Prop adjustment

[BruceinSanity]

We recently swapped the prop on Sanity Again, as the old one had had its shape significantly modified by various items in bridge holes and the like. We kept the same size (18 x 12), but got a Crowther rather than the original flimsy Aquafax job.

 

The guys who did it for us at Aqua in Mercia pointed out that the original was a long way back from the stern post (about 4") and moved the new one forward to the recommended 1.5". We now have a lot less noise vibration, as you'd expect, but the boat moves a bit slower on tickover than it did and the engine runs a tad hotter.

 

Is it possible that the prop is now too close to the stern post? Is it worth me trying moving it aft an inch to see if it makes a difference?

 

Sanity Again is a 70' Tim Tyler shell driven by a bog standard Beta 43/PRM 150 through a Centaflex coupling. Visual/manual checking of both prop and coupling shows that all is firmly fixed, nothing working loose.

 

If I do move the prop by releasing the shaft from the Centaflex, are there any wrinkles I should be aware of?

 

Thanks in advance for any advice…

 

[Timleech]

We recently swapped the prop on Sanity Again, as the old one had had its shape significantly modified by various items in bridge holes and the like. We kept the same size (18 x 12), but got a Crowther rather than the original flimsy Aquafax job.

 

The guys who did it for us at Aqua in Mercia pointed out that the original was a long way back from the stern post (about 4") and moved the new one forward to the recommended 1.5". We now have a lot less noise vibration, as you'd expect, but the boat moves a bit slower on tickover than it did and the engine runs a tad hotter.

 

Is it possible that the prop is now too close to the stern post? Is it worth me trying moving it aft an inch to see if it makes a difference?

 

Sanity Again is a 70' Tim Tyler shell driven by a bog standard Beta 43/PRM 150 through a Centaflex coupling. Visual/manual checking of both prop and coupling shows that all is firmly fixed, nothing working loose.

 

If I do move the prop by releasing the shaft from the Centaflex, are there any wrinkles I should be aware of?

 

Thanks in advance for any advice…

 

 

The usual recommended maximum is 1.5 times shaft diameter, so if you have a 1.5" shaft that would be 2.25" exposed shaft.

 

Tim

[churchward]

We recently swapped the prop on Sanity Again, as the old one had had its shape significantly modified by various items in bridge holes and the like. We kept the same size (18 x 12), but got a Crowther rather than the original flimsy Aquafax job.

 

The guys who did it for us at Aqua in Mercia pointed out that the original was a long way back from the stern post (about 4") and moved the new one forward to the recommended 1.5". We now have a lot less noise vibration, as you'd expect, but the boat moves a bit slower on tickover than it did and the engine runs a tad hotter.

 

Is it possible that the prop is now too close to the stern post? Is it worth me trying moving it aft an inch to see if it makes a difference?

 

Sanity Again is a 70' Tim Tyler shell driven by a bog standard Beta 43/PRM 150 through a Centaflex coupling. Visual/manual checking of both prop and coupling shows that all is firmly fixed, nothing working loose.

 

If I do move the prop by releasing the shaft from the Centaflex, are there any wrinkles I should be aware of?

 

Thanks in advance for any advice…

 

On the whole to minimise unsupported weight there should be as little as possible of expose shaft between the prop and the bearing. This will stop the bearing wearing faster than it should.

 

I can't see that the distance would have any effect on the engne temp. I would have thought that is an indication that the prop is making it work harder.

[Neil TNC]

We recently swapped the prop on Sanity Again, as the old one had had its shape significantly modified by various items in bridge holes and the like. We kept the same size (18 x 12), but got a Crowther rather than the original flimsy Aquafax job.

 

The guys who did it for us at Aqua in Mercia pointed out that the original was a long way back from the stern post (about 4") and moved the new one forward to the recommended 1.5". We now have a lot less noise vibration, as you'd expect, but the boat moves a bit slower on tickover than it did and the engine runs a tad hotter.

 

Is it possible that the prop is now too close to the stern post? Is it worth me trying moving it aft an inch to see if it makes a difference?

