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Erik Cornelison
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194 Posts

Initially Posted - 09/04/2018 : 15:41:50

Hey all, our family is having fun with the boat this summer. It�s new to us. I was just wondering how fast are your motors pushing you?

I can consistently sail 1-1.5 knots faster (some times even more) than my 9.9 Mercury Bigfoot will push me at full throttle, but I figure I�m at 7,800 ft elevation and lose some hp.

Also, anyone have a best speed-to-economy for GPH for a modern 9.9? I don�t think brand matters much.

I�m guessing around 4kts, hoping for 6 mpg.

Reason asking is we are planning a trip to Lake Powell, Utah this fall and I would like to get a guesstimate for fuel needed to head down the lake., and back.

If you know Lake Powell you know you may not be able to always sail it, hence the motor.

Love the boat, it performs better than expected.

Erik Cornelison
6th Generation Professional Sailor, First Gen Submarine Sailor.
1986 Standard Rig SW. #5234

Edited by - Erik Cornelison on 09/04/2018 15:43:11

islander
Master Marine Consultant

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Response Posted - 09/04/2018 : 16:25:04

Full throttle

Back it down there big boy. With a 9.9 about half to three quarters should push you along in the 4.5 to 5.5 range and is where most of use cruise along at. Full throttle is just a wast of fuel and the boat will try to climb it's own bow wake and the stern will just squat down with little speed increase compared the the extra fuel your burning. Your also just beating the motor up and the noise level has to be annoying.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Edited by - islander on 09/04/2018 16:44:39

glivs
Admiral

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Response Posted - 09/04/2018 : 18:02:37

I agree with Scott. I'm going on memory here and only have a few observations but my Mercury 9.9 w/ four-blade prop running at 1900 rpm (about half throttle) pushes me along on flat water with no wind at 5 to 5.2 kn and about 4.5 kn with a headwind of 5-10 kn. I haven't made any long trips since purchasing this motor so have no quantitative observations on fuel economy although a 2.5 gal tank lasts much of the summer (little boat time these past few years).

Gerry & Leslie; Malletts Bay, VT
"Great Escape" 1989 C-25 SR/WK #5972

Erik Cornelison
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Response Posted - 09/04/2018 : 18:36:51

quote:
Originally posted by islander

Full throttle Back it down there big boy. With a 9.9 about half to three quarters should push you along in the 4.5 to 5.5 range and is where most of use cruise along at. Full throttle is just a wast of fuel and the boat will try to climb it's own bow wake and the stern will just squat down with little speed increase compared the the extra fuel your burning. Your also just beating the motor up and the noise level has to be annoying.

Please read my post before replying, you didn't answer either question, instead you assume I'm being annoying to others and beating up my motor.

I was asking how fast others motor pushes their boat with a similar HP to compare and guess on how much fuel is used. Really annoying to get these kind of responses online.

Erik Cornelison
6th Generation Professional Sailor, First Gen Submarine Sailor.
1986 Standard Rig SW. #5234

Erik Cornelison
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Response Posted - 09/04/2018 : 18:40:32

quote:
Originally posted by glivs

I agree with Scott. I'm going on memory here and only have a few observations but my Mercury 9.9 w/ four-blade prop running at 1900 rpm (about half throttle) pushes me along on flat water with no wind at 5 to 5.2 kn and about 4.5 kn with a headwind of 5-10 kn. I haven't made any long trips since purchasing this motor so have no quantitative observations on fuel economy although a 2.5 gal tank lasts much of the summer (little boat time these past few years).

Thanks, that helps. I've used about four gallons this summer, but its only going in and out of the marina, we are sailing a lot and the lake is really small so no motoring.

Erik Cornelison
6th Generation Professional Sailor, First Gen Submarine Sailor.
1986 Standard Rig SW. #5234

glivs
Admiral

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Response Posted - 09/04/2018 : 19:25:43

Eric...Slow down. Scott did largely answer your questions if you grasped what he was saying and he did so in a friendly tone. He easily could have noted that your questions have been addressed many times over on this forum - use the search option above. This forum, however, is the product of a largely friendly community and is based on sharing individual experiences whether they or their interpretations are the same or not as yours.

