3/4 Throttle of Full Speed Ahead?

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rhythmsurfer

rhythmsurfer

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Oct 29, 2010
136
Hunter 36 Pensacola
Recently I have become addicted to fishing using my boat to troll. The boat is a 1981 Hunter 36 with a Yanmar 2QM20 which produces about 18hp pushing us along at 6-8 kts. I have motored out 25-30 miles off shore. As you can imagine the trips take 12-14 hrs, but they are really productive catching our limits of King Mackerel, Mahi-Mahi, and Bonito. No Marlin or Tuna yet :) Is it ok to run full throttle on a diesel or better to go at 3/4 throttle? I have a 3 bladed prop which I think is not original. No tach but I just "listen/feel" what I think is 3/4. I cut all the maintenance on the boat in half i.e. oil changes, fuel filters, belts and do my best to keep the little Yanmar happy. So what do you do when motoring?
Tony
 
B

Big Windy

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Jun 2, 2004
1,077
Several Catalinas C25/C320 USA
75% WOT is the suggested cruise power setting. For me that's about 2,700 RPM with a Yanmar 3GM30.
 
Bob J.

Bob J.

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Apr 14, 2009
775
Sabre 28 NH
If you look at the increase in speed with WOT, it's very minimal when compared to 3/4 or even 1/2 throttle. Hull speed in a sailboat is hull speed & you can't get much more out of her.

I see a center console fishing boat in your future!
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,354
Catalina 34 224 Maple Bay, BC, Canada
Don't understand how you can cut oil changes by half because you run at reduced throttle. Diesels LIKE to run at 75-80% load, keeps carbon from building up, especially in those Yanmar exhaust risers. If you continue to do this, just run at WOT for a while to keep it clean. Don't lug the engine.
 
rhythmsurfer

rhythmsurfer

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Oct 29, 2010
136
Hunter 36 Pensacola
Misfits I am looking.....maybe I can get a 420 for the good sailing days and a center console for the good fishing days.
 
kloudie1

kloudie1

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Nov 6, 2006
10,219
Hunter 34 Mandeville Louisiana
He is asking if it is ok to run at 3/4 or full throttle.. trolling for those fish requires 5-7 knots.. Without a tach reading, this is all guessing since we don't know if the prop pitch is anywhere close.. He is probably doing OK with pushing it to the top of a sweet spot as he says, very slightly under full throttle.. but again, without some kind of tach reading, we are all guessing..
RhythmSurfer, You can get a pretty inexpensive tachometer, either a laser one or a touch type .. Run at your ear's sweet spot and then take a tacho reading.. The tacho costs are $40 or so.. Since the engine is a 2 QM which has a continuous output rating at 2600 RPM.. It is fine to run it continuously between 2000 and 2600.. At around 1700, ya probably getting too slow..
 
Bob J.

Bob J.

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Apr 14, 2009
775
Sabre 28 NH
rhythmsurfer said:
Misfits I am looking.....maybe I can get a 420 for the good sailing days and a center console for the good fishing days.
Click to expand
Personally I'd keep the 36 & go find a nice 24' -26' CC w/ a T hardtop, set of outriggers & twin 150 or 200's on the transom. :)
 
rhythmsurfer

rhythmsurfer

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Oct 29, 2010
136
Hunter 36 Pensacola
Misfits I read your profile. Welcome to the dark side. I am trying to figure out the gas bill for a single engine CC. Claude I will probably invest in a laser tachometer. thanks for the advice. I just don't want to prematurely kill the engine. My wallet couldn't handle 10 grand for a new one.
 
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