Jp3 propeller dilemma

[Capella247]

Hi all,.  Seeking your advice.   Docked for day for blacking to discover a blade missing from my 24" crowther prop.  Argh !    Problem is a new one will take 6-8 weeks.   The boat is new to me hence me thinking the vibration was a drive plate or stern gland.   There's corrosion on the prop so has been like this for some time.    it's a paul barber tug 60.   I spoke to Angela at crowthers who has been very helpful.  The gearbox is a Borg warner velvet drive but I have no idea what the reduction ratio is no plate or marking other than the 71c on the casting of the front section.  The pitch is 15inch and I was hoping to make sure the replacement  prop was optimal.     So not knowing the reduction ratio is proving difficult to find something as an interim measure whilst waiting for a replacement.       The pitch seems low to me I was expecting 22 or so .   Crowthers said based on the serial number the prop was originally specced for a different engine.       So my options are order a new prop like for like and wait a couple of months.   This involves chugging 10 hours home with a knackered prop.   Or find a temporary replacement. 22 x 22 from say Michigan or as near as I can and suck and see a replace in a year if no good.   I ve tried marking the flywheel and rotating the prop by hand whilst in gear but it won't engage.  What would you do ?  Any thoughts ?   I remember 6 years ago using the boat when the prop was in tact and it seemed to crack along .  Although possibly a little high revved. 

Edited January 23, 2018 by Capella247

[BWM]

It would be worth enquiring with either Fal propellers or Crowther for the correct size, i'm sure they would help. Available clearance, boat dimensions and engine type/power is all the information they would need. I purchased mine from Fal and was impressed with quality and service, turn around time was reasonable too. As you say, the pitch seems very slight, from memory, the optimum quoted for my Jp3 was 28"×22" on a 72' craft. 

[Capella247]

Thanks crowthers struggled as I didn't know the gear box reduction. And couldn't guess from the pitch and engine hence checked the job card and discovered it was specced for a different engine.  I'm limited to around 24 inch currently there's a couple of inches of clearance currently so maybe 26. The main thing is whether to chug home whilst I wait for a direct replacement or just take a chance on a more typical pitched prop 

Edited January 23, 2018 by Capella247

[MtB]

I've an idea the 1:1 Velvet Drive has a different final drive casing from those with a reduction final drive. So if you can post up a photo we might at least be able to identify if you have a 1:1.

A 1:1 final drive might also explain the small size of the blade. 

[Capella247]

Hi mike thanks for responding here is a photo..... if that's the case would a 22  20  or 22 18 do the job as a n interim to get me home or would you just order the same on and risk cruising home with a two balde prop?  

[David Mack]

I'm not familiar with the velvet drive, but why can't you engage gear to count the revolutions of the prop shaft per turn of the flywheel? 

Edited January 24, 2018 by David Mack

[GRLMK38]

Would one of these help?

https://www.amazon.co.uk/Digital-Tachometer-Small-Engine-Non-contact/dp/B00HWLTW90/ref=pd_lpo_sbs_263_t_0?_encoding=UTF8&psc=1&refRID=90CKQCF90BB5V3QJCJX1

 

[Capella247]

I'm not familiar with this gear box either.   But tried that idea yesterday by rotating the fly wheel.   It doesn't engage at a low speed  

[David Mack]

21 minutes ago, Capella247 said:

I'm not familiar with this gear box either.   But tried that idea yesterday by rotating the fly wheel.   It doesn't engage at a low speed  

Some hydraulic gearboxes are arranged so that forward gear is normally engaged, and the hydraulics are used to put it in neutral or reverse. That way a boat at sea can still get home if the hydraulics fail. Does the velvet drive need hydraulic pressure to engage gear?

There may be a mechanical override to put it in permanent forward gear. PRM hydraulic boxes have this.

Edited January 24, 2018 by David Mack

[BWM]

Have you tried contacting Paul Barber? He might be able to throw some light on the spec of your gearbox. I would imagine either of the propellers you mentioned above would do for a temporary fix, with the smaller one being not too far from your current one. The concern with the original being so far out of balance it may damage the bearing.  

[Tony Brooks]

1. That photo shows a reduction box.

2. Velvet drives have no "get you home" device or procedure as far as I know.

3. I think a tachometer would be the only way to work out the reduction.

 

[alan_fincher]

6 minutes ago, Tony Brooks said:

3. I think a tachometer would be the only way to work out the reduction.

 

This is surely the way forward?

Simple hand held tacho first on the flywheel, then on the drive from the box.

Presumably they were only made in a small number of different ratios, so the measurements will not need to be spectacularly accurate to match to a ratio that is a possibility for that box.

 

[Bee]

https://www.ebay.co.uk/itm/boat-propeller-21-x-22/323023573668?hash=item4b35b492a4:g:24sAAOSwXPNaPo~c  Maybe some help? I have a 16 x ? RH 1.5 inch shaft that you can borrow if its any use, might be a slow trip but can guarantee its got 3 blades.

