Duo props Size?

[Liselle]

I need to replace the duo props on my Falcon 275. I have twin Volvo AD31 150 HP diesel's. The old props appear to be A8's. Can anyone confirm that these are the correct size for this setup. This will be my 1st season with this boat, any advice would be welcome.

 

[LeytonC]

A8 seems very big, my mate runs A5 on 41's - did your boat used to have petrols in it?

 

[Camayo]

Hi:

I also had A5s on mine with AD 31 24 foot planing hull, pulls the right revs.

 

[[2068]]

A8's sound quite big: My old boat with AD31's pulled 30kts with A6's, but your outdrive ratio might be different. A8's with a standard AD31 outdrive are meant to be in the 36knot plus range, and if your boat can't actually do that speed, you just end up overloading the engines.

What I would do:
- Try and find another Falcon 275 and see what it has fitted
- Find out what the top speed with AD31's was meant to be, find out the outdrive ratio (probably 1.95:1, but might not be) plus the weight of your boat, and have a chat with a Volvo Dealer...

dv.

 

[tamarind]

It does sound that A8's are a bit on the big side. Does the boat pull full revs aprox3800 rpm and get on the plane fairly quick. My boat is 34ft long 6 tons with AD41's 200hp withA7 props, so A8's on yours a bit big?

 

[Liselle]

Thanks for all the replies. I have found out today from a marine engineer, it seems with Duo props the larger the number the smaller prop. eg A8's are smaller than A6's.

I havent yet been able to make contact with another Falcon owner to compare.

I have found out however that the outdrive ratio is 2.3:1.
What ever that means!

Still digging.

 

[[2068]]

> A8's are smaller than A6's.

What I mean by "bigger": The pitch of A8's is greater than A6's, i.e. A8's are designed to be used on a boat with a higher top speed (e.g. 36-38) kts whereas A6's would be for a boat with a top speed of maybe 30 kts. The actual size (diameter) of the props just isn't relevant.

dv.

 

[derek482]

Way late but I have a Falcon 275 named H2O based in Poole. A8's are standard on the Falcon. If any one needs help or info re Falcons please contact me on my Email address as I have loads of info re Falcons and know the two guys who built them in Norfolk. New member an all that <span style="color:blue"> </span>