Westerly centaur engine replacement

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Catriem

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Hello to all the honorable members of this forum. I have owned a 1976 westerly centaur in Brittany for 20 years and I am French, please excuse my bad English.
I recently replaced my old MD 2 B with a refurbished volvo MD11D with MS2B tilted reverser. Gemini's post (JB1966) helped me a lot and I thank him.
Today my boat sails but the propeller is not optimal anymore because the ratio of the reverser makes it turn less quickly and I have to put a lot of power to have a decent speed. I would like to have an advice to replace the propeller for those who have a MS2B reverser.
I thank you for your help
 
Accueillir. Cela pourrait vous aider si vous écrivez la question en français, puis que Google la traduise en anglais, pour le bénéfice de la plupart d'entre nous sur ce forum ?

(Welcome. It could be of help to you if you write the question in French, and then have Google translate it into English, for the benefit of most of us on this forum?)
 
jamie N said:
Accueillir. Cela pourrait vous aider si vous écrivez la question en français, puis que Google la traduise en anglais, pour le bénéfice de la plupart d'entre nous sur ce forum ?

(Welcome. It could be of help to you if you write the question in French, and then have Google translate it into English, for the benefit of most of us on this forum?)
Click to expand...

I think that’s very rude. His English is better than some of the people who post on here.

Can you help him?

He has an MS2B gearbox fitted to a Centaur and wants to know what prop to fit.
 
Bienvenue sur le forum, Catriem. Il existe des calculateurs en ligne pour vous aider à choisir la meilleure hélice pour votre combinaison de bateau, l'espace maximum pour le diamètre de l'hélice, la puissance du moteur et le rapport de la boîte de vitesses, etc. Voici un lien vers un américain, mais il y en a aussi des britanniques et peut-être en français ceux. Calculateur de dimensionnement d'hélice

Il est probablement préférable de contacter un fournisseur d'hélices spécialisé pour obtenir ses conseils sur la meilleure taille, le pas et le nombre de pales. Je suis sûr que d'autres ici publieront bientôt un message pour recommander un tel fournisseur et donner des conseils supplémentaires.

Si vous (ou les modérateurs du forum) pouvez modifier le titre du fil pour le rendre plus clair, il s'agit du dimensionnement et de l'approvisionnement des hélices qui aideront à obtenir plus de réponses.

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Welcome to the Forum, Catriem. There are online calculators to help decide the best propellor to fit your combination of boat, maximum space for propellor diameter, engine power and gearbox ration, etc. Here is a link to an American one, but there are also British ones and perhaps French language ones. Propellor sizing calculator

It is probably best to contact a specialist propellor supplier to get their advice on the best size, pitch and number of blades.. I'm sure others here will post soon to recommend such a supplier and give further advice.

If you (or the Forum moderators) can change the title of the thread to make it clearer it is about propellor sizing and sourcing that will help getting more replies.
 
Thank you for your welcome and your answers. I will study this document and wait for other possible proposals. I think the propeller that was put on Gemini could also be a match because he installed the same MS2B inverter but I could not contact him directly.
 
Welcome to the madhouse! (maison de fous).

Your English is pretty good, so I'm not going to inflict my imperfect French on you. If you need a response in French, PM me and I'll do my best!

There are any number of prop calculators out there - just google Prop calculator. That will give you a starting point. If your prop is too different from the recommendations then yes, you need a new prop, and the right one will make a big difference. The next step is to choose a supplier - I can't help you with that, I used an English one - and talk to them. Let them do the sums (just make sure your figures are accurate) and let them work out what you need. After all, they're the experts.
 
Hi, thank you for your help, I used the calculation proposed by littlesister I give you the result here. JB1966 have you replaced your propeller? I would be interested in its characteristics. thanks Stemar for my English my friend google translate is an good help.
I will look on WOA.
Have a good day
 

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jamie N said:
Accueillir. Cela pourrait vous aider si vous écrivez la question en français, puis que Google la traduise en anglais, pour le bénéfice de la plupart d'entre nous sur ce forum ?

(Welcome. It could be of help to you if you write the question in French, and then have Google translate it into English, for the benefit of most of us on this forum?)
Click to expand...
When I was doing a lease which had to be in French I set up 2 computers, both with Google Translate so when I started doing the lease i typed it on one then typed the translation on the other one , and then altered it until both were mirror imageses but in a different language, although that is perhaps over the top for this purpose. Good Luck.
 
Catriem said:
Hi, thank you for your help, I used the calculation proposed by littlesister I give you the result here. JB1966 have you replaced your propeller? I would be interested in its characteristics. thanks Stemar for my English my friend google translate is an good help.
I will look on WOA.
Have a good day
Click to expand...
Not sure what figures you entered but I used the boat data from sailboatdata and the result was a 16*11 3 blade - a bit smaller than you show. Calculations here vicprop.com/displacement_size_new.php?action=calculate

This looks about right, but the engine is far too powerful for the boat (you can see you only need 15hp to reach hull speed) so exact size is not critical. You just need it big enough to ensure the engine is loaded. The reason for this type of engine in a Centaur is because at the time the smaller Volvo engine was jut a bit to small (13hp) and Volvo sold Westerly the next size up (originally 23hp) which was too big. If putting in a new engine a suitable choice would be one of the many 20hp engines, but of course more expensive and more work than a replacement MD11.
 
