy and slowing

anyone else with this issue? or is it just a bad day at the mould?

it wasnt just a small humm that happens ocasionally we're talking about three distinct tones that were increasingly severe
the top one would rattle screws out of a rolex
and IMHO was costing the boat 10- 15% boatspeed at worst ,let alone stopping it from accelerating

[Bob Perry]

Sideshow:
I'd check that rudder for trailing edge treatment first, that's easy, then symetry. That will require templating it. A slight change to the trailing edge could fix it. I have no idea how the trailing edge was designed but I favor a chamferred trailing edge. The three different tones is worrysome. Make sure the traliong edge is a crisp cut. You can't really do that in a mold but you can fair it by hand. Maybe Jim Betts has some ideas.
If it really as violent as you say then symetry could very well be the cause. You neeed to ask Betts for some rudder templates.

[owlslick]

bad / disturbed flow across the rudder

the leading or trailing edge needs adjustment ( shaping )

one the OEM rudders was humming and it was eliminated by sanding ( reshaping slightly with sander ) one of the edges. The price point is relatively high for the aftermarket rudder, I would contact the mfg and ask for guidence. I wouldn't think there is much room for error. Sending it back would be expensive and time consuming to let them do the adjusting, but probably the better option. The rudder mfg is probably not interested in an exchange.

[Clewless]

went sailing today on share kahn in 20+kts and the brand new betts rudder resonated for half of the time
I normally sail on tigger and we haven't had this issue with the new rudder, but this was bad
real bad, were talking as loud as a lawn mower and very persistant

hard to see why, pintles seem tight, just noisy and slowing

anyone else with this issue? or is it just a bad day at the mould?

it wasnt just a small humm that happens ocasionally we're talking about three distinct tones that were increasingly severe
the top one would rattle screws out of a rolex
and IMHO was costing the boat 10- 15% boatspeed at worst ,let alone stopping it from accelerating

Are you sure it was not there with the old OEM rudder? On most boats, the 8 kt humm is from the keel. Humms at 8 / 16 / 24 kts....

Clew

[Mark K]

Actually, the humming is an indication that the foil is quite symmetrical, usual cause being that the flow is exiting the trailing edge to symmetrically, believe it or not.

Take the rudder off and square off the trailing edge with a file (just take off what you need to get 90 degree edges), then put a tiny 45 degree bevel on one side only.

This prevent the oscillations from starting.

[knucklehead]

I templated & faired the rudder of my boat (not an FT10) a few months ago, and repainted it with a twin-pack polyurethane which has a high gloss finish. When I sailed the boat again the rudder was humming at 14-16kts boatspeed. I took the gloss off the paint and the hum was gone. Maybe there really is such a thing as TOO perfect?

[extrad]

I templated & faired the rudder of my boat (not an FT10) a few months ago, and repainted it with a twin-pack polyurethane which has a high gloss finish. When I sailed the boat again the rudder was humming at 14-16kts boatspeed. I took the gloss off the paint and the hum was gone. Maybe there really is such a thing as TOO perfect?

There is such a thing as too perfect.

IIRC and the numbers are rough (pun) for planing dinghies/fast sprotsboats etc. the hull shouldn't be any glossier than approx 600-800 grit wet and dry. Slower lead mines need 400 grit. High speed powerboats need glossier - ie 1200-2000grit.

[Bob Perry]

Mark:
"Too symetrical" that's a new one on me but you sound like you know what your're talking about so I will consider it. I do know that with other ruder and keel vibe problems fairing them to symetry has most often helped the problem. I agree with you trailing edge treatment.

Boy, 65 years old (almost) and still learning.

Bill Garden once told me. "If the rudder flutters check the trailing edge. If it's round square it. If it's square round it."

[Mark K]

Mark:
"Too symetrical" that's a new one on me but you sound like you know what your're talking about so I will consider it. I do know that with other ruder and keel vibe problems fairing them to symetry has most often helped the problem. I agree with you trailing edge treatment.

Boy, 65 years old (almost) and still learning.

Bill Garden once told me. "If the rudder flutters check the trailing edge. If it's round square it. If it's square round it."

"Too symmetrical" is a very inexact term for it. But if the trailing edge is loaded even a bit in one direction it tends not to start oscillating, and it's all very much about the trailing edge on hum.

