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FUEL CONSUMPTION

Aug 11, 2011
583
O'day 30 GEORGETOWN, MD
I'm curious to know what the fuel consumption is on a 1983 O'day 30 is based on my guess 2000 rpm on an Univversal M20 (16 HP)? I understand there are some variables in there, but if anyone has some infor, I'd appreciate knowing.
 
Oct 22, 2014
12,434
CAL 35 Cruiser Portland OR, moored EVERETT WA
You are right... Too many variables to give you a reliable number. I woud suggest you fill the tank go for a run and then refill the tank recording how long you powered at 2000 rpm and how much fuel was used.

As a genral consideration, I would start - assume - you use 1 gallon of fuel per hour. You are likely to find that it is better than that. Towards .5 gallons per hour. But if you have growth on your boat bottom, the prop is not the most efficient, etc your numbers will vary.

Keep a log and you will soon know your numbers.

Now attched is a link to your engine manual. Page 57 (i think) has your engine data for the M20. The recommended cruise range is 2000 to 2400 rpm. Diesels like to work. Depending on the prop you have you may find that 2000 will be too slow for the engine to be working at it’s best. Baby the engine and it will coke up and break down. Make it work and you will have a happy long life together. Try 2400. She will tell you what works best. Listen to the sound and the vibration of the boat and find your boat’s sweet spot.

https://www.westerbeke.com/operator's manual/200157_m12-m50_operator_man.pdf
 

RoyS

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Jun 3, 2012
727
Hunter 33 Steamboat Wharf, Hull, MA
I typically get two hours at 2,800 rpm per gallon with my 15 hp two cylinder Yanmar 2QM15 and 33' Hunter33. Your boat is similar.
 
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Jan 22, 2008
24
Oday 30 Stamford CT
Based on 2072 hours of operation my average is 1/3 gal per hour for my Universal 5416.
 
Aug 17, 2010
221
Oday 35 Barrington
1987 Universal M25 - Cruising RPM is 2500 - 2 bladed Michigan Sailer 16 RH 9 prop. Normal fuel consumption for my boat is 0.30 gallons per hour.
 
Jun 11, 2004
969
Oday 31 Redondo Beach
I burn about 1/3 gallon per hour on my 1985 O'day 31 with the original Universal M18 engine. That's over about the last 500 hours.
 
Jan 5, 2017
1,711
Beneteau First 38 Lyall Harbour Saturna Island
cruise RPM over ratedRPM divided by 3 times your HP times0.225 equals litres/hour
3.74 litres=1 USG.
After more than 4000 hours on a Perkins 4-108 I was guessing 2 litres per hour at 2000RPM. This formula says I only burned 1.998 litres/hour so I think it's pretty close. It doesn't matter how clean your bottom is, it takes X amount of fuel to produce Y HP. MPG will vary depending on bottom growth.
 
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Sep 11, 2015
145
Hunter 31 Marina del Rey
Small diesel engines consumer about 215g diesel/hp/hour in this range. I have done extensive testing on my Yanmer 2GM20f (16 hp, 3,600 rpms, so exactly the same as yours). At 2,000 rpm's the engine will make a max of five hp and consume a max of 0.35 gph. You are unlikely to exceed this figure but may be lower. For the other speeds, max fuel consumption is: 0.2 gph @ 1,200 rpm, 0.3 gph @ 1,800 rpm, 0.4 gph @ 2,200 rpm, 0.5 gph @ 2,500 rpm, 0.6 gph @ 2,700 rpm and 1.0 gph at 3,200 rpm. The engine is physically not capable at producing more for a given speed. In reality, your consumption will be lower depending on conditions.
 
Oct 26, 2010
1,065
Hunter 40.5 Beaufort, SC
Maybe I'm applying the math operators incorrectly but MD's formula appears to be linear (if the HP to be used in rated HP) and that doesn't seem to correlate to real world experience as my fuel consumption almost doubles from 2700 to 3600 rpm! (Or the experience from Pizzazz) I have also observed that my to achieve the desired rpm (say 2700) I have to have the throttle open a lot more with a dirty hull than a clean hull so it take more fuel to achieve the rpm.
 
