fuel efficient cruising

Larryrsf

Larryrsf

Member
My boat is a 74 V20 with an Evinrude 150. An outboard mechanic evaluated my engine and said it is in "new" condition internally, obviously from the compression numbers having had a recently overhauled power head. He said the carbs should be cleaned at the end of the season for optimum performance. I add the right amount of the recommended carb cleaner to the fuel tanks.

I have it in a marina on San Diego Harbor. It will be there until October at least. The harbor is usually choppy, making a very rough ride at higher speed than 20 MPH or so, when the boat is just planing.

How should I set the trim for best mileage? Obviously I start with it trimmed all the way down, which keeps the bow low enough to see over. But as it starts planing should I adjust the trim for optimum speed with the lowest RPM? It does 22MPH (accuracy of speedometer unknown) at 3000 rpm.

Obviously the smoothest ride is with the trim down and minimum speed to plane. But that may not be the most fuel efficient.

Larry
 
Larry, you don't say if you have trim tabs or are you just trimming the boat with your engine? Tabs make a hell of a difference.
 
At the risk of appearing stupid about boats, what are "trim tabs?" There is nothing like that on the transom of my boat. I have an optional swim step and the speedometer pitot tube extending down back there.

Larry
 
They are electric or hydraulic stainless steel flaps on each side of the transom that help control porpoising and makes a better ride. And yes, they do make a big difference.

But to answer your question, you are right in that all the way down isn't the best economy and highest speed / lowest RPM work in your favor. As you trim up more hull is coming out of the water, steering gets easier, speed increases and so on. My trim indicator died, but I can tell by feel exactly how my engine is trimmed.

I don't have a fuel flow meter but I believe the best RPM range for fuel economy on a V20 w/ 150 hp o/b is somewhere between 3700 - 4000 RPMs. In your scenario of going around 20 mph or so I wouldn't worry so much about economy as adjusting the trim for the best ride, including pounding and spray from the hull. I've found there are times when speeding up and adjusting trim you can get on top of the chop and find a better, dryer ride than if you tried to go slower. Not always the case, but sometimes.
 
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Thanks! Saturday was busy out there, every kind of boat including the heavy Harbor Cruise vessels. Lots of sailboats, even skidoos and a few runabouts really flying. So crossing those wakes was scary for my newbie-to-boating wife. I was praising the Wellcraft deep bow for efficiently slicing through most of that stuff. But we did get slammed by big waves a few times-- and since she wasn't standing with knees flexed like I was, she got slammed too, ha. I bought cushions for our "Bluewater" boat seats today. Hope that helps, but standing up is really the best answer to rough water.

Larry
 
Bean bags!!! Cannot stress it enough. You can get one called the "Big Joe" at Walmart for about $30. Money well spent. You won't be sorry. The lady will hug your neck, I promise! My crew catches quite a few snoozes while I'm at the helm banging the fillings out of my mouth.
 
Larryrsf said:
Thanks! Saturday was busy out there, every kind of boat including the heavy Harbor Cruise vessels. Lots of sailboats, even skidoos and a few runabouts really flying. So crossing those wakes was scary for my newbie-to-boating wife. I was praising the Wellcraft deep bow for efficiently slicing through most of that stuff. But we did get slammed by big waves a few times-- and since she wasn't standing with knees flexed like I was, she got slammed too, ha. I bought cushions for our "Bluewater" boat seats today. Hope that helps, but standing up is really the best answer to rough water.

Larry
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Just remember that you have a steering wheel to hang onto... she doesn't. If you're standing up in the boat MAKE SURE you both have on life preservers.... Accidents happen, and if you're standing, they can happen faster. Getting tossed overboard by a wave you didn't see coming and weren't ready for is NOT high on the fun things to have happen while boating.
I'm 70, a good swimmer, a certified Red Cross Lifesaving Instructor and I always wear my pfd while underway. NEVER be embarrassed to wear one. Get the canoe/kayak kind that you wear like a vest and has a zipper and wide arm holes and in minutes you'll forget you even have it on.
 
Blue_Runner said:
They are electric or hydraulic stainless steel flaps on each side of the transom that help control porpoising and makes a better ride. And yes, they do make a big difference.

But to answer your question, you are right in that all the way down isn't the best economy and highest speed / lowest RPM work in your favor. As you trim up more hull is coming out of the water, steering gets easier, speed increases and so on. My trim indicator died, but I can tell by feel exactly how my engine is trimmed.

I don't have a fuel flow meter but I believe the best RPM range for fuel economy on a V20 w/ 150 hp o/b is somewhere between 3700 - 4000 RPMs. In your scenario of going around 20 mph or so I wouldn't worry so much about economy as adjusting the trim for the best ride, including pounding and spray from the hull. I've found there are times when speeding up and adjusting trim you can get on top of the chop and find a better, dryer ride than if you tried to go slower. Not always the case, but sometimes.[/QUOTE]

here on lake erie where we usually have a chop speeding up and trimming up keeps things much more smooth and dry
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My boat is in a Marina on San Diego Harbor. So I am constrained to do my boating on that harbor. It is big enough that even light winds can kick up chop and even swells. And BIG boats, even ships pass through and create big swells from their wake. So the harbor is seldom smooth enough to plane without scaring the crap out of my passengers, ha.