The science of it is over my head, but here's a paper on vibration problems in hydrofoils by a real Mr. Science. Hydrofoil "singing" is dealt with in chapter 4.

http://docs.hydrofoils.org/hiper.pdf

I learned how to fix it from the early days of thin daggers in cats. Everybody had the problem at one time of another.

[Bob Perry]

Thanks for that Mark.

[Rasputin22]

It is actually Von Karmann doing the singing. Watch this clip and you can see how just knocking off the square edge on one side of the trailing edge will prevent the alternating vortices by upsetting the occillations. I like a bit of foil hum as it serves as an audible knotmeter and helps me optimise boatspeed without taking my eyes off the sails much like an audible variometer in a sailplane. With time you will get the pitch calibrated to the indicated speed from the knotmeter and find the groove, especially when surfing a wave or keeping a multihull in the 'power band' on a reach. If it is too loud though, it must have an adverse effect of speed...

[Rasputin22]

http://www.youtube.c...feature=related

Sorry, forgot the link!

[Rasputin22]

This one is even better, flow starts off laminar but then after a while breaks down into the alternating Von Karmann vortices. CFD will play a huge part in the upcoming wing design for the AC 72's...

http://www.youtube.c...feature=related

Not sure if this would work to dampen the vortices, but might be worth a try. There was a guy in the California surfing scene who came up with the idea of putting flexible chines of a sort on the bottom on his surfboards. His thinking was that in a hard bottom turn, if you could bet the sheet of water flowing diagonally across the bottom of the board, it would reduce wetted surface and reduce drag and add speed. He would mask off a tapered width of 1/2" or so across the board and then apply silicone caulk between the masking tape and then tool the silicone into a V shaped chine for the lack of a better word. Peel the tape and this little flap would offer little resistance to straight line speed as it was mostly parallel to the CL, but when the board was turned it would trip the flow! He would tryit for a day or so and then razor knife off the silicone and try a different configuration. I never got the knack of troweling the sticky crap into anything that could possibly help, but perhaps a nice clean trailing edge V added to the 1/8" flat on a well tuned foil would clean up the flow but due to the resilient nature of the silicone would damp out the vortice formation??? Worth a try?

[Bob Perry]

Rap:
Those are interesting buit is there on showing the flow around a chamferred trailing edge?
Thanks for that link.

[akasideshow]

This one is even better, flow starts off laminar but then after a while breaks down into the alternating Von Karmann vortices. CFD will play a huge part in the upcoming wing design for the AC 72's...

http://www.youtube.c...feature=related

Not sure if this would work to dampen the vortices, but might be worth a try. There was a guy in the California surfing scene who came up with the idea of putting flexible chines of a sort on the bottom on his surfboards. His thinking was that in a hard bottom turn, if you could bet the sheet of water flowing diagonally across the bottom of the board, it would reduce wetted surface and reduce drag and add speed. He would mask off a tapered width of 1/2" or so across the board and then apply silicone caulk between the masking tape and then tool the silicone into a V shaped chine for the lack of a better word. Peel the tape and this little flap would offer little resistance to straight line speed as it was mostly parallel to the CL, but when the board was turned it would trip the flow! He would tryit for a day or so and then razor knife off the silicone and try a different configuration. I never got the knack of troweling the sticky crap into anything that could possibly help, but perhaps a nice clean trailing edge V added to the 1/8" flat on a well tuned foil would clean up the flow but due to the resilient nature of the silicone would damp out the vortice formation??? Worth a try?

awesome links mate thanks heaps
this is how I had pictured it (from people describing it to me)
the answer that so many seem to disagree on though is a symmetrical or asymmetrical solution,
Betts prescribed an asymmetrical trailing edge as a solution, but it irks me somewhat to do anything asymmetrical to the underwater shape of a boat.

Fortunately it isn't the tiger i sail on normally so the PBO will have to make his own mind up on this one.

I'm still curious though if this is the only one of these rudders that has this issue

tiggers rudder has only a slight hum that certainly seems too small an issue for us to worry about, and the other tiger I've been on was much the same

could there be another factor contributing?
for example a loose pintle?
Would that allow the resonance to grow and become more established?