Oct 22, 2014
12,434
CAL 35 Cruiser Portland OR, moored EVERETT WA
I have to have the throttle open a lot more with a dirty hull than a clean hull so it take more fuel to achieve the rpm.
I’m not sure about this.
Yes if trying to get more speed thru the water you will need to open the throttle more and this would burn fuel at a greater rate but your RPM should also be higher. The drag is caused by the dirty hull.

A clean hull should reduce the drag (friction) on the hull thus allowing the hull to go at a higher speed thru the water. The speed will be accomplished at a lower RPM and consume less fuel for a given rpm.

Dirty or clean the RPM should yield nearly the same fuels consumption but vary the distance traveled in a fixed amount of time based on the hull’s condition.
 
May 7, 2012
775
Hunter e33 Maple Bay, BC
Dirty or clean the RPM should yield nearly the same fuels consumption but vary the distance traveled in a fixed amount of time based on the hull’s condition.
Agreed. However as proven by personnel experience, a fouled prop will reduce the RPM for a given throttle position. The dirtier the greater the reduction.
 
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Oct 26, 2010
1,065
Hunter 40.5 Beaufort, SC
My thoughts go back to when this happened. I think I was confusing a dirty hull with a prop that was fouled with barnacles rather than a dirty hull alone (the hull may have been dirty too). In that case the fouled prop was the culprit with regard to the rpm and the gowth on the hull was also contributing to the reduced speed through the water.

In any case, I could barely make headway against a 2 knot current with the throttle full on and could only do about 2000 rpm:yikes: I wasn't sure I would make it from the mooring to the dock. You can be sure that I didn't skip a hull and prop cleaning after that. You can be sure I haven't missed a hull and prop cleaning since then!

My rated rpm is 3600 rpm and no, it was not an engine problem. Right after the cleaning of the hull and prop I was back up to 3600 rpm at max throttle.
 
Oct 22, 2014
12,434
CAL 35 Cruiser Portland OR, moored EVERETT WA
Ha. Yes, but did you find an answer in this can that helped resolve your questions?
 
Aug 11, 2011
583
O'day 30 GEORGETOWN, MD
Yes: 3 Hours of motoring at an average of 2500 rpm per gallon. With a full 26 gallon tank of fuel I should be able to run 75 hours before panicking that I'm going to run out of fuel.
 
Oct 26, 2010
1,065
Hunter 40.5 Beaufort, SC
Yes: 3 Hours of motoring at an average of 2500 rpm per gallon. With a full 26 gallon tank of fuel I should be able to run 75 hours before panicking that I'm going to run out of fuel.
NOT SO FAST THERE!! There are a lot of other factors to consider. How far is your pickup from the bottom? You lose some capacity there. What is the shape of the tank, tapered/square etc (Doesn't impact fuel usage but may impact what your gauge reads) Is there wind and are there waves slamming you from head on slowing your progress so that the 12 hour trip you planned will take 16 hours or that are causing the boat to pitch and/or roll, exposing the pickup to momentarily sucking air? Are you really "full" - how do you know? Don't ask me how I know :yikes:. Explaining to the Admiral why you really weren't in danger after that long offshore passage when you ran out of fuel isn't something you want to do.

Better to use a more conservative approach for when you need to "panic". If I were going to use an estimate for how long I can run on a tank of fuel the way you did I'd make sure I had good towing insurance. :pray:
 
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Oct 22, 2014
12,434
CAL 35 Cruiser Portland OR, moored EVERETT WA
In flying they taught me to have a reserve level that we will call "Bingo". Bingo is the point in fuel consumption that I must turn back to my port. It will allow me to get to port based on the conditions and still provide me 15-30 minutes to safely tie up on the dock before the engine dies.

Taking in condition of your fuel, the useable gallons (as @smokey73 shares the waves, tank and fuel lines might conspire against you) your "Panic" point might be better at 70 hours than 75.

As I am often reminded, It is your boat and your decision. We all have a different level of "Pucker Factor".

Fortunately near shore on a boat with the number of the Tow Service on speed dial, your tolerance might be a little higher than at 500 feet no engine and a parachute that was packed 10 years ago.
 
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