Gerry & Leslie; Malletts Bay, VT
"Great Escape" 1989 C-25 SR/WK #5972

Voyager
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5231 Posts

Response Posted - 09/04/2018 : 20:10:54

Eric,
I have Honda 8 HP engine and although it�s not a Merc, it�s an outboard. And an 8HP is just a 9.9 that�s been detuned.

FWIW: My experience has been as follows:
The engine runs well at 3/4 throttle and doesn�t go significantly faster at full throttle. Maybe 5.5 vs 5.2 kts.

You did say something that I wonder about:

quote:
I can consistently sail 1-1.5 knots faster (some times even more) than my 9.9 Mercury Bigfoot will push me at full throttle, but I figure I�m at 7,800 ft elevation and lose some hp.

This tells me that your max speed using your engine is 1.0-1.5 kts less than about 5.2 kts. That means your engine achieves something like 3.7-4.2kts at full throttle.
Is this an accurate interpretation?
If so, something is radically wrong with this picture, even at altitude, since a carburetor adjustment would probably fix this.

My mileage varies with throttle setting, but if I run at 3/4 throttle I burn about 1 gallon for 75 minutes. Using 60DST equation I get:
75/60*5.2 = 6.5 nm on a gallon. Converting, 6.5nm*1.151=7.5 statute miles per gallon.

In previous discussions among the regulars here, these results are not unusual for 8.0s and 9.9s. Others who have a 9.9 HP Mercury outboard may have similar results.

If you get significantly less performance, you might want to check your spark plugs, carburetor, engine timing or choke settings.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - Voyager on 09/04/2018 20:19:24

sethp001
Mainsheet C-25 Tech Editor

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814 Posts

Response Posted - 09/04/2018 : 20:50:34

quote:
Originally posted by Erik Cornelison

Hey all, our family is having fun with the boat this summer. It�s new to us. I was just wondering how fast are your motors pushing you?

I can consistently sail 1-1.5 knots faster (some times even more) than my 9.9 Mercury Bigfoot will push me at full throttle, but I figure I�m at 7,800 ft elevation and lose some hp.

Also, anyone have a best speed-to-economy for GPH for a modern 9.9? I don�t think brand matters much.

I�m guessing around 4kts, hoping for 6 mpg.

I get 6.5 knots at full throttle with my 15hp Johnson. I rarely do that because I'm just wasting fuel when a third throttle will push me along at 4.5 knots.

Of course you know that motoring at less than full throttle will yield better fuel economy. But it's interesting that your motor, which should be more than powerful enough to push your boat along at hull speed, pushes the boat along slower than you can sail.

Seth
"Outlier" 1987 Catalina 25 SR/SK/Traditional Interior #5541
"Zoo" 1977 Morgan Out Island 30
"Nomad" 1980 Prindle 16
"Lost" 1988 Catalina Capri 14.2 (sold - yay!)
"Marine Tex 1" Unknown Origin POS 8' Fiberglass Dinghy
https://whichsailboat.com/2014/07/27/catalina-25-review/

keats
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Response Posted - 09/04/2018 : 21:40:41

quote:
Originally posted by Erik Cornelison

Hey all, our family is having fun with the boat this summer. It�s new to us. I was just wondering how fast are your motors pushing you?

I can consistently sail 1-1.5 knots faster (some times even more) than my 9.9 Mercury Bigfoot will push me at full throttle, but I figure I�m at 7,800 ft elevation and lose some hp.

Also, anyone have a best speed-to-economy for GPH for a modern 9.9? I don�t think brand matters much.

I�m guessing around 4kts, hoping for 6 mpg.

I think 6 mpg is a fair estimate. (I think I've owned cars that did that!) It purports well with data I've heard that a 9.9 will burn 1 gallon per hour at WOT. I've pencilled out 7-8 mpg in my limited calcs on my boat and I'm light on the throttle as it usually means we're steaming in and I'm in no rush.

