Replacement prop for Centurion 32

[PuffTheMagicDragon]

Hauled out last Monday and found that one blade was split to almost 3/4 of the chord and the other blade showed severe dezincification towards the root. Definitely a case for replacement, the problem is with what size.

As far as I can make out, the diameter appears to be around 15 inches but I have no idea of what the pitch is or was. I could not identify any markings on the hub; hardly surprising as it is 39 years old. The motor is an old Volvo MD2B with an MS gearbox at a 1.91:1 reduction. Maximum engine revs are 2500RPM. Fingers crossed, I do not anticipate replacing the engine any time soon and so I need to buy a left-handed prop (a new engine would probably take a RH prop).

Does anybody here know what size prop was originally fitted on a Centurion 32? Should I stick to a 2-bladed or should I go for 3-bladed? (shaft is on a P-bracket and is offset to port by the side of the skeg).

As always, TIA for any information that you can give me.

 

[Tranona]

Feed your boat's data into Propcalc on www.castlemarine.co.uk which will give you a good guide to size.

If buying new then give the same data to your chosen supplier and ask for their recommendation. It should be the same or similar to what you get from Propcalc, but best to take the supplier recommendation.

In general terms a 3 blade will be better at motoring but at the cost of extra drag when sailing. However a boat like yours deserves a folding or feathering prop to minimise drag under sail, but as with most things boaty better means lots more money.

 

[sarabande]

have you come across this site ?

http://www.centurion32.com/index2.html


Inside the pages it shows a 2 bladed prop.


I thought the Wauquiez site had a historic section, but the necessary page seems tobe at odds with itself.

http://www.wauquiez.com/FR/wauquiez/historique.aspx.


A quick search through the list of boats also shows a 2 bladed prop:-

http://www.centurion32.com/baboonty/index.html


But there is a Maxprop 3 blader here:-
http://www.centurion32.com/royana/index.html

 

[sarabande]

I think that Aelus IV has one. Also Bedouin ?

 

[Jabamusic]

3-blade on mine

 

[sarabande]

goodness gracious, that is almost an interference fit !

 

[charles_reed]

A 15" x 12" 3-blader would appear to be about right for engine and boat.
By all means use a programme like Propcalc, but be aware it's an approximation, taking little account of a boat's underwater profile and drag.
Alternatively buy one from a reliable, experienced supplier such as Lake Engineering and rely on their expertise.

 

[PuffTheMagicDragon]

Many thanks for the replies.

I have tried propcalc but it comes with a proposal for a two-bladed that is 17" in diameter! The suggestion for a three-bladed that is 15x13 is interesting and would probably be easier to source than one with two blades. I really would like to find one that is already machined. I could, as I did on my previous boat, just buy a casting and then machine it to fit the shaft that I have. However, in either case, I would still need to get the dimensions right.

About the Wauquiez site, it does not only lose itself in the links; I tried their 'contact' link to ask their advice but the email bounced and I got this automated reply:

"
Ceci est un message d'information envoyé par mail.goweb.fr.

Le serveur n'a pas pu transmettre votre message

Subject: Prise de contact de la part de Wally Vella-Zarb
Date: 11 May 2012 00:07:33 +0200



à cette adresse:

<p.bloch@wauquiez.com> (srvproxy.experton-revollier.fr: 550 No RDNS entry for 178.33.196.250)"

I shall now try to contact David Merlot who worked with Wauquiez for some thirty years, maybe he remembers.

Thanks again for your interest.

 

[Tranona]

Many thanks for the replies.

I have tried propcalc but it comes with a proposal for a two-bladed that is 17" in diameter! The suggestion for a three-bladed that is 15x13 is interesting and would probably be easier to source than one with two blades.

You probably cannot swing a 17" prop. You need ideally 15% diameter tip clearance or at a minimum 10%. Looking at the photo of the 3 blade prop it seems clearance will be your major constraint, so enter the max diameter into Propcalc and see what you get. You may end up with a less than ideal prop size simply because you don't have room.

Props are usually kept in stock pilot bored and then bored for the correct diameter/taper for your shaft. Supplier such as Norris, Sillette, Lake Engineering etc will supply to the correct size ready to fit.

 

[PuffTheMagicDragon]

I have just received a reply from m.Merlot:

"oui le pas est de 15 pouces et diametre 360mn sens de rotation à gauche
bonne soirée cordialement david "

It seems that I now need to source a LH 14x15 prop.

Once again, many thanks for your advice.

 

[bedouin]

Mine came with a 2 blade fixed 14 x 15 (IIRC) - and it was not particularly good. I have the same engine/gearbox as you.

Then I replaced it with a 15x12 3 blade Gori folding prop - and it is a great improvement, and I would certainly recommend 15x12 3 blade (either fixed or folding) over the original 2 blade.

15 inch is the maximum size you can fit.

 

[PuffTheMagicDragon]

Then I replaced it with a 15x12 3 blade Gori folding prop - and it is a great improvement, and I would certainly recommend 15x12 3 blade (either fixed or folding) over the original 2 blade.

Point taken about the three blades being better.

Unfortunately a Gori folding prop would be too much of a commitment at this stage, the reason being that I still need to see how well the engine and gearbox perform over a season. Should I need to replace them, the probability is that the new installation would require a right handed prop. I am assuming, perhaps incorrectly, that folding props are also 'handed'.

(At this time I am still struggling to separate the coupling (bronze) from the shaft so that I can replace the rubber hose of the stern gland. I have removed the nut but the shaft is refusing to budge. Heating with an oxy-acetylene flame next Monday seems to be the only choice...).

 

[Tranona]

Point taken about the three blades being better.

Unfortunately a Gori folding prop would be too much of a commitment at this stage, the reason being that I still need to see how well the engine and gearbox perform over a season. Should I need to replace them, the probability is that the new installation would require a right handed prop. I am assuming, perhaps incorrectly, that folding props are also 'handed'.

(At this time I am still struggling to separate the coupling (bronze) from the shaft so that I can replace the rubber hose of the stern gland. I have removed the nut but the shaft is refusing to budge. Heating with an oxy-acetylene flame next Monday seems to be the only choice...).

If the shaft is still in the boat, then put a spacer, probably a socket in between the two halves of the coupling, bearing on the end of the shaft and then tighten the coupling up with the bolts. If there is a nut on the end it is probably keyed and tapered, so it should just pop off once you put some pressure on it.

 

[PuffTheMagicDragon]

If the shaft is still in the boat, then put a spacer, probably a socket in between the two halves of the coupling, bearing on the end of the shaft and then tighten the coupling up with the bolts. If there is a nut on the end it is probably keyed and tapered, so it should just pop off once you put some pressure on it.

That is similar to what I tried this afternoon. The coupling on the gearbox side has threaded holes and the other half is attached with Allen bolts. I therefore made up four lengths of M10 studding and threaded them through the 'shaft' coupling flange and into the 'gearbox' flange. I then made up a spacer and proceeded to tighten the nuts on the studs as you have suggested. Unfortunately I couldn't manage to build up enough pressure - so far. Tapping with a hammer is something that I am avoiding because the coupling is made of bronze. I know, I know, so is the propeller. Perhaps I was having a senior moment and I will feel younger next Monday. Perhaps I will even let my mate show me how much he is stronger than I!