Props are expensive, second hand gearboxes are not - might it be better to change gearbox to suit the existing prop?
 
Really? a 3 blade 16" prop is about £450 and takes minutes to fit. There are only 2 gearbox ratio options on the MS2 gearbox and the chances of finding a good condition down angle gearbox with the alternative ratio (assuming it is actually suitable for the prop) are vanishingly small. any other gearbox would require an adaptor to fit the engine and probably changes to the sterngear and even moving the engine, never minf having to remove the engine and gearbox to replace the box.

The first thing to do is to measure the existing prop to see how far away it is from the ideal. It may well be that it can be repitched. From what the OP says it is too small because it was fitted originally to a less powerful engine and it may well be that pitch could go up an inch or 2 to absorb the extra power and lower the revs.
 
Tranona said:
Really? a 3 blade 16" prop is about £450 and takes minutes to fit. There are only 2 gearbox ratio options on the MS2 gearbox and the chances of finding a good condition down angle gearbox with the alternative ratio (assuming it is actually suitable for the prop) are vanishingly small. any other gearbox would require an adaptor to fit the engine and probably changes to the sterngear and even moving the engine, never minf having to remove the engine and gearbox to replace the box.

The first thing to do is to measure the existing prop to see how far away it is from the ideal. It may well be that it can be repitched. From what the OP says it is too small because it was fitted originally to a less powerful engine and it may well be that pitch could go up an inch or 2 to absorb the extra power and lower the revs.
Click to expand...
Fair enough, my thinking was simply that the prop apparently propelled the boat perfectly well before - the fact that the new engine is capable of more power doesn't mean it can be put to use - hull speed is hull speed. Fitting a bigger prop to match the unnecessary potential power output of the engine will simply introduce more drag when sailing - unless you go for folding or feathering, which introduces much higher cost.

I'm sure there's a gap in my logic somewhere - the availability of the correct gearbox being the most obvious.
 
Last edited:
Catriem said:
Hello to all the honorable members of this forum. I have owned a 1976 westerly centaur in Brittany for 20 years and I am French, please excuse my bad English.
I recently replaced my old MD 2 B with a refurbished volvo MD11D with MS2B tilted reverser. Gemini's post (JB1966) helped me a lot and I thank him.
Today my boat sails but the propeller is not optimal anymore because the ratio of the reverser makes it turn less quickly and I have to put a lot of power to have a decent speed. I would like to have an advice to replace the propeller for those who have a MS2B reverser.
I thank you for your help
Click to expand...

Is it possible that your tilted reverser is from a twin engined installation and you are using reverse gear for running ahead. Does your propeller turn faster when the propeller is actually running astern? If so you might require a different propeller to suite.
 
many answers thank you. I changed the engine. it is not possible to put my old engine gear back on an MD11D it is not the same coupling. The MS engine gear has a ratio of 1, the MS2B has a ratio of 2.3. So the propeller rotates about 4 times slower. Normally « «bilgediver « on the MS2B the propeller turns the same way in both directions. I am looking to have a speed of 5 knots at 1500 rpm and to have torque when maneuvering in ports. Increasing the pitch seems to me the solution while keeping the diameter
 
Catriem said:
Hi, thank you for your help, I used the calculation proposed by littlesister I give you the result here. JB1966 have you replaced your propeller? I would be interested in its characteristics. thanks Stemar for my English my friend google translate is an good help.
I will look on WOA.
Have a good day
Click to expand...
Hi,

This is the prop I fitted:

1656000001912.png

1656000029585.png

But your engine is very different in horsepower.

TM Norris were very helpful to me, and will likely confirm any calculations you may make.

Hope that helps.
 
Catriem said:
many answers thank you. I changed the engine. it is not possible to put my old engine gear back on an MD11D it is not the same coupling. The MS engine gear has a ratio of 1, the MS2B has a ratio of 2.3. So the propeller rotates about 4 times slower. Normally « «bilgediver « on the MS2B the propeller turns the same way in both directions. I am looking to have a speed of 5 knots at 1500 rpm and to have torque when maneuvering in ports. Increasing the pitch seems to me the solution while keeping the diameter
Click to expand...
I am not sure that is correct. According to the Volvo manual the MD2B gearbox has a reduction ratio of 1.87:1 which at 2500rpm maximum gives a shaft speed of 1337rpm. The MD11D has maximum rpm of 3000 and a reduction of 2.3:1 giving a shaft speed of 1304rpm - virtually the same. The propeller should be sized to allow the engine to reach close to maximum rated rpm and the way to check this is to make a series of runs at 200rpm from, say 1400 to the maximum and plot the speed. The hull speed of your boat is just over 6 knots but you should ne able to get up to 7 knots because of the excess power.

The calculated propeller size for the 2 different engines is also virtually the same as they have almost the same hp and shaft speed, but your cruising engine revs will be higher with the MD11D to provide the power demanded by the propeller.

Apologies for making a mistake earlier and thinking the boat had the original smaller Volvo engine.
 
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