That is a pretty good elevation and I wonder if your carb has been rejetted for that altitude?

At 800 feet, we hit hull speed at a little less than 3/4 throttle. That's in relatively calm conditions.

Have a great trip, it's no fun without some risk!

Tim Keating
1985 C-25 TR/FK #4940
Midsummer
Lake Don Pedro, CA

islander
Master Marine Consultant

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Response Posted - 09/05/2018 : 05:26:58

Erik, Sorry if you misinterpreted my answer but I did try to answer your questions.
you asked
I was just wondering how fast are your motors pushing you?
I said With a 9.9 about half to three quarters should push you along in the 4.5 to 5.5 range and is where most of us cruise along at.

You asked
Also, anyone have a best speed-to-economy for GPH for a modern 9.9? I don�t think brand matters much.

I�m guessing around 4kts, hoping for 6 mpg.
I said With a 9.9 about half to three quarters should push you along in the 4.5 to 5.5 range and is where most of us cruise along at.
I didn't answer GPH for a modern 9.9?
I didn't answer this because I have not traveled long distance with my boat so I don't know, I have a brand new 9.8 and there are many variables in how much fuel you will burn, Head into the wind, With the wind, Motor sailing, Current if any, Throttle setting and in fresh water you might have more drag because the boat sits lower than in salt water. Not sure of that. The rule of thumb for fuel is, One third out, One third back and one third reserve. That said I would use one gal. per hour as a good safe guess and should leave you with plenty reserve.
I would also add that I did not mean that your question or you were annoying. I was referring to the noise level of a motor at full throttle for long periods of time. This is a friendly Forum and as you know you will get many answers to a question. Some relevant and some not and none of use are experts, Just fellow sailors trying to help.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Edited by - islander on 09/05/2018 05:30:28

HerdOfTurtles
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Response Posted - 09/05/2018 : 13:57:51

I have a 6hp Tohatsu 4 stroke and get between 4-5 kts at 3/4 throttle depending on wind and sea state. I don't know the exact fuel burn as I have never run the engine for an extended period. I have read by searching here of folks attaining 4 kts speed and 1/3 gallon per hour fuel burn, so 12 mpg. Personally, I would err on the side of caution and estimate 8 mpg until I had enough time with my own boat and motor to plan for better economy. However, the 12 mpg claimed economy *sounds* about right.

I also routinely sail 1-1.5 kts faster than I motor.

Edit: Oh, wow 7800 ft elevation. I'm at 0 elevation and brackish water. I'm not exactly sure what being so high in elevation would do to your fuel economy but I imagine full throttle for you would be equivalent to about 3/4 throttle at sea level. And when I say equivalent I mean exactly the same. Same rpm, same noise, same fuel burn(though you probably have to use different main and idle carb jets) as if you were at sea level running 3/4 throttle.

1978 Standard Rig
Fin Keel
L-Dinette

Edited by - HerdOfTurtles on 09/05/2018 14:16:37

GaryB
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Response Posted - 09/05/2018 : 16:25:55

Guys, need to remember he said he was at 7,800 MSL. In a normally aspirated airplane at 7-8,000' the best you will get is approx. 75% of the power you would at sea level. To get 75% you have to use full throttle.

Eric - How fast do you go at full throttle at your altitude?

Sorry Herd... I didn't read your whole post before I posted. Didn't mean to be repetitive guys.

Association Member

GaryB
Andiamo
'89 SR/WK #5862
Kemah,TX

Edited by - GaryB on 09/05/2018 16:31:12

RichardG
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990 Posts

Response Posted - 09/06/2018 : 16:41:24

I usually go about 5.5 knots with the Tohatsu 6 (with high thrust prop) unless it's especially choppy. Even a little beam wind can help push it to 6 knots. It pretty much knows only two throttle settings - full and idle. I often go on 20 mile runs with little or no wind, and get about 8 miles(nautical)/gal.