My boat speedometer shows low 20s with 3000 RPM. It is on top and planning at that speed. I read that this boat with a good 150HP engine can hit 50MPH with just one or two people aboard. Maybe I will find lake-smooth conditions some morning and let er' rip!

Larry
 
Larryrsf said:
My boat is in a Marina on San Diego Harbor. So I am constrained to do my boating on that harbor. It is big enough that even light winds can kick up chop and even swells. And BIG boats, even ships pass through and create big swells from their wake. So the harbor is seldom smooth enough to plane without scaring the crap out of my passengers, ha.

My boat speedometer shows low 20s with 3000 RPM. It is on top and planning at that speed. I read that this boat with a good 150HP engine can hit 50MPH with just one or two people aboard. Maybe I will find lake-smooth conditions some morning and let er' rip!

Larry
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An old school 150 should push you close to 40, but not 50. it takes about 200 prop shaft horsepower to get into the 50 MPH range with a V-20. A good healthy late model 150 will get you low to mid 40's top speed. A 225 in healthy condition will break 50 with a good prop. And if your crazy enough a 250 can hit 60.
 
This morning I took it out to fill the tanks, then ventured out into the harbor. The water seemed smooth, few boats out there, so I let er' rip! I was amazed to hear that engine roar as it passed 3000 RPM. When it got to 5000, the boat was FLYING! The speedometer was reading middle 40s and that was with the engine trimmed all the way down. I suppose I could have obtained more speed by trimming the motor higher, but who cares? That speed is scary on even mildly choppy water.

So the all the questions about this engine are answered. It can develop massive power. I was glad for the opportunity to "blow the cobs out" and now I know what it can do. One day soon I will take it out early in the morning when the harbor is glassy smooth and really let er' fly for a few minutes.

larry
 
I am bidding on a Garmin GPSMAP 2010c on eBay. It would fit the bail dash mount for the old paper-printing fish-finder display that was installed when I got the boat. That GPS does locations, waypoints, etc. and also has a "through hull" fish finder head. I will install it, but I am really not much of a fisherman. Should more accurately read out speed and course, of course.

The cell phone boat aps are decent. I have "Boat Buddy." It uses GPS to track the course and waypoints, and also keeps track of gas levels in the tanks and other inventory-- and then records trips from the slip and back to the slip, giving exact mileage traveled, speed, and etc. That ap costs $10, but seems worth it. It will show a satellite view of each past trip with landmarks, etc.

Larry
 
It is idling at 1000 in neutral now and drops to 500RPM in either gear. Perfect. Very little clunk and unlikely it will die while maneuvering in a tight marina row of slips.

Following the advice of my outboard mechanic, a Mercury guy, I add an ounce of Quickare, a Mercury fuel additive, for every 10 gallons of gas. Maybe that is cleaning my carbs.

Larry
 
Not sure how accurate my speedometer is in the 40s. It is right on at 10MPH and 20MPH, checked against a GPS. But I was way too busy to cross-check the speedometer against my cell phone Boat Buddy ap at full throttle. The tach showed 5000 RPM and the speedometer jumped up to mid 40s. And that with the trim all the way down. I was alone in the boat and nothing with any weight was aboard. I don't know which prop I have. Someone said the engine should turn 5500 with the right prop.

Someday I will take it out early in the morning when the harbor is glassy smooth and see what it really does.

I hope to install a Garmin GPSMAP 2010 soon. It should read out accurate speed.

I am still wrestling with fuel gauges. I installed new SeaSense senders when the tanks were out. I brought the wires out to the dash. But I have been unable to get readings that are make sense even though I tried three different gauges. The previous owner of this old boat used a piece of round doweling to sound the tanks, pretty "old school" method. He had the stick marked at full and half full, which would be 20 and 10 gallons. That actually works, ha. And it is pretty reliable information!

Larry
 
I actually like the dowel idea, know a couple charter boat guys that use it. Keep in mind a belly tank gets smaller towards the bottom. 1000 idle speed is a little high. I may be wrong, but I thought 700-800 was about right.
 
larry, i had a 2010c for a couple of years, great unit. easy to navigate, etc. i'vr got a gsd20 black box for the sounder unit and a set of manuals, let me know if you need them. also be aware, garmin no longer supports that unit. mine lost the screen and no one would work on it. i also had a 2006c, same thing happened after about a year.
 
Cross boat wakes at a 45 angle with enough speed to keep bow up but back off on the back side if they are big so you don't fly.
When a boat is going the other way cross thru the wake at speed right after the boat passes...bump,bump,bump..and get into the smooth water behind it. Otherwise you will be in the waves forever.
 
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