[Christian]

http://www.tboat.com...sport-fast.html

[akasideshow]

thought this one shows quite well the reynolds number relationship to votrex shedding that extrad mentioned above

[extrad]

thought this one shows quite well the reynolds number relationship to votrex shedding that extrad mentioned above

Strange how conversations in the CY on a Sunday afternoon and posts here merge into one.

Good job we weren't discussing Colebrook White backwater step factors - that would surely bring out guns at 12 paces amongst hydrodynamicists

PS I think that the 1st step in resolving Shere Kahns ghetto blaster loud rudder hum issue would be to clean the bottom of the boat. Followed by confirming that it isn't the keel. (AKA put an unsymettrical chamfer on the back edge of the keel.)

[Bulga Naba]

For the record..... equipped with anew Betts rudder and having never had ahum off the keel previously, our rudder hum begins at exactly 6.9 knots downwind and never stops as the speed builds further. Me thinks that Mr. Betts should be responsible for a fix given the cost of the rudder. i surely would not want to being tweaking my trailinig edge without specific instructions from the builder; better that a technician responsible for the result does

[Bob Perry]

Sideshow:
Anything to report on your rudder hum problem yet?

[Christian]

While my boat is not a FT but to some degree similar in setup (transom hung rudder) and high aspect foils i can tell you that I do have a very little amount of humm - it starts at about 19 knots and stops at about 19.5 knots and doesn't re-appear (at least not under 26 knots). The humm used to be a little worse but got better after we rafaired both the hull and foils a couple of years ago - I did use the recommendations from Steve thompson I posted above regarding trailing edge treatment.

[Bob Perry]

That's just wonderful Christian. But this is the FD thread and my question was addresed to Matt with an FD 10m.

[port tack]

While my boat is not a FT but to some degree similar in setup (transom hung rudder) and high aspect foils i can tell you that I do have a very little amount of humm - it starts at about 19 knots and stops at about 19.5 knots and doesn't re-appear (at least not under 26 knots). The humm used to be a little worse but got better after we rafaired both the hull and foils a couple of years ago - I did use the recommendations from Steve thompson I posted above regarding trailing edge treatment.

Christian takie your Viper 870 and your 19.5 knots to a thread that gives a fuck! you fucktard want a be FT10 owner and don't even go into how you didn't follow threw with your order cause ??????? what ever the fuckin reason you come up with cause your boat is more of an orphan than a Tiger will ever be. Lots of luv to Perry, Scoot, and Hip for a really good boat.

While my boat is not a FT but to some degree similar in setup (transom hung rudder) and high aspect foils i can tell you that I do have a very little amount of humm - it starts at about 19 knots and stops at about 19.5 knots and doesn't re-appear (at least not under 26 knots). The humm used to be a little worse but got better after we rafaired both the hull and foils a couple of years ago - I did use the recommendations from Steve thompson I posted above regarding trailing edge treatment.

Christian takie your Viper 870 and your 19.5 knots to a thread that gives a fuck! you fucktard want a be FT10 owner and don't even go into how you didn't follow threw with your order cause ??????? what ever the fuckin reason you come up with cause your boat is more of an orphan than a Tiger will ever be. Lots of luv to Perry, Scoot, and Hip for a really good boat.

[akasideshow]

Sideshow:
Anything to report on your rudder hum problem yet?

this is a rudder on a tiger that I don't normally sail on,
so I'm not sure
but I'll find out from it's owner on sunday, unless he wants to chime i here and give us an update

[River Sailor]

#58 had hum on the OEM rudder, it started around 7 knts, it got very annoying and felt slow. I faired the trailing edge and added less than 1/4" of epoxy to the edge and ended with a blunt edge of about 1/16" in width. Recoated the rudder with interlux two part epoxy, wet sanded w/ 500 grit. Humm is gone, and feels like a hot knife through butter. It may not be any faster but it is definitely less distracting.

[Bob Perry]

Sideshow:
Thanks. I'd like to know how he has dealt with it.

Can you Fed Ex me some fish and chips?
I prefer the ones from the fish shop across the street from the Ashfield train station.
It's probably a Boutique now.

[Christian]

That's just wonderful Christian. But this is the FD thread and my question was addresed to Matt with an FD 10m.

Bob, I understand - my point was that foil humm is not unique to FT's and is something that happens on a lot of boats with high aspect foils and I posted some recommendations how to help minimize/eliminate the problem.

