cavitation on aluminium props.

BruceK said:
He's taken to stalking. Sending pictures from his boat in the yard of me transiting Beaumarris. Probably has a radar gun!

Anyway, returning to the boat Thursday for 5 more days of fun. I queried the props from the supplier who is querying the manufacturer and Volvo. So far the response seems to be..."they all do that sir"... which suits me fine because if they shred further I have a comeback.
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Hoping for a % on speeding fines!

It was great timing, just sat on the beach with a beer and fish and chips!
 
It's tough to get paint to stick to aluminium at the best of times, props give paint a hard time; don't look for problems where there aren't any. If the aluminium is pitting, then you might have a problem.
 
Bruce, didn't want to ask before as I couldn't really see the problem other than a bit of paint flaking.
From the last posters it seems that this is what is your concern and not something else more esoteric which I completely missed.

If so, care to explain how you apply a/f to your props, whole preparation/painting process please?

I had even worse performance than that on my props after half an hour :rolleyes: only to be given I trick that I've mentioned here before a couple of times:
Talking about velox primer and a/f, bloody expensive stuff (imho)
trick is to get a decent "coarse" finish on the prop surface, then take both 250ml cans to a paintshop that can "press" them in a spray can, get them in (iirc 3 spray cans per material) and spray them on in a haze sort of way, longish distance, where more than 50% of the material is wasted.
4-5 coats of primer in rapid succession (15mins apart under med summer conditions-ok 2h in welsh med I guess :p ) followed by 3-4 coats of a/f in a similar maner.

a/f now is mostly still there after two seasons (due to corona didn't get the boat on the hard last year) and even survived a diver scraping them not too kindly...

V.
 
A_8 said:
Have to say and maybe it's the pic through water but it looks like a not so good paint job and generally uneven prop surface and edges which might make it worse. Also IIRC my experience with different props was very different to yours so maybe there is something else going on.

That said I swapped C4 to J series (VP suggestion did not work great so had to go up one size) but remember some paint coming of quite quickly but then stopped.
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penfold said:
It's tough to get paint to stick to aluminium at the best of times, props give paint a hard time; don't look for problems where there aren't any. If the aluminium is pitting, then you might have a problem.
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vas said:
Bruce, didn't want to ask before as I couldn't really see the problem other than a bit of paint flaking.
From the last posters it seems that this is what is your concern and not something else more esoteric which I completely missed.

If so, care to explain how you apply a/f to your props, whole preparation/painting process please?

I had even worse performance than that on my props after half an hour :rolleyes: only to be given I trick that I've mentioned here before a couple of times:
Talking about velox primer and a/f, bloody expensive stuff (imho)
trick is to get a decent "coarse" finish on the prop surface, then take both 250ml cans to a paintshop that can "press" them in a spray can, get them in (iirc 3 spray cans per material) and spray them on in a haze sort of way, longish distance, where more than 50% of the material is wasted.
4-5 coats of primer in rapid succession (15mins apart under med summer conditions-ok 2h in welsh med I guess :p ) followed by 3-4 coats of a/f in a similar maner.

a/f now is mostly still there after two seasons (due to corona didn't get the boat on the hard last year) and even survived a diver scraping them not too kindly...

V.
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Thanks guys for responding. As you are all pretty much saying the same thing to answer I put on Trilux 33 as smooth as I could with a brush. The leading edges were a bit wonky despite best efforts and no I did not sand. Trilux is an ablating AF and my props never stop spinning in the river to a 3 - 4 knt current so I assumed any imperfections would soon be worn smooth just as on the drives and even quicker.

Volvo has come back saying it looks like galvination ???? Even though it's uniform across every blade, mid chord on both rear props and the supplier says normal wear.

I think LBRodders is closest to the truth in that if I am cruising with the drives in, then the angle of attack on the blade will be increased accordingly and I am driving with about a 4 degree trim in state which of course increases the angle of attack by 4% and that may be enough to cavitate the prop.
I suspect if Old Git sees this he is going to have a field day about leaking hydraulic rams. But no, mine are fine. I just like to sit while cruising in the sports boat not stand and I trim in on legs and planes to get the bow rise down to see clearly in front.
 
BruceK said:
I suspect if Old Git sees this he is going to have a field day about leaking hydraulic rams. But no, mine are fine. I just like to sit while cruising in the sports boat not stand and I trim in on legs and planes to get the bow rise down to see clearly in front.
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maybe fit a hydraulic ram on the helm seat then Bruce :p Tee off the rams so that you know for sure when you're out of fluid:
leg wont move && seat wont move == leak!
 
