3 blade prop question

[benlui]

I just had nanny diesel 21hp fitted to my shipman 28 and a 3 blade non folding prop. My question is, does this 3 blade slow the boat under sail down much compared to a 2 blade non folding prop? I am new to this forum, as I only purchased Ben Lui as of late. Also, has anyone any experience with nanny engines and are they reliable as I am having several issues on mine at only 30hrs. I replaced a MD5 Volvo penta 7.5hp which was almost 30 years old. Many thanks for your help.

 

[beneteau_305_553]

The difference between a 2 blade and a 3 blade is at worst like holding one hand in the water when sailing ie next to nothing.

nannis seem ok. Beneteau fit them as standard to some of their range.

 

[Tranona]

Welcome to the forum

A 21 seems a bit OTT for your boat. (obvious really as the original was a 7hp - 15 would be more than enough). Have you got the prop matched properly to the gearbox ratio and boat? A 3 blader will, of course produce more drag than a 2, but the trade off is better motoring performance. You could go to a two blader as you have ample power to swing the larger diameter (if you have the space) or you could bite the bullet spend a few more (well actually lots more) pounds and get a 3 bladed feathering prop if you are worried about the last bit of performance under sail.

The Nanni uses a Kubota base engine, as do Beta. Reliability should not be a problem. If the engine is new then any problems should be covered under warranty. A number of builders fit Nanni as original.

 

[benlui]

Thanks for the replies, the 21hp was less than 500 euro more than the 15hp so i thought why not. Yes, i looked at the 3 blade folding but not in the allowed budget. The prop and shaft were all changed to match the gear box ratio(all fitted by professional marine company in crosshaven in ireland so i trust all is in order. I hope sailing doesn't continue to be this expensive or i'll be broke in no time haha all comments appreciated guys thanks

 

[SAWDOC]

[ QUOTE ]
My question is, does this 3 blade slow the boat under sail down much compared to a 2 blade non folding prop?

To be positive - my mate fitted a 3 blade prop after his two blade effort struggled manfully to get him home in a blow. Never any such problems since!

 

[weaver_fish]

I would go three blade feathering - I am amazed at the transformation on my boat from a three bladed fixed. Easily more than 1/2 a knot quicker - which is quite significant in a small boat and in light airs.

Try darglow's featherstream - you might be surprised with the quote.

http://www.darglow.co.uk/html/products/feather.htm

 

[cmedsailor]

I have often the opportunity to compare my boat with 2 blades with another exactly same model boat but with 3 blades. Both propellers are factory fitted by the way. Conclusion: It looks like TWO DIFFERENT boats. Under sail my boat really flies in comparison with the 3 blades (I am always amazed). Under motoring in calm weather is more or less the same. But under motoring against rough sea, well, it's one of these times I wish I had 3 blades (but only feathering because I would never sacrifice sailing performance).

 

[Tranona]

Easy to be wise after the event, but perhaps a better compromise for sailing/motoring would have been the smaller engine and put the 500 euros towards a feathering propeller. You have a very slippery boat and I would think a 2 bladed folder might also be worth considering. Otherwise support the Featherstream - have one on my boat.

 

[DaveS]

Probably not what you want to hear since you've already bought the prop, but I would agree with others re. fitting a feathering type. I replaced a 2 blade fixed with a Kiwiprop 3 blade featherer and performance under both motor and sail improved noticeably.

 

[benlui]

I think I will change it to a 3 blade featherer as i plan to do some light racing soon. Thanks for the help guys