Is 5 Better than 3 Props ....

[Gludy]

My new boat had a set of five blade props fitted and they were way out for the boat.

In examining them it was found that they were not even as stamped and that one blade was a different pitch to the other blades. In other words a real mess that has delayed the commisioning of my boat. It is the prop makers fault.

A set of three blade props work almost perfectly on the boat and with a slight tuning could exactly match it.

So because of the mess I have been given a choice - I am to try out the 3 blades and then the brand new 5 blades that will be made to spec this time. Its my choice which to take, The five blade props cost a great deal more, really high prices but offer smoother running, less prop noise, maybe a small drop in top speed and good grip on the water in the marina etc (although i do have stern and bow thrusters).

For those who are interested in props, I will report the results of the rials on this thread.

Are there any views at this stage?

 

[Major Catastrophe]

Yes, Whatever you decide, have a spare set made now (two), as it would prob be cheaper than trying to match/balance one later.

 

[Gludy]

The htree blades - yes you could have a spare set but the cost of a spare five blade set is off the wall....... that iis a good point, for the 3 blade props, that had not occured to me - thank you.

I wonder how many boats do have a spare set of props?

 

[DAKA]

I only have experience with aluminum but I noticed as the blades increase they get thinner and weaker (in theory they can be thinner as they have less work to do )

Did you notice if the blade from a 3 blade prop was thicker than a blade from a 5 blade prop, if so I would go for the stronger 3 blade ready for hitting debris or in your case taking the ground.

 

[Gludy]

Yes- you are right about the thickness. That is another advanatage for the three blade.

The 5 blades cost many times the cost of even a set of 3 blades. They are making a totally new set after the mess up and I can choose without even given a reason - so they may take some time before they can ever sell the five blades.

Apparantly the 5 bladers are smoother and produce less noise .... it seens that this is a lot of money to fork out for such a small advantage - so far two reasons that had never even occured to me have come up for the 3 blades.

I am having legs fitted to the boat - the decision took a while - as long as I know what ground I am on - it should be OK..... my heart will be in my mouth the first few times though. They have supplied legs for boats up to 60 tons. Mine is only 32 tons.

 

[pheran]

Did you consider 4-bladers or have I missed something? Quieter and smoother than 3 without the cost of 5 blades. Don't think I could be doing with legs. My boat is designed to take the ground but on two huge 'bilge keels' (yes, it IS a mobo) with skegs to protect its 4-blade props. 25 tonnes all up.

 

[davedpc]

For some reason M/c bravo 2 props. dont seem to deterioratr like Volvo.

 

[Deleted User YDKXO]

I've had 3, 4 and 5 bladed props on the boats I've had. I've got 5 bladed props on my current boat and the boat doesnt feel perceptibly smoother than my previous boat which had 4 bladers. All I know is that the boat is a bit slower than I would expect but then it is a heavy lump. I do remember having boats (eg Turbo 36) which had 3 bladers and the prop noise/vibration was quite intrusive
Given that fewer bladed props are supposedly more efficient, then I guess in your case you should use props with as few blades as possible but still give acceptable noise/vibe levels
I'm somwhat surprised that Tarquin don't seem to have a pretty good idea of which props offer the best compromise. I'll be very interested in your results

 

[Gludy]

No- my boat has been held up 3 months now, so I am not a happy bunny.

Very few of them have been fitted with the five blade props - all they can say is that the maker claims 5 blade props are smoother etc.

I can at least trial them and choose which ones.

 

[Gludy]

What did Ferretti say that made you choose the five blade props?

 

[Deleted User YDKXO]

Paul, my boat was secondhand so there was no choice but I believe that all Ferrettis get 5 bladed props plus a spare set as well. It can only be for reasons of noise/vibration but, as I said, I'm a touch disappointed with the top speed of my boat which may or may not be down to the props
I do wonder whether there is another reason for using 5 bladers in that I guess that 5 bladers are a smaller diameter than the equivalent 4 or 3 blader and this would allow the propshaft to be mounted closer to the horizontal leading to an increase in efficiency but of course this is not a consideration in your case