Thread: Under propped?
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Old 03-15-2014, 06:43 AM   #5
psneeld's Avatar
City: AICW
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 20,120
Originally Posted by Jeff S View Post
I have a 1977 Davis (Defever) 40' Trawler. (14"-7" beam, 4' draft)
Single Ford Lehman 120 - 2500 RPM max.
Velvet drive gearbox 2.37-1 ratio, 39,000 lbs+/_
Current prop 25x16 3 blade RH, 1.75" shaft
At slack current I run at 2200-2300 to maintain 8 knots.

I talked to another owner of an identical boat that is over propped with a 25x21 prop and he runs approx. 1600 RPM to get 8 knots, but cannot reach the 2500 RPM's.

So, I am looking to find the optimal pitch/prop type to get off the top end of my RPM's, maintain the 8 knots and help my fuel efficiency.

Any comments would be appreciated!

Can't help with Defevers but...

Another 40 Albin on here runs a 120 with a 2:1 tranny and a 20X16 prop... gets 2500 RPM and around 6-7 knots down at 1600

I have a 40 Albin..not sure of my gearbox and run a 22x17 prop. Not sure I get to 2500 rpm and don't really care too much as I rarely run over 1800...I do cruise at 1600-1700 and get 6.3 knots.

I have a hard time believing your friend is hitting 8 knots at 1600...but I guess it's possible depending on his tranny.
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