I’m not sure that right regards trim as the boat moves about the drive in effect.

let’s say at 0 trim the drives a dead level in the water and the bow is 5 degrees up.

you trim to -2 degrees and the bow comes down to 3 degrees but the boat has moved about the drive so the drive/props are still level?

appreciate there will be a point where the lever force can’t overcome the buoyancy of the hull though
 
Mr Googler said:
I’m not sure that right regards trim as the boat moves about the drive in effect.

let’s say at 0 trim the drives a dead level in the water and the bow is 5 degrees up.

you trim to -2 degrees and the bow comes down to 3 degrees but the boat has moved about the drive so the drive/props are still level?

appreciate there will be a point where the lever force can’t overcome the buoyancy of the hull though
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My menatal agligity so eraly in the moaning is not so good until I've had a few jo's. Park that one with me.
 
seastoke said:
Do you fancy tycock
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North West Ventures were at Ty Coch this last weekend and it was empty. No pub, no peeps nothing. As such it's a ways to go for not much to do but if that's the consensus then I may go down there. Let's put a pin in it, you're just as liable to stay in the marina and wash your boat. Ya? Ya!
 
Mr Googler said:
I’m not sure that right regards trim as the boat moves about the drive in effect.

let’s say at 0 trim the drives a dead level in the water and the bow is 5 degrees up.

you trim to -2 degrees and the bow comes down to 3 degrees but the boat has moved about the drive so the drive/props are still level?

appreciate there will be a point where the lever force can’t overcome the buoyancy of the hull though
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By trimming the engines you are making them impart a non forward force on them and that is what gives you the trimming moment on the boat. At the prop that equates to unequal drive on the blade surface. Hence why at large leg trim angles you lose a lot of drive because your props are inefficient.

Always best to use trim tabs to trim the boat, and leg trim to counter that to put them in the most efficient position to drive the boat forward. Its this combo that @BruceK may have the balance just off. As we all know its a fine art of matching best boat running angle with that of the engine, most often not the same. Add into that @BruceK 's perfect seat position and its a conundrum.
 
BruceK said:
North West Ventures were at Ty Coch this last weekend and it was empty. No pub, no peeps nothing. As such it's a ways to go for not much to do but if that's the consensus then I may go down there. Let's put a pin in it, you're just as liable to stay in the marina and wash your boat. Ya? Ya!
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Pub opens today. With that the hoardes will come (y)
 
LBRodders said:
By trimming the engines you are making them impart a non forward force on them and that is what gives you the trimming moment on the boat. At the prop that equates to unequal drive on the blade surface. Hence why at large leg trim angles you lose a lot of drive because your props are inefficient.

Always best to use trim tabs to trim the boat, and leg trim to counter that to put them in the most efficient position to drive the boat forward. Its this combo that @BruceK may have the balance just off. As we all know its a fine art of matching best boat running angle with that of the engine, most often not the same. Add into that @BruceK 's perfect seat position and its a conundrum.
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I use my trim tabs but there comes a point where they act as a brake and the legs need to be trimmed in still.
 
BruceK said:
I use my trim tabs but there comes a point where they act as a brake and the legs need to be trimmed in still.
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Yeah exactly. Its a balance that is difficult to quantify what is doing what. How much load each is taking - its difficult to know!

Where's your booze stashed?! Maybe needs to be more fwd. Let us know exactly where it is and we'll make a judgement :p
 
Ty Coch Friday is a no. Sat and Sun is a possibility and Monday a no.

I'd suggest a Friday departure and anchor at Llandwyn. Sat am departure for Porthdinllaen and stay untill Sunday HW where you want to cross the bar back into the saftey of the Strait. Suggest Monday at Aber. Conversely, leave Porthdinllaen for Cemaes Sunday afternoon.
Personally I think Cemaes would be a best bet for an all weekender. I'll throw that over to you lot
 
BruceK said:
Thanks guys for responding. As you are all pretty much saying the same thing to answer I put on Trilux 33 as smooth as I could with a brush. The leading edges were a bit wonky despite best efforts and no I did not sand. Trilux is an ablating AF and my props never stop spinning in the river to a 3 - 4 knt current so I assumed any imperfections would soon be worn smooth just as on the drives and even quicker.
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Whenever I've had my duo props refurbed the supplier he has told me not to anti foul them because of the cavitation at that point will expose the metal too quickly, just use a suitable ali paint similar to how you receive them from new.
 
Chris_d said:
Whenever I've had my duo props refurbed the supplier he has told me not to anti foul them because of the cavitation at that point will expose the metal too quickly, just use a suitable ali paint similar to how you receive them from new.
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I moor in barnacle city. No AF and the beasties have a field day.
 
BruceK said:
I moor in barnacle city. No AF and the beasties have a field day.
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Fair enough, but if its just the anti foul coming off probably no big deal, I have antifouled them in the past and it always comes off at the root area similar to yours and thats even when only doing 5knts on the river :)
 
BruceK said:
North West Ventures were at Ty Coch this last weekend and it was empty. No pub, no peeps nothing. As such it's a ways to go for not much to do but if that's the consensus then I may go down there. Let's put a pin in it, you're just as liable to stay in the marina and wash your boat. Ya? Ya!
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My engine was over heating the strainer was full of bits of paint really strange .
 
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