DF 140hp fourstrokes

[Striker08]

Hi i was wondering can any one give me some advice. I have 7.3m plate alloy cat with 2x DF 140 2005 model fourstrokes with approx 160hrs. The problem is i think these engines are pigs and it is not true all the hype that surrounds them. I run 13 7/8 x 17 stainless which were on the boat. I get about 30mph flat out with all my fuel and gear and max revs of 5200 rpm. I was wondering if any one has any ideas i want to get more speed out of my boat thanx.

[Outsider1]

Hi Striker,

Have a look at this boat test from Seamedia (Fisherman and Boatowner magazine). It is a twin DF140 installation on a 6.8m alloy Cat.

A couple of things stand out;

- They were propped with 13 7/8 by 19" Solas props
- They achieves WOT of 6,200 rpms
- Top speed was 36.8 knots

http://www.seamedia.com.au/sea_library/engines_drives.php

Cheers

Dave

[FNQCairns]

Hi i was wondering can any one give me some advice. I have 7.3m plate alloy cat with 2x DF 140 2005 model fourstrokes with approx 160hrs. The problem is i think these engines are pigs and it is not true all the hype that surrounds them. I run 13 7/8 x 17 stainless which were on the boat. I get about 30mph flat out with all my fuel and gear and max revs of 5200 rpm. I was wondering if any one has any ideas i want to get more speed out of my boat thanx.

Be careful of the diameter your props have, 1/8 of an inch more diameter than you actually need is akin to throwing fists full of dollars ovebard every hour the props spin.
Twin engines on cats are outside of my condfidence level although the rule above is physics not marketing or urban belief.

if it were my craft I would hunt high and low for 2 props that are still 17p but have less diameter, props can be defined by an area to pitch ratio but try and get a good answer of this specification from prop sellers:-/.

IMO ANY brand 3 blade prop you can find and make fit that is say 13.5x17p (alum even) will return a little smile to your face (smaller than it could be but still a smile) although to do it all properly you need to know what cup and what the area ratio of each prop actually is and compare all, 4 blade props usually fail this test but do better to a degree a hideously propped boat so they have their place and make owners happy.

You are correct though that 140 is a relativel low torque engine which can make achieving it's best a bit of a battle.

cheers fnq