[TigerinCT]

That's just wonderful Christian. But this is the FD thread and my question was addresed to Matt with an FD 10m.

Bob, I understand - my point was that foil humm is not unique to FT's and is something that happens on a lot of boats with high aspect foils and I posted some recommendations how to help minimize/eliminate the problem.

Christian - thanks for the contributions even if slightly off topic. I think a lot of people get a bit protective or defensive given the mud that has been thrown at the FT10 over the past few years. Thanks for trying to stay above it.

[Christian]

Christian takie your Viper 870 and your 19.5 knots to a thread that gives a fuck! you fucktard want a be FT10 owner and don't even go into how you didn't follow threw with your order cause ??????? what ever the fuckin reason you come up with cause your boat is more of an orphan than a Tiger will ever be. Lots of luv to Perry, Scoot, and Hip for a really good boat.

EMF!

[Bob Perry]

Christian: please translate "EMF". I'm sure it's another one of your positive contributions to this forum. Care to enlighten us? Or at least me?

[Rasputin22]

Empathetic Mother F***ers???

[Christian]

Christian: please translate "EMF". I'm sure it's another one of your positive contributions to this forum. Care to enlighten us? Or at least me?

Coined by the Editor - Eat My Fuck



Only used when people call me fucktard or some other pretty lame namecalling

[Bob Perry]

Well just as I figured unfortunately. And your intellectual response to "lame name calling" is "EMF"? I'm out of my league.

I was more hoping for:
Everglades Marine Foundation
or
Egyptian Mummified Frogs

[Bob Perry]

So that's it?
When someone's intellectual retort is "EMF" it kinds of brings an end to any adult discussion.

I really don't carte if Scot said it first.
As my Dad would have said, "If Scot jumped of a bridge so you have to do it?"

[Shaggy]

I like the frog thing....

[eerie sailor]

I always thought EMF stood for "Excellant My Friend" . I guess you can learn something new on this internet thing daily.

[eerie sailor]

I always thought EMF stood for "Excellant My Friend" . I guess you can learn something new on this internet thing daily.

[Bob Perry]

I was thinking along the lines of:
"Elect More Frontiersmen"

Or from a Native American perspective:
"Eviscerate More Frontiersmen"

At least something that made grammatical sense. Christian is speaking ESL.

"Well Scot said it."

As all of our Dads used to say, "If Scot told you to jump off a bridge would you do it?"
Jeesus, if I had a dime for everytime I heard that.

[Mark K]

I was under the impression it meant "Exactly, My Friend".

[austin1972]

Huh!
I thought it stood for German Shorthaired Pointer.

[Bob Perry]

Austin:
that was very funny and I could use some funny today.
How is my calf doing? Are you putting a blanket over it at night? Are you taking it for walks?
Can I have a new pic?
Was it scared on the 4th of July?
I hope you brought it into the house for that night.

I'm thinking that we skip the cutting off the balls thing and let it grow into a huge Bull.
I'd like that.
By then it would be house broken and think of the surprise on your friend's face when they see a 3,257 lb. bull sitting watching TV in your living room.
Bulls like to watch golf.

[GybeSet®]

Sideshow:
Thanks. I'd like to know how he has dealt with it.

Can you Fed Ex me some fish and chips?
I prefer the ones from the fish shop across the street from the Ashfield train station.
It's probably a Boutique now.

chish&fips Ashfield link

good news it's stil there , if anything all vacancies there become chinese takeaways, asian groceries or yum-cha joints ! it's full on one of sydneys 2nd tier chinatowns

ur making me hungry

[austin1972]

I just saw your calf today but no pics. They've been on the DL until today. I'll get a pic.
The only reason bulls like golf is it's grass pasture porn. Can you imagine a swimming pool of scotch?

Watch Temple Grandin. Good flick.

My neighbor's mom from the conservative rural south calls tattoos 'skin illustrations'. As in, "Why on Gawd's great earth would you wanna be gettin' yerself painted with no skin illustration?"

[akasideshow]

I just saw your calf today but no pics. They've been on the DL until today. I'll get a pic.
The only reason bulls like golf is it's grass pasture porn. Can you imagine a swimming pool of scotch?

Watch Temple Grandin. Good flick.