[MtB]

2 hours ago, Capella247 said:

Hi mike thanks for responding here is a photo..... if that's the case would a 22  20  or 22 18 do the job as a n interim to get me home or would you just order the same on and risk cruising home with a two balde prop?  

 

You're welcome. Yes as Tony says, yours has reduction final drive. Here is a photo for comparison of a 1:1 Velvet Drive I happen to have lying around here, showing yours is different:

IMG_3483.JPG

[MtB]

What size shaft do you have? And which rotation? There are a couple of possible replacements for sale in the 2017/3 issue of the HNBOC news mag. A 22x20 describes as suitable for a JP3, and 26x19 for a 2" shaft.

[Capella247]

2 hours ago, alan_fincher said:

This is surely the way forward?

Simple hand held tacho first on the flywheel, then on the drive from the box.

Presumably they were only made in a small number of different ratios, so the measurements will not need to be spectacularly accurate to match to a ratio that is a possibility for that box.

 

Hi this seems a good way forward.  Although Ive been boating for all these years I have never thought about propellers until now!  I will try this when back in the water and engine running.  And that should hopefully confirm the reduction.   Cheers tom

[Dalslandia]

if it is this gear box it have 6 different gear ratios to chose from

www.regalpts.com/PowerTransmissionSolutions/Brands/Velvet%20Drive/V7172pg1.pdf

[alan_fincher]

31 minutes ago, Capella247 said:

Hi this seems a good way forward.  Although Ive been boating for all these years I have never thought about propellers until now!  I will try this when back in the water and engine running.  And that should hopefully confirm the reduction.   Cheers tom

Assuming it is not raw water cooled, and you don't run it for too long, I can't see why you couldn't do this out of water, (having someone on guard to make sure nobody goes near the propeller, though!).

FAL Scottish propellers have been mentioned.  When I was in a similar dilemma they were in a position to supply a new prop in days, whereas Crowthers wanted months. (They think nothing of re-pitching a stock propeller to suit your needs).  Much cheaper than Crowthers too. I didn't need to go this route in the end, but might get you a prop quickly to get you travelling home efficiently raher than limping along?

I found FAL great to deal with - they re-pitched my existing prop, without bother, after Crowthers had said they would not be able to.

[MtB]

10 minutes ago, alan_fincher said:

Assuming it is not raw water cooled, and you don't run it for too long, I can't see why you couldn't do this out of water, (having someone on guard to make sure nobody goes near the propeller, though!).

 

Am I getting confused? 

Is this a proposal to measure the rpm of the output shaft of the Velvet Drive using a hand held tachometer? 

If so, then the only ways I can think of are to press it against the end of the prop shaft right by the propeller nut, i.e. near the rotating propeller! Or to disconnect the prop shaft inside the boat in which case the prop won't be rotating in the first place. 

Or is there another way to do it? 

[Dalslandia]

Mike, the tach suggested was a hand held optical, a mechanical will work as you suggest

[MtB]

17 minutes ago, Dalslandia said:

Mike, the tach suggested was a hand held optical, a mechanical will work as you suggest

 

Ah ok thanks, I've been back and found the link. Looks v useful, I'll get one myself!

[Dalslandia]

yes it looks handy

[Capella247]

3 hours ago, Mike the Boilerman said:

What size shaft do you have? And which rotation? There are a couple of possible replacements for sale in the 2017/3 issue of the HNBOC news mag. A 22x20 describes as suitable for a JP3, and 26x19 for a 2" shaft.

This would have been ideal as it is a 2 inch rh prop.  I wish I had seen this earlier as I ve since sourced a get me by prop of 24 22 which has a five inch hub correct taper etc and should hopefully bolt straight on.   This may well be over the top for my reduction ratio.   Whatever that turns out to be.   But if it's a disaster I'll save up for a new one or second hans of a right size later in the year.    Thanks for everyone's advice and I'll be getting a tachometer to work it out once back on my home mooring.  Nothing like a broken propeller to ruin a couple of days.   Hopefully the old one will have some scrap value or I'll turn it into a feature on the patio.    Cheers Tom 

Edited January 24, 2018 by Capella247

[BWM]

Please let us know how you get on. As Alan mentioned above Fal would almost certainly be able to resize/re-pitch the propeller that you have bought if it is necessary. 

[Capella247]

5 hours ago, BWM said:

Please let us know how you get on. As Alan mentioned above Fal would almost certainly be able to resize/re-pitch the propeller that you have bought if it is necessary. 

Yes I will provide an update. The prop arrives on Tuesday so hope to get some time off work later next week to move home.  The boatyard are quiet due to a stoppage to the east and so are flexible.  Still waiting for the boat to dry to black it's so damp at the moment.  I'll report back on propeller performance.  Spoke to several propeller suppliers today including fal everyone very helpful.  The existing propeller pitch has confused matters.     I also called Paul barber but he didn't recall ever installing a jp3 with a Borg warner gear box. So it may have been retrofitted at a later date.   The prop though was ordered by paul according to crowthers job card so maybe originally it was 1:1 as suggested    I have missed Capella's hydraulic drive today