RichardG 81 FK/SR #2657
Terminal Island, CA

Stinkpotter
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Djibouti
9013 Posts

Response Posted - 09/06/2018 : 18:18:51

The good news is Powell is less than half your elevation and probably closer to �our� average. With (now Bruce�s) Honda 8, I figured a gallon per hour at about 5 knots (5.75 mph), so around 6 mpg�but that was pretty conservative in my experience. Mine would cruise cmfortably above 5 kts at around 2/3 throttle. Full throttle would approach 6 kts, but the transom would squat adding wake and drag (and noise). That�s at zero altitude, but I don�t think motors are optimized for zero feet. 6.3 kts is the theoretical limit for the C-25, but approaching that requires an exponential increase in thrust and gas.

So why not a 6hp? Pushing into wind and 3-4� Long Island Sound chop.

(BTW Bruce, yours isn�t a �detuned 9.9��according to a factory rep, it�s cammed for more torque for diaplacement hulls and therefore the better choice for a sailboat�and that�s from the company that makes more money on the identical but more expensive 9.9.)

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 09/06/2018 20:03:23

Voyager
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Response Posted - 09/06/2018 : 20:10:24

quote:
Originally posted by Stinkpotter

(BTW Bruce, yours isn�t a �detuned 9.9��according to a factory rep, it�s cammed for more torque for diaplacement hulls and therefore the better choice for a sailboat�and that�s from the company that makes more money on the identical but more expensive 9.9.)

Dave, thanks for the update on the Honda engine. There are any number of brands that twiddle their performance so they can rate their 9.9s as 8s for regulatory reasons or for branding reasons. Getting into the cam and valve timing and compression across the combustion cycle is a very clever approach.

Erik, Thinking about your situation, while you�re on a smaller lake at altitude, would you need a 15 HP engine to get enough torque to push your boat at 5.0-5.5 kts? You should be pleasantly surprised by your current engine out on Lake Powell.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - Voyager on 09/06/2018 20:12:08

AlMo
1st Mate

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Response Posted - 09/07/2018 : 20:50:18

Density altitude is a pilot concept, I've rarely seen it used in sailing, but then Tahoe and even Powell are high enough altitude lakes to bring that into play. So here's the "wonky stuff" needed to calculate engine performance at higher than sea level: https://www.experimentalaircraft.info/flight-planning/aircraft-performance-3.php. I am making the assumption air-cooled (airplane) and water-cooled (sailboat) engines follow roughly the same curve. Don't know if this addresses either of Erick's original questions or not.

I do know this is a friendly board, with relatively "troll free" discussions, hope we keep it that way!

1978 C25 "X Lives" #1035
SR/SK

JohnP
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Response Posted - 09/10/2018 : 12:33:26

I have motored a little more than 40 miles with my Honda 9.9hp motor (into a 3-5 knot breeze) with a 5 gallon gas tank and have fuel left at the end. That's about 8 MPG.

JohnP
1978 C25 SR/FK "Gypsy"
Mill Creek off the Magothy River, Chesapeake Bay
Port Captain, northern Chesapeake Bay

jerlim
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Response Posted - 09/12/2018 : 05:38:04

We get about 4 mpg with our 8 hp Merc, as averaged in varying conditions.

Jerry

WesAllen
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Response Posted - 09/12/2018 : 07:55:28

9.9 Merc Big Foot on mine and use 9 gals to go from Key West to Everglade City. Roughly 10 mpg but was ideal conditions (flat seas).(3/4 throttle) But that was the best, usually not quit that good. 8-7 mpg would be more realistic.

Wesley Allen
"Breaking Wind"
1982 C-25 SR/TR/SK #2773
Hemlock, MI

Frank Law
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Response Posted - 09/12/2018 : 11:45:55

Relating to altitude while driving a car? While driving a 1967 V W camper we were on a level stretch of road ,at an altitude of 10,000 / 11,000 ft?? (higher) and the camper would go no faster than 35 mph . This was in Colorado near Leadville . They use different carbs for this reason.

Frank Law
Ex C-25 owner

sailboat
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Response Posted - 09/12/2018 : 22:24:27

I think a gasoline engine loses 3 percent power for each 1000 feet of altitude. So at 7800 feet the earlier figure of 75% power available and that at full throttle is pretty accurate. Speed and efficiency unknown.