 

Sanity Again is a 70' Tim Tyler shell driven by a bog standard Beta 43/PRM 150 through a Centaflex coupling. Visual/manual checking of both prop and coupling shows that all is firmly fixed, nothing working loose.

 

If I do move the prop by releasing the shaft from the Centaflex, are there any wrinkles I should be aware of?

 

Thanks in advance for any advice…

 

 

ISTR that with the Centralex you remove the cone bolts, them screw 4 back into the unused holes, that helps split the cone.

With Earnest (58ft 6ins Beta 1903 (43) PRM 150 1.96 : 1 "Slipper stern"), Crowthers recommended either an 18 x 12 or 18 x 13, we went for the 18 x 13...and there it has stayed for 12 years....with my fettling over the years it is probably nearer a 17.5 x 13.

[bizzard]

Its possible that if the old prop struck hard and solid things whilst having 4 odd inches of shaft exposed, that the shaft may have a slight set in it ''bent'' and this set is now binding in the tube bearing. The shaft should turn easily by hand when g/box is in neutral, or disconnected from gearbox. Also make sure the gland-packing adjuster is not too tight.

Any of this could cause the engine to labour when idling in gear, and engine temperature to rise a little higher.

Edited July 30, 2012 by bizzard

[Albion]

We recently swapped the prop on Sanity Again, as the old one had had its shape significantly modified by various items in bridge holes and the like. We kept the same size (18 x 12), but got a Crowther rather than the original flimsy Aquafax job.

 

The guys who did it for us at Aqua in Mercia pointed out that the original was a long way back from the stern post (about 4") and moved the new one forward to the recommended 1.5". We now have a lot less noise vibration, as you'd expect, but the boat moves a bit slower on tickover than it did and the engine runs a tad hotter.

 

Is it possible that the prop is now too close to the stern post? Is it worth me trying moving it aft an inch to see if it makes a difference?

 

Sanity Again is a 70' Tim Tyler shell driven by a bog standard Beta 43/PRM 150 through a Centaflex coupling. Visual/manual checking of both prop and coupling shows that all is firmly fixed, nothing working loose.

 

If I do move the prop by releasing the shaft from the Centaflex, are there any wrinkles I should be aware of?

 

Thanks in advance for any advice…

 

 

The noise/vibration reduction is clearly the decently shaped prop. Depending on the 'fineness' of the end of the swim, by moving the prop forward it will have masked the water flow to the prop slightly compared to the old prop, exposed as it was, 4 ins back. This could explain the slight reduction in speed at tickover. It isn't a truly fair comparison though as you are talking two different prop manufacturers with shape and blade differences that must occur. Can you remember what the end of the swim looked like? I doubt Tylers would have just put a chunk of RSJ on the end like some builders do but it may not be particularly fine. It's OK, I've just remembered the photos on your blog and the end of the swim is very good, really pointed. So really you are left with the slight masking by the prop going forward and the differences between the props. Might be worth moving it back to the max overhang recommended.

There shouldn't be any significant difference in engine temp IMO.

Roger

[BruceinSanity]

Its possible that if the old prop struck hard and solid things whilst having 4 odd inches of shaft exposed, that the shaft may have a slight set in it ''bent'' and this set is now binding in the tube bearing. The shaft should turn easily by hand when g/box is in neutral, or disconnected from gearbox. Also make sure the gland-packing adjuster is not too tight.

Any of this could cause the engine to labour when idling in gear, and engine temperature to rise a little higher.

 

The shaft is turning freely and the gland is OK, Thanks. thinking about it, the engine is now swinging rather more weight, which might account for the odd degree warmer, I guess.

[bizzard]

The shaft is turning freely and the gland is OK, Thanks. thinking about it, the engine is now swinging rather more weight, which might account for the odd degree warmer, I guess.

That's good and a relief for you.