My neighbor's mom from the conservative rural south calls tattoos 'skin illustrations'. As in, "Why on Gawd's great earth would you wanna be gettin' yerself painted with no skin illustration?"

just to bring it back slightly on topic, I talked to the owner on sunday and he was waiting to finish the series, (last sunday), before taking it to a man called Bruce (who most sydney types will know) to get his midas fingers involved.
It may seem like overkill to some getting a boatbuilder involved, but i think its a good call.
this way it will be put right, not made worse, no problems created, no butchering. Or at least if there is, it will be made right again by someone who knows how.
Will let you know of the "fix" and its effectiveness in due course

[RobG]

That's just wonderful Christian. But this is the FD thread and my question was addresed to Matt with an FD 10m.

Bob, I understand - my point was that foil humm is not unique to FT's and is something that happens on a lot of boats with high aspect foils and I posted some recommendations how to help minimize/eliminate the problem.

Lucky you weren't as off-topic as the dude who posted a link to docs about hydrofoiling Russian ferries.

And here was me stumbling across this thread when searching for posts about singing rudders. I fixed it by sanding the trailing edges finer, but since I don't have an FT10 that information will be useless to anyone here.

[Christian]

That's just wonderful Christian. But this is the FD thread and my question was addresed to Matt with an FD 10m.

Bob, I understand - my point was that foil humm is not unique to FT's and is something that happens on a lot of boats with high aspect foils and I posted some recommendations how to help minimize/eliminate the problem.

Lucky you weren't as off-topic as the dude who posted a link to docs about hydrofoiling Russian ferries.

And here was me stumbling across this thread when searching for posts about singing rudders. I fixed it by sanding the trailing edges finer, but since I don't have an FT10 that information will be useless to anyone here.

Yeah those FT-s are soooooo special that the tricks that fix problems on other boats simply are not good enough for the FT folks since they are very special too

[GRUMPY]

I thought (hoped) this board might have taken a more friendly route...

[Snapper]

Chamfer the trailing edge if it's humming. Fixed.

[Mark K]

That's just wonderful Christian. But this is the FD thread and my question was addresed to Matt with an FD 10m.

Bob, I understand - my point was that foil humm is not unique to FT's and is something that happens on a lot of boats with high aspect foils and I posted some recommendations how to help minimize/eliminate the problem.

Lucky you weren't as off-topic as the dude who posted a link to docs about hydrofoiling Russian ferries.

And here was me stumbling across this thread when searching for posts about singing rudders. I fixed it by sanding the trailing edges finer, but since I don't have an FT10 that information will be useless to anyone here.

Yeah those FT-s are soooooo special that the tricks that fix problems on other boats simply are not good enough for the FT folks since they are very special too

I don't own an FT10.

[gmacon]

I know this is an old topic, but I too have a hum, a violent floor shaking hum that you swear will shake every screw on the boat loose! The boat is a perfectly smooth Star that I re-faired the keel on over the winter. I thought it to be the rudder until reading this forum. During a particularly violent hummer of a sail in moderate breeze, the "humm" mysteriously and suddenly abated to a quite flutter. Upon haul-out, the trailing edge of my razor sharp bulb, solid glass by the way, was shredded to bits. Maybe there is something to too symmetrical, to sharp on some boats!

[Kmag]

While my boat is not a FT but to some degree similar in setup (transom hung rudder) and high aspect foils i can tell you that I do have a very little amount of humm - it starts at about 19 knots and stops at about 19.5 knots and doesn't re-appear (at least not under 26 knots). The humm used to be a little worse but got better after we rafaired both the hull and foils a couple of years ago - I did use the recommendations from Steve thompson I posted above regarding trailing edge treatment.

Christian takie your Viper 870 and your 19.5 knots to a thread that gives a fuck! you fucktard want a be FT10 owner and don't even go into how you didn't follow threw with your order cause ??????? what ever the fuckin reason you come up with cause your boat is more of an orphan than a Tiger will ever be. Lots of luv to Perry, Scoot, and Hip for a really good boat.

While my boat is not a FT but to some degree similar in setup (transom hung rudder) and high aspect foils i can tell you that I do have a very little amount of humm - it starts at about 19 knots and stops at about 19.5 knots and doesn't re-appear (at least not under 26 knots). The humm used to be a little worse but got better after we rafaired both the hull and foils a couple of years ago - I did use the recommendations from Steve thompson I posted above regarding trailing edge treatment.