Mike
Chariots of Fire
1981 Cat-25. sail number 2230
SR/SK Dinette Version

Voyager
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Response Posted - 09/13/2018 : 18:49:52

So if I rent a car in Denver at 5000ft, does that mean the car will drive like a dog? I�ve never noticed any performance degradation while driving around Denver and I�ve driven there a lot. Does the computer just compensate for altitude without anybody having to think about it?
I�ve even driven up at elevation in the hills outside of Boulder and the car ran like a champ.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - Voyager on 09/13/2018 18:51:26

GaryB
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Response Posted - 09/13/2018 : 18:56:44

quote:
Originally posted by Voyager

So if I rent a car in Denver at 5000ft, does that mean the car will drive like a dog? I�ve never noticed any performance degradation while driving around Denver and I�ve driven there a lot. Does the computer just compensate for altitude without anybody having to think about it?
I�ve even driven up at elevation in the hills outside of Boulder and the car ran like a champ.

Up to a point. Go up to Pikes Peak and it will probably be gasping for air as much as you. LOL

Maybe cars shipped to the Denver area have the computer and fuel system setup for the higher altitude?

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GaryB
Andiamo
'89 SR/WK #5862
Kemah,TX

Stinkpotter
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Djibouti
9013 Posts

Response Posted - 09/14/2018 : 12:06:49

The consensus I've seen is the EFI system automatically leans out the mixture to compensate for the thinner air, so to get the same power, you'll push the peddle down a little more. And "peddle to the metal" won't give you as much as it did at sea level, if that's a concern.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

hbushey
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Response Posted - 09/24/2018 : 20:40:41

quote:
Originally posted by Stinkpotter

The good news is Powell is less than half your elevation and probably closer to �our� average. With (now Bruce�s) Honda 8, I figured a gallon per hour at about 5 knots (5.75 mph), so around 6 mpg�but that was pretty conservative in my experience. Mine would cruise cmfortably above 5 kts at around 2/3 throttle. Full throttle would approach 6 kts, but the transom would squat adding wake and drag (and noise). That�s at zero altitude, but I don�t think motors are optimized for zero feet. 6.3 kts is the theoretical limit for the C-25, but approaching that requires an exponential increase in thrust and gas.

So why not a 6hp? Pushing into wind and 3-4� Long Island Sound chop.

(BTW Bruce, yours isn�t a �detuned 9.9��according to a factory rep, it�s cammed for more torque for diaplacement hulls and therefore the better choice for a sailboat�and that�s from the company that makes more money on the identical but more expensive 9.9.)

Dave�s advice for me to go with the Honda BF-8 over the 9.9 was some of the best I�ve been given on this site. With a 25� shaft, this engine has performed flawlessly. With a 25KT headwind and 2-3 foot waves on Lake Tahoe last week, I was still able to maintain 4.5KT STW getting back to the marina. Saved me a good chunk of change over the 9.9HP. Electric start and the 12A alternator make this engine awesome.

Now my Garhauer motor mount... That�s a whole other issue.

Heather and Scott
�Respite�
1989 C-25 TR/WK

bigelowp
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Response Posted - 09/26/2018 : 07:42:45

FWIW -- I have a Tohatsu 9.8 (same engine as Mercury) with a three blade prop. I rarely go over half throttle and the boat will move along at @4-4.5knts, I have never gone full throttle as it has never to date been needed. Now chop vs. swell will make some difference and four blade prop vs. three blade, as well as what pitch the prop is, will also make a difference. We are lucky to be on a mooring so often we sail of and back on to the mooring resulting in over ten years with the engine the most fuel I have used is one half of the 3.5 gal tank. I have no idea what altitude does to fuel consumption but my guess (and it is just a guess) is that it would be minimal for such a small engine.

Peter Bigelow
C-25 TR/FK #2092 Limerick
Rowayton, Ct
Port Captain: Rowayton/Norwalk/Darien CT

Edited by - bigelowp on 10/01/2018 16:14:27

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