Propellor interference noise

[GILow]

Originally Posted by Compass790

Maaate I think his prop blades are composite, hence the black colour but I can see your other points.
Sometimes ya just need to have a bitch about it.

No, I don’t have to have a bitch about anything.

Read the question I asked. Look hard at what I actually posted not what someone with comprehension issues thinks I wrote.

[GILow]

Originally Posted by MicHughV

I did remember once seeing a guy building up a " fairing" in front of his prop behind the keel...it's something that has to be "shaped"...I seem to recall closed cell foam was used and it was shaped with a rasp...prior to the foam, some small holes were drilled into that flat surface behind the keel and some screws or bolts were epoxied into the holes...this gave the foam some " grip" to the back of the keel, the foam was also glued here....WEST maybe, I don't recall.....after shaping it was glassed....but I think a coat of WEST epoxy would likely also work.
My recollection is that it made a world of difference in performance and noise.

Yes, building things up was one of the options I was considering.

If there was a significant risk of damage to the prop or drivetrain I would go that way.

Nobody is suggesting I need to worry so I will just put up with the noise since, as I mentioned, I motor very rarely anyway.

[GILow]

Originally Posted by MicHughV

my english is terrible....sorry.....was trying to describe the turbulent water seen behind a a plank moved thru' the water..the prop has to grab ahold of this " turbulent" water to move forward, not good.....clean water flow is the happy medium.

Your English is fine, and your reading skills are way better than some members of this forum.

[GILow]

Originally Posted by FPNC

What is the diameter of the propeller and what is the gear reduction ratio?

About 19” with a two to one gearbox.

I did discuss the option of a smaller prop and a lower reduction ratio with the prop vendor but we couldn’t come up with an option that would not have lead to very poor performance. Given the weight and windage of the boat we felt the loss of power would become a safety issue. As it is, I’ve put in the smallest engine I dared.

The thing is, the Kiwiprop is perfect for my needs. The feathering aspect really helps in light winds, but the reverse is fantastic and has made manoeuvring the boat much, much less stressful.

In the face of this, the slight noise is a minor concern. Particularly if no damage is likely to result.

[GILow]

Originally Posted by Wotname

However surely that section of the hull would be solid glass, no?

:

Oddly enough, given how the boat was constructed, no it isn’t. It’s actually very cleanly moulded there. Still thick as a brick sh-t house (like some posters really) but not thick enough to grind back in any significant manner.

[Compass790]

Originally Posted by GILow

No, I don’t have to have a bitch about anything.

Read the question I asked. Look hard at what I actually posted not what someone with comprehension issues thinks I wrote.

OOOHH quite the sensitive one.
Ok I apologise for the bitch bit.
As for the rest I do think I understand what more space means but yet you go on to say "Yes, building things up was one of the options I was considering" Which is it then? That does not require an answer.



However I will not post any more as I've upset you. Good luck with sorting it

[Wotname]

Originally Posted by GILow

Oddly enough, given how the boat was constructed, no it isn’t. It’s actually very cleanly moulded there. Still thick as a brick sh-t house (like some posters really) but not thick enough to grind back in any significant manner.

Interesting.....

Now I don't know if you are hurting anything but I do have opinions on how to change stuff - I luv changing stuff .

If I was altering the 'square' aft section of the hull, I would glue on a block of wood, grind / sand to desired shape and glass over (with epoxy) assuming there is room to do so. If not enough space, then consider filling the void in the interior section of the hull before shaping. But I dunno how Swannie built the boat, how the cutless bearing is supported, how the stern tube is arranged (if any) and so on.

I'm sure you know these things or can suss them out so I have nothing meaningful to add ATM.

We know the existing tip clearance is well before the benchmark minimum and maybe would be very difficult to change so I would look at making everything else as close to ideal as possible. Is the 'chittering' noise detrimental - again I dunno but I personally would find it very annoying and a distraction; both in a calm or a gale - times when the engine might be running.

[GILow]

Originally Posted by Wotname

Interesting.....

Now I don't know if you are hurting anything but I do have opinions on how to change stuff - I luv changing stuff .

If I was altering the 'square' aft section of the hull, I would glue on a block of wood, grind / sand to desired shape and glass over (with epoxy) assuming there is room to do so. If not enough space, then consider filling the void in the interior section of the hull before shaping. But I dunno how Swannie built the boat, how the cutless bearing is supported, how the stern tube is arranged (if any) and so on.

I'm sure you know these things or can suss them out so I have nothing meaningful to add ATM.

We know the existing tip clearance is well before the benchmark minimum and maybe would be very difficult to change so I would look at making everything else as close to ideal as possible. Is the 'chittering' noise detrimental - again I dunno but I personally would find it very annoying and a distraction; both in a calm or a gale - times when the engine might be running.

It really is a juggling act.

If I build up the trailing edge then it will end up closer to the prop, possibly exacerbating the noise issue.

I am very reluctant, verging on refusing to consider removing any bit of the hull. The greatest asset this boat has is the bullet proof build that the Swansons were famous for. The construction around that bit of the boat seems pretty critical too.

No, it seems unlikely that I am doing damage. I will keep an eye on the propeller tips as per boatpoker's caution. There is no evidence of trouble so far and there's about 100 hours on the propeller now.

As for the noise itself... Not too bad... if I am not worried about it causing damage then I don't think it will worry me all that much.

[malbert73]

I had same issue on my old Luders 33 with 4 blade variprop. I did grind away the aperture ahead of prop to taper it and fair it and it made a difference. You can maybe grind away the square edges and then add laminate for strength. I also was able to enlarge aperture at top and bottom in same way. It all made a significant difference

[MicHughV]

I can offer this.....some years ago I got interested in propellors and performance,etc...

The propellor handbook by Dave Gerr....its has a ton of information in there....everything you would possibly want to know about props, apertures,etc..

PDF Download Propeller Handbook, Second Edition: The ...mellieoglesbygunn.files.wordpress.com › 2017/05

[MicHughV]

I didn't attach the link right, but you can google "The propellor Handbook" by Dave Gerr and it will take you to a free download...

It is substantive and parts take reading several times to fully comprehend, but will certainly guide any decision you might want to make.

[GILow]

Originally Posted by MicHughV

I didn't attach the link right, but you can google "The propellor Handbook" by Dave Gerr and it will take you to a free download...

It is substantive and parts take reading several times to fully comprehend, but will certainly guide any decision you might want to make.

Good book, but sadly lacking clear guidance on how to modify a Swanson 42.

Maybe the later edition has that chapter.

[Jim Cate]

Originally Posted by GILow

Good book, but sadly lacking clear guidance on how to modify a Swanson 42.

Maybe the later edition has that chapter.

Matt, I think that is covered in the Husqvarna chain saw instruction manual...


Hope it is goin' well, mate!

Jim

[GILow]

Originally Posted by Jim Cate

Matt, I think that is covered in the Husqvarna chain saw instruction manual...





Hope it is goin' well, mate!



Jim

More than likely you are correct, it seems an appropriate tool for the job.

Splashing tomorrow morning with the tide, all will be revealed to me soon.

[topmast]

Can you eliminate other possible causes? Things like engine alignment, a whumpy shaft ,or bent at the cutlass, cutlass failing ,misaligned from birth, or lacking cooling flow due to hidden growth, damaged blade pitch.thust bearing in tranny not happy.?