[BruceinSanity]

The noise/vibration reduction is clearly the decently shaped prop. Depending on the 'fineness' of the end of the swim, by moving the prop forward it will have masked the water flow to the prop slightly compared to the old prop, exposed as it was, 4 ins back. This could explain the slight reduction in speed at tickover. It isn't a truly fair comparison though as you are talking two different prop manufacturers with shape and blade differences that must occur. Can you remember what the end of the swim looked like? I doubt Tylers would have just put a chunk of RSJ on the end like some builders do but it may not be particularly fine. It's OK, I've just remembered the photos on your blog and the end of the swim is very good, really pointed. So really you are left with the slight masking by the prop going forward and the differences between the props. Might be worth moving it back to the max overhang recommended.

There shouldn't be any significant difference in engine temp IMO.

Roger

 

Yes, I might try just even half an inch further back. It's not a big deal, we're not talking massive overheats or anything, I just wondered if it was possible that it was now too far forward.

 

As far as engine temp is concerned, see my answer to Bizzard, and indeed the fact that the water the boat is floating in is actually decently warm now might make a difference. It was running at 76ºC and is now more like 78º.

 

Thanks for all the advice, everyone, helpful as ever.

 

[NB Lola]

This may sound trite, not intended.

 

As Aqua fitted your new prop set up, let them know about your experience, if you are still near enough. Am sure they will reflect and advise of/make any necessary changes

[Roger Crown]

 

It was running at 76ºC and is now more like 78º.

 

Hi Bruce

 

You have me intrigued on this one, you have a Beta 43 with I guess the deluxe panel which has a very basic temp gauge.

How are you determining temp rise within a couple of degrees?

 

All the best

 

Roger

[BruceinSanity]

 

You have me intrigued on this one, you have a Beta 43 with I guess the deluxe panel which has a very basic temp gauge.

How are you determining temp rise within a couple of degrees?

 

 

Hi

 

It's Braidbar's own panel, but I guess not that different from the Beta. The gauge reads from 40 - 120 with 80 at the centre, and up til now it's been running with the pointer about one width below the 80 mark, whereas now it runs with it just touching 80. Hence my guess that we've gone from maybe 75 - 78 to 78- 80.

 

So not the sort of thin g to worry about, but clearly a bit warmer than before. If anything, I'm happier to have the engine that bit hotter in normal running.

 

take care

 

Bruce

 

This may sound trite, not intended.

 

As Aqua fitted your new prop set up, let them know about your experience, if you are still near enough. Am sure they will reflect and advise of/make any necessary changes

 

Yeah, I'm sure they would, but we're at Penkridge now.

 

As I say, I'm not lying awake nights worrying about this, and I want to see how things go on a variety of waters. We're at Braidbar in Poynton in September, and I may wait until we get there to start fiddling with it, or I may have a go at it earlier.

[steelaway]

Hi

 

It's Braidbar's own panel, but I guess not that different from the Beta. The gauge reads from 40 - 120 with 80 at the centre, and up til now it's been running with the pointer about one width below the 80 mark, whereas now it runs with it just touching 80. Hence my guess that we've gone from maybe 75 - 78 to 78- 80.

 

So not the sort of thin g to worry about, but clearly a bit warmer than before. If anything, I'm happier to have the engine that bit hotter in normal running.

 

take care

 

Bruce

 

 

 

Yeah, I'm sure they would, but we're at Penkridge now.

 

As I say, I'm not lying awake nights worrying about this, and I want to see how things go on a variety of waters. We're at Braidbar in Poynton in September, and I may wait until we get there to start fiddling with it, or I may have a go at it earlier.

 

 

 

I would have thought that the thermostat would still be controlling the engine temperature?

How do you find the new prop is it significantly better?

 

Alex

[BruceinSanity]

I would have thought that the thermostat would still be controlling the engine temperature?

How do you find the new prop is it significantly better?

 

Alex

 

Good point, but certainly getting just a slightly higher reading now, especially when running the washing machine this morning, so a bit of extra load on the alternator (NOT for water heating, please note!)