Christian takie your Viper 870 and your 19.5 knots to a thread that gives a fuck! you fucktard want a be FT10 owner and don't even go into how you didn't follow threw with your order cause ??????? what ever the fuckin reason you come up with cause your boat is more of an orphan than a Tiger will ever be. Lots of luv to Perry, Scoot, and Hip for a really good boat.

So what in the f is a Viper 870? Raced a bunch on the 830 and the 640 but would love to see a 870

[Bob Perry]

Con:
I don't think you want a razor sharp trailing edge on any appendage. Snaps is right, chamfer it. But it appears it has self chamfered.

[Ship o' Fools]

I know this is an old topic, but I too have a hum, a violent floor shaking hum that you swear will shake every screw on the boat loose! The boat is a perfectly smooth Star that I re-faired the keel on over the winter. I thought it to be the rudder until reading this forum. During a particularly violent hummer of a sail in moderate breeze, the "humm" mysteriously and suddenly abated to a quite flutter. Upon haul-out, the trailing edge of my razor sharp bulb, solid glass by the way, was shredded to bits. Maybe there is something to too symmetrical, to sharp on some boats!

Class rules prohibit fairing so the correct terminology is that you fixed defects.

[Christian]

While my boat is not a FT but to some degree similar in setup (transom hung rudder) and high aspect foils i can tell you that I do have a very little amount of humm - it starts at about 19 knots and stops at about 19.5 knots and doesn't re-appear (at least not under 26 knots). The humm used to be a little worse but got better after we rafaired both the hull and foils a couple of years ago - I did use the recommendations from Steve thompson I posted above regarding trailing edge treatment.

Christian takie your Viper 870 and your 19.5 knots to a thread that gives a fuck! you fucktard want a be FT10 owner and don't even go into how you didn't follow threw with your order cause ??????? what ever the fuckin reason you come up with cause your boat is more of an orphan than a Tiger will ever be. Lots of luv to Perry, Scoot, and Hip for a really good boat.

While my boat is not a FT but to some degree similar in setup (transom hung rudder) and high aspect foils i can tell you that I do have a very little amount of humm - it starts at about 19 knots and stops at about 19.5 knots and doesn't re-appear (at least not under 26 knots). The humm used to be a little worse but got better after we rafaired both the hull and foils a couple of years ago - I did use the recommendations from Steve thompson I posted above regarding trailing edge treatment.

Christian takie your Viper 870 and your 19.5 knots to a thread that gives a fuck! you fucktard want a be FT10 owner and don't even go into how you didn't follow threw with your order cause ??????? what ever the fuckin reason you come up with cause your boat is more of an orphan than a Tiger will ever be. Lots of luv to Perry, Scoot, and Hip for a really good boat.

So what in the f is a Viper 870? Raced a bunch on the 830 and the 640 but would love to see a 870

Donno what a Viper 870 is. I have an 830. There is a T870 (same designer) but is is a slightly more crusier design. Obviously the poster (before you ) is a little off................................and an idiot too.

[Polaris]

Having the squared off back edge (3mm) on keel, bulb, and rudder help prevent the laminar flow from each side of the foil from meeting each other at the aft end causing a vortex. "Class rules prohibit fairing", I would think that class rules prohibit changing from the original foil design. If your keel or rudder foil was done improperly leaving you with a crap foil, you should be able to repair it to class specs and have it inspected with templates by the class measurer, or you are left at a disadvantage. Taking waves out of your hull, refairing, isn't considered alteration.

When I received our boat, not an FT10 (but alot like it), our keel had no foil at all, professionally faired from the factory my ass. We still get a little buzz at 9.5 knots, but nothing else.

[doooouglus]

I know this is an old topic, but I too have a hum, a violent floor shaking hum that you swear will shake every screw on the boat loose! The boat is a perfectly smooth Star that I re-faired the keel on over the winter. I thought it to be the rudder until reading this forum. During a particularly violent hummer of a sail in moderate breeze, the "humm" mysteriously and suddenly abated to a quite flutter. Upon haul-out, the trailing edge of my razor sharp bulb, solid glass by the way, was shredded to bits. Maybe there is something to too symmetrical, to sharp on some boats!

Check that the engine box door is flush with the hull... we had a similar prob and this was the fix.

Doug