[BruceinSanity]

Just to put a cap on this topic: I've moved the prop back just ½" and it's made all the difference. Steering feels much less strained especially with some revs on, and the boat is back to doing her usual speed at tickover.

 

 

 

Isn't it amazing what ½" can do?

 

 

Many thanks to everyone for the helpful advice.

[blackrose]

Just to put a cap on this topic: I've moved the prop back just ½" and it's made all the difference. Steering feels much less strained especially with some revs on, and the boat is back to doing her usual speed at tickover.

 

 

 

Isn't it amazing what ½" can do?

 

 

Many thanks to everyone for the helpful advice.

 

Could be that moving the prop back is allowing more water onto it. The prop is always in the lee of the swim (unless you're in reverse), and perhaps on some setups a prop that's too close the the stern post can't get enough water?

[slammer]

Just to put a cap on this topic: I've moved the prop back just ½" and it's made all the difference. Steering feels much less strained especially with some revs on, and the boat is back to doing her usual speed at tickover.

 

 

 

Isn't it amazing what ½" can do?

 

 

Many thanks to everyone for the helpful advice.

 

 

Hi Bruce

Just a quick query , did you just unbolt the centraflex and slide the shaft aft half inch and then re tighten the coupling ? Would like to do the same on my set up .

[BruceinSanity]

Could be that moving the prop back is allowing more water onto it. The prop is always in the lee of the swim (unless you're in reverse), and perhaps on some setups a prop that's too close the the stern post can't get enough water?

 

I'm sure that's it. If the prop is too near the sternpost, water can't reach the centre of it properly. That's why it feels the same as when you've got a bit of stuff wrapped round the shaft.

[BruceinSanity]

Hi Bruce

Just a quick query , did you just unbolt the centraflex and slide the shaft aft half inch and then re tighten the coupling ? Would like to do the same on my set up .

 

Yes. Undo the eight bolts that hold that aftmost flange on, and use four of them in the four "spare" holes in the flange. Those four are threaded, and force the flange back away from the body of the coupling. The shaft comes with it because there's a collet cone on the flange, gripping the shaft. The main challenge is finding a way of jamming the whole thing so's it don't turn whilst you're unbolting. I used the toe of a crowbar at the front of the coupling, wedging it against the bolt heads on that side, but you could go down the weedhatch with a big block of wood and jam the prop.

 

Once it was free, I moved the shaft and collet back until I could put a block of softwood between the shaft end and the coupling. I then tapped the collet along the shaft as much as I wanted.

 

Then it's just a case of putting it all back, re-fixing the eight bolts (I went round them all twice nipping them up). Clear everything out of the way, start the engine and run in gear forward and back. Nip up the bolts again and the job's a good 'un.

 

Good luck!

[Timleech]

Yes. Undo the eight bolts that hold that aftmost flange on, and use four of them in the four "spare" holes in the flange. Those four are threaded, and force the flange back away from the body of the coupling. The shaft comes with it because there's a collet cone on the flange, gripping the shaft. The main challenge is finding a way of jamming the whole thing so's it don't turn whilst you're unbolting. I used the toe of a crowbar at the front of the coupling, wedging it against the bolt heads on that side, but you could go down the weedhatch with a big block of wood and jam the prop.

 

Once it was free, I moved the shaft and collet back until I could put a block of softwood between the shaft end and the coupling. I then tapped the collet along the shaft as much as I wanted.

 

Then it's just a case of putting it all back, re-fixing the eight bolts (I went round them all twice nipping them up). Clear everything out of the way, start the engine and run in gear forward and back. Nip up the bolts again and the job's a good 'un.

 

Good luck!

 

To be secure, the shaft does need to run the full length of the collet, so don't pull it back too far!

 

Tim

[BruceinSanity]

To be secure, the shaft does need to run the full length of the collet, so don't pull it back too far!

 

Tim

 

Good point, didn't think to point that out! My shaft had plenty ahead of the collet, so the thought didn't arise

 

Thinks, should I rephrase that?

 

Nah, it's Friday!

 

[slammer]

Thanks for the advice ..